退火在雷射濺鍍磊晶薄膜之效應

Abstract

本實驗目的是研究利用脈衝式雷射分子束磊晶(Laser MBE)的鍍膜方式下，在鈦酸鍶(SrTiO3，全名Strontium titanate)(100)拋光基板上成長同質磊晶(SrTiO3/SrTiO3)，並使用反射式高能量電子繞射系統(RHEED)研究鈦酸鍶薄膜成長機制。由於雷射分子束磊晶（Laser MBE）可以在實驗過程中任意調整雷射重複率來改變薄膜蒸鍍速率，故本實驗充分利用此優點並配合不同的退火時間，觀察到RHEED強度分別在振盪週期、下降深度、下降所需時間以及退火曲線等所受到的影響。我們發現薄膜成長初期可以用二項特性時間尺度(characteristic temporal scale)和一項空間尺度(spatial scale)來描述所觀察到之RHEED強度變化行為。其中一項時間尺度，大約是10~20秒，應為鍍著物鬆弛時間。第二項大約是50秒，為決定RHEED強度是否會繼續退火前之振盪，並保持強度。空間尺度則為RHEED強度開始產生振盪時，需0.4~0.6單層的覆蓋率。在實驗條件最佳化的情況下，可以在鈦酸鍶拋光基板成長很好的鈦酸鍶，RHEED強度可持續振盪且不衰減。由研究退火在成長鈦酸鍶薄膜於不同參數(退火時間、雷射重複率)變化下所觀察到成長機制上的影響，而歸納出數個參數相關之實驗式，用以得知上述氧化物磊晶薄膜成長初期的動態行為。

Our goal is investigating homoepitaxy of thin film with as-polished SrTiO3 substrate under the deposition of Laser MBE, and using Reflection High Energy Electron Diffraction to in-situ monitor the evolution of thin film growth. With the characteristic feature of Laser MBE, we can adjust laser repetition rate so that it is possible to manipulate the depositing rate as well. We take this advantage and study the mechanism the thin film growth with various annealing times. It is then observed the dependence of period of RHEED oscillations, the dropping time, and the curve of annealing with different times vs. laser repetition rate, respectively. In the initial stage of growth of thin film, it was found that there are two characteristic temporal scales and one spatial scale to describe the change of RHEED intensity. One characteristic temporal scale is about 10-20 sec. , in which the relaxation time of adatoms is realized. The other is about 50 sec.. It then determines whether the RHEED intensity will follow the foregoing oscillation. The spatial scale indicates that it need the coverage of about 0.4-0.6 monolayer (ML) for the RHEED intensity start oscillation. Under the optimal condition, we can grow SrTiO3 thin film on as-polished SrTiO3 very well, the RHEED intensity kept going the direction of oscillation and did not decay. Based on all these findings, several important empirical formulas related directly to the initial stage of growth mechanism for the epitaxial thin film have been established. We hope that the above observations, to the extent, will assist the future research for epitaxial processing of the oxide thin films.