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【交流】N摻雜不能形成P型ZnO? 已有14人參與
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最近出版的APL發(fā)表了UCSB研究組Chris G. Van de Walle教授的論文Why nitrogen cannot lead to p-type conductivity in ZnO。[Appl. Phys. Lett. 95, 252105 (2009); doi: 10.1063/1.3274043]此研究一經(jīng)發(fā)出變收到了凝聚態(tài)與材料物理領(lǐng)域的極大關(guān)注。他們的計(jì)算強(qiáng)烈的質(zhì)疑以前的P型ZnO結(jié)果,并指出N摻雜能形成深能級,而不是之前廣泛報(bào)道的淺受主,這說明使用N摻雜并不能形成P型ZnO。 事實(shí)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,他們就指出之前P型ZnO很多結(jié)果并不可靠。不過,該項(xiàng)研究并未引起當(dāng)時(shí)科學(xué)界的足夠重視。然而,最近的很多工作都表明他們結(jié)果的正確性。他們的另外一些研究同時(shí)也證實(shí)Li, N, P, As, or Sb摻雜來實(shí)現(xiàn)受主,并實(shí)現(xiàn)p型摻雜的方式是錯(cuò)誤的。[A. Janotti, E. Snow, and C. G. Van de Walle, Appl. Phys. Lett. 95, 172109 (2009)]. 把工作重新拉回到間隙子的摻雜方式中來。 —————————————————— 下面為轉(zhuǎn)載 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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金蟲 (正式寫手)
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計(jì)算結(jié)果未必可靠吧,很多人沒做出來ZnO-p摻雜,不代表就做不出來P摻雜。只是表明這個(gè)不是那么容易的,也許有些細(xì)節(jié)上的實(shí)驗(yàn)問題。 當(dāng)然本人也是懷疑浙大關(guān)于P摻雜ZnO結(jié)果的證實(shí)性,之所以懷疑,是因?yàn)樗麄儧]有公開站出來反擊這些懷疑,如果沒有問題,給其他一些懷疑的人,寄一些P型ZnO,讓他們?nèi)y試。不過也許是他們不屑這么做,但是,我就是懷疑他們。 關(guān)于計(jì)算N摻雜是否形成深能級,與p摻雜應(yīng)該是不矛盾的吧。P摻雜,我以為主要是改變能帶結(jié)構(gòu),是雜質(zhì)的擴(kuò)展態(tài)與原來的能帶結(jié)構(gòu)相互耦合的結(jié)果,而是否形成深能級,則與電離能之類的有關(guān),是局域態(tài)的缺陷。二者未必是沖突的。(一些揣測) |
金蟲 (正式寫手)
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