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Solid state UV emitters have many advantages over conventional UV sources. The (Al,In,Ga)N material system is best suited to produce LEDs and laser diodes from 400 nm down to 210 nm—due to its large and tuneable direct band gap, n- and p-doping capability up to the largest bandgap material AlN and a growth and fabrication technology compatible with the current visible InGaN-based LED production. However AlGaN based UV-emitters still suffer from numerous challenges compared to their visible counterparts that become most obvious by consideration of their light output power, operation voltage and long term stability. Most of these challenges are related to the large bandgap of the materials. However, the development since the first realization of UV electroluminescence in the 1970s shows that an improvement in understanding and technology allows the performance of UV emitters to be pushed far beyond the current state. One example is the very recent realization of edge emitting laser diodes emitting in the UVC at 271.8 nm and in the UVB spectral range at 298 nm. This roadmap summarizes the current state of the art for the most important aspects of UV emitters, their challenges and provides an outlook for future developments. [ABSTRACT FROM AUTHOR]

Display technology has developed rapidly in recent years, with III–V system-based micro-light-emitting diodes (μLEDs) attracting attention as a means to overcome the physical limitations of current display systems related to their lifetime, brightness, contrast ratio, response time, and pixel size. However, for μLED displays to be successfully commercialized, their technical shortcomings need to be addressed. This review comprehensively discusses important issues associated with μLEDs, including the use of the ABC model for interpreting their behavior, size-dependent degradation mechanisms, methods for improving their efficiency, novel epitaxial structures, the development of red μLEDs, advanced transfer techniques for production, and the detection and repair of defects. Finally, industrial efforts to commercialize μLED displays are summarized. This review thus provides important insights into the potential realization of next-generation display systems based on μLEDs. [ABSTRACT FROM AUTHOR]

Highlights • (10 1 ¯ 0) m -plane AlGaN grown on m-plane sapphire over the entire range of composition. • The structural, morphological and optical properties were investigated. • The AlN mole fraction for m -plane layers is comparable with c -plane co-loaded layers. • The crystal-field splitting energy has a bowing parameter of about −0.15 eV. Abstract Heteroepitaxial growth of single-phase nonpolar (10 1 ¯ 0) m -plane Al x Ga 1 - x N layers on m -plane sapphire substrates was investigated by metalorganic vapour phase epitaxy. Different Al/Ga gas phase ratios were used to adjust the AlN mole fraction over the entire range of composition. All m -plane AlGaN layers show an orthorhombic distortion in the wurtzite unit cell due to anisotropic in-plane strain. This distortion decreases with increasing AlN mole fraction due to a decreased anisotropic biaxial strain. The AlN mole fraction of m -plane layers and c -plane co-loaded layers estimated by X-ray diffraction is comparable. This is consistent with their comparable energy bandgaps, which were estimated from room-temperature dielectric functions. The dependence of the energy bandgap on composition indicates a bowing parameter of about 0.9 eV. The crystal-field splitting energy is found for the m -plane layers with a bowing parameter b cf of about −0.15 eV. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to retrospectively compare the enlargement and migration of the femoral tunnel aperture after anatomic rectangular tunnel anterior cruciate ligament (ACL) reconstruction with a bone-patella tendon-bone (BTB) or hamstring tendon (HT) graft using three-dimensional (3-D) computer models.Methods: Thirty-two patients who underwent ACL reconstruction and postoperative computed tomography (CT) at 3 weeks and 6 months were included in this study. Of these, 20 patients underwent ACL reconstruction with a BTB graft (BTBR group), and the remaining 12 with an HT graft (HTR group). The area of the femoral tunnel aperture was extracted and measured using a 3-D computer model generated from CT images. Changes in the area and migration direction of the femoral tunnel aperture during this period were compared between the two groups.Results: In the HTR group, the area of the femoral tunnel aperture was significantly increased at 6 months compared to 3 weeks postoperatively (P < 0.05). The average area of the femoral tunnel aperture at 6 months postoperatively was larger by 16.0 ± 12.4% in the BTBR group and 41.9 ± 22.2% in the HTR group, relative to that measured at 3 weeks postoperatively (P < 0.05). The femoral tunnel aperture migrated in the anteroinferior direction in the HTR group, and only in the inferior direction in the BTBR group.Conclusions: The femoral tunnel aperture in the HTR group was significantly more enlarged and more anteriorly located at 6 months after ACL reconstruction, compared to the BTBR group.Level Of Evidence: IV. [ABSTRACT FROM AUTHOR]

Highlights • MOVPE-growth and high-temperature annealing of m -plane AlN on m -plane sapphire. • (10 1 ¯ 0) XRC FWHM along [0001]/[11 2 ¯ 0] decreased from 2900/1940 to 1030/800 arcsec. • The density of basal stacking faults decreased from ~ 2.8 × 10 5 to ~ 1. 5 × 10 4 cm−1. • Larger effective bandgap after annealing (6.15 eV) than as-grown layers (6.04 eV). Abstract Heteroepitaxial growth of AlN layers on (10 1 ¯ 0) m -plane sapphire substrates was investigated by metalorganic vapour phase epitaxy. Different nucleation temperatures were used to achieve single phase (10 1 ¯ 0) AlN layers. The crystallinity of the layers further increased with increasing annealing temperature and annealing time. The full-width at half maximum of the symmetric (10 1 ¯ 0) X-ray rocking curves decreased from about 2900/1940 arcsec to 1030/800 arcsec along [0001]/[11 2 ¯ 0] AlN. The density of basal stacking faults of the annealed layers was found to decrease from ∼ 2.8 × 105 to ∼ 1.5 × 104 cm−1. The annealed layers had a larger effective optical bandgap energy of ∼ 6.15 eV than ∼ 6.04 eV of the as-grown layers due to their better crystallinity and structural order. [ABSTRACT FROM AUTHOR]

