Thermal stability of InN epilayers grown by high pressure chemical vapor deposition

The thermal stability of InN layers grown on sapphire by high-pressure chemical vapor deposition has been studied by thermal desorption, atomic force microscopy, X-ray diffraction, and infrared reflection measurements. Desorption products from samples grown with group V/III precursor ratios from 1200 to 4800, but otherwise identical growth conditions, have been monitored using differentially-pumped mass spectrometry while the sample temperature was ramped from room temperature to 825 °C. No significant desorption of nitrogen from the surface was observed below 630 °C, with a rapid increase of desorption of molecular nitrogen at substrate temperatures above 630 °C. No significant desorption of NH*/NH2* fragments was observed. From Arrhenius plots, the activation energy for desorption of nitrogen was found to be 1.6 ± 0.2 eV. It was observed that the activation energy for the desorption of nitrogen from InN samples was independent of V/III precursor ratio. However, the temperature corresponding to the maximum desorption was found to be dependent on V/III precursor ratio, increasing from 749 °C for V/III precursor ratio of 1200 to 776 °C for V/III precursor ratio of 4800. The observed shift in the peak desorption temperature with increasing group V/III precursor ratio is attributed to the decrease in extended defects and the increase in grain size.