Intersubband transitions in dilute(In,Ga)(As,N)∕(Al,Ga)Asmultiple quantum wells analyzed within a three-bandk∙pmodel

Abstract

We study the influence of nitrogen (N) on the intersubband absorption spectra of dilute $(\mathrm{In},\mathrm{Ga})(\mathrm{As},\mathrm{N})∕(\mathrm{Al},\mathrm{Ga})\mathrm{As}$ multiple quantum wells (MQWs). For MQWs with $6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ well width and ${\mathrm{Al}}_{0.33}{\mathrm{Ga}}_{0.67}\mathrm{As}$ barriers, the main absorption band at $1365\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ exhibits with increasing N content a slight redshift in contrast to an expected blueshift, a remarkable decrease of the intensity, and a strong asymmetric broadening on the high-frequency side. In addition, a minor absorption feature appears on the high-frequency side. For MQWs with $3\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ well width and ${\mathrm{Al}}_{0.42}{\mathrm{Ga}}_{0.58}\mathrm{As}$ barriers, the strong asymmetric main absorption band at $1820\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ exhibits with increasing N content a blueshift, a decreasing intensity, and a minor absorption feature on the low-frequency side, which cannot be attributed to an intersubband transition by only taking into account the effect of N on the discontinuity of the conduction band edges in the MQWs. We analyze the transition energies within a three-band $\mathbf{k}∙\mathbf{p}$ band-anticrossing model for heterostructures. Because of the presence of the localized N state in the quantum well, a set of N-like states is formed in each quantum well due to the confinement. These N-like states couple to the original quantum well states, and mixed subbands are formed. The dependence of the calculated wave numbers for bound-to-bound as well as bound-to-continuum intersubband transitions on the nitrogen content are in good agreement with the experimental data.