Background: Radial/oblique tears of the midbody of the lateral meniscus significantly impair the ability of the meniscus to withstand the tibiofemoral load, requiring meniscal repair. However, healing status after meniscal repair has not been fully elucidated. This study aimed to evaluate arthroscopic findings after inside-out suture repair for isolated radial/oblique tears of the midbody of the lateral meniscus.Methods: From 2011 to 2015, 18 consecutive patients with isolated radial/oblique tears of the midbody of the lateral meniscus underwent arthroscopic inside-out repair with the tie-grip suture technique. All knees were stable with no previous surgery. All patients were evaluated by second-look arthroscopy at six months postoperatively. Activities including jogging were not allowed until meniscal status was evaluated arthroscopically. To analyze factors associated with healing rates, age, time from injury to initial surgery, and tear zone were compared.Results: Second-look arthroscopy revealed complete healing in four (22%) patients, partial healing in seven (39%), and failure to heal in seven (39%). Significant differences were observed for tear zone (p < 0.0001), but not for age and timing of repair.Conclusions: Arthroscopic evaluation revealed that inside-out repair with the tie-grip suture technique for isolated radial/oblique tears of the midbody of the lateral meniscus achieved complete or partial healing only in 61% of patients. Satisfactory results were observed particularly in patients with tears extending to the vascular zone, whereas those with tears in the avascular zone failed to achieve healing. Therefore, the operative indication of inside-out repair for radial/oblique tears of the midbody of the lateral meniscus might be limited to tears extending into the vascular zone. Given that 39% of cases were arthroscopically considered a failure even if patients complained of no symptoms in daily life, decisions should be made carefully to allow patients to return to sports activities. [ABSTRACT FROM AUTHOR]

For rooting the development of GaN-based optoelectronic devices, understanding the roles of midgap recombination centers (MGRCs), namely, nonradiative recombination centers and deep-state radiative recombination centers, on the carrier recombination dynamics is an essential task. By using the combination of time-resolved photoluminescence and positron annihilation spectroscopy (PAS) measurements, the origins of major MGRCs in the state-of-the-art GaN epilayers, bulk crystals, and Mg-implanted layers were identified, and their concentrations were quantified for deriving the capture coefficients of minority carriers. In this article, potential standardization of the room-temperature photoluminescence lifetime for the near-band-edge emission (τ PL RT ) as the concentration of major MGRCs well below the detection limit of PAS is proposed. For n-GaN substrates and epilayers grown from the vapor phase, τ PL RT was limited by the concentration of carbon on N sites or divacancies comprising a Ga vacancy (VGa) and a N vacancy (VN), [VGaVN], when carbon concentration was higher or lower, respectively, than approximately 1016 cm−3. Here, carbon and VGaVN act as major deep-state radiative and nonradiative recombination centers, respectively, while major MGRCs in bulk GaN crystals were identified as VGa(VN)3 vacancy clusters in Na-flux GaN and VGa or VGaVN buried by a hydrogen and/or VGa decorated with oxygen on N sites, VGa(ON)3–4, in ammonothermal GaN. The values of τ PL RT in n-GaN samples are compared with those of p-GaN, in which τ PL RT was limited by the concentration of VGa(VN)2 in Mg-doped epilayers and by the concentrations of VGaVN and (VGaVN)3 in Mg-implanted GaN right after the implantation and after appropriate activation annealing, respectively. [ABSTRACT FROM AUTHOR]

This article combines two papers, “Nobel Lecture: Growth of GaN on sapphire via low-temperature deposited buffer layer and realization of p-type GaN by Mg doping followed by low-energy electron beam irradiation,” Rev. Mod. Phys., 87 (2015) 1133, and “MOCVD of nitrides,” Handbook of Crystal Growth Second Edition, Volume III, Part A, Chapter 16, Elsevier, 683–704, 2015. For more detailed information, please read the two original papers. [ABSTRACT FROM AUTHOR]

In summary, this Special Topic provides an excellent overview and cross section of key challenges in the development of high-efficiency, high power, and long lifetime UV/DUV LEDs as well as the rapidly emerging area of UVB and UVC laser diodes. Recently, several groups have reported current-injection laser diodes in the UVB and UVC spectral region with emission wavelength as short as 272 nm.[[17]] Even though the demonstrated devices are still a long way from what is needed for practical systems, these breakthroughs illustrate that semiconductor UV/DUV laser diode technologies show great potential. Finally, Kondo I et al. i demonstrate high-power operation of AlGaN-based UVB laser diodes.[41] By improving the injection efficiency through modulation of the polarization charge at the interface between the p-side waveguide layer and the EBL, they were able to show pulsed laser diodes with a peak light output power of 150 mW at a lasing wavelength of 300 nm. Group III-nitride based light emitters in the ultraviolet (UV) and deep ultraviolet (DUV) spectral range are the fundamental building block for several key applications. [Extracted from the article]

Dieser Aufsatz ist eine persönliche Schilderung der Forschungsarbeiten, die zur Entwicklung einer Methode zur Kristallzüchtung von Galliumnitrid (GaN) auf einem Saphir-Substrat führten. Die Ergebnisse bereiteten den Weg für die Entwicklung von smarten Anzeigesystemen auf der Basis blauer LEDs. Die wichtigsten Arbeiten wurden Mitte bis Ende der 80er Jahre durchgeführt. Die Hintergründe der Arbeiten des Autors und die Ereignisse, die in der Technologie für die GaN-Züchtung und die Erzeugung von p-GaN resultierten, werden zusammengefasst. [ABSTRACT FROM AUTHOR]

This Review is a personal reflection on the research that led to the development of a method for growing gallium nitride (GaN) on a sapphire substrate. The results paved the way for the development of smart display systems using blue LEDs. The most important work was done in the mid to late 80s. The background to the author's work and the process by which the technology that enables the growth of GaN and the realization of p-type GaN was established are reviewed. [ABSTRACT FROM AUTHOR]

This is a personal history of one of the Japanese researchers engaged in developing a method for growing GaN on a sapphire substrate, paving the way for the realization of smart television and display systems using blue LEDs. The most important work was done in the mid to late 1980s. The background to the author's work and the process by which the technology enabling the growth of GaN and the realization of p-type GaN was established are reviewed. [ABSTRACT FROM AUTHOR]

