No abstract

No abstract

Experiments and modelling of new three-terminal heterojunction phototransistors with double emitters (DE-HPTs) but no base contact are reported for comparison with single-emitter HPTs (SE-HPT) without base electrode and conventional HPTs with a base electrode using the same epi-layers. Double emitters having a different area ratio (A 1 : A 2 ) but a fixed total area together with a collector form a three-terminal device. As a voltage-bias emitter instead of a current-bias base is used, a DE-HPT exhibits an enhanced collector photocurrent in comparison with a SE-HPT with the same total emitter area. Experimental results reveal that 2 : 1 and 1 : 1 DE-HPTs exhibit a 1.85-and 1.5-fold optical gain, respectively, over that from a SE-HPT. Other key features of a DE-HPT include the following:(1) the differential emitter voltage used is as small as several hundred millivolts, (2) not only a positive but also a negative voltage can be used to enhance the final collector photocurrent and (3) polarity-dependent characteristics are obtainable for an A 1 : A 2 DE-HPT. Moreover, a new circuit model with three sets of parallel diodes is proposed to explain the performance enhancement and polarity-dependent behaviours. Theoretical results are in very good agreement with experimental ones and indicate that more than three-fold enhancement is expected.

This paper reports the formation of GaAs V-grooves with well-controllable notch angles. The key methodology used to control the notch angle of a V-groove is to preset the temperature of the etching chemicals. Due to increased chemical reaction at the GaAs surface at high temperature, diffusion-limited etching dominates the etched process, resulting in highly isotropic etched profiles. It is found that the notch angle of a V-groove increases with increasing temperature of the etching chemicals. The etching angle used to define the slope of a V-groove increases from 30 to 55 • as the temperature decreases from 96 • C to 0 • C. Then V-gates formed by depositing Au metal on V-grooves with different notch angles were employed in the fabrication of InGaP/InGaAs heterojunction doped-channel FETs (HDCFETs). Effects of temperature-dependent notch angle on V-gate HDCFETs were investigated in detail, including dc, ac performances and short-channel effects. Experimental results reveal that a small notch-angle V-gate is quite promising for high-frequency applications. Finally, comparisons between simulated results for planar-gate HDCFETs and experimental results for V-gate HDCFETs are used to determine the equivalent gate length of a V-gate. It is found that the equivalent gate length of a V-gate is in the range of 0.1-0.2 µm.

Effect of composite collector design on the breakdown behavior of InGaP/GaAs double heterojunction bipolar transistor J. Appl. Phys. 93, 605 (2003); 10.1063/1.1521513Analysis of collector-emitter offset voltage of InGaP/GaAs composite collector double heterojunction bipolar transistor Fabrication, characterization, and theoretical modeling of two-terminal and three-terminal heterojunction phototransistors ( 2T-and 3T-HPTs) based on InGaP/ GaAs are reported. For a current-bias 3T-HPT, an independent current flowing into or out of base electrode is employed to modulate the operating point of a heterojunction bipolar transistor (HBT). The operating point of a HBT in the presence of a positive bias current can be tuned to a higher current level where the current gain is larger. It is found that the optical gain increases from 28.4 for a 2T-HPT to 34 for a 3T-HPT with a bias current of 10 A. The achievement of tunability of the operating point of a HBT has also been attempted with an independent voltage source. Nevertheless, our work reveals that the p -i -n photocurrent generated within the B -C region contributes very little to the final collector photocurrent for a voltage-bias 3T-HPT, resulting in a rather small optical gain in the range 0.8-1.6. A simple equivalent circuit model is developed to explain the differences between a current-and a voltage-bias 3T-HPT. Our calculated results are in good agreement with the experimental ones.