大氣噴射電漿於氧化鋅鎂/氧化鋅異質接面結構之應用

Abstract

本研究使用大氣噴射電漿(APPJ)退火之濺鍍氧化鋅(zinc oxide)薄膜性質，並將其應用於氧化鋅鎂/氧化鋅(MgZnO/ZnO)異質結構。因APPJ所產生之氮氣電漿具有高反應性，故可在短時間內達到與熱退火相同之效果。藉由X光繞射儀與紫外光-可見光譜進行分析，顯示大氣電漿處理氧化鋅薄膜可增加其薄膜結晶性，並釋放濺鍍過程中在薄膜內所產生之殘留壓應力。在我們先前的研究中指出，在具有高缺陷密度的濺鍍氧化鋅鎂/氧化鋅異質結構中要能夠形成二維電子氣體(2DEG)，氧化鋅熱退火過程為一關鍵步驟。本研究結果顯示30秒的大氣電漿處理足以取代30分鐘400 °C熱退火，使濺鍍之多晶MgZnO/ZnO異質結構因極化效應產生位能阱，並侷限大量自由載子於MgZnO/ZnO介面，形成二維電子氣體。 另外我們也研究了溶膠-凝膠法製備之氧化鋅鎂薄膜在不同的預烤溫度與不同大氣電漿處理時間下其薄膜之其表面型態、光學性質、晶體結構與電阻率。在較高之預烤溫度下，其薄膜繞射峰相對強度較強表示其結晶性較好；而隨著大氣電漿後處理時間的增加其繞射峰相對強度也變強。以溶膠-凝膠法製備MgxZn1-xO之薄膜其在可見光區平均光學穿透超過80%，而光學能隙則隨著鎂含量的增加而增加，這是由於鎂原子進入至氧化鋅之晶格中取代鋅所造成；同樣的，隨著鎂含量的增加其薄膜電阻率也隨之上升，在鎂含量達20%時期薄膜電阻率較氧化鋅薄膜有2~3個數量級的上升。隨著大氣電漿處理的時間增長，穿透光譜的吸收邊緣斜率也有一系列的變化，這是由於量子局限效應的影響，較大晶粒會造成的能帶溝值的下降。

Rf-sputtered ZnO films, annealed by atmospheric pressure plasma jet (APPJ), are characterized and used for MgZnO/ZnO heterostructures. The highly reactive N2 plasma generated by APPJ allows much shorter treatment time compared with conventional thermal anneals. The APPJ treatment can increase the crystallinity of ZnO films and release the compressive residue stresses, verified by XRD and UV–Vis transmission measurements. In our previous studies, we demonstrate that thermal anneal is the critical step for the formation of two-dimensional electron gases in defective rf-sputtered MgZnO/ZnO heterostructures. This thesis reports the experimental results that APPJ treatments can be used for the same purpose with a much shorter processing time. A thirty-second APPJ anneal on ZnO can be used to replace 400 °C × 30 min furnace-anneal to promote the formation of 2DEGs in MgZnO/ZnO heterostructure. The ultra-short processing time is attributed to the synergy of plasma reactivity and temperature of APPJ. This thesis also reports the characterization of sol-gel derived MgZnO thin films converted by APPJs. The MgZnO films exhibit high transparency (> 80%) in the visible light wavelength region. The optical band gap reveals a blue shift as the Mg content increases. The resistivity of the MgxZn1-xO films increases by two to three orders of magnitude for 20% Mg content thin film, owing to the substitution of Mg atoms into the Zn lattice sites. The absorption band edge becomes sharper as the APPJ treatment time increases. This can be attributed to the grain growth of the films. As the grain size is small, the quantum confinement effect causes the slight decrease of the band gap, resulting in the slope alteration at the absorption edge.