Purpose: The displacement and deformation of the knee meniscus significantly affect its roles; however, little is known about the displacement and deformation patterns of a torn medial meniscus. The objective of this study was to evaluate quantitatively the patterns of displacement and deformation in horizontally torn medial menisci during knee flexion. Methods: Twenty patients with horizontally torn medial menisci underwent three-dimensional (3-D) magnetic resonance imaging at varying degrees of knee flexion, and 3-D computer models of the tibia, tibial articular cartilage, and meniscus were generated. Based on these, the size of the horizontal tear (% tear) was evaluated and defined as the circumferential ratio between the length of the horizontal tear and that of the entire meniscus. The 3-D meniscus models were automatically superimposed over images taken at 0, 20, 40, and 60° of knee flexion by the voxel-based registration method. Meniscal motion and deformation during knee flexion were visualized and quantitatively calculated on the mid-sagittal plane. Correlations between the size of horizontal tear, displacement/deformation of torn menisci, and clinical symptoms were evaluated after conservative treatment for 3 months. Results: The % tear was 35.7 ± 12.5 % (range 13.7-55.5 %). During knee flexion, all torn menisci moved posteriorly, with gradual widening of horizontal and vertical gaps ( p < 0.05). A direct correlation was observed between % tear and change in the vertical tear gap during knee flexion ( p < 0.05). There was an inverse correlation between Lysholm score and % tear ( p < 0.05). Conclusion: Medial meniscal horizontal tears widen and deform during knee flexion, and % tear correlates with the change in the vertical gap. Patients with a lower % tear are more capable of performing activities of daily living after conservative treatment. This method may help clarify the cause of pain in patients with medial meniscus tears as well as facilitate the selection of an appropriate treatment plan. Level of evidence: Case series, Level IV. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the clinical outcome of anatomical double-bundle anterior cruciate ligament (ACL) reconstruction using multistranded hamstring tendons via an outside-in approach. Methods: One hundred and twenty-one patients (mean age 28 ± 10 years) who underwent ACL reconstruction were examined. Using an outside-in femoral drill guide, an upper femoral tunnel for the anteromedial (AM) graft was created just below the superior articular cartilage margin of the medial wall of the lateral condyle through a small incision. A lower femoral tunnel for the posterolateral (PL) graft was drilled in the centre of the inferior-posterior half of the attachment area behind the resident's ridge in the same manner. Two tibial tunnels were created at the centre of the AM and PL bundle footprints of a normal ACL. Patients were evaluated at 24 months postoperatively. Results: According to the IKDC form, 52 knees (43 %) were graded as normal, 64 (53 %) as nearly normal, 1 (1 %) as abnormal and 4 (3 %) as graft rupture due to re-injury. Loss of knee extension of <5° was observed in one patient (1 %). Among 111 patients who were directly evaluated, none showed loss of flexion of <5°. Lachman sign was negative in 103 patients (93 %), while the pivot shift test result was negative or equivalent to that of the contralateral healthy knee in 103 patients (93 %). The mean side-to-side difference in anterior laxity at manual maximum force with the KT-2000 arthrometer was 0.9 ± 1.1 mm, and 94 % of patients showed a range between −1 and +2 mm. Conclusion: The anatomical double-bundle outside-in ACL reconstruction provided a satisfactory short-term outcome. Level of evidence: Case series, Level IV. [ABSTRACT FROM AUTHOR]

The anisotropic hole transport along [0001] and [11 2 ¯ 0] in the p-doped (10 1 ¯ 0) GaN layer was compared for layers grown on bulk (10 1 ¯ 0) GaN substrates and on (10 1 ¯ 0) sapphire. The sheet resistance along [0001] was 1.1 times larger on GaN substrates and even 1.2 times larger on sapphire than that along [11 2 ¯ 0]. The anisotropic hole transport on bulk GaN substrates is due to the anisotropy of the hole's effective mass and the different contribution of carriers in different bands, whereas the larger anisotropy for GaN on sapphire is also due to additional scattering at stacking faults. The annealing process of metal Mg applied to the m-plane p-type GaN successfully results in a robust p-type ohmic contact, functioning as a p + + layer. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to describe a safer and more anatomical technique of MPFL reconstruction and to report the short-term results. The subjects included 20 patients with patellar dislocation with a mean age of 23. The operation was performed using a double-looped autogenous semitendinosus tendon graft. Two small bone tunnels were made at the medial edge of the patella, mimicking the wide patellar insertion of the MPFL and a bone tunnel was made at the femoral insertion site. The free ends of the graft attached to the patella and the loop end was fixed to the femoral side. Five patients were available for follow-up interviews by telephone and the remaining 15 were directly examined by physical examination and radiographic evaluation at 2years or longer postoperatively. The average follow-up period was 30months. Re-dislocation or patellar fracture was not seen in any patients. The average Kujala''s score was 96 with a range from 84 to 100. Six patients were classified as excellent and 14 as good, according to the Crosby and Insall grading system. Radiographically, narrowing of the patellofemoral joint space was observed in 2 cases with previous osteochondral fracture out of those who were directly examined. The dual tunnel MPFL reconstruction produces favorable results in subjective and functional assessment of outcome without complications. [Copyright &y& Elsevier]

The objective of this article is to describe the clinical outcome of the transitional double-bundle procedure for anatomical ACL reconstruction. Subjects included 78 patients (average age 25 years) who had undergone ACL reconstruction with the transitional double-bundle procedure with multi-stranded hamstring tendons. The femoral socket for the anteromedial (AM) graft was created at 5–6 mm from the mid-sagittal line of the intercondylar notch at 2:00 or 10:00, and that for the posterolateral (PL) graft was drilled adjacent to the AM socket at 3:00 or 9:00. For the tibial side, two tunnels were made at the center of the footprint of the AM and PL bundles of the normal ACL. Patients were evaluated at 24 months or longer postoperatively based on the IKDC Knee Examination Form. Subjectively, 32 knees (41%) were graded as normal; 41 (53%), as nearly normal; 4 (5%), as abnormal; and 1 (1%) as graft rupture by re-injury. The average side-to-side difference in anterior laxity at manual maximum force with the KT-2000 arthrometer was 0.9 mm ± 1.2. Seventy patients (93%) had a range between −1 mm and 2 mm. In conclusion the transitional double-bundle ACL reconstruction provided a satisfactory outcome after a short-term follow-up. [ABSTRACT FROM AUTHOR]

The genus Leptopulvinaria Kanda is revised and placed in the tribe Pulvinariini as understood by Hodgson. The species L. kawaii sp. nov., which has been misidentified as Pulvinaria camelicola or P. floccifera by several researchers, is recognized as a second species of the genus, in addition to the type species L. elaeocarpi Kanda. Adult females of L. elaeocarpi and L. kawaii are redescribed and a key to the species is presented. [ABSTRACT FROM AUTHOR]

