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Yasuyuki MIYAMOTO Shinnosuke TAKAHASHI Takashi KOBAYASHI Hiroyuki SUZUKI Kazuhito FURUYA
We investigated collector current spreading in InGaAs single heterojunction bipolar transistors (SHBTs) having a collector thickness of 75 nm. SHBTs were fabricated with three different emitter widths -- 200, 400, and 600 nm -- and the highest cutoff frequency that was obtained was 468 GHz. The relationship between the current density at the highest cutoff frequency and the emitter width could not be used to estimate the current spreading because it was independent of the collector-base voltage. However, the relationship between the current density with the increase in the total collector-base capacitance and the emitter width indicates current spreading in the collector. The current spreading was estimated to be approximately 90 nm.
Che-ming WANG Kuang-Po HSUEH Yue-ming HSIN
A thin high-doping layer was inserted in the uniform doped collector to extend the operational current before current gain and cut-off frequency roll-off. Two times higher collector current before onset of Kirk effect was obtained and the resulted John figure of merit was improved from 846 to 1008 V-GHz.