Shu-Yi Tsai

Study on the low leakage current of an MIS structure fabricated by ICP-CVD

As the dimensions of electric devices continue to shrink, it is becoming increasingly important to understand how to obtain good quality gate oxide film materials wilth higher carrier mobility, lower leakage current and greater reliability. All of them have become major concerns in the fabrication of thin film oxide transistors. A novel film deposition method called Inductively Coupled Plasma-Chemical Vapor Deposition (ICP-CVD) has received attraction in the semiconductor industry, because it can be capable of generating high density plasmas at extremely low temperature, resulting in less ion bombardment of the material surface. In this work, we present the results of crystallized silicon dioxide films deposited by inductively coupled plasma chemical vapor deposition technique at an extremely low temperature of 90°C. The value of the refractive index of the crystallized ICP-CVD SiO2 film depends on the r.f. power of the ICP system, and approximates to be 1.46. This value is comparable to that of SiO2 films prepared by thermal oxidation. As the r.f. power of ICP applied more than 1250 Watts, still only the (111) diffraction peak is observed by XRD, which implies a very strong preferred orientation or single crystal structure. Too low or too high r.f. power both produces amorphous SiO2 films. From the I-V curve, the MIS device with a SiO2 dielectric film has a lower leakage current density of 6.8×10-8A/cm2 at 1V as the film prepared at 1750 watts. The highest breakdown field in this study is 15.8 MV/cm. From the FTIR analysis, it was found that more hydrogen atoms incorporate into films and form Si-OH bonds as the r.f. power increases. The existence of Si-OH bonds leads to a poor reliability of the MIS device.

Heterojunction photodiodes based on p-NiO/ n-ZnO for ultraviolet detection

All oxide-based, nano-transparent p-n heterojunction device consisting of p-NiO and n-ZnO thin films was fabricated by r.f. sputtering method. The structural and electric properties of the p-NiO/n-ZnO heterojunction were characterized by X-ray diffraction (XRD), UV-visible spectroscopy, Hall measurement, and photocurrent measurements. The XRD shows that ZnO films are highly crystalline in nature with a preferred orientation along the (0 0 2) direction. The p-NiO/n-ZnO heterojunction device has an average transmittance of over 80% in the visible region. The current-voltage curve of the heterojunction demonstrates obvious rectifying diode behavior in a dark environment. The lowest leakage current is 4.35×10−8 A/cm2 for p-NiO/n-ZnO heterojunction device. The realization of all-wide-band-gap p-NiO/n-ZnO heterojunction will provide a promising application of UV light emitting diodes.