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The internal field of GaN/AlGaN/GaN heterostructure on Si-substrate was investigated by varying the thickness of an undoped-GaN capping layer using electroreflectance spectroscopy. The four samples investigated are AlGaN/GaN heterostructure without a GaN cap layer (reference sample) and three other samples with GaN/AlGaN/GaN heterostructures in which the different thickness of GaN cap layer (2.7 nm, 7.5 nm, and 12.4 nm) has been considered. The sheet carrier density (ns) of a two-dimensional electron gas has decreased significantly from 4.66 × 1012 cm−2 to 2.15 × 1012 cm−2 upon deposition of a GaN capping layer (12.4 nm) over the reference structure. Through the analysis of internal fields in each GaN capping and AlGaN barrier layers, it has been concluded that the undiminished surface donor states (ns) of a reference structure and the reduced ns caused by the Au gate metal are approximately 5.66 × 1012 cm−2 and 1.08 × 1012 cm−2, respectively.

High quality nonpolar a -plane GaN templates were grown by utilizing sidewall lateral epitaxial overgrowth (SLEO) technique with threading dislocation density of ∼106–107 cm–2. 360 nm GaN/AlGaN multiple quantum well ultraviolet light emitting diodes were grown with metalorganic chemical vapor deposition. Reduced defect density SLEO a- plane, planar a -plane, and planar c -plane templates were co-loaded for device growth and processed together in order to make relative device performance comparison. For SLEO a -plane LEDs E EL peak position was measured at 360 nm and it was independent of drive current. The linewidth of the emission was 7 nm. The series resistance of these diodes was as low as 16.5 Ω and the forward voltage was measured as 4.08 V at 20 mA. The external quantum efficiency of the high quality SLEO a -plane devices was ∼275× higher than planar a -plane devices. The highest output power was realized at 200 mA as 65 μW. The effect of contact geometry on electrical and optical characteristics of the devices was also discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Improved nonpolar m -plane light emitting diodes (LEDs) with a thick InGaN multi-quantum-well (MQW) structure have been fabricated on low extended defect bulk m -plane GaN substrates using metal organic chemical vapor deposition (MOCVD). The peak wavelength of the electroluminescence emission from the packaged LEDs was 402 nm, which is in the blue-violet region. The output power and EQE were 28 mW and 45.4%, respectively, at a pulsed driving current of 20 mA. With increasing current, the output power increased linearly, and fairly flat EQE was observed with increasing drive current. At 200 mA, the power and EQE were 250 mW and 41%, respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We demonstrate highly manufacturable nonpolar (m-plane) InGaN/GaN laser diodes without any Al-containing waveguide cladding layers. These devices utilize thick InGaN quantum wells to generate transverse optical mode confinement and can be grown and fabricated in a manner analogous to InGaN/GaN light emitting diodes. Pulsed lasing operation was demonstrated, with threshold voltages and current densities of 6.7 V and 3.7 kA/cm2, respectively.

High power and high efficiency nonpolar m-plane (1100) nitride light emitting diodes (LEDs) have been fabricated on low extended defect bulk m-plane GaN substrates. The LEDs were grown by metal organic chemical vapor deposition (MOCVD) using conditions similar to that of c-plane device growth. The output power and external quantum efficiency (EQE) of the packaged 300 ×300 µm2 was 23.7 mW and 38.9%, respectively, at 20 mA. The peak wavelength was 407 nm and

This study examined the effect of electron-beam (E-beam) irradiation on the AIGaN/GaN HEMTs for the reduction of gate leakage. After E-beam irradiation, the gate leakage current significantly decreased from 2.68 x 10(-8) A to 4.69 x 10(-9) A at a drain voltage of 10 V. The maximum drain current density of the AIGaN/GaN HEMTs with E-beam irradiation increased 14%, and the threshold voltage exhibited a negative shift, when compared to that of the AIGaN/GaN HEMTs before E-beam irradiation. These results strongly suggest that the reduction of gate leakage current resulted from neutralization nitrogen vacancies and removing of oxygen impurities.

Violet InGaN/GaN light emitting diodes (LEDs) was fabricated on semipolar GaN bulk substrates. The output power and external quantum efficiency at a driving current of 20 mA were measured. The first nonpolar m-plane nitride laser diodes (LDs) were realized on low extended defect bulk m-plane GaN substrates.

The present article is a follow-up of our previous article [Jpn. J. Appl. Phys. 45 (2006) 7661]. InGaN-based light-emitting diodes of nonpolar orientation were grown on high-quality commercial GaN substrates. Results of low-temperature characterization showed that they were electrically conductive at temperature as low as 5 K. This experimental confirmation of electrical conduction at low temperature contradicts our previous results and the discussion of conduction mechanism returns to an impurity-concentration-related mechanism.

The first nonpolar m-plane (1-100) nitride laser diodes (LDs) have been realized on low extended defect bulk m-plane GaN substrates. The LDs were grown by metal organic chemical vapor deposition (MOCVD) using conditions similar to that of c-plane device growth. Broad area lasers were fabricated and tested under pulsed conditions. Lasing was observed at duty cycles as high as 10%. These laser diodes had threshold current densities (Jth) as low as 7.5 kA/cm2. Stimulated emission was observed at 405.5 nm, with a spectral line-width of 1 nm.

