Sidewall Lateral Epitaxial Overgrowth Research Articles

GaN microrod sidewall epitaxial lateral overgrowth on a close-packed microrod template

We demonstrate a GaN growth method using microrod sidewall epitaxial lateral overgrowth (MSELO) on a close-packed microrod template by a nonlithographic technique. The density and distribution of threading dislocations were determined by the density and distribution of microrods and the nucleation model. MSELO exhibited two different nucleation models determined by the direction and degree of substrate misorientation and the sidewall curvature: one-sidewall and three-sidewall nucleation, predicting the dislocation density values. As a result, the threading dislocation density was markedly decreased from 2 × 109 to 5 × 107 cm−2 with a small coalescence thickness of ∼2 µm for the close-packed 3000 nm microrod sample.

Atomic structure of prismatic stacking faults in nonpolar a-plane GaN epitaxial layers

In this study, a-plane GaN was grown on r-plane sapphire by sidewall lateral epitaxial overgrowth. Prismatic stacking faults (PSFs) in the window region of the GaN layer were identified to have an atomic configuration similar to the model presented by Northrup [Appl. Phys. Lett. 72, 2316 (1998)], which was demonstrated by comparing high-angle annular dark-field scanning transmission electron microscopy images with the atomic configurations of the Drum model, the Amelinckx model, and simplified Northrup model, respectively. The Northrup PSF structure has been further confirmed by the scattering contrast analysis in transmission electron microscopy experiments.

Extended defect structure of a-plane GaN produced by sidewall lateral epitaxial overgrowth

This paper demonstrates the use of Sidewall Lateral Epitaxial Overgrowth (S-LEO) on a-plane GaN thick films on r-plane sapphire by hydride vapor phase epitaxy (HVPE). Comprehensive study of the extended defect microstructure of the a-plane GaN films was carried out using cross-sectional and plan-view transmission electron microscopy (TEM). A very low density of primary threading dislocations and a heterogeneous microstructure can be found in the GaN films. In the window region and N-face wing region, the extended defects included type I 1 and type I 2 basal stacking faults (BSFs), as well as prismatic stacking faults (PSFs) on a-planes. The density of type I 1 BSFs was in the order of ∼2×10 5 cm −1, type I 2 BSFs in the order of ∼10 4 cm −1, and corresponding localized partial dislocation density less than 1.5×10 9 cm −2. PSFs on a-planes were connected to two neighboring type I 1 BSFs with an estimated density of 3×10 2 cm −1 in the plan-view images. In the Ga-face overgrowth regions, the density of BSFs was lower than 10 4 cm −1. However, inversion domains bounded by (1 1̄ 0 2), (1 1̄ 0 2̄), and (1 1̄ 0 0) planes were found in the Ga-face wing regions. The nature of inversion domain boundaries (IDB) on m-planes can be explained by the Auserman-Gehamn model using high-angle annular dark-field TEM images.

Realization of high‐crystalline‐quality and thick GaInN films

AbstractWe report on the growth of a completely relaxed, high‐ crystalline‐quality, and thick GaInN layer on a grooved m‐plane GaN template using sidewall epitaxial lateral overgrowth (SELO) technology. We grew GaInN‐based multiple quantum wells (MQWs) on this GaInN layer, and the PL intensity was compared with that for the same GaInN/GaN MQWs on m‐plane GaN grown by SELO. The PL peak intensity obtained from the GaInN/GaN MQW on the high‐crystalline‐quality thick GaInN on grooved GaN was approximately 1.7 times higher than that on the SELO m‐plane GaN template. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrical properties and deep traps spectra in undoped and Si-doped m-plane GaN films

Structural and electrical properties of nonpolar m-GaN films grown on m-SiC using standard metalorganic chemical vapor deposition (MOCVD) and two versions of sidewall epitaxial lateral overgrowth were studied. It is shown that lateral overgrowth allows one to dramatically reduce the dislocation density from over 109 cm−2 to ∼107 cm−2. In good correlation with that we observed a strong reduction in the density of electron traps Ec−0.25 eV and Ec−0.6 eV from over 1015 cm−3 to ∼1014 cm−3, respectively, in MOCVD m-GaN and in laterally overgrown m-GaN. Preliminary studies of the effects of changing the V/III ratio and of Si doping were performed. The MOCVD m-GaN films grown with high V/III ratio of 1000 were semi-insulating, with the Fermi level pinned near the 0.6 eV traps. Decreasing the V/III value to 250 shifted the Fermi level upward, close to the level of the 0.25 eV traps. Si doping in laterally overgrown samples strongly suppressed the formation of major electron traps but enhanced the formation of hole traps near Ev+0.9 eV. We also report on electrical properties of the GaN interface with the AlN buffer used to facilitate good quality growth on SiC. These properties are dominated by a high concentration of 0.15 eV traps.

Low extended defect density nonpolar m-plane GaN by sidewall lateral epitaxial overgrowth

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.

