High-Performance InGaP/GaAs HBTs With Compositionally Graded Bases Grown by Solid-Source MBE

摘要

N-p-n InGaP/GaAs heterojunction bipolar transistors (HBTs) with compositionally graded In{sub}xGa{sub}(1-x)As (Be doped) bases have been successfully grown by solid-source molecular beam Epitaxy (SSMBE) using a gallium phosphide (GaP) decomposition source. In this paper, the dc and RF characteristics of HBTs with different indium mole fractions in the graded In{sub}xGa{sub}(1-x)As base (x : 0 → 0.1 and x : 0 → 0.05) are measured to investigate optimum-grading profiles. The measured average current gains, βs of a control sample, a 10% graded-base sample and a 5% graded-base sample, are 162, 397 and 362, respectively. To our knowledge, these current gains are the highest values ever reported in compositionally graded-base InGaP/GaAs HBTs with a base sheet resistance R{sub}sh of ～200 Ω/sq establishing a new benchmark for InGaP/GaAs HBTs. Furthermore, these compositionally graded-base HBTs show higher unity current/gain cutoff frequency, f{sub}T and maximum oscillation frequency, f{sub}(max)-Compared to the control sample with the same base thickness, the base transit time TB of the graded sample is reduced by ～15% to ～20% by the induced built-in potential, resulting in an increase of /max from 16 to 18.5 GHz in a device with an emitter size of 10 × 10 μm{sup}2. Additionally, for the 5% graded-base sample, with a 5 × 5 μm{sup}2 emitter region, f{sub}T and f{sub}(max) are 16.3 and 33.8 GHz, respectively, under low-level collector current. These results demonstrate that InGaP/GaAs HBTs with In{sub}xGa{sub}(1-x)As graded-base layers (x : 0 → 0.05) have the potential for high-speed analogue to digital converters.