The optical properties of non-square quantum wells with applications to optoelectronic devices.

This thesis reports a theoretical study of the optical properties of disordered single quantum wells (QWs) produced by interdiffusion between the well-barrier interface which results in a non-square QW. An error function and a hyperbolic function are used to model the confinement profile of interdiffused QWs, where an analytical solution is obtained for the former while only numerical solution is possible for the latter. The models developed here are all based on room temperature properties for the AlGaAs/GaAs, InGaAs/GaAs, and InGaAs/InP material systems. The subband structures are calculated with the consideration of conduction-band non-parabolicity, valence band-mixing, and spatially dependent strain and effective masses due to the non-linear confinement profile. Excitons are also included in addition to the continuum states below the barrier band-edge. The results demonstrate a non-monotonic variation of the subband-edge, the refractive index peaks, and the birefringence during the initial stages of interdiffusion. The model also predicts strong lateral confinement of photons for the propose of waveguiding in selectively disordered QW structures. The quantum confined Stark effect in disordered QWs provides a larger Stark shift and a much reduced absorption peak than the square-QW case, thereby demonstrating that such non-square QWs may provide a higher ON/OFF ratio and a lower driving voltage for electro absorption modulators. The intersubband transitions of the disordered QWs can increase the detection wavelength range in the far IR region with an almost constant absorption peak, which may be used to produce a wide bandwidth detector. The effect of strain provides an extra degree of freedom to tune the absorption edge of the disordered QW around 1 ?m, and because of strain, the amount of disordered band-edge shift is enhanced. A novel profile of two mini-wells in the valence-band are created for the case of cation interdiffusion of Ino 53Gao.47As/InP QWs; initial results show confinement of carriers within the mini-wells which may give rise to interesting transitions for optical applications. The results presented here show that non-square QW produced by QW disordering may be modeled by either hyperbolic or error functions and are potentially very useful for the modification and optimization of optoelectronic device characteristics