Organometallic Vapor Phase Lateral Epitaxy of Low Defect Density GaN Layers
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present, the size and growth rate of these crystals are limited. The initial results of research regarding the lateral epitaxial overgrowth (LEO) of GaN layers on amorphous SiO 2 have been reported by the authors[4,5]. Additional results from studies[6] concerning the selective growth of GaN hexagonal pyramids for field emitters showed that lateral overgrowth unintentionally occurred over the Si0 2 mask layers under selected growth conditions. Transmission electron microscopic study also revealed that these overgrown regions of pyramids contained a very low density of dislocation ( and < 11 00> directions in each GaN film. Prior to lateral overgrowth, the patterned samples were dipped in a 50% buffered HC1 solution to clean the underlying GaN layer.
S~SiO2
Mask (0. 11gm)
AIN Buffer Layer (0.1 gm)
2nd LEO-GaN
Figure 1. Schematic diagram showing the first and second lateral epitaxial overgrowths of GaN layers from within stripe openings and over the top surfaces of two Si0 2 masks. The lateral overgrowth of GaN was achieved at 1000 - 1100'C and 45 Torr. Triethylgallium (13 - 39 gmol/min) and NH 3 (1500 sccm) precursors were used in combination with a 3000 sccm H2 diluent. The second lateral epitaxial overgrowth was conducted on the first laterally grown layer via the repetition of Si0 2 deposition, lithography and lateral epitaxy, as shown in Figure 1. The samples were characterized using scanning electron microscopy (SEM-JEOL 6400 FE), atomic force microscopy (AFM-Digital Instrument NanoScope III) and transmission electron microscopy (TEM-TOPCON 002B, 200KV). RESULTS AND DISCUSSION Figure 2 shows the representative cross-sectional morphologies of two GaN stripes selectively grown for 60 min along < 1120> and < 11 00>. Truncated triangular stripes having (1101) slant facets and a narrow (0001) top facet were observed for window openings along . Rectangular stripes having a (0001) top facet, (1120) vertical side facets and (1 T01) slant facets developed in samples grown along . Observations via SEM of GaN stripes grown for different times up to 3 min revealed similar morphologies regardless of stripe orientation. The stripes subsequently developed into different shapes if the growth was continued. The amount of lateral growth exhibited a strong dependence on stripe orientation. Results obtained under various growth conditions showed that the lateral growth rate of the oriented stripes was much faster than those along < 1120 >. We believe that the different morphological development as a function of window orientation is related to the stability of the crystallographic planes in the GaN structure. Stripes oriented along always had wide (1101) slant facets and either a very 302
(a) Figure 2. Scanning electron micrographs showing the morphologies of GaN layers grown on stripe openings oriented along (a) < 1120 > and (b) < 11 00>.
Figure 3. Scanning electron micrographs of < 1 100> oriented GaN stripes grown at TEG flow rates of (a) 13 pmol/min and (b) 39 Pmol/min for 60nain. narrow or no (0001) top facet dependin
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