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Eu-doped GaN (GaN:Eu) is a good candidate for realizing red laser diodes with temperature stability. Nanocolumn crystals are useful for achieving a high optical gain by a high Eu concentration because they can suppress the degradation of crystalline quality. In this study, regularly arranged GaN:Eu or InGaN:Eu/GaN quantum well (QW) nanocolumns were fabricated using the Ti-mask selective-area growth technique by RF-plasma-assisted molecular beam epitaxy. A sharp luminescence corresponding to inner shell electron transition was observed at approximately 620 nm for both the samples. The regular arrangement resulted in a high extinction ratio and uniform emission distribution. Many undesirable nanocrystals observed on the Ti mask due to low-temperature growth of GaN:Eu were easily removed by preparing a SiO2 layer under the Ti mask and lifting it using a HF treatment. The main peaks and emission efficiency of the InGaN:Eu QW nanocolumns depended on the column diameter, with thick nanocolumns (diameters of more than 260 nm) showing a high emission efficiency. These results suggested that regularly arranged GaN:Eu nanocolumns can be one of the basic technologies for the realization of novel optical devices.

In this work Ga adatom incorporation diffusion length was quantified in two different directions, 〈1 1 0〉 and 1 1 ¯ 0 > , during MBE growth of a GaP layer. Thickness distribution was measured for the GaP layer grown on striped patterned GaP substrate and the data was analyzed based on a one-dimensional diffusion growth model between two different adjacent facets. It was quantitatively revealed that the diffusion length of the Ga adatoms increased with growth temperature and an anisotropy in the diffusion length was observed along 110 > and 1 1 ¯ 0 > directions. The influence in the morphology due to the diffusion length anisotropy was discussed with the RHEED patterns.

This study presents a new model for point-defect modification in III-V-N alloys through first-principle calculations and several validation experiments conducted in our previous study, which explain the enhanced crystallinity of III-V-N alloys caused by proton irradiation and rapid thermal annealing (RTA). Validation experiments clarified that the conversion efficiency of the GaAsPN solar cell increased after proton irradiation followed by RTA, whereas that of the GaP solar cell decreased after the same process. Thus, the improved crystallinity of the GaAsPN alloy by this process is attributed to the decrease in nitrogen-related point defects in the crystal. The detailed annihilation mechanism of the nitrogen-related point defect was then studied using first-principle calculations demonstrating that the representative nitrogen-related point defects can change to a lower-energy state when a vacancy forms at its neighboring group V site, leading to the annihilation of the defects. It was concluded that vacancies created by proton irradiation enhance the annihilation of nitrogen-related point defects.

This study presents the positive effects of proton/electron irradiation on the crystallinity of GaP-based dilute nitride alloys. It is found that proton/electron irradiation followed by rapid thermal annealing enhances the PL peak intensity of GaPN alloys, whereas major photovoltaic III–V materials such as GaAs and InGaP generally degrade their crystal quality by irradiation damage. Atomic force microscopy and transmission electron microscopy reveal no degradation of structural defects. GaAsPN solar cell test devices are then fabricated. Results show that the conversion efficiency increases by proton/electron irradiation, which is mainly caused by an increase in the short-circuit current.

This paper presents the impact of temperature and nitrogen-composition on the growth mode and crystallinity of GaAsPN alloys. Reflection high-energy electron diffraction results combined with transmission electron microscopy analysis revealed that maintaining two-dimensional (2-D) growth required higher temperatures when nitrogen composition increased. Outside the 2-D growth windows, stacking faults and micro-twins were preferentially formed at {1 1 1} B planes rather than at the {1 1 1} A planes and anomalous growth was observed. The photoluminescence spectra of GaAsPN layers implies that the higher temperature growth is effective for reducing the nitrogen-related point defects.

