Sung Min Hwang

Investigation of carrier transport properties in semipolar (112¯2) GaN films with low defect density

We report on the anisotropic carrier transport properties of semipolar (112¯2) GaN films with low defect density. We utilized the asymmetric lateral epitaxy to obtain various semipolar (112¯2) GaN films having significantly reduced partial dislocations and basal-plane stacking faults (BPSFs). The directionally dependent carrier transport was observed with the lower sheet resistances (Rsh) along the [11¯00] direction. The Rsh ratios of semipolar (112¯2) GaN films were found to be relatively smaller than those of nonpolar a-plane GaN films, possibly due to low BPSF density and the reduced in-plane electric field induced by BPSF along the [112¯3] direction at wurtzite domain boundaries.

Structural and electrical anisotropies of Si-doped a-plane (11?20) GaN films with different SiNx interlayers

The effects of different SiNx interlayers on the structural and electrical properties of nonpolar Si-doped a-plane (11–20) GaN films grown on r-plane (1–102) sapphire were investigated. The surface roughness depends strongly on the SiNx coverage, deposition temperature and number of SiNx layers. The in-plane anisotropy of on-axis x-ray rocking curves (XRCs) (full width at half-maximum) was significantly decreased by the introduction of multiple SiNx-treated GaN interlayers, indicating coherently scattering domains of uniform size. Off-axis XRC measurements were also employed to investigate the effects on the mosaic twist corresponding to edge dislocation and the I1-type basal-plane stacking fault (BSF) density. Hall effect measurement showed that the electrical conductivity was the highest when multiple SiNx/GaN interlayers were employed. The measured sheet resistances (Rsh) along the c-axis were higher than those along the m-axis. These anisotropic conductivities could be explained by BSFs acting as carrier scattering centers. The ratios of Rsh along the two in-plane orientations also correlated well with the BSF densities.

Effect of Basal-plane Stacking Faults on X-ray Diffraction of Non-polar (1120) a-plane GaN Films Grown on (1102) r-plane Sapphire Substrates

We report the effect of basal-plane stacking faults (BSFs) on X-ray diffraction (XRD) of non-polar (1120) a-plane GaN films with different SiNx interlayers. Complete SiNx coverage and increased three-dimensional (3D) to two-dimensional (2D) transition stages substantially reduce BSF density. It was revealed that the Si-doping profile in the Sidoped GaN layer was unaffected by the introduction of a SiNx interlayer. The smallest in-plane anisotropy of the (1120) XRD ω-scan widths was found in the sample with multiple SiNx layers, and this finding can be attributed to the relatively isotropic GaN mosaic resulting from the increase in the 3D-2D growth step. Williamson-Hall (WH) analysis of the (h0h0) series of diffractions was employed to determine the c-axis lateral coherence length (LCL) and to estimate the mosaic tilt. The c-axis LCLs obtained from WH analyses of the present study’s representative a-plane GaN samples were well correlated with the BSFrelated results from both the off-axis XRD ω-scan and transmission electron microscopy (TEM). Based on WH and TEM analyses, the trends in BSF densities were very similar, even though the BSF densities extracted from LCLs indicated that the values were reduced by a factor of about twenty.

Performance of GaAs-AlGaAs V-grooved inner stripe quantum-well wire lasers with different current blocking configurations

GaAs-AlGaAs V-grooved inner stripe (VIS) quantum-well wire (QWW) lasers grown by metalorganic chemical vapor deposition with different current blocking configurations, n-blocking on p-substrate (VIPS), p-n-p-n blocking on n-substrate (VI(PN)/sub n/S) and p-blocking on n-substrate (VINS) have been fabricated and characterized. The VIPS QWW lasers show the most stable characteristics with effective current confinement: one of the lasers shows fundamental transverse mode, lasing up to 5 mW/facet, typical threshold current of 39.9 mA at 818.5 mm, an external differential quantum efficiency of 24%/facet, and characteristic temperature of 92 K. The current tuning rate was almost linear at 0.031 mm/mA, and the temperature tuning rate was measured to be 0.14 nm//spl deg/C. Comparison of the light output versus current characteristics of the lasers with different current blocking configurations is presented here.

Fabrication of V-grooved inner stripe GaAs-AlGaAs quantum-wire lasers

V-grooved inner stripe (VIS) GaAs-AlGaAs quantum-wire (QWR) lasers were successfully fabricated by, combining two-step metalorganic chemical vapor deposition (MOCVD) growth with a wet-etching technique. In order to achieve low threshold current density and high reliability, a conductive stripe width (W), a thickness (t/sub p-CBL/), and a doping concentration (n/sub p-CBL/) of the p-GaAs current-blocking layer (CBL) were determined to be W=1.2 /spl mu/m, t/sub p-CBL/=2 /spl mu/m, and n/sub p-CBL/=1/spl times/10/sup 18/ cm/sup -3/. The leakage currents passing through the CBL were also estimated using a modified P-SPICE. Thus far, a threshold current of 45 mA and an output power of 4 mW at 51 mA have been achieved under room-temperature pulsed operation for some devices with uncoated facets.

Formation of submicrometer current-blocking layer for high-power GaAs/AlGaAs quantum wire array laser

Short-period GaAs quantum wire (QWR) array was grown by metalorganic chemical vapor deposition on submicron gratings. And a new lithography technique to fabricate submicron current-blocking layer on the short-period QWR array without any external masks was developed. The methods include the followings. The photoresist was coated on the nonplanar top of the laser diode structure. The photoresist stripes were designed to remain over each QWR with a flood exposure and a develop technique. The GaAs contact layers on the parts of the (111)A and all the (100) top quantum wells were removed by employing the photoresist remaining on the top valley as masks. The submicron current-blocking layer was produced all over the regions except QWRs, by sputtering SiO2 film followed by lift-off and metal evaporation. It must help a majority of current pass into QWR active region.

Effect of SiNx interlayer on structural and electrical properties of nonpolar a-plane (11-20) gallium nitrides

We investigated the effects of SiNx interlayers on the structural and electrical properties of nonpolar a-plane (11-20) GaN grown on r-plane (1-102) sapphire substrates by metal–organic chemical vapor deposition (MOCVD). The Nomarski optical microscope images showed that the deposition conditions of the SiNx layer could strongly affect the a-plane GaN surface morphology due to the different SiNx coverage. Basal-plane stacking faults (BSFs) and threading dislocation (TD) densities were reduced in the a-plane GaN samples with high SiNx coverage and multiple SiNx-treated GaN interlayers. These results indicate that TD reduction is associated with an increase in the 3D growth step and with the blocking of TD propagation. From on-axis (11-20) X-ray rocking curve (XRC) measurements, the anisotropy of full width at half maximum (FWHM) can be attributed to the crystal mosaicity due to insertion of different SiNx interlayers. The anisotropy of sheet resistance between the c-and m-axis was also clearly seen in a-plane GaN samples with a high density of defects, which was attributed to the BSFs as scattering centers.

Aligned In0.5Ga0.5As quantum dots on laser-patterned GaAs substrate

It has been studied the selective InGaAs quantum dots growth on laser-patterned GaAs substrate by atmospheric pressure metal organic chemical vapor deposition. We have patterned the samples below etching threshold power density 8.84 MW/cm2 by argon ion laser. The depth and lateral size of the pattern are about 8 nm and 100 nm, respectively. The QDs were grown on AlGaAs matrix.