Thickness-related features observed in GaN epitaxial layers

Electrical properties of gallium nitride ~GaN! epitaxially grown on sapphire show significant dependence on layer thickness. In this letter we show some of the main features observed by spectral photoconductivity ~PC!, electron beam induced current, and current–voltage characteristics. We focus our attention on the blueshift of the PC peak corresponding to the energy gap, which we associated to the strain acting in the GaN epilayers. The good energetic resolution of photoconductivity spectra allows for a direct study of the energy gap dependence on thickness.