This paper presents intentional doping of n - and p -type GaAs 0.19 P 0.76 N 0.05 alloys by molecular beam epitaxy, followed by rapid thermal annealing (RTA). Sulfur and magnesium were respectively used as n - and p -type dopants. The carrier concentrations were controllable between 10 17 and 10 19 cm −3 by adjusting the dopant cell temperature. It was revealed that Hall mobility of the n -type GaAsPN alloys was increased by the RTA process compared to as-grown ones, whereas no significant difference was apparent in the p -type alloys. It is believed that improvement of the conduction band spatial uniformity was mainly responsible for the Hall mobility increase of the n -type GaAsPN alloys by RTA. Finally, a p-i-n GaAsPN diode structure was grown on n -type GaP substrates. A current-voltage characteristic showed a typical rectifying curve with a built-in voltage of 1.8 V and an ideality factor of 1.45. The reverse saturation current was estimated to be less than 10 nA/cm 2 .

Dilute III-V nitride alloys such as GaPN and GaAsPN are essential candidates of materials for light emitting or light absorbing devices on Si substrates due to their perfect lattice matching to Si. For device applications, impurity doping and the concentration control are important issues. However, with the conventional dopants such as Si, Te and S, carrier concentration drastically decreased with N composition increased. This paper presents intentional doping of germanium (Ge) to GaP-based III-V-N alloys by using molecular beam epitaxy. The carrier concentration of Ge-doped GaAsPN was increased with N composition in contrast to conventional dopants such as S and Si. From temperature characteristics of Hall effect measurement, it is revealed that activation energy is decreased with N composition, while Ge concentration in the alloy is constant value. In addition, we found that background doping level of Ge is extremely low $( compared to S. As a result, Ge is a promising candidate as a new dopant for III-V-N alloys.

Fabrication and device characteristics of GaN-based inverter is investigated towards future GaN-based functional monolithic integrated circuit. n-channel enhancement and depletion mode MOSFETs (E-MOSFET and D-MOSFET) were fabricated on a low-density Mg-doped p-GaN substrate. Threshold voltage control of MOS-FET to obtain D-MOSFET was made by preferential Si implantation. Operation of E-MOSFET and D-MOSFET was confirmed in I D -V DS and I D -V GS characteristics. Successful operation of E/D type inverter with a maximum voltage gain beyond unity was demonstrated in monolithically integrated E-MOSFET and D-MOSFET on a same chip.

The necessity for improved renewable energy sources has increased in recent years, particularly solar cells have been continuously improving. This study proposes a type-II quantum dot (QD) structure using InP and GaP-based III–V–N alloys to enhance electron/hole spatial separation for photovoltaic applications. With appropriate size and thickness, InP QD/GaAsPN enables type-II band alignment. Additionally, it has a tunable bandgap of approximately 1.7 eV with strain compensation conditions on a Si substrate, which enables dislocation-free III–V/Si tandem cells. Self-assembled nanostructures of InP were fabricated on GaP, and two types of islands were observed. Growth parameters were investigated to ensure better control over the morphology of islands. Subsequently, the optimized parameters were employed for fabricating a 30-period good quality InP/GaP stacked QD structure without any strain compensation layers. These results may help in designing more efficient GaP-based III–V–N solar cells on Si substrates.

This paper presents the growth of GaAsN pseudo-alloys by a surface nitridation method that consisted of a repeated cycle of nitridation of the GaAs (001) surface, growth interruption and growth of a GaAs overlayer. Surface reconstruction during the nitridation process changed from (2×4) to (1×4) and (3×4) phases above 540 °C with the increase of nitridation time, resulting in a higher N compositions of the alloys. It was revealed that an excessive nitridation resulted in the degradation of the photoluminescence (PL) intensity. While the N composition slightly decreased with the interruption time, less impact appeared on their crystallinity characterized by PL measurement. As a result, the N composition was controllable between 1% and 5% by the combination of growth temperatures (460–600 °C) and thicknesses of the GaAs overlayer (2–8 monolayers; MLs). The thickness of the GaAs overlayer should be designed over 4 ML to form a flat surface for the next nitridation process. The integrated PL intensity of GaAs 0.97 N 0.03 alloys was increased by 7 times compared to the one grown by conventional growth method (continuous supply), indicating the improved crystalline quality of the GaAsN alloys.

