Abstract
Classical magnetoresistance techniques have proven to be quite useful for obtaining mobility profiles in GaAs MESFET structures. Here we extend these techniques to Al x Ga 1− x As/GaAs MODFET structures, which are more complicated because of multi-band conduction effects. A multi-band geometric-magnetoresistance (GMR) theory is developed in the relaxation-time approximation, and average and differential mobility expressions are defined. The magnetic-field dependences of these quantities permit determination of the mobilities associated with the various conducting bands. We apply this analysis to an Al 0.3Ga 0.7As/GaAs MODFET structure and obtain results for μ 0, the lowest subband mobility, μ 1–3, a combination of higher-subband mobilities, and μ AlG, the mobility in the heavily doped Al 0.3Ga 0.7As layer. Complicating factors such as finite Hall field, energy-dependent relaxation time, parasitic resistance and gate current are also considered.
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