Electrical Studies of Low-Temperature Neutron- and Electron-Irradiated Epitaxial n-Type GaAs

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Abstract
An investigation of electron‐ and neutron‐produced defects in epitaxially grown n‐type (n≃2×1015 cm−3) GaAs has been performed using Hall effect and electrical‐conductivity measurements. Electron irradiation (2 MeV) at 80°K decreases both the carrier concentration and the mobility. Below room temperature annealing of electrically active defects is observed near 250°K in agreement with thermal‐conductivity and length‐change measurements of electron‐produced defect annealing in n‐type bulk‐grown GaAs. An electron‐irradiation‐produced carrier removal rate of 2.9 cm−1 at 80°K, an observed electronic energy level at ∼Ec − 0.14 eV, and a major annealing recovery stage near 500°K, are in reasonable accord with previous results from bulk‐grown n‐type GaAs. The accord between the present results from epitaxially grown GaAs and previous results from bulk‐grown GaAs suggests that crystal growth method does not play a dominant role in electrically active defect formation under electron irradiation. Neutron irradiation (approximately fission spectrum) at 76°K also decreases both the carrier concentration and the mobility in n‐type epitaxial GaAs. A light sensitivity of the carrier concentration and mobility is observed in GaAs after neutron irradiation. By analogy to Si and because disordered regions have been observed in electron microscope measurements on neutron‐irradiated GaAs, the neutron‐produced light sensitivity is ascribed to disordered regions. In contrast with electron produced defects in GaAs, neutron‐produced defects in the epitaxial layer exhibit only small and diffuse annealing throughout the 76°−600°K temperature range investigated. The mobility degradation after 400°K annealing is measurement‐temperature dependent and decreases with increasing measurement temperature between 76° and 300°K. The carrier removal rate, on the other hand, is nearly independent of measurement temperature and is 3.0 cm−1 at 296°K. This carrier removal rate is in reasonable agreement with previous results on bulk‐grown n‐type GaAs irradiated at ∼375°K. Gunn effect oscillators are critically dependent upon carrier concentration, therefore carrier removal is expected to be the dominant failure mechanism for these devices under irradiation.