以X光吸收光譜研究銻氮砷化鎵材料短距離結構變化

Abstract

本論文的研究主題為低含氮化合物半導體銻氮砷化鎵(GaAsSbN)在熱退火前後N原子的短距離結構變化。我們利用VFF(Valence force field) model建立1000顆原子大小超晶格，建立不同的N原子短距離結構模型，透過FEFF9軟體進行模擬可以得到不同結構下的吸收頻譜。經由N K-edge量測結果與FEFF9頻譜模擬進行XANES(X-ray absorption near edge structure)比對可以推測N原子短距離結構，Sb K-edge量測分析EXAFS(extended X-ray absorption fine structure) Ga-Sb平均鍵長並配合VFF model分析可以加以驗證結果。 綜合XANES、EXAFS結果我們發現在GaAsSbN as grown的樣品中，N原子的短距離結構主要是以沿著[0 0 1]方向形成NN1 pair，並有4顆Sb原子聚集在此NN1 pair的共同第二層，我們稱為NN1+Sb4 model。在熱退火800℃後，部份NN1 pair分解成isolated N的型式，且有2顆Sb原子聚集在isolated N的第二層，因此同時存在NN1+Sb4 model以及isolated N+Sb2 model兩種模型。而在熱退火850℃後，NN1+Sb4 model幾乎全部分解成isolated N+Sb2 model，N原子的短距離結構主要是以isolated N+Sb2 model為主。

This study is about the changes of the short-range configuration of N atoms in dilute nitride GaAsSbN after thermal annealing. We use valence force field model to construct 1000 atoms supercells with different N-centered short-range structure. Then we used FEFF9 program to calculate their XANES(X-ray absorption near edge structure) spectra. The XANES of N K-edge experiment result is compared with the simulations from FEFF9 to realize the short-range structure of N atoms, and the Sb K-edge EXAFS(extended X-ray absorption fine structure) fitting results of average GaSb bond length are compared to the VFF calculation to confirm the results. After comparing the results of XANES and EXAFS, we find there exist NN1 pairs along [0 0 1] direction with four Sb atoms clustering in their commom second shell, called NN1+Sb4 model. After thermal annealing at 800℃, some part of the NN1 pairs dissociate into isolated N with two Sb atoms clustering in the second shell. After 850℃ annealing, however, the short-range structure of N atoms is the isolated N+Sb2 model.