Radiation effects on III-V heterostructure devices

Graduation date: 2003The neutron and electron radiation effects in Ill-V compound semiconductor\ud heterostructure devices are studied in this thesis. Three types of devices\ud investigated are AlGaAs/GaAs high electron mobility transistors (HEMTs),\ud AlGaAs/InGaAs/GaAs heterostructure insulated gate field effect transistors\ud (HIGFETs), and InP/InCaAs/InGaAs single heterojunction bipolar transistors\ud (SHBTs). HEMTs and HIGFETs are primarily investigated for neutron\ud irradiation effects. Detailed optimized processing of HEMT devices is introduced.\ud Numerical as well as analytical models that incorporate radiation\ud induced degradation effects in HEMTs and HIGFETs are developed.\ud The most prominent radiation effects appearing on both HEMT and HIGFET\ud devices are increase of threshold voltage (V[subscript T]) and decrease of transconductance\ud (g[subscript m]) as radiation dose increases. These effects are responsible for drain current\ud degradation under given bias conditions after irradiation. From our experimental\ud neutron irradiation study and our theoretical models, we concluded that\ud threshold voltage increase is due to the radiation-induced acceptor-like (negatively\ud charged) traps in the GaAs channel region removing carriers. The mobility\ud degradation in the channel is responsible for g[subscript m] decrease. Series resistance\ud increase is also related to carrier removal and mobility degradation. Traps introduced\ud in the GaAs region affect the device performance more than the traps\ud in the AlGaAs doped region. V[subscript T] and g[subscript m] of HIGFET devices are less affected\ud by neutron radiation than they are in HEMTs. This difference is attributed to\ud different shapes of the quantum well in the two devices.\ud The main effects of electron and neutron irradiation of SHBTs are decrease\ud of collector current (I[subscript c]), decrease of common-emitter DC gain, increase of the\ud collector output conductance (ΔI[subscript c]/ΔV[subscript CE]), and increase of collector-collector\ud offset voltage. The decrease of breakdown voltage of reverse biased base-emitter\ud junction diode is responsible for increasing the output conductance after irradiation.\ud Base-collector junction degradation also induces collector-emitter offset\ud voltage increase