Recently, due to its smallest band gap among the nitride semiconductors, InN has attracted great interest as a promising material for THz emission, high frequency communication electronics, solar cells and various sensors. Indeed good quality InN layers have been grown by molecular beam epitaxy (MBE), but such material is still not commercially available. In addition, results on HVPE growth of InN and InGaN materials are still limited, and the  reported material does not reach the device-quality level. In this work, we have carried out transmission electron microscopy of high-quality HVPE-grown InN layers with good optical, and substantially improved electrical properties. For comparison, we have also investigated InN layers grown on HVPE GaN templates by MBE.

The HVPE InN layers were grown in a temperature range from 500 to 600ºC on GaN/sapphire template substrates using InCl₃ –NH₃ gas system. Ar is used as a carrier gas. InN growth rate ranged from 0.3 to 0.5 µm/hour. Layers with thickness from 0.02 to 2.5 microns have been investigated.

In all the InN layers grown on GaN/sapphire substrates, the high density of threading dislocations in InN close to InN/GaN interface decreases markedly with the distance from the interface. High resolution TEM and analytical microscopy show that the interface with GaN is sharp at atomic scale and no In inclusions have been detected. By both techniques the InN layers exhibit good crystalline quality and their polarity has been determined when the thickness was above 0.4-0.5 µm. The MBE layers exhibit a PL edge around 0.8 eV at room temperature. For the HVPE layers, the PL edge position changes from one sample to the next, in the range 1-2 eV.  These results will be discussed in correlation with SIMS and Raman investigations.

This work is supported by the EU under Contract RAINBOW: PITN-GA-2008-213238

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