Carrier transport in disordered multiple quantum wells

We present in this dissertation, a study of the cross-well transport of carriers in annealed Multiple Quantum Wells (MQW). The design of the devices using MQW structures depends critically on the amount of time required by the photogenerated carriers to influence the optical properties. It is therefore very important from the design considerations to understand the basic mechanisms that control the carrier escape from the intrinsic region of the reverse biased p-i-n junction structure with the MQW fabricated in the intrinsic region. Fine-tuning of the performance of these devices can be achieved through band gap engineering. This can be done by selectively intermixing the well and the barrier region. In this work, we have identified and explored the effect of finite barrier width, initial barrier concentration and annealing time on the barrier height. We have used a more general method, the Runge-Kutta method, to calculate the energy levels in annealed quantum wells. The results from this method are in good agreement with those from other existing numerical methods. The advantage comes from the fact that Runge-Kutta method is accurate when Quantum wells of arbitrary shapes are used. We have also defined the superlattice limits and the essential difference between energy levels in the as-grown wells and the annealed quantum wells.; We have presented a new formulation of the thermionic emission taking into account the effect of valence band mixing and 2D density of states in the calculation of the rate of carrier escape due to emission. We have also considered resonant non-resonant and thermally assisted tunneling time constants. We have used these time constants in the solution of the system of differential equations which represent the rate equations for the carrier escape from the intrinsic region. While no such experimental data is yet available for comparison, we have seen a qualitative agreement with existing measurements.