Gas-source MBE growth and n-type doping of AlGaAs using TEG, TEA, AsH3 and Si2H6

Abstract

We have studied gas-source molecular beam epitaxy (GSMBE) growth and n-type doping of AlGaAs using triethylgallium, triethylaluminum, arsine (AsH3) and disilane (Si2H6), focusing on (1) the effect of substrate temperature (520–690°C) and AsH3 flow rate (2–7 SCCM) on the carbon and oxygen incorporation of AlxGa1−xAs (x ∼ 0.28), and (2) the variation of the carrier concentration of n-type AlxGa1−xAs (x = 0–0.28) with Si2H6 flow rate (0.4–10 SCCM). The carbon concentration decreased with increasing substrate temperature up to 610°C, then increased with increasing substrate temperature using an AsH3 flow rate of 2 SCCM. Below 610°C, an increase in AsH3 flow rate resulted in a reduction in the carbon concentration. We obtained a carbon concentration of 1 × 1018 cm-3 at a substrate temperature of 520°C and an AsH3 flow rate of 7 SCCM. The addition of molecular hydrogen was found to further reduce the carbon concentration, and the lowest value obtained was 8.2 × 1017 cm-3 at a substrate temperature of 520°C using 4 SCCM AsH3 and 4.5 SCCM of molecular hydrogen. The oxygen concentration was not affected by the substrate temperature, but showed a slight decrease with increasing AsH3 flow rate. The lowest oxygen concentration was 2.5 × 1017 cm-3 at 7 SCCM AsH3 flow rate. The variation of the hole concentration with growth conditions was similar to that observed for carbon. The 4.2 K photoluminescence was dominated by a free-to-bound emission having a full-width-at-half-maximum of 18 meV, which is thought to be related to shallow carbon acceptors. Si2H6 was shown to be a suitable cold n-type gaseous dopant source for GSMBE growth of AlGaAs. The carrier concentration of the n-type AlxGa1−xAs (x = 0–0.28) epilayer was reproducibly controlled between 5 × 1017 and 2 × 1018 cm-3.