SELFALIGNED AIGAAS/GAAS HBT GROWN BY MOMBE

The very low parasitic resistance npn GaAs/AlGaAs hetero-junction bipolar transistors (HBT) grown by metal organic molecular beam epitaxy (MOMBE) using all gaseous source dopants are reported. The carbon and tin dopants were introduced through the uses of trimethygallium (TMGa) and tetraethyltin (TESn). To achieve the low parasitics, the graded InGaAs emitter cap layer was doped with tin to 5 x 10(19) cm-3 and the doping level in the subcollector was 3 x 10(18) cm-3. The emitter and collector sheet resistances were 25-OMEGA/open-square-box and 10-OMEGA/open-square-box, respectively. The 800 angstrom thick base layer was carbon doped to a level of 7 x 10(19) cm-3. The base contact resistance and sheet resistance were 0.1-OMEGA mm and 180-OMEGA/open-square-box, respectively. With a thin AlGaAs surface passivation layer for the emitter-base junction, the common emitter DC current gain was maintained up to 25, even for 2 x 5-mu-m2 emitter size devices. The unity short circuit current gain cutoff frequency f(T), and maximum oscillation frequency f(max), were 48 and 63 GHz, respectively.