The surface donor state of AlGaN/GaN heterostructure on Si-substrate was investigated at the presence of Schottky gate metal (Au,Ni) on the surface by using electroreflectance spectroscopy. The sheet carrier density of two-dimensional electron gas (2DEG) decreased significantly from 1.03×1013cm-2 to 5.74×1012cm-2 for Au and from 1.03×1013cm-2 to 3.68×1012cm-2 for Ni upon the introduction of Schottky gate metal. Through the analysis of the depletion of 2DEG, which is attributed to both Schottky junction and the lowered energy of Schottky barrier height, it was concluded that the diminished sheet carrier density of 2DEG originated from the reduction of surface donor state induced by gate metal.

Sidewall lateral epitaxial overgrowth (SLEO) is demonstrated by metal organic chemical vapor deposition for nonpolar {11¯00} m-plane GaN films. m-plane GaN films were grown by metal organic chemical vapor deposition on m-plane 6H SiC substrates with an AlN initiation layer. Subsequently, an SiO2 stripe dielectric pattern was formed with 2μm window openings parallel to the [112¯0] a-direction and an 8μm mask and then the m-plane GaN was etched through the window openings to reveal Ga-face (0001) and N-face (0001¯) sidewalls. The SLEO growth was achieved in two growth steps—lateral growth from the sidewalls and subsequent growth through and then over the dielectric mask openings. In comparison to planar m-plane GaN films grown on 6H SiC, the threading dislocation density was reduced from low 1010to3×108cm−2 and the stacking fault density was reduced by one order of magnitude.

This paper discusses radiative recombination efficiency in electroluminescence of InGaN-based light-emitting diodes prepared on the (1?0??0) plane. Radiative efficiency was studied over a wide range of temperatures and drive currents on four types of LED samples with different InGaN active-layer thicknesses. Efficiency was minimally affected by active-layer thickness, yet was a strong function of temperature and current. Efficiency reduction at high current was observed on these LEDs, which confirms strain-induced electric polarization fields are not a dominant mechanism. Luminescence intensity was found to be proportional to the square root of current at low temperature. Acceptor freeze-out was suggested to induce hole depletion at increased current; shortage of holes resulted in reduced efficiency and triggered off electron injection into the p-type layer to sustain total current. Injected electrons were shown to lead to the square-root relationship by solving rate equations.

Nonpolar m-plane (11¯00) InGaN-based light emitting diodes (LEDs) grown on low-extended defect density bulk m-plane GaN substrates offer great potential for high performance devices due to the absence of polarization-related internal electric fields. To optimize the quantum well (QW) structure, systematic sets of near blue-ultraviolet LEDs using different well widths, barrier widths, and QW periods were packaged and tested. With increasing current, high power LEDs were realized with fairly flat external quantum efficiency and blueshift-free peak wavelength for QWs with thicknesses from 8to20nm, barrier widths from 10to22nm, and QW numbers from 4 to 10.

The role of extended defects in determining the atomic scale surface morphology of nonpolar {11¯00} m-plane gallium nitride has been elucidated. The heteroepitaxially grown m-GaN films are commonly reported to yield striated surface morphologies (slate morphology) correlated with their high densities of basal plane stacking faults. Here, the growth window was explored to allow nonslate morphologies for hydride vapor phase epitaxy. Lateral epitaxial overgrowth was then utilized to produce m-GaN films with three regimes of different extended defect contents. Elimination of stacking faults from the m-GaN yielded step-flow features with an average step height of 4–7 ML even for slate morphology growth conditions.

We report on the structural and electroluminescence characteristics of blue and cyan a-plane InGaN/GaN light-emitting diodes (LEDs). Cross-sectional transmission emission microscopy revealed the generation of occasional “asymmetric V-defects” in the active region. The blue and cyan LEDs exhibited rectifying behavior with forward voltages of 2.4 and 3.5 V at 20 mA, respectively and series resistances of 7 and 8 Ω, respectively. On-wafer dc output powers as high as 1.8 and 1.0 mW were measured at a drive current of 300 mA for the blue and the cyan LEDs, respectively. Electroluminescence measurement revealed an initial blue shift in the emission wavelength with the increase in the drive current. We speculate that the emission wavelength shift is due to the band-filling effect as a result of localization in the inclined non-{1120} oriented facets, which are polar in nature.

We report on the use of in-situ SiNx nanomask for defect reduction in nonpolar a-plane GaN films, grown by metal-organic chemical vapor deposition. High-resolution x-ray diffraction analysis revealed that there was a monotonic reduction in the full width at half maximum, both on-axis and off-axis, with the increase in the SiNx thickness. Atomic force microscopy images revealed a significant decrease in the root-mean-square roughness and the density of submicron pits. Cross-section and plan-view transmission electron microscopy on the samples showed that the stacking fault density decreased from 8×105to3×105cm−1 and threading dislocation density decreased from 8×1010to9×109cm−2. Room temperature photoluminescence measurement revealed that the band-edge emission intensity increased with the insertion of the SiNx layer, which suggests reduction in the nonradiative recombination centers.

In this paper, we report on the growth and fabrication of high power and high efficiency nonpolar m-plane (11 macr00) nitride light emitting diodes (LEDs) on low defect density bulk m-plane GaN substrates. The LEDs were grown by MOCVD on free-standing bulk m -plane GaN. All MOCVD growth was performed at atmospheric pressure, at typical V/III ratios (>3000), and at typical temperature ranges (875 to 1185degC). Standard processing was used to fabricate the LEDs. After device fabrication, the LEDs were diced and packaged using standard die and wire bonding techniques and then molded with epoxy.