Impact Of Cbr_4, V/iii Ratio, Temperature And Ash_3 Concentration On Movpe Growth Of Gaassb:c

摘要

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_(inter) 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 Reff～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 Rinlet 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×l0~(20)cm~(-3) at Tg=550℃. However, we demonstrate that GaAs_(0.7)Sb_(0.3) with doping levels of 1×10~(2O)cm~(-3) could only be achieved by decreasing T_g to 510℃.