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We have developed a swift and simplistic protein immunoassay using aptamer functionalized AlGaN/GaN high electron mobility transistors (HEMTs). The unique design of the sensor facilitates protein detection in a physiological salt environment overcoming charge screening effects, without requiring sample preprocessing. This study reports a tunable and amplified sensitivity of solution-gated electric double layer (EDL) HEMT-based biosensors, which demonstrates significantly enhanced sensitivity by designing a smaller gap between the gate electrode and the detection, and by operating at higher gate voltage. Sensitivity is calculated by quantifying NT-proBNP, a clinical biomarker of heart failure, in buffer and untreated human serum samples. The biosensor depicts elevated sensitivity and high selectivity. Furthermore, detailed investigation of the amplified sensitivity in an increased ionic strength environment is conducted, and it is revealed that a high sensitivity of 80.54 mV/decade protein concentration can be achieved, which is much higher than that of previously reported FET biosensors. This sensor technology demonstrates immense potential in developing surface affinity sensors for clinical diagnostics.

In this research, we have realized an electrical double layer (EDL) gated high electron mobility transistor (HEMT) as DNA sensor. The sensing area on the gate electrode which is separated from the transistor channel is immobilized with probe DNA to capture target DNA from physiological salt environment. The detection limit of the sensor can be as low as 1 fM with very high sensitivity. The specificity of the DNA sensor is also demonstrated by controlling the hybridization temperature. By choosing the hybridization temperature slightly lower than the melting temperature of the well-matched sequence, the binding ratio can be controlled between the fully-matched and mismatched one. The sensor has demonstrated specificity, with the ability to achieve single base mismatch resolution. The sensor has the potential for rapid DNA sensing applications in cells, biomarkers and viruses.

Lead ion selective membrane (Pb-ISM) coated AlGaN/GaN high electron mobility transistors (HEMT) was used to demonstrate a whole new methodology for ion-selective FET sensors, which can create ultra-high sensitivity (−36 mV/log [Pb2+]) surpassing the limit of ideal sensitivity (−29.58 mV/log [Pb2+]) in a typical Nernst equation for lead ion. The largely improved sensitivity has tremendously reduced the detection limit (10−10 M) for several orders of magnitude of lead ion concentration compared to typical ion-selective electrode (ISE) (10−7 M). The high sensitivity was obtained by creating a strong filed between the gate electrode and the HEMT channel. Systematical investigation was done by measuring different design of the sensor and gate bias, indicating ultra-high sensitivity and ultra-low detection limit obtained only in sufficiently strong field. Theoretical study in the sensitivity consistently agrees with the experimental finding and predicts the maximum and minimum sensitivity. The detection limit of our sensor is comparable to that of Inductively-Coupled-Plasma Mass Spectrum (ICP-MS), which also has detection limit near 10−10 M.

This study reports the fabrication and characterization of electrical double layer gated AlGaN/GaN High electron mobility (HEMT) biosensor array to capture, detect and count circulating tumor cells (CTCs) of colorectal cancer (CRC). GaN HEMT chips were assembled into a sensor array on a thermo-curable polymer substrate in a simple and robust packaging process. The array had multiple aptamer immobilized sensing sites and was highly sensitive and selective with up to single cell resolution. The present method can detect cells in their native electrolyte composition, in a very short time with extremely low cost compared to the conventional circulating tumor cell assays. The effect of cellular binding in different test environments was further studied and reported. The electrical response of the sensor was discovered to be relevant to the transmembrane potential of the cell. This whole cell sensor array has the potential to be used as a point-of-care diagnostic tool in varied applications such as detection of rare cells, pathogens and studying the dynamics of cellular interactions.

In this study, a new type of field-effect transistor (FET)-based biosensor is demonstrated to be able to overcome the problem of severe charge-screening effect caused by high ionic strength in solution and detect proteins in physiological environment. Antibody or aptamer-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) are used to directly detect proteins, including HIV-1 RT, CEA, NT-proBNP and CRP, in 1X PBS (with 1%BSA) or human sera. The samples do not need any dilution or washing process to reduce the ionic strength. The sensor shows high sensitivity and the detection takes only 5 minutes. The designs of the sensor, the methodology of the measurement, and the working mechanism of the sensor are discussed and investigated. A theoretical model is proposed based on the finding of the experiments. This sensor is promising for point-of-care, home healthcare, and mobile diagnostic device.

