Investigation Of P-type Conducting SnO₂-based Thin Films And Their Homojunction And Heterojuntion

As transparent conductive oxide (TCO) thin films, p-type doped semiconductor material is widely researched in recent years, lack of good p-TCO thin films in optoelectronic properties is the main problem for its application in electronic devices. This dissertation presents the preparation, structure and properties of a new type transparent p-SnO2 thin films and SnO2-based homogeneous and heterogeneous junction which have good photo-electrical performances. The main results and conclusions are as follows.(1) Sb-doped SnO2 (ATO) thin films were deposited on quartz glass substrates and the effects of annealing temperature on p-type conducting and performance were discussed. The results indicated that the annealing temperature was critical to prepare such p-type conducting ATO films. It was found that 973K is the optimum annealing temperature to get p-ATO films with highest hole concentration (5.83×1019cm-3). If the temperature is too low, it is difficult that Sn ion is replaced by Sb; whereas Sb3+ is oxidized to Sb5+ under high temperature. In addition, the average transmittance of films in visible region is high as 80%.(2) Sb-doped SnO2 thin films were deposited on single crystal silicon substrate and the effects of substrate temperature on p-type conducting and performance were studied. The results indicated that substrate temperature was critical to prepare p-ATO films. As the substrate temperature increases, the nano-particles in the films change their morphology from sphere-type to cone-like, and last to nanorod-array-like, the lattice of crystals becomes perfect, which decreases the grain boundary scattering and results in good performance of p-type conducting. It was found that 523K is the optimum substrate temperature to get p-ATO films with highest hole concentration (1.64×1020cm-3) and mobility (8.33cm2V-1s-1). At 523K, the thin-films are highly crystallized with nanorod-array-like structure, optimum grain size (about 50 nm in radius of the rods) and (101) plane orientation.(3) p-type SnO2:Zn thin films were prepared by depositing Zn-doped SnO2 thin films or sandwich structure Zn/SnO2/Zn films on quartz glass substrates following heating-treatment or thermal diffusion process, and their visible light transmittance is higher than 80%. However, p-type conductivity is much smaller than thsoe of SnO2:Sb thin films, due to Zn doping in SnO2 belongs to deep-level doping.(4) p-n and p-i-n homojunctions or heterojunctions were assembled using the above prepared p-SnO2 and other n-type and intrinsic materials. The results show that p-n (p-ATO/n-ATO) and p-i-n (p-ATO/i-SnO2/n-ATO and p-ATO/i-ZnO/n-ATO) homojunctions or heterojunctions deposited on single crystal Si substrate have very good rectification properties, small leakage currents, large backward breakdown voltages and open circuit voltages of>3V; the pn junctions (p-ATO/n-ATO and p-SnO2:Zn/n-ATO) deposited on the quartz glass substrates have also the rectification characteristics in IV curves, with small leakage currents, smaller backward breakdown voltages and open-circuit voltage smaller than 3V. The pn junctions on quartz glass substrates are transparent in all the visible region and the average transmittance of 85% was achieved.