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February 1991 - present
Publications
Publications (630)
Gallium oxide (Ga2O3) based phototransistor can be used as a switch and an amplifier in typical digital and analog UV photonic applications, respectively. The light detection capability in Ga2O3 is very high, but these phototransistors suffer from poor drain current saturation with bias. Furthermore, the transistor switching action generally necess...
InGaAs/GaAsSb “W” quantum wells with GaAsP barriers are grown on GaAs (001) substrates by molecular beam epitaxy. We investigate the effect of the Sb composition in GaAsSb on the photoluminescence (PL) wavelength. X-ray rocking curve (XRC) measurements and simulations are performed to investigate the material composition and layer thickness. Low-te...
The effect of the GaAsP strain-compensating layer on type-II GaAs1−xSbx/InyGa1−yAs was investigated. GaAsSb/InGaAs multiple quantum wells (MQWs) without and with GaAsP strain-compensating layers were grown by molecular beam epitaxy. Increasing Sb or In compositions can extend photoluminescence (PL) emission at longer wavelength along with the highl...
This study provides experimental evidence of charged interface states limited scattering in III-nitride heterostructures. Temperature-dependent Hall measurements and temperature-dependent ID–VG measurements indicate a significant influence of the charged interface states on the electron mobility in different AlGaN/GaN heterostructures where the cha...
The range of applications of the common III-nitride semiconductors (Al, Ga, In)N can be extended through bandgap engineering with the inclusion of boron and forming their heterojunctions. In this study, the band alignments of B(Al, Ga)N alloys with common III-nitrides are investigated using x-ray photoemission spectroscopy. A type-I straddling-gap...
Gallium Arsenide thin films have been successfully grown onto (1102) sapphire substrates by Molecular Beam Epitaxy methods using a graded growth procedure. The initial layers of GaAs were grown at lower growth rates and at lower substrate temperatures, followed by a thicker GaAs layer grown at usual growth rate of 1 pm /h. The films grown at temper...
In this work, Al0.83In0.17N/GaN/Al0.18Ga0.82N/GaN epitaxial layers used for the fabrication of double-channel metal–oxide–semiconductor high-electron mobility transistors (MOSHEMTs) were grown on silicon substrates using a metalorganic chemical vapor deposition system (MOCVD). A sheet electron density of 1.11 × 1013 cm−2 and an electron mobility of...
Multiple-mesa-fin-channel array patterned by a laser interference photolithography system and gallium oxide (Ga2O3) gate oxide layer deposited by a vapor cooling condensation system were employed in double-channel Al0.83In0.17N/GaN/Al0.18Ga0.82N/GaN heterostructured-metal-oxide-semiconductors (MOSHEMTs). The double-channel was constructed by the po...
This work demonstrates high-performance AlInGaN/AlN/GaN high electron mobility transistors grown on 150 mm p-type low resistivity (resistivity 20-100 Ω-cm) silicon substrate with state-of-the-art Johnson’s figure-of-merit (JFOM). Current gain cut-off frequency (fT) of 83 GHz and 63 GHz and power gain cut-off frequency (fmax) of 95 GHz and 77 GHz wi...
A novel lattice matched double barrier Al0.72In0.16Ga0.12N/Al0.18In0.04Ga0.78N/GaN normally-off high electron mobility transistor (HEMT) is designed and simulated by solving a set of thermodynamic transport equations. Using the experimentally calibrated physical models with bearing mobility degradation by surface roughness in account, the recess ga...
In this work, we investigate the dynamic buffer response of AlInN/GaN high electron mobility transistors (HEMTs) grown on silicon substrates. Significant improvements in vertical breakdown voltage, reduced buffer conduction and charge trapping effect are observed on the samples with a superlattice layer in the buffer. The dynamic response of the bu...
The large bandgap and high p-type conductivity of sp²-bonded boron nitride (BN) make the compound very attractive for deep ultraviolet light-emitting diodes (DUV LEDs). However, integrating the promising sp² material in the DUV LED structure is challenging. This is because the reported growth conditions for scalable high-quality BN, including the h...