In this research, we have designed, fabricated and characterized an electrical double layer (EDL)-gated AlGaN/GaN high electron mobility transistor (HEMT) biosensor array to study the transmembrane potential changes of cells. The sensor array platform is designed to detect and count circulating tumor cells (CTCs) of colorectal cancer (CRC) and investigate cellular bioelectric signals. Using the EDL FET biosensor platform, cellular responses can be studied in physiological salt concentrations, thereby eliminating complex automation. Upon investigation, we discovered that our sensor response follows the transmembrane potential changes of captured cells. Our whole cell sensor platform can be used to monitor the dynamic changes in the membrane potential of cells. The effects of continuously changing electrolyte ion concentrations and ion channel blocking using cadmium are investigated. This methodology has the potential to be used as an electrophysiological probe for studying ion channel gating and the interaction of biomolecules in cells. The sensor can also be a point-of-care diagnostic tool for rapid screening of diseases.

The microwave and low frequency noise characteristics of 6 inch InAlN/AlN/GaN high electron mobility transistor (HEMT) were demonstrated and investigated on silicon-on-insulator (SOI) substrate for the first time. The InAlN HEMT on SOI substrate was grown by metal organic chemical vapor deposition (MOCVD) on a p-type (111) Si SOI substrate with a p-type (100) Si handle wafer for possible heterogeneous integration. The Raman spectroscopy measurement indicates that the smaller epitaxy stress was obtained by adopting SOI wafer and X-ray diffraction measurements revealed that InAIN HEMT on SOI achieves a flat surface and an abrupt heterointerface. The InAlN HEMT on SOI exhibits a lower leakage current compared to the device on high resistivity (HR) Si substrate and thus improves the off-state breakdown voltage from 134 V to 198 V. Moreover, the buried SiO2 in SOI substrate also efficiently suppresses the signal loss resulting in the better bandwidth and the microwave power performance. Based on the low frequency noise measurement, InAlN HEMT on SOI substrate also performs a relatively slight degradation after hot carrier stress.

Pt/GaN Schottky diodes were fabricated for detecting hydrogen sulfide at 200°C. Ga-face GaN was grown on c-plane sapphire substrate by a metal-organic chemical vapor deposition (MOCVD) system. Hydrogen sulfide was mixed with nitrogen and detected from 0.1~10 ppm with the Pt/GaN Schottky diodes. Hydrogen sulfide caused the current increase in both forward and reversed bias of the Schottky diode. Real-time detection of the hydrogen sulfide was conducted at a forward bias 1.18 V in nitrogen ambient. The sensors show good linear dependence of the current change at forward bias versus the H2S gas concentration. The sensitivity in the two ranges from 0.1~1 ppm and 1~10 ppm of hydrogen sulfide, are 14.62 and 5.844 μA/ppm, respectively. The detection limit of the sensor is around 0.2 ppm of hydrogen sulfide at the forward bias at 200°C. The results show that the Pt/GaN Schottky diodes are promising for low cost and high sensitivity hydrogen sulfide detection.

AlGaN/GaN high electron mobility transistors (HEMTs) were used to sense the binding between double stranded DNA (dsDNA) and the severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein (N protein). The sensing signals were the drain current change of the HEMTs induced by the protein–dsDNA binding. Binding-site models using surface coverage ratios were utilized to analyze the signals from the HEMT-based sensors to extract the dissociation constants and predict the number of binding sites. Two dissociation constants, K D 1 = 0.0955 nM, K D 2 = 51.23 nM, were obtained by fitting the experimental results into the two-binding-site model. The result shows that this technique is more competitive than isotope-labeling electrophoretic mobility shift assay (EMSA). We demonstrated that AlGaN/GaN HEMTs were highly potential in constructing a semiconductor-based-sensor binding assay to extract the dissociation constants of nucleotide–protein interaction.

