Carbon incorporation in GaAs layer grown by atomic layer epitaxy

The mechanism by which carbon is incorporated into GaAs layers by atomic layer epitaxy using trimethylgallium or triethylgallium was investigated. The carbon density varied from 1×10 ¹³ to 8×10 ¹⁸ cm ^-3 with the trimethylgallium (or triethylgallium) and arsine pulse durations and mole fractions. It was also observed that the carbon incorporation drastically changed at the pulse duration and mole fraction where the growth rate per gas cycle started to saturate to one monolayer (0.283 nm/cycle for a (100) substrate). The results were explained by the selective adsorption of carbon on surface gallium, the reaction of methygallium with arsine, and the exchange interaction between arsenic and carbon atoms. Even when the trimethylgallium source was used, the epitaxial layers grown under the optimized growth conditions exhibited an electron concentration of 1×10 ¹⁴ cm ^-3 and a mobility of 80 000 cm ²/V·s at 77 K, a photoluminescence spectrum with several sharp excitonic lines at the band gap energy, and an extremely low level of carbon related peaks.