Absorption coefficient for the intraband transitions in quantum dot materials

Abstract

In this paper, we present calculations of the absorption coefficient for transitions between the bound states of quantum dots grown within a semiconductor and the extended states of the conduction band. For completeness, transitions among bound states are also presented. In the separation of variables, single band k-p model is used in which most elements may be expressed analytically. The analytical formulae are collected in the appendix of this paper. It is concluded that the transitions are strong enough to provide a quick path to the conduction band for electrons pumped from the valence to the intermediate band.

Symmetry considerations in the empirical k.p Hamiltonian for the study of intermediate band solar cells

“…An analogous study was made in [14] of the transitions between the confined and extended CB states. It was found that, although the overlap between confined and extended states is small, the high density of extended states leads to a significant absorption coefficient.…”

“…We can define the polarization by the Euler angles (<f>,&) characterizing its direction. Thus (14) and the same for its components. We use the following nomenclature,…”

“…Furthermore, in many cases the light is not polarized and the average of a set of polarizations is to be taken. An interesting case is, for instance, vertical unpolarized light, in which case the absorption is proportional to (|Mx| 2 + |My| )/2 [14].…”

“…The transitions from this state to the rest of the CB states -bounded or extended -are one of the aspects to be understood. A single band effective mass treatment is enough for this task and a simplified model has already been published on this topic, involving the energy spectrum of the CB detached states as well as the transition between confined states [12,13] and between these and the extended states modified by the QD presence [14].…”

Realistic Detailed Balance Study of the Quantum Efficiency of Quantum Dot Solar Cells

“…[ 4,5 ] In order to better understand the problems facing existing QD-IBSCs, there have been several recent theoretical studies into the absorption of subbandgap photons by the QDs. Optical matrix elements have been calculated for intraband (IB ↔ CB) [ 9,10 ] and interband (VB ↔ IB) [ 11,12 ] transitions using, in the former case, a one-band k·p method, and, in the latter case, the so-called empirical k·p Hamiltonian (EKPH) method, [ 11 ] which is a four-band k·p method.…”