Theoretical And Experimental Study On Doped Ga₂O₃ Films

With the development of semiconductor opto-electric technology, wide band-gap transparent conductive oxide thin films have been one of the researched focuses in semiconductor materials fields. Monoclinic Gallium oxide (β-Ga₂O₃) as a kind of direct wide bandgap compound semiconductor material has been widely used as various gas sensors, ultraviolet detectors, solar cells, lithography, surface modification, DNA detection, liquid crystal display (LCD), transparent electrode materials in ultraviolet photoelectric devices and many other fields. Conventional TCO are opaque in the deep-ultraviolet region due to a small band gap (<4eV), such as ITO. However, the band gap of theβ-Ga₂O₃ is 4.5⁵ eV. It is considered to be a good deep ultraviolet transparent conductive material. It is the transparent conductive material, which has the largest forbidden band gap so far. The poor conductivity of the intrinsicβ-Ga₂O₃ limits its application in photoelectric device. In recent years, experimental and theoretical studies on improving its electro-optical property by doping have attracted more and more researcher's attention.This paper discusses the widely uesed transparent conductive oxide thin films materials. Its preparation method and application in modern technology of galum oxide are summarized and prospected. Cu dopedβ-Ga₂O₃ thin films are prepared by RF magnetron reactive sputtering. The influences of the annealing on the crystal quality and optical properties are studied. The X-ray diffractometer, UV-VIS spectrophotometer, scanning electron microscope, fluorescent photometric, X-ray photoelectron energy spectrometer is used to characterize and analyze the structure, optical and surface morphology properties. Our expermental results show that the crystal quality deteriorates and the effictive optical forbidden band gap shrinks with increasing the Cu impurity concentration. After post-annealing, the transmittance and the absorption of the Cu-dopedβ-Ga₂O₃ decrease and increase respectively. The UV, blue and green characteristic emission bands are observed. The UV and blue emission are enhanced by Cu-doping and a new blue emission peak centred at 475 nm appears for the Cu-doped sample.The electronic and optical properties of the Sn, Si and Cu dopingβ-Ga₂O₃ are studied by the first-principles theory calculation. Our results indicate that Sn or Si plays as donor when the Ga atoms are substitud by the Sn or Si. The n-type conductivity is obtained after Sn or Si doping. The Fermi energy level moves forward to the conduction band and the donor impurity level is introduced into the conduction band bottom. These can help to improve the conductivity of theβ-Ga₂O₃. The Cu atom which substitutes the Ga atom is an acceptor and introduces acceptor impurity level on the top of the valence band, which indicates that Cu doping has the P-type conductivity. It is hopeful for new generation of photoelectric device in the ultraviolet region.