Design of an a-Si:H(n)/gaas(p)/gaas(n) high-gain heterojunction bipolar transistor with 10 ghz cut-off frequency

A simulation study aimed at designing a GaAs-based heterojunction bipolar transistor employing a wide gap emitter made of hydrogenated amorphous silicon (a-Si:H) with optimal high frequency characteristics is performed. The analysis indicates that the emitter thickness has a strong in.uence on the maximum device current, while the base thickness weakly a.ects the cut- o. frequency. The role played by the electronic properties of the thin .lm amorphous emitter is discussed, leading to the conclusion that the device’s ac characteristics are principally limited by the poor carrier mobility typical of a-Si:H. However, a cut-o.frequency close to 10 GHz can be predicted for an optimised device with standard values of the material electronic parameters.