| In information field, electronic products based on informational and functional oxide materials have been widely used in the areas of storage, photoelectric detection, and automatic control, et al. In these fields, transparent conductive oxide with good optical and electrical properties is widely used in flat-panel displays, light-emitting diodes, solar cells, touch pad, ultraviolet detector, and so on. Whereas most of the well-known transparent conductive oxides (TCOs) are n-type materials, applications where TCOs work as active devices require both transparent n-type and p-type materials. The interest in the delafossite family as stable and prototype p-type wide band transparent semiconductors without any doping has been increased since p-type CuAlO2films have been successfully fabricated. In the delafossite compounds, the hybridization of Cu3d10energy levels in the close energy proximity with O2p levels increases energy of the valence band maximum and delocalizes hole state to form an intrinsic p-type semiconductor.Today, there are many research scholars of p-type delafossite materials all over the world. Some people study the internal level structure of delafossite by first-principles density functional theory and generalized gradient approximation. While more scholars engaged in preparation technology of delafossite material to improve the performance of the delafossite film. Compared to other preparation film methods, the sol-gel technique can offer a high flexibility of composition and dopant by the stoichiometry. It is also a widely used in large scale production lines due to the low cost and simple processes. Therefore, we prepared delafossite films by the sol-gel method in this article.In addition, optical spectroscopy is a powerful nondestructive probe technique for optical characterization. By spectral measurements, one can determine the optical constants, lattice dynamics, OBG, Photoluminescence (PL) properties, and electronic transitions of the materials. These important informations correlate with the carrier mobility, physical transition, chemical composition, crystalline quality, energy level of impurities, and the presence of defects in the materials. Therefore, the spectral measurement is important in the material structure study. And the energy band structure plays a very important role in the design of optoelectronic devices. In this dissertation, we use spectroscopic measurement to study the photoelectric transition and optical electrical properties of delafossite materials, which make up for the inadequacies in the current research. By spectral analysis, the delafossite electronic energy bands, electronic transitions, and free carrier information can be obtained.The main works and innovations of this dissertation are listed as follows:1. The CuGaO2films were prepared by the sol-gel method, the highly c-axis orientation and optical transparency (60-80%) in the visible region were obtained, and the optical band gap and internal electronic transitions were studied under the different temperature.The CuGaO2films were prepared on sapphire (001)substrate by the sol-gel method with different preparation temperature. We studied the film structure and properties with different temperature, obtained the best preparation temperature being900℃. The highly c-axis orientation and optical transparency (60-80%) in the visible region were obtained at900℃. It indicates that the Alg phonon mode shifts about20cm-1with the temperature due to the thermal expansion of the lattice and anharmonic phonon coupling. Moreover, temperature-dependent dielectric function has been investigated and three electronic transitions located at about1.05,2.67, and3.99eV can be uniquely assigned. It was found that the direct transitions play a dominant role in the optical response from transmittance spectra. It was found that the optical band gap of the CuGaCh film decreases with the temperature, which mainly originated from the electron-phonon interactions.2. The CuGa1-xCrxO2(0≤x≤1) solid solution films were grown by the sol-gel method. A new energy level in the CuGa0.8Cr0.2O2film was found, which improved the film electrical property.Pure phase CuGa1-xCrxO2(0≤x≤1) solid solution films were prepared on (001) sapphire substrates by the sol-gel method. The structure, vibration modes, and compositions of the films were analyzed by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Due to the interatomic potential becoming weaker between Cu and O atoms with increasing the Cu-O bond length, the peak positions of the A1g and Ag phonon modes shifted toward a lower frequency with increasing x. The optical transmittance of the films approached about60-80%in the visible region and the values of the direct band gap linearly decrease from3.56to3.09eV with increasing x. The Cr effect on the electronic band transition has been investigated in detail. The new energy state located at0.17eV above the top of the valence band is observed in the CuGa0.8Cr0.2O2film, which can be derived from the defect energy level. It can induce the increment of the hole in the valence band, contribute to the electrical conductivity, and lower the thermal activation energy. Moreover, the CuGa0.8Cr0.2O2film is found to be of the larger electrical conductivity being0.071S cm-1at room temperature.3. The CuCr1-xMgxO2(0≤x≤12%) films were prepared by the sol-gel method, and a Mg composition dependence study has been discussed in detail.Highly-transparent CuCr1-xMgxO2(O≤x≤12%) films were prepared on (001) sapphire substrates by the sol-gel method. The microstructure, phonon modes, optical band gap, and electrical transport properties have been systematically discussed. It was found that the Mg-doping induced the increase of the crystal quality and the enhancement of the (00l) preferred orientation. The spectral transmittance of the films approaches about70-75%in the visible-near-infrared wavelength region. The direct and indirect band gaps decline and climb up with increasing Mg composition. The direct and indirect band gaps of CuCr0.94Mg0.06O2film were3.0and2.56eV, respectively. It shows a crossover from the thermal activation behavior to that of three-dimensional variable range hopping from the temperature-dependent electrical conductivity. In the higher temperature region, the hopping of holes between the nearest-neighbor Cu sites can determine the electrical transport properties. In the lower temperature region, the weakening of the thermal energy may depress the hole hopping between the nearest-neighbor Cu sites, and the contribution of the hopping to the Cr sites becomes more dominant, so the hopping to the Cu site in the other Cu layers becomes relatively dominant. The crossover temperature decreases with increasing Mg-doping composition, which is due to the change of the spin-charge coupling between the hole and the local spin at the Cr site. It should be noted that the electrical conductivity of the CuCr1-xMg,O2films becomes larger with increasing x value. The highest electrical conductivity of3.85S cm-1at room temperature for x=12%is four orders magnitude larger than that (8.81×10-4S cm-1) of the pure CuCrO2film. The high spectral transmittance and larger conductivity indicate that the Mg-doped CuCrO2films are promising for applications in the optoelectronic fields. |
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