Search

Despite recent advances in growth and characterization of GaN:Be, reliable conductive p‐type GaN:Be remains elusive. In this work, GaN is co‐doped with Be and Mg to improve the incorporation and ionization efficiency of both Be and Mg. Be and Mg are found to interact in complex ways rendering GaN:Be,Mg semi‐insulating. Rather than improving Be and Mg incorporation efficiency, there is an apparent mutual inhibition of incorporation when Be and Mg are co‐dopants. Furthermore, photoluminescence measurements indicate that the BeGa acceptor is reduced in particular, relative to the total [Be]. The same effect is not observed for Mg. From this, it is concluded that Mg preferentially incorporates into Ga lattice sites over Be, and excess Be that cannot incorporate into substitutional sites instead occupies interstitial sites. The interstitial Be acts as donor defect, which compensate Mg acceptors. This provides an explanation for the observed reduction in BeGa‐related luminescence intensity (without an associated decrease in [Be]) in GaN:Be with significant [Mg] content. [ABSTRACT FROM AUTHOR]

The rough morphology at the growth surface results in the non-uniform distribution of indium composition, intentionally or unintentionally doped impurity, and thus impacts the performance of GaN-based optoelectronic and vertical power electronic devices. We observed the morphologies of unintentionally doped GaN homo-epitaxially grown via MOCVD and identified the relations between rough surfaces and the miscut angle and direction of the substrate. The growth kinetics under the effect of the Ehrlich–Schwoebel barrier were studied, and it was found that asymmetric step motions in samples with a large miscut angle or those grown at high temperature were the causes of step-bunching. Meandering steps were believed to be caused by surface free energy minimization for steps with wide terraces or deviating from the [ 1 1 ¯ 00 ] m-direction. [ABSTRACT FROM AUTHOR]

We demonstrate a broadband second-harmonic generator for the green spectral range based on a periodical polarity GaN waveguide structure. We grew the structure with a periodicity of 4 μ m using an MOCVD (metal-organic chemical vapor deposition) reactor. We tested the structure using femtosecond laser pulse pumping and obtained the second harmonic ( λ SH =512 nm) conversion efficiency 0.79 · 10 - 7 % · W - 1 for the pump peak power of 440 kW inside the waveguide. Based on the theoretical modeling of the dispersion curves of the pump and the second harmonic, we found multiple crossings, including an extended crossing. We relate this fact to the experimentally measured broadened second harmonic spectrum. [ABSTRACT FROM AUTHOR]

Heavily Si-doped GaN epitaxial layers (n+GaN) have been grown on semi-insulating 6H-SiC substrate by metal–organic chemical vapor deposition at 1030°C using H2 and N2 as carrier gases. Thin film characterization results demonstrated that n+GaN grown in N2 carrier gas has superior morphological and crystalline quality to that grown in H2. The surface morphology of n+GaN grown with N2 carrier gas is insensitive to the growth rate and SiH4 flow with Si doping concentration up to 1.1 × 1020/cm3. Secondary ion mass spectrometry analysis confirmed that C and O impurity levels in n+GaN are one order of magnitude lower with N2 carrier gas than with H2. The results thus indicate that 100% N2 could be a better carrier gas candidate to enable a broader process window for future HEMT S/D n+GaN selective area epitaxial process applications. [ABSTRACT FROM AUTHOR]

The rough morphology at the growth surface results in the non-uniform distribution of indium composition, intentionally or unintentionally doped impurity, and thus impacts the performance of GaN-based optoelectronic and vertical power electronic devices. We observed the morphologies of unintentionally doped GaN homo-epitaxially grown via MOCVD and identified the relations between rough surfaces and the miscut angle and direction of the substrate. The growth kinetics under the effect of the Ehrlich–Schwoebel barrier were studied, and it was found that asymmetric step motions in samples with a large miscut angle or those grown at high temperature were the causes of step-bunching. Meandering steps were believed to be caused by surface free energy minimization for steps with wide terraces or deviating from the [11¯00] m-direction.

