We have pointed out for the epitaxy of InN and InN-based ternary alloys that N-polarity growth regime is preferable than In-polarity one in the viewpoint of getting higher-quality epilayers as well as constructing fine structure InN-based heterojunctions. This situation is very much different from that of other typical III-nitrides of GaN, AlN and Ga(Al)-rich ternary/quaternary alloys including InGaN, where Ga- or Al- polarity is better than N-polarity. The reason for the different situation in epitaxy of InN-based III-nitrides is attributed to that of about 100 deg higher possible-epitaxy temperatures in N-polarity than In-polarity (~600 deg for N-polarity but ~500 deg for In polarity). The higher epitaxy temperatures result in both (a) much easier epitaxy control under around unity surface stoichiometry to avoid the appearance of In-droplets on the surface during growth and (b)better matching in epitaxy temperatures between InN-well and GaN and/or AlN-based barriers when fabricating InN-based nano-heterostructures.
In this paper, we report our recent results on the epitaxy of N-polarity InN-based ternary alloys of InGaN and AlInN both on GaN and InN underlayers. Further, we have investigated to fabricate InN-based nano-heterostructures including InN/GaN, InN/InGaN, and InN/AlInN MQWs under the N-polarity growth regime.
The InN-based epilayers and MQWs were characterized by HR-XRD, AFM, TEM, Hall and PL measurements. We have succeeded for the first time in fabricating very fine InN-based nano-heterostructures which were revealed by the clear satellite diffraction peaks and sharp hetero-interfaces by XRD and TEM, respectively.
Finally we conclude that the N-polarity growth regime is very important in the epitaxy of InN itself, InN-based ternary alloys and fine MQWs structures.

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