Room temperature photoreflectance (PR) measurements have been carried out on a series of pseudomorphic AlGaAs/InGaAs/AlGaAs high electron mobility transistor (HEMT) structures with different doping profiles grown by molecular beam epitaxy. The GaAs and AlGaAs features in the PR spectrum were studied and their origins were determined by a sequential etching method. It was found that the GaAs buffer layer and AlGaAs barrier layer dominate the GaAs and AlGaAs features in the PR spectrum, respectively. The electric fields for Franz-Keldish oscillations (FKOs) associated with the E0 transition of both GaAs and AlGaAs are affected by the doping on both sides of the InGaAs channel, but are not directly related to the channel carrier concentration. The aluminum composition in the AlxGa1−xAs layers was determined and compared with the results of FKO energy and the critical-point energy methods.
Abstmct-We have successfully fabricated state-of-the-art low-noise planar doped pseudomorphic (PM) InCaAs high electron mobility transistors (HEMT's) with a gate length of 0.1 p m for W-band operation. These devices feature a multiple-finger layout with air bridges interconnecting the sources to reduce gate resistance. The device exhibits a minimum noise figure of 2.5 dB with an associated gain of 4.7 dB at 92.5 GHz. This result is the best reported for any transistor fabricated on GaAs substrates at this frequency.
Photoreflectance (PR) and photoluminescence (PL) techniques were used to characterize the AlGaAs/GaAs heterojunction bipolar transistor (HBT) wafers grown by molecular beam epitaxy (MBE). The line shape of the PR GaAs signal is closely related to the cleanliness of the MBE system. The Franz–Keldysh oscillations of the GaAs signal become sharper, well defined, and the oscillation amplitude increases slightly as the MBE system is cleaned up. The dc current gain of the HBT devices was observed to increase accordingly. The origin for this correlation is discussed. The PL spectra of the HBT device wafers indicate that the intensity of the free-to-bound transition corresponding to the donor to valence band becomes strong in high gain device wafers.
We report the growth and device characterization of InAlAs/InGaAs/InP double-heterojunction bipolar transistors in a solid source molecular beam epitaxy system with a valved-phosphorus cracker. Linearly graded InGaAlAs base-collector and emitter-base junctions were used. Photoreflectance characterization shows excellent growth reproducibility. The dc current–voltage characteristics of a 1.5×10 μm2 device indicate high breakdown voltage, low offset voltage, and good linearity. Breakdown voltage of an InP-collector device with compositionally graded base-collector junction is 19 V compared to 11 V for an InGaAs-collector device. By comparison, a chirped superlattice base-collector junction shows significant current oscillations due to the carrier tunneling effect. High-frequency performance was similar to previously reported InGaAs-collector devices; unity current-gain frequency and unity maximum-available power gain frequency are 75 and 140 GHz, respectively.
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