This paper reports on improved AlGaN/GaN metal oxide semiconductor high-electron mobility transistors (MOS-HEMTs). TiO2 is used to form the dielectric and passivation layers. The TiO2 film is characterized using X-ray photoemission spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). The quality of the gate oxide is improved by annealing at 300 °C in N2. Experimental results indicate that the annealed MOS structure effectively reduces the gate leakage current. The high performance of the annealed MOS-HEMTs and their stable operation at elevated temperatures up to 450 K is demonstrated. Furthermore, annealing improves their output power characteristics. [ABSTRACT FROM AUTHOR]

Remote epitaxy is an emerging technology for producing single-crystalline, free-standing thin films and structures. The method uses 2D van der Waals materials as semi-transparent interlayers that enable epitaxy and release of epitaxial layers at the 2D layer interface. The use of single-layer graphene as the interlayer for heterogeneous remote epitaxial GaN nucleation layer and GaN film on the sapphire substrate was studied. The result shows that GaN nucleation island has a good orientation. Through parameter adjustment, a dense GaN nucleation layer was obtained. AFM observation and XRD detection confirm that GaN thin film has lower surface roughness and dislocation density compared with film that grow directly on sapphire substrate under the same conditions. The existence of graphene after growing GaN film was confirmed by Raman spectra. [ABSTRACT FROM AUTHOR]

This paper reviews some of the basic issues in homoepitaxial growth of III-nitrides to enable a vertical device technology. It focuses on the use of metal organic chemical vapor deposition (MOCVD) to grow GaN and explores the effects of the native substrate characteristics on material quality, interface composition, and device performance. A review of theoretical work understanding dopants in the ultra-wide III-nitride semiconductors, AlN and BN, is also included for future efforts expanding the technology into those materials. [ABSTRACT FROM AUTHOR]

Epitaxial lateral overgrowth (ELO) of GaN epilayers on a sapphire substrate was studied by using a laser-patterned graphene interlayer. Monolayer graphene was transferred onto the sapphire substrate using a wet transfer technique, and its quality was confirmed by Raman spectroscopy. The graphene layer was ablated using a femtosecond laser, which produced well-defined patterns without damaging the underlying sapphire substrate. Different types of patterns were produced for ELO of GaN epilayers: stripe patterns were ablated along the  [ 1 ¯ 100 ] sapphire  and  [ 11 2 ¯ 0 ] sapphire    directions, a square island pattern was ablated additionally. The impact of the graphene pattern on GaN nucleation was analyzed by scanning electron microscopy. The structural quality of GaN epilayers was studied by cathodoluminescence. The investigation shows that the laser-ablated graphene can be integrated into the III-nitride growth process to improve crystal quality. [ABSTRACT FROM AUTHOR]

We report the electrical properties of Al0.3Ga0.7N/GaN heterojunction field effect transistor (HFET) structures with a Ga2O3 passivation layer grown by metal–organic chemical vapor deposition (MOCVD). In this study, three different thicknesses of β-Ga2O3 dielectric layers were grown on Al0.3Ga0.7N/GaN structures leading to metal-oxide-semiconductor-HFET or MOSHFET structures. X-ray diffraction (XRD) showed the ( 2 ¯ 01) orientation peaks of β-Ga2O3 in the device structure. The van der Pauw and Hall measurements yield the electron density of ~ 4 × 1018 cm−3 and mobility of ~770 cm2V−1s−1 in the 2-dimensional electron gas (2DEG) channel at room temperature. Capacitance–voltage (C-V) measurement for the on-state 2DEG density for the MOSHFET structure was found to be of the order of ~1.5 × 1013 cm−2. The thickness of the Ga2O3 layer was inversely related to the threshold voltage and the on-state capacitance. The interface charge density between the oxide and Al0.3Ga0.7N barrier layer was found to be of the order of ~1012 cm2eV−1. A significant reduction in leakage current from ~10−4 A/cm2 for HFET to ~10−6 A/cm2 for MOSHFET was observed well beyond pinch-off in the off-stage at -20 V applied gate voltage. The annealing at 900° C of the MOSHFET structures revealed that the Ga2O3 layer was thermally stable at high temperatures resulting in insignificant threshold voltage shifts for annealed samples with respect to as-deposited (unannealed) structures. Our results show that the MOCVD-gown Ga2O3 dielectric layers can be a strong candidate for stable high-power devices. [ABSTRACT FROM AUTHOR]

The ex situ sputtered AlN buffer and GaN epilayer grown on top of it by metalorganic chemical vapor deposition were studied comprehensively by a variety of techniques including atomic force microscope, high resolution x-ray diffraction, Raman and x-ray photoelectron spectroscopy characterizations. It exhibited that the AlN buffer deposited by using sputtering technique could be oxidized with exposure in atmosphere. Such oxidation phenomenon significantly influences the characteristics of GaN epilayer, for example leading to poor surface morphology, high dislocation density, and large compressive stress. This study demonstrated the effect of oxygen impurities on GaN growth and has an important guiding significance for the growth of high-quality III-nitride related materials. [ABSTRACT FROM AUTHOR]

