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I explore the effects of strain on the material and device properties of semiconductor quantum wells, describing the valence band with a 4 x 4 k$\cdot$p Hamiltonian and assuming parabolic conduction bands. Coulombic bound states in the presence of strain, electric fields, and free carriers are calculated nonvariationally for In$\sb{x}$Ga$\sb{1-x}$As (on GaAs) and Si$\sb{1-x}$Ge$\sb{x}$ (on Si) quantum wells. I find that $-$2% strain reduces the acceptor binding energy by 30%, and that a carrier concentration of 4 $\times$ 10$\sp{11}$ cm$\sp{-2}$ completely screens out the excitonic absorption at T = 300K. I study the properties of strained-layer quantum well lasers grown on GaAs and InP, calculating the optical properties from the bands and using them in a numerical solution of the multimode rate equations. It is found that an introduction of $-$1.4% strain improves the intrinsic static characteristics by a factor of 3-4, in terms of lower threshold current, greater mode suppression, and lower non-lasing photon population. I also find that the strained system responds 4 times faster when the laser is switched from the off state to a given lasing mode photon density. I calculate CHSH Auger rates in strained In$\sb{0.53+x}$Ga$\sb{0.47-x}$As on InP from an 8 x 8 strain-dependent tight binding bandstructure, evaluating the multidimensional transition integral with a change of variables and monte-carlo technique. I find that $-$2% strain increases the Auger coefficient by a factor of 50 due to the reduction in the net bandgap. Applying the results to determine the Auger component of the threshold current in strained quantum well lasers, I find that the Auger current and the threshold current both decrease by 60% with the addition of up to 20% excess In. Lastly, I present a theoretical analysis of the optical applications of resonant tunnelling diodes, calculating the electronic properties with a self-consistent travelling wave model that includes effective mass mismatches. I find that it is possible to operate a conventional device as an intersubband laser if the transition energy is large (0.5 eV) and the linewidth is minimal (5 meV). A bound state device can produce a modulation ratio of 5:1 at the excitonic peak with an absorption length of 40 $\mu$m in a waveguide geometry.