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Radiation effects in III-V semiconductors and heterojunction bipolar transistors



Graduation date: 2001The electron, gamma and neutron radiation degradation of III-V semiconductors\ud and heterojunction bipolar transistors (HBTs) is investigated in this thesis.\ud Particular attention is paid to InP and InGaAs materials and InP/InGaAs\ud abrupt single HBTs (SHBTs). Complete process sequences for fabrication of\ud InP/InGaAs HBTs are developed and subsequently employed to produce the\ud devices, which are then electrically characterized and irradiated with the different\ud types of radiation. A comprehensive analytical HBT model is developed and radiation\ud damage calculations are performed to model the observed radiation-induced\ud degradation of SHBTs.\ud The most pronounced radiation effects found in SHBTs include reduction\ud of the common-emitter DC current gain, shift of the collector-emitter (CE) offset\ud voltage and increase of the emitter, base and collector parasitic resistances. Quantitative\ud analysis performed using the developed model demonstrates that increase\ud of the neutral bulk and base-emitter (BE) space charge region (SCR) components\ud of the base current are responsible for the observed current gain degradation. The\ud rise of the neutral bulk recombination is attributed to decrease in a Shockley-Read-Hall (SRH) carrier lifetime, while the SCR current increase is caused by rising SCR\ud SRH recombination and activation of a tunneling-recombination mechanism. On\ud the material level these effects are explained by displacement defects produced\ud in a semiconductor by the incident radiation. The second primary change of the\ud SHBT characteristics, CE offset voltage shift, is induced by degradation of the\ud base-collector (BC) junction. The observed rise of the BC current is brought on\ud by diffusion and recombination currents which increase as more defects are introduced\ud in a semiconductor. Finally, the resistance degradation is attributed to\ud deterioration of low-doped layers of a transistor, and to degradation of the device\ud metal contacts

Year: 2000
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Provided by: ScholarsArchive@OSU
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