Wide Band Gap Semiconductors

The effects of aluminum, indium and tin dopants on the microstructure and electrical properties of ZnO thin films prepared on silica glass substrates by the sol–gel method were investigated. As a starting material, zinc acetate dihydrate was used. 2-methoxyethanol and monoethanolamine were used as the solvent and stabilizer, respectively. The dopant sources were aluminum chloride, indium chloride and tin chloride. For each dopant, films doped with 1 at.% aluminum, 1 at.% indium and 2 at.% tin concentrations exhibited a stronger c-axis orientation perpendicular to the substrate and had larger grain, a high smooth surface morphology as well as high conductivity and transmittance than the others. In addition, the electrical resistivity value of ZnO thin films reduced by applying the second heat-treatment in nitrogen with 5% hydrogen. When the aluminum doping concentration was 1 at.%, the film had a columnar structure, a resistivity value of 1.1×10−2 Ω cm and a transmittance higher than 90% in the visible spectra region.

We investigate the breakdown (Vbr) enhancement potential of the field plate (FP) technique in the context of AlGaN/GaN power HEMTs. A comprehensive account of the critical geometrical and material variables controlling the field distribution under the FP is provided. A systematic procedure is given for designing a FP device, using two-dimensional (2-D) simulation, to obtain the maximum Vbr , with minimum degradation in on-resistance and frequency response. It is found that significantly higher Vbr can be achieved by raising the dielectric constant (εi) of the insulator beneath the FP. Simulation gave the following estimates. The FP can improve the Vbr by a factor of 2.8-5.1, depending on the 2-DEG concentration (ns) and εi. For n s=1×1013/cm2, the Vbr can be raised from 123 V to 630 V, using a 2.2 μm FP on a 0.8 μm silicon nitride, and 4.7 μm gate-drain separation. The methodology of this paper can be extended to the design of FP structures in other lateral FETs, such as MESFETs and LD-MOSFETs

We have observed significant instability in the threshold voltage of 4H-SiC metal-oxide-semiconductor field-effect transistors due to gate-bias stressing. This effect has a strong measurement time dependence. For example, a 20-mus-long gate ramp used to measure the I-V characteristic and extract a threshold voltage was found to result in a instability three to four times greater than that measured with a

Using a GaN nanorod template in a hydride vapor phase epitaxy (HVPE) system can manufacture a freestanding GaN (FS-GaN) substrate with threading dislocation densities down to ~ 107 cm-2. In this letter, we report InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown on this FS-GaN substrate. The defect densities in the homoepitaxially grown LEDs were substantially reduced, leading to improved light emission efficiency. Compared with the LED grown on sapphire, we obtained a lower forward voltage, smaller diode ideality factor, and higher light-output power in the same structure grown on FS-GaN. The external quantum efficiency (EQE) of LEDs grown on FS-GaN were improved especially at high injection current, which brought the efficiency droop phenomenon greatly reduced at high current density.

Abstract—Strain-compensated InGaN–AlGaN quantum wells (QW) are investigated as improved active regions for lasers and light emitting diodes. The strain-compensated QW structure consists of thin tensile-strained AlGaN barriers surrounding the InGaN QW. The band structure ...

We report on the calculation of electrical characteristics of AlGaN/GaN heterojunction field effect transistors (HFETs). The model is based on the self-consistent solution of the Schrodinger and Poisson equations coupled to a quasi-2D model for the current flow. Both single and double heterojunction devices are analyzed for [0001] or [000-1] growth directions. The onset of a parasitic p-channel for particular growth directions and alloy concentrations is also shown

Abstract—Improvement of light extraction efficiency of InGaN LEDs using colloidal-based SiO2 /polystyrene (PS) mi-crolens arrays was demonstrated. The size effect of the SiO2 mi-crospheres and the thickness effect of the PS layer on the light ex-traction efficiency of III-nitride LEDs ...

We demonstrate the surface plasmon (SP) enhanced green light-emitting diodes (LEDs). The Au nanoparticles were embedded in the p-GaN of LEDs. The photoluminescence and electroluminescence measurements showed improved optical properties of LEDs with Au nanoparticles due to an increase in the spontaneous emission rate by resonance coupling between the excitons in multiple quantum wells and localized surface plasmons in Au nanoparticles. The optical output power of SP-enhanced green LEDs with Au nanoparticles was increased by 86% without showing degradation of the electrical characteristics of LEDs compared to LEDs without Au nanoparticles.

In this work, we investigated the dye-sensitized solar cells (DSSCs) using photoanode, which were fabricated directly from electrospinning of TiO2 nanofibres onto the substrate. The electrochemical impedance spectroscopy (EIS) and current–voltage diagram were used to analyse electron transport in electrospun nanofibres and determine their applicability in DSSCs. In order to improve the short-circuit photocurrent of fabricated cells, we treated the electrospun TiO2 electrode with the TiCl4 aqueous solution. The modification of the photoelectrode significantly improves the power conversion efficiency (over 26%) of the solar cells attributed to the higher electron lifetime (τ) and reduction in recombination processes as indicated by the EIS of the solar cells.

Previously developed methods used to grow Ge1-ySny alloys on Si are extended to Sn concentrations in the 1019-1020 cm-3 range. These concentrations are shown to be sufficient to engineer large increases in the responsivity of detectors operating at 1550 nm. The dopant levels of Sn are incorporated at temperatures in the 370–390 °C range, yielding atomically smooth layers devoid of threading defects at high growth rates of 15–30 nm/min. These conditions are far more compatible with complementary metal-oxide semiconductor processing than the high growth and processing temperatures required to achieve the same responsivity via tensile strain in pure Ge on Si. A detailed study of a detector based on a Sn-doped Ge layer with 0.25% (1.1 × 1020 cm-3) Sn range demonstrates the responsivity enhancement and shows much better I-V characteristics than previously fabricated detectors based on Ge1-ySny alloys with y = 0.02.

Efficient deep‐blue organic light‐emitting diodes were demonstrated using 4,4'‐bis(9‐ethyl‐3‐carbazovinylene)‐1,1'‐biphenyl doped in double‐emission layers (D‐EMLs). The D‐EML system, which consists of 2‐methyl‐9,10‐di(2‐naphthyl)anthracene and 1,4‐(dinaphthalen‐2‐yl)‐naphthalene as blue hosts, was employed to broaden the recombination zone and to ensure the good confinement of the holes and electrons. The optimized device showed a peak current efficiency of 4.47 cd/A, a peak external quantum efficiency of 4.09%, and Commission Internationale de L'Eclairage coordinates of (0.16, 0.10).

Threshold voltage and drain current instabilities in state-of-the-art 4H-SiC MOSFETs with thermal as-grown SiO2 and NO-annealed gate oxides have been studied using fast I-V measurements. These measurements reveal the full extent of the instability underestimated by dc measurements. Furthermore, fast measurements allow the separation of negative and positive bias stress effects. Postoxidation annealing in NO was found to passivate the