Preparetion And Properties Of P-Type Transparent Oxides Semiconductor CuCrO₂ Thin Films

Transparent Semiconductor Oxides(TOS) have the feature of optical transparency in the visible region and controllable electrical conductivity, and they are widely used as transparent electrode for solar cells, liquid crystal display, light emitting diodes in electronic industry. However, the application of TOS has been restricted to n-type semiconductor, the lack of p-type TOS has limited their applications. Based on the theory called the chemical modulation of the valence band(CMVB), we selected delafossite structure CuCrO2 as the subject to investigate. We prepared the CuCrO2 films by radio frequency magnetron sputtering technique. The main results we achieved are as following:1. The optimized parameters have been obtained successfully to deposited CuCrO2 films. The substrate temperature has been investigated. The maximum conductivity of CuCrO2 film is 27.1 S·cm-1 when the substrate temperature reaches at 500℃. The transmittance of CuCrO2 film is about 10%-15% in the visible light range. Since the transparency of deposited CuCrO2 films is very low, CuCrO2 films were annealed under high pure nitrogen atomosphere. The average transmittance increases with the increase of annealing temperature, but the conductivity decreased with the increasing of annealing temperature. The optimum properties for CuCrO2 films are obtained by annealing at 900℃. Moreover, the sputtering power influences the properties of CuCrO2 films. It is founded that the optical transmittance of the films decreases, but the conductivity of the films enhances when the sputtering power increases. The CuCrO2 films have optimum properties of transparent conductivity at 100W. Furthermore, by adjusting oxygen partial pressure on the properties of the films were studied. The conductivity of the films decreases notably when sputtering at oxygen partial pressure. The transmittance is 10%-15% in the visible range. After annealing at 900℃,the transmittance of the films increases to 60%-70% for the films deposited at oxygen partial pressure, but the films are not conductive. The conductivity of the films at 0% oxygen partial pressure is 1.5×10-3 Scm-1. Considering the optimum sputtering parameter, the substrates temperature is 500℃, the sputtering power is 100W, the partial oxygen pressure is 0%, and the annealing temperature is about 900℃.2. Zn, Mg doped CuCrO2 with delafossite structure were successfully prepared by radio frequency magnetron sputtering technique. The transmittance is about 30%-50% in the visible light range. The temperature dependence of conductivity can be described by the thermal activation theory when the temperature is above 200K. At the room temperature, the maximum electrical conductivity for all doped CuCrO2 film is 0.062 S·cm-1 for 9mol% Mg doped CuCrO2 which is 400 times higher than that of undoped sample. Hall effects measurements prove that the sample is p-type semiconductor.3. The thickness effect on the structure, optical and electrical properties of the 9mol% Mg doped CuCrO2 thin films were investigated. The grain size increases as the film thickness grows, while the compressive strain increases as the film thickness decreases. The average transmittance of the films decreases as film thickness grows in the visible range. The electrical conductivity decreases monotonously as the film thickness decreases mainly because of hole concentration and mobility declining. The hole concentration decreases when the lattice compressive strain enhances. The carrier mobility declining as the grain size becomes larger because of the stronger grain boundary scattering effect.4. As for the device applications, p-CuCrO2:Mg(9mol%)/n-Si p-n junction has been prepared on low resistance Si substrate. Based on the linear I-V characterization of Ni-Si-Ni, Ni-CuCrO2:Mg(9mol%)-Ni, the I-V characterization shows that the junction has the rectifying property with the cut-in voltage of 1V. The ratio of the forward current to the reverse current reached 8.2 at the bias voltage of 5V. Using the theory of p-n+ one-sided step junction to simulate I-V curves, it is found that the effects of the interfacial states and junction resistance should not be neglected to analyze the rectifying property of the heterojunctions.