To clarify the importance of the femoral socket location in bi-socket Anterior cruciate ligament (ACL) reconstruction. Subjects included 261 patients with an average age of 26 years who received ACL reconstruction via the high-femoral socket procedure (Group H) and 43 patients with an average age of 29 years who received ACL reconstruction via the low-femoral socket procedure (Group L) with a minimal follow-up of 24 months. In Group H, the femoral sockets were created at 1:00 or 11:00 and 2:00–2:30 or 9:30–10:00 of the intercondylar notch. In Group L, the two femoral sockets were drilled at 2:00 or 10:00 and 3:00 or 9:00. For the tibial side, a single tunnel was made at the center of the footprint. Evaluation was performed based on the IKDC Knee Examination Form. While 137 knees (52%) were graded as normal, 100 (38%) as nearly normal, 8 (3%) as abnormal, and 2 (1%) as severely abnormal with 14 (5%) re-injury in Group H, 38 knees (74%) were graded as normal, and 7 (16%) as nearly normal with 3 (7%) re-injury in Group L, showing a better subjective evaluation ( P = 0.007). The average side-to-side differences in anterior laxity at manual maximum force with the KT-1000 were 1.1 ± 1.6 mm for Group H and 1.0 ± 1.6 mm for Group L without statistically significant differences excluding re-injured cases. There were 204 patients (83%) from Group H and 33 (83%) from Group L with values between −2 and 2 mm, while 228 (92%) patients from Group H and 38 (95%) from Group L had values distributed between −3 and 3 mm. While the bi-socket ACL reconstruction provided objectively satisfactory clinical outcomes in more than 90% of the patients, the low-femoral socket placement was found to subjectively achieve better outcomes. [ABSTRACT FROM AUTHOR]

To clarify the importance of the femoral socket location in bi-socket Anterior cruciate ligament (ACL) reconstruction. Subjects included 261 patients with an average age of 26 years who received ACL reconstruction via the high-femoral socket procedure (Group H) and 43 patients with an average age of 29 years who received ACL reconstruction via the low-femoral socket procedure (Group L) with a minimal follow-up of 24 months. In Group H, the femoral sockets were created at 1:00 or 11:00 and 2:00-2:30 or 9:30-10:00 of the intercondylar notch. In Group L, the two femoral sockets were drilled at 2:00 or 10:00 and 3:00 or 9:00. For the tibial side, a single tunnel was made at the center of the footprint. Evaluation was performed based on the IKDC Knee Examination Form. While 137 knees (52%) were graded as normal, 100 (38%) as nearly normal, 8 (3%) as abnormal, and 2 (1%) as severely abnormal with 14 (5%) re-injury in Group H, 38 knees (74%) were graded as normal, and 7 (16%) as nearly normal with 3 (7%) re-injury in Group L, showing a better subjective evaluation (P = 0.007). The average side-to-side differences in anterior laxity at manual maximum force with the KT-1000 were 1.1 +/- 1.6 mm for Group H and 1.0 +/- 1.6 mm for Group L without statistically significant differences excluding re-injured cases. There were 204 patients (83%) from Group H and 33 (83%) from Group L with values between -2 and 2 mm, while 228 (92%) patients from Group H and 38 (95%) from Group L had values distributed between -3 and 3 mm. While the bi-socket ACL reconstruction provided objectively satisfactory clinical outcomes in more than 90% of the patients, the low-femoral socket placement was found to subjectively achieve better outcomes. [ABSTRACT FROM AUTHOR]

Field doses of six selected insecticides were tested against the immature (pupae) and mature (adult) stages ofDiadegma semiclausum(Hellén) andOomyzus sokolowskii(Kurdjumov), parasitoids of the diamondback moth,Plutella xylostella(L.). Effects of contact toxicity (direct spraying) of the six insecticides on emergence of parasitoids were found negligible on both species except permethrin which caused 37.5% mortality. All adults of both parasitoid species died 24 hours after exposure to chlorfenapyr, emamectin benzoate and permethrin. In contrast, the three insect growth regulators (IGRs), chlorfluazuron, flufenoxuron and teflubenzuron, were found harmless to both species, and adult mortality of both parasitoid species was 0–16.7%. However, parasitism by the females of both parasitoid species was severely impaired when the females were offered the three IGR diluted solutions for 24 hours. Effects of oral toxicities of the IGRs on longevity of both parasitoids after 12 hours exposure were found to be significantly different between males and females. Compatibility of tested insecticides with D. semiclausum and O. sokolowskii and integration of compatible insecticides with these parasitoids in integrated pest management programs of crucifers are discussed. [ABSTRACT FROM AUTHOR]

A new soft scale insect of the tribe Pulvinariini,Pulvinaria hakonensissp. nov., is described from Japan based on several adult females. The lectotype ofPulvinaria neocellulosaTakahashi, 1940 is designated and the species is redescribed and recorded from Japan for the first time. [ABSTRACT FROM AUTHOR]

Sulfidation of CrO3–Al2O3 catalysts (11.1, 16.6 and 22.2 wt.% CrO3) synthesized by incipient wetness impregnation method was monitored by a 35S radioisotope ([35S]H2S) pulse tracer in situ method. This original method permitted us a better understanding of these relatively poorly documented catalytic systems. Experiences confirmed that, in a first step, for temperatures inferior to 400 °C, CrSx species are progressively formed. Then, in a second step for a temperature near 400 °C, formation of Cr2S3 entities is achieved, leading to their decomposition into CrS. This showed that the catalytic phase morphology depends drastically on the sulfidation temperature. Moreover, it was found that the increase in DBT activity with the Cr content previously observed was due to a modification of the nature of the active phase and not to an increase in its quantity. Indeed, whilst the sulfur quantity that accumulated on the catalysts containing 11.1 and 22.2 wt.% CrO3 was almost the same, the DBT HDS activity of the latter was ∼50% higher. [Copyright &y& Elsevier]

But Akasaki still thought the development of the blue LED followed the LED invented by Jacques Pankove, Herbert Maruska, and their group members at RCA and Stanford University. So Akasaki made up his mind to move in 1981 to Nagoya University, where he developed a new crystal-growth method, metal-organic vapor-phase epitaxy. , a 2014 Nobel laureate in physics who brought highly efficient general lighting for the 21st century to people all over the world, passed away on 1 April 2021 in Nagoya, Japan, at age 92. [Extracted from the article]

