利用脈衝雷射沈積層狀半導體硒化鎵薄膜於化學處理矽基板之製程與特性研究

Abstract

本實驗使用準分子脈衝雷射濺鍍硒化鎵薄膜於不同pH值氫氟酸浸泡之矽基板Si(111)上進行異質成長，並以原子力顯微鏡、X光繞射、掃描式電子顯微鏡、穿透式電子顯微鏡、拉曼光譜、低掠角X光繞射以及電子微探儀做一探討。在基板製備方面，我們發現初始SiO2/Si介面之平整度為單氫鍵結之關鍵，原子級的平坦將可延展擴大單氫鍵結台階的範圍。由X光繞射、掃描式電子顯微鏡、原子力顯微鏡、電子微探儀、拉曼光譜以及低掠角X光繞射推論較佳之成長溫度應在400℃~450℃之間，Ga2Se3應只存在於介面處以及相變化的產生在550℃以上較為明顯。由掃描式電子顯微鏡剖面推論硒化鎵薄膜退火溫度應該在500℃以下為佳，由原子力顯微鏡觀察成長後之薄膜表面為使表面能量降到最低而有蜷曲狀結構產生，且由原子力顯微鏡表面結構分佈及電子微探儀Ga/Se比例推論退火時間太長可能導致薄膜的再揮發。由穿透式電子顯微鏡橫截面分析，我們得知硒化鎵薄膜的確是層狀結構，單層厚度約為8Å且與文獻報導一致。由拉曼光譜及低掠角X光繞射得知成長薄膜約在110nm時應力解除。最後由掃描式電子顯微鏡剖面圖及俯視圖推論薄膜應為SK成長模式。

Layered semiconductor GaSe thin films are grown on pH-modified Si(111) substrates. AFM, XRD, SEM, TEM, Raman spectroscopy, GIXD, and EPMA are used to investigate the substrate preparation, growth temperature and phase transition, annealing effect, cross section, interface and stress as well as growth mode. We found that the initial SiO2/Si interface plays a key role in the monohydride passivation and atomically flat surface can extend the terrace region significantly. Based on the results of XRD, SEM, AFM, EPMA, Raman spectroscopy, and GIXD, we conclude that the proper growth temperatures should be around 400℃-450℃, and Ga2Se3 phase should exist at the interface only, and the obvious phase transition should be above 550℃. According to SEM section analysis, we know that the proper annealing temperature should be below 500℃. From AFM and EPMA, there are spiral features in the film surfaces, and the annealing effect should be time-limited in case of Se or GaSe re-evaporation. The structure of GaSe is layered from the direct evidence of TEM cross-section analysis and the thickness of monolayer is about 8Å. Based on Raman spectroscopy and GIXD, the stresses are released around 110nm under the conditions of laser fluence 0.75-1.5J/cm2 and repetition rate 4Hz. Finally, from SEM section analysis, we conclude that the growth mode of GaSe thin film should be SK.