New interpretation of quantum wire luminescence using a non standard description of the valence band states

Abstract

Theoretical predictions1 have shown that confined structures, quantum wires (QWR) or quantum dots (QD), should have higher gain and absorption, compared to quantum wells, owing to the discontinuity in the joint density of states. We use a non standard description of the valence band states2 to evaluate the absorption of V-shaped quantum wires close to the band edge. We choose the projection axis of the angular momentum of the valence band states along the non-confined direction of the wire. This description has two advantages: (i) the masses are isotropic along the two confined directions and (ii) the light hole (lh) and heavy hole (hh) states are decoupled at kz=0, if the kinetic energy of the confined holes is the same along both confined directions and the energy separation between the {lh,hh}i and {lh,hh}i+1 subbands is high. This description is particularly advantageous close to the band edge where transitions are mostly excitonic. Photoluminescence (PL) and photoluminescence excitation (PLE) measurements made on V-shaped quantum wires are reinterpreted: the lowest energy transition is a e1-lh1 excitonic transition and the second lowest is a e1-hh1 excitonic transition. This new interpretation is the first to explain the lower intensity of the lowest energy peak observed in PL and PLE measurements. To assess the impact of the non-uniformity of the wires, we evaluate the absorption of V-shaped QWR (V-QWR) grown by MBE deposition over a non-planar substrate3.