We report on the growth of AlPN on GaN/sapphire templates by metalorganic vapor phase epitaxy using tertiarybutylphosphine (tBP) and NH3 as group-V precursors. P is easy to incorporate into the group-III lattice site, forming PAl anti-site defects and shrinking lattice constants that are even beyond AlN since Al is larger than P. We found that higher temperatures favor P incorporation on the N-sublattice, forming AlPyN1−y, while growth temperatures below 1000 °C result in dominant P incorporation on the Al-sublattice, forming PAl anisites. Similarly, larger NH3 flows stabilize GaN, leading to flat interfaces, but favor the formation of PAl. Furthermore, the P incorporation into AlPyN1−y is non-linear. At very low tBP flows, it initially increases to reach a maximum. Further increasing the tBP flow increases mostly the incorporation of P on the Al-sublattice, and the c-lattice constant decreases again. This leaves a small window of low V/III ratios below 5 and low P/N ratios of 1% or smaller, leading up to ∼4% P incorporation at typical growth temperatures of GaN. However, at such low V/III ratios, GaN is not stable even with N2 carrier gas and requires optimized switching sequences to minimize its decomposition and preserve flat interfaces. Eventually, a 10 nm coherent layer of AlP0.01N0.99 could be reproducibly grown on top of GaN channels with a smooth surface, an abrupt AlPN/GaN interface, and a two-dimensional electron gas with an electron mobility of ∼675 cm2/V s and a sheet carrier density of 1.5 × 1013 cm−2 at room temperature. [ABSTRACT FROM AUTHOR]

The growth of GaN on sapphire by OMVPE using a low-temperature deposited buffer layer was characterized by in situ TEM observation. The crystalline quality, especially tilting and twisting of the mosaic GaN crystal, was characterized by conventional X-ray diffraction together with grazing-incidence X-ray diffraction. Strain and relaxation of the AlGaN and GaInN on GaN were also characterized by asymmetrical X-ray diffraction. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(10): 48–54, 1998 [ABSTRACT FROM AUTHOR]

This Letter reports an investigation of hole transport in p-GaN/AlGaN/GaN heterostructures through experimental and theoretical analyses under varied conditions. Highly non-linear current–voltage (I–V) characteristics, obtained via the linear transmission line method measurements, are utilized for this study. At low bias voltage, the transport can be ascribed to the Schottky nature of the contact, while at high bias, the conduction is observed to be governed by space-charge limited current (SCLC). The Schottky characteristics (Schottky barrier height and non-ideality factor) and the SCLC exponent were analyzed for devices with varying contact spacings and at different high temperatures. The SCLC exponent, m, is in the range of 2 ≤ m ≤ 4 depending on the applied voltage range, revealing the existence of the trap states in the channel region. The findings of this work indicate that the charge injection, field-induced ionization, and trap states in the p-GaN channel are critical factors in the current transport of p-GaN/AlGaN/GaN heterostructure. [ABSTRACT FROM AUTHOR]

Heterogeneous integration is important to create multi-functionality in future electronic devices. However, few thermal studies of the interfaces formed in these integrated devices have been reported before. Recently, integrated interfaces by surface-activated bonding were found to have high thermal boundary conductance, which provides a solution for heat dissipation of GaN and β-Ga2O3-based power electronics. Here, we review the recent progress on the interfacial thermal transport across heterogeneously integrated interfaces, including transferred van der Waals force bonded interfaces, surface-activated bonded interfaces, plasma bonded interfaces, and hydrophilic bonded interfaces. This Perspective specifically focuses on applications of thermal management strategies of electronics, especially power electronics. Finally, the challenges, such as high-throughput thermal measurements of buried interfaces, thermal property-structure relations of interfaces bonded under different conditions, theoretical understanding of interfacial thermal transport, and device demonstrations, are pointed out. [ABSTRACT FROM AUTHOR]

The precise control of Mg concentration ([Mg]) in p-type GaN layers from 2.3 × 1016 to 2.0 × 1019 cm−3 was demonstrated by halide vapor phase epitaxy (HVPE) on n-type GaN (0001) freestanding substrates. [Mg] in GaN layers could be controlled well by varying the input partial pressure of MgCl2 formed by a chemical reaction between MgO solid and HCl gas under the thermodynamic equilibrium condition. In the sample with [Mg] of 2.0 × 1019 cm−3, a step-bunched surface was observed because the surface migration of Ga adatoms was enhanced by the surfactant effect of Mg atoms. The samples show high structural qualities determined from x-ray rocking curve measurements. The acceptor concentration was in good agreement with [Mg], indicating that almost all Mg atoms act as acceptors. The compensating donor concentrations in the samples were higher than the concentrations of Si, O, and C impurities. We also obtained the Mg acceptor level at a sufficiently low net acceptor concentration of 245 ± 2 meV. These results show that the HVPE method is promising for fabricating GaN vertical power devices, such as n-channel metal–oxide–semiconductor field-effect transistors. [ABSTRACT FROM AUTHOR]

As the size of micro light-emitting diodes (μLEDs) decreases, μLEDs encounter etching damage especially at the sidewalls that critically affects their properties. In this study, we investigated the influence of etching bias power (Pbias) on the performance of μLEDs and found that the current–voltage and light output–current characteristics of μLEDs were enhanced when Pbias was reduced. It was shown that at low Pbias, the chemical reaction between etching gas and gallium nitride, rather than ion sputtering, dominated the etching process, leading to low plasma damage and rough surface morphology. Additionally, to understand the etching-induced surface roughening behaviors, various substrates with different threading dislocation densities were treated at low Pbias. It was found that for the sample (with p-contact size of 10 × 10 μm2), the efficiency droop was approximately 20%, although the current reached 10 mA due most probably to the suppressed polarization effect in the quantum well. It was further observed that the external quantum efficiency (EQE) was dependent on Pbias, where the lowest Pbias yielded the highest maximum EQE, indicating that the plasma damage was mitigated by reducing Pbias. Optimization of dry etching and polarization-suppression conditions could pave the way for realizing high-performance and brightness μLEDs for next-generation displays. [ABSTRACT FROM AUTHOR]

Advances in obtaining untwinned (10 1 ¯ 3)-oriented semi-polar GaN enable a new crystal orientation for the growth of green and red LED structures. We present a scanning electron microscopy study that combines the structural characterization of electron channeling contrast imaging with the optical characterization of cathodoluminescence hyperspectral imaging on a (10 1 ¯ 3) GaN layer. An extensive defect analysis revealed that the dominant defects consist of basal plane stacking faults (BSFs), prismatic stacking faults, partial dislocations, and threading dislocations. With a defect density of about an order of magnitude lower than in comparable. The optical properties of the defects have been characterized from 10 to 320 K, showing BSF luminescence at room temperature indicating a reduced density of non-radiative recombination centers in the as-grown samples compared to established semi- and non-polar orientations. Our findings suggest that growth along (10 1 ¯ 3) has the potential for higher radiative efficiency than established semi-polar orientations. [ABSTRACT FROM AUTHOR]

