Chih-Kai Wang

A new Pt/oxide/In/sub 0.49/Ga/sub 0.51/P MOS Schottky diode hydrogen sensor

A new and interesting Pt/oxide/In/sub 0.49/Ga/sub 0.51/P metal-oxide-semiconductor (MOS) Schottky diode hydrogen sensor has been fabricated and studied. The steady-state and transient responses with different hydrogen concentrations and at different temperatures are measured. The presence of dipoles at the oxide layer leads to an extra electrical field and the variation of Schottky barrier height. Even at room temperature, a very high hydrogen detection sensitivity of 561% is obtained when a 9090 ppm H/sub 2//air gas is introduced. In addition, an absorption response time less than 1 s under the applied voltage of 0.7 V and 9090 ppm H/sub 2//air hydrogen ambient is found. The roles of hydrogen adsorption and desorption for the transient response at different temperatures are also investigated.

A novel Pd/oxide/GaAs metal-insulator-semiconductor field-effect transistor (MISFET) hydrogen sensor

A novel and high-performance Pd/oxide/GaAs hydrogen sensor based on a metal-insulator-semiconductor field-effect transistor (MISFET) is fabricated and studied. In the presence of the interfacial oxide, high sensitivity and significant increase in output drain current are observed. In the presence of hydrogen, a 2×200 µm2 gate dimension device shows good dc characteristics including high turn-on voltage, an obvious variation of drain current and a short response time. In addition, under the applied voltage of -4 V and 537 ppm hydrogen in air, a very high sensitivity of 9473 is obtained. This performance shows that the device studied has a good potential for high-speed and high-sensitivity hydrogen sensor and MISFET integrated circuit applications.

On the high-performance n+-GaAs/p+-InGaP/n-GaAs high-barrier gate camel-like HFETs

Abstract The high-performance n + -GaAs/p + -InGaP/n-GaAs high-barrier gate camel-like HFETs are successfully fabricated and demonstrated. The p + -InGaP layer is introduced to increase the barrier height and carrier confinement. Experimentally, good DC and AC device performances are obtained. For the studied 1×100 μm 2 device A (B), a gate–drain turn-on voltage of 1.6 (1.2) V, gate–drain breakdown voltage over 40 V with low leakage current of 400 (37) μA/mm, drain–source off-state breakdown voltage of 38 (39.7) V, maximum transconductance g m,max of 145 (147) mS/mm, unity current gain cut-off frequency f T of 17 (15) GHz, and maximum oscillation frequency f max of 33 (28) GHz are obtained, respectively, at room temperature. Moreover, the studied devices also show significantly wide and flat I DS operation regimes of g m , f T and f max .

Characterization of InP/InGaAs double-heterojunction bipolar transistors with tunnelling barriers and composite collector structures

We study and demonstrate the dc performance of two InP/InGaAs double-heterojunction bipolar transistor (DHBTs) with the undoped tunnelling barrier and composite collector structures. Due to the mass filtering effect for holes, a thin InP tunnelling barrier can be used to replace the wide-gap emitter. By varying the thickness of the barrier, distinct collector current ideality factors can be obtained which reveal different injection mechanisms at the emitter. The 4000 A InP collectors with InP/InGaAs abrupt junctions and InP/InGaAsP/InGaAs step-graded junctions achieve high breakdown voltages of 9.2 and 14.6 V, respectively. Furthermore, the abrupt junction and δ-doping structure eliminate carrier blocking across the base-collector heterojunction more effectively than the step-graded junction. We find that the reduction of the multiplication avalanche of the step-graded junction DHBT leads to the severe self-heating effect. For the abrupt junction DHBT, the dc current gain is almost independent of the perimeter-to-area ratio of the emitter due to the low surface recombination.

Comparative study on dc characteristics of In0.49Ga0.51P-channel heterostructure field-effect transistors with different gate metals

DC characteristics of interesting In0.49Ga0.51P-channel heterostructure field-effect transistors (HFETs) with different gate metals, e.g., Pt, Pd and Au, have been studied and demonstrated. A very thin and fresh oxide layer is introduced to increase the gate turn-on and breakdown voltages and reduce the gate leakage current. It is found that, metal-oxide-semiconductor field-effect transistors show higher barrier height, turn-on voltage, breakdown voltage, off-state voltage, output current and transconductance than metal-semiconductor field-effect transistors. In addition, the barrier height and turn-on voltage are increased with the increasing metal work function. However, the breakdown voltage is decreased with the increasing metal work function. All studied devices show good performances of high breakdown voltage, high output drain saturation and flat and wide transconductance operation regimes. The temperature-dependent behaviours are also studied. It is known from experimental results that In0.49Ga0.51P HFETs show good potentiality in high-temperature electronics applications.

