Chun-Yuan Chen

Characteristics of Pd/InGaP Schottky diodes hydrogen sensors

Pd/InGaP hydrogen sensors based on the metal-oxide-semiconductor (MOS) and metal-semiconductor Schottky diodes have been fabricated and systematically studied. The effects of hydrogen adsorption on device performances such as the current-voltage characteristics, barrier height variation, hydrogen coverage, and heat of adsorption are investigated. The studied devices exhibit very wide hydrogen concentration detection regimes and remarkable hydrogen-sensing properties. Particularly, an extremely low hydrogen concentration of 15 ppm H/sub 2//air at room temperature can be detected. In addition, under the presence of oxide layers in the studied MOS device structure, the enhancements of barrier height and high-temperature operating capability are observed. The initial heat of adsorption for Pd/oxide and Pd/semiconductor interface are calculated as 355 and 65.9 meV/atom, respectively. Furthermore, the considerably short response times are found in studied devices.

A new Pd-oxide-Al/sub 0.3/Ga/sub 0.7/As MOS hydrogen sensor

A new and interesting Pd-oxide-Al/sub 0.3/Ga/sub 0.7/As MOS hydrogen sensor has been fabricated and studied. The steady-state and transient responses with different hydrogen concentrations has been measured at various temperatures. Based on the large Schottky barrier height and presence of oxide layer, the studied device exhibits a high hydrogen detection sensitivity and wide temperature operating regime. The studied device exhibits the low-leakage current and obvious current changes when exposed to hydrogen-contained gas. Even at room temperature, a very high hydrogen detection sensitivity of 155.9 is obtained when a 9090 ppm H/sub 2//air gas is introduced. Furthermore, when exposed to hydrogen-contained gas at 95/spl deg/C, both the forward and reverse currents are substantially increased with increased hydrogen concentration. In other words, the studied device can be used as a hydrogen sensor under the applied bidirectional bias. Under the applied voltage of 0.35 V and 9090 ppm H/sub 2//air hydrogen ambient, a fast adsorption response time about 10 s is found. The transient and steady-state characteristics of hydrogen adsorption are also investigated.

A hydrogen sensing Pd/InGaP metal-semiconductor (MS) Schottky diode hydrogen sensor

An interesting hydrogen sensing Pd/InGaP metal-semiconductor (MS) Schottky diode has been fabricated and studied. Both the steady state and the transient condition of the hydrogen adsorption process are investigated. Even at room temperature, an extremely low hydrogen concentration of 15 ppm H2/air can be detected. In addition, the wide operating temperature range of 250 K of the studied Pd/InGaP hydrogen sensor is found. From experimental results, it is shown that the variation of Schottky barrier height increases with the increase of the operating temperature and hydrogen concentration. As the operation temperature is elevated, the water formation effect is also studied in the quasi-equilibrium region under the transient condition.

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.

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.

Comprehensive study of InGaP/AlxGa1-xAs/GaAs heterojunction bipolar transistors with different doping concentrations of AlxGa1-xAs graded layers

The performances of InGaP/AlxGa1−xAs/GaAs heterojunction bipolar transistors (HBTs) with different doping concentrations of AlxGa1−xAs graded layers are theoretically studied. The use of the AlxGa1−xAs graded layer plays a key role in affecting the direct current and radio frequency performances of the studied HBTs. It is found that the studied devices with suitable doping concentrations of AlxGa1−xAs graded layers exhibit lower offset voltages, saturation voltages, and base and collector current ideality factors. Furthermore, due to the use of proper doping concentrations of AlxGa1−xAs graded layers, the studied devices show high values of the unity current gain cut-off frequency (fT) and maximum oscillation frequency (fmax). It is known that, from the theoretical analysis, the appropriate doping concentration of the AlxGa1−xAs graded layer is 1 × 1016 to 1 × 1018 cm−3. Consequently, this work is promising for device engineers to design high-performance HBT structures.

Characteristics of a new camel-gate field effect transistor (CAMFET) with a composite channel structure

A new camel-gate field effect transistor (CAMFET) with a composite channel structure has been fabricated and demonstrated. Due to the n+-InGaP/p+-InGaP/GaAs camel gate and InGaAs/GaAs composite channel structures employed, good device performance is observed. Experimentally, at room temperature, a gate-drain breakdown voltage over 15 V, maximum transconductance gm,max of 111.5 mS mm?1, voltage gain AV of 93.4, unity current gain cut-off frequency fT of 16.2 GHz and maximum oscillation frequency unity fmax of 24.2 GHz are obtained simultaneously for a 1 ? 100 ?m2 device. The studied device also shows good properties in a higher temperature regime. Moreover, the studied device exhibits relatively negligible temperature-dependent characteristics over the operating temperature range from 300 to 420 K. Therefore, the studied device provides promise for high-temperature and high-performance microwave electronic 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 .

Comparative studies of InP/InGaAs single and double heterojunction bipolar transistors with a tunnelling emitter barrier structure

The DC performances of InP/InGaAs single and double heterojunction bipolar transistors (SHBT and DHBT) are compared and studied. The temperature-dependent characteristics of both devices are also presented. Due to the use of a 4000 A InP collector, the studied DHBT exhibits a higher breakdown voltage than the SHBT. The common-emitter breakdown voltages of the studied SHBT and DHBT are higher than 2 and 10 V, respectively. In addition, based on the employment of a tunnelling emitter barrier, the emitter injection efficiency is improved substantially, so a very low offset voltage (<50 mV) is obtained for the studied SHBT device. Furthermore, the common-emitter DC current gain of the studied SHBT is relatively independent of the temperature at low and middle current regimes. On the other hand, the studied DHBT has a smaller current gain due to the collector current blocking effect described.

Temperature-dependent dc characteristics of an InGaAs∕InGaAsP heterojunction bipolar transistor with an InGaAsP spacer and a composite-collector structure

The temperature-dependent dc characteristics of an interesting heterojunction bipolar transistor with an InGaAsP spacer and an InGaAs∕InGaAsP composite-collector structure are studied and demonstrated. By employing the intermediate band-gap In0.72Ga0.28As0.61P0.39 material at the emitter-base and base-collector heterojunction, the electron blocking effect is effectively eliminated. The studied device gives the promising dc performances including the small offset and saturation voltages without degrading the breakdown behaviors. The typical incremental current gain of 114 and the maximum dc current gain of 118 are obtained. It is worthwhile to note that the desired current amplification over 11 decades of the magnitude of collector current IC is obtained in the studied device. Moreover, the switching or hysteresis phenomenon usually observed in InP-based devices is not seen in the studied device.