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A GaN-based Schottky diode synthesized with a hybrid surface structure is used to fabricate a new room-temperature (25 °C) hydrogen and ammonia gas sensor. This hybrid surface structure includes platinum (Pt) nanoparticle (NP)/SiO2 nanosphere (NS) mixtures and a Pt thin film. The employed hybrid surface structure can effectively increase the catalytic reactivity of the Pt metal and enhance the related gas-sensing characteristics. In the experiment, a higher sensing response of $7.3\times 10^{{5}}$ ( $2.1\times 10^{{1}}{)}$ is obtained under 1% H2/air (1000 ppm NH3/air) gas at 25 °C. Moreover, extremely low detecting levels of 100 ppb H2/air and 100 ppb NH3/air are acquired at 25 °C. The related hydrogen- and ammonia-sensing mechanisms are elucidated in this work. For wireless transmission and Internet of Things (IoT) application, the Kalman filter and shape-preserving piecewise cubic interpolation (SPPCI) algorithms are employed to substantially reduce redundant data and restore original results. More than 86.7% (97%) of the original data points are removed with a small mean recovery error (MRE) of 3% (0.3%) under 1% H2/air (1000 ppm NH3/air) gas at 25 °C.

A palladium (Pd) thin film is decorated on a radio frequency (RF) sputtered aluminum-doped zinc oxide (AZO) thin film to produce a hydrogen sensor. Due to the catalytic activity of the Pd metal, the studied thin film-based device shows remarkably enhanced hydrogen-sensing characteristics. Experimentally, a very high sensing response of $1.12\times 10 ^{4}$ with a response time of 23 s is obtained under 1% H2/air gas at 300 °C. Furthermore, even under an extremely low concentration of 40-ppb H2/air, a sensing response of 0.17 is acquired. The optimal operating temperature of the studied device is 300 °C. A hypothesis is used to interpret the related hydrogen-sensing mechanism of the studied device. A thermodynamic analysis is employed to study the surface coverage of hydrogen molecules on the device’s surface. Furthermore, for the application in wireless transmission of the Internet of Things (IoT), an interesting Kalman algorithm is used to reduce redundant data, save hardware costs, and reduce network congestion. The simulated results show that 93.9% of the redundant data can be removed. The studied device exhibits advantages of a simple structure, easy fabrication, low cost, a widespread sensing range of hydrogen concentration, a very high sensing response, and an extremely low detecting limit, as well as being suitable for IoT application.

An interesting ammonia (NH3) sensor based on a tungsten trioxide (WO3) thin film decorated with platinum (Pt) nanoparticles (NPs) is fabricated and demonstrated herein. Pt NPs are prepared by a rapid thermal evaporation (RTE) approach. The small size of these Pt NPs causes an increased surface area/volume ( ${S}_{A}/{V}$ ) ratio and enhanced sensing performance. The experimental results indicate good properties, including a higher sensing response of 72.61 under 1000 ppm NH3/air gas, a lower optimum operating temperature of 225 °C, and a lower detecting limit (≤ 1 ppm NH3/air). The studied device also has the advantages of a simple structure, easy fabrication, relatively low cost, a wide concentration detection range, and stable sensing performance. In addition, a first-order differential (FOD) and shape-preserving piecewise cubic interpolation (SPPCI) algorithms are employed to effectively reduce the redundant results and recover the reduced data for wireless transmission application. Thus, the studied Pt NP/WO3 thin film-based device shows a promise for high-performance ammonia sensing applications.

A hybrid structure of platinum nanoparticles (Pt NPs) and a Pt thin film are employed to fabricate a new Pt NP/Pt thin film/GaN-based Schottky diode-type ammonia sensor. Pt NPs are formed by a drop coating and UV illumination approach. The increased surface-area-to-volume ratio and “spillover” effect of Pt NPs are beneficial in ammonia sensing. Due to the synergistic catalytic activity of Pt NPs and Pt thin film, the studied device shows good ammonia sensing properties, including a high sensing response of 522.1 under 1000-ppm NH3/air gas at 473 K and an extremely low detecting level of 0.4-ppm NH3/air. A thermodynamic analysis is employed to study the related ammonia sensing mechanism. Furthermore, a Kalman filter and the related algorithm are introduced to effectively reduce the redundant data without affecting the original sensing results. Based on the good performance and advantages of a relatively simple structure and easy fabrication, the studied device is promising for ammonia sensing and wireless transmission applications.

We demonstrated the methylammonium lead iodide (CH3NH3PbI3) perovskite-based solar cells (SCs) with nickel (Ni)-oxidized nickel oxide (NiO x ) hole transport layer. The CH3NH3PbI3 perovskite-based SCs with Ni-oxidized NiO x have better short-circuit current density ( $J_{\rm SC})$ , open circuit voltage ( $V_{\rm OC})$ , and conversion efficiency ( $\eta $ %) than poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). In addition, the transmittance and work function increased with increasing oxidation temperature of Ni-oxidized NiO x layer. The larger transmittance and work function of Ni-oxidized NiO x could result in less light absorption and hole transport energy loss, respectively. Furthermore, Ni-oxidized NiO x at 450 °C shows the smoothest surface morphology, which could result in the spin-coated CH3NH3PbI3 perovskite film to have better crystal quality. Therefore, the SCs with 450 °C Ni-oxidized NiO x hole transport show the largest $\eta $ % of 7.75% that is $\sim 1.78$ times larger than that of SCs with PEDOT:PSS hole transport layer.

