Energy level spectroscopy of InSb quantum wells using quantum-well LED emission

Abstract

We have investigated the low-temperature optical properties of InSb quantum-well (QW) light-emitting diodes, with different barrier compositions, as a function of well width. Three devices were studied: QW1 had a 20 nm undoped InSb quantum well with a barrier composition of ${\text{Al}}_{0.143}{\text{In}}_{0.857}\text{Sb}$, QW2 had a 40 nm undoped InSb well with a barrier composition of ${\text{Al}}_{0.077}{\text{In}}_{0.923}\text{Sb}$, and QW3 had a 100 nm undoped InSb well with a barrier composition of ${\text{Al}}_{0.025}{\text{In}}_{0.975}\text{Sb}$. For QW1, the signature of two transitions (CB1-HH1 and CB1-HH2) can be seen in the measured spectrum, whereas for QW2 and QW3 the signature of a large number of transitions is present in the measured spectra. In particular transitions to HH2 can be seen, the first time this has been observed in AlInSb/InSb heterostructures. To identify the transitions that contribute to the measured spectra, the spectra have been simulated using an eight-band $\mathbf{k}.\mathbf{p}$ calculation of the band structure together with a first-order time-dependent perturbation method (Fermi golden rule) calculation of spectral emittance, taking into account broadening. In general there is good agreement between the measured and simulated spectra. For QW2 we attribute the main peak in the experimental spectrum to the CB2-HH1 transition, which has the highest overall contribution to the emission spectrum of QW2 compared with all the other interband transitions. This transition normally falls into the category of ``forbidden transitions,'' and in order to understand this behavior we have investigated the momentum matrix elements, which determine the selection rules of the problem.