Graduate Thesis Or Dissertation
 

Radiation effects in compound semiconductor heterostructure devices

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gx41mn326

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  • Radiation studies were performed on compound semiconductor heterostructure devices. The objective was to understand the degradation processes caused by the exposure of these devices to radiation. Preliminary experiments were focussed on studying the degradation phenomenon in single heterojunctions and single quantum wells. It was found that ionizing radiation like gamma rays did not have any sig­nificant effect on the integrity of the III-V interface. Gamma and neutron radiation experiments were performed on heterostructure field effect transistor structures to study the degradation seen in the mobility and sheet carrier concentration of the carriers in the 2-DEG channel in these devices. In this experiment it was found that samples whose surface was protected with oxide passivation suffered less dam­age due to gamma radiation than the samples with unprotected surfaces. However, neutron radiation generated extensive damage in the 2-DEG channel and this radi­ation is believed to introduce charged defects into the spacer and channel regions in these devices. The fabrication process for heterostructure bipolar transistors (HBTs) was developed and high energy electron radiation studies were performed on GaAs/ AlGaAs HBTs of different emitter areas and base widths. The high and low gain devices showed gain degradation of 40 and 14 %, respectively, after an-elec­tron fluence of about 9 x 10¹⁵ e/cm² The factors that were found to determine the extent of degradation in the DC performance of the HBTs were base width, emitter contact area, surface condition, initial gain value and the collector current at which the gain was determined. Gamma radiation studies were performed on resonant tunnel diodes. It was found that the peak and valley current levels were almost unaffected even after a radiation dose of 40 MRad. The voltage at which the resonant peak occurs was found to increase and it is believed that damage caused to the contact regions is responsible for this shift.
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