This paper reports a new method to reduce threading dislocation density in GaN epilayers grown on (111) Si substrates by metalorganic chemical vapor deposition. This method utilizes an insitu SiNx mask to produce a self-assembled double-island structure, which effectively reduces threading dislocation density from 9.6 × 109 cm−2 to 2.6 × 109 cm−2 without using any lithographic and regrowth processes. InGaN light-emitting diodes fabricated on the double-island buffer layer exhibit nearly 20% improvement on the optical output power as well as less energy localization effect, compared to those without the double-island buffer layer. The mechanisms of double-island formation as well as dislocation reduction are proposed based on transmission electron microscopy investigations. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0051412jss] All rights reserved.

As acquired immunodeficiency syndrome (AIDS) caused by HIV-1 (human immunodeficiency virus type 1) has been in the top 10 leading causes of death for recent years, there have been many promising treatment discovered. One of the treatments is by taking non-nucleoside reverse transcriptase inhibitors (NNRTI) to suppress the activity of the HIV-1. The binding affinity of NNRTI to the reverse transcriptase (RT) of HIV-1 is an important factor determining the efficiency of the drug performance. The HIV-1 RT immobilized AlGaN/GaN high electron mobility transistors (HEMTs) were used to find the dissociation constant of NNRTIs. Comparing to conventional drug analyzing, HEMTs assisting experiments are much faster in processing time and lower cost.

Antibody-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) were used for detecting peptides and revealing the number of binding sites of the antibody and the dissociation constants. Two binding sites were found on this antibody for the peptide and the dissociation constants of the antibody-peptide complex were extracted from a two-binding-site model. The estimated dissociation constants are consistent with the detection limit of the sensor showing the important role of the dissociation constants in the performance of the sensors. The results demonstrate that the AlGaN/GaN HEMTs cannot only be used for biosensors, but also can be used for the biological affinity study.

The thermal stability and reliability of AlGaN/GaN high electron mobility transistors (HEMTs) on Si substrates with a 2-μm thick copper interconnection (Cu-INTC) were evaluated. The use of metallic copper as a conducting metal has the advantages of higher thermal conductivity, low cost and low sheet resistance. For comparison, traditional gold metal interconnection (Au-INTC) devices were fabricated under the same process conditions. Thermal infrared (IR) microscopy measurements show that the Cu-INTC devices could function at a lower channel temperature (TCHANNEL) than traditional Au-INTC devices with the same drain current density, because of the low resistivity of the metal. The typical peak transconductance (gm), output power (POUT), power gain (Gp) and power-added-efficiency (PAE) during operation at 100 °C were 87.53 mS/mm, 22.85 dBm, 11.1 dB and 25.9% for a Cu-INTC power device with gate width of 1 mm and these measured results were better than those of Au-INTC devices. They indicate that the copper metal provides great potential for high-power AlGaN/GaN HEMT applications.

Antibody-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect a short peptide consisting of 20 amino acids. One-binding-site model and two-binding-site model were used for the analysis of the electrical signals, revealing the number of binding sites on an antibody and the dissociation constants between the antibody and the short peptide. In the binding-site models, the surface coverage ratio of the short peptide on the sensor surface is relevant to the electrical signals resulted from the peptide–antibody binding on the HEMTs. Two binding sites on an antibody were observed and two dissociation constants, 4.404×10−11 M and 1.596×10−9 M, were extracted from the binding-site model through the analysis of the surface coverage ratio of the short peptide on the sensor surface. We have also shown that the conventional method to extract the dissociation constant from the linear regression of curve-fitting with Langmuir isotherm equation may lead to an incorrect information if the receptor has more than one binding site for the ligand. The limit of detection (LOD) of the sensor observed in the experimental result (∼10 pM of the short peptide) is very close to the LOD (around 2.7–3.4 pM) predicted from the value of the smallest dissociation constants. The sensitivity of the sensor is not only dependent on the transistors, but also highly relies on the affinity of the ligand-receptor pair. The results demonstrate that the AlGaN/GaN HEMTs cannot only be used for biosensors, but also for the biological affinity study., Highlights ► AlGaN/GaN high electron mobility transistors detected a short peptide. ► Antibody immobilized on transistors bind the peptide to form a complex. ► Binding affinity of the complex was studied using binding-site models. ► Dissociation constants and the number of binding sites were revealed.