The degradation of an AlGaN‐based deep‐ultraviolet laser diode during operation is studied. A rapid increase in threshold current without any facet mirror damage under direct current stress below the threshold current is observed, which is considered to limit the lifetime of continuous wave lasing to the level of seconds. The evolution of current–light and current–voltage characteristics suggests that the dominant mechanism of degradation is the increased loss of carriers before they can reach the active layer, i.e., the decrease in carrier injection efficiency. The decrease in emission intensity, which is more pronounced at lower current densities, and subsequent increase in sub‐threshold current indicate the increase in defect density under current stress, which is similar to the well‐analyzed degradation mechanism found in AlGaN‐based light‐emitting diodes. [ABSTRACT FROM AUTHOR]

Increasing the injection efficiency, a critical factor constraining the reduction in threshold current in AlGaN-based deep-ultraviolet laser diodes, represents one of the paramount remaining technical challenges. In this study, the impact of compositionally graded layers that were unintentionally formed at the interface between the p-cladding and the core layer on carrier injection efficiency was analyzed. Experimental evaluations using laser diodes have shown that the elimination of an unintentionally formed layer increases the injection efficiency above the threshold current, from the conventional 3% to 13%. It has been postulated that the electron overflow toward the p-side exerts a substantial deleterious effect on the injection efficiency. An improvement in this aspect is achieved by increasing the electron-blocking capability due to the improved interface abruptness between the p-cladding layer and the core layer. The lasing threshold was strongly reduced, and characteristic temperature increased from 76 to 107 K for the improved devices. [ABSTRACT FROM AUTHOR]

Background: Open reduction and internal fixation (ORIF) has been widely performed because the osteochondral component of the osteochondritis dissecans (OCD) lesion is the most suitable for reconstructing the joint structure. Purpose: To evaluate radiological healing in terms of reconstructed bony structure after ORIF with bone graft by computed tomography (CT), to identify preoperative prognostic factors for failure, and to determine the cutoff value of radiological healing for risk of failure. Study Design: Case-control study; Level of evidence, 3. Methods: A retrospective cohort study of 42 patients (44 knees) who underwent internal fixation with bone graft for OCD lesions of the knee from 2004 to 2018 was conducted. All patients were evaluated 6 months postoperatively, and if not healed 6 months after surgery, they were evaluated by CT periodically thereafter. Radiological healing was judged according to the following 3 criteria: (1) reossification of the OCD lesion, (2) bony continuity between the OCD lesion and basal floor, and (3) reconstructed bony surface of the femoral condyle reconstructed to match the normal joint. Then, the percentage of the radiological healing area was calculated as the ratio of the healing length to the total lesion length. The nonhealing area was calculated by multiplying the sum of the total nonhealing length. Clinical failure was defined as any definitive reoperation for the same OCD lesion, such as fragment excision, or a cartilage restoration procedure. After 6 months, all eligible patients underwent arthroscopy to check for protrusion of the absorbable pin into the joint; the removal of an absorbable pin protruding into the joint was not considered a failure. Results: Clinical failure was recorded for 4 cases (9.1%). The mean overall percentage of the radiological healing area of OCD 6 months after ORIF with bone graft was 79.5% ± 24.4%, and the mean overall nonhealing area at 6 months was 87.8 ± 107.9 mm2. The percentages of radiological healing area of stable (International Cartilage Regeneration & Joint Preservation Society OCD II) lesions and femoral condylar (lateral femoral condyle + medial femoral condyle) lesions were significantly lower than unstable lesions and femoral groove lesions, respectively (P =.01 and P =.03, respectively). On receiver operating characteristic curve analysis, the cutoff points for predicting a significantly increased risk of failure were 33.9% (sensitivity, 100%; specificity, 100%; area under the curve, 1) for the percentage of radiological healing area and 222.9 mm2 (sensitivity, 95%; specificity, 100%; area under the curve, 0.956) for the nonhealing area 6 months postoperatively. Conclusion: A stable lesion and a femoral condylar lesion were the predictors of poor radiological healing on CT images 6 months after ORIF with bone graft. The risk of failure was increased significantly in cases with only approximately one-third of the lesion healed or in cases with large nonhealing areas at 6 months postoperatively. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the impact of periphery, width, length and area on the external quantum efficiency (EQE) of stripe-type InGaN-based red micro-light-emitting diodes (µ LEDs). A longer periphery resulted in a higher light extraction efficiency ( η e ) via the sidewall regardless of the area of the µ LEDs. However, as the injection current increased a somewhat larger efficiency droop was observed at the longer periphery due to current crowding. Additionally, larger µ LEDs experienced more self-heating than smaller ones, resulting in a red shift of wavelengths and a larger efficiency droop. When the current density exceeded 100 A cm−2, the EQE ratio of smaller-area μ LEDs to larger-area ones increased significantly due to the difference in efficiency droop. Besides, a short light propagation length and a long emission width yielded a higher η e . Hence, the periphery, width, length and area of the µ LEDs determine EQE, which provides insight into the pixel design of µ LED displays. [ABSTRACT FROM AUTHOR]

Minority carrier properties in dopant-free p-type distributed polarization doped (DPD) AlGaN layers were investigated on the basis of the forward-biased current density–voltage (J–V) characteristics of p–n+ diodes. The fabricated p-DPD AlGaN/n+–AlGaN:Si diodes exhibited ideal electrical characteristics despite the absence of acceptor atoms in the p-type layer. The extracted Shockley–Read–Hall lifetime exceeded 300 ps, which was longer than that reported for p-GaN:Mg on GaN substrates with a similar acceptor concentration (20–50 ps). Moreover, the electron diffusion coefficient was about 20 cm2 s−1 at any temperature, which was convincing in terms of the electron mobility in DPD layers. The results suggest that p-DPD AlGaN has more desirable minority carrier properties than conventional p-GaN:Mg, particularly for bipolar device applications. [ABSTRACT FROM AUTHOR]

In this study, vertical-type thick BGaN PIN diodes were successfully fabricated to improve the neutron capture rate of BGaN diodes by improving the BGaN epitaxial growth technique. In this technique, 5-μm-thick epitaxial growth was achieved using trimethylboron as a B metal-organic source, which suppressed the gas-phase reaction. The α-particle energy spectrum, the neutron pulse signal, and the residual energy of particles emitted from a neutron capture reaction were measured using the fabricated BGaN diodes by performing radiation detection measurements. The detected signal position in the neutron detection signal spectrum was similar to that of 2.3 MeV α-particles. These results indicate that vertical-type BGaN diodes can be used as effective neutron detectors. [ABSTRACT FROM AUTHOR]

