利用KrF準分子雷射濺鍍AgGaS2非線性光學薄膜

Abstract

我們首次嘗試且成功的利用KrF準分子雷射將Ag2S與Ga2S3的混合粉末濺鍍成AgGaS2薄膜於石英玻璃基板上。我們改變鍍膜時基板的溫度及雷射脈衝重覆率，並由X光繞射及拉曼光譜分析得知為高指向(112) AgGaS2薄膜，且在基板溫度550℃，脈衝重覆率20Hz時，X光繞射訊號有最窄半高寬0.28°。而由光學顯微鏡觀察及EPMA分析得知此時薄膜上Ag顆粒的分佈最少。此外，在基板溫度550℃、脈衝重覆率20∼30 Hz時，其Raman光譜中A1 mode有較好對稱性和窄半高寬及較高強度。在PL光譜，發現在2.156、2.454、2.682 eV有三個發光峰存在，分別為深層能階發光、DAP躍遷發光、激子發光。隨著薄膜品質變好，DAP躍遷發光的強度變強、半高寬變窄(約為0.2 eV)，深層能階的發光也越不明顯。藉由室溫穿透光譜得知AgGaS2薄膜在2.64 eV有一吸收邊緣。 嘗試通入He後，從X光AgGaS2 (112)繞射訊號的半高寬變窄為0.24°、Ag繞射訊號的變小及Raman與PL強度變強得知薄膜品質的確獲得改善。

We have successfully grown AgGaS2 thin films on quartz glass substrates by means of KrF excimer laser deposition from a mixture target of Ag2S and Ga2S3. We change substrate temperature from 430℃ to 570℃ and pulse repetation rate from 10 to 40 Hz. From X-ray diffraction and Raman scattering, all deposited films were chalcopyrite-type, polycrystalline AgGaS2 compound highly oriented in the (112) direction. The film grown at a substrate temperature 550℃, pulse repetition rate 20 Hz had the narrowest FWHM of XRD and density of Ag droplets on the deposited film surface was smallest from optical micro-scope and EMPA analysis. In addition, at substrate temperature 550℃ and pulse repetition rate 20-30 Hz, the A1 Raman mode indicates the deposited AgGaS2 films have better symmetry, narrower FWHM and larger intenisty. In PL spectrum measured at 17K, three emission peaks found at 2.156, 2.454 and 2.682 eV were deep-level, DAP transition and excition emission, respectively. Intensity of DAP transition emission become larger as well as the FWHM of emission peak was narrower (about 0.2 eV) while the quality of deposited AgGaS2 become better. The absorption edge of the deposited films was at about 2.64 eV at room temperature from measuements of UV-visible transmission. At the final part of the exprement, we tried to improve quality of deposied films by means of introducing He as ambient gas during film growth. The FWHM of dirffaction peak in the (112) direction of deposited AgGaS2 film have reduced from 0.281°to 0.244°by introducing He to vacuum champer and the ratio of intensity of (112) dirffaction peak to intensity of Ag (111) dirffaction peak also increase by serval times. Furthermore, the intensity of A1-mode Raman spectra and the one of DAP transition emission also have increased. From the fact that we mentioned above, the quality of deposied films have improved by introducing He as ambient gas during film growth.