Use of CCl 4 and CHCl 3 in gas source molecular beam epitaxy for carbon doping of GaAs and Ga xIn 1−xP

Abstract

Carbon tetrachloride (CCl 4) and chloroform (CHCl 3) have been studied as carbon doping sources for the compound semiconductors GaAs, GaP, InP, and Ga 0.51In 0.49P grown by gas source MBE from elemental Group III sources and thermally cracked Group V hydride sources. Hole concentrations up to 1.3×10 20 cm −3 have been measured by Hall effect in CCl 4-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 CHCl 3 results in carbon and hole concentrations approximately a factor of 15 lower than that from CCl 4. The sensitivity of carbon incorporation to varying substrate temperature and V/III ratio has been observed to be significantly reduced with CCl 4 and CHCl 3 from that obtained under similar growth conditions with trimethylgallium (TMG) in metalorganic MBE (MOMBE). The GaAs growth rate is unaffected by the CCl 4 flux over the range of CCl 4 flow investigated. CCl 4 has also been successfully employed as a carbon doping source for GaP, with a hole concentration of 1×10 20 cm −3 achieved for growth at 600°C. Films of Ga 0.51In 0.49P grown at 515°C exhibit only marginal p-type conductivity with p = 5 × 10 16 cm −3 when doped with CCl 4, despite an incorporated atomic concentration of [ C] = 5 × 10 19 cm −3. Films of InP grown at 515°C are n-type with n = 9 × 10 17 cm −3 despite substantial incorporated carbon equal to 1 × 10 20 cm −3.