High-linearity Ga 0.51 In 0.49 P/In 0.15 Ga 0.85 As pseudomorphic high electron-mobility transistors have been successfully fabricated and demonstrated in both direct-current and alternating-current performance. Together with a wide-gap Ga 0.51 In 0.49 P gate insulator, a gate-to-drain breakdown voltage of 33 V is further improved to over 40 V by selectively removing mesa sidewalls. The transconductance and current density of a 1ϫ100 m 2 device at room temperature ͑77 K͒ are 90 ͑120͒ mS/mm and 646 ͑780͒ mA/mm, respectively. The measured f T and f max are 12 and 28.4 GHz, respectively. These are consistent with 1 m gate devices when the parasitic capacitance is reduced by selectively removing mesa sidewalls.

Temperature-dependent dc performances of lattice-matched InP/InGaAlAs heterojunction bipolar transistors (HBTs) using the InGaAlAs quaternary alloy as the base and collector layers are studied and reported. When compared with conventional InP/InGaAs HBTs, the device studied exhibits a higher common-emitter breakdown voltage and a lower output conductance even at high temperature. The variations of offset voltage and ideality factor at different temperatures have been analysed. In addition, with decreasing temperature from 25 • C toward −196 • C, an irregular temperature behaviour of current gain is observed. At high current levels, the temperature-dependent current gain is mainly determined by the reduced reverse hole injection current. As the current level is lowered, the dominance of reverse hole injection current is correspondingly replaced by the recombination current.

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In this paper, we demonstrate the qualitative influence of a δ-doping sheet and setback layer on the performance of an InGaP/GaAs heterojunction bipolar transistor (HBT). The results of a theoretical simulation show that the potential spike is reduced by the simultaneous employment of an appropriate setback layer and δ-doping sheet. Due to the reduction in the potential spike, a high current gain, even at a small collector current regime, and small offset voltage can be attained. Experimentally, an offset voltage as small as 55 mV and current gain of 11 at collector current of 0.5 µA are obtained without a passivation structure.

Based on the compositional dependence on the conduction band discontinuity, a significant heterojunction bipolar transistor (HBT) with a continuous conduction band heterointerface between the InP emitter and the In0.53Ga0.25Al0.22As base is fabricated. Experimentally, due to the elimination of the potential spike, a very low offset voltage of 50 mV is observed. Also, the studied device exhibits better breakdown characteristics and lower output conductance as compared with other InP/InGaAs or AlInAs/InGaAs HBTs. Furthermore, attributed to the enhancement of the hole confinement by an inserted δ-doped sheet at the emitter–base interface, a dramatic current gain about 4 is found even under an ultralow current operation regime (IC⩽5 nA).