光調制反射光譜技術量測分析低溫砷化鎵深層能階之研究

Abstract

光調制反射光譜﹙photoreflectance；PR﹚為光學的量測技術，故可用來量測高阻值的材料。本研究即是以此方法對低溫砷化鎵做深層能階的量測，利用PR技術測量分析各種溫度下樣品深層能階的時間常數，據此繪得阿瑞尼斯圖，而可分析得深層能階的游離能及載子捕捉截面積。對以分子束磊晶技術﹙MBE﹚低溫﹙250 ﹚成長的GaAs樣品分析，我們獲得其深層能階到傳導帶的游離能分別為0.0587eV、0.591eV及0.657eV，根據一些相關的文獻可知，0.591eV的深層能階可歸自於砷的沈積﹙precipitate﹚，而0.657eV的深層能階可能是由於砷的錯位﹙antisite﹚所造成，0.0587eV的深層能階尚未見諸文獻，而我們以PR技術卻可明顯地檢測分析獲得，這樣的結果，顯示PR測量技術除了具有非破壞性的先天優點，又有較諸其他深層能階量測技術更強檢測能力的應用潛力。

Photoreflectance (PR) spectroscopy is an optical and non-destructive technique and is widely used to characterize electronic properties of semiconductor materials and structures. We applied PR method to measure the deep levels of low-temperature grown GaAs samples. By analyzing the transient response of PR spectrum amplitude to the modulation frequence, we can acquire the time constants of deep levels at various sample temperatures. The Arrhenius plot relating the measured time constants and sample temperatures provides the information of the ionization energies and carrier-capture cross-section areas of deep levels. In this study, we characterize the deep levels of GaAs grown at 250 by molecular beam epitaxy (MBE) technique. By using this optical deep level transient spectroscopy (DLTS) technique, we found three deep levels along with the sample. The ionization energies of these deep levels are 0.657, 0.591, and 0.0587eV, respectively. The deep levels with 0.591 and 0.657eV ionization energies are attributed to the As precipitation and As antisite in the low-temperature GaAs sample, respectively. The 0.0587eV-related deep level has not yet been reported in the literature. Although the factor causing this deep level was not analyzed , we are confident on the validity of our measurement data which are partially consistent with possible known data. In summary, we demonstrated the versatile power of PR technique to characterize the electronic properties of semiconductors. By using the PR technique to perform the optical DLTS, we found some special deep level which was not be identified by other conventional DLTS system.