Sensitivity of Fermi level position at Ga-polar, N-polar, and nonpolar m-plane GaN surfaces to vacuum and air ambient
Sensitivity of Fermi level position at Ga-polar, N-polar, and nonpolar m-plane GaN surfaces to vacuum and air ambient
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Ga 极性、N 极性和非极性 m 面 GaN 表面的费米能级位置对真空和空气环境的灵敏度
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发表时间：
2016
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通讯作者：
R. Kudrawiec
中科院分区：
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作者：
Ł. Janicki;Manolo Ramírez;J. Misiewicz;G. Cywiński;M. Boćkowski;G. Muzioł;C. Chèze;M. Sawicka;C. Skierbiszewski;R. Kudrawiec
Ga极性，N极性，和非极性m面GaN UN+结构已在空气和真空环境中的非接触电反射（CER）检查。该技术对表面电场非常敏感，表面电场随表面费米能级位置的变化而变化。对于UN+ GaN结构[即，GaN（未掺杂）/GaN（n型）/衬底]，预计未掺杂的GaN层中会出现均匀的内置电场，这在CER光谱中通过Franz-Keldysh振荡（FKO）表现出来。当从空气环境改变到真空环境时，在N-极性和非极性m-平面结构的CER光谱中观察到FKO的明显变化。这意味着这些表面对环境大气非常敏感。与此相反，在Ga极性结构中仅可以看到FKO的小变化。这清楚地表明，在GaN表面处的费米能级位置的环境灵敏度随晶体取向而变化，并且对于N极性和非极性m平面表面非常高。N极性和非极性m平面表面的这种特征对于在这些晶体取向上生长的GaN基器件可能是非常重要的，并且可以用于一些器件中，例如，传感器.
Ga-polar, N-polar, and nonpolar m-plane GaN UN+ structures have been examined in air and vacuum ambient by contactless electroreflectance (CER). This technique is very sensitive to the surface electric field that varies with the Fermi level position at the surface. For UN+ GaN structures [i.e., GaN (undoped)/GaN (n-type)/substrate], a homogeneous built-in electric field is expected in the undoped GaN layer that is manifested by Franz–Keldysh oscillation (FKO) in CER spectra. A clear change in FKO has been observed in CER spectra for N-polar and nonpolar m-plane structures when changing from air to vacuum ambient. This means that those surfaces are very sensitive to ambient atmosphere. In contrast to that, only a small change in FKO can be seen in the Ga-polar structure. This clearly shows that the ambient sensitivity of the Fermi level position at the GaN surface varies with the crystallographic orientation and is very high for N-polar and nonpolar m-plane surfaces. This feature of the N-polar and nonpolar m-plane surfaces can be very important for GaN-based devices grown on these crystallographic orientations and can be utilized in some of the devices, e.g., sensors.