Comparison of Chemical, Electronic, and Optical Properties of Mg-Doped AlGaN

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• 作者：Jaakko Mäkelä ; Marjukka Tuominen ; Tiina Nieminen ; Muhammad Yasir ; Mikhail Kuzmin ; Johnny Dahl ; Marko Punkkinen ; Pekka LaukkanenKalevi Kokko ; Jacek Osiecki ; Karina Schulte ; Mika Lastusaari ; Hannu Huhtinen ; Petriina Paturi
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：December 22, 2016
• 年：2016
• 卷：120
• 期：50
• 页码：28591-28597
• 全文大小：538K
• ISSN：1932-7455

文摘

Hydrogen, carbon, and oxygen are common unintentional impurities of Al_(x)Ga_(1–x)N crystals. This impurity structure and its interplay with Mg impurities in Al_(x)Ga_(1–x)N semiconductors are relevant to develop the p-type nitride crystals for various devices (e.g, LEDs, transistors, gas sensors) but are still unclear. Here we have investigated Mg-doped Al_0.5Ga_0.5N before and after postgrowth annealing with valence-band and core-level photoelectron spectroscopy, photoluminescence, and resistivity measurements. First, it is found that a surface part of the Al_0.5Ga_0.5N crystal is surprisingly inert with air and stable against air exposure-induced changes. Thus, the relatively surface-sensitive photoelectron spectroscopy measurements reflect in this case also the bulk crystal characteristics. The measurements reveal the presence of deep states up to 1 eV above valence-band maximum before and after the annealing and that oxygen and carbon occupy N lattice sites (i.e., O_N and C_N). The model where C_N-induced acceptor states in the band gap participate in the blue emission (photoluminescence) is supported. Furthermore, the presented Mg 2p core-level spectra demonstrate that part of Mg atoms forms direct bond(s) with oxygen in the bulklike structure of Al_0.5Ga_0.5N and that the chemical environment of Mg atoms is much richer than was expected previously.