The effects of ex situ high temperature annealing (T≳500 °C) on the hole and hydrogen concentration of the base and on the dc device characteristics of InGaP/GaAs heterojunction bipolar transistors grown by low-pressure metalorganic chemical vapor deposition have been studied. Using rapid thermal annealing, hydrogen can be completely annealed out of the base, activating the carbon acceptors. Due to the low diffusivity of carbon, the high temperatures necessary to remove most of the hydrogen do not degrade the device characteristics. Using this simple technique to eliminate hydrogen from the base prior to device fabrication should improve the reliability of GaAs-based transistors with a carbon-doped base. Results also indicate that unlike carbon-doped In0.53Ga0.47As, hydrogen does not significantly affect the minority carrier characteristics of carbon-doped GaAs.

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IntroductionThe effects of rapid thermal annealing on InPhGaAs 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" C under N2 completely eliminates hydrogen from the base. By using shorter anneals and/or lower temperatures, the dc and rf devjce 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.

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