Topics in the theory of semiconductors: I. Novel semiconductors II. Uniaxial stress dependence of deep impurities

This thesis is devided into four self-contained chapters. Chapters 1, and 3 deal with the electronic energy band structures of novel semiconductors and chapter 4 deals with the uniaxial stress dependence of deep substitutional impurity levels in semiconductors. Chapter 1: The electronic energy band structure and deep substitutional impurity levels for metastable are predicted with a nearest-neighbor, tight-binding model. Gel_xS~ is a semiconductor-metal alloy which may have applications in infrared detection or as a Gunn device. Doping anomalies are found: deep impurity levels in the band gap of Ge necessarily make deep-to-shallow transitions as the Sn concentration increases and some impurities have false valences. Chapter 2: The electronic energy band structure and deep substitutional impurity levels for InN and the alloys Inl_xGaxN and Inl_xA£xN are predicted with a nearest-neighbor, tight-binding model. These wurtzite alloys have direct fundamental energy band gaps ranging in the optical spectrum from orange visible light through ultraviolet. Dopants are suggested for possible application of these materials as light-emitting diodes and solid-state lasers. 2 iv Chapter 3: Energy band gaps for the metastable, substitutional, crystalline alloys are predicted. These materials undergo a zincblende-to-diamond, order-disorder, structural phase transition as a function of composition x. The alloys exhibit V-shaped bowing in the energy band gap as a function of composition and a general lowering of the band gap: both effects are due to the phase transition. Chapter 4: The uniaxial stress dependence of energy levels of deep substitutional impurities in zincblende III-V and diamond Group-IV semiconductors for applied stress in the [100], [110] , and [Ill] crystallographic directions are predicted. Stress applied in the [110] direction, in particular, causes shifts and splittings of the deep levels associated with an impurity to (i) uniquely determine the symmetry of the levels (s-like or p-like) and (ii) identify the site (anion or cation) of the associated impurity. Parts of this thesis have been published or are accepted for publication: Chapter 1, D. Y. Jenkins and J. D. Dow, Phys. Rev. B, in press and Chapter 3, D. Y. Jenkins, K. E. Newman, and J. D. Dow, Phys. Rev. B 32, 4034 (1985).U of I OnlyThesi