Search

全天空短波輻射量為主要的常規氣象觀測參數之一，此資料廣泛應用於氣候變遷與太陽能應用領域。自2002年起，中央氣象局於各局屬氣象站全面更新為Eppley公司出產的 Precision Spectral Pyranometer (PSP)進行觀測，屬於具有高準確度符合A級(class A)之輻射計，然而，未搭配統一的校正程序及資料品管流程(Quality Control, QC)，以致資料應用上產生疑慮。因此，本研究建置一套適合臺灣氣象局輻射資料之QC流程，檢視2002至2020年共達19年，30個局屬氣象站地面自動氣象觀測系統(ASOS)之全天空短波輻射資料，標註可疑或異常的觀測資料，並給予資料相對應之旗標(Flag 0-7)，以提升大氣輻射資料的可用性。 長期資料品管流程可分為兩階段檢驗流程，第一階段以單站長期資料進行處理，先濾除異常值後，進行物理可能極限(Physically Possible Limits)與極端最小極限(Extremely Rare Minimum Limits)檢定，用以偵測資料中異常大的誤差值與較大的隨機誤差，此階段30個局屬站之資料品保可用率皆超過90%，接著進行每日氣候最大值(Daily Climate Maximum)檢定，檢視資料於連續6個月期間，掌握是否存在儀器老化、校正係數偏離、儀器毀損故障等情形，扣除有上述疑慮之資料後，各測站之資料品保可用率下降至53-95%之間，其中校正係數偏離是影響資料品質的主要原因，凸顯定期校正輻射儀器之重要性。第二階段為使用第一階段篩選出的高品質資料，進一步加入鄰近測站倆倆進行相關性及時序比較，我們進一步檢查出資料處理器(data logger)所記錄的異常值，並予以濾除；同時在這個階段我們也加入人工判定，註記有疑慮的觀測資料區間。最後，本研究以2020年為基礎，比對QC後高品質地面觀測資料與Himawari-8衛星反演日射量差異，結果顯示兩者的相關係數高達0.96，各月的相關係數介於0.94至0.97。進一步檢驗衛星反演在時空上的表現，結果顯示，在花蓮地區衛星反演比地面觀測高約27.9%，北部地區則有約4.6%的低估，月份上，偏高情形以3月的6.5%最為明顯，整體來說，衛星反演相比地面觀測普遍呈現高估的情形。本研究發展出一套嚴格的輻射資料QC流程，確認過去長達19年的地表太陽輻射資料可靠度，有利於後續科學研究發展。 Solar shortwave irradiance is one of the main conventional meteorological observation parameters which is widely used in the fields of climate change and solar energy. Since 2002, the Central Weather Bureau (CWB) in Taiwan has upgraded its weather stations’ pyranometer with the Precision Spectral Pyranometer (PSP) manufactured by Eppley Company. The PSP is a class A pyranometer with high accuracy. However, the lack of complete procedures for calibration and data quality control (QC) has led to doubts about the data usage. Therefore, this study aims to establish a research-based QC procedure for the solar radiation data obtained from 30 weather stations of CWB in 2002 to 2020 (a total of 19 years). Suspicious or abnormal data are given corresponding flags (Flag 0-7) which can serve as a guidance to users who using the data set. The long-term data quality control procedure we developed can be divided into a two-stage inspection process. The first stage is to process long-term data station-by-station. For any station, the procedure starts with filtering out abnormal values, then the Physically Possible Limits and Extremely Rare Minimum Limits are applied, these two limits testing are used to detect abnormally large error values and large random errors in the data. At this stage, the data quality assurance availability rate of the 30 weather stations is all greater than 90%. Finally, the Daily Climate Maximum test (i.e., verifying within 6 consecutive months, whether there exists a circumstance of instrument aging, calibration coefficient drafting, instrument damage, etc.) is applied. After removing the data with the above test, the data quality assurance availability rate of each weather station drops to 53-95%. It is worth to mention that the calibration coefficient drafting is the main reason that affects the quality of the data. It highlights the necessary of a periodic calibration for solar radiation instruments in the network. For the second stage, we used the high-quality data screened in the first stage, and further diagnose the correlation and liner regression between two adjacent stations. We accidentally found the outliers recorded by the data logger. The bad data has been filtered out from the data set. In this stage, we also considered a manual judgment and marked the questionable data. In this study, we further compared the high-quality surface solar radiation data (applied abovementioned QC procedure) with the data retrieved from Himawari-8 satellite in 2020. The results show that the overall correlation coefficient between the two data sets is extremely high, up to 0.96. The correlation coefficient among each month ranges from 0.94 to 0.97. Overall, the satellite retrieved data shows overestimation. A largest overestimation was found for Hualien region (27.9%), while for the northern region tends to underestimation (4.6%) as compared with observation. For monthly comparison, the month of March revealed a larger overestimation of 6.5%. This study has developed a strict QC process for surface solar radiation data and has reviewed the data reliability for the past 19 years. The high-quality data produced from this study is beneficial to the development of subsequent scientific research. &nbsp

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.

