以物理氣相傳輸法成長硒化鋅單晶

Abstract

由於硒化鋅具有寬的直接能帶間隙(300K時，Eg=2.7eV)，在此能隙下電子 可做直接躍遷放出藍光，因此可應用於藍光二極體及半導體雷射方面。而 硒化鋅單晶在光電元件應用上的瓶頸即是高品值硒化鋅單晶尚未獲得。利 用物理氣相傳輸法成長硒化鋅單晶，可減少晶體內部的雙晶及雜質濃度， 以期獲得高品值硒化鋅單晶。而影響以物理氣相傳輸法成長硒化鋅單晶長 晶速率的主要因素為硒化鋅的化學計量比。本研究藉由三種不同的純化方 法以調整硒與鋅之化學計量比並比較其單晶成長的速率。經由三種不同的 方式在1043±3℃下純化後長晶，當長晶條件為：長晶爐傳動速度2.3mm/ day、石英尖管角度30°時皆能得到硒化鋅單晶。所得單晶經氫氧化鈉水 溶液蝕刻後，以SEM觀察判斷蝕刻晶面的密勒指數及計算蝕坑密度。再以 X-ray定方向後切割、拋光，以Double Crystal Rocking Curve分析三種 不同純化方式所得晶體的結晶性。實驗証明，以方法A 為純化方法所得晶 體優於方法B 及方法C 兩種純化方法所得晶體。 ZnSe has been of interest as one of the primary candidates for blue light emitting diode application for long, because of its efficiency in direct band to band transitions (2.7eV at 300K). High quality ZnSe single crystals are required for applications in optoelectronic devices. Physical vapor transport method enables us to obtain ZnSe crystal without heavy twins, and it is less vulnerable to contamination compared with bulk growth techniques. In this study, special care has been taken to purify the starting materials and to adjust stochiometry. Three bake-out processes for the source materials at 1043±3℃ were considered in correlation with the growth results. Single crystals were conical tip of 30°. Dislocation etch pits were revealed by etching in boiling 50% NaOH solution. Observation with optical and scanning electron microscopies (SEM) indicated that the grown facets were {110} planes. Crystals were grown preferentially along [111]B direction. The etch pit density (EPD) was measured on the as-grown {110} facets. Double crystal x-ray diffraction materials purified with method A is superior than those from the other two methods.