Shiou-Ying Cheng

Hydrogen-sensitive characteristics of a novel Pd/InP MOS Schottky diode hydrogen sensor

Steady-state and transient hydrogen-sensing characteristics of a novel Pd/InP metal-oxide-semiconductor (MOS) Schottky diode under atmospheric conditions are presented and studied. In presence of oxide layer, the significant increase of barrier height improves the hydrogen sensitivity even at lower operating temperatures. Even at a very low hydrogen concentration environment, e.g., 15 ppm H/sub 2/ in air, a significant response is obtained. Two effects, i.e., the removal of Fermi-level pinning caused by the donor level in the oxide and the reduction of Pd metal work function dominate the hydrogen sensing mechanism. Furthermore, the reaction kinetics incorporating the water formation upon hydrogen adsorption is investigated. The initial heat of adsorption for the Pd/oxide interface is estimated to be 0.42 eV/hydrogen atom. The coverage dependent heat of adsorption plays an important role in hydrogen response under steady-state conditions. In accordance with the Temkin isotherm behavior, the theoretical prediction of interface coverage agrees well with the experimental results over more than three decades of hydrogen partial pressure.

Influences of sulfur passivation on temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs PHEMT

The influences of (NH/sub 4/)/sub 2/S/sub x/ 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/spl times/100 /spl mu/m/sup 2/ 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) /spl mu/A/mm at V/sub GD/=-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 (>0.9g/sub m,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 f/sub T/ (maximum oscillation frequency f/sub max/) are 22.2 (87.9) and 19.5 (59.3) GHz at 250 and 400 K, respectively, with considerably broad operating regimes (>0.8f/sub T/,f/sub max/) larger than 455 mA/mm. Moreover, the relatively lower variations of device performances over wide temperature range (300/spl sim/510 K) are observed.

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 InGaP/GaAs S-shaped negative-differential-resistance (NDR) switch for multiple-valued logic applications

In this paper, a novel InGaP/GaAs multiple S-shaped negative-differential-resistance (NDR) switch based on a heterostructure-emitter bipolar transistor (HEBT) structure is fabricated and demonstrated. An interesting multiple NDR phenomenon resulting from an avalanche multiplication and successive two-stage barrier lowering process is observed under the inverted operation mode. The three-terminal-controlled and temperature-dependent NDR characteristics are also investigated. In addition, a typical transistor performance is found under the normal operation mode. Consequently, owing to the presented different stable operation points and transistor action, the studied device shows a good potential for multiple-valued logic and analog amplification circuit applications.

Influences of surface sulfur treatments on the temperature-dependent characteristics of HBTs

The temperature-dependent DC characteristics of InGaP-GaAs heterojunction bipolar transistors with and without sulfur treatment are systematically studied and demonstrated. Due to the use of sulfur passivation, the series resistance of base-emitter junction of studied device can be effectively reduced. In addition, the device with sulfur treatment can be operated under ultra low collector current regimes (I/sub C//spl les/10/sup -11/ A). Experimentally, a long-time sulfur treatment is not appropriate. In this work, the studied device with sulfur treatment for 15 min is a good choice. Furthermore, at measured temperature (298 K-398 K), the studied device with sulfur treatment can reduce collector-emitter offset voltage and the impact of emitter size effect. Moreover, as the temperature is increased, the device with sulfur treatment will exhibit higher DC current gain and more stable temperature-dependent performances. This will extend the application regimes of the studied device in low-power and communication systems.

Comprehensive study of an InGaP/AlGaAs/GaAs heterojunction bipolar transistor with a continuous conduction-band structure

A newly designed In0.49Ga0.51P/AlxGa1−xAs/GaAs heterojunction bipolar transistor with a continuous conduction-band structure is theoretically analysed and investigated. By introducing a compositionally linear-graded AlGaAs layer into conventional InGaP/GaAs heterojunctions, a zero conduction-band discontinuity and a completely deleted potential spike can be obtained. Due to the suppression of potential spikes at the emitter/base junction, the studied device shows better dc performances such as a lower offset voltage (≤25 mV), lower saturation voltage (≤0.3 V), uniform current gain (~40) and lower turn-on voltage (~1.15 V). In addition, better ac performances are achieved. Consequently, the designed structure provides promise for high-performance analogue, digital and microwave device applications.

Temperature-dependent investigation of a high-breakdown voltage and low-leakage current Ga/sub 0.51/In/sub 0.49/P/In/sub 0.15/Ga/sub 0.85/As pseudomorphic HEMT

We reported a newly designed double delta-doped GaInP/InGaAs pseudomorphic HEMT with high temperature-dependent performances. In addition to the novel aspects of the proposed HEMT structure, temperature-dependent behaviors including a high-voltage (40 V) and a low-leakage current (17 nA/mm) are further improved by eliminating mesa-sidewall effect. We obtained nearly current-independent transconductance in the temperature of 300-450 K. The measured current gain cutoff frequency f/sub T/ and maximum oscillation frequency f/sub max/ for a 1-/spl mu/m gate device are 12 and 28.4 GHz, respectively.

Temperature-dependence investigation of a high-performance inverted delta-doped V-shaped GaInP/In/sub x/Ga/sub 1-x/As/GaAs pseudomorphic high electron mobility transistor

A newly designed inverted delta-doped V-shaped GaInP/In/sub x/Ga/sub 1-x/As/GaAs pseudomorphic high electron mobility transistor (PHEMT) has been successfully fabricated and studied. For a 1/spl times/100 /spl mu/m/sup 2/ device, a high gate-to-drain breakdown voltage over 30 V at 300 K is found. In addition, a maximum transconductance of 201 mS/mm with a broad operation regime for 3 V of gate bias (565 mA/mm of drain current density), a very high output drain saturation current density of 826 mA/mm, and a high DC gain ratio of 575 are obtained. Furthermore, good temperature-dependent performances at the operating temperature ranging from 300 to 450 K are found. The unity current gain cutoff frequency f/sub T/ and maximum oscillation frequency f/sub max/ up to 16 and 34 GHz are obtained, respectively. Meanwhile, the studied device shows the significantly wide and flat gate bias operation regime (3 V) for microwave performances.

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

DC characterization of an InP-InGaAs tunneling emitter bipolar transistor (TEBT)

The dc performances of a novel InP-InGaAs tunneling emitter bipolar transistor (TEBT) are studied and demonstrated. The studied device can be operated under an extremely wide collector current regime larger than 11 decades in magnitude (10/sup -12/ to 10/sup -1/ A). A current gain of 3 is obtained even operated at an ultralow collector current of 3.9/spl times/10/sup -12/ A (1.56 /spl times/10/sup -7/ A/cm/sup 2/). The common-emitter and common-base breakdown voltages of the studied device are higher than 2 and 5 V, respectively. Furthermore, a very low collector-emitter offset voltage of 40 mV is found. The temperature-dependent dc characteristics of the TEBT are measured and studied. Consequentially, based on experimental results, the studied device provides the promise for low-power electronics applications.