Discussion of Article 46 in Volume 3

This is a discussion of the MIJ-NSR article entitled X-ray reciprocal lattice mapping and photoluminescence of GaN/GaAlN Multiple Quantum Wells; strain induced phenomena. by R. Langer, J Simon, O. Konovalov, N. Pelekanos, A. Barski, M. Leszczyński

Description of the paper by the reviewer(s):

Reviewer 1: Careful XRD analysis of MBE grown AlGaN/GaN quantum well structures deposited on MOCVD-grown GaN allow to construct the image of this structure in reciprocal space. Clear evidence for pseudomorphic growth on the MOCVD-grown template is found. The PL results are discussed in terms of a redshift induced exclusively by piezoelectric effects, although carrier localization due to compositional fluctuations should at least be discussed as an alternative explanation for the observed shift.

Comments on this paper by the reviewer(s):

Reviewer 1: This paper contains interesting original research and is worth publication provided three issues are addressed: (1) The observed redshift can be due to the piezoelectric effect as suggested in the paper, it can as well be due to carrier localization in compositional fluctuations of the quantum well that result in fluctuations of the bandgap. Both these possibilities are currently widely debated in the literature and without additional arguments simply omitting the localization possibility does not seem to be appropriate. This paper cannot be used as PROOF that all observed redshift is due to the peizoelectric effect. (2) The referee is a bit disturbed that the phrases: "GaN pseudosubstrates" in the abstract and in the text even "GaN substrates" (e.g. in section 3) might make the reader infer these layers are of better quality then conventionally grown layers on sapphire. However, these layers might be worse then layers grown in one growth cycle directly on sapphire as the transport of the MOCVD GaN/sapphire structures through air definitely results in surface oxidation and contamination. Therefore, already the abstract should be changed: instead of "on GaN pseudosubstrates" it should read "on MOCVD-grown GaN/sapphire layer." Similarly, in the text the term "on GaN subststrates" should always be replaced by a correct description. (3) Finally, Fig. 1 contains XRD data that are presented as reciprocal space images. This is a formally correct way, but for the reader difficult to compare with other XRD data. The referee suggests to replace at least one pairs of scales (e.g., top and right side) with a scale calibrated in arcmin or arcsec to allow such a comparison.

This discussion is moderated by R. Langer.

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