In this study, multistacked InAs submonolayer (SML) quantum dots (QDs) were sandwiched in an InGaAs/GaAsSb dot-in-a-double-well (DDwell) structure to enhance the crystal quality and optical properties of QDs. The photoluminescence (PL) intensity of the InAs SML QDs with the DDwell structure was 5.5 times higher than that of conventional InAs/GaAs S...
A significant improvement in electron mobility has been achieved by several authors on AlInGaN/GaN heterostructures by adding a small amount of Ga to the AlInN alloy. In this study, we propose that thermodynamic stability plays an important role in controlling the electron transport properties of these heterostructures. A quantitative investigation...
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 physiological salt environment overcoming charge screening effects, without requiring sample pre-processing. This study reports a tunable and...
MOCVD grown boron doped GaN films were observed strong phase separation with poor surface morphology and high structural defect due to the wide miscibility gap between BN and GaN. The shift of the E2-high peak in Raman spectrum implied that boron substituted nitrogen during growth and induced BN defects which is proved by lower formation energy of...
In this study, a high-performance InAlN/GaN high electron mobility transistor (HEMT) was fabricated using low-temperature microwave annealing (MWA) as the ohmic metal alloy process for the first time. Ni–Al alloy aggregation is significant for InAlN devices because of the high Al fraction in InAlN layer. Furthermore, the indium segregation and out-...
Exposure to heavy metal ions poses grave danger to public health and reliable and affordable water quality monitoring system that can rapidly screen for heavy metal ion contamination is necessary. In this research, we have developed a unique sensing methodology to detect heavy metal ions such as Pb²⁺ and Hg²⁺ in water sources, using ion-selective h...
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 lar...
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 l...
In this research, we have designed, fabricated and characterized 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 investi...
In this research, the development of a highly sensitive FET based biosensor technology for whole cell sensing and cellular transmembrane potential measurement is discussed and a quantitative model is proposed to elucidate the sensor mechanism. Electrical double layer (EDL) gated FET biosensor platform offers high sensitivity target analyte detectio...
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 d...
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 packag...
In this work, low turn-on voltage (Von), low leakage current (IR) and high breakdown voltage (VBR) AlGaN/GaN Schottky barrier diodes (SBDs) are fabricated on 6-inch Silicon substrates using an anode recess process combined with SF6 plasma treatment. Using this process, turn-on voltage is reduced from 1.3 V to 0.6 V, compared to the planar untreated...
In this study, we report the development of a high sensitivity assay for the detection of cardiac troponin I using electrical double layer gated high field AlGaN/GaN HEMT biosensor. The unique gating mechanism overcomes the drawback of charge screening seen in traditional FET based biosensors, allowing detection of target proteins in physiological...
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 us...
The low-frequency noise (LFN) and reverse recovery charge characteristics of a six-inch InAlN/AlN/GaN Schottky barrier diode (SBD) on the Si-on-insulator (SOI) substrate were demonstrated and investigated for the first time. Raman spectroscopy indicated that using SOI wafers lowered epitaxial stress. According to the DC and LFN measurements at temp...
We have successfully mitigated the out-diffusion of Ge during molecular beam epitaxy of InGaAs on Ge by using a GaAsSb barrier layer as evidenced by secondary ion mass spectroscopy. Compared to GaAs, this GaAsSb barrier layer also results in a smoother surface morphology with its root-mean-square roughness of 0.7 nm due to the surfactant effect of...
High quality Y2O3 on GaSb was achieved using both molecular beam epitaxy (MBE) and atomic layer deposition (ALD) with interfacial characteristics studied by in-situ X-ray photoelectron spectroscopy (XPS) and metal-oxide-semiconductor (MOS) electrical measurements. Ga-oxide and stoichiometric Sb-oxides were obtained in the MBE-Y2O3/GaSb and non-stoi...
