An investigation was made of the behavior of Zn impurities in heterojunction bipolar transistor structures that had been grown by using a low-pressure metalorganic chemical vapor deposition technique. In this technique, Zn was anomalously diffused into InP/InGaAs heterojunction bipolar transistors with a heavily Si-doped (2 x 1019/cm3) sub-collector layer when the growth temperature before base-layer growth was higher or lower than about 600C. On the other hand, an abrupt Zn profile in the same heterojunction bipolar transistor structure was obtained when the growth temperature of the sub-collector layer was 600C. Two types of point defect reaction, which depended strongly upon the growth temperature, were proposed. In one type, excess group-III interstitials which were produced in a heavily Si-doped sub-collector layer were easily removed. In the other type, the equilibrium concentration of charged group-III vacancies decreased as the growth temperature was increased. According to this model, complete suppression of unwanted Zn diffusion could be achieved by using a growth interruption technique to obtain point defect equilibrium before base-layer growth at 550C when the growth temperature of the sub-collector layer was either lower or higher than 600C. It was concluded that interruption of the growth for a suitable period of time before base-layer growth, or the use of a suitable growth temperature for the sub-collector, was essential in order to obtain an abrupt Zn profile in a heterojunction bipolar transistor structure with a heavily doped sub-collector layer.

T.Kobayashi, K.Kurishima, U.Gösele: Journal of Crystal Growth, 1995, 146[1-4], 533-7