The dependence of the electrical characteristics of the GaN epitaxial layer on the thermal treatment of the GaN buffer layer

Abstract

The GaN buffer layer was grown on the sapphire substrate by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) at 525 °C. The following 1.3 μm epitaxial GaN growth was carried out at 1025 °C. We varied the ramping rate from 12.5 to 100 °C/min to study the quality of the epitaxial GaN. It has been found that the x-ray peak width, photoluminescence (PL) linewidth, Hall mobilities, and carrier concentrations of GaN epitaxial layer strongly depend on the in situ thermal ramping rate. An optimum thermal ramping rate was found to be of 20 °C/min. The maximum mobility is 435 cm2/V s at carrier concentration of 1.7×1017 cm−3. The minimum full width at half maximum (FWHM) of x ray and PL were 5.5 min and 12 meV occur at a ramping rate of 20 °C/min. The decrease of the mobility at high and low ramping rate can be attributed to the thermal stress and the reevaporation of the GaN buffer layer.