Effects of Growth Temperatures on Crystal Quality of GaN by Vapor Phase Epitaxy Using GaCl₃ and NH₃

Abstract

Thick epitaxial growth of GaN by vapor phase epitaxy (VPE) is an indispensable technique to form GaN substrates which have been commonly used for blue-violet GaN-based lasers with sufficiently long lifetime. Although the growth has been established in view of the mass-production of the GaN substrate, the crystal quality has never been sufficiently correlated with the growth conditions. In this paper, the effects of the growth temperatures on the crystal quality of VPE-grown GaN films are studied in detail. It is noted that the GaN films are grown by a single-zone VPE using externally placed GaCl3 and NH3 as source precursors. The growth exhibits the growth rate of 14 µm/h at highest and far higher growth rate is possible by increasing the carrier flow rate and/or temperature of the GaCl3. The experimental results reveal that the surface morphology and optical properties are strongly dependent on the growth temperature. At around 975 °C with very narrow temperature window, very smooth surface together with a very sharp photoluminescence (PL) peak originating from bound excitons is observed. Growth at lower temperatures than the optimized window results in rough surface with many pits on it. Higher temperature results in many cracks and peeling-off on the surface with the sign of three-dimensional growth. Peaks originating from residual acceptors are dominant in the PL spectra of the films with rough surfaces grown at higher or lower temperatures from the optimized window. Flattening the surface of GaN at the optimized temperatures by the enhanced lateral growth is essential to grow thick GaN by the VPE with good crystalline quality free from the incorporation of the residual acceptors.

Suppression of cluster formation in GaN growth by tri-halide vapor phase epitaxy with external GaCl3 gas supply system

“…One is vaporization of solid GaCl 3 , which has a high vapor pressure (4500 Pa at 100 °C), and a high flow rate can be easily obtained. Several groups including ours [29][30][31] have reported high-speed growth of GaN with rates of about 10-50 μm h −1 by this method. Another method is the synthesis of GaCl 3 by the reaction of metallic gallium with Cl 2 gas.…”

GaN epitaxial growth on 4 degree off-axis Si- and C-face 4H-SiC without buffer layers by tri-halide vapor-phase epitaxy with high-speed wafer rotation

“…[9][10][11][12][13] The epitaxy of GaN, halide vapor-phase epitaxy (HVPE), in which the growth rate is faster than that of MO-CVD, has been studied to achieve high-crystal-quality GaN epilayers with a high growth rate, typically using a horizontal gas flow reactor with an internal GaCl source gas supply system using Ga metal placed inside the reactor. [14][15][16][17][18][19] Recently, tri-halide vapor-phase epitaxy (THVPE) of thick GaN using GaCl 3 has been reported; [20][21][22][23][24][25][26][27] these reports suggest that THVPE has much higher growth rates than conventional HVPE under the same growth conditions and GaCl 3 source gas can be supplied from outside the reactor. However the high-speed rotation effect of GaN growth on SiC has not yet been utilized for GaN HVPE or THVPE.…”