Threshold voltage uniformity and characterization of microwave performance for GaAs/AlGaAs high electron-mobility transistors grown on Si substrates

Abstract

We report on DC and microwave characteristics for high electron-mobility transistors (HEMT's) grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). Threshold voltage (V/sub th/) distribution in a 3-in wafer shows standard deviation of V/sub th/ (/spl sigma/V/sub th/) of 36 mV with V/sub th/ of -2.41 V for depletion mode HEMT's/Si and /spl sigma/V/sub th/ of 31 mV with V/sub th/ of 0.01 V for enhancement mode, respectively. The evaluation of V/sub th/ in a 1.95/spl times/1.9 mm/sup 2/ area shows high uniformity for as-grown HEMT's/Si with /spl sigma/V/sub th/ of 9 mV for V/sub th/ of -0.10 V, which is comparable to that for HEMT's/GaAs. Comparing the V/sub th/ distribution pattern in the area with that for annealed HEMT's/Si, it is indicated that the high uniformity of V/sub th/ is obtained irrelevant of a number of the dislocations existing in the GaAs/Si. From microwave characteristic evaluation for HEMT's with a middle-(10/spl sim/50 /spl Omega//spl middot/cm) and a high-(2000/spl sim/6000 /spl Omega//spl middot/cm) resistivity Si substrate using a new equivalent circuit model, it is demonstrated that HEMT's/Si have the disadvantage for parasitic capacitances and resistances originated not from the substrate resistivity but from a conductive layer at the Si-GaAs interface. The parasitic parameters, especially the capacitances, can be overcome by the reduction of electrode areas for bonding pads and by the insertion of a dielectric layer under the electrode, which bring high cut-off frequency (f/sub T/) and maximum frequency of operation (f/sub max/) of 24 GHz for a gate length of 0.8 (/spl mu/m). These results indicate that HEMT's/Si are sufficiently applicable for IC's and discrete devices and have a potential to be substituted for HEMT's/GaAs.