In this note, we demonstrate the high-temperature growth of GaN on ScAlMgO4 substrates by metalorganic vapor phase epitaxy when a thin Al film is deposited ex situ on the ScAlMgO4 surface, prior to GaN growth. Mirror-like high-quality GaN epitaxial layers were obtained when N2 was used as carrier gas during the reactor temperature ramp-up preceding GaN growth, leading to a higher GaN quality compared to direct growth on ScAlMgO4 using a trimethylaluminium preflow. This opens a pathway for high-temperature GaN growth on ScAlMgO4 when an Al precursor line is not present. [ABSTRACT FROM AUTHOR]

We demonstrate controlled Si doping in the low doping range of 5 Ă— 1015â€"2.5 Ă— 1016 cmâˆ'3 with mobility >1000 cm2 Vâˆ'1 sâˆ'1 in GaN films grown by metalorganic chemical vapor deposition. The carbon-related compensation and mobility collapse were prevented by controlling the electrochemical potential near the growth surface via chemical potential control (CPC) and defect quasi-Fermi level (dQFL) point-defect management techniques. While the CPC was targeted to reduce the net CN concentration, the dQFL control was used to reduce the fraction of C atoms with the compensating configuration, i.e. C N âˆ' 1. The low compensating acceptor concentration was confirmed via temperature-dependent Hall effect analysis and capacitanceâ€"voltage measurements. [ABSTRACT FROM AUTHOR]

Thermal degradation in blue InGaN multi-quantum well (MQW) structures induced by varying high p-GaN growth temperature and the subsequent influence on the optical properties of MQW are investigated. The results indicate that higher p-GaN growth temperatures improve p-GaN layer contact quality, but may lead to an optical property degradation of InGaN MQWs. A stratified thermal degradation mechanism is observed. The degradation primarily affects the upper quantum barrier layers and results in indium desorption and re-evaporation, where elevated p-GaN growth temperatures may induce more indium segregation and decomposition than in lower layers of MQW. In extreme conditions, such as 1060℃, indium atoms in lower layers escape, causing partial lattice structure corruption and severe degradation in MQW structure, which is also more distinctive in the upper layers. • Growth of p-GaN at high temperatures leads to thermal degradation in InGaN quantum well. • Startified thermal degradation process is observed, as the upper quantum barrier in InGaN is primarily affected. • The upper quantum barrier is more affected by indium atom evaporation and aggregation as temperature rises. • Extremely high p-GaN growth temperatures may cause destructive effects on the quantum well structure. [ABSTRACT FROM AUTHOR]

This paper reviews some of the basic issues in homoepitaxial growth of III-nitrides to enable a vertical device technology. It focuses on the use of metal organic chemical vapor deposition (MOCVD) to grow GaN and explores the effects of the native substrate characteristics on material quality, interface composition, and device performance. A review of theoretical work understanding dopants in the ultra-wide III-nitride semiconductors, AlN and BN, is also included for future efforts expanding the technology into those materials.

Epitaxial lateral overgrowth (ELO) of GaN epilayers on a sapphire substrate was studied by using a laser-patterned graphene interlayer. Monolayer graphene was transferred onto the sapphire substrate using a wet transfer technique, and its quality was confirmed by Raman spectroscopy. The graphene layer was ablated using a femtosecond laser, which produced well-defined patterns without damaging the underlying sapphire substrate. Different types of patterns were produced for ELO of GaN epilayers: stripe patterns were ablated along the [1¯100]sapphire and [112¯0]sapphire directions, a square island pattern was ablated additionally. The impact of the graphene pattern on GaN nucleation was analyzed by scanning electron microscopy. The structural quality of GaN epilayers was studied by cathodoluminescence. The investigation shows that the laser-ablated graphene can be integrated into the III-nitride growth process to improve crystal quality.

