THRESHOLD VOLTAGE UNIFORMITY AND CHARACTERIZATION OF MICROWAVE PERFORMANCE FOR GAAS ALGAAS HIGH-ELECTRON-MOBILITY TRANSISTORS GROWN ON SI SUBSTRATES/

We report on de and microwave characteristics for high electron-mobili ty transistors (HEIMT's) grown on Si substrates by metal-organic chemi cal vapor deposition (MOCVD), Threshold voltage (V-th) distribution in a 3-in wafer shows standard deviation of V-th (sigma V-th) of 36 mV w ith V-th of -2.41 V for depletion mode HEMT's/Si and sigma V-th of 31 mV with V-th, of 0.01 V for enhancement mode, respectively, The evalua tion of V-th in a 1.95 x 1.9 mm(2) area shows high uniformity for as-g rown HEMT's/Si with sigma V-th of 9 mV for V-th of -0.10 V, which is c omparable to that for HEMT's/GaAs. Comparing the V-th distribution pat tern in the area with that for annealed HEMT's/Si, it is indicated tha t the high uniformity of V-th is obtained irrelevant of a number of th e dislocations existing in the GaAs/Si, From microwave characteristic evaluation for HEMT's with a middle-(10 similar to 50 Omega . cm) and a high-(2000 similar to 6000 Omega . cm) resistivity Si substrate usin g a new equivalent circuit model, it is demonstrated that HEMT's/Si ha ve the disadvantage for parasitic capacitances and resistances origina ted not from the substrate resistivity but from a conductive layer at the Si-GaAs interface, The parasitic parameters, especially the capaci tances, can be overcome by the reduction of electrode areas for bondin g pads and by the insertion of a dielectric layer under the electrode, which bring high cut-off frequency (f(T)) and maximum frequency of op eration (f(max)) of 24 GHz for a gate length of 0.8 (mu m). These resu lts indicate that HEMT's/Si are sufficiently applicable for IC's and d iscrete devices and have a potential to be substituted for HEMT's/GaAs .