The Polarity of GaN: a Critical Review
- PDF / 657,141 Bytes
- 12 Pages / 792 x 792 pts Page_size
- 74 Downloads / 209 Views
Internet Journal of Nitride Semiconductor Research:
Email alerts: Click here Subscriptions: Click here Commercial reprints: Click here Terms of use : Click here
The Polarity of GaN: a Critical Review E. S. Hellman MRS Internet Journal of Nitride Semiconductor Research / Volume 3 / January 1998 DOI: 10.1557/S1092578300000831, Published online: 13 June 2014
Link to this article: http://journals.cambridge.org/abstract_S1092578300000831 How to cite this article: E. S. Hellman (1998). The Polarity of GaN: a Critical Review . MRS Internet Journal of Nitride Semiconductor Research, 3, pp e11 doi:10.1557/S1092578300000831 Request Permissions : Click here
Downloaded from http://journals.cambridge.org/MIJ, IP address: 139.184.14.159 on 21 Sep 2015
MRS
Internet Journal Nitride Semiconductor Research
The Polarity of GaN: a Critical Review E. S. Hellman1 1Bell
Laboratories, Lucent Technologies,
(Received Tuesday, May 19, 1998; accepted Friday, July 31, 1998)
GaN, AlN and InGaN have a polar wurtzite structure and epitaxial films of these materials typically grow along the polar axis. Although the polarity of these nitrides has been studied by quite a number of techniques, many results in the literature are in conflict. In this paper an attempt is made to lay out a set of polarity assignments to provide a context for discussion of these results. A “standard framework” is proposed to correlate the disparate results, and the framework is used to draw general conclusions about the polarity of bulk crystals, VPE and MBE epitaxial films, and devices.
1
Introduction
Success in the field of nitride semiconductor research has required participants to recognize that the nitrides are very different from the traditional III-V semiconductors. [1]. One important difference that has often been ignored is the fact that epitaxial growth of nitrides is typically done along a polar axis of the material. [a] The polarity has been overlooked for mostly experimental reasons; it has been difficult to measure which polarity is which. For example, convergent beam electron diffraction (CBED) done by different transmission electron microscopists has given contradictory results. Conventional diffraction techniques are prevented by symmetry from distinguishing the two orientations. In addition to the experimental difficulties, discussion of the polarity issue has been hindered by the use of confusing terminology. [2] Recent device work has determined the piezoelectric polarity, but confusion concerning sign conventions for piezoelectric coefficients has left the crystallographic polarity unresolved. This paper will critically review the status of polarity determinations in GaN, including recent work correlating etching, surface structure, and device results. A set of polarity assignments, which we call “the standard framework”, is laid out so that conflicts in the literature can be examined and discussed. 2
Which Face is Which?
Figure 1 illustrates the crystal structure of GaN. Wurtzite GaN, InGaN and AlN epitaxial films are almost always gr
Data Loading...