The existence of high threading dislocation density (TDD) in GaN-based epilayers is a long unsolved problem, which hinders further applications of defect-sensitive GaN-based devices. Multiple-modulation of epitaxial lateral overgrowth (ELOG) is used to achieve high-quality GaN template on a novel serpentine channel patterned sapphire substrate (SCPSS). The dislocation blocking brought by the serpentine channel patterned mask, coupled with repeated dislocation bending, can reduce the dislocation density to a yet-to-be-optimized level of ∼2 × 10(5) to 2 × 10(6) cm(-2). About 80% area utilization rate of GaN with low TDD and stress relaxation is obtained. The periodical variations of dislocation density, optical properties and residual stress in GaN-based epilayers on SCPSS are analyzed. The quantum efficiency of InGaN/GaN multiple quantum wells (MQWs) on it can be increased by 52% compared with the conventional sapphire substrate. The reduced nonradiative recombination centers, the enhanced carrier localization, and the suppressed quantum confined Stark effect, are the main determinants of improved luminous performance in MQWs on SCPSS. This developed ELOG on serpentine shaped mask needs no interruption and regrowth, which can be a promising candidate for the heteroepitaxy of semipolar/nonpolar GaN and GaAs with high quality.

In this work, multi-finger current aperture vertical electron transistors (CAVETs) are fabricated with co-integrated high electron mobility transistors (HEMTs). The devices are realized by Mg-ion implantation and metalorganic chemical vapor deposition (MOCVD) regrowth. The intrinsic CAVET design is optimized for robust device performance and applied on multi-finger devices having a total gate periphery of ${W}_{{\text {G}}} =13.5$ mm and ${W}_{{\text {G}}} =77$ mm. Mappings of the transfer characteristics revealed reliable turn-off behavior demonstrating the suitability of the intrinsic device layout. The largest CAVETs revealed a total ON-state resistance of ${R}_{ \mathrm{\scriptscriptstyle ON}} = 1.67\,\,\Omega $ and a maximum drain current of ${I}_{{\text {D},\text {MAX}}} =20.3$ A at ${V}_{\text {GS}} = {3}$ V. A pulse robustness of ${P}_{\text {PULS}} =976$ W at ${V}_{\text {DS}} =50$ V and a pulsewidth of 500 $\mu \text{s}$ is shown without thermal destruction. Additionally, HEMTs are co-integrated on-chip. This combination of HEMTs and reliable large area CAVETs enables the design of high-performance, monolithically integrated GaN power circuits (GaN power ICs) based on the CAVET technology. [ABSTRACT FROM AUTHOR]

We report the electrical properties of Al0.3Ga0.7N/GaN heterojunction field effect transistor (HFET) structures with a Ga2O3 passivation layer grown by metal–organic chemical vapor deposition (MOCVD). In this study, three different thicknesses of β-Ga2O3 dielectric layers were grown on Al0.3Ga0.7N/GaN structures leading to metal-oxide-semiconductor-HFET or MOSHFET structures. X-ray diffraction (XRD) showed the (2¯01) orientation peaks of β-Ga2O3 in the device structure. The van der Pauw and Hall measurements yield the electron density of ~ 4 × 1018 cm−3 and mobility of ~770 cm2V−1s−1 in the 2-dimensional electron gas (2DEG) channel at room temperature. Capacitance–voltage (C-V) measurement for the on-state 2DEG density for the MOSHFET structure was found to be of the order of ~1.5 × 1013 cm−2. The thickness of the Ga2O3 layer was inversely related to the threshold voltage and the on-state capacitance. The interface charge density between the oxide and Al0.3Ga0.7N barrier layer was found to be of the order of ~1012 cm2eV−1. A significant reduction in leakage current from ~10−4 A/cm2 for HFET to ~10−6 A/cm2 for MOSHFET was observed well beyond pinch-off in the off-stage at -20 V applied gate voltage. The annealing at 900° C of the MOSHFET structures revealed that the Ga2O3 layer was thermally stable at high temperatures resulting in insignificant threshold voltage shifts for annealed samples with respect to as-deposited (unannealed) structures. Our results show that the MOCVD-gown Ga2O3 dielectric layers can be a strong candidate for stable high-power devices.

