N-p-n InGaP/GaAs Dual-Emitter heterojunction phototransistor (DEPT) with/without InGaP-passivation layer have been fabricated to investigate the influence of surface leakage on the device optical performance. The comparison between DEPT with a voltage-biased emitter and HPT with a voltage-biased base is also included. There are four (three) operating regions appearing in the optical characteristics of the DEPT (HPT): negative-saturation, negative-tuning, positive-tuning, and positive-saturation (cut-off, tuning, and saturation) regions. The InGaP-passivated DEPT with the extrinsic base surface passivated by InGaP, exhibits the maximum optical gains of 46.57, 46.86 and 47.39 while the non-passivated one shows those of 32.02, 33.55 and 33.57 under the optical powers of 8.62, 13.2 and 17.5 μW, respectively. However, the optical gains are only in the range of 0.93~2.0 (0.83~1.64) for the InGaP- passivated HPT (non-passivated HPT) for all the illuminating conditions.
The influence of gate metal with thermal annealed process adopt to control the distance between gate and channel on pseudomorphic Al0.24Ga0.76As/ In0.22Ga0.78As double heterojunction high electron mobility transistors (DH-HEMTs) were studied. Compared to device with gate-recess process, the distance of gate-to-channel could be controlled through the thermal annealed process and therefore exhibit a lower series resistance. Measured transconductance of 150 mS/mm and an open- drain voltage gain of 136 for the DH-HEMT with an as deposited gate are enhanced to 175 mS/mm and 160 for the DH-HEMT with a 330-{degree sign}C annealed gate. Good device linearity is also obtained with a low second-harmonic to fundamental ratio of 3.55 %. In addition, good microwave performances such as unit-current gain- and maximum power gain- frequency were also obtained from devices with gate-annealed process.
Dual-emitter heterojunction phototransistors (DEPT) with an voltage-biased emitter is compared with the conventional heterojunction phototransistor with a voltage-biased emitter. There are four (three) operating regions in the photocurrent- voltage characteristics of the DEPT (HPT): negative-saturation, negative-tuning, positive-tuning, and positive-saturation (cutoff, positive-tuning, and positive-saturation) regions. The obtained optical gains are only 0.784~1.64 with a gain-tuning efficiency of 4.4 V-1 for the HPT while those are in the range of 12.9 ~ 32.3 with the maximum gain-tuning efficiency of 43.4 V-1 for the DEPT. The power- and voltage-tunable optical gains are both expected for the DEPT. However, the conventional HPT exhibits only voltage-tunable characteristics. DEPTs with different emitter area ratio are also discussed. The maximum gain-tuning efficiency is 75.3 for the DEPT with emitter area ratio of 8:1 under optical power of 0.423 μW. The obtained results introduce the potential of employing the DEPT for low- power optical detection.
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