In 0.5 Ga 0.5 As ∕ In 0.5 Al 0.5 As metamorphic high electron mobility transistos were fabricated with different gate-metal formations: mesa type or air type and without or with a buried gate. Only air-type devices with a buried gate show no kink effect. Experimental results indicate that gate-feeder metal and annealing process give effects on gate current and noise figure. The peak gate current of 12 (120)μA∕mm for air-type (mesa-type) devices before annealing is improved to 8 (55)μA∕mm after annealing. At 1.8GHz, associated gain of 25dB is obtained at Fmin=1.24dB for air-type devices after annealing, while 23dB is obtained at Fmin=1.25dB before annealing.
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.
Depletion-mode δ-doped In 0.5 Ga 0.5 As/In 0.5 Al 0.5 As mHEMTs have been metamorphically grown on a GaAs substrate and successfully fabricated with different kinds of gate-metal formation. The gate-metal formations include a combination of mesa-or air-type gate feeder with or without a buried gate (before or after annealing). Only the air-type mHEMT with a buried gate shows no clear kink-effect behaviour. For a 1 µm gate mesa-type (air-type) mHEMT, a maximum extrinsic transconductance of 412 (414) and 535 (472) mS mm −1 is obtained before annealing and after annealing. There is a 207 mV (205 mV) shift in V TH after the mesa-type (air-type) mHEMT is annealed. Experimental results indicate that both the gate-feeder metal and the annealing process have a significant effect on output conductance, gate leakage current, breakdown voltage, high frequency and noise performances. The peak gate leakage current density of 12 (120) µA mm −1 for the air-type (mesa-type) mHEMT before annealing is improved to 8 (55) µA mm −1 after annealing. At 2.4 (5.4) GHz, gain = 23 (20) dB can be obtained at F min = 1.27 (1.76) dB for the air-type mHEMT after annealing, while gain = 22 (18.5) dB is obtained at F min = 1.36 (2.0) dB before annealing. For the mesa-type mHEMT, these values are gain = 20 (16.5) dB at F min = 1.47 (2.25) dB and gain = 19.5 (14) dB at F min = 1.68 (3.11) dB.
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