Takumi Shibata

Strain relaxation and strong impurity incorporation in epitaxial laterally overgrown GaN: Direct imaging of different growth domains by cathodoluminescence microscopy and micro-Raman spectroscopy

Epitaxial lateral overgrowth GaN structures oriented along the 〈112_0〉 direction were comprehensively characterized by cathodoluminescence (CL) microscopy and micro-Raman spectroscopy. CL microscopy directly visualizes the significant differences between the overgrown areas on top of the SiO2 mask and the coherently grown regions between the SiO2 stripes in quantitative correlation with micro-Raman spectroscopy mapping of the local strain and free carrier concentration. The overgrown GaN shows a partial strain relaxation and a high carrier concentration that strongly broadens the luminescence. A strong impurity incorporation is evidenced in the coalescence regions. In contrast, the local luminescence from the areas of coherent (0001) growth is dominated by narrow excitonic emission, demonstrating the superior crystalline quality.

Selective area growth and epitaxial lateral overgrowth of GaN by metalorganic vapor phase epitaxy and hydride vapor phase epitaxy

Abstract Recent results on the selective area growth (SAG) and epitaxial lateral overgrowth (ELO) of GaN via metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HYPE) are reported. GaN sub-micron dots have been fabricated successfully via MOVPE-SAG on dot-patterned GaN (0001) epitaxial layer/sapphire substrate and also on dot-patterned sapphire substrate using AlN low temperature (LT) buffer layer. The smooth surface is obtained via MOVPE-ELO for both the 〈11 2 0〉 and 〈1 1 00〉 sub-micron SiO 2 stripes. The reduction in dislocation density is confirmed by using TEM. Furthermore, the HVPE-ELO of GaN is performed on two mask patterns with the 〈11 2 0〉 and 〈1 1 00〉 stripes. In the 〈11 2 0〉 stripe the ELO layer surface is not uniform, covered with {1 1 01} facets in which the growth rate is very slow. On the other hand, in the〈1 1 00〉 stripe the surface of the ELO layer becomes uniform with (0001) face. The defect structures of the ELO layers are characterized by a growth pit density (GPD) using a thin InGaN epitaxial layer grown on the ELO GaN layer and a cathodoluminescence (CL). It is found that the defect structures are strongly related to the growth mechanism during the ELO process.

Optical microscopy of electronic and structural properties of epitaxial laterally overgrown GaN

Local strain relaxation as well as inhomogeneous impurity incorporation in epitaxial laterally overgrown GaN (ELOG) structures is microscopically characterized using spectrally resolved scanning cathodoluminescence (CL) and micro-Raman spectroscopy. We correlate the different CL emission spectra with results of spatially resolved Raman-scattering experiments sensing the local strain and free-carrier concentration.

Hydride vapor-phase epitaxy growth of high-quality GaN bulk single crystal by epitaxial lateral overgrowth

Selective area growth (SAG) of GaN using the HVPE method was carried out to obtain a high-quality GaN bulk single crystal. Selectivity of the GaN growth was excellent and the GaN layer had no cracks. The FWHM (195 arcsec) of the X-ray rocking curve for (0004) diffraction was narrower than that (348 arcsec) of the sample grown by the conventional method. Overgrowth of the GaN on the SiO 2 mask was enhanced in the direction. Cathode luminescence intensity of this overgrowth region was much stronger than that of the window region. It was found that a reduction in stress is achieved by narrowing the window area, and the epitaxial lateral overgrowth on the mask is effective in obtaining high-quality GaN layer.

Selective Area Growth of GaN Using Tungsten Mask by Metalorganic Vapor Phase Epitaxy

We studied selective area growth (SAG) of GaN using a tungsten (W) mask with an atmospheric metalorganic vapor phase epitaxy (MOVPE) system. No GaN polycrystals were observed on the W mask regions, and the selectivity of GaN growth on window regions proved to be excellent. The GaN stripes developed into different shapes depending on the direction of stripe mask patterns. If the stripe was along , a triangular shape with {1101} facets was formed. If the stripe was along , a trapezoidal shape with a smooth (0001) surface on top and rough surfaces on both sides was obtained. The lateral overgrowth of GaN on the W mask occurred in both cases. The growth mechanisms and the facet formation were similar to those found in SAG using a SiO2 mask.

Time-resolved microphotoluminescence of epitaxial laterally overgrown GaN

Epitaxial laterally overgrown GaN (ELOG) structures are microscopically characterized using spatially resolved microphotoluminescence (micro-PL) and time-dependent spectroscopy. To understand the influence of the different lateral growth mechanisms on the peak position and the temporal behavior of the transition lines, we correlated the different micro-PL emission spectra with results of spatially resolved time-dependent spectroscopy experiments.

Epitaxial lateral overgrowth of GaN structures : spatially resolved characterization by cathodoluminescence microscopy and micro-Raman spectroscopy

The epitaxial lateral overgrowth of GaN structures is comprehensively characterized by scanning cathodoluminescence microscopy and micro-Raman spectroscopy. The samples under study consist of a 3-μm thick GaN buffer layer grown by MOVPE on (0001) sapphire and subsequently structured using a SiO 2 mask. The resulting stripe pattern is overgrown with HVPE GaN. Mask orientations along and are compared. CL microscopy directly visualizes the significant differences between the overgrown areas on top of the SiO 2 -mask and the coherently grown regions between the SiO 2 -stripes. The overgrown GaN shows a blue shift and a strong broadening of the luminescence. In contrast, the local luminescence from the areas of coherent (0001)-growth is dominated by narrow excitonic emission. The CL results are correlated with micro-Raman spectroscopy yielding information on the local strain and free carrier concentration.