We specifically studied the influence of a setback-layer thickness on the device performances so as to optimize the required value. Theoretical analysis shows that an optimized setback-layer thickness is available to effectively reduce the barrier height while maintain good device performances. In this work, the effects of a setback-layer thickness on the DC and RF performances of an InGaP/GaAs heterojunction bipolar transistor (HBT) are investigated. Based on the theoretical analysis, the optimized setback-layer thickness WSB is about of 10~30Å for analog amplification. On the other hand, for digital saturated logic application, <i>i.e</i>., a small offset voltage with an acceptable current gain, the optimized W<sub>SB</sub> could be up to 50 Å. Therefore, this analysis and predication may cause the considerable promise for practical circuit applications.
An interesting InGaP/InGaAs quantum-well delta-doped-channel field-effect transistor is fabricated and demonstrated. Due to the employed InGaAs dual quantum-well delta-doped-channel structure and Schottky behaviors of InGaP "insulator," good DC properties including higher turn-on voltage, lower leakage current, better linearity, and good RF performances are obtained. In addition, the experimental results are fitted well with theoretical simulation data based on a two-dimensional simulator. Moreover, the studied device exhibits relatively negligible temperature-dependent characteristics over wide operating temperature region (300<T<450K). Therefore, the studied device provides the promise for high-temperature and high-performance microwave electronic applications.
The DC performances of a novel InP/InGaAs tunneling emitter bipolar transistor (TEBT) are studied and demonstrated. The studied device can be operated under an extremely wide collector current regime larger than 11 decades in magnitude (10<sup>-12</sup> to 10<sup>-1</sup>A). A current gain of 3 is obtained even operated at an ultra-low collector current of 3.9x10<sup>-12</sup>A (1.56x10<sup>-7</sup> A/cm<sup>2</sup>). The common-emitter and common-base breakdown voltages of the studied device are higher than 2 and 5V, respectively. Furthermore, a very low collector-emitter offset voltage of 40 mV is found. The temperature-dependent DC characteristics of the TEBT are measured and studied. Consequentially, based on experimental results, the studied device provides the promise for low-power electronics applications.
The characteristics of a GaAs graded-period (delta) -doped superlattice grown by molecular beam epitaxy were studied. It is shown that a novel S-shaped negative differential conductivity (NDC) occurred both at 300 K and 77 K. Besides, a two-state avalanche multiplication process, i.e., a middle quasi-stable region is seen at 77 K. Finally, there is an interesting hysteresis phenomenon due to the trapped holes created by the avalanche multiplications. The significant control voltage ratio, Vs/V(Eta) , of the studied structure introduces a good potential for application on the switching field.
A novel functional resonant-tunneling bipolar transistor (RBT) has been fabricated and demonstrated. In the proposed device, electrons are injected from emitter to base by resonant- tunneling through the minibands in the i-AlGaAs/n<sup>+</sup>-GaAs superlattice. The main features of the proposed device is the significant double negative-differential-resistance (NDR). Two high peak-to-valley current ratios of 4:1 and 2.6:1 were obtained at 77 K. In the transistor operation, a common-emitter current gain of 60 and a collector offset voltage smaller than more than 0.2 V at 77 K were obtained. As control base current increases sufficiently to cause the base-emitter junction drop beyond flat-band condition, two different transistor action regions with smaller current gains of 38 and 35 are found, respectively. Furthermore, the first peak current is nearly equal to the second peak current and much larger than the second valley current. Therefore, it is attractive to exploit the device in multiple- valued logic circuits and frequency multiplier.