Photoluminescence Spectroscopy of the Low-Density Two-Dimensional Electron System in Electric Fields


Masumi Yamaguchi, Shintaro Nomura*, Hiroyuki Tamura, and Tatsushi Akazaki
Physical Science Laboratory, *Univ. of Tsukuba

 At low temperature, the photoluminescence (PL) spectrum of a two-dimensional electron system (2DES) reflects the potential fluctuation. We have studied the random-potential screening across the metal-insulator transition of the 2DES formed in a double-gated GaAs quantum well [1]. Here, we investigated the PL spectra of 2DES-hole emission in various perpendicular electric fields and found that the difference in the PL linewidth in electric fields decreases with electron density [2].
 As shown in Fig. 1, the emission energy of PL decreases with perpendicular electric fields due to the quantum confined Stark effect (QCSE). In addition, the PL linewidth increases with perpendicular electric fields due to the monolayer well-width fluctuation since the QCSE energy shift depends on the well width. Below ne〜4x1010 cm-2, 2DES is highly inhomogenous because of the Coulomb random potential of remote charge. In this case, the PL linewidth, which is the superposition of individual emission energies at different positions, increases with perpendicular electric fields. On the other hand, when the electron state extends to an area larger than the spatial range of the well-width fluctuation, the electric field dependence of PL linewidth disappears because the electrons feel the spatially averaged potential.
 Figure 2 shows the slopes of the PL linewidth against perpendicular electric fields as a function of electron density. Below 4x1010 cm-2, the slope decreases with increasing electron density and becomes almost zero above 6x1010 cm-2. This reflects the spatial extension of the 2DES over the Coulomb disorder and the well-width fluctuation range as electron density increased.
 This work was supported by KAKENHI.

[1] M. Yamaguchi et al., Phys. Rev. Lett. 100 (2008) 207401.
[2] M. Yamaguchi et al., Physics Procedia 3 (2010) 1183.

Fig. 1. Photoluminescence spectrum at
ne=2x1010 cm-2 for various
perpendicular electric fields.
Fig. 2. lectron density dependence of the slope
of the PL linewdith change against
perpendicular electric fields.

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