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Comparative study on a novel Al2O3-dielectric graded-barrier (GB) AlxGa1−xN/AlN/GaN/Si (x = 0.22 ∼ 0.3) metal-oxide-semiconductor heterostructure field-effect transistor (MOS-HFET) formed by using the ultrasonic spray pyrolysis deposition (USPD) technique has been made with respect to a conventional-barrier (CB) Al0.26Ga0.74N/AlN/GaN/Si MOS-HFET and the reference Schottky-gate HFET devices. The GB AlxGa1−xN was devised to improve the interfacial quality and enhance the Schottky barrier height at the same time. A cost-effective ultrasonic spray pyrolysis deposition (USPD) method was used to form the high-k Al2O3 gate dielectric and surface passivation on the AlGaN barrier of the present MOS-HFETs. Comprehensive device performances, including maximum extrinsic transconductance (gm,max), maximum drain-source current density (IDS,max), gate-voltage swing (GVS) linearity, breakdown voltages, subthreshold swing (SS), on/off current ratio (Ion/Ioff), high frequencies, and power performance are investigated. [ABSTRACT FROM AUTHOR]

Al0.26Ga0.74N/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) grown on a Si substrate with Al2O3/TiO2 stacked gate dielectrics formed by using non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique are investigated. High permittivity (k) values of Al2O3 and TiO2 were characterized to be 9 and 46.1, respectively, with an equal layer thickness of 10 nm. The present MOS-HFET (Schottky-gate HFET) design has demonstrated enhanced device characteristics at 300 K, including maximum drain–source current density (IDS,max) of 725 (530) mA/mm, IDS at VGS = 0 V (IDSS0) of 471 (383) mA/mm, gate-voltage swing (GVS) of 2.5 (1.6) V, two-terminal gate-drain breakdown voltage (BVGD) of −182 (−121) V, turn-on voltage (Von) of 4.9 (3.2) V, three-terminal off-state drain-source breakdown voltage (BVDS) of 174 (103) V, on/off current ratio (Ion/Ioff) of 5.6 × 107 (3.7 × 103), unity-gain cut-off frequency (fT) of 10.3 (6.8) GHz, maximum oscillation frequency (fmax) of 14.8 (8.6) GHz, and power-added efficiency (P.A.E.) of 38.5% (31.7%) at 2.4 GHz. High temperature device characteristics up to 450 K are also discussed. [ABSTRACT FROM AUTHOR]

This work investigates GaN/Al0.24Ga0.76N/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) grown on a Si substrate with MgO gate dielectric by using the non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique. The oxide layer thickness is tuned to be 30 nm with the dielectric constant of 8.8. Electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM), transmission electron microscopy (TEM), C–V, low-frequency noise spectra, and pulsed I–V measurements are performed to characterize the interface and oxide quality for the MOS-gate structure. Improved device performances have been successfully achieved for the present MOS-HEMT (Schottky-gate HEMT) design, consisting of a maximum drain-source current density (IDS, max) of 681 (500) mA/mm at VGS = 4 (2) V, IDS at VGS = 0 V (IDSS0) of 329 (289) mA/mm, gate-voltage swing (GVS) of 2.2 (1.6) V, two-terminal gate-drain breakdown voltage (BVGD) of −123 (−104) V, turn-on voltage (Von) of 1.7 (0.8) V, three-terminal off-state drain-source breakdown voltage (BVDS) of 119 (96) V, and on/off current ratio (Ion/Ioff) of 2.5 × 108 (1.2 × 103) at 300 K. Improved high-frequency and power performances are also achieved in the present MOS-HEMT design. [ABSTRACT FROM AUTHOR]

