臨場摻雜原子層沉積法成長P型氧化鋅薄膜

Abstract

近年來，由於氧化鋅的寬能隙特性，使其成為熱門之透明氧化物半導體材料。然而由於使用原子層沉積法所製備之的氧化鋅薄膜，擁有較高之電子濃度，因此利用原子層沉積P型氧化鋅薄膜仍為一大技術挑戰，在P型薄膜研究中，迄今尚未發現利用六甲基磷酰胺(HMPA)做為前驅物成長P型氧化鋅磊晶薄膜於M軸取向(m-plane)之藍寶石基板上，因此其成長機制及N轉P之機轉參數仍有其研究價值。 本論文將使用原子層沉積法在m-plane藍寶石基板成長P型氧化鋅磊晶薄膜，利用磷元素摻雜成長一系列不同摻雜濃度之樣品，並且在大氣環境下，進行攝氏300度至700度之後退火，同時藉由高解析度同步輻射X光繞射(XRD)、低溫光激螢光光譜(LTPL)及常溫霍爾電性量測(Hall)，來探討氧化鋅薄膜材料從電子傳導型轉變為電洞傳導型之機制。 由X光繞射實驗結果得知：以HMPA為摻雜前驅物成長之氧化鋅薄膜證實為磊晶形態。同時發現材料隨著摻雜濃度提高，ZnO(200) 繞射峰之峰值位置會向高角度偏移。在樣品進行大氣退火後，發現其隨著退火溫度提升，自由電子濃度逐漸下降，且電阻率上升。將退火提升至500度時，電子濃度下降至最小值為-1.17*1019 [1/cm3]，當退火溫度進一步達600度時，材料特性首次由電子傳導型(n-type) 轉變為電洞傳導型材料(p-type)。然而當退火溫度再進一步上升至700度時，我們發現氧化鋅材料卻再次由P-type轉變回N-type。我們利用LTPL量測結果可以發現，經由高溫大氣退火後，此機轉乃是因為材料中氧間隙(Oi) 缺陷之消長， 所導致摻雜氧化鋅薄膜在N-P型之間轉變之重要關鍵之一。

Recently, due to the wide bandgap feature of zinc oxide, which becomes popular transparent conduction oxide (TOC) material. However, we still faces considerable challenges for growth p-type ZnO materials. That is due to higher electron concentration of ZnO thin films prepared by atomic layer deposition (ALD). For our best knowledge, there is no report for p-type ZnO thin films grown by ALD and incorporate with hexamethylphosphoramide (HMPA). Therefore, the growth condition and the mechanism of N-P transformation still remind the value to catch our attention. In this thesis, the p-type (hole conduction) ZnO epitaxial thin film was deposited by Atomic Layer Deposition (ALD) method on m-plane sapphire substrate, using phosphorus as dopant element for different incorporation ratio and annealing under the atmosphere, the annealing temperature ranged from 300 to 700 oC. We adopted high-resolution X-ray diffraction (XRD) with synchrotron source, low-temperature photoluminescence (LTPL) and Hall electrical measurements (Hall), we can explore how the zinc oxide thin film conversion from n-type into the p-type. The results of XRD indicated using the HMPA as the dopant source, we have successfully deposited the ZnO thin films into epitaxial structure. Moreover, we also founded that the peak of ZnO(200) shifted to higher angle as higer doping concentration. For electrical measurement, the electron carrier concentration of ZnO films were decrease as increasing the annealing temperature, and the resistivity showed opposite behavior. When annealing temperature up to 500 oC, the electron concentration of the ZnO reached the minimize point, for temperature continuously up to 600 oC, first time we founded the ZnO turn its conduction type, from n-type to p-type. However, as the annealing temperature over 700 oC, the hole conduction properties (p-type) of the zinc oxide will restore to electron conduction (n-type). Combined with low-temperature photoluminescence spectra, we founded that the amount of Oi in the material played in rule to dominate the conduction type of zinc oxide thin films.