Dawei Yan

Forward current transport mechanisms in Ni/Au-AlGaN/GaN Schottky diodes

The forward current transport mechanisms in Ni/Au-AlGaN/GaN Schottky diodes are studied by temperature dependent current-voltage (T-I-V) measurements from 298 to 473u2009K. The zero-bias barrier height qϕBn and ideality factor values determined based on the conventional thermionic-emission (TE) model are strong functions of temperature, which cannot be explained by the standard TE theory. Various transport models are considered to analyze the experimental I-V data. The fitting results indicate that the increased current at low bias is due to the trap-assisted tunneling with an effective trap density of about 8.8u2009×u2009106u2009cm−2, while the high-bias current flow is dominated by the TE transport mechanism, accompanied by a significant series resistance effect. By fitting the high-forward-bias I-V characteristics, the effective qϕBn values with a small negative temperature coefficient are obtained. The temperature dependence of the saturation tunneling current and qϕBn is finally explained by considering the thermall...

Comparison of electrical characteristics between AlGaN/GaN and lattice-matched InAlN/GaN heterostructure Schottky barrier diodes

Abstract Lattice-matched Pt/Au–In0.17Al0.83N/GaN hetreojunction Schottky barrier diodes (SBDs) with circular planar structure have been fabricated. The electrical characteristics of InAlN/GaN SBD, such as two-dimensional electron gas (2DEG) density, turn-on voltage, Schottky barrier height, reverse breakdown voltage and the forward current-transport mechanisms, are investigated and compared with those of a conventional AlGaN/GaN SBD. The results show that, despite the higher Schottky barrier height, more dislocations in InAlN layer causes a larger leakage current and lower reverse breakdown voltage than the AlGaN/GaN SBD. The emission microscopy images of past-breakdown device suggest that a horizontal premature breakdown behavior attributed to the large leakage current happens in the InAlN/GaN SBD, differing from the vertical breakdown in the AlGaN/GaN SBD.

Highly textured conductive and transparent ZnO films for HIT solar cell applications

In this paper, aluminium-doped zinc oxide (AZO) thin-films were fabricated on both glass and silicon substrates by radio-frequency magnetron sputtering at various working pressures of 0.15–0.46 Pa. The effect of working pressure on the structural, electrical, and optical properties of the deposited AZO films was carefully studied. The lower working pressure is more favourable to large grain size, smooth surface, low electrical resistivity, and moderate optical transparency. For the AZO films deposited at lower working pressures, the larger grain size can be ascribed to the higher kinetic energy of the sputtered particles while the lower electrical resistivity is strongly related to both the presence of fewer grain boundaries due to the larger grain size and more activated amount of dopants in the films. We then applied AZO films deposited at 0.15 Pa to Al/AZO/n-a-Si : H/i-a-Si : H/p-c-Si/Al heterojunction Si solar cells with intrinsic thin layer (HIT) solar cells and achieved highly textured surfaces via acid etching. The HIT solar cells after acid texturing showed a higher external quantum efficiency (EQE) value than those with smooth AZO films mainly in the wavelength region from 300 to 500 nm, leading to an obvious increase in the conversion efficiency from 14.1% to 14.7%.

Current transport mechanisms in lattice-matched Pt/Au-InAlN/GaN Schottky diodes

Lattice-matched Pt/Au-In0.17Al0.83N/GaN hetreojunction Schottky diodes with circular planar structure have been fabricated and investigated by temperature dependent electrical measurements. The forward and reverse current transport mechanisms are analyzed by fitting the experimental current-voltage characteristics of the devices with various models. The results show that (1) the forward-low-bias current is mainly due to the multiple trap-assisted tunneling, while the forward-high-bias current is governed by the thermionic emission mechanism with a significant series resistance effect; (2) the reverse leakage current under low electric fields (<6 MV/cm) is mainly carried by the Frenkel-Poole emission electrons, while at higher fields the Fowler-Nordheim tunneling mechanism dominates due to the formation of a triangular barrier.

A Comprehensive Study of Reverse Current Degradation Mechanisms in Au/Ni/n-GaN Schottky Diodes

In this paper, we perform a comprehensive study on the reverse current degradation mechanisms in Au/Ni/n-GaN Schottky diodes based on an in-depth understanding on the defect-related current transport mechanisms. Instead of traditional Poole–Frenkel (PF) emission model, an extended bulk-limited PF transport process, including the compensation effect, is adopted to explain the variation of the PF current slope as a function of the stress time, which majorly takes place inside the depletion region near the neutral semiconductor side. Based on the electrostatic analysis, we develop a shallow donor-like defects model to address the current degradation kinetics, which states that the energetic electrons produced by Fowler–Nordheim tunneling can induce significant Joule heating effect during the subsequent drift move of field, and give rise to the formation of the donor-like defects, and in turn enhance the surface electrical field to cause a significant increase of the tunneling component, in good agreement with the emission microscope observations.

Tunneling-Hopping Transport Model for Reverse Leakage Current in InGaN/GaN Blue Light-Emitting Diodes

The nature of charge transport in GaN-based light-emitting diodes (LEDs) under reverse biases still remains elusive as the bias- and temperature-dependent characteristics of the current can hardly be formulated using a single transport mechanism. In this letter, based on numerical fitting, we develop a combined tunneling-hopping transport model to describe the complete electrical characteristics of the reverse leakage current in InGaN/GaN blue LEDs. This model depicts that the current behaviors are majorly limited by the charge transport process through the depletion region near the neutral n-side, where electrons at the valance band are ready to tunnel into the unoccupied localized gap states in neighborhood near the electron quasi-Fermi level (<inline-formula> <tex-math notation=LaTeX>

Current and light emission efficiency behaviors in GaN-based LEDS

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Progressive current degradation and breakdown behavior in GaN LEDs under high reverse bias stress

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Hot electrons induced degradation in lattice-matched InAlN/GaN high electron mobility transistors

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Performance enhancement of AlGaN-based ultraviolet light-emitting diodes by tailoring polarization in electron blocking layer

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