Rapid growth of <i>α</i> -Ga <sub>2</sub> O <sub>3</sub> by HCl-boosted halide vapor phase epitaxy and effect of precursor supply conditions on crystal properties
Yuichi Oshima, Katsuaki Kawara, Takayoshi Oshima, Mitsuru Okigawa, Takashi Shinohe
Abstract
Abstract We investigated the effect of supply conditions of GaCl, O 2 , and additional HCl on the growth rate of (0001) α -Ga 2 O 3 by halide vapor phase epitaxy and the crystal properties. The parasitic gas-phase reaction was markedly suppressed by supplying HCl gas in addition to GaCl and O 2 , and a rapid growth rate as high as 101 μ m h −1 was achieved. Thermodynamic analysis revealed that the addition of HCl works to convert GaCl into GaCl 3 , and it was elucidated that the parasitic gas-phase reaction was suppressed because α -Ga 2 O 3 was grown through the chemical reaction of GaCl 3 and the oxygen sources (O 2 and/or H 2 O), the equilibrium constant of which is much smaller than that when GaCl is used. The full-width at half-maximum of the x-ray rocking curve of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>10</mml:mn> <mml:mover accent="true"> <mml:mn>1</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mn>2</mml:mn> </mml:math> diffraction measured in skew-symmetric geometry decreased with increasing growth rate by increasing the precursor supply, whereas that of symmetric 0006 diffraction did not show a systematic tendency. H and Cl impurities were detected in the unintentionally doped epilayers by secondary ion mass spectrometry. [Cl] increased rapidly with increasing growth rate, reaching 1.4 × 10 18 cm −3 at 101 μ m h −1 . The VI/III ratio difference did not have a significant effect on [H] or [Cl]. α -Ga 2 O 3 islands were formed through selective area growth, and the lateral/vertical growth rate ratio decreased with increasing growth rate.