Structural and optical characterization of GaN nanostructures formed by using N⁺ implantation into GaAs at various temperature

Abstract

We have investigated the evolution of GaN phase nanocrystallite formation in a GaAs matrix by using nitrogen-ion implantation and subsequent rapid thermal annealing. A semi-insulating GaAs (100) wafer was implanted with 50-keV nitrogen ions at fluences in the range of 0.5 ∼ 4.0 × 10¹⁷ cm⁻² at temperatures of room temperature, 500 °C and 700 °C, followed by post-implantation annealing at 500 ∼ 900 °C under a pure nitrogen gas flow. In the case of high-temperature implantation, there were no significant changes in the UV-VIS absorption spectra after high-temperature annealing compared with the spectra of the as-implanted sample. On the other hand, microscopic blistering and/or exfoliation is preferred after post-implantation annealing at high temperatures above 600 °C. As a consequence, low-temperature implantation (<200 °C is recommended in order to keep a morphologically-clean sample surfaces especially at an implantation fluence of 2 × 10¹⁷ cm⁻² or more. Formation of nanometer-sized GaN crystallites was confirmed by using X-ray diffraction, cross-sectional transmission electron microscopy and low-temperature photoluminescence spectroscopy, and the effects of different annealing conditions on the evolution of the structures of the crystallites are described.