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A new field-effect resistive hydrogen sensor, based on the current-voltage characteristics in the linear region of an AlGaAs-based psuedomorphic high-electron-mobility transistor structure and high hydrogen sensitivity of a palladium metal, is studied. This studied resistive sensor shows that it provides the promise for low-power GaAs-based electronic and microelectromechanical-system applications.

Conformal passivation on an InGaP/GaAs HBT with significant reduction in the base surface-recombination effect is demonstrated. Experimental results show that the surface-recombination current and surface channel phenomenon could be further reduced by the conformal passivation.

A comprehensive study of emitter-ledge thickness of InGaP/GaAs heterojunction bipolar transistors (HBTs) is conducted. Results reveal that the recombination rate and electron densities are drastically increased near the exposed base surface between the base contact and the emitter ledge.

GaAs/InGaP and AlGaAs/GaAs/InAlGaP npn heterostructural optoelectronic switches (HSOSs) have been fabricated to demonstrate the bulk-barrier and potential-spike height effects on the switching. It is seen that the illumination decreases the switching voltage VS and increases the switching current IS in the GaAs/InGaP HSOS characteristics. But in the AlGaAs/GaAs/InAlGaP HSOS, the VS and IS present contrary trends. These characteristic variation differences in the two HSOSs are mainly due to the photogenerated carriers that affect the bulk-barrier and potential-spike heights. [ABSTRACT FROM AUTHOR]

The influence of emitter ledge length on the performance of InGaP/GaAs heterojunction bipolar transistors is comprehensively investigated. Due to the band-bending effect at the intersection of the emitter ledge edge with the exposed base surface, an undesired potential saddle point is formed. Moreover, emitter ledge passivations that are longer or shorter than an optimal length result in the deterioration of device performance. Based on the theoretical analysis and experimental results, the surface recombination effect of the device with an emitter ledge length of 0.8 μm is negligible compared with the unpassivated device. Also, the device with the emitter ledge length of 0.8 μm shows nearly the best dc characteristics and acceptable rf performance. Therefore, the optimum emitter ledge length in this study is near 0.8 μm. [ABSTRACT FROM AUTHOR]

In this work, the characteristics of the InGaP/GaAs heterojunction bipolar transistors with different emitter-edge-thinning thickness were systematically investigated. A stronger downward-band-bending phenomenon was observed at the edge of emitter-edge- thinning intersection with the exposed base surface. This band bending induced the presence of a potential saddle point, which substantially increased the recombination rates and electron densities. In addition, the decision of emitter-edge-thinning thickness plays a key role in reducing surface recombination at the potential saddle point. As the emitter-edge-thinning thickness was selected between 100 and 200 A, the lowest recombination rate and electron density and highest dc current gain could be obtained. Furthermore, good agreements between the theoretical analyses and experimental results were found. [ABSTRACT FROM AUTHOR]

The thermal stability performance of double δ-doped In0.42Al0.58As/In0.46Ga0.54As metamorphic heterostructure field-effect transistors with Au and Ti/Au metal gates are comprehensively studied and demonstrated. By evaporating the Ti/Au metal gate, the thermal stability of device characteristics are significantly improved as compared with the device with conventional metal gate (Au). Experimentally, the device with a Ti/Au metal gate simultaneously exhibits the considerably lower temperature degradation in tum-on voltage (–2.19 mV/K), breakdown voltage (–34 mV/K), logic swing (–1.24 mV/K), transition region width (0.05 mV/K), on-off current ratio (–3.55/K), threshold voltage (–0.25 mV/K), impact ionization-induced gate current (1.63 × 10-3 μA/mm K), output conductance (1.23 μS/mm K), and voltage gain (–0.33 /K) as the temperature is increased from 300 to 510 K. Consequently, the studied device with a Ti/Au metal gate is a good candidate for high-speed and high-temperature digital and switching circuit applications. [ABSTRACT FROM AUTHOR]

Temperature-dependent characteristics of high electron mobility transistors (HEMTs) with sulfur and SiNx passivations are comprehensively studied and demonstrated. Experimentally, for the studied device with formal passivations, better dc and microwave characteristics are obtained over a wide operating temperature range. In particular, as compared with the device only with sulfur passivation, the slight degradations of device performance are caused by the temperature stress during the deposition of SiNs layer and presence of surface traps at the SiNx/AlGaAs interface. However, under an accelerated stress test, this formal-passivated device shows improved reliability performance. Based on these good results, the formal-passivated HEMT is expected to exhibit relatively better long-term operation stability and reliable device characteristics. [ABSTRACT FROM AUTHOR]