For the first time, a rare-earth-doped GaN nanocolumn light-emitting diode is fabricated on an n-type (111) Si substrate, grown by rf-plasma-assisted molecular beam epitaxy. The nanocolumn structure remained in the n-GaN and europium-doped GaN active regions, but the lateral growth was enhanced in the p-GaN region such that a continuous film was obtained. Clear diode characteristics and a sharp red luminescence with two dominant peaks at 620.3 and 633.8 nm were observed at room temperature. The shift in the wavelength with an increase in the injected current was

We have examined the influence of electron irradiation and rapid thermal annealing on photoluminescence emission from GaAsNBi alloys. Electron irradiation of a 1-eV compressively strained GaNAsBi-on-GaAs epilayer, grown by molecular beam epitaxy and subsequently rapidly thermally annealed, is found to induce much stronger photoluminescence than what is observed for an identical as-grown sample upon annealing. At the same time, annealing of the irradiated sample caused a negligible spectral blueshift and reduced alloy potential energy fluctuations. These irradiation-related phenomena occurred without a change in the alloy macroscopic composition as revealed by x-ray diffraction and are mainly related to the nitrogen incorporated into non-substitutional sites in the quaternary alloy.

We investigated the effect of Mg codoping on luminescence properties of AlGaN:Eu to improve emission through synergy effect between an increase in bandgap by AlGaN and the Mg codoping technique. The luminescence properties of AlGaN:(Eu, Mg) are strongly influenced by the Mg concentration and Al composition. Mg codoping in AlGaN was observed to contribute to increasing photoluminescence (PL) integrated intensity and to improve thermal quenching from 7.3% to 60% while the dominant optical site remained site B (622.3-nm peak) with low excitation cross section. The total concentration of optically activated Eu at 25 K was a constant at for either optical site, indicating that Mg codoping did not affect the formation of optical sites. The PL decay times at room temperature (RT) increased with Mg concentration because of suppression of the back-transfer process. For optimized Mg concentration, an increase in the Al composition contributed to the total activated Eu concentration and changed the dominant optical site from A (620.3-nm peak) to B. The activation energy E a , which is the difference in energy between the 5 D 0 energy level and the trap level in the host material, was estimated from temperature dependence of PL decay time. The E a for site A was larger than that for site B, suggesting that the back-transfer rate for site A was less than that for site B.

We have demonstrated a novel selective area growth (SAG) method based on rf-plasma-assisted molecular beam epitaxy for AlGaN nanocolumns using nanotemplates. The nanotemplates, which were prepared on a metal-organic chemical vapor deposition-GaN template, consisted of a triangular lattice of nanopillars with a lattice constant from 200 to 400 nm. For nanopillars with a lattice constant of 400 nm, the gap width between adjacent pillars was varied from 30 to 130 nm. The well-controlled SAG of GaN nanocolumns was achieved on nanopillar arrays with gap widths of less than approximately 45 nm. The beam shadowing effect, which was induced in the high-density nanopillar arrays with small gaps, was a key mechanism in the SAG. This gap width condition for SAG was satisfied for lattice constants from 200 to 400 nm. Using the nanotemplate SAG technology, the SAG of AlGaN nanocolumn arrays was achieved for Al compositions of 0.13, 0.22, 0.43, and 1. Single-peak photoluminescence (PL) spectra of AlGaN were observed, whose wavelengths were close to the calculated bandgap wavelengths using the bandgaps of AlN (6.015 eV) and GaN (3.39 eV) and a bowing parameter of 0.98 eV.

