Influence of arsenic species on the growth and properties of GaAsBi alloys

Due to the significant bandgap reduction associated with bismuth incorporation, dilute bismuthide semiconductor alloys have been proposed for high-efficiency optoelectronic devices. To achieve significant incorporation of bismuth into GaAsBi, molecular beam epitaxy at low temperature is required. Furthermore, many groups use As$_{\mathrm{2}}$ for low-temperature growth of GaAsBi, presumably due to historical reports of improved photoluminescence for low-temperature growth of GaAs with As$_{\mathrm{2}}$ in comparison with As$_{\mathrm{4}}$. Here, we show that Bi incorporation into GaAs is favorable over a wider range of growth conditions with As$_{\mathrm{4}}$ in comparison with As$_{\mathrm{2}}$. The preference for Bi incorporation with As$_{\mathrm{4}}$ is associated with the differences in the likelihood for As$_{\mathrm{2}}$ vs. As$_{\mathrm{4}}$ to replace weakly bonded surface Bi$_{\mathrm{2}}$. For growth with As$_{\mathrm{4}}$, the electron mobility for GaAsBi:Si is as high as 2500 cm$^{\mathrm{2}}$/V-s for Si-doped (n $\approx $ 10$^{\mathrm{18}}$ cm$^{\mathrm{-3}})$ GaAsBi, higher than reported values for growth using As$_{\mathrm{2}}$. The hole mobility of Si-doped GaAsBi is essentially independent of $x$ up to 0.043, making Si a promising alternative to C or Be for $p$-type doping of GaAsBi and related bismuthide alloys. In addition, a comparison of the photoluminescence spectra of films grown with both As$_{\mathrm{2}}$ and As$_{\mathrm{4}}$ will be discussed.