Kuei-Yi Chu

Hydrogen Sensing Characteristics of a Pd/AlGaN/GaN Schottky Diode

In this paper, the interesting hydrogen sensing properties of a Pd-gate AlGaN/GaN Schottky diode are investigated. A significantly low detection limit of 850 ppb H2/air gas can be observed with increasing the temperature to 423 K. The experimental results indicate that hydrogen molecules cause great influences on the diode breakdown voltage. Also, the diode exhibits an ultrahigh sensing response of 2.04×105 at 423 K when exposure to a 9660 ppm H2/air gas. The transient response time and reversibility of the studied device can be improved by increasing the operating temperature.

Hydrogen sensing properties of a Pt-oxide-GaN Schottky diode

The interesting hydrogen sensing properties of a Pt-oxide-GaN metal-oxide-semiconductor-type Schottky diode are comprehensively studied and demonstrated. In the hydrogen-containing environment, the shift in current-voltage curves and decrease in turn-on voltage are found to be caused by the lowering of Schottky barrier height. Also, the corresponding series resistance is decreased from 191.8 (in air) to 155.3 Ω (for a 9970 ppm H2/air gas) at 30 °C. As the carrier gas is replaced by a nitrogen gas, a significant variation of 0.32 V and 19.56 Ω in the turn-on voltage Von and series resistance Rs values, respectively, is obtained at 30 °C, even at an extremely low hydrogen concentration of 4.3 ppm H2/N2. Since the oxygen atoms will be dissolved on the Pt metal surface and react with hydrogen atoms by the formation of hydroxyl and water, the number of adsorbed hydrogen atoms on the Pt surface is reduced. Moreover, the shorter response time constant and the larger initial rate of current density variation are ...

Further Suppression of Surface-Recombination of an InGaP/GaAs HBT by Conformal Passivation

Conformal passivation on an InGaP/GaAs HBT with significant reduction in the base surface-recombination effect is demonstrated. Not only dc behaviors but also RF performances are remarkably improved compared with the conventional emitter-ledge structure. Based on the conformal passivation, i.e., the base surface is covered by the depleted InGaP ledge structure and sulfur ((NH4)2Sx ) treatment, lower base surface-recombination current density, lower specific contact resistance, lower sheet resistance, higher current gain, higher collector current, and higher maximum oscillation frequency are obtained

Improved dc and microwave performance of heterojunction bipolar transistors by full sulfur passivation

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.

Improved Current-Spreading Performance of an InGaN-based Light-Emitting Diode with a Clear P-GaN/N-GaN Barrier Junction

The InGaN-based light-emitting diode (LED) with a clear p-GaN/n-GaN barrier junction is fabricated and investigated. Due to the built-in potential induced by this junction, superior current spreading performance is achieved. In addition, the suppression of current crowding phenomenon yields the reduced parasitic effect. Therefore, under an injection current of 20 mA, improved behaviors including lower turn-on voltage, lower parasitic series resistance, and significantly enhanced electrostatic discharge (ESD) performance are presented.

The Effect of Sulfur Treatment on the Temperature-Dependent Performance of InGaP/GaAs HBTs

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

A Hydrogen Gas Sensitive Pt – In0.5Al0.5P Metal-Semiconductor Schottky Diode

A new and interesting compound semiconductor Schottky diode hydrogen sensor based on a Pt-In0.5Al0.5P metal-semiconductor (MS) structure is fabricated and demonstrated. The hydrogen sensing characteristics including hydrogen detection sensitivity of the studied device under different hydrogen concentrations and temperature are measured and studied. The hydrogen detection sensitivity is related to a change in the contact potential at the Pt-semiconductor interface. Experimentally, the studied hydrogen sensor can be operated systematically under the applied bi-polarity voltage biases. When the temperature is increased from 30 to 250degC, the hydrogen relative sensitivity ratio (Sr), under the applied forward (reverse) bias of 0.3 V, is decreased from 181.2% (250.3%) to 28.2% (33.5%) upon exposing to the 9970 ppm H2/air gas. Moreover, the hydrogen effect in the Schottky barrier height lowering is observed.

Comparative study on temperature-dependent characteristics of InP∕InGaAs single- and double-heterojunction bipolar transistors

Interesting temperature-dependent characteristics of InP∕InGaAs-based single-heterojunction bipolar transistor (SHBT) and double-heterojunction bipolar transistor (DHBT) devices are compared and studied. Experimentally, both studied devices show wider collector current (IC) operation regions, with over 11 decades in magnitude of collector current (IC=10−12to10−1A). However, the studied DHBT exhibits improved breakdown characteristics [common-emitter breakdown voltage (BVCEO)=8.05V and common-base breakdown voltage (BVCBO)=11.3V] and low output conductance at high temperature. Moreover, the undesired current-blocking effect, switching, hysteresis phenomenon usually found in an InP∕InGaAs conventional DHBT are not observed in the DHBT device. As compared with the studied SHBT, the studied DHBT shows a lower multiplication factor and weaker temperature dependence. Therefore, it is known that, based on experimental results, the studied DHBT device provides the promise for low-voltage and low-power circuit app...

On the Hydrogen Sensing Behaviors of an InAlAs-Based Schottky Diode with a Thin Pt Catalytic Metal

A hydrogen sensor based on a Pt/In0.52Al0.48As Schottky diode with a thin (50 A) Pt catalytic metal is studied and presented. Because of the inherent properties of Pt (high work function) and In0.52Al0.48As (large bandgap), the studied device demonstrates considerable benefits including low hydrogen gas detection limit (<14 ppm H2/air), high sensitivity (1974% under 9970 ppm H2/air gas), wide operating temperature range (≥160 °C), fast response time (≤4 s), and widespread reverse voltage operating regime (-0.5 to -5 V). In addition, surface morphology and piezoelectric effect play key roles in the hydrogen sensing performance. Compared with similar devices with thicker (100 A) Pt metal, the studied sensor device exhibits a higher hydrogen detection sensitivity under lower hydrogen concentration (≤1000 ppm H2/air) environments.

Effect of Nonannealed Ohmic-Recess Structure on Temperature-Dependent Characteristics of Metamorphic High-Electron-Mobility Transistors

The interesting temperature-dependent characteristics of an In 0.5 Al 0.5 As/In 0.5 Ga 0.5 As metamorphic high-electron-mobility transistor (MHEMT) using the nonannealed and ohmic-recess (NAOR) technique to reduce parasitic resistance are comprehensively studied and demonstrated. The proposed NAOR technique could reduce the parasitic resistance caused by large conduction-band discontinuity at InAlAs/InGaAs interface. Therefore, the improvement of device performance in terms of dc and parasitic resistance as well as radio frequency characteristics can be expected. In particular, as compared with the traditional MHEMT device, the higher gate/drain breakdown voltage of 22.93 (16.89) V, lower gate leakage current of 0.83 (259) μA/mm at V GD = -14 V, higher drain saturation current of 327 (299) mA/mm, higher maximum transconductance of 302.4 (269.6) mS/mm, and lower parasitic resistance of 1.67 (2.02 Ω mm) are obtained, respectively, for the studied NAOR device at 300 (500) K. The corresponding unity current gain cutoff frequency f T (maximum oscillation frequency f max ) are 21.4 (65.5) and 19.3 (55.5) GHz at 250 and 400 K, respectively. Moreover, the relatively lower variations of device performance over a wide temperature range (300-500 K) are obtained.