The electrical, structural, and chemical properties of HfO2/Al2O3/GaSb metal-oxide-semiconductor capacitors (MOSCAPs) fabricated on Sb-rich (2 × 5) and Sb-stabilized (1 × 3) surfaces by atomic layer deposition are characterized. A combination of the transmission electron microscopic, x-ray photoelectron spectroscopic, and atomic force microscopic o...
With continuous increase in transistor count and clock frequency, the power density of current Si integrated circuits has reached a level that calls for a revolutionary change in transistor technology. High hole mobility Ge and high electron mobility InGaAs have been considered to be the most promising channel materials for p-channel and n-channel...
Undoped and Ga-doped ZnO films are grown on GaN templates by plasma-assisted molecular beam epitaxy for systematic investigation of the influence of native defects on their electrical properties. The distinct electrical properties of the undoped and Ga-doped ZnO films are observed after thermal treatment in a nitrogen and an oxygen ambient. It is f...
Influences of energy band lineup at the tunneling junction on the performance of GaAs x Sb 1−x /In y Ga 1−y As heterojunction tunneling field-effect transistors (HTFETs) have been investigated using TCAD simulations. The results show that devices with low off-current, high on-current, and low subthreshold swing over a wide current range can be achi...
In this paper, we report that a nearly defect free In 0.71 Ga 0.29 As fin structure can be selectively grown inside oxide nano-trenches on a Ge template by using composition-graded InGaP as a buffer layer. A growth model is proposed to explain the strain energy accommodation behavior from Ge to In 0.70 Ga 0.30 P and then to In 0.71 Ga 0.29 As. This...
Dynamic resistance of AlGaN/GaN Metal-Insulator-Semiconductor- High Electron Mobility Transistors (MIS-HEMTs) has been extensively investigated lately because of its great impact to the energy efficiency of the devices. There have been many reports on the observation of degradation of dynamic on-resistance (Ron) after an off-state stress. Lots of e...
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...
High breakdown voltage and thermally stable AlGaN/GaN Schottky barrier diodes (SBDs) were fabricated using diamond-like carbon (DLC) anode design on a silicon (111) substrate. The DLC metal-hydrocarbon target in this study is tungsten-carbide and this film coating was prepared by reactive DC magnetron sputtering in a high temperature chamber. Based...
This paper provides a comprehensive study of the fiber dispersion effect for the generation of quasi-sinusoidal terahertz modulations on optical pulses, which are especially beneficial for the applications of terahertz photonic generation and low-frequency coherent Raman spectroscopy. Instead of compensating the fiber group-velocity dispersion in a...
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...
Y2O3, as a common high κ gate dielectric, has been directly deposited on (In)GaAs, GaSb, and Ge using electron beam evaporation in ultra-high vacuum. These semiconductors have distinctly different chemical bonding and surface electronic characteristics. No interfacial passivation layer was employed. High-quality Y2O3/semiconductor interfaces have b...
Semipolar {101¯1} InGaN quantum wells are grown on (001) Si substrates with an Al-free buffer and wafer-scale uniformity. The novel structure is achieved by a bottom-up nano-heteroepitaxy employing self-organized ZnO nanorods as the strain-relieving layer. This ZnO nanostructure unlocks the problems encountered by the conventional AlN-based buffer,...
In this study, conventional multiple-frequency capacitance–voltage (C-V) curves of a metal-insulator-semiconductor structure were modified into barrier capacitance–barrier voltage (Cbr–Vbr) curves to study the interface state of an Al2O3/III-N interface. By eliminating the contribution of a serially connected insulator capacitance (Ci), the variati...
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 ca...
In this work, the InAs/AlSb high electron mobility transistors (HEMTs) on GaAs semi-insulating substrate using refractory iridium (Ir) gate technology was proposed. The Ir-gate exhibited a superior metal work function which was beneficial for increasing Schottky barrier height of InAs/AlSb heterostructures to 0.58 eV. Compared to the Ti-gate HEMT,...
