HOT-ELECTRON IMPACT CROSS-SECTIONS OF IMPURITIES IN SEMICONDUCTORS

This paper is devoted to the discussion of inelastic scattering of a high-energy conduction electron incident on an impurity in a semiconductor. On the one hand the rate of inelastic collisions of a hot electron samples the high-energy tail of the electron distribution, and thus may serve as a test of high-field transport theories. On the other hand the excited impurity may release its energy radiatively, and this is used in solid-state displays. We adopt a description of the impurity which emphasizes the structure of the excitable shell in a solid-state environment. Then we describe the direct and exchange paths between the initial and the final state, which we relate to spin selection rules. The scattering amplitudes are calculated to first order, with emphasis on the functional structure of each term. A crude computation of impact cross sections near the excitation threshold is performed, giving a rough magnitude of 10(-18) cm(2) which may be enhanced by exchange effects for a valence shell containing many electrons. More importantly, taking three examples we qualitatively discuss the factors affecting the cross section according to the structure of the impurity valence shell, and its location in the host lattice. The conclusions are of direct interest to device designers wanting to optimize the impact yield of hot-electron electroluminescence devices.