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The interesting hydrogen sensing performances of a Pt-oxide-AlGaAs (MOS) high electron mobility transistor (HEMT) are studied and demonstrated. The effects of hydrogen adsorption on device performances such as the threshold voltage shift ΔVth, drain saturation current variation ΔIDS, and transient response are presented. ΔVth and ΔIDS decreased with increasing operating temperature. This suggests that, at higher temperature, less hydrogen atoms diffuse through the Pt bulk and reach the interface between the Pt metal and oxide layer resulting from the relatively faster formation rate of hydroxyl on the Pt surface. The response curves of the studied Pt-AlGaAs MOS HEMT show various profiles at different temperatures. The influences of hydrogen concentration and temperature on the interface sites occupied by adsorbed atoms are also studied.

A new hydrogen sensor based on a GaAs-based high electron mobility transistor (HEMT) with a catalytic Pt-oxide-Al0.24Ga0.76As (MOS) gate structure is fabricated and demonstrated. The threshold voltage shift, hydrogen detection sensitivity, and transient responses of the device under different hydrogen concentrations and temperature are measured and studied. Based on the transistor amplification action, even at an extremely low hydrogen concentration of 14ppm H2/air, the studied device shows significant drain current variation (about 0.12mA). Furthermore, the studied device can be operated under wider operating temperature regimes with remarkable hydrogen-sensing properties. The decreased hydrogen detection capability with increasing operating temperature demonstrates the exothermic reaction of the hydrogen adsorption and desorption processes.

For enhancing hydrogen detecting ability. a high-performance hydrogen sensor based on a high electron mobility transistor structure by utilising a Pd/oxide/Al 0.24 Ga 0.76 As MOS structure is fabricated and investigated. At different temperatures, hydrogen-sensing characteristics of the studied device under steady- and transition-state with different concentration hydrogen gases are measured. Even at an extremely low hydrogen concentration of 4.3 ppm H 2 /air, the current modulation can be found significantly. Furthermore, in comparison with other FET-type hydrogen sensors, under 9970 ppm H 2 /air, the studied device exhibits a much shorter response time of 10.95 s.

The dc performances of an interesting InP/InGaAs tunneling-emitter bipolar transistor (TEBT) with double heterostructures are studied and demonstrated. The studied device has a higher breakdown voltage than conventional InP single heterojunction bipolar transistors between the collector and base. The base–collector junction breakdown voltage VBR up to 15.6 V is obtained. Both of the common-emitter and common-base breakdown voltages of the studied device are higher than 10 V. Furthermore, low variations of dc current gains are found as the temperature is increased from 25 to 175 °C. The elimination of knee-shaped characteristics and near unity ideality factors of collector and base currents (ηC and ηB) are obtained due to the use of a δ-doping sheet and spacer layer. In addition, the studied TEBT device has a stable dc current gain distributed regime as the temperature is increased from 25 to 175 °C.

A highly hydrogen-sensitive Pd/InP metal-oxide-semiconductor (MOS) Schottky diode hydrogen sensor is presented. The role of donor level in the interfacial oxide layer replacing the amphoteric native defects leads to enhanced barrier height and high sensitivity. According to reaction kinetics studies, the maximum change in barrier height achieves 0.31 eV. Short response and recovery times in the transient characteristics demonstrate the high hydrogen adsorption and desorption rates at high temperatures.

The temperature dependence of gate current and breakdown behavior in an n+-GaAs/p+-InGaP/n--GaAs high-barrier gate field-effect transistor has been studied and demonstrated. Due to the presence of an n+-GaAs/p+-InGaP/n--GaAs high-barrier gate structure, the device shows high-breakdown characteristics. In addition, we found that the off-state breakdown voltage BV DS is dominated by channel and gate breakdowns at T=300 to 420 K, and gate current I G comes mainly from the tunneling mechanism within this temperature range. However, as the temperature is increased above 420 K, the I G is seriously affected by the substrate leakage current and BV DS is only dominated by gate breakdown.

A novel InGaP/GaAs camel-like field-effect transistor (HFET) has been fabricated successfully and demonstrated. Because of the use of an n/sup +/-GaAs/p/sup +/-InGaP/n-GaAs camel-like gate and GaAs/InGaAs double channel, the gate barrier height and carrier confinement are improved. Therefore, low-leakage and high-breakdown characteristics are obtained. Experimentally, this device provides high-breakdown characteristics and good device performance over a wider temperature operation range of 30-210/spl deg/C. Therefore, the studied InGaP/GaAs structure is suitable for high-power and high-temperature applications.

An interesting multiple negative-differential-resistance (NDR) phenomenon is observed in AlGaAs/InGaAs/ GaAs heterostructure bipolar transistors with abrupt or graded AlGaAs confinement layers under the inverted operation mode. The switching behaviors are mainly due to avalanche multiplication and a two-stage barrier lowering effect. The switching properties of the first S-shaped NDR observed in the device with the abrupt confinement layer are better than those observed in the device with the graded confinement layer, due to the former device's superior confinement effect on holes and electrons. The control voltage efficiency of the second S-shaped NDR is nearly equal in the studied devices because the InGaAs quantum well dominates the properties of this NDR.

A new high performance field-effect transistor using step-doped n-In0.15Ga0.85As channels was fabricated and demonstrated. For a 1 × 100 µm2 device, a high gate breakdown voltage of 15 V, a maximum drain saturation current of 735 mA/mm, a maximum transconductance of 200 mS/mm, and a wide gate voltage range > 3 V, with the transconductance > 60 mS/mm, are obtained.

Language, writing, and the computer, as Wang (1986) states, must rank among the highest of our most important inventions since each has profoundly determined the development of the human species. There have been numerous interactions among these three types of human institutions. Writing, of course, is largely a reflection of language. Since its inception four decades ago, the computer has depended on various forms of language and writing to communicate with its human creators. Some of these forms were specially invented programming languages for a small breed of people.