Lateral AlGaN/GaN Schottky barrier diodes on silicon (111) substrate have been fabricated and characterized. The Hall measurement shows the mobility of 1430 cm2/V-s with a sheet carrier density of 9.8 × 1012 cm-2 for the AlGaN/GaN structure. The specific on-state resistance (Ron) is 1.27 mΩ-cm2, while the forward turn-on voltage is 1.43 V at the current density of 100 A/cm2 for device with Schottky-to-ohmic distance of 10 μm. The measured reverse breakdown voltage (VB) at room temperature is up to 600 V without edge termination. The figure-of-merit, (VB)2/Ron, is 302.7 MWcm-2, and fast reverse recovery time is observed for device switched from a forward current density of 720 A/cm2 to a reverse bias of 30 V with di /dt of 60 A/μs. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fibrinogen found in blood plasma is an important protein biomarker for potentially fatal diseases such as cardiovascular diseases. This study focuses on the development of an assay to detect plasmatic fibrinogen using electrical double layer gated AlGaN/GaN high electron mobility transistor biosensors without complex sample pre-treatment methods used in the traditional assays. The test results in buffer solution and clinical plasma samples show high sensitivity, specificity, and dynamic range. The sensor exhibits an ultra-low detection limit of 0.5 g/l and a detection range of 0.5–4.5 g/l in 1× PBS with 1% BSA. The concentration dependent sensor signal in human serum samples demonstrates the specificity to fibrinogen in a highly dense matrix of background proteins. The sensor does not require complicated automation, and quantitative results are obtained in 5 min with

High-performance AlGaN/GaN Schottky barrier diodes are fabricated on a composite AlGaN/AlN buffer layer with low screw-type and high edge-type dislocation densities. Without edge termination, the devices with 30-μm anode-to-cathode spacing exhibit a high breakdown voltage (VB) of 3489 V, a low leakage current (IR) of less than 0.2 μA at -2000 V, and a low specific on-resistance (Ron) of 7.9 mΩ·cm2, resulting in a figure of merit (VB2/Ron) as high as 1.54 GW/cm2. Their switching characteristics as revealed by the reverse-recovery transient waveform exhibit a short reverse-recovery time of 17 ns.

This letter reports an InGaN light-emitting diode (LED) structure that has an n-type Al0.1Ga0.9N/GaN/In0.06Ga0.94N current spreading layer under its multiple-quantum-well active region. As indicated by simulation, the Al0.1Ga0.9N/GaN/In0.06Ga0.94 N heterostructure induces a higher electron concentration than an n-AlGaN/GaN cladding layer and an n-GaN/InGaN current spreading layer that are used in conventional LEDs. As a result, the proposed n-type spreading layer is expected to alleviate current crowding and improve external quantum efficiency. Experimentally, the light output uniformity across the chips is greatly improved. The output power and wall-plug efficiency are enhanced by about 18.2% and 22.2% at an injection current of 350 mA for the LEDs employing the new double-heterostructure current spreading layer.

In this study, we used antibody-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) for detecting a short peptide, and revealing the number of binding sites of the antibody for the peptide and the dissociation constants of the antibody-peptide complex. In our case, two binding sites were found on the ferritin heavy chain (FHC) antibody and the dissociation constants of the antibody-peptide complex were 2.723×10−11M and 6.994×10−9M for the two binding sites, respectively. The estimated dissociation constants are consistent within the reasonable range of the IGg antibody-antigen complexes binding constants. It also reveals the limit of detection is not only decided by the performance of the transistors but also the dissociation constant of the detected molecules. To our knowledge, it is the first time that AlGaN/GaN HEMTs using on the study of protein-peptide binding affinity. The results show that AlGaN/GaN HEMTs can not only be used as biosensors, but also a good tool and platform for analytical chemistry with numerous advantages since they are label-free, low-cost, biocompatible, stable in high temperature, real-time detection. Compared with other methods and techniques investigating the binding and kinetics of biological molecules, we do demonstrate AlGaN/GaN HEMTs have great potential to compete with conventional or proposed methods.