Learning by the actual experience of fabrication and evaluation of a p-n junction is a very effective way for students to obtain a deep meaningful understanding of the fundamentals of semiconductor physics. To achieve this requirement at a real-world classroom situation, a simplified fabrication process for making the silicon p-n junction as the educational application was studied. The process without using the lithography process, and in use of simple thermal diffusion furnace under the air environment for the impurity thermal diffusion process by using phosphorous silicate glass (PSG) thin film prepared by the Sol-Gel material as the phosphorus (P) diffusion source was proposed and tested. As the results, it was obtained that the impurity concentration and diffusion depth were controlled well by this method, and good rectification phenomenon of the p-n junction was successfully observed. The typical diode factor n of the p-n junction was approximately 2.3. The p-n junction also performed well as a solar cell. The FF is approximately 0.7. These results show that it is possible to use the p-n junction prepared by this simplified process as the educational device to help students’ understanding of the theory of the p-n junction.

In this study, we have investigated SiO2 deposition by chemical vapor deposition enhanced by neutral oxygen at the ground state extracted from a surface-wave generated plasma proposed by our group at 350°C using hexamethyldisilane (HMDS) as a precursor. Good properties of deposited SiO2 having refractive index of n = 1.45–1.46 have been confirmed by ellipsometry. Stoichiometric SiO2 was also confirmed by X-ray photoelectron spectroscopy (XPS) with single peak of Si 2p and O 1s. High quality SiO2 film deposition was also confirmed by Fourier transform infrared spectrometer (FT-IR) analysis indicating formation of chemical bonding in SiO2 with no unwanted bonds due to -OH or -CH3 groups.

Eu-doped GaN (GaN:Eu) is a promising solid-state material for quantum information devices owing to its ideal quantum levels. However, a decrease of Eu concentration and the unification of optical sites are required for these devices to access an Eu ion. In this article, the effect of Eu concentration on the optical properties of Mg-codoped GaN:Eu was evaluated. The photoluminescence intensity from Eu ions increased linearly with increasing Eu concentration up to 1 × 1019 cm−3, beyond which the intensity saturated. This resulted from the increase of the sharp luminescence line at 620.5 nm (site A), which has a large excitation cross section, with increasing Eu concentration in the range of low Eu concentrations; an excess Eu concentration leads to the formation of other types of optical sites with a low transfer efficiency or inactive sites. For a low Eu concentration of 3 × 1018 cm−3, all optical sites except a specific optical site corresponding to site A disappeared, and the unification of optical sites was suggested. This result is expected to be valuable to realize quantum information devices.

Nanocolumn light-emitting diodes (LEDs) are expected to achieve the monolithic integration of the three primary-color micro-LEDs for micro-LED displays. From the viewpoints of low cost and large-area substrates, a technology for the regular arrangement of nanocolumns on Si substrates is required. The improvement of GaN nanocolumns on Si would be an important advance for the preparation of high efficiency optical devices. In this paper, the effects of column diameter and height on the photoluminescence (PL) and cathodoluminescence properties of GaN nanocolumn arrays were investigated. The PL intensity of the 700-nm high (tall) nanocolumn was three times stronger than that of the 350-nm high (short) nanocolumn. Although the PL intensity decreased dramatically with an increasing diameter for the shorter nanocolumns, it retained its high value (up to 220 nm) for the taller GaN nanocolumns. For the latter specimens, a decrease in the number of emitting nanocolumns, which would reduce emission efficiency, was suppressed by the dislocation filtering effect. Moreover, yellow luminescence was suppressed for taller nanocolumns. In the low-temperature-PL spectra, the peak observed at 3.41 eV, related to a stacking fault, increased with diameter regardless of height. These results indicate that the appropriate design of column height and diameter is of considerable importance for obtaining high efficiency emissions. Finally, InGaN/GaN quantum wells were fabricated on the regularly arranged GaN nanocolumn platform. Blue, green, and red (RGB) emission colors with no significant change in emission intensity were observed. These results constitute an important step toward the monolithic integration of RGB micro-LEDs.

