Molecular beam epitaxy growth and characterization of InGaAlAs-collector heterojunction bipolar transistors with 140 GHz: F-max and 20 V breakdown

The molecular beam epitaxy (MBE) growth, material characterization, and device performance of InGaAlAs-collector heterojunction bipolar transistors that dramatically increase device breakdown without compromising high-frequency performance is described. This performance is achieved by the use of large band gap InGaAlAs collectors with a pulse-doped layer at the beginning of the graded collector-to-base junction to suppress current-blocking effects. Double-crystal x-ray diffraction measurements indicate these complex structure can be grown using MBE with very close lattice matching to the underlying InP substrate. From photoreflectance spectra the collector composition, field present at the collector-to-base junction, and various transitions associated with the graded emitter can be measured. The use of an In-0.53(Ga0.50Al0.50)(0.47)As collector was found to increase breakdown characteristics (BVcba = 20 V, V-A = 250 V) substantially compared to an In0.53Ga0.47As collector (BVcba = 11 V, V-A = 7 V). For the In-0.53(Ga0.50Al0.50)(0.47)As collector current blocking effects were only found at very high current levels (similar to 100 kA/cm(2)) allowing this device to achieve very good rf performance (f(t) = 58 GHz and f(max) = 140 GHz). For higher Al compositions in the collector the breakdown voltage was found to increase further but current-blocking effects became more severe and rf performance began to suffer. (C) 1996 American Vacuum Society.