On the basis of a Pt/In0.52Al0.48As metal-semiconductor structure, a novel hydrogen sensor is fabricated and demonstrated. The studied Pt/In0.52Al0.48As Schottky diode-type hydrogen sensor exhibits significant sensing performance including high relative sensitivity ratio of about 2600% (under the 1% H2/air gas and VR = -0.5 V at 30 °C), large current variation of 310 pA (under the 1% H2/air gas and VR = -5 V at 200 °C), widespread reverse-voltage regime (0 ~ -5 V), stable hydrogen-sensing current-voltage (I-V) curves, and fast transient response time of 1.5 s. The calculated Schottky barrier-height change and series-resistance variation, from the thermionic-emission model and Norde method, are 87.0 meV and 288 Ω, respectively (under the 1% H2/air gas at 30 °C). The hydrogen concentrations and operating temperatures tested in this letter are in the range of 15 ppm-1% H2/air and 30 °C-250 °C, respectively. Based on the excellent integration compatibility with InP-based electronic devices, the studied device provides the potentiality in high-performance sensor-array applications. [ABSTRACT FROM AUTHOR]

Temperature-dependent dc characteristics and RF performances of InGaP/GaAs heterojunction bipolar transistors with sulfur treatment are systematically studied. The base-surface-recombination current, specific contact resistance, and sheet resistance of the studied devices can be effectively reduced by sulfur treatment. Practically, long-time sulfur treatment is not appropriate. In this paper, the studied device with the sulfur treatment for 12-15 min is a good choice. Experimentally, the collector-emitter offset voltage DeltaVCE and dc current gain with sulfur treatment can be substantially reduced and increased, respectively, over the 300-K-400-K temperature range. Moreover, as the temperature is increased, the device with sulfur treatment exhibits temperature-independent or thermally stable performances. The devices with sulfur treatment also exhibit improved RF characteristics [ABSTRACT FROM PUBLISHER]

The temperature-dependent dc characteristics of InGaP/GaAs heterojunction bipolar transistors with and without full sulfur passivation are systematically studied and demonstrated. The studied device with full sulfur passivation shows lower specific contact resistance ρC, lower sheet resistance Rsh, lower collector-emitter offset voltage ΔVCE, and higher dc gain βF than devices without sulfur passivation. The device with full sulfur passivation also exhibits better rf performance. In addition, the studied device with full sulfur treatment shows lower temperature variation coefficients of ρC, Rsh, ΔVCE, and βF. Thus, the device with sulfur treatment presents relatively temperature-independent characteristics that can extend the transistor action to higher temperature regimes. [ABSTRACT FROM AUTHOR]

The temperature-dependent characteristics of an InGaP/InGaAs/GaAs heterostructure field-effect transistor (HFET), using the (NH4)2Sx solution to form the InGaP surface passivation, are studied and demonstrated. The sulfur-passivated device shows significantly improved dc and RF performances over a wide temperature range (300-510 K). With a 1×100-μm2 gate-dimension HFET by (NH4)2Sx treatment, the considerably improved thermal stability over dc performances including lower temperature variation coefficients on the turn-on voltage (-1.23 mV/K), the gate-drain breakdown voltage (-0.05 mV/K), the gate leakage current (1.04 μA/mm·K), the threshold voltage (-1.139 mV/K), and the drain-saturation-current operating regimes (-3.11×10-4/K) are obtained as the temperature is increased from 300 to 510 K. In addition, for RF characteristics, the sulfur-passivated device also shows a low degradation rate on drain-saturation-current operating regimes (-3.29×10-4/K) as the temperature is increased from 300 to 400 K. These advantages provide the promise for high-speed high-frequency high-temperature electronics applications. [ABSTRACT FROM PUBLISHER]

The influences of (NH4)2Sx treatment on an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) are studied and demonstrated. Upon the sulfur passivation, the studied device exhibits better temperature-dependent dc and microwave characteristics. Experimentally, for a 1 × 100 μm² gate/dimension PHEMT with sulfur passivation, the higher gate/drain breakdown voltage of 36.4 (21.5) V, higher turn-on voltage of 0.994(0.69) V, lower gate leakage current of 0.6 (571) μA/mm at VGD = -22 V, improved threshold voltage of -1.62 (-1.71) V, higher maximum transconductance of 240 (211) mS/mm with 348 (242) mA/mm broad operating regime (> 0.9gm,max), and lower output conductance of 0.51 (0.53) mS/mm are obtained, respectively, at 300 (510) K. The corresponding unity current gain cutoff frequency fT (maximum oscillation frequency fmax) are 22.2 (87.9) and 19.5 (59.3) GHz at 250 and 400 K, respectively, with considerably broad operating regimes (> 0.8fT, fmax) larger than 455 mA/mm. Moreover, the relatively lower variations of device performances over wide temperature range (300 ∼ 510 K) are observed. [ABSTRACT FROM AUTHOR]

The effect of (NH4)2Sx treatment on the device characteristics of an InGaP/InGaAs/GaAs heterostructure field-effect transistor are studied and demonstrated. Experimentally, it is found that the sulfur-passivated device shows significant dc characteristics including higher forward voltage, lower leakage current, lower output conductance, and higher voltage gain. The superior microwave performances with flat and wide operating region of drain saturation current are simultaneously obtained. Furthermore, the improved thermal stabilities over wide temperature range of sulfur-passivated devices are attained. Based on these advantages, the studied device with (NH4)2Sx treatment shows the promise for high-temperature and high-performance microwave applications. [ABSTRACT FROM AUTHOR]