The effect of confinement on the temperature dependence of the excitonic transition energy in GaAs/Al_xGa_1−xAs quantum wells

Abstract

We determined by means of photoluminescence measurements the dependence on temperature of the transition energy of excitons in GaAs/Al x Ga 1−x As quantum wells with different alloy concentrations (with different barrier heights). Using a fitting procedure, we determined the parameters which describe the behavior of the excitonic transition energy as a function of temperature according to three different theoretical models. We verified that the temperature dependence of the excitonic transition energy does not only depend on the GaAs material but also depends on the barrier material, i.e. on the alloy composition. The effect of confinement on the temperature dependence of the excitonic transition is discussed.

Effects of confinement on the electron–phonon interaction in Al0.18Ga0.82As/GaAs quantum wells

“…Figure 3(a) shows the experimental values of the exciton recombination energies for different well widths extracted from the PL spectra of figures 2 and 3(b) shows the experimental data published by da Silva et al [18] for different values of the Al concentration in 60 Å thick Al x Ga 1−x As/GaAs QWs. The theoretical values of E X in figures 3(a) and (b) were calculated using the expression…”

“…They also verified that the exciton emission 0 Figure 3. Heavy-hole-free exciton recombination energy: (a) extracted from the PL spectra shown in figure 2, (b) experimental data from [18], and theoretical data of E X (star symbols) and E b (sphere symbols) obtained with the fractional-dimensional formalism (see the text).…”

“…For x 0.20 the parameters have their values increased with increase of the Al concentration as observed for Al x Ga 1−x As bulk material, and for x ≈ 0.40 the parameters surpass the values obtained for GaAs bulk [21,22,25]. Another work investigating the temperature dependence of E X , in the temperature range 12 K T 100 K, in 60 Å thick AlGaAs/GaAs QWs showed that confinement effects lead to an abrupt decrease of the p and α p parameters of the Pässler-p model as compared to the GaAs bulk values [18].…”

“…For instance, for GaAs and Al x Ga 1−x As materials, the thermal dilatation of the lattice leads to a reduction of only ∼2% of E X in the temperature range 0 K < T 100 K [17]. Due to this small contribution, several models describing the temperature dependence of E X were proposed in the literature taking into account the electronphonon interaction but neglecting the contribution of the thermal expansion of the lattice [18]. Among them we find the semi-empirical model proposed by Viña et al [19], which uses the Bose-Einstein statistical distribution of energy for the phonon modes, and more recent analytical models such as the ones proposed by Pässler [12,20].…”

“…Studies performed on Al x Ga 1−x As/GaAs QWs comparing several theoretical models usually used to describe the temperature dependence of the exciton recombination energy indicate that the Pässler-p model is more appropriate for obtaining information about confinement effects in these systems. In general, the fit parameters of the Pässler-p model are strongly dependent on the Al concentration of the Al x Ga 1−x As barrier material [13,18,21,22]. For instance, the parameter related to the mean energy of the phonons in the temperature scale increases its magnitude with the increase of the Al concentration in the range 0 x 0.45 [21,23,24].…”