Impact of CBr 4, V/III ratio, temperature and AsH 3 concentration on MOVPE growth of GaAsSb:C

Abstract

We investigate the impact of the carbon tetrabromine (CBr 4) and arsine (AsH 3) concentrations, the V/III ratio at the gas inlet ( R inlet) and the temperature ( T g) on the growth rate, the solid composition, the incorporated carbon (C) and free hole concentration in GaAsSb:C grown by metal-organic vapor-phase epitaxy (MOVPE). The introduction of CBr 4 deeply perturbs the growth when compared to when no C-doping is used. The growth of GaAsSb:C using CBr 4 behaves as if an effective V/III ratio ( R eff) were defined as the R inlet leading to the same growth rate in the absence of CBr 4 under the same group V inlet flux. This consideration allows (and/or accounts) for the growth of high-quality layers with R inlet≪1, and explains alloy composition and growth rate variations as well as non-monotonic variations of the free hole concentration with increasing CBr 4 flow. We show how R eff∼1 can be experimentally determined to optimize the growth conditions in MOVPE reactors. An increase of the CBr 4 flux enhances the solid arsenic (As) concentration and reduces the growth rate. The As concentration dependence on the CBr 4 flux becomes stronger at higher R inlet. Although the incorporated C density monotonically increases with increasing CBr 4 flow, the hole concentration increases and then drops. This drop is attributed to the amphoteric character of C and/or to the formation of C–C bonds. The peak hole density is enhanced from 2.5×10 19 to over 1.6×10 20 cm −3 by reducing R inlet from 0.72 to 0.25. Furthermore, the hole density decreases from 1.6×10 20 to 5.5×10 19 cm −3 if the AsH 3 concentration increases from 0.31 to 0.51. Thus, alloys with As-rich composition obtained by increasing the AsH 3 composition in the gas phase cannot achieve hole concentrations as high as 1×10 20 cm –3 at T g=550 °C. However, we demonstrate that GaAs 0.7Sb 0.3 with doping levels of 1×10 20 cm –3 could only be achieved by decreasing T g to 510 °C.