The characterization of high electron mobility transistors using Shubnikov–de Haas oscillations and geometrical magnetoresistance measurements

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Abstract
Shubnikov–de Haas oscillations and geometrical magnetoresistance measurements are used to determine the two most important parameters, channel concentration and mobility, respectively, for high electron mobility transistors. To deduce useful data from measurements, the theory of the Shubnikov–de Haas oscillation for the two-dimensional electrons is derived and discussed in detail. The experimental data for the channel concentration as a function of gate voltage is used to check the accuracy of the charge-control law. We also derive a simple formula of the geometrical magnetoresistance to calculate the mobility for any aspect ratio. The concentration and mobility deduced from the Shubnikov–de Haas and geometrical magnetoresistance measurements give us insight on the nature and properties of the devices. The experimental data shows that the impurity scattering is the dominant mechanism for the low channel concentration. The maximum transconductance occurs at a compromise between the charge-control ability of the gate voltage and the channel mobility. Near the cutoff region the decrease of the conductivity is due to the decrease of both the channel concentration and the mobility.