| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 104 === Recently, to fabricate the deep ultraviolet photodetectors, the use of materials with the shorter cut-off wavelength and the higher transmittance is required. Therefore, the wide-bandgap (AlGa)2O3 (AGO) thin films are worth developing. In this research, the wide-bandgap AGO thin films have been prepared on sapphire substrates by pulsed laser deposition (PLD). The effects of gas atmosphere (Ar and O2 atmospheres), laser repetition rate, deposition pressure, and substrate temperature on the crystal quality of AGO film were investigated. Furthermore, the elemental composition, transmittance, and bandgap of AGO film was also analyzed.
Firstly, the XRD result indicates the AGO film grown in Ar atmosphere is amorphous. On the contrary, (-402) and (-603) diffraction peaks are exhibited in the XRD pattern of the AGO film grown in O2 atmosphere. Moreover, the microstructural observations by transmission electron microscopy confirm the AGO film prepared in O2 atmosphere is single crystalline along [-201] growth direction. Actually, the film’s properties also can be affected by changing the deposition pressure. When the AGO was prepared at a deposition pressure of 7×10-2 torr, this film possessed both a higher crystal quality and a smoother surface. Then, under these above-mentioned optimum conditions, the substrate temperature was increased from 400 to 800 °C to deposit the AGO films. According to the XRD results, the AGO films deposited at 500-800 °C had the single crystalline phase in comparison to the amorphous phase of 400 °C-grown AGO film. From the elemental composition analyses, it revealed the Al contents of these AGO films grown at 400-800 °C can reach to 12-14 at.%. At the substrate temperatures of 400-800 °C, the transmittance (@250-1000 nm) of these AGO films are all higher than 80%. In addition, the bandgap value of AGO film was increased to 5.4 eV, compared with that of Ga2O3 film (4.9 eV). It was also found that the variation trend of bandgap values for these AGO films obtained from transmittance spectra was in good agreement with that from cathodoluminescence spectra. The results reveal the bandgap value of AGO film can be successfully modified via the PLD growth.
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