Competition between confinement potential fluctuations and band-gap renormalization effects in ${\text{In}}_{0.53}{\text{Ga}}_{0.47}\text{As}/{\text{In}}_{0.525}{\text{Ga}}_{0.235}{\text{Al}}_{0.25}\text{As}$ single and double quantum wells

We present the results of our studies on the emission properties of ${\text{In}}_{0.53}{\text{Ga}}_{0.47}\text{As}/{\text{In}}_{0.525}{\text{Ga}}_{0.235}{\text{Al}}_{0.25}\text{As}$ single and coupled double quantum wells (CDQWs) with different degrees of potential fluctuation. We have verified that the curve of the temperature $\left(T\right)$ dependence of the emission peak energy $\left(E_{\text{PL}}\right)$ is significantly influenced by the potential fluctuations (which are magnified by the presence of the internal barrier in the CDQW) as well as by the excitation density used in the photoluminescence (PL) measurements. As the excitation power increases, two effects occur simultaneously: the filling of the band-tail states related to potential fluctuations and the band-gap renormalization (BGR) caused by the increase in the density of photogenerated carriers. As the optical density increases, the $E_{\text{PL}}$ can shift to either higher (blueshift) or lower (redshift) energies, depending on the temperature at which the measurements are carried out. The temperature at which the displacement changes from a blueshift to a redshift is governed by the magnitude of the potential fluctuations and by the variation of BGR with excitation density.

Figure 1

PL peak energy $\left(E_{\text{PL}}\right)$ for the QW100 well as a function of temperature for laser powers of 1.25 mW (triangles), 10 mW (squares), and 115 mW (circles). The inset is an amplification of the figure in the low temperature range (below 100 K).

Figure 2

$E_{\text{PL}}$ as a function of temperature for the coupled double quantum wells (a) SPK10, (b) SPK20, and (c) SPK30, with powers of 1.25 mW (triangles), 10 mW (squares), and 115 mW (circles). The insets are amplifications of the figures in the low temperature range.

Figure 3

PL spectra at 8.5 K as a function of power for (a) QW100, (b) SPK10, and (c) SPK20 and SPK30.

Figure 4

$E_{\text{PL}}$, at 8.5 K, as a function of power for QW100 (filled circles), SPK10 (empty circles), SPK20 (filled triangles), and SPK30 (empty triangles).

Figure 5

$E_{\text{PL}}$ for the QW100 well as a function of temperature, with powers of 1.25 mW (empty squares) and 115 mW (full squares), where the points relative to 115 mW were shifted by 57 K in the temperature scale. The continuous lines refer to the fits obtained using the Passler model from Ref. 22 for each of those curves.

Figure 6

(a) PL spectra of QW100. Dotted line, PL spectrum obtained at 8.5 K with a power of 115 mW; continuous line, spectrum obtained at 65 K with a power of 1.25 mW. (b) PL spectra of QW100 at 8.5 K obtained using excitation powers of 0.05 mW (continuous line) and 115 mW (dotted line).

Figure 7

PL spectral features for QW100 at 8.5 K versus the logarithm of the excitation power. Filled squares, high-energy edge at half maximum; empty squares, PL peak energy; filled circles, low-energy edge at half maximum; empty circles, renormalized band edge (see text).