A platinum (Pt) catalytic metal and a hydrogen peroxide oxidation approach are utilized to fabricate a hydrogen sensor based on a GaN Schottky diode. The presence of a gallium oxide dielectric layer between the Pt metal and the GaN surface can increase the adsorption sites for dissociated hydrogen species, thereby improving the related sensing ability towards hydrogen gas. Experimentally, under introduced 1% hydrogen/air gas, the studied device shows a high sensing response ratio of 1.03 × 105 at 300 K. In addition, the lowest detecting level of 1 ppm hydrogen at 300 K is obtained. This device also exhibits good high-temperature durability (≥573 K) and a high sensing speed. The response (recovery) time constant at 300 K is only 74 (103) sec even under a very low hydrogen concentration of 1 ppm; these time constant values are much smaller than those of palladium metal-based sensors. Under the 1% hydrogen/air, the response (recovery) time constant at 300 K is drastically reduced to 15 (19) sec. Furthermore, in order to improve the feasibility of transmitting the sensing data, the concept of linear differentiation method is employed to eliminate redundant data. The simulation result shows that the average of the reduced ratios can achieve 77.88%. Therefore, this Schottky diode device not only shows promise to detect hydrogen gas, but also can be utilized effectively in the transmission of sensing data.

A GaN-based Schottky diode incorporating a catalytic Pt thin film and a GaOx dielectric is demonstrated for ammonia (NH3) gas sensing. The GaOx dielectric is formed by a proper hydrogen peroxide (H2O2) treatment on the GaN surface. Based on the effective dissociation of ammonia molecules on Pt surface and suppressed leakage current resulting from the presence of GaOx oxide, the studied Pt/GaOx/GaN Schottky diode exhibits good ammonia sensing performance. Experimentally, a very high sensing response of 252 under 1000 ppm NH3/air gas and an extremely low detection level of 0.4 ppm NH3/air are obtained at 473K, the optimal operating temperature. The sensing speed can be enhanced with an increase in temperature and ammonia concentration. The related response and recovery time constants are compared to those of reported Schottky diode-type ammonia sensors. Therefore, based on these good properties and the advantages of a simple structure and easy fabrication, the studied device provides promise for high-performance ammonia sensing applications.

Hydrogen sensing characteristics of a novel metal-oxide-semiconductor (MOS) Schottky diode are thoroughly investigated. The MOS structure consists of a gallium nitride (GaN)-based semiconductor system, a nickel oxide (NiO) layer, and palladium (Pd) catalytic materials. A well-prepared Pd/NiO/GaN-based diode shows several advantages in relation to hydrogen sensing, including a simple structure, high sensing speed, wide flexibility for operation under both forward and reverse applied voltages, and a good sensing response of 8.1 × 103 under an applied forward voltage of 0.25 V, at 300 K in a 1% H2/air ambience. Furthermore, under an applied reverse voltage of −2 V and at a high temperature of 573 K, this MOS diode shows a response as high as 1.8 × 104 towards 1% H2/air mixture gas. The Schottky diode sensor with a novel Pd/NiO/GaN structure demonstrated in this study is a promising candidate for high-performance hydrogen sensing applications.

An interesting hydrogen sensor based on a Pd/HfO2/GaOx/GaN metal-oxide-semiconductor (MOS) structure is fabricated and demonstrated. The HfO2 and GaOx layers are prepared using a sputtering approach and hydrogen peroxide (H2O2) treatment. The hydrogen sensing characteristics of the studied device are comprehensively studied. Experimentally, good hydrogen sensing characteristics, including a high sensing response of 8.47 × 105, a low detection level of 5 ppm H2/air, and reversible, short response and recovery times upon exposure to different hydrogen concentrations and temperatures are obtained. The influence of humidity on hydrogen sensing performance is also studied. The exothermic action of the hydrogen adsorption process leads to a decreased hydrogen sensing response at higher temperatures. Consequently, the studied Pd/HfO2/GaOx/GaN MOS diode is promising for high-performance hydrogen sensing applications and integration with other GaN-based high-speed devices on a chip.

