DEPENDENCE OF DC CURRENT GAIN AND FMAX OF ALINAS GAINAS HBTS ON BASE SHEET RESISTANCE/

To investigate the effect of base sheet resistance on dc current gain and maximum frequency of oscillation (f(max)) values, AlInAs/GaInAs HB T wafers were grown with base Bc doping levels in the range of 2 x 10( 19) to 1.6 x 10(20) cm-3. To confine the p-dopant within a nominal bas e thickness of 0.05 mum, the MBE growth was performed over a substrate temperature range of 430 to 280-degrees-C. The resulting base sheet r esistances of 11 wafers were in the range of 900 down to 141 OMEGA/sq. DC current gains of greater than 20 were obtained with a base sheet r esistance of 250 OMEGA/sq while the current gain dropped to 5 for a sh eet resistance of 141 OMEGA/sq. The f(max) did not scale with the squa re root of the base resistance as predicted by the classical expressio n.