In this article, we used AlGaN/GaN high electron mobility transistors (HEMTs) to construct the first label-free semiconductor-sensor-based binding assay to our knowledge. Our results suggested that the nucleotide-c terminal domain of SARS coronavirus (SARS-CoV) nucleocapsid protein interaction is a two-step binding event with two dissociation constants (Kd 1 = 0.052 nM, and Kd 2 = 51.24nM) extracted by using the modified two-binding-site Langmuir isotherm equation proposed here. We found that there were at least two protein binding sites on the specific 41-base SARS-CoV double-stranded DNA (dsDNA) genome (29,580–29621) conjugated with a 20-mer poly-dT tail. This result presented a high binding affinity is comparable with the antibody-antigen reaction, and suggested this designed dsDNA could be treated as an aptamer for SARS-CoV N protein capture.

We demonstrate that Ti/Al/Cr/Mo/Au ohmic contact has an extremely smooth surface morphology of 29.0 nm and a low specific contact resistivity (! c ) of 1.1×10 -6 ohm-cm 2 on n-type AlGaN/GaN heterostructures. The use of Cr interlayer in Ti/Al/Cr/Mo/Au contacts leads to significantly improved contact morphology without any degradation on the contact resistance. This is attributed to the reduced inter-diffusion and reaction between the layers in the contact stack. Keywords: ohmic contacts, AlGaN/GaN heterostructures, Surface morphology, thermal stability. *chyi@ee.ncu.edu.tw ; phone: +886-3-4258241; fax: +886-3-4255830 Introduction Wide band gap AlGaN/GaN heterostructures have been wide ly used in high electron mobility transistors (HEMTs) for high temperature, high frequency, and high power applications. For high power devices, ohmic contacts with low contact resistance, smooth surface and clear edge definition are essential as th ey are closely related to the performance, reliability and reproducibility of the devices [1-4]. The most common ohmic contact metallization scheme for AlGaN/GaN HEMTs is based on Ti/Al, with overlayers of either, Ti, Ni, or Mo. It is followed by an Au layer to reduce sheet resistance and avoid oxidation during the high temperature annealing process, which is necessary to achieve low specific contact resistivity. However, the morphology of the annealed metal contact often becomes rough due to intermixing and/or alloying after the hi gh temperature heat treatments. A rou gh surface and edge morphology results in poor reliability and reproducibility. In order to decrease surface roughness, Al-free metallization or Ti-based contacts containing Mo have been proposed. Deposition of W or W-containing alloys on top of the Ti-based metallization has also been reported [5-6]. In this work we carry out a comparative study on the specific contact resistivity and surface morphology of Ti/Al/Ni/Au, Ti/Al/Mo/Au, Ti/Cr/Ni/Au, Ti/Cr/Mo/Au, and Ti/Al/Cr/Mo/Au metal contact stack on AlGaN/GaN structures . Reliability test of Ti/Al/Cr/Mo/Au contacts is investigated and discussed.

Aluminum nitride is a material of great potential for high power electronic devices, UV photonic devices as well as acoustic devices. However, the lack of a good crystal growth technology for bulk material and substrate hinders the development of these AlN-based devices. While AlN has been successfully grown on sapphire substrate for some time, the presence of a large number of dislocations in the material is still a major barrier to overcome [1]. In this work, we demonstrate a low-dislocation-density AlN template on sapphire by inserting an AlN interlayer by metal-organic chemical vapor deposition. The main idea of our approach is to change the growth mode in the course of the epitaxial growth by decreasing growth temperature and changing V/III ratio. As the growth mode changes, dislocations tend to be redirected and/or form dipole half loops via annihilation processes [2]. The etch-pit-density of the AlN templates is reduced from 3.6×10 9 cm -2 to 1.7×10 9 cm -2 . Accordingly, the full width at half maximum of the (0002) x-ray rocking curve is reduced from 37 arcsec to 12 arcsec. The result indicates that the AlN template has low screw and mixed type dislocations. AlGaN/GaN Schottky diodes fabricated on this high quality AlN template exhibit very high breakdown voltage (> 2000 V), which sets a record-high figure of merit of 1.15 GW/cm 2 .