The sensing characteristics of a Pt/NiO thin film-based resistor-type ammonia gas sensor are comprehensively studied and demonstrated. Experimentally, the studied Pt/NiO ammonia gas sensor exhibits improved performance, including a higher sensing response of ratio of 1278%, an extremely low detection limit of 10 ppb NH3/air, and fast speeds, at an optimal operating temperature of 300 °C. Based on the advantages indicated above and the benefits of its simple structure, relatively easy fabrication, and inherent p-type semiconductor properties, the studied device is promising for high-performance ammonia gas sensing and complementary metal oxide sensor (CMOS) array applications.

A new Pd nanoparticle (NP)/Pd film/GaN-based Schottky diode-type hydrogen sensor is fabricated and studied. Pd NPs are formed using a proper photochemical approach based on a drop of PdCl2 solution and UV illumination. Experimentally, excellent hydrogen sensing performance, including an extremely high sensing response (4.2 × 106@1% H2/air gas) with a very low detection limit (≤0.8 ppm H2/air) is obtained at 25 °C. This is mainly caused by the enhanced surface area/volume ratio of the Pd NPs and the catalytic reactivity of the Pd film. Furthermore, the studied device exhibits sensitive responses to humid ambiences at 25 °C. Therefore, based on the reported benefits and relatively simple process flow, the studied device is a promising high-performance hydrogen sensor.

The interesting bimetallic catalysts incorporating a GaN/AlGaN heterostructure are used herein to produce a new Schottky diode-type hydrogen sensor. This bimetallic-catalytic structure includes palladium (Pd) nanoparticles (NP) and a platinum (Pt) thin film. Due to the increased surface area/volume (SA/V) ratio and spill-over effect of Pd NPs and the catalytic reactivity of the Pt thin film, the result is prominent hydrogen sensing performance. In our experiment, the studied Pd NP/Pt thin film/GaN/AlGaN-based sensor exhibits a very high sensing response of 2.35 × 107 (under 1% H2/air gas at 300 K) with short response and recovery times of 18 s and 12 s. In addition, an extremely low detecting level (≤ 1 ppm H2/air) is acquired. The studied device shows the hydrogen sensing ability among widespread range for operating temperature (300-473 K) and hydrogen concentration (1 ppm - 1% H2/air). The humidity effect on the sensing response is studied in this work. Moreover, the related hydrogen sensing mechanism and a theoretical analysis used to study the hydrogen coverage at the Pt/GaN interface are included in this work. For the Internet of Things (IoT) application, a modified Kalman algorithm is used to substantially reduce the redundant data. More than 1040 (71.9%) data points of the original data under 100 ppm H2/air gas at 300 K are removed. Furthermore, the related mean recovery error (MRE) is only 5.75%.

A simple platinum nanoparticle (Pt NP)/WO3 semiconducting metal oxide (SMO)-based structure is fabricated and completely studied as a hydrogen gas sensor. In this work, simple rapid thermal evaporation (RTE) was employed to fabricate Pt NPs. This approach could easily produce Pt NPs with a small grain size and uniformity on the WO3 thin film. Experimentally, at 200 °C, the studied device exhibited an excellent hydrogen sensing response of 1.41 × 106 (under a 1% H2/air gas), a very low detecting level of 1 ppm H2/air, and a relatively shorter response (recovery) time of 201 s (26) s. Moreover, first order differential (FOD) and shape-preserving piecewise cubic interpolation (SPPCI) were also employed to overcome the wireless transmission problem for the Internet of Things (IoTs). Furthermore, based on the thermodynamic analysis, the surface coverage performance was studied for this device. As the result, the studied device exhibited practically adsorption with hydrogen gas at 200 °C. The studied device is therefore promising for high-performance hydrogen sensing 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.

In this study, we conducted a fully integrated point-of-care prothrombin time test on a microfluidic disk analyzer. The microfluidic functions integrated on the disk were capable of separating whole blood, decanting plasma, and mixing it with reagents in sequence under alternate spinning. The assay protocol was completed by alternate spinning without using microvalves or surface modification. Clinical sample tests on prothrombin time measurement were conducted by both the microfluidic disk analyzer and the reference instrument used in medical centers. The test results showed a good correlation and agreement between the two instruments.