One approach to improving the output power of ultraviolet (UV-C) light-emitting diodes (LEDs) is to adopt an electron-blocking layer (EBL) with a high barrier. However, the intended effect may not be realized because of the composition pulling effect, which is the unintended occurrence of a gradient layer at an AlGaN/AlGaN hetero-interface with substantial differences in the Al composition. Here, we demonstrate that low-temperature growth (i.e., <1000 °C) can be used to control the unintentional gradient layer at an AlN/AlGaN hetero-interface between a barrier layer and AlN-EBL with a difference in Al compositions of more than 30%. LEDs with an emission wavelength of 265 nm were fabricated, and an AlN-EBL was grown at low temperature to realize an abrupt interface. At an applied current of 100 mA, growing the EBL under low-temperature conditions improved the forward voltage by 0.5 V and remarkably improved the peak luminous intensity by 1.4–1.6 times. Our results can be used to realize UV-C LEDs with a steep EBL and further improve their device characteristics. [ABSTRACT FROM AUTHOR]

Nonradiative recombination rate that consists of dislocation‐related nonradiative recombination rate (A0) and surface recombination rate (As) is one of the major parameters determining the performance of microlight‐emitting diodes (µLEDs). Recent demonstrations improving the efficiency of blue InGaN or red AlGaInP µLEDs using specific methods such as atomic layer deposition or chemical treatment confirm the suppression of As. However, it is hardly found that those methods effectively improve the efficiency of red InGaN µLEDs so far. Here, it is discovered that the dislocation leads to an ineffective As. First, an intrinsic As degrades the external quantum efficiency (EQE) of blue InGaN µLEDs, resulting in EQE decreases with shrinking size. Second, panchromatic cathodoluminescence finds evidence that most of the carriers can be trapped before reaching the sidewall due to high A0. This results in shortened diffusion length of carriers and reduces the number of carriers reaching the sidewall. Consequently, the opposite trend of increasing EQE with shrinking size occurs in the case of red InGaN µLEDs due to an ineffective As. Furthermore, an 8.3 nm quantum well of InGaN with 13% Indium content that can reach a ≈690 nm wavelength at the low current is shown. [ABSTRACT FROM AUTHOR]

We attempted to grow (10–13) semi-polar GaN on graphene to confirm the possibility of a remote epitaxy of semi-polar GaN. Single crystalline (10–13) GaN was obtained on an optimized template using optimized growth conditions. However, (10–13), (0002), and other GaN orientations were found under the same growth conditions on a graphene-coated template. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy revealed that multi-domain GaN and (0002) GaN occurred in areas with a damaged graphene interfacial layer and intact graphene, respectively. Raman spectroscopy confirmed that graphene could survive under the growth conditions used here. Using cross-sectional scanning electron microscopy, we propose a simple approach to distinguish damaged graphene. Although the remote epitaxy of semi-polar GaN has not been demonstrated despite the usage of an optimized template and growth conditions, our results confirm the importance of the interfacial state in determining the crystallinity of the overgrown layer. [ABSTRACT FROM AUTHOR]

Ga-rich zones created along macrosteps in n-AlGaN plausibly function as electron pathways of AlGaN-based deep-ultraviolet (DUV) LEDs fabricated on AlN templates using 1.0°-miscut c(0001) sapphire substrates toward the m[1-100] axis. This work was performed to clarify AlN mole fractions (xAl) of Ga-rich zones. xAl ≃ (7/12, 6/12, and 5/12) was observed in Ga-rich zones in AlαGa1−αN (α ≃ 0.63, 0.55, and 0.43, respectively) by the method proposed in our previous article in which we showed that Ga-rich zones of Al8/12Ga4/12N were created in Al0.7Ga0.3N. xAl in the Ga-rich zones obtained from an energy-dispersive x-ray signal by scanning transmission electron microscopy calibrated by Rutherford backscattering well agreed with xAl obtained by cross-sectional cathodoluminescence (CL) spectroscopy using scanning electron microscopy. A weak CL shoulder peak corresponding to Al4/12Ga8/12N was also observed for Al0.43Ga0.57N. In addition, xAl ≃ n/12 (n = 6–9) in Al-rich zones appeared in the rest of the Ga-rich zones. Furthermore, nanobeam electron diffraction patterns of the Ga-rich zones indicated a high possibility of a regular configuration of Ga and Al atoms on the c(0001) plane in our samples. Consequently, xAl values in nonflat AlGaN layers with macrosteps were often determined to be near n/12 (n: integer). Thus, Ga-rich zones (xAl = n/12: n = 4–8) formed in our nonflat AlGaN layers, which originated from the macrosteps along [11–20] edgelines normal to the m[1–100] axis, are suggested to be metastable. The creation of discrete xAl in Ga-rich zones should contribute to the stable production of DUV-LEDs using high-miscut sapphire substrates. [ABSTRACT FROM AUTHOR]

Review: personal account of the background of the studies that led to the technologies for growing GaN and producing p-GaN; 61 refs. [ABSTRACT FROM AUTHOR]

AlGaN-based deep-ultraviolet light-emitting diodes (LEDs) incorporating uneven multiple quantum wells (MQWs) with inclined and terrace zones, which were fabricated on an AlN template with dense macrosteps, have exhibited a high internal quantum efficiency (IQE). To investigate the microscopic structure of uneven MQWs, cathodoluminescence (CL) mapping characterization was carried out, and the maps of the CL intensity at 300 K relative to that at 38 K were obtained for uneven MQWs that targeted 265 and 285 nm LEDs. At an electron beam current of less than 1.0 nA, the signals from inclined and terrace zones of the uneven MQWs were confirmed to satisfy the nonsaturated excitation condition at 300 K. Nonradiative recombination (NR) was insufficiently frozen even at 38 K, specifically on the terraces in the 265 nm MQW, suggesting high concentrations of NR centers due to point defects (PDs). In contrast, NR in the 285 nm MQW at 38 K was closer to freeze-out. The concentration of PDs in the 285 nm MQW was likely to be lower than that in the 265 nm MQW. Finally, the ratios of the CL intensity at 300 K to those at 38 K were mapped, demonstrating an approach to creating an approximate map of IQE. The values in the CL intensity ratio maps are discussed by considering the analytical error factors. The results support the model of localized current injection through Ga-rich stripe zones in the n-AlGaN cladding layer. [ABSTRACT FROM AUTHOR]

