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The interesting InGaP/GaAs heterojunction bipolar transistors (HBTs) with different surface passivations on the base surface are fabricated and studied. Experimentally, the HBT device with sulfur treatment passivation displays the lowest offset voltage. However, the device with a 0.02 μm-thick emitter ledge structure reveals better transistor behaviors such as higher current gain and lower base surface recombination current. In addition, it also exhibits improved thermal stability. For the reliability test, the device with a 0.02 μm-thick emitter ledge structure shows the best performance. Therefore, from experimental results, the HBT device performance could be improved by appropriate base surface treatments, e.g., sulfur passivation and emitter ledge structure.

The breakdown behaviors of InP/InGaAs single heterojunction bipolar transistor (SHBT) and double heterojunction bipolar transistor (DHBT) are studied and demonstrated. By using a composite collector structure at the base–collector heterojunction, the undesired current-blocking effect, switching, hysteresis phenomenon usually found in an InP/InGaAs conventional DHBT are not observed in our DHBT device. Experimentally, as compared with the studied SHBT, the studied DHBT reveals the enhanced breakdown voltages, lower collector leakage current I CO , and smaller electron impact ionization α . Moreover, the temperature-dependent electron impact ionization characteristics and electrical reliability for both devices are also studied. Therefore, the studied DHBT device provides the promise for millimeter-wave and power circuit applications.

The effects of base current on the collector-emitter offset voltage for InGaAsP/InP heterojunction bipolar transistors (HBTs) have been examined both experimentally and theoretically. The junction area ratio of emitter-base and collector-base obviously affects the value of offset voltage. We demonstrate that decreasing base current increases the offset voltage. A double-base InGaAsP(p)/InGaAs(p+)/InP HBT (DBHBT) and a traditional single-base InGaAsP/InP HBT (SBHBT) have been fabricated and characterized. We examined theoretically the electron diffusion current of the DBHBT and found that the turn-on voltage of the EB junction for a DBHBT is low, and the offset voltage of a DBHBT is low. The DBHBT with low-high doping and wide-narrow bandgap design shows a small offset voltage that is not due to a heterojunction at the collector. The experimental results show that low offset voltage (ΔVCE = 63 mV) and high current gain (βac = 140) of the DBHBT are excellent compared to those (ΔVCE = 130 mV and βac = 100) of the SBHBT. The offset voltage of the SBHBT is increased with decreasing base current. However, the offset voltage of a DBHBT is insensitive to the base current value. The effective electron diffusion lengths in the bases of the DBHBT and SBHBT are about 3.35 and 3.83 μm respectively.

This paper deals with a theoretical and experimental study of InGaAsP/InP double-collector heterojunction bipolar transistors (HBTs) fabricated by liquid phase epitaxy. A thin undoped n−-InGaAsP layer was used as sub-collector. Good performance was achieved, e.g. high current gain (= 140 for a.c. and 120 for d.c.), low offset voltage (< 100 mV), and small emitter-size effect. Theoretically, the thermionic field-diffusion model was used to calculate the current transport of the InGaAsP/InP HBTs. A detailed analytical simulation of the characteristics of offset voltage and Gummel plot of the InGaAsP/InP HBT is presented.

An interesting InP/InGaAs double heterojunction bipolar transistor (DHBT) with a step-graded InAlGaAs/InP collector structure are demonstrated and studied. By use of the step-graded InAlGaAs/InP collector structure at the base-collector heterojunction, the current blocking effect is effectively eliminated. Experimentally, the studied device shows a relatively better common-emitter breakdown voltage and low output conductance though at high temperature. Also, the studied device shows a wider collector current density operation region which over 11 decades in magnitude of collector current density (10~6 to 105 A/cm2). Moreover, the studied device also shows the relatively weaker temperature dependence on the electron impact ionization alpha. Consequently, the studied DHBT device provides the promise for low-voltage and low-power circuit applications.

The dc and electron impaction ionization characteristics of an InP/InGaAs double heterojunction bipolar transistor with a step-graded InAlGaAs collector structure are studied and reported. From the experiments, the studied device shows a better common-emitter breakdown voltage and lower output conductance at higher temperature operations. Due to the insertion of a step-graded InAlGaAs collector structure at the base-collector heterojunction, the usually observed switching and hysteresis phenomena in InP/InGaAs-based HBTs are not seen in the studied device. The temperature-dependent electron impact ionization characteristics are also investigated. Above all, the studied DHBT device provides the promise for millimeter-wave and power circuit applications.

Interesting temperature-dependent characteristics of InP∕InGaAs-based single-heterojunction bipolar transistor (SHBT) and double-heterojunction bipolar transistor (DHBT) devices are compared and studied. Experimentally, both studied devices show wider collector current (IC) operation regions, with over 11 decades in magnitude of collector current (IC=10−12to10−1A). However, the studied DHBT exhibits improved breakdown characteristics [common-emitter breakdown voltage (BVCEO)=8.05V and common-base breakdown voltage (BVCBO)=11.3V] and low output conductance at high temperature. Moreover, the undesired current-blocking effect, switching, hysteresis phenomenon usually found in an InP∕InGaAs conventional DHBT are not observed in the DHBT device. As compared with the studied SHBT, the studied DHBT shows a lower multiplication factor and weaker temperature dependence. Therefore, it is known that, based on experimental results, the studied DHBT device provides the promise for low-voltage and low-power circuit app...