This work has investigated the effects of etching treatment on as-grown and regrown GaN-on-GaN structures intended for vertical p-n power device applications. Surfaces of thick unintentionally doped (UID) GaN layers, grown homoepitaxially via metal-organic chemical vapor deposition on freestanding GaN bulk substrates, were subjected to RF-plasma dry etching, and additional layers of UID-GaN/p-GaN were then grown. The as-grown and regrown structures were examined in cross section using transmission electron microscopy. Two different types of etching treatment were used, fast-etch-only and multiple etches with decreasing power. Images of the fast-etch-only devices clearly showed the GaN-on-GaN interface at the etched location, and low device breakdown voltages were measured (reverse bias in the range of 45–95V). In comparison, no interfaces were visible in devices after multiple etching steps, and the corresponding device breakdown voltages were markedly higher (reverse bias ~1200–1270V). These results emphasize the importance of optimizing surface etching techniques for avoiding degraded performance in GaN-on-GaN power devices that require GaN regrowth. [ABSTRACT FROM AUTHOR]

Vertical GaN-on-GaN p-n diodes grown by ammonia molecular beam epitaxy (NH3 MBE) are reported in this letter for prospective high-power application devices. The diodes, consisting of only $4~\mu \text{m}$ drift layer with low unintentional background doping of $\sim 3\times {10}^{{15}}{\mathrm {cm}}^{\text {-3}}$ , showed a maximum breakdown voltage of >1.0 kV and a low differential specific on-resistance of 0.28 $\text{m}\Omega $ -cm2. Moreover, these diodes exhibited an excellent rectifying behavior with a low minimum ideality factor of 1.36 and a punch-through electric field comparable to the state-of-the-art vertical GaN-on-GaN p-n diodes grown by metalorganic chemical vapor deposition (MOCVD). These results suggest that all-MBE vertical GaN-on-GaN p-n diodes grown by NH3 MBE can be promising for small-size high-power electronic devices. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effects of InGaN/GaN-based interlayer (IL) and electron emitting layer (EEL) consisting of a GaN barrier layer grown with different metal-organic (MO) precursors of gallium (Ga), which were grown underneath the active layer. The growth behavior of GaN with triethyl Ga (TEGa) showed an increasing growth time due to a lower growth rate compared with GaN grown with trimethyl Ga (TMGa), resulting in the formation of columnar domains and grain boundary with reduced defect. UV-A light emitting diode (LED) chips with three types of ILs and EELs, grown with different MO sources, were fabricated and evaluated by light output power (LOP) measurements. The LOP intensity of UVLED-III with the GaN barrier layer-based IL and EEL grown by TEGa was enhanced by 1.5 times compared to that of the IL and EEL grown with TMGa at 300 mA current injection. Use of the GaN barrier layer in ILs and EELs grown by TEGa improved the crystal quality of the post grown InGaN/GaN multiple quantum well, which reduces leakage current. Therefore, for the UV-A LED with ILs and EELs grown with TEGa MO precursors, electrical and optical properties were improved significantly. [ABSTRACT FROM AUTHOR]

The effect of annealing temperature and time on the luminescence intensity of the InGaN/GaN heterostructure subjected to ion beam etching was studied. We show that annealing at a temperature of 1100°C makes it possible to eliminate the radiation defects in the GaN layers that arise in the etching process with a focused Ga+ ion beam (30 keV). [ABSTRACT FROM AUTHOR]

In this work, we demonstrate the capability of the hot-wall metalorganic chemical vapor deposition to deliver high-quality n -Al x Ga 1 − x N (x = 0 – 0.12, [Si] = 1 × 1 0 17 cm−3) epitaxial layers on 4H-SiC(0001). All layers are crack-free, with a very small root mean square roughness (0.13 – 0.25 nm), homogeneous distribution of Al over film thickness and a very low unintentional incorporation of oxygen at the detection limit of 5 × 1 0 15 cm−3 and carbon of 2 × 1 0 16 cm−3. Edge type dislocations in the layers gradually increase with increasing Al content while screw dislocations only raise for x above 0.077. The room temperature electron mobility of the n -Al x Ga 1 − x N remain in the range of 400 – 470 cm2/(V.s) for Al contents between 0.05 and 0.077 resulting in comparable or higher Baliga figure of merit with respect to GaN, and hence demonstrating their suitability for implementation as drift layers in power device applications. Further increase in Al content is found to result in significant deterioration of the electrical properties. • High-quality, crack-free n -Al x Ga 1-x N (x = 0 – 0.12) epitaxial layers on 4H-SiC(0001). • Smooth surface, homogeneous Al content and low background impurity concentrations. • High electron mobility and comparable or higher BFOM than GaN for 5% and 7.7% of Al. • Deterioration of crystal quality and electron mobility for Al content of 12%. • n -Al x Ga 1-x N layers with 5% to 8% of Al are suitable for vertical power devices. [ABSTRACT FROM AUTHOR]

