Properties of AlN/GaN Heterostructures Grown at Low Growth Temperatures with Ammonia and Dimethylhydrazine
, Nirupam Hatui 2, Thomas E. Mates 1, Pratik Koirala 3, Adedapo A. Oni 3, Shuji Nakamura 1,2, Steven P. DenBaars 1,2 and Stacia Keller 2Round 1
Reviewer 1 Report
Manuscript reports on growth of AlN/GaN heterostructures at low temperature (550C) by MOCVD. Samples were characterized thoroughly, and authors concluded that by employing FME approach and various N-precursors combination good quality AlN/GaN interfaces can be demonstrated. The work is well performed and presented but it is incremental and novelty or in-depth scientific arguments/discussion is limited, (DMHy was reported before including N-precursors for ALD). On the other hand, the presented approach and results demo that by rectifying engineering growth modality a desirable lowering of AlN/GaN growth temperature is feasible. Unfortunately, as the authors have admitted a 2DEG formed within LT GaN suffers from structural imperfection what reduced the overall transport properties of the developed AlN/GaN heterostructures.
In our frank opinion, despite of the fact that incremental progress toward LT growth has been demonstrated, manuscript lacks insightful discussion and critical trade-off comparison with other approaches on the feasibility of the proposed growth sequence. For example, how narrow is the growth parameters window for achieving structures with improved sheet charge and mobility? The DMHy was known as suitable precursors for LT growth but it was not widely adopted for III-ns yet (why?) and manuscript does not address this issue clearly.
On the other note manuscript requires one more round of final proofreading to catch minor issues.
Authors may wish to comment on the above concerns before final acceptance.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
To grow heterojunctions with controlled electronic properties at the interface is an important task of modern electronics. In this regard one of the promising are nitride components, such as AlN and GaN addressed in the present work. The authors have demonstrated somewhat new fabrication routes of heterojunctions exploring metalorganic chemical vapor deposition using NH3 and DMHy as N-precursors. They have demonstrated and interesting dependence of charge mobility on the fabrication temperature and the interface layer. The latter has an immediate application in the modern technology of production of electronic devices.
The strength of the work: Quite deep and unambiguous insight into the physicochemical basics of formation of heterojunctions with the aid of corresponding set of complimentary techniques, data interpretation and sample preparation.
The weakness: There might be chemical transformation upon heterojunctions formation, especially at the interface and the temperature, so it would be useful to follow these changes, as they may affect the electronics, for instance, by XPS.
In general, the work is scientifically sound, well arranged and clearly presented, typesetting and figure quality are appropriate, reference list is comprehensive and up-to-dated. In my view, the manuscript is suitable for publication in Crystals in its present form.
Author Response
We thank the reviewer for the comments. In terms of measurements to determine the composition of the thin AlN layers, we have reported in the manuscript the EDX data for the sample grown with DMHy which shows no significant Ga incorporation in the AlN. In terms of the sample grown with ammonia, from the XRD we believe there was no significant Ga incorporation. For this sample, we have also collected XPS showing 96% Al content in the sample when measured perpendicular to the sample surface. This confirms our XRD result, although we did not present that data in the paper as we did not collect XPS on all the samples. XPS may be useful going forward to provide an additional characterization technique to confirm our findings.
