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Selection rules of intersubband transitions in conduction-band quantum wells

1994; American Physical Society; Volume: 50; Issue: 11 Linguagem: Inglês

10.1103/physrevb.50.7474

1095-3795

Rui Q. Yang, J. M. Xu, M. Sweeny,

Spectroscopy and Laser Applications

In this work, optical intersubband transitions in conduction-band quantum wells have been reexamined in the multiband scheme. A generalized theory, with emphasis on the selection rules for the in-plane polarization, is developed in Kane's k\ensuremath{\cdot}P formalism. By taking into account the interband couplings, it is shown that the optical transition between any pair of electron subbands can occur with either the normal-to-plane polarized light or the in-plane polarized light. The characteristics of intersubband transitions depend upon whether the subband index differences \ensuremath{\Delta}n are odd integers (\ensuremath{\Delta}n=1,3,. . .) or even integers (\ensuremath{\Delta}n=2,4,. . .). In the case of \ensuremath{\Delta}n being even integers, intersubband transitions of both polarizations are allowed for electrons with a finite in-plane wave vector. In fact, the transition rates are proportional to the value of the in-plane wave vector, and the in-plane polarized transition is dominant. In the case of \ensuremath{\Delta}n being an odd integer, optical intersubband transitions of both polarizations can occur with a zero in-plane wave vector, but the normal-to-plane polarized transition is dominant. Consequences for device implementation such as a normal-incidence infrared photodetector that makes use of the allowed in-plane polarized optical transitions are discussed.