Fuwen Qin

Low resistance Ti Ohmic contacts to 4H-SiC by reducing barrier heights without high temperature annealing

Ti Ohmic contacts to relatively highly doped (1 × 1018 cm−3) n-type 4H-SiC have been produced, without high temperature annealing, by means of low temperature electronic cyclotron resonance microwave hydrogen plasma pre-treatment (HPT) of the SiC surface. The as-deposited Ti/4H-SiC contacts show Ohmic properties, and the specific contact resistance obtained is as low as 2.07 × 10−4 Ω·cm2 after annealing at low temperatures (400 °C). This is achieved by low barrier height at Ti/SiC interface, which could be attributed to decrease of surface states density by the HPT releasing Fermi level pinning, and to band-gap narrowing, image-force, and thermionic-field emission at high doping.

Effects of surface properties on barrier height and barrier inhomogeneities of platinum contacts to n-type 4H-SiC

We investigated the Schottky barrier of Pt/4H-SiC contact as a function of 4H-SiC surface properties which effectively controlled by electronic cyclotron resonance hydrogen plasma pretreatment for different periods and annealing. It is found that the effective barrier height monotonically increases with decreasing the degree of Fermi level pinning. Electrically homogeneous contacts are observed when the Fermi level (FL) is “pinned (Bardeen limit)” and “free-pinned (Schottky limit).” However, a partial pinning of FL leads to Gaussian distribution of inhomogeneous barrier height. These results could be correlated with changes in the magnitude and spatial distribution of surface state density after different pretreatments.

Improvement of SiO2/4H-SiC interface properties by electron cyclotron resonance microwave nitrogen-hydrogen mixed plasma post-oxidation annealing

We proposed an electron cyclotron resonance microwave nitrogen-hydrogen mixed plasma post-oxidation annealing process for SiO2/4H-SiC interface and investigated its effect on the electrical properties of the interface. The results indicate that this process could significantly reduce the density of interface traps (Dit) without degrading the oxide insulating properties. The best result is achieved for the 10-min annealed sample. The N and H, which are only concentrated at the SiO2/SiC interface, both play roles in reducing the Dit. N is more effective in passivating the shallow interface traps, while H is more effective in passivating the deep interface traps.

Deposition and properties of highly c-oriented of InN films on sapphire substrates with ECR-plasma-enhanced MOCVD

InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl indium (TMIn) and N2 were applied as precursors of In and N, respectively. The quality of as-grown InN films were systematically investigated as a function of TMIn fluxes by means of reflection high-energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), and atomic force microscopy (AFM). The results show that the dense and uniform InN films with highly c-axis preferred orientation are successfully achieved on sapphire substrates under optimized TMIn flux of 0.8 ml·min−1. The InN films reported here will provide various opportunities for the development of high efficiency and high-performance semiconductor devices based on InN material.

Chemical and electronic passivation of 4H-SiC surface by hydrogen-nitrogen mixed plasma

We propose a low-temperature electron cyclotron resonance microwave hydrogen-nitrogen mixed plasma treatment method for passivating 4H-SiC surface and investigate the effects of treatment on the structural, chemical, and electronic properties of the surface. The results indicate that the method is highly controllable and could result in an atomically ordered, unreconstructed, smooth, and clean SiC surface. The absence of surface band bending is indicative of an electronically passivated SiC surface with a surface state density as low as 5.47 × 1010 cm−2. This effect could be attributed to the simultaneous effects of H and N passivating on SiC surface.

Effects of Low Temperature Electronic Cyclotron Resonance Hydrogen Plasma Treatment and Annealing on the Electrical Properties of Ti and Ni Contacts to 4H-SiC

The effects of low temperature electronic cyclotron resonance microwave hydrogen plasma pretreatment and post-annealing on the electrical properties of Ti and Ni contacts to 4H-SiC were investigated. The HPT improves the Ohmic behavior of Ti/4H-SiC contact significantly. In contrast, it remarkably enhances the rectifying behavior of Ni/4H-SiC contact. The properties of Ti Ohmic contact and Ni rectifying contact improve with increasing annealing temperature up to 400 °C. However, they are deteriorated above 400 °C. X-ray photoelectron spectroscopy measurements confirm that the surface Fermi level (EFs) moves toward the conduction band edge by the HPT. It almost attains the bulk Femi level position after annealing at 400 °C with the surface states density (Ds) as low as 4.43×1011 cm-2 eV-1. However, after annealing above 400 °C, EFs moves back closer to midgap with an increase of Ds. The experimental results are found to obey the barrier height theory of Cowley and Sze.

ZnO-based graphite-insulator-semiconductor diode for transferable and low thermal resistance high-power devices

ZnO-based graphite-insulator-semiconductor (GIS) diode was fabricated on the high thermal and electrical conductive graphite substrate, with a SiO2 thin layer employed as the insulator layer. The current-voltage characteristics exhibit an excellent rectifying diode-like behavior with an obvious turn on voltage of 2.0 V and rather low leakage current of ∼10−4 A. An interesting negative capacitance phenomenon was also observed from the GIS diode. The excellent heat dissipation performance of the GIS diode compared with conventional sapphire based devices was experimentally demonstrated, which was of special interest for the development of high-power semiconductor devices with sufficient power durability.

Deposition of Ti–Si–N films on Al substrates by magnetron sputtering

Abstract The objective of this work is to settle the problem of adhesion between hard films and soft metal substrates. Hard Ti–Si–N films were deposited onto soft Al substrates with a double target magnetron sputtering system. The composition, structure, surface morphologies and mechanical properties were characterised by electron probe microanalyser, X-ray diffraction, atomic force microscope, scratch test and nanoindentation respectively. The as-deposited films had good adhesion to the Al substrates and had a smooth and lustrous surface. The maximum hardness of the films achieved was as high as 27·2 GPa at the Si target power of 80 W.

Bias effects on AlMgB thin films prepared by magnetron sputtering

AlMgB thin films were deposited on silicon (100) substrate using a three-target magnetron sputtering system in argon atmosphere. The influence of negative bias voltage on the thickness, morphology, microstructure, local bonding and hardness of the deposited films was investigated. Experimental results show that all films are X-ray amorphous, and the properties of the deposited films have a strong dependence on the applied substrates negative bias voltage. Deposited at high negative bias voltage, the AlMgB thin films are found to be generally dense, having a smooth surface and containing more well-formed B12 icosahedra, which consequently increase the hardness of the deposited films. However, deposited at low negative bias voltage, the AlMgB thin films exhibit loose structure, coarse surface and contain few B12 icosahedra. It is shown that the hardness of the dense and smooth AlMgB thin films can reach 22 GPa at the negative bias voltage of 400 V.

Passivation effects of phosphorus on 4H-SiC (0001) Si dangling bonds: A first-principles study*

The effect of phosphorus passivation on 4H-SiC(0001) silicon (Si) dangling bonds is investigated using ab initio atomistic thermodynamic calculations. Phosphorus passivation commences with chemisorption of phosphorus atoms at high-symmetry coordinated sites. To determine the most stable structure during the passivation process of phosphorus, a surface phase diagram of phosphorus adsorption on SiC (0001) surface is constructed over a coverage range of 1/9–1 monolayer (ML). The calculated results indicate that the 1/3 ML configuration is most energetically favorable in a reasonable environment. At this coverage, the total electron density of states demonstrates that phosphorus may effectively reduce the interface state density near the conduction band by removing 4H-SiC (0001) Si dangling bonds. It provides an atomic level insight into how phosphorus is able to reduce the near interface traps.