Abstract
Although saturation of interface traps in multiple quantum wells (MQWs) was observed in time resolved photoluminescence (PL) under intense laser radiation,1 observation of similar phenomenon in cw regime, which is supposed to exhibit new features, has not been reported to the best of our knowledge. Here, we report our first measurements of cw intensity-dependent PL excitation (PLE) spectra of multiple narrow stepped quantum wells (MNSQWs) at room temperature. Using narrow SQWs in contrast to wide SQWs, cw saturation of interface traps has been observed3 for the first time (we believe) using laser intensity more than two orders of magnitudes lower than that in Ref. 1. The sample grown by epitaxy on a Si-doped (100) n' GaAs substrate consists of thirty individual pairs, each of them consisting of one GaAs QW 19 A thick and one Al0.2Ga0.9,As shallow QW 55 Å thick to form a stepped potential (see inset in Fig. 1). A 100-Å Al0.1Ga0.5 barrier is used to isolate the adjacent SQWs from each other. The MNSQWs are sandwiched between two undoped AL0.45Ga0.55As layers, each 3000 Å thick, which can be used to prevent the impurities from diffusing into MNSQWs. PLE spectra were measured at different pump laser intensities as shown in Fig. 1. A pronounced peak and a broad peak near λ≃7317 Å and λ =7203 Å can be identified as the heavy-hole and light-hole transition peaks, respectively. As laser intensity increases, PLE intensity initially increases proportionally to the square of the laser intensity [see Fig. 2(a)], which indicates that nonradiative recombination (NR) dominates over radiative recombination. As laser intensity increases, normalized PLE intensity (i.e., divided by the square of laser intensity) above the light- hole transition energy still increases [see Fig. 2(b)], which can be interpreted as saturation of interface traps by electrons similar to that by holes in Ref. 1.
© 1992 Optical Society of America
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