Improved quality nonpolar a ‐plane GaN/AlGaN UV LEDs grown with sidewall lateral epitaxial overgrowth (SLEO)

AbstractHigh 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)

Improvement in performance of m‐plane GaInN light emitting diode grown on m‐plane SiC by sidewall epitaxial lateral overgrowth

AbstractGaInN‐based light‐emitting diodes having m‐plane heterostructures and multi quantum well (MQW) were fabricated on m‐plane SiC by sidewall‐seeded epitaxial lateral overgrowth. Defects such as stacking faults or dislocations strongly affect the emission wavelength and efficiency of MQW. Control of the V/III ratio during growth is found to be very effective for growing GaN from only one sidewall, by which we can reduce the area of the high‐defect‐density region. A light emitting diode (LED) with high internal quantum efficiency and an almost single peak LED was successfully fabricated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrical characterization of low defect density nonpolar (11¯20) a-plane GaN grown with sidewall lateral epitaxial overgrowth (SLEO)

We studied the effect of extended defects on electrical characteristics of Si doped n-type nonpolar a-plane GaN films. The n-type GaN layers were grown on co-loaded reduced defect density sidewall lateral epitaxial overgrowth (SLEO) a-plane GaN templates and high defect density planar a-plane GaN templates by metalorganic chemical vapor deposition (MOCVD). The highest conductivity value was observed at the carrier concentration of 1.05 × 1019 cm−3 as 261.12 cm2/Vs for SLEO a-GaN and 106.77 cm2/Vs for the planar a-plane GaN samples. At the same doping level, the carrier compensation for SLEO samples was ∼12% less than planar samples.

Growth evolution in sidewall lateral epitaxial overgrowth (SLEO)

Sidewall lateral epitaxial overgrowth (SLEO) is a technique to reduce the extended defect densities in non-polar III-nitrides in a single re-growth by employing lateral overgrowth from sidewalls of an etched nitride through the mask openings. The technique involved depositing a stripe patterned mask over a-plane (1 1 2¯ 0) GaN along 〈1 1¯ 0 0〉 GaN and creating vertical {0 0 0 1} c-plane sidewalls by etching of nitride through the openings in the mask at a depth so that in the first growth stage, coalescence was achieved from the sidewalls before the growth of defected material trench bottom impeded lateral sidewall growth. After achieving the first-stage coalescence from the sidewalls, the material was grown over in two subsequent stages—growing up through the window openings, and then over the mask region until a smooth coalesced film was achieved. In this paper, we describe the effect of growth variables on material quality in all three stages of growth evolution in SLEO until coalescence. With the SLEO technique, threading dislocation densities of 10 6–10 7 cm −2 and stacking fault densities of 10 3–10 4 cm −1 were achieved in non-polar a-plane (1 1 2¯ 0) GaN grown over r-plane sapphire.

One-step lateral growth for reduction in defect density ofa-plane GaN onr-sapphire substrate and its application in light emitters

Low defect density a-plane GaN films were successfully grown by sidewall epitaxial lateral overgrowth (SELO) technology. Using this technology, a-plane GaN films with atomically flat surface were grown. The threading dislocation and stacking fault densities in the overgrown regions were lower than 10 6 cm -2 and 103 cm -1 , respectively. We also fabricated and characterized a-plane-GaN-based LEDs using SELO technology. The light output power of a blue-green LED was shown to monotonically increase with decreasing of threading dislocation density.

Improved quality (112¯0)a-plane GaN with sidewall lateral epitaxial overgrowth

We demonstrate a technique to reduce the extended defect densities in a-plane GaN deposited on r-plane sapphire. The SiO2 lateral epitaxial overgrowth mask consisted of ⟨11¯00⟩GaN stripes. Both the mask and GaN were etched through the mask openings and the lateral growth was initiated from the etched c-plane GaN sidewalls, and the material was grown over the mask regions until a smooth coalesced film was achieved. Threading dislocation densities in the range of 106–107cm−2 were realized throughout the film surface. The on-axis and off-axis full width at half maximum value and surface roughness were 0.082°, 0.114°, and 0.622 nm, respectively.

Details of the improvement of crystalline quality of a-plane GaN using one-step lateral growth

ABSTRACTLow defect density a-plane GaN films were successfully grown by sidewall epitaxial lateral overgrowth (SELO) technique. Control of V/III ratio during the growth of GaN by metalorganic vapor phase epitaxy (MOVPE) was found to be very important to achieve a complete overgrowth on the SiO2 mask regions and atomically flat surface. The threading dislocation and stacking fault densities in the overgrown regions were lower than 106 cm−2 and 103 cm−1, respectively. The root mean square roughness was 0.09 nm. We also fabricated and characterized a-plane-GaN-based-light-emitting diodes (LEDs) using SELO technique. The light output power of the blue-green LED steeply increased with the decrease of threading dislocation density from 1010 cm−2 to 108 cm−2 and tended to saturate at lower dislocation densities.