The hydrogen response characteristics and sensing properties or catalytic Pd/Al/sub 0.3/Ga/sub 0.7/As metal-oxide-semiconductor (MOS) and metal-semiconductor (MS) Schottky diodes are systematically studied. The effects of hydrogen adsorption on device performances such as the current-voltage characteristics, sensitivity, barrier height variation, heat of adsorption, and transient response are investigated. The studied devices can be operated under very wide hydrogen concentration regimes with remarkable hydrogen-sensing properties. Particularly, at an extremely low hydrogen concentration of 15 ppm H/sub 2//air, both steady-state and transient responses at room temperature can be detected. In addition, under the presence of oxide layer in the studied MOS device, a larger change of barrier height and higher hydrogen response are observed. In addition, according to the van't Hoff equation, the initial values of heat adsorption for Pd/semiconductor and Pd/oxide interface are calculated as 7.29 and 49.6 KJ/mole, respectively.

A new InGaP-InGaAs-GaAs double channel pseudomorphic high-electron mobility transistor (DC-PHEMT) has been fabricated successfully. The detailed temperature-dependent performance is investigated. The key features of the studied device are the use of an InGaAs DC structure, triple /spl delta/-doped carrier supplier layers and good Schottky behavior of the InGaP "insulator". For a 1-/spl mu/m gate length device, the turn-on voltage of 1.46 (1.16) V, gate leakage current of 60 [600] /spl mu/A/mm at V/sub GD/ = 15 V, maximum extrinsic transconductance of 162 [145] mS/mm with 310 [260] mA/mm broad operation regime (> 0.9g/sub m,max/), output conductance of 0.41 (0.43) mS/mm, and voltage gain of 390 [335] are obtained at T = 300 [480] K, respectively. In addition, good microwave performance with a flat and wide operation regime is obtained.

The temperature-dependent characteristics of an n+-InGaAs/n-GaAs composite doped channel (CDC) heterostructure field-effect transistor (HFET) have been studied. Due to the reduction of leakage current and good carrier confinement in the n+-InGaAs/n-GaAs CDC structure, the degradation of device performances with increasing the temperature is insignificant. Experimentally, for a 1 x 100 μm2 device, the gate-drain breakdown voltage of 24.5 (22.0) V, turn-on voltage of 2.05 (1.70) V, off-state drain-source breakdown voltage of 24.4 (18.7) V, transconductance of 161 (138) mS/mm, output conductance of 0.60 (0.60) mS/mm, and voltage gain of 268 (230) are obtained at 300 (450) K, respectively. The shift of Vth from 300 to 450 K is only 13 mV. In addition, the studied device also shows good microwave performances with flat and wide operation regime.

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.

Two InGaP/GaAs resonant tunneling bipolar transistors (RTBTs) with different superlattice (SL) structures in the emitters are fabricated and studied. The uniform and modulated widths of barriers are respectively utilized in the specific SL structures. Based on the calculations, the ground state and first excited state minibands are estimated from the transmission probability. The electron transport of RT through SL structures is significantly determined by the electric field behaviors across the barriers. Experimentally, the excellent transistor characteristics including the small saturation voltage, small offset voltage and high breakdown voltages are obtained due to the insertion of /spl delta/-doping sheet at the base-collector (B-C) heterointerface. Furthermore, at higher current regimes, the double- and quaternary-negative difference resistance (NDR) phenomena are observed in agreement with the theoretical prediction at 300 K.

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.

A new field-effect transistor using a high-barrier n/sup +/ -GaAs/p/sup +/-InGaP/n-GaAs camel-like gate and GaAs/InGaAs heterostructure-channel has been fabricated successfully and demonstrated. Experimentally, an ultra high gate-drain breakdown voltage of 52 V, a high drain-source operation voltage over 20 V with low leakage currents, and a high drain-source off-state breakdown voltage of 39.7 V are obtained for a 1/spl times/100 /spl mu/m/sup 2/ device. The high breakdown behavior is attributed to the use of high barrier camel-like gate and heterostructure channels to reduce the undesired leakage current. Furthermore, the studied device also shows high breakdown behavior in a high temperature environment and good microwave characteristics. Therefore, based on these characteristics, the studied device is suitable for high-breakdown, low-leakage, and high-temperature applications.

A novel multiple-state switching device based on an InP/AlInGaAs heterojunction bipolar transistor (HBT) structure has been successfully fabricated and demonstrated. The common-emitter current gain up to 25 is obtained under the forward operation mode. However, the anomalous multiple-negative-differential-resistance (MNDR) phenomena controlled either by electrical or optical input signals are observed under the inverted operation mode. The studied device exhibits a single-route S-shaped NDR behavior in the dark and a distinct significant S-shaped MNDR phenomena by introducing an incident light source at room temperature. Moreover, the anomalous multiple-route and multiple-step current-voltage (I-V) characteristics are also observed at 77 K. The switching behaviors are attributed to the avalanche multiplication, barrier lowering effect and potential redistribution process. Experimental results show that the studied device provides a good potentiality for multiple-valued logic and optoelectronic switching system applications.

A novel double ion-implant Ti-salicide technology combining As pre-amorphization implant plus Si ion-mixing implant without the additional lithography process has been developed successfully and reported. Based on this technology, the good performances of uniform Ti-silicide formation, low and narrow distribution of sheet resistances both on n/sup +//p/sup +/ poly-gate and source/drain diffusion layers, and lower leakage currents in the n/sup +//p-well and p/sup +//n-well junctions are obtained simultaneously. In addition, excellent behavior of a 0.24-/spl mu/m NMOSFET and PMOSFET fabricated by this technology are also achieved.