High current gain InGaP/GaAs heterojunction bipolar transistors grown by multi-wafer gas-source molecular beam epitaxy system

Abstract

We report for the first time on the high quality and highly uniform InGaP/GaAs heterojunction bipolar transistors with a carbon-doped base grown by a multi-wafer gas-source molecular beam epitaxy (GSMBE) system, which was developed by ourselves. A large-area uniform growth of p-type GaAs and InGaP has been realized. The variation in layer thickness of these layers was less than ± 1.8% across three 3-inch wafers. A large-area (200 × 200 μm 2) heterojunction bipolar transistor (HBT) with a base-sheet resistance of 350 Ω showed a high current gain of 190. This is effectively the highest value considering the base sheet resistance, and is comparable to the best data of AlGaAs/GaAs HBTs reported so far. The small signal current gains showed an excellent uniformity of 3% across one of five 2-inch wafers. The wafer-to-wafer variation of current gains for the two 2-inch wafers, in the same growth run, was less than 3%. The base sheet resistances also showed an excellent uniformity of 0.86%. In addition the average base sheet resistances of the two 2-inch wafers was the same. The device also showed an excellent high-frequency characteristics. The cut-off frequency ( f t ) of 61 GHz, and the maximum-oscillation frequency ( f max ) of 94 GHz were obtained for the transistor having a base dopant concentration of 4 × 10 19 cm −3. These promising results demonstrate the high potential capability of multi-wafer GSMBE for the production of InGaP/GaAs HBTs.