Nanoscale Electrostructural Characterization of Compositionally Graded AlxGa1鈥搙N Heterostructures on GaN/Sapphire (0001) Substrate

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• 作者：Andrian V. Kuchuk ; Petro M. Lytvyn ; Chen Li ; Hryhorii V. Stanchu ; Yuriy I. Mazur ; Morgan E. Ware ; Mourad Benamara ; Renata Ratajczak ; Vitaliy Dorogan ; Vasyl P. Kladko ; Alexander E. Belyaev ; Gregory G. Salamo
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：October 21, 2015
• 年：2015
• 卷：7
• 期：41
• 页码：23320-23327
• 全文大小：487K
• ISSN：1944-8252

文摘

We report on Al_xGa_1鈥?i>xN heterostructures resulting from the coherent growth of a positive then a negative gradient of the Al concentration on a [0001]-oriented GaN substrate. These polarization-doped p鈥?i>n junction structures were characterized at the nanoscale by a combination of averaging as well as depth-resolved experimental techniques including: cross-sectional transmission electron microscopy, high-resolution X-ray diffraction, Rutherford backscattering spectrometry, and scanning probe microscopy. We observed that a small miscut in the substrate orientation along with the accumulated strain during growth led to a change in the mosaic structure of the Al_xGa_1鈥?i>xN film, resulting in the formation of macrosteps on the surface. Moreover, we found a lateral modulation of charge carriers on the surface which were directly correlated with these steps. Finally, using nanoscale probes of the charge density in cross sections of the samples, we have directly measured, semiquantitatively, both n- and p-type polarization doping resulting from the gradient concentration of the Al_xGa_1鈥?i>xN layers.