Electrical properties of low-temperature grown Mg-modulation-doped InGaN/GaN superlattice (MD-SLS) for green light-emitting diodes (LEDs) are investigated. Room-temperature Hall effect measurements indicate that the MD-SLS has conductivity comparable to that of high-temperature grown p-type GaN. The light output intensity of green LEDs with the p-InGaN/GaN MD-SLS is approximately doubled as compared with that of the LEDs with a high-temperature grown p-GaN.

The electrical characteristics of a series of AlInN high-electron-mobility transistors (HEMTs) with a GaN cap layer ranging from 0 to 26 nm are investigated for power switching applications. The breakdown voltage (VB), mobility of two-dimensional electron gas, on-state resistance (Ron), and dynamic Ron of the HEMTs are improved by increasing the cap layer thickness. The improved electrical characteristics are attributed to the GaN cap layer, which not only reduces the surface E-field but also raises the conduction band of the barrier layer and effectively prevents electrons from being trapped in the AlInN barrier and above.

GaN-based high electron mobility transistors (HEMTs) have attracted tremendous attention because of its wide bandgap and high power handling capability, which are the two fundamental merits for power electronics applications. Lattice-matched AlInN/GaN heterostructure has been considered a promising alternative to its AlGaN/GaN counterpart due to its stronger spontaneous polarization, which induces higher carrier concentration and therefore reduces channel resistance. In addition, InAlN lattice-matched to GaN would not be subject to the inverse piezoelectric effect that deteriorates device reliability as observed on AlGaN/GaN HEMTs. While a few excellent device characteristics have been demonstrated over the years, AlInN/GaN HEMTs are in general still more vulnerable than AlGaN/GaN HEMTs. It is desirable to clarify the origin(s) of this problem to expedite the development of high power AlInN/GaN HEMTs and the devices alike. In this talk, we will present our recent works on the growth and electrical characterization of AlInN/GaN HEMTs, including capping layer designs, off-state breakdown mechanisms, dynamic resistance measurements as well as low frequency noise measurements. Solutions to cope with the material issues and process issues will also be addressed.

