Highly carbon-doped Ga0.47In0.53As contact layers grown by using carbontetrabromide in MBE on MOVPE 1.55 μm GaInAsP/InP MQW laser structures

We report on carbon incorporation in (Ga,Al)InAs/InP using carbontetrabromide as the dopant precursor in molecular beam epitaxy. For Ga0.47In0.53As we find an increasing free hole concentration with decreasing growth temperature in the range from 450 to 515°C. In contrast, the carbon incorporation is independent of the growth temperature. At 450°C the electrical activation of carbon is almost 100% and free hole concentrations up to 2–3×1020cm−3 are achieved. The ratio of free hole concentration to carbon incorporation starts to diminish below 1.0 above hole concentrations of 8×1019cm−3. We consider a net selective etching of indium at the growing surface due to the CBr4 precursor at very high doping levels. For (Ga,Al)InAs growth temperature dependence of the free hole concentration is not observed. Although the supply of CBr4 is fixed the free carrier concentration and simultaneously the carbon incorporation increase with an increasing aluminium content in the layer. This holds even true for an aluminium mole fraction down to only 0.5%. These results are exploited for producing highly p-doped Ga0.47In0.53As contact layers, which are uniform over large areas, on MOVPE grown 1.55μm GaInAsP/InP MQW laser structures in a two-step epitaxy process. First results on broad area laser structures already show comparable data to MQW laser structures of the same design but completely produced by MOVPE.