InGaN/GaN micro-crystals (μ-crystals) are self-contained and individually-addressable light emitting crystals that have unique potential in the development of ultra-small and ultra-high resolution pixels for next-generation displays. In this study, we explore the electrically-driven light emission behavior of vertically standing InGaN/GaN micro-crystals (μ-crystals) with well-defined crystal facets and tunable size. InGaN/GaN μ-crystals have hollow pedestals weakly bound to the substrate surface, thus enabling individual manipulation and/or collective transfer to other target surfaces. Cyclic bending tests and finite element analysis (FEA) of the strain distribution further highlight the excellent mechanical deformability of a device layout consisting of μ-crystal pixels embedded in a polymeric matrix. Light-emitting diodes (LEDs) with individual InGaN/GaN μ-crystals exhibit strong electroluminescence (EL) with unique features such as variations in emission spectra with respect to crystal diameter and driving voltage bias. Comparative analyses of photoluminescence, cathodoluminescence, and electric potential simulation indicate a strong correlation between the EL wavelengths and dominant emitting regions of InGaN/GaN polyhedral crystal planes. This is further supported by scanning transmission electron microscopy of quantum well structures, which strongly depend on both size and the crystal facets. • Self-contained InGaN/GaN MQW micro-crystal arrays are employed as light emitting pixels on a deformable substrate. • The μ-crystal LEDs exhibit a variation of emission spectra with respect to the crystal diameter and driving voltage bias. • Optoelectrical and structural analysis of InGaN/GaN μ-crystal LEDs reveals the multicolor emission mechanism. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effects of InGaN/GaN-based interlayer (IL) and electron emitting layer (EEL) consisting of a GaN barrier layer grown with different metal-organic (MO) precursors of gallium (Ga), which were grown underneath the active layer. The growth behavior of GaN with triethyl Ga (TEGa) showed an increasing growth time due to a lower growth rate compared with GaN grown with trimethyl Ga (TMGa), resulting in the formation of columnar domains and grain boundary with reduced defect. UV-A light emitting diode (LED) chips with three types of ILs and EELs, grown with different MO sources, were fabricated and evaluated by light output power (LOP) measurements. The LOP intensity of UVLED-III with the GaN barrier layer-based IL and EEL grown by TEGa was enhanced by 1.5 times compared to that of the IL and EEL grown with TMGa at 300 mA current injection. Use of the GaN barrier layer in ILs and EELs grown by TEGa improved the crystal quality of the post grown InGaN/GaN multiple quantum well, which reduces leakage current. Therefore, for the UV-A LED with ILs and EELs grown with TEGa MO precursors, electrical and optical properties were improved significantly.

A series of AlN/GaN heterostructures were grown on 150 mm Si substrates by metal organic chemical vapor deposition (MOCVD). Different cap layer structures, including gallium nitride (GaN) and silicon nitride (SiN _x ), were used to passivate the heterostructure surface. A 3.5 nm thick SiN _x cap is able to maintain the two dimensional electron gas (2DEG) stability in a long period. An AlN/GaN heterostructure with a 4.5 nm thick AlN barrier exhibits the best 2DEG properties, in terms of sheet resistance, carrier mobility and stability. The carrier mobility of the 2DEG can be enhanced by a combination of SiNx and GaN cap layers to over 1400 cm ^2 /Vs.

The effect of the growth temperature and the flow of trimethylgallium on the process of selective epitaxy of gallium nitride in windows of submicron size have been studied. The conditions under which homogeneous nucleation and coalescence of nuclei are combined with a low growth rate are determined. The steady growth of variously oriented gallium nitride strips with a height of 50 nm and a width of 600 nm was realized. [ABSTRACT FROM AUTHOR]

AlGaN/GaN heterostructures were grown on Si (1 1 1) substrates with different AlN nucleation layers (NL) by metal–organic chemical vapor deposition (MOCVD). The results indicate that the growth temperature of AlN NL has a noticeable influence on the structural, electronic and optical properties of the AlGaN/GaN heterostructures. Optimizing the growth temperature to 1040 °C led to quasi-2D smooth surface of the AlN NL with providing sufficient compressive stress to suppress cracking of the subsequent GaN layer during the cooling process, resulting in improved crystalline quality of GaN layer and superior two-dimensional electron gas (2DEG) performance of the AlGaN/GaN heterostructure. [ABSTRACT FROM AUTHOR]