Crystal growth of dilute BGaP alloys by solid-source molecular-beam epitaxy (MBE) equipped with electron beam evaporation system as the B source is investigated with changing growth condition of the growth temperature and the V/III ratio. The B composition for BGaP alloys increases with decrease of growth temperature and increase of III/V ratio. The B incorporation into the GaP matrix is difficult compared to other group-III atoms (Al or In) incorporations due to bonds in the matrix are highly strained calculated by valence force-field model. The possibilities of forming and conserving B3P bonds opportunity increased with decrease of growth temperature and increase of the V/III ratio.

A report on the fabrication and characterization of high performance conventional and ring-shaped AlGaN/GaN Schottky barrier diode on Si is presented. The resulting device exhibited low leakage current, which led to a detectivity performance of 3.48×1013 and 1.76×1013 cm Hz1/2 W−1, respectively, for both conventional and ring-shaped Schottky diode. The differential resistances of both devices were obtained at approximately 1.37×1012 and 1.41×1013 Ω, respectively. The zero bias peak responsivities of conventional and ring-shaped Schottky diodes were estimated to be 3.18 and 2.08 A cm−2/W, respectively. The typical UV to visible rejection ratio was observed over three orders of magnitude at zero bias. The C–V measurements was used to calculate and analyze the polarization sheet charge density of the AlGaN barrier layer by using self-consistently solving Schrodinger’s and Poisson’s equations. It is demonstrated that the ring shape of the Schottky barrier has higher polarization sheet charge density, which has the consequence that the Schottky shape has influence on the strain of the AlGaN barrier layer.

Eu doped GaN (GaN:Eu) shows a sharp line emission and thermal stability of the emission wavelength. To improve the optical properties, GaN:Eu nanocolumns were grown on GaN nanocolumn platform with high crystalline quality by rf-plasma-assisted molecular beam epitaxy. Although it was revealed that an increase of Eu concentration brought about the polycrystalline growth, photoluminescence (PL) intensity from Eu3+ monotonically increased with increasing Eu concentration without concentration quenching, which suggests that the nanocolumn crystal is a valuable way to develop the novel optical devices utilizing GaN:Eu.

We report metal organic vapor phase epitaxy (MOVPE) growth of GaPN alloys by surface nitridation with ammonia (NH 3 ). A N composition is controlled up to 1.6 % in the present work by changing nitridation time, NH 3 flow rate, interruption, and growth temperature, while few N incorporation (< 0.1%) was confirmed in a continuous supply method. A typical FWHM value of X-ray rocking curve of the GaPN alloys is comparable to that of GaP substrates, indicating a high crystalline quality.

The educational method which is including designing, making, and evaluating actual semiconductor devices with learning the theory is one of the best way to obtain the fundamental understanding of the device physics and to cultivate the ability to make unique ideas using the knowledge in the semiconductor device. In this paper, the simplified Boron thermal diffusion process using Sol-Gel material under normal air environment was proposed based on simple hypothesis and the feasibility of the reproducibility and reliability were investigated to simplify the diffusion process for making the educational devices, such as p-n junction, bipolar and pMOS devices. As the result, this method was successfully achieved making p+ region on the surface of the n-type silicon substrates with good reproducibility. And good rectification property of the p-n junctions was obtained successfully. This result indicates that there is a possibility to apply on the process making pMOS or bipolar transistors. It suggests that there is a variety of the possibility of the applications in the educational field to foster an imagination of new devices.

Surface treatments of GaN in HCl-based solutions are studied by X-ray photoelectron spectroscopy (XPS) and electrical characterization of fabricated GaN surfaces. A dilute-HCl treatment (HCl:H2O=1:1) at room temperature and a boiled-HCl treatment (undiluted HCl) at 108°C are made on high-temperature annealed n-GaN. From the XPS study, removal of surface oxide by the dilute-HCl treatment was found, and more thoroughly oxide-removal was confirmed in the boiled-HCl treatment. Effect of the surface treatment on electrical characteristics on AlGaN/GaN transistor is also studied by applying treatment processes prior to the surface SiN deposition. Increase of drain current is found in boiled-HCl treated samples. The results suggest that the boiled-HCl treatment is effective for GaN device fabrication.

