GaInP/GaAs HBT with a selective buried sub-collector layer grown by MOCVD

Abstract

This paper presents a method to reduce the extrinsic base-collector capacitance for HBT using a selective buried sub-collector (SBSC) layer. An experimental carbon-doped GaInP/GaAs HBT with SBSC grown by MOCVD was fabricated and compared with a normal HBT. The base sheet resistance is 200 Ω/square and the emitter area is 3×11 μm2. A current gain of 30 and a BVceo of 10 V are obtained. Both values of gain and BVceo for the HBT with SBSC are the same as that of a normal HBT, which indicates that the regrown interface between the sub-collector and the collector does not degrade the device current gain and breakdown voltage. The value of the total collector capacitance of the HBT with SBSC is reduced to about half of a normal HBT with the same device size. A cutoff frequency of 47 GHz and a maximum oscillation frequency of 100 GHz for the HBT with SBSC are obtained. About 30% increase in fmax is observed at Jc< 3×104 A/cm2 and Vce > 2.5 V due to the reduction of collector capacitance indicating that the RF performance of the HBT can be improved significantly by using SBSC.