Measurement of the low-field electron mobility and compensation ratio profiles in GaAs field-effect transistors

A novel technique for measuring the low-field electron mobility as a function of depth into the active layer of a nonuniformly doped GaAs Schottky barrier field-effect transistor (MESFET) has been developed. This technique is based on measurements of the current-voltage characteristics and the transconductance under low-field conditions as well as capacitance-voltage measurements. By comparison of the measured electron mobility with previous theoretical results the compensation ratio profile can be determined. Measurements on ion-implanted and epitaxial GaAs MESFET’s show that, for depths >0.1 μm, the nonuniform mobility profile is correlated with the donor density profile and sensitive to the compensation ratio, indicating that ionized impurity scattering is important over the range of carrier densities typically used in these devices.