Among the nitride semiconductors InN, shows the smallest effective mass and the highest electron drift velocity thus setting it as a candidate for applications in ultrahigh speed electronic devices. The band gap of 0.7 eV obtained for InN makes it also suited for high efficiency solar cells. In good quality layers hall mobility of 1000 cm²/s and residual carrier concentrations as low as 10¹8 /cm³ have been reported.
In this work we investigate the microstructure of InN layers grown by MOCVD on different buffer layers using TEM (AlN, directly on sapphire, GaN). The polarity of the layers is determined by Convergent Beam Electron Diffraction (CBED). We analyze the typical defects that form in these layers as well as the interfacial relationships between the substrate/buffer and active layers at atomic scale. The large mismatch between InN and sapphire or GaN leads to particular interface structures which critically depend on the growth conditions. It has been possible to point out typical interface structures from optimized growth conditions, and this will be discussed in the light of the PL emission intensity and peak position.
In MBE layers, we also confirm the growth polarity of the layers and it is pointed out that the layers contain a huge amount of dislocations, but no In precipitates, by cross section and planar view observations.
Our local analysis at atomic scale allows to clearly detemine the origin of the PL emission below 0.8 eV as related to the local chemical composition and structure of the InN layers.