Density Dependence of Electron and Hole Effective Masses in GaAs Gated Quantum Well


Masumi Yamaguchi1,2 and Shintaro Nomura2,3
1Physical Science Laboratory, 2CREST-JST, 3University of Tsukuba/NTT Research Professor

  Several scattering mechanisms, such as scattering by surface charge and by donor ions, interfacial scattering, and the impurity scattering, limit the electron mobility of semiconductors. In the case of the conventional semiconductor hetero-junction, the scattering by donor ions at the doped layer causes an unavoidable reduction of the electron mobility at low electron density. The enhancement of the electron effective mass or the increase in the spin susceptibility, which has been observed by the Subnikov-de Hass oscillation measurements at low electron density, is attracting much attention in the semiconductor physicists. However, it is hard to observe them with low-mobility samples since these phenomena are induced by electronelectron interaction. Because our gated undoped quantum well has no donor layer, a high mobility is maintained even at low electron density and the electron density can be controlled continuously by the gate bias. In addition to conventional electric transport measurements, we performed photoluminescence measurements over the insulator to metallic regime by changing the electron density (ns). We determined the electron and hole effective masses within a wide range of the electron density [1].
  The electron and hole effective masses in the low magnetic field regime were obtained from the Landau level splitting of the photoluminescence peaks (Fig. 1). An increase of the electron effective mass with decreasing electron density was obtained at ns< 1×1011 cm-2 (Fig. 2). Moreover, we found that the hole effective mass also increases with decreasing electronic density and that the hole is localized at ns< 3×1010 cm-2.
  Using this gated quantum well, we are exploring the spin polarized state predicted to appear due to the electron-electron interaction in ultralow electron density.

[1] S. Nomura, et al., Phys. Rev. B 76 (2007) 201306R .

Fig. 1. Landau level fan obtained from the photoluminescence peaks.
Fig. 2. Electron and hole effective masses

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