THERMAL-RESISTANCE AND ELECTRONIC CHARACTERISTICS FOR HIGH-ELECTRON-MOBILITY TRANSISTORS GROWN ON SI AND GAAS SUBSTRATES BY METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION

We report dc and microwave characteristics of 0.8 mum gate length GaAs /AlGaAs high electron mobility transistors (HEMTs) grown on Si substra tes by metal-organic chemical vapor deposition (MOCVD) and demonstrate direct evaluation of thermal resistance for these HEMTs on Si for the first time. A maximum transconductance of 330 mS/mm is obtained, whic h is almost the same as that for HEMT/GaAs fabricated simultaneously. From microwave S-parameter measurements, a current gain cutoff frequen cy (f(T)) of 9.8 GHz is obtained for the HEMTs on Si, which is about 2 0% lower than that for HEMT/GaAs, because of the larger parasitic capa citances for HEMT/Si mainly caused by the device-process-related facto rs. Thermal resistance evaluation of these HEMTs utilizing the gate Sc hottky junction has revealed that thermal resistance for HEMT/Si is tw ice as small as that for HEMT/GaAs, namely 36 +/- 5 deg/W and 57 +/- 5 deg/W, respectively. From these results, it is shown that GaAs on Si is applicable to high-speed devices and very effective in improving th e performances of CaAs ICs which are fairly influenced by the power di ssipation.