Optically in-situ monitored growth of carbon doped InAlAs by LP-MOVPE using CBr4

Carbon-doped InAlAs, AlAs and InAs layers have been grown by LP-MOVPE using carbontetrabromide (CBr4) as the dopant source. Optical in-situ together with ex-situ characterization techniques were used to measure the epilayers growth rate, C and p-type doping level and InAlAs alloy composition. We investigated the influence of growth parameters on C incorporation and on CBr4 etching effect. Both decrease as the growth temperature or the V/III ratio increases. The indium content in InAlAs was found to increase with the CBr4 flow, especially at low V/III ratio. AlAs and InAs undoped and doped layers, grown using the same growth conditions on GaAs and InAs substrates, respectively, allowed to separately quantify the CBr4 etching effect on the AlAs and InAs fraction of the InAlAs layers. We found that CBr4 does not etch AlAs but reacts strongly with the TMAl vapor phase. On the contrary, CBr4 etches constantly the InAs solid phase, and independently of the TMIn flow. These two differences explain consistently the diversity reported in the InAlAs composition variation as a function of CBr4 flow rate.