Experiments and modelling of double-emitter HPTs with different emitter-area ratios for functional applications

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.

Dynamic Performance of Dual-Emitter Phototransistor as Electro-Optical Switch

“…However, a positive (negative) V E21 of several hundreds of millivolts is sufficient to enhance and saturate the I CP at 129 (90) mA. As proposed by Tan et al, 6) this is because an electrical input at E2 modulates and forces more I ph to flow across the B-E1 junction, which results in a higher current density and a current gain. The table inserted in Fig.…”

“…The inset in Fig. 1 shows the circuit configuration used for measuring DEPT static performance similarly to that reported by Tan et al 6) Shown in the inset of Fig. 2 under illumination, a 1-V clock at a frequency of 1 or 50 kHz is applied to E2.…”

“…Recently, Tan et al have proposed a new phototransistor with dual emitters (DEPT). 6) Nevertheless, no further circuit applications or detailed dynamic performance was investigated. In this study, InGaP/GaAs DEPTs were fabricated and employed in application to electro-optical switching devices.…”

“…1 shows a list of some measured I CP s, demonstrating the static performance of the DEPT and supporting their proposed concept. 6) Since the I CP and current-gain enhancement are due to the emitter bias and photocurrent modulation, we define them as the emitter-induced gain high (EIGH) from photocurrent modulation, which is the basic concept for discussing DEPT dynamic performance.…”

Investigation of optically generated kink effect in GaAs-based heterojunction phototransistors

“…However, in principle three terminal (3T-HPT) operations provide higher gain for phototransistors. In 3T-HPT operation, an additional dc bias at base is used to push the HPT's quiescent bias current to a higher level where the current gain is larger [10]. As HPTs are current controlled devices, the 3T optical gain as current-bias HPT configuration is higher than that of a voltage-bias configuration [11,12].…”