砷離子佈植氮化鎵薄膜之深植能階研究

Abstract

砷離子佈植氮化鎵薄膜之深植能階研究 研究生：李文祺 指導教授：陳衛國 教授 國立交通大學電子物理研究所 摘要 我們使用了深植暫態能譜量測法(DLTS)研究砷離子佈植氮化鎵薄膜之缺陷特性，藉此瞭解同電性雜質砷摻雜在氮化鎵薄膜中產生的效應。此外我們還做了冷激光光譜(Photoluminescence, PL)、冷激光激發光譜(Photoluminescence excitation, PLE)、吸收光譜的量測，協助我們更精準地明白缺陷特性。 經離子佈植並退火後的薄膜，在冷激光光譜中發現其I2及黃光頻譜大量減少，同時一新的砷相關光出現(470~486nm)。冷激光激發光譜量測顯示，黃光頻譜的發光機制應與氮空缺(VGa)引進的深層受子(deep acceptor)有關。吸收光譜則顯示在波長470nm~485nm有較高的吸收率，亦即在這波段可能存在一寬的吸收能帶。 在未摻雜的薄膜中我們僅量到一個能階位置在傳導帶下方0.895eV處的能階A1’。而在砷離子佈植退火後的樣品中，我們發現三個新的能階E1’,E2’,EAs(分別位在傳導帶之下0.16eV, 0.6eV, 0.766eV處)及隨離子佈植濃度增加而減少的A1’。其中EAs之缺陷濃度隨砷離子佈植濃度增加而增加，顯示此能階與砷摻雜有關。 最後我們提出雜質砷離子佔據鎵空缺的可能性。此假設可以合理地解釋我們觀察到的實驗結果。首先是黃光頻譜因著鎵空缺被砷離子佔據而減少而大量降低。而砷離子佔據鎵空缺將形成一個深植雙重施子(deep double donor)，這與我們在DLTS量到的EAs的能階位置及吸收光譜的吸收帶位置符合。所以我們推測砷離子佈植使得砷佔據了鎵空缺(AsGa)，因而減少了黃光頻譜並引進了砷相關光。

Deep Level Transient Spectrum of As-implanted GaN film Student：Wen-Chi Lee Advisor：Prof. Wei-Kuo Chen Institute of Electrophysics National Chiao Tung University Abstract Deep Level Transient Spectrum (DLTS) and Photoluminescence(PL)、Photoluminescence Excitation(PLE) have been utilized to investigate defects in As-implanted GaN film. We attempted to understand the mechanism of Arsenic impurity in GaN. We found from PL spectrum that the I2 and YL emission reduced a great amount while a new As-related broad band emerged. According to the PLE spectrum, the origin of YL emission in our sample was gallium vacancy, which is a deep acceptor in the band gap. Absorption spectrum then revealed that a greater absorption rate has taken place around 470nm~485nm. Therefore, there might be a wide energy band exists around 470nm~485nm and caused more absorption. We only observed an energy level A1’ at 0.859eV below conduction band in our undoped sample. On the other hand, we found three new energy levels E1’, E2’, EAs (0.16eV, 0.6eV, 0.766eV below the conduction band individually) and diminished A1’ in our As-implanted sample. Particularly, the intensity of EAs increases as the dosage of As-implantation increases, i.e. EAs is a As-related defect. We then propose the possibility of As atom occupying gallium vacancy. This suggestion can reasonably explain our observations. First, the YL emission declined for the gallium vacancies being occupied by As atoms. And the defect AsGa would be a deep double donor in band gap, this concept consists with the position of EAs measured in DLTS and the position of greater absorption in absorption rate spectrum. We therefore conjecture that As-implantation caused the As atom to replace gallium vacancy and decrease of YL emission and introduction of As-related emission.