Intersubband resonances in InAs/AlSb quantum wells: Selection rules, matrix elements, and the depolarization field

Abstract

We present both theoretical and experimental results on the intersubband resonance in InAs/AlSb quantum wells. From a Kane (k•p) description of the band structure we investigate the effect of the large nonparabolicity and of the high Fermi wave vector on the selection rules and matrix elements. The 1-2 transition in parallel excitation (x) is shown to be very weak from simple parity arguments; in perpendicular excitation (z) the matrix element ͗z͘ is shown to be largely unaffected by nonparabolicity. The 1-3 transition turns out to be very weak in both geometries. Two band-gap engineering approaches to enhancing the parallel excitation of 1-2 are considered but the effect remains small as compared to the conventional z excitation. In z excitation the depolarization field condenses all the oscillator strength into essentially one sharp line despite the broadening expected from the nonparabolicity in the band dispersions. Inclusion of the depolarization field in the theory gives us good agreement with both the experimentally determined line shape and ͗z͘ matrix element.

Resonant inversion of the circular photogalvanic effect inn-doped quantum wells

“…Similar arguments hold for C 2v symmetry (relevant for (001)-oriented samples) under oblique incidence (see Fig. 4) although the simple selection rules are no longer valid [13]. This is pointed out in more detail at the end of the next section.…”

“…For direct inter-subband transitions under normal incidence selection rules allow only the spin-flip transitions, (e1, −1/2) → (e2, 1/2) for σ + photons and (e1, 1/2) → (e2, −1/2) for σ − photons [13]. Due to these selection rules together with energy and momentum conservation laws the optical inter-subband transition under, for example, σ + photoexcitation is only allowed for the fixed wavevector k x given by…”

Intersubband spin-density excitations in quantum wells with Rashba spin splitting

“…30 If one is only interested in the electronic structure of the conduction band of a quantum well, it is convenient to reduce the multi-band Hamiltonian described above to a 2 × 2 conduction band Hamiltonian. 33,34,35,36,37 The single-particle states (1) can then be simplified to the following two-component form:…”

Pure spin photocurrents

“…While in the one-band approximation the intersubband absorption can only be induced by the e ⊥ component of the polarization vector, in a multi-band model optical transitions between the electron subbands e1 and e2 are allowed for any polarization [33]. Moreover, k·p admixture of the valenceband and remote conduction-band states to the electron wave functions adds both spin-dependent [34] and klinear terms to the matrix elements of the optical transitions.…”