Banner
WideGap2001
Shield

Index

Doping Issues in Wide Band-Gap Semiconductors

Exeter, United Kingdom
21-23 March 2001
Next

Invited talk abstract

Dopant engineering in wide-band-gap semiconductors

Chris G. Van de Walle

Xerox PARC, 3333 Coyote Hill Road, Palo Alto, CA 94304, USA

Sukit Limpijumnong (1) and Joerg Neugebauer (2)

(1) Xerox PARC, 3333 Coyote Hill Road, Palo Alto, CA 94304, USA, (2) Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin, Germany

Lack of control over the conductivity of wide-band-gap semiconductors still presents a serious obstacle to optimum device performance. After describing the first-principles approach we have developed to address these problems, I will focus on three issues: acceptor doping of nitrides, conductivity control in ZnO, and the role of hydrogen in dopant engineering of semiconductors in general. P-type doping of nitrides still relies entirely on magnesium. Our recent investigations indicate that beryllium could be a promising alternative, provided compensation by beryllium interstitials can be brought under control. I will describe two strategies for achieving this, one being post-growth drift of interstitial Be (for which we have generated the required knowledge about its diffusion characteristics), the other the use of H as a codopant to suppress compensation by interstitials. The beauty of using H as a codopant is that it can be neutralized or removed from the p-type layer after growth, resulting in acceptor activation. The challenges involved in using other codopants, such as oxygen, will be discussed. When H is incorporated, acceptor-hydrogen complexes are formed, and their detection forms a powerful means of monitoring the activation process.

We have studied the vibrational modes of these complexes in detail, including anharmonic effects. In the process, we have identified a configuration of the Mg-H complex that is consistent with the recent IR spectroscopy results of Clerjaud et al. [1]. Turning to ZnO, we are confronted with the same problems that GaN faced about a decade ago: lack of understanding about unintentional n-type doping, and inability to achieve p-type. I will summarize our current thinking about the source of n-type conductivity, and the prospects for achieving p-type doping. Finally, since hydrogen plays an important role in many of these phenomena, I will discuss our present understanding of the electronic behavior of hydrogen in semiconductors and oxides in general. Our initially startling discovery that hydrogen acts as a donor in ZnO and in InN can actually be consistently explained in this broader context.

This work was supported in part by ONR (Contract No. N00014-99-C-0161) and by AFOSR (Contract No. F4920-00-C-0019).

[1] B. Clerjaud, D. Cote, A Lebkiri, C. Naud, J. M. Baranowski, K. Paula, D. Wasik, and T. Suski, Phys. Rev. B 61 (2000) 8238.