GaN vertical trench-MOSFETs incorporating molecular beam epitaxy (MBE) regrown channel are developed and investigated. The channel regrowth by MBE prevents repassivation of the p-type GaN body while promising higher channel mobility. Two different designs of the lateral portion of the regrown channel are compared: without or with an n+-GaN buried layer. Without an n+ buried layer, a respectable 600-V breakdown voltage (BV) is measured in the absence of edge termination, indicating a decent critical field strength (>1.6 MV/cm) of the regrown channel. However, the ON-resistance is limited by the highly resistive lateral channel due to Mg incorporation. With an n+ buried layer, the limitation is removed. Excellent ON-current of 130 mA/mm and ON-resistivity of $6.4 ~\rm {m\Omega \cdot cm^{2}}$ are demonstrated. The BV is limited by high source–drain leakage current from the channel due to drain-induced barrier lowering (DIBL) effect. Device analysis together with TCAD simulations points out the major cause for the DIBL effect: the presence of interface charge beyond a critical value ( $\sim 6\times 10^{12}\,\,\rm {cm^{-2}}$ ) at the regrowth interface on etched sidewalls. This paper provides valuable insights into the design of GaN vertical trench-MOSFET with a regrown channel, where simultaneous achievement of low ON-resistivity and high BV is expected in devices with reduced interface charge density and improved channel design to eliminate DIBL. [ABSTRACT FROM AUTHOR]

In this paper, GaN-based yellow light-emitting diodes (LEDs) were homoepitaxially grown on free-standing (0001) GaN substrates by metal-organic chemical vapor deposition. X-ray diffraction (XRD), photoluminescence (PL), and electroluminescence (EL) measurements were conducted to investigate the structural, optical, and electrical properties of the yellow LED. The XRD measurement results showed that the InGaN/GaN multiple quantum wells (MQWs) in the LED structure have good periodicity because the distinct MQWs related higher order satellite peaks can be clearly observed from the profile of 2θ-ω XRD scan. The low temperature (10 K) and room temperature PL measurement results yield an internal quantum efficiency of 16% for the yellow LED. The EL spectra of the yellow LED present well Gaussian distribution with relatively low linewidth (47–55 nm), indicating the homogeneous In-content in the InGaN quantum well layers in the yellow LED structure. It is believed that this work will aid in the future development of GaN on GaN LEDs with long emission wavelength. [ABSTRACT FROM AUTHOR]

This letter presents an analysis of N-polar metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with a 40 nm MOCVD SiNx passivation and a trench-gate design. A device with a 50 nm gate-length (Lg) demonstrates a 313 GHz power gain cutoff frequency (fmax) at a quiescent drain bias (V $_{{DS,Q}} ) of 26 V. The high fmax\cdot VDS,Q of 8.1 THz \cdot V exhibits great potential of the device in high-frequency power applications. Investigation on small-signal parameters shows that fmax improves with V $_{{DS,Q}}$ due to a reduction of gate-drain capacitance (cgd) and an increase of output resistance (rds). When comparing with the previously reported planar HEMT design, the shorter Lg enabled by the trench-gate design enhances the intrinsic current gain cutoff frequency (f $_{{T,int}}$ ) leading to a higher peak fmax at a higher V $_{{DS,Q}}$ . [ABSTRACT FROM PUBLISHER]

The GaN was grown on Si(100) with Er 2 O 3 (110) buffer by metal organic chemical vapor deposition (MOCVD). The results showed the polycrystalline nature of the layers with dominant non-polar (11–20) and semi-polar (10–13) orientations. GaN was formed in a two step process regime: low temperature growth was followed by high temperature growth regime. At a low temperature GaN tends to crystalize with dominant non-polar (11–20) orientation, while high temperature leads to preferential semi-polar (10–13) orientation growth. Additionally, the effects of parameters such as growth temperature, V/III-ratio and type of carrier gases on structural, morphological and optical properties of GaN was discussed in the current work. [ABSTRACT FROM AUTHOR]

