INGAAS/IN(ALGA)AS RHETS WITH INAS PSEUDOMORPHIC BASE

We have designed and fabricated an InGaAs/In(AlGa)As RHET with an InAs pseudomorphic base to increase current gain and to reduce base resistance. The conduction band discontinuity between the InAs base and the In(AlGa)As collector barrier was estimated from the thermionic current. We found that the band discontinuity was about 0.38 eV, which agrees well with the calculated band discontinuity taking into consideration the effect of strain. The common-emitter current gain doubled and the base resistance decreased 20% compared to InGaAs-base RHET's with the same doping concentration. We measured a current gain cutoff frequency of 65 GHz and a maximum oscillation frequency of 50 GHz at 77 K.