Recent progress on light-emitting diode having a Eu-doped GaN active layer is reported. Although the first success on LED using GaN:Eu has been achieved by OMVPE, the factors to be controlled during the crystal growth are not well understood. We found that GaN:Eu co-doped with Mg in NH 3 -MBE shows a Eu site which is excited only by the above band-gap excitation. The luminescence intensity is enhanced at least 10 times than that without Mg co-doping. The LED operation fabricated using Mg co-doping technique is successfully demonstrated.

We have grown self-assembled InGaAsN/GaP quantum dots (QDs) with an In composition of 50% via the Stranski–Krastanov growth mode of molecular-beam epitaxy, obtaining high-density InGaAsN islands of 8×10 10 cm −2 . When the InGaAsN islands are directly exposed to the P 2 beam, we observe a quantum-well-like hetero-interface using cross-sectional transmission electron microscopy (XTEM). This result indicates that the InGaAsN island density is remarkably reduced by As/P exchange reactions. To suppress these exchange reactions, we deposit Ga corresponding to 1 monolayer on the InGaAsN islands. When the Ga deposition sequence is finished, we use XTEM to detect InGaAsN islands embedded in GaP, which indicates that As/P exchange reactions can be suppressed by Ga deposition. Subsequently, we grow a multiple-stacked InGaAsN/GaP 5QDs using the Ga deposition sequence and report their room-temperature photoluminescence spectra.

We have developed a growth procedure for realizing a low defect density GaP layer on an Si substrate. The growth procedure consists of two parts. One is the post-growth annealing for the annihilation of stacking faults (SFs). We have investigated an annihilation mechanism with molecular beam epitaxy grown GaP layers. 1-monolayer-thick SFs typically generate from the GaP/Si interface in a non-annealed GaP layer. In a 700 °C annealed GaP layer, generation points of these SFs tend to shift toward the GaP surface. In a 730 °C annealed GaP layer, SFs density is effectively decreased. These results suggest that SFs are annihilated through the climb motion of two partial dislocations during the post-growth annealing. Another one is the optimized shutter sequence for migration enhanced epitaxy. We have revealed that it is effective for the suppression of both three-dimensional growth and melt-back etching to increase in a stepwise manner the number of supplied Ga atoms per cycle. As a result, the generation of threading dislocations and pits is remarkably suppressed. A root mean square surface roughness of 0.13 nm is obtained within the critical thickness. We have estimated etch pit density (EPD) to be ∼7×10 5 cm −2 with a GaPN/GaP/Si structure. To the best of our knowledge, this value is same as that of commercially available GaP substrates and is the lowest one in the EPD of GaP/Si heteroepitaxy.

We have demonstrated the acceptor concentration control for p-type GaPN grown by molecular beam epitaxy (MBE) using Mg as the acceptor element. The hole concentration increases up to 2×1019 cm-3 at 300 K and does not remarkably vary after thermal treatment and thus Mg is successfully doped into GaPN. Subsequently, we have investigated the electrical and luminescence properties of Mg-doped p-type GaPN grown by MBE. The activation energy is estimated to be about 37 meV, indicating Mg is a shallow acceptor element for p-type GaPN grown by MBE. When the hole concentration is larger than ∼1018 cm-3, the photoluminescence (PL) intensity decreases with increasing the hole concentration. By time-resolved PL (TRPL) measurement, this PL quenching is caused by the non-radiative centres due to Mg doping when the hole concentration is larger than ∼1018 cm-3. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have demonstrated that Mg is a controllable acceptor element for p-type GaAsN alloys grown by solid-source molecular-beam epitaxy (MBE), where a hole concentration has been realized up to 1.5×10 20 cm −3 and has been controlled along the vapor pressure curve of Mg using a standard effusion cell. In addition, electrical and luminescence characterizations have been investigated for GaAsN:Mg samples grown by solid-source MBE. The activation energy of Mg for the GaAsN:Mg samples is close to the impurity energy of Mg in GaAs (28 meV). Thus Mg is a very shallow acceptor element for GaAsN alloys. From photoluminescence (PL) measurements, the integrated PL intensity drastically increases with increasing a hole concentration up to 8.6×10 19 cm −3 at 300 K. This result suggests that the hole concentration can increase up to 8.6×10 19 cm −3 without significantly increasing the non-radiative recombination centers related to Mg doping when Mg is the acceptor element.

