This investigation reports on the first symmetrically double-delta-doped channel InAlAs/InGaAs/GaAs metamorphic field-effect transistor ͑MFET͒. Two types of devices are fabricated as follows. In the fabrication of the first, the gate recessing steps are carried out using nonselective etching solution ͑phosphoric acid/hydrogen peroxide mixtures͒. In the fabrication of the second, a pH 5.5 selective succinic acid:ammonia hydrogen peroxide:water wet chemical etching liquid is adopted to form the gate recess. A succinic acid-based solution is found to be a better selective etchant of an InGaAs/InAlAs system than the more commonly used phosphoric acid-based solutions, in terms of the etching selectivity and the smoothness of the etched surface. The etch-stop mechanism is inferred from Auger electron spectroscopy to involve the formation of nonvolatile aluminum oxide, in strong agreement with the X-ray photoelectron spectroscopy spectra. Nearly kink-free current-voltage characteristics are achieved. The assessment of these structures for application in power field-effect transistor devices reveals that high frequency, high transconductance devices are feasible. As far as the authors are aware, this study is the first to compare MFETs that use a nonselective wet gate recess with those that use a selective wet gate recess.The speedily widening market for wireless communication devices in the past has increased the need for GaAs-based epitaxial materials. 1-3 Field-effect transistors ͑FETs͒ are important in today's high frequency communication systems. 4 The development of high electron mobility transistors ͑HEMTs͒ in the late 1970s in the AlGaAs/GaAs materials system gave device designers the opportunity to exploit the high mobility of undoped GaAs to improve fieldeffect transistor performance. The primary motivation for the use of the AlGaAs/GaAs system is that AlGaAs is lattice-matched to GaAs over the entire compositional range. 5,6 The GaAs/InGaAs pseudomorphic high electron mobility transistor ͑PHEMT͒ has attracted interest as an alternative to the AlGaAs/GaAs HEMTs because it exhibits excellent carrier confinement and a depressed deep-level concentration in the material with the higher bandgap, which results in persistent photoconductivity at cryogenic temperatures. 7 Most importantly, InGaAs layers on GaAs substrates have been popular for use in PHEMTs because they have favorable transport over GaAs, substrates of which are relatively cost-effective. To grow pseudomorphic strained layers, the critical thickness at which the strain in a lattice mismatched layer relaxes through the generation of misfit dislocation must be known. 8,9 An improvement over the GaAs/InGaAs PHEMT is the AlGaAs/InGaAs PHEMT with a small AlAs mole fraction, 10-12 which has a larger conduction-band discontinuity than the GaAs/InGaAs PHEMT, supporting a greater carrier concentration without experiencing the effects related to a large mole fraction of AlGaAs. Although excellent performance has been achieved by growing pseudomorphic strained ch...
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