A general expression for the momentum matrix elements for both intrasubband and intersubband transitions in n- or p-type doped quantum wells, wires, and dots is derived within the envelope-function approximation, in the process unifying the description of optical absorption in n- and p-type heterostructures. The derivation is nontrivially extended to the case of wave-function penetration into the barrier in a way that satisfies the principle of microscopic reversibility. The contribution of the valence-band anisotropy is shown to contribute to normal-incidence absorption in p-type heterostructures.

• Received 28 September 1994

DOI:https://doi.org/10.1103/PhysRevB.51.1613