CARBON INCORPORATION IN ALGAAS GROWN BY CBE

The incorporation of carbon into unintentionally doped AlxGa1-xAs epilayers grown by chemical beam epitaxy (CBE) using arsine and various combinations of group III sources was investigated. Growth of unintentionally doped AlxGa1-xAs using triethylgallium (TEGa)+triisobutylaluminum (TIBAl) resulted in lower hole and carbon concentrations than those grown from TEGa+triethylaluminum (TEAl). The carbon concentration in AlGaAs epilayers increased with decreasing growth temperature below 560°C and increased with increasing growth temperature above 560°C. This "U-shaped" dependence of carbon concentration on growth temperature exhibited its minimum value at ∼ 560°C for both the TEGa+TEAl and TEGa+TIBAl systems. The alkyl-Al compounds are thought to be the controlling species for the carbon incorporation in the low temperature regime, while the AlCH3 formed through β-methyl elimination is responsible for the carbon incorporation in the high temperature regime. Based on this study, we are able to grow high quality AlGaAs epilayers with reduced carbon contamination by using TIBAl instead of TEAl at the growth temperature of 560°C with a V/III ratio of 20. AlGaAs/GaAs modulation-doped structures grown from TEGa+TIBAl show a two-dimensional electron gas mobility as high as 88,600 cm2/V·s at 77 K, which is a 40% improvement over that grown from TEGa+TEAl, with a sheet carrier concentration of 6x1011 cm-2 and a spacer layer thickness of 150 Å. © 1990.