Use of CCl₄ and CHCl₃ in gas source molecular beam epitaxy for carbon doping of GaAs and Ga_xIn_1-xP

Abstract

Carbon tetrachloride (CCl4) and chloroform (CHCl3) have been studied as carbon doping sources for the compound semiconductors GaAs, GaP, InP, and Ga0.51In0.49P grown by gas source MBE from elemental Group III sources and thermally cracked Group V hydride sources. Hole concentrations up to 1.3×1020 cm-3 have been measured by Hall effect in CCl4-doped GaAs, which agrees closely with the atomic C concentration from secondary ion mass spectrometry, indicating complete electrical activity of the incorporated carbon. For comparable dopant flow rates, use of CHCl3 results in carbon and hole concentrations approximately a factor of 15 lower than that from CCl4. The sensitivity of carbon incorporation to varying substrate temperature and V/III ratio has been observed to be significantly reduced with CCl4 and CHCl3 from that obtained under similar growth conditions with trimethylgallium (TMG) in metalorganic MBE (MOMBE). The GaAs growth rate is unaffected by the CCl4 flux over the range of CCl4 flow investigated. CCl4 has also been successfully employed as a carbon doping source for GaP, with a hole concentration of 1×1020 cm-3 achieved for growth at 600°C. Films of Ga0.51In0.49P grown at 515°C exhibit only marginal p-type conductivity with p = 5 × 1016 cm-3 when doped with CCl4, despite an incorporated atomic concentration of [C] = 5 × 1019 cm-3. Films of InP grown at 515°C are n-type with n = 9 × 1017 cm-3 despite substantial incorporated carbon equal to 1 × 1020 cm-3. © 1991.