Stress relaxation of AlGaN on nonpolar m-plane GaN substrate

Abstract

The stress relaxation with increasing thickness of metal-organic vapor phase epitaxy grown Al0.19Ga0.81N on quasi-bulk (101¯0) m-plane GaN substrates was investigated by x-ray diffraction. The anisotropic in-plane stress leads to an orthorhombic distortion of the lattice, which requires special mathematical treatment. Extending earlier works, we developed a method to calculate the distortion along [12¯10], [0001], and [101¯0] and obtained the lattice parameters, Al content, and strain values. The stress relaxation along the two in-plane directions involves two different mechanisms. First, the stress along [12¯10] relaxes by the onset of misfit dislocations through the {101¯0}⟨12¯10⟩ slip system while for thicker layers the stress along [0001] relaxes by crack formation. Comparing the cathodoluminescence emission at room temperature with the expected bandgap showed that both tensile in-plane strains along [12¯10] and [0001] decrease the bandgap.

Growth of N-Polar (0001) GaN in Metal–Organic Vapour Phase Epitaxy on Sapphire

“…The crystal quality was assessed by X-ray diffraction (XRD) using multi-axis X-ray diffractometers of various makers and measuring open detector rocking curve scans of 5-8 reflections. The lattice constants were evaluated from the 2Θ angles of 5-8 planes in a similar way as we recently described for the m-plane orientation [13]. Room-temperature photoluminescence (PL) was measured with a HeCd laser with an excitation power of 10 mW and a spot size of around 0.01 cm 2 and collected with a 2048 pixel CCD with a resolution of 0.7 nm.…”