MIJ-NSR Language Recommendations

To facilitate the clear communication of research results, the MIJ-NSR Journalmaster will from time to time make recommendations concerning language, terminology and conventions to be used in MIJ-NSR papers. Researchers are encouraged to adopt these conventions in all their published work, but especially in any paper submitted for publication in MIJ-NSR.

Recommendation #1: GaN Polarity

The language used in the literature to describe the polarity of GaN has been quite confusing. Some authors have used identical terms to describe opposite situations. This confusion is entirely unnecessary and unfortunate. The situation is particularly bad for wurtzite GaN.

Recommendations:

Ga-Face and N-face: Use Ga-face to describe a surface whose gallium atoms have a single bond point up, normal to the surface. The gallium atoms are bonded to three nitrogen atoms in the direction away from the surface. Remember, a face has one nose. Use N-face for the opposite surface, whose nitrogen atoms have one bond pointing up (and whose gallium atoms have their rears showing, with three bonds pointing out.)
Related Nomenclature: The wurtzite (0001) and zincblende (111)Aor surfaces of GaN are Ga-face. The wurtzite (000) and zincblende ()B surfaces of GaN are N-face. Remember, the A is in gAllium and you measure nitrogen pressure in Bars.
Ga- and N- Termination: Termination should only be used to describe a surface property, and should never be used to describe a bulk polarity. Researchers who are familiar with GaAs research are familiar with As and Ga terminated (100) surfaces. These are polar surfaces, but <100> is not a polar direction; the only difference is which atom comes last. A Ga-face surface might be nitrogen terminated if it is covered with nitrogen, but without flipping the crystal, it will never be N-face
Ga- and N- Polar: Avoid using the terminology Ga-Polar or N-Polar, unless you define your terms.

References

Two papers in MIJ-NSR which discuss polarity are Volume 1, Paper 16 and Volume 1, Paper 33. The latter paper has this figure showing the GaN polarity:
F. A. Ponce et al., Appl. Phys. Lett. 69(3), 337 (1996), have a diagram illustrating the standard Miller indices notation we recommend. They use "Ga terminated" where "Ga face" is recommended here.
The convention for setting the directions for Miller indices in the wurtzite structure can be found in Volume 1 of Crystal Structures, 2nd Edition, p.111 by R. W. G. Wyckoff (Interscience, New York, 1963). To reiterate, the positive c direction points from Ga to N.