Direct measurement of population-induced broadening of quantum well intersubband transitions

Abstract

The dependence of the absorption spectral linewidth of quantum well intersubband transitions on the electron population in the well is experimentally demonstrated. We show that the dependence of the spectral linewidth on the population is substantial and accounts for some of the broadening previously attributed to donor scattering. © 1997 American Institute of Physics. ͓S0003-6951͑97͒04530-0͔In the single band model, also known as the parabolic effective mass model, intersubband transitions in quantum wells ͑QWs͒ are discrete. In practice, electron-electron interaction, QW width nonuniformity, electron interactions with rough interfaces and with impurities and their enhancement by electric fields, and the optical and acoustic phonons contribute to the experimentally observed linewidth of intersubband transition in QWs. [1][2][3][4][5] There have been quite a few theoretical reports to explain the experimental observation, [1][2][3][4][5][6][7][8] and, there has been controversy over the contribution of population density to the intersubband broadening. Bandara et al. 6,7 predicted that the dependence of the exchange interaction on the in-plane momentum (k ʈ ) could contribute a substantial fraction of experimentally observed linewidths. Zaluzny, 8 on the other hand, claimed that the k ʈ dependence is offset by the depolarization and excitonlike manybody effects. In this letter, we report on the experimental study of the dependence of intersubband transition broadening on electron population using a structure consisting of 50 periods of an asymmetric coupled double QWs ͑ACDQWs͒. External applied bias was used to shift the population between the coupled QWs whose absorption was measured with a monolithically integrated QW infrared photodetector ͑QWIP͒ directly on the ACDQW structure. 9,10 The monolithically integrated structure was grown by molecular beam epitaxy on a ͑100͒ semi-insulating GaAs substrate. The ACDQWs consisted of an undoped 9-nmthick GaAs narrow well, an undoped 3-nm-thick Al 0.4 Ga 0.6 As barrier, and a selectively doped 10.8-nm-thick GaAs wide well. The wide well was nominally Si doped to 2ϫ10 18 cm Ϫ3 from 0.5 to 4.5 nm away from the barrier. The periods were separated by 42.2 nm of undoped Al 0.4 Ga 0.6 As layers. This structure was designed to provide the largest possible charge transfer between the narrow well and the wide well with external applied bias. The absorption spectrum of the monolithically integrated QWIP was designed to overlap with that of the narrow well in the ACDQWs, while the wide well in the ACDQWs had an absorption spectrum peaked at the tail of the QWIP photoresponse spectrum. The QWIP was separated from the ACDQW structure by a 0.6-m-n ϩ -GaAs and a 0.2-m GaAs buffer layer. The QWIP consisted of 15 periods of 6.5-nm-thick Si-doped GaAs wells with nominal doping density of 1.1ϫ10 12 cm Ϫ2 and 44-nm-thick Al 0.18 Ga 0.82 As barriers. The absorption spectrum of the grown structure, shown in Fig. 1, was performed using Fourier transform spectrometer with 1000 K blackbody radi...

Nanogroove control of intersubband absorption in AlGaAs/GaAs step quantum wells

“…The smallest FWHM of IOA for w 2 nm = (see figure 3) corresponds to the lowest averaged electronic energy 10.3 meV, and the biggest FWHM for w 1 nm = corresponding to the highest averaged electronic energy 24.4 meV. These results are consistent with the observed data [18].…”

Phase dependences of optical dispersion and group velocity in an Er3+-doped yttrium aluminium garnet crystal

“…In the radiative limit, the coherence decay rates are given by 2. The dephasing rate γ deph ij corresponding to each respective transition is determined by electronelectron scattering, interface roughness, phonon scattering and alloy scattering contribution [39], strongly affected by temperature and electron population [40]. In [41], we have found that the dephasing time of Er 3+ :YAG crystal with Er 3+ concentration of 0.1%, T 2 = 75 µs on the 4 I 15/2 ↔ 4 I 13/2 transition of Er 3+ at 1526.97 nm, and the corresponding homogeneous linewidth h = 4.286 kHz.…”