利用原子層沉積技術成長n型與p型氧化鋅薄膜及其光電特性研究

Abstract

本論文利用原子層沉積技術 (Atomic Layer Deposition, ALD)成長鈦(Ti)摻雜與鎂(Mg)摻雜之氧化鋅(ZnO)薄膜並研究其光電特性。本論文分為三個不同的主題，第一個研究主題為成長鈦摻雜之氧化鋅(Titanium-doped ZnO, ZnO:Ti)薄膜於藍寶石(sapphire)基板上，研究結果顯示ZnO:Ti薄膜具有高的載子濃度(2.6 x 1020 cm-3) 、低電阻率(9.7 x 10-4Ω-cm)以及高的可見光穿透度(>93%)。因而被視為有機會取代ITO之透明導電薄膜。此外由光激發光(photoluminescence, PL)的量測可以得知，ZnO:Ti薄膜於380nm 波段具有相當強的自發性發光(spontaneous emission)，且PL頻譜呈現近乎無缺陷(defect-free)的狀態，且在室溫下具有相對低之雷射閥值（約為153 kW/cm2）。 第二個部分為成長氧化鋅薄膜於砷化鎵(GaAs)基板上，並在氧氣(oxygen)氣氛下經由熱退火處理以製作p型氧化鋅。隨著退火溫度的上升，可以觀察到電子濃度明顯的下降，以及p型導電型態的出現。我們可以得到具有高的電洞濃度 (3.44×1020 cm-3)和低電阻率(7.51×10-4 Ω-cm) 的p型氧化鋅薄膜，p型導電型態可以持續穩定超過至240天。推測原因為熱退火處理使得砷原子擴散進入ZnO中形成如AsZn-2VZn等複合物(Complex)，形成受子能階(acceptor level)以提供電洞。 最後一部分為在藍寶石基板上成長不同鎂摻雜濃度之氧化鋅薄膜，並以離子佈植技術(Ion Implantation)將砷離子佈植進入氧化鋅鎂(MgZnO)薄膜當中。當鎂摻雜濃度達20%時，室溫PL頻譜中可以觀察到近能隙發光(near-band-edge emission)發生明顯藍位移的現象(181meV)。另外研究結果指出，鎂的摻雜濃度和退火溫度對薄膜的電性影響甚鉅，可以得到電洞濃度為5.3x1016 cm-3之p型氧化鋅鎂薄膜。

This thesis can be divided into three different parts. The first topic is the fabrication and optical characteristics of Ti-doped ZnO films, the second topic reports the formation of p-type ZnO deposited by ALD on GaAs substrate, and the third topic presents the characteristics of Arsenic-implanted MgZnO films. The ZnO:Ti films deposited by ALD exhibited low resistivity (9.7 x 10-4Ω-cm), high carrier concentration (2.6 x 1020 cm-3), and high transparency (>93%) in the visible spectrum. As a result, the ZnO:Ti films are considered to be a promising substitute for ITO films. Photoluminescence (PL) spectra consisted of a strong spontaneous emission associated with the near-band-edge emission at 380 nm and a negligible defect-related band. The optically-pumped stimulated emission with a low threshold intensity 153 kW/cm2 was observed at room temperature, indicating a good optical and crystalline quality of the of ZnO:Ti films. Long-term stable p-type ZnO films were grown by atomic layer deposition (ALD) on semi-insulating GaAs substrates and followed by thermal treatements. The p-type ZnO film with a hole concentration as high as 3.44×1020 cm-3 and long-term stability up to 240 days was obtained. The results can be attributed to the diffusion of arsenic atoms from GaAs into ZnO as well as the activation of As-related acceptors by the thermal treatment. The final part of the thesis reports the characteristics of arsenic-implanted MgZnO films. The electrical properties of As-implanted MgZnO films were significantly influenced by the annealing temperature and Mg-doping concentration. As the doping of Mg content in the ZnO films increased, a blueshift in the PL spectrum was observed. The p-type As-implanted MgZnO film with a hole concentration of 5.3x1016 cm-3 was obtained in this study.