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In this paper, the influence of spacer layers on DC performance of InP/InGaAs δ-doped heterojunction bipolar transistors (HBT's) is investigated by theoretical analysis and experimental results. As compared to previous δ-doped HBT's, the studied device has another left-side InGaAs spacer added between δ-doped sheet and InP emitter layers at base–emitter (B–E) junction. The left-side spacer more effectively helps to maintain the integrity of uniform-doped InP emitter and the quality of interface; reduce the emitter barrier for electrons, decrease the collector–emitter offset voltage, and increases the confinement effect for holes. An analytical model related to the potential spike at B–E junction and base recombination current is developed to demonstrate the transistor performances. Experimentally, transistor performances with a maximum current gain of 455 and a low offset voltage of 55 mV are achieved.

In this paper, we report the influence of a δ -doped sheet on the DC characteristics of InP/InGaAs δ -doped heterojunction bipolar transistors. The employment of a δ -doped sheet at the base–emitter (B–E) junction efficiently eliminates the potential spike at the B–E junction, lowers the collector–emitter offset voltage, and increases the confinement effect for holes, simultaneously. An analytical model related to the elimination of the potential spike and the components of base recombination currents is developed to investigate the transistor performances. Experimentally, for the studied device with a δ -doping density of 2×1012 cm−2, a maximum current gain of 455 and a low offset voltage of 55 mV are achieved. The experimental results are consistent with the theoretical analysis.

In this paper, a functional InGaP/GaAs/InGaAs step-compositional-emitter heterojunction bipolar transistor (SCEBT) is demonstrated. The excellent transistor performance, including a high current gain and a low collector–emitter offset voltage, is achieved under normal operation mode. In particular, an interesting three-state S-shaped negative-differential-resistance (NDR) switch is observed under inverted operation mode at room temperature because of the reduction of base barrier height and discontinuous confinement effects for electrons in a InGaP/GaAs heterojunction and InGaAs quantum well, respectively. The three-terminal base-controlled NDR characteristics and multiple-valued logic applications are also investigated. Consequently, the transistor action and switching characteristics of the studied SCEBT are promising for signal amplifier and logic circuit applications.

The influence of δ -doping channels on the performance of n + -GaAs/p + -InGaP/n-GaAs camel-gate field effect transistors is investigated by theoretical analysis and experimental results. The depleted pn junction of the camel gate and the existence of considerable conduction band discontinuity at the InGaP/GaAs heterojunction enhance the potential barrier height and the forward gate voltage. As the concentration–thickness products of the n-GaAs layer and δ -doping layer are fixed, the higher δ -doping device exhibits a higher potential barrier height, a larger drain current, and a broader gate voltage swing, whereas the transconductance is somewhat lower. For a n + =5.5×10 12 cm −2 δ -doping device, the experimental result exhibits a maximum transconductance of 240 mS/mm and a gate voltage swing of 3.5 V. Consequently, the studied devices provide a good potential for large signal and linear circuit applications.

A high-performance InP/InGaAs -doped pnp heterojunction bipolar transistor (HBT) has been first fabricated and demonstrated. The addition of a -doped sheet between two undoped spacer layers effectively eliminates the potential spike at emitter-base junction, lowers the emitter-collector offset voltage, and increases the barrier for electrons, simultaneously. Experimentally, a maximum current gain of 50 and a low offset voltage of 70 mV are obtained, respectively. To our knowledge, the offset voltage of the studied device is the lowest value for the reported InP/InGaAs pnp HBTs.

A functional InGaP/GaAs double heterostructure-emitter bipolar transistor is fabricated and demonstrated. Due to the large valence band discontinuity to conduction band discontinuity ratio at the InGaP/GaAs heterojunction and the symmetrical structure, excellent transistor performance, with a high current gain of 195 and a low collector-emitter (C-E) offset voltage of 60 mV, is achieved. In particular, attributed to the avalanche multiplication and confinement effect for electrons at the InGaP/GaAs heterojunction, interesting multiple S-shaped negative-differential-resistance switches are observed under large C-E forward voltage.