A non-filter virus inactivation unit was developed that can control the irradiation dose of aerosolized viruses by controlling the lighting pattern of a 280 nm deep-UV (DUV)-LED and the air flowrate. In this study, the inactivation properties of aerosolized SARS-CoV-2 were quantitatively evaluated by controlling the irradiation dose to the virus inside the inactivation unit. The RNA concentration of SARS-CoV-2 remained constant when the total irradiation dose of DUV irradiation to the virus exceeded 16.5 mJ/cm2. This observation suggests that RNA damage may occur in regions below the detection threshold of RT-qPCR assay. However, when the total irradiation dose was less than 16.5 mJ/cm2, the RNA concentration monotonically increased with a decreasing LED irradiation dose. However, the nucleocapsid protein concentration of SARS-CoV-2 was not predominantly dependent on the LED irradiation dose. The plaque assay showed that 99.16% of the virus was inactivated at 8.1 mJ/cm2 of irradiation, and no virus was detected at 12.2 mJ/cm2 of irradiation, resulting in a 99.89% virus inactivation rate. Thus, an irradiation dose of 23% of the maximal irradiation capacity of the virus inactivation unit can activate more than 99% of SARS-CoV-2. These findings are expected to enhance versatility in various applications. The downsizing achieved in our study renders the technology apt for installation in narrow spaces, while the enhanced flowrates establish its viability for implementation in larger facilities. [ABSTRACT FROM AUTHOR]

Deep ultraviolet (DUV) photons interact strongly with a broad range of chemical and biological molecules; compact DUV light sources could enable a wide range of applications in chemi/bio-sensing, sterilization, agriculture, and industrial curing. The much shorter wavelength also results in useful characteristics related to optical diffraction (for lithography) and scattering (non-line-of-sight communication). The family of III–N (AlGaInN) compound semiconductors offers a tunable energy gap from infrared to DUV. While InGaN-based blue light emitters have been the primary focus for the obvious application of solid state lighting, there is a growing interest in the development of efficient UV and DUV light-emitting devices. In the past few years we have witnessed an increasing investment from both government and industry sectors to further the state of DUV light-emitting devices. The contributions in Semiconductor Science and Technology ’s special issue on DUV devices provide an up-to-date snapshot covering many relevant topics in this field. Given the expected importance of bulk AlN substrate in DUV technology, we are pleased to include a review article by Hartmann et al on the growth of AlN bulk crystal by physical vapour transport. The issue of polarization field within the deep ultraviolet LEDs is examined in the article by Braut et al. Several commercial companies provide useful updates in their development of DUV emitters, including Nichia (Fujioka et al ), Nitride Semiconductors (Muramoto et al ) and Sensor Electronic Technology (Shatalov et al ). We believe these articles will provide an excellent overview of the state of technology. The growth of AlGaN heterostructures by molecular beam epitaxy, in contrast to the common organo-metallic vapour phase epitaxy, is discussed by Ivanov et al. Since hexagonal boron nitride (BN) has received much attention as both a UV and a two-dimensional electronic material, we believe it serves readers well to include the article by Jiang et al on using BN for UV devices; potentially as a p-type wide band gap semiconductor contact. Finally, an in-depth discussion of one DUV application in defense, the non-line-of-sight (NLOS) communication, is given by Drost and Sadler. Overall, we believe that this special issue of Semiconductor Science and Technology provides a useful overview of the state-of-art in the field on DUV materials and devices. In view of the rapidly growing interest in this field, the demonstrated enhanced device performance, and the wide range of applications, this special issue can be considered a very timely contribution. Finally, we would like to thank the IOP editorial staff, in particular Alice Malhador, for their support and also like to thank all contributors for their efforts to make this special issue possible. [ABSTRACT FROM AUTHOR]

AlN‐based field‐effect transistors (FETs) enable high‐breakdown voltage, high drain current, and high‐temperature operation. To realize high‐frequency devices, N‐polar AlGaN/AlN heterostructure FETs are focused on. N‐polar Al0.1Ga0.9N/Al0.9Ga0.1N/AlN FET is fabricated using metal–organic vapor‐phase epitaxy, and its electrical characteristics are evaluated. An N‐polar AlN layer is grown on a sapphire substrate with a misorientation angle of 2.0° toward m‐axis, on which a 20 nm thick Al0.9Ga0.1N base layer and a 20 nm Al0.1Ga0.9N channel layer are grown. The static FET operation is confirmed to exhibit an n‐channel and pinch‐off. Normally, during operation with a turn‐on voltage of −3.2 V, a high operating breakdown voltage of 620 V and high operating temperature of 280 °C are also confirmed. [ABSTRACT FROM AUTHOR]

The metal stop laser drilling of GaN‐on‐GaN devices is demonstrated using a UV sub‐nanosecond laser as a light source. By monitoring the Bremsstrahlung emission at the drilling point, metal stops with a precision higher than 1 μm are realized for vias with a depth of 100 μm. From in situ laser‐induced breakdown spectroscopy measurements, it is shown that endpoint detection is realized with high signal‐to‐noise ratio owing to the difference in the emission process between the strongly excited semiconductor and the metal. Herein, a through‐substrate electrode with a resistance of less than 5 mΩ on GaN‐on‐GaN high‐electron‐mobility transistor (HEMT) wafers is demonstrated. The fabrication of through‐substrate electrodes by this technique provides a simple process that does not require lithography or other complex processes. This process is expected to be useful in the fabrication of future GaN‐on‐GaN devices, including very thin GaN‐on‐GaN HEMTs. [ABSTRACT FROM AUTHOR]

We investigated the hole mobility limiting factors in dopant-free p-type distributed polarization-doped (DPD) AlGaN layers by an experimental method. p-DPD AlGaN exhibited a higher hole mobility than GaN:Mg with a similar room temperature hole concentration across all temperature ranges owing to the absence of ionized impurity scattering. In addition, unlike in n-DPD AlGaN, alloy scattering was not always critical in p-DPD AlGaN. The extracted alloy scattering potential was only 0.3 eV, which resulted in a reduced effect of alloy scattering and originated from a small valence band offset in the GaN/AlN heterojunction system. The results suggest that DPD principally enables the fabrication of low-resistance p-type nitride semiconductor thin films as a result of the high hole concentration and high hole mobility. [ABSTRACT FROM AUTHOR]