Experimental evaluation of the InP-InGaAs-HBT power-gain resonance

An InP-InGaAs HBT has been evaluated that exhibits resonant hole modulation effects at a sufficiently low frequency for the resonance to be completely characterized by network analyzer measurements. It is shown that the frequency dependence of both the unilateral power gain and the current gain are modified by this effect, thus affecting the associated cutoff frequencies f/sub max/ and f/sub T/. A new power gain expression G/sub p/ based on measured small-signal parameters is introduced to circumvent the ambiguity in the unilateral power gain. Finding f/sub max/ and f/sub T/ by means of extrapolation of G/sub p/ and h/sub 21/, respectively, from a region below the resonance frequency is proposed to yield appropriate estimates of the figures-of-merit for device applications.