Influence of growth parameters on the composition and impurity levels of intrinsically carbon doped AlxGa1−xAs

Intrinsically carbon doped AlxGa1−xAs was grown by metalorganic chemical vapor deposition (MOCVD). The influence of the growth temperature, the V/III ratio and the aluminum fraction on the carbon, hydrogen, oxygen and aluminum incorporation was investigated over a wide parameter range. Secondary ion mass spectroscopy (SIMS) analysis was correlated with capacitance voltage (CV) measurements. It was found that a reduction of the growth temperature and the V/III ratio results in a strong decrease of the incorporated aluminum fraction in the layer, in particular in the range suitable for intrinsic carbon doping. This was explained by a lower decomposition rate of trimethyl aluminum compared to trimethyl gallium. For almost the entire investigated parameter range the carbon levels in the layer exceeded the carrier concentration due to deactivation by hydrogen and carbon incorporation on Ga-, Al- or interstitial sites. At a growth temperature of 530 °C, however, all incorporated carbon is active, even at a maximal carrier concentration of 1.7×1020 cm−3. With the results obtained from this study, the carbon concentration and the aluminum fraction of intrinsic carbon doped layers can be controlled for a large range of growth conditions.