Gate dielectric plays an integral role in advancing the performance and reliability of GaN-based transistors. Si-alloying of aluminum oxide (Al2O3) dielectrics have been shown to provide a promising route to improve gate dielectric properties in GaN. In this letter, we report on the first demonstration of a GaN FET with aluminum silicon oxide (AlSiO) as the gate dielectric. Vertical normally-off GaN MOSFETs were fabricated on bulk GaN substrate. Excellent dc performance was achieved with a breakdown voltage of 1.2 kV, an ON-resistance of 2 \textm\Omega .cm2, and a threshold voltage of 1.5 V (defined at I\textsf {DS} =1\,\,\mu \text{A} /mm). A high breakdown electric-field of 2.3 MV/cm was calculated in these devices. In addition to vertical GaN MOSFET results, a comparative study of Al2O3 and AlSiO-based in situ GaN MOS capacitors, including time-dependent dielectric breakdown characteristics is also presented. [ABSTRACT FROM AUTHOR]

In this work, high quality AlGaN/GaN double channel heterostructures were grown by metal organic chemical vapor deposition and the coupling correlation between the two channels, as well as the strain state of this multilayer structure are investigated in detail. It was revealed that the stronger coupling correlation affect the 2DEG distribution and leads to the lower channel is similar to the upper channel with the thinner thickness of the upper channel. In addition, the impact of the multilayer strain state on the characteristics of double channel heterostructures was discussed. Moreover, the effects of coupling correlation and strain state on the performance of double channel high electron mobility transistor (HEMT) was shown by 2-D simulation. This work is not only beneficial for the further study of the double (multiple) channel heterostructures and devices, but also instructive to the design and realization of the future atomic hyperfine structures of nitride semiconductors. • High quality AlGaN/GaN double channel heterostructures with different channel thickness were grown by MOCVD. • The coupling correlation between the upper and lower channel was investigated to explore the 2DEG distribution. • The impact of the multilayer strain state on the characteristics of double channel heterostructures was discussed in detail. [ABSTRACT FROM AUTHOR]

3rd group element nitride based semiconductor compounds are widely used in various optical and electronic devices. One problem in the fabrication of GaN based device heterostructures is the synthesis of p conductivity epitaxial layers. Magnesium is a typical doping impurity for GaN. The choice of optimum doping and thermal activation conditions is of utmost importance for the synthesis of low-Ohmic p-GaN epitaxial layers. The effect of thermal annealing of GaN:Mg layers on acceptor impurity activation has been investigated. Hole concentration increased and mobility decreased with an increase in thermal annealing temperature. The sample annealed at 1000 °C demonstrated the lowest value of resistivity. Rapid thermal annealing (annealing with high heating speed) considerably improved the efficiency of Mg activation in the GaN layers. The optimum time of annealing at 1000 °C has been determined. The hole concentration increased by up to 4 times compared to specimens after conventional annealing.

We have grown an AlIn(Ga)N/GaN heterostructure which is a promising alternative to the AlGaN/GaN heterostructure. The mobility and the carrier concentration of the two-dimensional electron gas (2DEG) formed at the AlIn(Ga)N/GaN heterointerface were strongly dependent on both the growth temperature and pressure. Two optimized growth conditions for the heterostructure with a low sheet resistance less than 300 Ω/sq were obtained by varying the growth temperature and pressure from 750 to 1070 °C and 100 to 300 torr, respectively: (i) AlIn(Ga)N/GaN heterostructure with high 2DEG carrier concentration of 2.4 × 1013 cm−2 with mobility of 1010 cm2 V−1s−1 (grown at 900 °C and 100 torr); (ii) AlIn(Ga)N/GaN heterostructure with high 2DEG mobility of 1910 cm2 V−1s−1 with carrier concentration of 1.13 × 1013 cm−2 (grown at 900 °C and 300 torr). Both structures would be useful for different purpose of device application. [ABSTRACT FROM AUTHOR]

Injecting current with a uniform carrier concentration is important for applications with three-dimensional architectures such as vertical power devices or displays. In III-nitride nanostructures, dopants not only incorporate differently depending on the surface orientation but can also seriously affect the kinetic equilibrium shapes of the nanorods. Herein, we report selective-area growth of doped GaN nanorods grown by pulsed-mode metalorganic chemical vapor deposition. Two dopants, Si and Mg, were employed as donor and acceptor atoms, respectively, for a mono-doping approach. Furthermore, a mixed flow of Si and Mg was supplied for a co-doping approach. We compared the morphological effects and growth rates of each doped GaN nanorod array. Then, we proposed appropriate growth mechanisms for the doped GaN nanorods on the basis of our structural characterizations. These results might extend the morphological functionality of GaN nanorods by including doping and may also provide an appropriate foundation for the design of nanostructure-based electronic or photonic devices. [ABSTRACT FROM AUTHOR]