A new electroless plating (EP)-Pd/GaOx/GaN Schottky diode-type hydrogen sensor is fabricated and comprehensively studied herein. The GaOx dielectric is formed as a result of a proper H2O2 treatment on the GaN surface. In addition, a 20-period sensitization/activation process and an appropriate EP approach of the Pd catalytic layer are employed to facilitate a high-performance metal-semiconductor (M-S) Schottky contact. Experimentally, an extremely high hydrogen sensing response of 5.5 × 106 (under 1% H2/air gas) and a relatively low detection limit of 5 ppm H2/air are obtained at 300 K. The corresponding response and recovery times are 22 s and 21 s at 300 K, respectively. A new data transmission algorithm based on the Kalman algorithm is also proposed in this work. According to the simulation results, the data transmission volume can be reduced by 90%. The average recovery error rate is less than 0.38%. Furthermore, our developed reduced redundancy method can pre-warn the user of sensor failure. Based on the advantages mentioned above, therefore, the studied device is promising for high-performance hydrogen sensing and Internet of Things (IoT) applications.

In this paper, a wireless hydrogen sensing system using a Pd/AlGaN/GaN heterostructure field-effect transistor (HFET) is developed and demonstrated. This HFET device shows good hydrogen sensing performance, including higher drain current variation (0.17 mA @ 1 ppm ${\rm H}_{2}$ /air gas), fast response speed, and superior repeatability behaviors. For the sensing application, a readout circuit is designed to display the value of hydrogen concentration. Then, these data are fed into single chip microprocessor for later processing and wireless transmission. In addition, a grey polynomial differential model algorithm is employed to significantly reduce the redundant data for alleviate the wireless transmission load. The wireless monitoring of hydrogen concentration in a remote site longer than 50 m in distance is successfully demonstrated. From the experimental results, the proposed wireless hydrogen sensing system shows the advantages of high hydrogen sensing performance, easy operation, low cost, high portability, and effective wireless transmission.

Recently, since the wireless sensor network exhibits powerful performance, it has been frequently used in transmission of information in various fields. However, many problems are gradually revealed in the information transfer process. When wireless sensor networks transmit data packets for communication, the large amount of data makes the transmission very difficult. In the meantime, information is often intercepted or stolen by competitors that will cause data loss and leakage of important information. The study has resolved such information transmission problems successfully, high order polynomials is used to approximate data and transfer the simulation parameters, reduce the data transmission amount effectively and achieve better encryption effect. During the data transmission, the network simply transfers fitting parameters to reduce transmission amount. AES encryption mechanism is adopted in the process of parameter transmission to protect the data. Even competitors intercept data, it will still need to be decrypted. Assuming that competitors decrypt data successfully, they could only get the simulation parameters not the real data. Therefore, the scheme achieves the purpose of data protection. The advantage of this method is it avoids the large amount of data transmission and ensures the security and accuracy of the data. This data fitting method of encrypted transmission improves the wireless sensor network data transmission specifications and rationality, enhances the efficiency of data transmission and ensures the security and availability of data.

An interesting heterostructure field-effect transistor (HFET) based hydrogen sensing system is developed and demonstrated. Even at a low hydrogen concentration of 15 ppm H 2 /air, the studied sensor still exhibits high sensitivity at room temperature. Furthermore, a simple sensing system is also designed and reported. In contrast to conventional hydrogen measurement, the detecting system consists of a hydrogen sensor and some sensing circuits. This proposed hydrogen detection system is based on the micro-controller with advantages of low cost, fast response, portable, and easy operation. From experimental results, the proposed system is shown to be good for use.

The interesting hydrogen gas sensing characteristics, based on a field-effect transistor (FET)-based sensor, are studied and analyzed. In addition, a new grey algorithm is developed to reduce the computing complexity. From experimental results, the studied device exhibits good hydrogen performance for wide hydrogen concentration detection and widespread operation temperature. For practical applications, it is important to reduce the computational complexity and eliminate data redundancy. In this paper, a new grey polynomial differential model (GPDM) is developed to analyze hydrogen gas sensing properties. Based on the proposed model, the simulated data points are substantially decreased from 4000 points (the measured results) to 68 points (GPDM data). It is worth to note that, the simulated curve still retains the original features of experimental hydrogen transient response. The error rate between the simulated data and experimental results is only of 0.091%. Therefore, the reported GPDM presents the promise on the analysis of hydrogen gas sensing performance by reducing the undesired computing complexity and data redundancy.