AlInN, a material lattice-matched to GaN, is very promising for high current, high transconductance, and high RF performance high-electron-mobility transistors (HEMTs). However, it is challenging to grow high quality AlInN HEMTs due to the large immiscibility and distinct thermal stability of AlN and InN, which causes premature voltage breakdown. Several methods have been proposed to solve this problem, such as using a thin AlInN barrier layer and field plate structure (VB = 400 V), Schottky source/drain (VB = 460 V), or 5 % AlGaN back barrier layer (VB = 3 KV). However, most of these methods are still problematic in maintaining a low Ron and high VB simultaneously. GaN cap has been widely used to achieve good surface smoothness and reduce current collapse in AlGaN/GaN-based HEMTs. GaN MOS-HEMTs with a thick GaN cap layer to reduce the surface field for high breakdown voltage have also been reported (VB = 840 V). Our study shows that GaN cap layer also has a positive influence on AlInN HEMTs in reducing current collapse phenomenon, dissipating electric field near the gate edge and enhancing the breakdown voltage. By using a GaN cap layer, AlInN-based HEMTs, exhibiting low Ron and high VB simultaneously, have been demonstrated on 6 inch silicon substrates in this work. Two AlInN-HEMT structures denoted as sample A and B were prepared by metal-organic chemical vapor deposition on 6 inch Si (111) substrates. Sample A is a typical HEMT structure without a GaN cap, while sample B has an additional 13 nm-thick GaN cap layer on top of the AlInN layer. Room temperature Hall mobility, two-dimensional electron gas (2DEG) concentration and sheet resistance (Rsh) of sample A are 886 cm2/V.s, 2.49x1013 cm-2 and 283 ohm/sq, while those of sample B are 1,450 cm2/V.s, 1.61x1013 cm-2 and 267 ohm/sq, respectively. Due to the reverse polarization effect of GaN cap on sample B, the 2DEG concentration of sample B is lower than that of sample A. Dynamic Ron of power electronics reflects acceptor-like defect in the material which could be improved by decreasing electric field at the gate edge or decreasing the defect density in the material. Devices were tested under off-state condition with a constant Vd for 1 second, then switched to on-state to observe the variation of Ron. Sample A exhibits serious degradation on dynamic Ron with time. The ratio of dynamic Ron over static Ron of sample A reaches 5 under 20 V of Vd stress, while that of sample B can be maintained at 1.3 under the same test conditions. As the off-state stress Vd increases, the dynamic Ron ratio of sample B also increases significantly and reaches 5 under 60 V of Vd stress. The improvement of dynamic Ron on AlInN HEMT with a GaN cap implies the trap density of sample B is significantly reduced The on-state I-V characteristics of the HEMTs shows that Id,max of sample A and B at Vg of 0 V are 480 mA/mm and 660 mA/mm, respectively. Thus, the extracted Ron is improved from 4.6 mohm-cm2 of sample A to 3.7 mohm-cm2 of sample B. This is consistent with their Hall results. The extrapolated threshold voltage (Vth ) of sample B is -9.1 V, which is larger than -6.3 V of sample A due to its thicker intermediate layer and the presence of the GaN cap layer. With the help of a GaN cap layer, which disperses the electrical field near the gate edge, sample B has a lower drain leakage current than sample A. While the VB of sample A reaches 530 V, indicating the crystal quality of AlInN is comparable to that of the traditional AlGaN-based HEMTs, the GaN cap extends the breakdown voltage of sample B to 675 V.

Human immunodeficiency virus (HIV) Reverse Transcriptase (RT)-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) and binding-site models were used to find out the dissociation constants of the HIV RT-inhibitor complex and the number of the binding sites on RT for the inhibitor, Efavirenz. One binding site on the RT for the inhibitor is predicted and the dissociation constant extracted from the binding-site model is 0.212 nM. The AlGaN/GaN HEMTs and the binding-site-models are demonstrated to be good tools to assist drug developments by elucidating the dissociation constants and the number of binding sites, which can largely reduce the cost and time for drug developments.

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The epitaxial growth of GaN on patterned c-plane sapphire substrates having microlenses with a flat top, a dull tip, or a sharp tip is carried out. The growth mode, dislocation density, residual strain, and optical properties of GaN are investigated and correlated with the shape of the microlens. Because the growth of GaN does not take place on top of the microlens with a sharp tip, this type of patterned substrate leads to a wider low dislocation density lateral growth region, while it also gives rise to a higher compressive residual strain in GaN. For GaN grown on the microlens with a dull tip, many dislocations appear, resulting from the extra facets on the lens. It, however, has the lowest compressive strain among the samples studied. This work provides a guideline for preparing microlens patterned sapphire substrates for potential applications in high brightness InGaN light emitting diodes as both dislocation density and strain influence their internal quantum efficiency.

A comparative study of the specific contact resistivity and surface morphology of Ti/Al/Ni/Au, Ti/Cr/Mo/Au, and Ti/Al/Cr/Mo/Au metal contact stacks on AlGaN/GaN heterostructures is reported. Compared to the conventional Ti/Al/Ni/Au contact, the Ti/Al/Cr/Mo/Au contact has much smoother surface and achieves minimum specific contact resistivity of 1.1×10−6 Ω cm2. This contact maintains its low contact resistivity after storage at 200 °C for 100 h in N2. The robustness of this contact is attributed to the Cr and Mo layers, which suppress the formation of Al–Au alloys in the contact stack.