Passivation of carbon acceptors during growth of carbon-doped GaAs, InGaAs, and HBTs by MOCVD

Abstract

Carbon dopedp-type GaAs and In_0.53Ga_0.47As epitaxial layers have been grown by low-pressure metalorganic chemical vapor deposition using CC1₄ as the carbon source. Low-temperature post-growth annealing resulted in a significant increase in the hole concentration for both GaAs and In_0.53Ga_0.47As, especially at high doping levels. The most heavily doped GaAs sample had a hole concentration of 3.6 × 10²⁰ cm⁻³ after a 5 minute anneal at ≈400° C in N₂, while the hole concentration in In_0.53Ga_0.47As reached 1.6 × 10¹⁹ cm⁻³ after annealing. This annealing behavior is attributed to hydrogen passivation of carbon acceptors. Post-growth cool-down in an AsH₃/H₂ ambient was found to be the most important factor affecting the degree of passivation for single, uncapped GaAs layers. No evidence of passivation is observed in the base region of InGaP/GaAs HBTs grown at ≈625° C. The effect ofn-type cap layers and cool-down sequence on passivation of C-doped InGaAs grown at ≈525° C shows that hydrogen can come from AsH₃, PH₃, or H₂, and can be incorporated during growth and during the post-growth cool-down. In the case of InP/InGaAs HBTs, significant passivation was found to occur in the C-doped base region.