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The rf performance of 1 × 200 μm2 AlGaN/GaN MOS-HEMTs with Sc2O3 used as both the gate dielectric and as a surface passivation layer is reported. A maximum fT of ∼11 GHz and fMAX of 19 GHz were obtained. The equivalent device parameters were extracted by fitting this data to obtain the transconductance, drain resistance, drain–source resistance, transfer time and gate–drain and gate–source capacitance as a function of gate voltage. The transfer time is in the order 0.5–1 ps and decreases with increasing gate voltage. [Copyright &y& Elsevier]

The dc and power characteristics of AlGaN/GaN MOS-HEMTs with Sc2O3 gate dielectrics were compared with that of conventional metal-gate HEMTs fabricated on the same material. The MOS-HEMT shows higher saturated drain–source current (∼0.75 A/mm) and significantly better power-added efficiency (PAE, 27%) relative to the HEMT (∼0.6 A/mm and ∼5%). The Sc2O3 also provides effective surface passivation, with higher drain current, lower leakage currents and higher three-terminal breakdown voltage in passivated devices relative to unpassivated devices. The PAE also increases (from ∼5% to 12%) on the surface passivated HEMTs, showing that Sc2O3 is an attractive option for reducing gate and surface leakage in AlGaN/GaN heterostructure transistors. [Copyright &y& Elsevier]

A finite element simulation was used to quantitatively estimate the effectiveness of flip-chip bonding in the temperature rise of bulk GaN Schottky rectifiers under various conditions of current density, duty cycle, forward turn-on voltage and on-state resistance. The temperature difference between flip-chip bonded devices and bottom bonded devices was 20 °C even at modest current densities. The maximum temperature in the bulk cases occurred in the center of the GaN substrate thickness. The transit time of the temperature reaching the steady state for the flip-chip bonding device is in the range of millisecond, which is faster than that of most power switch applications. Flip-chip bonding is suggested to improve the heat dissipation of high power, bulk GaN rectifiers. [Copyright &y& Elsevier]

The finite difference method was used to analyze the thermal characteristics of continuous wave 850 nm AlGaAs/GaAs implant-apertured vertical-cavity surface-emitting lasers (VCSELs). A novel flip-chip design was used to enhance the heat dissipation. The temperature rise in the active can be maintained below 40 °C at 4 mW output power with 10 mA current bias. By contrast, the temperature rise reaches above 60 °C without flip-chip bonding. The transient temperature during turn-on of a VCSEL was also investigated. The time needed for the device to reach the steady-state temperature was in the range of a few tenths of a millisecond, which is orders of magnitude larger than the electrical or optical switch time. Flip-chip bonding will reduce the shift of the wavelength, peak power, threshold current, and slope efficiency during VCSEL operation. [Copyright &y& Elsevier]

An AlGaN/GaN high electron mobility transistor structure was used for sensing different liquids present in the gate region. The forward current showed significant decreases upon exposure of the gate area to solvents (water, acetone) or acids (HCl). The pH sensitivity is due to changes in net surface charge that affects the relative depletion in the channel of the transistor. The results indicate that nitride-based heterostructures may have application in integrated chemical, gas and fluid monitoring sensors. [Copyright &y& Elsevier]

GaN/SiC and Al0.25Ga0.75 N/SiC heterojunction diodes were fabricated using Al/Ti for p-ohmic contact to the SiC and Ti/Al/Pt/Au for n-ohmic contact to the GaN and AlGaN. Annealing at 850 °C for 20 s (GaN) or 120 s (AlGaN) was required for achieving specific contact resistances in the 10−6 Ω cm2 range. The reverse breakdown voltage showed a negative temperature coefficient in both types of sample, with value ∼5.5±2.5×10−3 V/K. The I–V characteristics of both heterojunctions show evidence of tunneling via defect states. [Copyright &y& Elsevier]