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InP-In0.53Ga0.47As-InP double heterojunction bipolar transistors (DHBTs) were grown on a GaAs substrate using a metamorphic buffer layer and then fabricated. The metamorphic buffer layer is InP - employed because of its high thermal conductivity to minimize device heating. An fτ and fmax of 268 and 339 GHz were measured, respectively - both records for metamorphic DHBTs. A 70-nm SiO2 dielectric sidewall was deposited on the emitter contact to permit a longer InP emitter wet etch for increased device yield and reduced base leakage current. The dc current gain β is ≈35 and VBR,CEO=5.7 V. The collector leakage current Icbo is 90 pA at Vcb=0.3 V. These values of fτ, fmax, Icbo, and β are consistent with InP based DHBTs of the same layer structure grown on a lattice-matched InP substrate.