This paper reports our continuous efforts and achievements in understanding and improving AlInN/AlN/GaN heterostructure for high performance field-effect transistors and switching devices. AlInN/AlN/GaN high electron mobility transistors (HEMTs) with high electron mobility and low sheet resistance have been demonstrated on 6" Si(111) substrates. It...
The effects of in-situ and ex-situ surface treatments on the electrical properties of GaSb metal-oxide-semiconductor capacitors (MOSCAPs) are compared and investigated. The in-situ approach can provide a native oxide-free GaSb surface subsequent high-κ dielectric deposition. HfO2/Al2O3/p-GaSb MOSCAPs fabricated on an Sb-stabilized surface exhibit c...
This study applied a methodology for defining the threshold voltage shift (ΔVTH) transient of AlGaN/GaN heterostructure field-effect transistors (HFETs) to observe the influence of traps in AlGaN/GaN HFETs with different buffer layers: a carbon-doped (C-doped) buffer and an Al0.05Ga0.95N back barrier layer. This methodology involves synchronous swi...
Stressed C–V measurement was used to extract the trap profiles in AlGaN/GaN HFETs with field plates enduring high-voltage off-state stress. The C–V measurement results also correlated with the degradation in dynamic on-resistance (RDS,on) after transistors were stressed with similar stress conditions. Based on the correlation between the trap profi...
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 it...
High mobility III-V compound semiconductors have been extensively investigated recently for future complementary metal-oxide-semiconductor (CMOS) applications. GaSb, which has high electron and hole mobilities as well as a narrow bandgap is an attractive material for future high-speed and low-power integrated circuits. Due to the easy formation of...
In this work, the 6-inch AlSb/InAs on Si (0 0 1) substrate is used to increase device integration and cost-effective purpose. The iridium (Ir)-gate was used for the InAs/AlSb on silicon substrate and temperature-dependent characteristics were also studied. The Ir-gate exhibited a superior metal work function which was beneficial for increasing the...
Growth of InGaSb/AlSb high hole mobility quantum well field effect transistors (QW FETs) on Si substrates with a step-graded GaAsSb metamorphic buffer layer by molecular beam epitaxy is explored. With an optimized growth temperature for the InGaSb/AlSb QW, hole mobility of 770 cm2/V·s and 3,060 cm2/V·s has been achieved at room temperature and 77 K...
A measurement methodology involving high-voltage capacitance-voltage (C-V) was proposed to determine the trapping profile of a stressed AlGaN/GaN heterostructure field-effect transistor (HFET). Comparing the curves between initial (device without stress) and stressed (device with stress) C-V measurements revealed that the transient behavior was dom...
In this study, Ga-doped ZnO (GZO) thin films were deposited on GaN templates by using plasma-assisted molecular beam epitaxy. To obtain low resistivity GZO films, in-situ post-annealing under Zn overpressure was carried out to avoid the generation of acceptor-liked Zn vacancies. The resultant films showed optical transparency over 95% in the visibl...
This paper discusses the impact of the back-gate bias on the dc, low-frequency noise, and dynamic behavior characteristics of a p-GaN gate high-electron mobility transistor on silicon substrate. This paper is investigated to understand the physical mechanisms of the back-gate terminal modulation of normally OFF GaN power devices. When a negative ba...
Two quantum control spectroscopic techniques were applied to study InAs quantum dot (QD) devices, which contain different strain-reducing layers. By adaptively control light matter interaction, a delayed resonant response from the InAs QDs was found to be encoded into the optimal phase profile of ultrafast optical pulse used. We verified the delaye...
Molecular beam epitaxy deposited rare-earth oxide of Y2O3 has effectively passivated GaSb, leading to low interfacial trap densities of (1–4) × 1012 cm−2 eV−1 across the energy bandgap of GaSb. A high saturation drain current density of 130 μA/μm, a peak transconductance of 90 μS/μm, a low subthreshold slope of 147 mV/decade, and a peak field-effec...