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[交流] 【交流】N掺杂不能形成P型ZnO？已有14人参与

最近出版的APL发表了UCSB研究组Chris G. Van de Walle教授的论文Why nitrogen cannot lead to p-type conductivity in ZnO。[Appl. Phys. Lett. 95, 252105 (2009); doi: 10.1063/1.3274043]此研究一经发出变收到了凝聚态与材料物理领域的极大关注。他们的计算强烈的质疑以前的P型ZnO结果，并指出N掺杂能形成深能级，而不是之前广泛报道的浅受主，这说明使用N掺杂并不能形成P型ZnO。

事实上，早在去年[O. Bierwagen, T. Ive, C. G. Van de Walle, and J. S. Speck, Appl. Phys. Lett. 93, 242108 (2008)]的工作中，他们就指出之前P型ZnO很多结果并不可靠。不过，该项研究并未引起当时科学界的足够重视。然而，最近的很多工作都表明他们结果的正确性。他们的另外一些研究同时也证实Li, N, P, As, or Sb掺杂来实现受主，并实现p型掺杂的方式是错误的。[A. Janotti, E. Snow, and C. G. Van de Walle, Appl. Phys. Lett. 95, 172109 (2009)]. 把工作重新拉回到间隙子的掺杂方式中来。

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下面为转载

Dec 23, 2009 Computational scientists at the University of California, Santa Barbara (UCSB), have provided convincing evidence that nitrogen, which is widely believed to be a shallow acceptor in ZnO, is in fact a very deep acceptor and cannot lead to p-type conductivity.
ZnO has been intensively pursued as an optoelectronic material, in hopes of developing it into a wide-band-gap light emitter that would compete with GaN-but with the advantage that large single-crystal substrates are commercially available.  A large part of the effort has been directed at establishing p-type doping, which is very challenging in wide-band-gap oxides in general.  Dozens of papers claiming observations of p-type conductivity have appeared in the scientific literature.  However, independent verification of these reports has been lacking, as have convincing demonstrations of pn junctions.

The UCSB team, consisting of John Lyons, Anderson Janotti, and Professor Chris Van de Walle, performed cutting-edge first-principles calculations based on the hybrid functional methodology.  In an Applied Physics Letter published online today [Appl. Phys. Lett. 95, 252105 (2009); doi: 10.1063/1.3274043] they report that nitrogen acceptors have an ionization energy of 1.3 eV-much too large to enable p-type doping.

They also address why the behavior of nitrogen has been misinterpreted in so many of the previous investigations.  In optical studies, the near-band-gap photoluminescence line most commonly associated with nitrogen is now known to be caused by stacking faults.  Optical absorption and emission associated with the nitrogen deep acceptor in fact occurs at much lower energies, at wavelengths that have been all but ignored in prior studies (see Figure).  When it comes to electrical measurements of acceptor-doped ZnO, the researchers point out there are many potential pitfalls, as addressed in a UCSB paper published last year [O. Bierwagen, T. Ive, C. G. Van de Walle, and J. S. Speck, Appl. Phys. Lett. 93, 242108 (2008)], casting doubt on most of the p-type conductivity reports published to date.

Does this mean that all hope for p-type ZnO has to be abandoned?  “We are convinced that none of the substitutional acceptors (including Li, N, P, As, or Sb) will yield p-type conduction” commented Project Scientist Anderson Janotti.  “Interstitial doping, on the other hand, still looks promising, although it may be difficult to accomplish in actual device fabrication.”  UCSB results on fluorine doping were the subject of another recent publication [A. Janotti, E. Snow, and C. G. Van de Walle, Appl. Phys. Lett. 95, 172109 (2009)].

“Our finding that nitrogen is not a shallow acceptor will come as a disappointment to many who are excited about ZnO as an optoelectronic material” said Van de Walle.  “However, we hope it will contribute to resolving the conflicting and controversial results that have plagued the literature, and will refocus ZnO research efforts on the many exciting applications that do not require ambipolar doping, such as transistors and sensors.”

Optical absorption and emission associated with nitrogen, a deep acceptor in ZnO.
The diagram, based on first-principles computations, illustrates optical absorption by nitrogen acceptors being triggered by green light (2.4 eV), and emission (photoluminescence) occurring at red wavelengths (1.7 eV).  Previous optical investigations have focused on the energy range near the ZnO band gap (3.4 eV, UV), due to the misconception that nitrogen was a shallow acceptor.

[ Last edited by dawnlight on 2010-1-24 at 22:03 ]

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