利用機械剝離法製作GaSe薄膜並探討光學與電學特性

Abstract

GaSe是近年來熱門研究的二維層狀結構材料，單一層由四層原子層Se-Ga-Ga-Se利用共價鍵連結，並且由凡德瓦爾力做為層與層之間的吸引力。GaSe具有非常多的非線性光學特性，並且在高真空有不錯的熱與抗氧化的穩定性，已經利用在量子井結構中製作可見光發光原件上。由於過去文獻都著重於GaSe晶體特性的探討，或者利用MBE、PLD等方式成長GaSe薄膜進行研究，利用機械剝離法製做高品質的GaSe薄膜進行探討在文獻中是非常少的，文獻[2]曾用機械剝離法製做GaSe薄膜進行光學特性探討並應用在光偵測器原件上得到不錯的成果。本實驗利用布氏垂直生長法得到的硒化镓晶體並利用機械剝離法在SiO2/Si基板上製成GaSe薄膜，利用原子力顯微鏡(AFM)測定膜厚之後，更深入的探討薄膜厚度改變造成光學與電學特性的變化。本實驗將GaSe薄膜聚焦量測得到拉曼光譜、PL螢光光譜、XPS和KFM，我們發現在薄膜接近100 nm附近的時候拉曼光譜的表現在A1' mode(134 cm-1, 308 cm-1)薄膜厚度越薄會出現先藍移後紅移的現象，另外在PL螢光光譜上出現在100 nm附近開始有band gap打開的現象造成波峰開始出現藍移，而在XPS的表現上我們發現在100 nm以下Se (3d)軌域的電子束縛能比原子態的束縛能小，而整體電子束縛能的變化在100 nm以下的絕對值呈現越來越小的趨勢，可以解釋為什麼拉曼光譜A1' mode(134 cm-1, 308 cm-1)在100 nm之後表現為何薄膜厚度越博波峰位置紅移的現象。最後KFM的量測結果我們可以推得GaSe的厚度變化對應到的功函數變化，並且間接推得費米能階的位置，最後我們針對GaSe薄膜能帶變化做出了說明。

Abstract

GaSe is a popular research in recent years, the two-dimensional layered materials, single layer consists of four atomic layer Se-Ga-Ga-Se use covalent bonds, and by the force as where Deval attraction between layers . GaSe has a lot of non-linear optical properties, and has good thermal and oxidation stability in high vacuum, already used in the quantum well structure on the production of visible light. As previous studies have focused on the discussion of GaSe crystal properties, or used MBE, PLD, etc. to grow GaSe film, the study in the properties of high quality GaSe thin film by mechanical exfoliation method is very few, the literature has used mechanical exfoliation method to study GaSe thin film optical properties and then used in optical sensor. In our study, the high quality of GaSe crystal grown by vertical growth of Bridgman method has been used to be the source of GaSe thin film produced by mechanical exfoliation method on SiO2/Si substrate. GaSe films are using atomic force microscopy (AFM) to get thickness, and then the more in-depth discussion of optical and electrical properties changing with film thickness has been involved. Our experiments will focus on the measurements of GaSe thin film Raman spectra, PL fluorescence spectra, XPS and KFM. By the results we found that the performance of Raman spectra of A1' mode (134 cm-1, 308 cm-1) has changed when the film thickness close to 100 nm. When the thickness getting thinner, the Raman peaks of A1’ mode appear red-shifted from the first blue-shift phenomenon. PL spectra began to appear blue-shifted peak at thickness near 100 nm meaning the band gap began to open phenomena. In the performance of XPS we found that less than 100 nm the Se (3d) orbital electron binding energy smaller than the binding energy of Se (3d) atomic states, and the overall change in the electron binding energy of the absolute value (Ga (3d) + Se (3d)) less than 100 nm showed the trend of more and more small, may explain why the Raman spectral A1' mode (134 cm-1, 308 cm-1) peak position red-shift phenomenon at near 100 nm film thickness. Finally KFM measurement results we can get the changes of GaSe thickness variation corresponding to the work function, and infer the location of the Fermi level, and finally we can build the model of electron band energy in GaSe film.