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This paper reports Al 0.27 Ga 0.73 N/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) with stacked Al 2 O 3 /HfO 2 gate dielectrics by using hydrogen peroxideoxidation/sputtering techniques. The Al 2 O 3 employed as a gate dielectric and surface passivation layer effectively suppresses the gate leakage current, improves RF drain current collapse and exhibits good thermal stability. Moreover, by stacking the good insulating high-k HfO 2 dielectric further suppresses the gate leakage, enhances the dielectric breakdown field and power-added efficiency, and decreases the equivalent oxide thickness. The present MOS-HEMT design has demonstrated superior improvements of 10.1% (16.4%) in the maximum drain-source current (I DS, max ), 11.4% (22.5%) in the gate voltage swing and 12.5%/14.4% (21.9%/22.3%) in the two-terminal gate-drain breakdown/turn-on voltages (BV GD /V ON ), and the present design also demonstrates the lowest gate leakage current and best thermal stability characteristics as compared to two reference MOS-HEMTs with a single Al 2 O 3 /(HfO 2 ) dielectric layer of the same physical thickness.

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A lattice-matched δ-doped In0.34Al0.66As0.85Sb0.15/InP heterostructure field-effect transistor (HFET) which provides large band gap (∼1.8 eV), high Schottky barrier height (φB>0.73 eV), and large conduction-band discontinuity (ΔEc>0.7 eV) has been proposed. In0.34Al0.66As0.85Sb0.15/InP heterostructures are shown to be type II heterojunctions with the staggered band lineup. This HFET demonstrates a output conductance of less than 1 mS/mm. Two-terminal gate-source breakdown voltage is more than 20 V with a leakage current as low as 170 μA at room temperature. High three-terminal off-state breakdown voltage as high as 36 V, and three-terminal on-state breakdown voltage as high as 18.6 V are achieved. The gate voltage swing is also significantly improved.

High-temperature threshold characteristics of a symmetrically graded δ-doped InAlAs∕InxGa1−xAs∕GaAs (x=0.5→0.65→0.5) metamorphic high electron mobility transistor (MHEMT) have been investigated. The thermal threshold coefficients, defined as ∂Vth∕∂T, are superiorly low at 0.9mV∕K from 300to420K and at −0.75mV∕K from 420to500K. An interesting polarity change of the thermal threshold coefficient was observed around 420K due to the variation of thermal modulation effects. The present MHEMT device, with stabilized thermal threshold variations and superior high-temperature linearity characteristics, is promising for high-temperature circuit applications.

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