STUDIES OF THE DC, LOW-FREQUENCY, AND MICROWAVE CHARACTERISTICS OF UNIFORM AND STEP-DOPED GAAS/ALGAAS HEMTS

A theoretical and experimental study of step-doped HEMTs (high electron mobility transition) with lightly and heavily doped regions is presented. Threshold voltage control and sensitivity with respect to growth parameters and recess etching, as well as design criteria, are investigated for these structures. A three-regime charge control model is used to predict their performance. Using the same semianalytical theory, which was validated with the help of a self-consistent analysis, both conventional and step-doped HEMTs with an i-layer are compared. 1-μm gate-length n-channel HEMTs with step-doped profile thicknesses of 25, 50, and 100 angstrom were fabricated and tested at low and high frequencies. The low-frequency noise can be controlled by the step thickness, and a noise analysis is presented. Cutoff frequencies of 16 to 18 GHz and maximum oscillation frequencies of 41 to 59 GHz were measured and correlated to the step thickness.