Al0.25Ga0.75N/GaN enhancement-mode (E-mode) metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs) obtained by the ozone water oxidization method are investigated in this work. Decreased gate leakage and reduced channel depletion are obtained by forming the Al2O3 dielectric layer of the MOS gate structure by a cost-effective oxidization method. Pulse current–voltage (I–V), low-frequency noise, and Hooge coefficient measurements are compared to verify the interface quality improved by the oxide passivation effect. In comparison, a conventional Schottky-gate HEMT device is also fabricated on the same epitaxial sample. Enhanced device gain, current drive density, breakdown, on/off current ratio, and high-temperature stability up to 450 K are also investigated in this work. [ABSTRACT FROM AUTHOR]

This work investigates Al2O3/AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) grown on SiC substrate by using the non-vacuum ultrasonic spray pyrolysis deposition (USPD) method. The Al2O3 was deposited as gate dielectric and surface passivation simultaneously to effectively suppress gate leakage current, enhance output current density, reduce RF drain current collapse, and improve temperature-dependent stabilities performance. The present MOS-HEMT design has shown improved device performances with respect to a Schottky-gate HEMT, including drain-source saturation current density at zero gate bias (IDSS: 337.6 mA mm−1 → 462.9 mA mm−1), gate-voltage swing (GVS: 1.55 V → 2.92 V), two-terminal gate-drain breakdown voltage (BVGD: −103.8 V → −183.5 V), unity-gain cut-off frequency (fT: 11.3 GHz → 17.7 GHz), maximum oscillation frequency (fmax: 14.2 GHz → 19.1 GHz), and power added effective (P.A.E.: 25.1% → 43.6%). The bias conditions for measuring fT and fmax of the studied MOS-HEMT (Schottky-gate HEMT) are VGS = −2.5 (−2) V and VDS = 7 V. The corresponding VGS and VDS biases are −2.5 (−2) V and 15 V for measuring the P.A.E. characteristic. Moreover, small capacitance-voltage (C–V) hysteresis is obtained in the Al2O3-MOS structure by using USPD. Temperature-dependent characteristics of the present designs at 300–480 K are also studied. [ABSTRACT FROM AUTHOR]

This work presents AlGaN/GaN high-electron mobility transistors (HEMTs) that are grown on silicon. Various passivation layers are deposited on AlGaN/GaN HEMTs. AlGaN/GaN HEMTs were fabricated with TiO2 dielectrics, and their performance was compared with that of unpassivated and that of HfO2-passivated HEMTs. The TiO2-passivated HEMT with a gate length of 1 μm exhibits a maximum extrinsic transconductance of 134.4 mS mm−1, a current-gain cutoff frequency of 10.62 GHz, and a maximum frequency of oscillation of 16.37 GHz. Capping with any of the dielectric materials used herein improves the device performance over that of the unpassivated HEMTs. Additionally, experimental data demonstrate that the use of TiO2 is a favorable alternative to HfO2 passivation. This work is the first to present the microwave power of TiO2-passivated AlGaN/GaN HEMTs. [ABSTRACT FROM AUTHOR]

Most photovoltaics operate at high temperature under sunlight. In this work, the thermal instability of diiodooctane-based high-efficiency bulk heterojunction (BHJ) organic photovoltaics (OPVs) is studied. The BHJ layers were heated to various temperatures to investigate the changes in their physical properties using atomic force microscopy phase images. The mobilities of the carriers were characterized at various temperatures using the space-charge-limited current method, and the carrier lifetime was calculated by applying impedance spectroscopy to the simulated equivalent circuit of the OPV devices. [ABSTRACT FROM AUTHOR]

This work proposes an approach for improving the performance of poly(3-hexylthiophene) (P3HT-) based organic photovoltaics (OPVs). P3HT-based bulk heterojunction (BHJ) film can absorb the energy from 532 nm laser light and be transformed into favorable morphology. A combination of traditional thermal annealing and laser annealing improved device performance, with a slight increase in fill factor and a significant improvement in short-circuit current density. Better crystallization and a higher degree of molecular order in the thermal/laser coannealed P3HT-based BHJ film were observed through X-ray diffraction and Raman spectroscopy. [ABSTRACT FROM AUTHOR]