Single Crystal Growth and Stoichiometory Control of Ecologically Friendly Semiconductor β-FeSi_2

由于β-FeSi_2的理论直接带隙为0.85 eV，符合石英光纤的最小吸收窗口，因此β-FeSi_2作为一种新型的光电子器件材料，近年来得到了广泛的研究。此外，在Si衬底上制备β-FeSi_2基光发射器或光探测器也可用于光集成电路。尽管表征高质量单晶揭示了其固有特性以及由偏离化学计量引起的杂质和原生缺陷的影响，但尚未生长出高质量单晶。本研究分别采用化学气相传输法（CVT）和分子束外延法生长了块状单晶和外延薄膜，阐明了CVT生长的传输机制和最佳生长条件。CVT生长的单晶在低温下具有清晰的光致发光和高的电子迁移率。此外，利用固体源分子束外延技术，在580℃下，首次在氢终止的Si（111）衬底上成功地生长了厚度为180 nm的高质量β-FeSi_2外延膜。在Fe/Si源流量比为1：2的条件下生长的β-FeSi_2薄膜具有比其它方法生长的薄膜更好的上级形貌和结晶度。

Ecologically friendly semiconductor β-FeSi_2 has been intensively investigated in recent years as a promising material for future optoelectronic devices, because β-FeSi_2 has theoretical direct band gap 0.85 eV that fits the minimum absorption window of the quartz fiber. In addition, fabrication of β-FeSi_2 based light emitters or detectors on Si substrate leads to optical integrated circuits. Although characterizing the high quality single crystal reveals its intrinsic properties as well as the effects of impurities and native defects caused by the deviation from stoichiometry, a high quality single crystal has not been grown. In the present study, bulk single crystals and thin epitaxial films were grown by chemical vapor transport (CVT) and molecular beam epitaxy, respectively.Transport mechanism and optimum growth condition were clarified for CVT growth. CVT grown single crystal showed a clear photoluminescence and a high electron mobility at a low temperature. In addition, a high quality β-FeSi_2 epitaxial film with the thickness of 180 nm has been successfully grown for the first time on hydrogen terminated Si(111) at 580℃ by using solid source molecular beam epitaxy. The β-FeSi_2 film grown with stoichiometric Fe/Si source flux ratio 1:2 has a superior morphology and crystallinity comparing to the published results of the films grown by other methods.