Effects of annealing on the performance of InP/lnGaAs HBTs grown by LP-MOCVD

The effects of rapid thermal annealing on InP/InGaAs heterojunction bipolar transistors with a carbon-doped base have been studied. The hydrogen concentration in the base has been studied as a function of the anneal temperature and time. A 10 minute anneal at 590/spl deg/C under N/sub 2/ completely eliminates hydrogen from the base. By using shorter anneals and/or lower temperatures, the dc and rf device performance were studied as a function of the base hydrogen concentration. The results show that the base sheet resistance decreases with annealing time as does the dc current gain. As expected, the maximum frequency of oscillation increases as the base resistance decreases. The unity current-gain cutoff frequency, however, is significantly enhanced by removing hydrogen despite the resulting increase in the base hole concentration. A likely explanation for this behavior is that a large percentage of the hydrogen in the InGaAs base region incorporates as a compensating donor rather than forming a neutral CH complex.