Preparation And Applicatons Of N-type ZnO Based Thin Films And Heterojunctions

Znic oxide (ZnO) has been considered as one of the most promising candidates to replace ITO, owing to its wide direct energy gap (3.37 eV at room emperature), abundant raw material, environmental friendliness, high radiation resistance and relatively low growth temperature. Moreover, the bandgap of ZnO can be controlled by alloying with MgO, from 3.37 to 4.05 eV. However, employing ZnMgO as a substitute for ZnO has limitations, due to the decreased conductivity. In order to compensate for the decrease of conductivity, we carried out some investigation fluorine-doped ZnMgO (ZMOF) transparent conductive thin films.Fabricating high quality and reproducible p-type ZnO is a huge challenge continues to be the problem of ZnO homojunctions. To avoid this problem, some researchers have made ZnO-based heterojunction using NiO which is a suitable material for ZnO based heterojunctions because of its p-type conductivity and its wide 3.7 eV direct bandgap. MgO and NiO can be alloyed for the entire MgO mole-fraction range from 0 to 1, thus creating bandgaps that vary from 3.7 to 7.8 eV. On the basis of ZnO/NiO heterojunctions, we used Ni1-xMgxO to fabricate heterojunctions with ZnO and ZnMgO and took a further study about their band structures. The main work included:1. Highly transparent and conducting ZMOF thin films were deposited on quartz substrates by pulsed laser deposition (PLD). The thin films deposited at 350 ℃ show the best crystallinity, and the lowest resistivity of 6.92×10-4 Ωcm, the average optical transmittance in the entire visible wavelength region is higher than 85%. We fabricated textured ZMOF thin films through eching.2. ZMOF thin films have been prepared on polycarbonate (PC) substrates by PLD. A ZnO buffer layer was deposited on the PC substrates before that ZMOF thin films were deposited. Compared with the single layer ZMOF films, the electrical resistivity of ZMOF/ZnO films decreased from 1.55 Ωcm to 1.70×10-2 Ωcm, the mobility increased from 0.573 cm2V-1 to 11.7 cm2V-1s-1.3. Radio frequency magneton sputtering technique was used to process F doped ZnO (FZO) thin films as the representative of ZnO thin films for vacuum annealing and H plasma treatment. The treated FZO thin films show better crystal and electrical qualities with the mobility of rendering 3-10 multiples growth. The high conductivity and stability of treated FZO thin films has been proposed by first-principles calculations based on density functional theory.4. Ni1-xMgxO thin films with different Mg contents were deposited on quartz substrates and solar-blind photodetectors were fabricated. We studied the effects of RTA on the properties of Ni1-xMgxO films and NiMgO-based UV photodetector. It is observed that the crystalline quality of films was improved and the bandgap was widened after RTA treatment. Furthermore, the dark current of the photodetector decrease obviously after RTA treatment which can improve the performance of the device through improving the ratio of signal-to-noise. The valence band offsets of ZnO/Ni1-xMgxO heterojunctions grown by PLD were measured by X-ray photoelectron spectroscopy (XPS). The conduction band minimum of the Ni1-xMgxO region shifts to higher energy with increased Mg content. Wide-bandgap Zn1-xMgxO/Ni1-yMgyO heterojunctions were fabricated on quartz substrates by PLD and their band offsets are measured by XPS. Alloying with Mg can tune the positions of VBM, CBM and bandgaps of Zn1-xMgxO and Ni1-xMgxO, according to which we can design various heterojunction devices with desired CBM and VBM values by appropriate Mg composition. Also, the blue shift of the absorption edges of the Zn1-xMgxO/Ni1-yMgyO heterojunctions has a significant impact on the design and application of deep-ultraviolet optoelectronic devices.