The influence of uniaxial compression upon the Hall effect ad resistivity of cadmium-doped samples of InSb at 77 K, 64 K, and 12 K are reported. Unilaxial compressions as high as 6 kbar were applied to samples oriented in the {001} and {110} directions. The net hole concentration of the samples were about 5x10^13 cm^-3 at 77 K as determined from the Hall coefficient at 24 kilogauss. The net concentration of hole carriers decreases and then increases exponentially with stress at 77 k and 64 k, while at 12 k there is only a monotonic increase of carrier concentration with stress. Analysis of the hole concentration as a function of stress shows the presence of a deep acceptor level located about 90 meV above the valence band edge in additionb to the 10 meV vadmium acceptor level. The shallow acceptor level does not split with stress. The hole density data is represented very well by models which describe both the variation in the net density of states and motion of the acceptor levels as a function of stress.

Call number: LD2668 .T4 1963 W87 / Master of Science

A one-dimensional analytical model of dark current has been developed to facilitate the investigation and analysis of dark current from gate-controlled photovoltaic InSb arrays. The applied gate voltage is an essential parameter in the model. The expressions relating this parameter to surface potential are derived separately for the cases of accumulation and depletion at the surface of n-type InSb material under the gate. In addition, the measured dark current is compared with that from the analytical model, and the discrepancy is discussed in terms of the intrinsic carrier concentration, surface recombination velocity, and geometry of the array. The components of dark current are mainly associated with surface state generation-recombination, field induced tunneling, and the depletion region from the bulk and surface. The experimental results are obtained at temperatures between 30K and 40K.

Thesis (Ph. D.)--University of Wisconsin, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Highly sensitive magneto-optical techniques have been used to investigate weak linear and nonlinear optical absorption mechanisms in p- and n-type InSb. As a result, new absorption processes involving both impurities and free carriers have been identified and studied in detail. For p-InSb, magneto-optical spectra has been obtained over a wide range of temperatures and photon energies. The spectra obtained at higher sample temperatures are seen to result from combined-resonance transitions of free holes between heavy-and light-hole Landau levels, while bound-hole transitions between ground heavy-hole-like and excited light-hole-like acceptor states are observed at lower temperatures. Analysis of the combined-resonance data along with extensive intra-conduction band and two-photon interband data using a modified Pidgeon and Brown 8X8 energy band model has allowed the determination of a single set of band parameters for InSb that quantitatively describes these different sets of data. In addition, a ground state binding energy of 8.1 meV for Cd acceptors and 42.5 meV for Au acceptors has been extracted from the analysis of the bound-hole spectra. For n-lnSb, photo-Hall techniques have been developed and used to study both resonant impurity and two-photon magneto-absorption (TPMA) processes in detail. As a result, LO-phonon-assisted impurity cyclotron resonance harmonic (LOICRH) transitions from the shallow Te donor level have been observed for the first time. In addition, transitions from deep levels are also observed in the photo-Hall signal obtained at sample temperatures greater than 20K. Both time-resolved and intensity-dependent measurements on impurity and TPMA processes are reported and the results compared directly with the predictions of rate equations describing the photoexcited carrier dynamics. These investigations have yielded important information about the optical properties of n-InSb; e.g. impurity and two-photon absorption coefficients, photo-excited carrier lifetimes, and recombination rates.

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A high resolution photoconductivity investigation of two 13 -3 photon magneto-absorption (TPMA) in n-InSb (n - 9 x 10 cm ) has been performed. This is the first time that two-photon absorption in a semiconductor has been studied with cw lasers only. With a stable cw CC>2 laser and a highly sensitive sampling and magnetic field modulation technique, a minimum of 4 2 transitions in the TPMA photoconductivity spectra can be observed. Most of these transitions are a result of the usual spherical approximation TPMA selections rules (An =0, ±2; As = 0 for e ⊥ B and Δn = 0; Δs = 0 for e || B) . However, some transitions, in particular several near the TPMA band edge, are not explained by these rules. The TPMA spectra have been found to depend upon crystallographic orientation. This has not been previously observed. The temperature variation of the fundamental energy gap Eg between 2 and 100° K is also obtained from TPMA experiments.

Systems that exhibit the extraordinary magnetoresistance (EMR) effect and other more disordered semiconductor-metal hybrid structures have been investigated numerically with the use of the finite element method (FEM). Initially, modelling focused on circular geometry EMR devices where a single metallic droplet is embedded concentrically into a larger semiconducting disk. The dependence of the magnetoresistance of such systems on the transverse magnetic field (0 5T) and filling factor (1/16 15/16) are reported and generally show a very good agreement with existing experimental data. The influence of the geometry of the conducting region of these EMR systems was then investigated. The EMR effect was found to be highly sensitive to the shape of the conducting region with a multi-branched geometry producing a four order of magnitude enhancement of the magnetoresistance over a circular geometry device of the same filling factor. Conformal mapping has previously been shown to transform a circular EMR device into an equivalent linear geometry. Such a linear EMR device has been modelled with the EMR mechanism clearly observed. The magnetoresistive response of a circular EMR device upon changes to: the mobility of the semiconducting region; the ratio of metal to semiconductor conductivity; and the introduction of a finite resistance at the semiconductor-metal interface, have also been investigated. In order for a large EMR effect to be observed the system requires: the semiconductor mobility to be large; the conductivity of the metal to be greater than two orders of magnitude larger than that of the semiconductor; and a very low interface resistance. This modelling procedure has been extended to include inhomogeneous semiconductor-metal hybrids with a more complex and disordered structure. Two models are presented, both based upon the random distribution of a small proportion of metal inside a semiconducting material. The resultant magnetoresistance in each case is found to have a quasi-linear dependence on magnetic field, similar to that observed in the silver chalcogenides.