The ZnO nanorods-based ammonia (NH3) gas sensors with different electrode spacing are fabricated and studied. Experimentally, the hexagonal ZnO nanorods were prepared by a hydrothermal method. The diameter and length of ZnO nanorods were about 179±2, 1806±5 nm, respectively. By shrinking the electrode spacing, the sensor response of studied device is improved and the sensor response is enhanced more than ten times in magnitude. The improved NH3 sensing ability caused by shrink electrode spacing is attributed to the presence of more grain boundaries and depletion layers. Therefore, the studied device with the shrink of electrode spacing provides a promise for high-performance ammonia sensing applications.

GaN-based light-emitting diodes (LEDs) grown on c-plane vicinal sapphire substrates are fabricated and characterized. All the electrical characteristics demonstrate that the LED with a 0.2° tilt sapphire substrate exhibits the lowest defect density while that with a 1.0° tilt sapphire exhibits the highest one. At 2 mA, the enhanced output power of 23.3% indicates the substantial reduction of defect-related nonradiative recombination centers in MQW for the LED device with a 0.2°-tilt sapphire. At 60 mA, the improved value is up to 45.7%. This is primarily caused by the presence of indium quantum dots (QDs) in MQW which provides increased quantum efficiency (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper, orthogonal collocation method (OCM) is applied to solve the free vibration of nonlocal Timoshenko beams with various boundary conditions by using piecewise cubic Hermite polynomials (CHPs). In the numerical implementation, approximation solution and its space derivatives over the interval are approximated by the combination of the CHPs and unknown parameters. Through the generalized eigen-value problem analysis, the vibration frequencies of beams can be determined precisely. Form numerical analysis by using OCM sufficiently indicate that it has excellent convergence rate, and very close to analytical solutions.

An InGaN/GaN multiple-quantum-well (MQW) light-emitting diode (LED) with a ten-period i (undoped) -InGaN/p (Mg doped) -GaN (2.5 nm/5.0 nm) superlattice (SL) structure, was fabricated. This SL structure that can be regarded as a confinement layer of holes to enhance the hole injection efficiency is inserted between MQW and p-GaN layers. The studied LED device exhibits better current spreading performance and an improved quality, compared with a conventional one without SL structure. Due to the reduced contact resistance as well as more uniformity of carriers injection, the operation voltage at 20 mA is decreased from 3.32 to 3.14 V. A remarkably reduced reverse-biased leakage current (10−7–10−9 A) and higher endurance of the reverse current pulse are found. The measured output power and external quantum efficiency (EQE) of the studied LED are 13.6 mW and 24.8%, respectively. In addition, significant enhancement of 25.4% in output power as well as increment of 5% in EQE for the studied devices is observed, as the studied devices show superior current spreading ability and reduction in dislocations offered by the SL structure.

The hydrogen sensing properties of a Pd/InAlAs metamorphic high electron mobility transistor (MHEMT) are investigated. Experimentally, a threshold voltage shift (Δ V th ) of 260 mV is observed upon exposing to a 1% H 2 /air gas. The drain current sensing response ( S R ) shows the strong dependence on the gate bias voltage V GS . A maximum S R of 107% is found at the applied voltage of V GS = −0.5 V. In addition, the temperature behavior of S R is predominantly determined by the hydrogen sticking coefficient and the exothermic reaction of hydrogen adsorption. It is also found that rectification ratio R can be changed with different hydrogen concentrations Furthermore, the response rate analyses reveal that the initial response rate is increased with the hydrogen concentration and temperature. The activation energy E a of 2.88 kJ mol −1 suggests that the studied Pd/InAlAs MHEMT hydrogen sensor has a low barrier for the adsorption of hydrogen.

In this work, the comprehensive study of the hydrogen adsorption effects on the Pd/AlGaN-based MOS Schottky diode with SiO 2 passivation is demonstrated. Hydrogen sensing performance of the proposed device is significantly enhanced with the insertion of SiO 2 layer. The MOS diode exhibits a maximum sensing response value of 3.3 × 10 5 at 70 °C under a 1% H 2 /air gas. Additionally, the operating temperature for the maximum sensing response is decreased from 150 °C to 70 °C with the insertion of SiO 2 layer. Moreover, the lowering of Schottky barrier height is 230 (200) meV for the MOS (MS) diode at room temperature. The hydrogen adsorption effect also largely influence the effective Richardson's constant. Furthermore, the transient-state experiments reveal that the MOS Schottky diode exhibits an activation energy of 14.1 kJ/mol which is lower than the MS Schottky diode (25 kJ/mol). Therefore, hydrogen sensing performance of the AlGaN-based Schottky diode can be significantly enhanced with the SiO 2 passivation on the AlGaN surface.