Using combined excitation emission spectroscopy, we performed a comparative study of europium ions in GaN in samples that have been in situ doped during interrupted growth epitaxy (IGE) or conventional molecular beam epitaxy (MBE) as well as samples that were grown using organometallic vapor phase epitaxy (OMVPE) and subsequently ion implanted with Eu ions. Through site-selective resonant excitation, we are able to unambiguously assign all major observed transitions to a combination of different incorporation sites and electron–phonon coupled transitions. We identified at least nine different incorporation sites of Eu ions in GaN and studied how these sites behave under different excitation conditions and how their relative number is modified by different growth and doping conditions. The coupling to phonons has also been studied for a series of AlxGa1−xN samples with x=0…1. We find that a main site most resembling an unperturbed Eu ion on Ga site is always dominant, while the minority sites are changing substantially in relative numbers and can occur in some samples fairly close in emission intensity to the main site. In terms of the excitation pathway after the creation of electron-hole pairs, we found three types of centers: (1) sites that are dominantly excited through shallow defect traps; (2) sites that are excited through a deep defect trap; (3) sites that cannot be excited at all including the majority of the main sites. We interpret this finding to indicate that the ion in this environment is not very efficient in trapping excitation and that the indirect excitation involving other traps depends on the ion/trap distance. Many of the main sites are far away from these traps and cannot be excited through this channel at all. The efficiency of excitation is highest for the deep traps, indicating that it would be desirable to enrich the respective site, as has been done with some success in the IGE grown samples.

We demonstrated an appropriate growth procedure for GaAsN/GaP(N) single quantum wells (SQWs) with abrupt heterointerfaces in solid-source molecular beam epitaxy able to prevent the formation of unwanted As/P intermixing layers caused by residual As pressure. It was clarified that a GaP capping layer, grown on the top of the GaAsN SQW, was effective in avoiding the P/As exchange reaction on the GaAsN SQW surface. In fact, gettering by Ga was effective in removing the residual As 2 pressure, thus preventing the formation of the unwanted As/P intermixing layer. Then, we suggested that a GaAs 0.965 N 0.035 /GaP 0.98 N 0.02 SQW has a type-I band alignment with the conduction band offset larger than 300 meV. Finally, we fabricated a GaAs 0.965 N 0.035 /GaP SQW light-emitting diodes (LEDs) on the Si substrate. The GaAs 0.965 N 0,035 /GaP SQW LED emitted in the infrared region at a wavelength at 860 nm. Therefore, the GaAsN/GaP(N) SQW can be used as a direct-transition active layer in light-emitting devices on Si, to realize monolithic optoelectronic integrated circuits and systems operating in the wavelength range around 850 nm.

The epitaxial growth of doped ZnO films is of great technological importance. Present paper reports a detailed investigation of Sc-doped ZnO films grown on (1 0 0) silicon p-type substrates. The films were deposited by sol–gel technique using zinc acetate dihydrate as precursor, 2-methoxyethanol as solvent and monoethanolamine (MEA) as a stabilizer. Scandium was introduced as dopant in the solution by taking 0.5 wt% 1 of scandium nitrate hexahydrate. The effect of annealing on structural and photoluminescence properties of nano-textured Sc-doped films was investigated in the temperature range of 300–550 °C. Structural investigations were carried out using X-ray diffraction, scanning electron microscopy and atomic force microscopy. X-ray diffraction study revealed that highly c-axis oriented films with full-width half maximum of 0.21° are obtained at an annealing temperature of 400 °C. The SEM images of ZnO:Sc films have revealed that coalescence of ZnO grains occurs due to annealing. Ostwald ripening was found to be the dominant mass transport mechanism in the coalescence process. A surface roughness of 4.7 nm and packing density of 0.93 were observed for the films annealed at 400 °C. Room temperature photoluminescence (PL) measurements of ZnO:Sc films annealed at 400 °C showed ultraviolet peak at about (382 nm) with FWHM of 141 meV, which are comparable to those found in high-quality ZnO films. The films annealed below or above 400 °C exhibited green emission as well. The presence of green emission has been correlated with the structural changes due to annealing. Reflection high energy electron diffraction pattern confirmed the nearly epitaxial growth of the films.

