Effects of neutral buried p-layer on high-frequency performance of GaAs MESFETs

Fully ion-implanted n/sup +/ self-aligned GaAs MESFETs with Au/WSiN refractory metal gates have been fabricated by adopting neutral buried p-layers formed by 50-keV Be-implantation. S-parameter measurements and equivalent circuit fittings are discussed. When the Be dose is increased from 2*10/sup 12/ cm/sup -2/ to 4*10/sup 12/ cm/sup -2/, the maximum value of the cutoff frequency with a 0.2- mu m gate falls off from 108 to 78 GHz. This is because a neutral buried player makes the intrinsic gate-source capacitance increase markedly, while its influence on gate-drain capacitance and gate-source fringing capacitance is negligible. The maximum oscillation frequency recovers, however, due primarily to the drain conductance suppression by the higher-concentration buried p-layer. An equivalent value of over 130 GHz has been obtained for both 0.2- mu m-gate GaAs MESFETs.<
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