In this study, the effects of annealing conditions on the magnetic characteristics of multilayered perpendicular magnetic tunnel junctions (pMTJ) of the structures SiNx/Pt/(Co/Pd) 10/MgO/(Co/Pt) 5/Pt with various MgO barrier thicknesses were explored. We found that both the fixed and free layers exhibit coercivity growth with increasing annealing temperature. Insertion of a 0.4 nm Mg layer under the MgO barrier layer increases the corecivities further. Magnetoresistance measured by the current-in-plane tunneling (CIPT) method reveals that the insertion of Mg layers on both side of the MgO layer can increase the MR ratio by up to 32%.

An interesting Pd/Al 0.24 Ga 0.76 As-based field-effect-transistor-type hydrogen detector is fabricated and studied. The corresponding electronic and hydrogen sensing properties are measured and investigated. Based on the measured results, a hydrogen sensing model is developed. Theoretically, the dipolar layer formed by the hydrogen atoms adsorbed at the Pd–AlGaAs interface can be considered as a two-dimensional layer. Under the 980 ppm H 2 /air environment, the concentration of hydrogen adsorption sites available at the metal–semiconductor interface, n i , and the effective distance, d , from the Pd–AlGaAs interface to adsorbed hydrogen atoms are 9.5 × 10 13 cm −2 and 3 A, respectively. The simulated curves show excellent agreement with experimental results. In addition, an anomalous decrease phenomenon in transient response is observed which may be caused by the formation of hydroxyl species and water.

In this work, the temperature dependences of a Pd/AlGaN Schottky diode-type hydrogen sensor are investigated. The effects of temperature on parameters such as breakdown voltage, response time, and series resistance are presented. Experimentally, under a fixed current bias of −2×10−5 A a reverse voltage response as high as 6 V is observed. The hydrogen adsorption effect also exhibits influences on the series resistance which is decreased by 18 Ω upon exposing to hydrogen gas at 200 °C. Besides, the ideality factor n shows a decreasing trend with the introduction of hydrogen gas. The voltage dependence on sensor performance is also studied. By increasing the voltage from 0.35 to 1 V, the response time is decreased by 15 s under the 1010 ppm H2/air gas. Furthermore, based on the kinetic adsorption analysis the rate constant kr increases from 6.22×10−1 to 1.54 s−1 at 300 °C with exposing to 99.4 and 9660 ppm H2/air gases, respectively. Therefore, on the basis of the compatibility with AlGaN-based microwave devices, the studied Pd/AlGaN hydrogen sensor shows the promise for fabricating the on-chip wireless senor systems.

The hydrogen sensing and response characteristics of Pt/GaN (metal–semiconductor, MS) and Pt/SiO 2 /GaN (metal–insulator–semiconductor, MIS) Schottky diodes under different-concentration hydrogen gases are studied over a wide temperature range in an air atmosphere. Experimentally, the studied MS and MIS devices exhibit hydrogen sensing performance, including forward-bias hydrogen response ( S F ) of 609 (MS) and 14,690 (MIS) (in 9970 ppm H 2 /air), reverse-bias hydrogen response ( S R ) of 5630 (MS) and 44,640 (MIS) (in 9970 ppm H 2 /air), Schottky barrier height variation (Δ ϕ b ) of 195.9 (MS) and 231.6 meV (MIS) (in 9970 ppm H 2 /air), respectively. Based on the equilibrium adsorption analysis, the hydrogen adsorption enthalpy (Δ H °) of the studied MS and MIS devices are −10.21 kJ/mol and −19.5 kJ/mol, respectively. The studied MIS device further shows the excellent performance for high temperature detection and improved activity of hydrogen adsorption reaction. Experimentally, the hydrogen detection adsorption time constants ( τ a ) of the studied MS and MIS devices decrease from 25 to 3 s and from 12 to 2 s, respectively, as the temperature increases from 300 to 700 K. In addition, according to the kinetic adsorption analysis, the activation energy ( E a ) of the studied MS and MIS devices are 4.498 kJ/mol and 2.885 kJ/mol, respectively. This implies that the studied MIS device can also perform more rapid hydrogen detection. Therefore, the studied Pt/SiO 2 /GaN (MIS) Schottky diode exhibits a promise for high performance hydrogen sensor applications.