We investigated the surface morphology of 50-nm-thick GaP layers grown on Si substrates, by atomic force microscopy. Pits with a density of about 10 8 cm -2 were observed at the surface of GaP layers grown by conventional migration-enhanced epitaxy (MEE). The pit diameter increased with increasing the growth temperature in the range from 440 'C up to 540°C. Transmission electron microscope (TEM) observations revealed that the origin of the pits was the melt-back etching of the Si surface by Ga droplets. The Ga droplets are thought to form during the initial MEE growth on a P-prelayer. By changing the conventional MEE growth mode into molecular beam epitaxy growth mode for the initial 2 monolayers, the melt-back etching was suppressed. As a result, a pit-free GaP layer was successfully grown on a Si substrate with a root-mean-square surface roughness of 0.2 nm. In addition, no stacking faults were observed in cross-sectional TEM images. Finally, anti-phase domains completely self-annihilated within 10 nm from the interface.

Structural-defect-free growth of III–V–N alloys on a Si substrate has been established, which was based on lattice-matching. The electric conductivity and photoluminescence properties of a basic III–V–N alloy of GaPN were investigated, which were grown by molecular beam epitaxy (MBE) and MOVPE. The carrier concentration was controlled by S and Mg doping for n and p types, respectively. Specific features were observed in n-GaPN. Photoluminescence intensity was increased by rapid thermal annealing (RTA). These characteristics relate to N-related defects. InGaPN/GaPN LEDs and Si MOSFETs were fabricated in the Si/InGaPN/GaPN DH layers grown on the Si substrate with structural-defect-free growth process. The results lead to monolithic optoelectronic integrated circuits (OEICs). Some of the possible applications are described. The key issues for realizing the monolithic OEICs are the reduction of point defects of III–V–N layers and the growth of III–V compounds with high light emission efficiency.

The doping control of GaPN grown by organometallic vapor-phase epitaxy was investigated. The carrier concentration of p-GaPN could be regulated by C self-doping generated from organometallic sources. The carrier concentration of C-doped p-GaPN was controlled by [TBP]/[TEGa] ratio and decreased with increasing N-content due to the formation of acceptor–H complexes. The carrier concentration of S-doped n-GaPN could be controlled by [H2S]/[TBP]. The doping efficiency of the GaPN was decreased to 1 10 as compared with GaP. The ideality factor and series resistance in GaPN pn-junction light-emitting diode on Si were estimated as 7.3 and 17.5 Ω, respectively. We consider that the large ideality factor result from the valence band offset at p-Si/p-GaPN interface. In the light output-current characteristic of the LED, the light output increased nonlinearly in the current range below 10 mA. This indicates that GaPN layers are affected by non-radiative recombination centers.

We employ the optically detected magnetic resonance (ODMR) technique to study and identify important grown-in defects in Ga(In)NP grown by molecular-beam epitaxy (MBE). Several types of defects were revealed from ODMR studies. The dominant defects were found to be related to Ga interstitials, evident form their characteristic hyperfine interaction arising from the spin interaction between the electron and the Ga nucleus. Some other as yet unidentified intrinsic defects were also found to be commonly present in the alloys. The effects of growth conditions (ion bombardment, N2 gas flow, etc.) and post-growth rapid thermal annealing on the formation of these defects were studied in detail, shedding light on the formation mechanism of defects.