InP/InGaAs double heterojunction bipolar transistor (DHBT) with an emitter tunneling barrier and composite collector structure

The DC performances of a novel InP/InGaAs double-heterojunction bipolar transistor (DHBT) with the undoped tunneling barrier and composite collector structure are studied and demonstrated. Due to the mass filtering effect for holes, a thin InP tunneling barrier can be used to replace the wide-gap emitter. Experimentally, an extremely small offset voltage of 25 mV and breakdown voltage BV/sub CEO/ of 9.2 V are obtained. Furthermore, the abrupt junction and /spl delta/-doping structure can eliminate the carrier blocking effect effectively when electrons are transported across the base-collector heterojunction. Meanwhile, the DC current gain is almost independent of the perimeter-to-area ratio of the emitter due to the low surface recombination.

A comparative study of GaAs- and InP-based superlattice emitter resonant tunneling bipolar transistors (SE-RTBT's)

Abstract The InP/InGaAs and InGaP/GaAs superlattice emitter resonant tunneling bipolar transistors (SE-RTBTs) have been fabricated and demonstrated. By the employment of five-period superlattice in the emitter layer, the RT effect in saturation regime is observed at 77 K for InP/InGaAs SE-RTBT. In addition, due to the larger valence band discontinuity ΔE V at InGaP/GaAs heterojunction, the RT effect is observed both in saturation and forward active regimes at 300 K for InGaP/GaAs SE-RTBT. The confinement effect for minority carriers is enhanced due to the insertion of superlattice. The common emitter current gains up to 170 and 220 are observed for InP/InGaAs and InGaP/GaAs SE-RTBTs, respectively. Lower offset voltages of about 125 mV are observed in the studied devices.

On the InGaP/InxGa1−xAs pseudomorphic high electron-mobility transistors for high-temperature operations

Abstract The high-temperature characteristics of a novel InGaP/In x Ga 1− x As pseudomorphic transistor with an inverted delta-doped channel are reported. Due to the presented wide-gap InGaP Schottky layer and the V-shaped In x Ga 1− x As channel structure, the degradation of device performance with increasing the temperature is not so significant. Experimentally, for a 1×100 μm 2 device, the gate–drain voltages at a gate leakage current of 260 μA /mm and the maximum transconductances g m,max are 30 (22.2) V and 201 (169) mS/mm at the temperature of 300 (450) K, respectively. Meanwhile, broad and flat drain current operation regimes for g m , f T and f max are obtained.

High-performance n/sup +/-GaAs/p/sup +/-In/sub 0.49/Ga/sub 0.51/P/n-GaAs high-barrier gate heterostructure field-effect transistor

A new heterostructure field-effect transistor (HFET) using an n/sup +/-GaAs/p/sup +/-In/sub 0.49/Ga/sub 0.51/P/n-GaAs high-barrier-gate structure has been fabricated successfully and demonstrated. The heavily doped p/sup +/-In/sub 0.49/Ga/sub 0.51/P layer is introduced to increase the barrier height and to suppress the tunneling current. Therefore, the leakage current is reduced and breakdown voltage is improved substantially. Experimentally, for a 1/spl times/100 /spl mu/m/sup 2/ device, a high gate-drain breakdown voltage of 52 V and high drain-source operation voltage of 20 V with low leakage current are obtained. The high breakdown characteristics of the studied device indicate that devices with n/sup +/-GaAs/p/sup +/-In/sub 0.49/Ga/sub 0.51/P/n-GaAs high-barrier-gate structure are suitable for high-power circuit applications.

InP/InGaAs heterojunction bipolar transistors with superlattice emitter structure

A heterojunction bipolar transistor with superlattice emitter structure based on InP/InGaAs material system has been demonstrated. Two devices with different period of superlattice and emitter thickness were proposed. By introducing the superlattice into the emitter, the confinement of holes is enhanced. Experimentally, for higher periods of superlattice, the current gain is enhanced and more stable temperature-dependent characteristics are observed. The common-emitter current gains up to 170 and 54 are obtained for the studied devices with emitter thickness of 800/spl Aring/ and 150/spl Aring/, respectively.