Magnetotransport in uniform and modulated electron gases in wide parabolic quantum wells
This thesis presents a study of electron gases in wide parabolic quantum wells (WPBWs) at temperatures to <50 mK and in magnetic fields to 8 T. The authors present data demonstrating that these wells can contain wide e([approximately]900 [angstrom]) uniform or periodically modulated electron layers. Samples were grown via molecular beam epitaxy using the digital alloy technique. The authors have made magnetotransport measurements in a WPBW with a superposed square superlattice potential. Hall effect data indicate a high-mobility ([mu] [approximately] 10[sup 5] cm[sup 2]/V s) electron gas is present. Fourier analysis of low-field (<0.3 T) Shubnikov-de Haas oscillations gives a power spectrum with several clearly defined peaks, indicating multiple subbands are occupied. From the spectrum are obtained separations E[sub F]-E[sub i] of the Fermi level from the subband bottoms which are in excellent agreement with results of self-consistent calculations, indicating filling of several periods of a remotely-doped superlattice with high-mobility electron gas. The subband structures of the electron gas in a WPBW without superlattice via capacitance-voltage (CV) profiling were studied by applying a magnetic field in the sample plane to separate features due to subband depopulations from those due to nonuniformities in the gas. The field dependence of the depopulation voltages is in excellent agreement with results of self-consistent calculations. The authors show that the density profile of the gas in the magnetic quantum limit is uniform to [+-]20%. They have measured magnetoresistance in the same sample for current oriented parallel (R[sub [parallel]]) and perpendicular (R[sub [perpendicular]]) to an in-plane field. They identify subband depopulation features in (R[sub [perpendicular]]) and (R[sub [parallel]]) via their temperature dependence and through comparison with CV profiling results.
- Research Organization:
- Harvard Univ., Cambridge, MA (United States)
- OSTI ID:
- 7197008
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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