Neutron Damage Mechanisms in Silicon at 10°k
Neutron-irradiation effects on the photoconductivity and electrical properties of arsenic-doped silicon were measured at 10K so that the degradation mechanisms in infrared detectors fabricated from doped silicon could be examined. The measurements were performed at reduced optical background so that both thermal and optical generation were minimized as they are in the conditions under which the detectors are operated. The primary effects of the neutrons on the measured properties were (l) the introduction of acceptors (at a rate to 16 cm-1) which decreased the electron (majority-carrier) lifetime and thus the optical response, and (2) the production of bandtailing, which may be associated with cluster damage. The bandtailing diminished significantly, or even disappeared, with annealing up to 100K, but all the other effects remained essentially unchanged with annealing as high as 673K. The possibility of the bandtailing remaining after 100K annealing appeared to be related to the amount of damage present. It was hypothesized that a certain defect concentration and/or cluster size was required for the bandtailing to be observed.
Electron Paramagnetic Resonance of the Aluminum Interstitial in Silicon
Electron-paramagnetic-resonance spectra of the ${\mathrm{Al}}^{++}$ interstitial (Si-$G18$) produced in aluminum-doped ($p$-type) silicon by room temperature or 4\ifmmode^\circ\else\textdegree\fi{}K electron irradiations are presented and show that the ${\mathrm{Al}}^{++}$ is located in the tetrahedral interstitial site. The hyperfine interactions with the ${\mathrm{Al}}^{27}$ and surrounding ${\mathrm{Si}}^{29}$ atoms indicate that the wave function for the paramagnetic electron is localized mostly within \ensuremath{\sim}5 \AA{} of the ${\mathrm{Al}}^{++}$ and that within this region the surrounding lattice has ${T}_{d}$ symmetry. From a qualitative description of this wave function in terms of a molecular orbital, an attempt has been made to assign the ${\mathrm{Si}}^{29}$ superhyperfine lines observed in the Si-$G18$ spectrum to particular lattice sites. The ground-state energy level for this paramagnetic electron is on or below the substitutional aluminum acceptor level. From energy arguments, it appears that this electron is in a localized resonant state within the valence band or in a bound state in the band gap below the bottom of the valence band.
Lattice Absorption in Gallium Arsenide
A series of detailed measurements of the lattice absorption bands of gallium arsenide has been made over the wavelength range 10–40 μ and over the temperature range 20–292°K. These results can be interpreted in terms of multiple phonon interactions involving five characteristic phonon energies. These results, along with the known elastic constants, have enabled us to supply all the relevant data for a computation of the complete phonon spectrum using an extension of the shell model.