Niangjuan Yao

Preparation and properties of ZnO:Mo thin films deposited by RF magnetron sputtering

Mo doped ZnO thin films (ZnO:Mo, MZO) were prepared on quartz glass substrates by RF magnetron sputtering at the lower substrate temperatures (room temperature (RT) and 100°C). Their structural, electrical and optical properties were studied by X-ray diffractometry (XRD), four probe technique, Hall measurement, and UV-VIS-NIR spectrophotometer, respectively. XRD showed that the resultant films were wurtzite structure with c-axis preferential orientation. As the substrate temperatures increasing, the thickness of the film increased and the crystallinity became better. The resistivity of the films were 3.44x10-3 Ω•cm and 3.31x10-3 Ω•cm for the films deposited at RT and 100°C, respectively. The corresponding average transmittance in visible and near IR region (400-1100nm) was 81.7 % and 74.5 %, respectively. In addition, for the film deposited at 100°C, the refractive index (n) and band gap (Eg) were obtained by fitting the transmittance spectra and discussed.

Fabrication and performance of a double layered Mn-Co-Ni-O/Mn-Co-Ni-Cu-O thin film detector

A thermal sensitive infrared and THz detector was fabricated by a double layered Mn-Co-Ni-O/Mn-Co-Ni-Cu-O films. The Mn-Co-Ni-O material, as one type of transition metal oxides, has long been used as a candidate for thermal sensors or infrared detectors. The resistivity of a most important Mn-Co-Ni-O thin film, Mn1. 96Co0.96Ni0.48O4(MCN) , is about 200 Ω·cm at room temperature, which ranges about 2 orders larger than that of VOx detectors. Therefore, the thickness of a typical squared Mn-Co-Ni-O IR detector should be about 10 μm, which is too large for focal plane arrays applications. To reduce the resistivity of Mn-Co-Ni-O thin film, 1/6 of Co element was replaced by Cu. Meanwhile, a cover layer of MCN film was deposited onto the Mn-Co-Ni-Cu-O film to improve the long term stability. The detector fabricated by the double layered Mn-Co-Ni-O/Mn-Co-Ni-Cu-O films showed large response to blackbody and 170 GHz radiation. The NEP of the detector was estimated to be the order of 10-8 W/Hz0. 5. By applying thermal isolation structure and additional absorption materials, the detection performance can be largely improved by 1-2 orders according to numerical estimation. The double layered Mn-Co-Ni-O film detector shows great potentials in applications in large scale IR detection arrays, and broad-band imaging.

Performance of terahertz photodetectors based on MSM structures of Mercury-Cadmium-Telluride under low temperature

High sensitive Terahertz detection can be achieved by properly constructing Metal-Semiconductor-Metal (MSM) structure with semiconductor materials. In this study, Mercury-Cadmium-Telluride (MCT) film was used to fabricate MSM Terahertz detectors. The working temperature was altered to study the IV characteristics of MCT detectors under RT and 77 K, as well as the response signals to 0.0375 THz and 150 GHz sources. The results showed that the response speed was greatly improved under low temperature condition, and the time constant decreased to smaller than 3 μs at 77 K, comparing to some hundred μs at room temperature (RT). However, due to the variation in IV characteristics under low temperature, the working current of the detector was much lower than that at RT for identical voltage bias, and the low frequency response was 6 times larger than that at RT under the same bias current. The MCT detector is shown to be highly sensitive for THz detection and its detection ability can be further improved by lowering down the working temperature.

Preparation of CuInSe2 thin films by spin-coating and selenization

In order to fabricate low cost and printable CuInSe2 (CIS) thin film solar cells, a chemical process has been developed to fabricate uniform CIS films with large grain size and close stoichiometry to chalcopyrite phase. Cu(NO3)2, InCl3 and ethyl cellulose (EC) were adopted to form the starting solution. CIS films were prepared by spin-coating and selenization. Precursor films and CIS films were investigated by SEM, EDS and XRD. CuCl and InCl3 crystals appeared in the precursor films. During the selenization process, CuCl first reacted with Se vapor to form Cu2-xSe. With increasing selenization temperature, InCl3 reacted with Cu2-xSe to form CIS accompanying the evaporation of chlorine in the form of gas. It is revealed that the element ratio in final CIS film is determined by the raw material ratio in the starting solution and the selenization temperature.

Effects of post annealing on structural, electrical and optical properties of ZnO:Al thin films prepared by RF magnetron sputtering

Al doped ZnO (ZnO:Al, AZO) thin films were deposited on ordinary soda-lime glass (SLG) substrates by RF magnetron sputtering. Effects of post annealing (300~600 °C for 2~30 min in air and N2, respectively) were studied. All the films were wurtzite structure with highly c-axis preferential orientation. Their electrical properties were relatively stable at the post annealing temperature of 300 °C. As the temperature further increasing, post annealing in air leaded to drastic degradation in the electrical properties, while that in N2 had relatively small influence. Diffusion of alkali ions from SLG substrates was deduced to be one of the influence factors for electrical properties. The spectra measurements showed that the post annealing mainly affected the transmittance in the near-infrared and infrared (NIR-IR) range and the optical band gap (Eg). The variation of Eg was attributed to the Burstein-Moss (BM) shift modulated by many-body effects.