Density of States of Electrons Bound to Impurities in Quantum Wells of GaAlAs/GaAs

摘要

The Density of State (DOS) for electrons bound to impurities in quantum wells of GaAlAs/GaAs heterostructures is calculated according to a realistic model that takes into account diagonal disorder due to dispersion in binding energy and off-diagonal disorder due to randomness in the transfer matrix element. The first one comes out of the dependence of the binding energy on the distance of the impurity to the walls. The second one results from the structural disorder. A method is presented which applies when the ratio between the impurity layer thickness delta and the most likely distance between impurities bar R is small. For instance, if the impurity concentration is 10 to the 15th/cu m and delta = 100 A, delta/bar R = 0.079. If the well width is in the range 100 A is equal to or less than L is equal to or less than 600 A it is found that both diagonal and off-diagonal disorders are of the same order, giving a bandwidth in the range of 1.2 to 5.5 meV. The off-diagonal disorder starts to become dominant as the number of impurities per unit area increases.