In this letter, InGaN-based solar cells with a p-InGaN/i-InGaN/n-GaN double-heterojunction structure were fabricated and characterized. Two kinds of sapphire substrates [i.e., a conventional sapphire substrate (CSS) and a patterned sapphire substrate (PSS)] were used for epitaxial growth. Both the solar cells grown on the CSS and the PSS demonstrated a high open-circuit voltage of 2.05 and 2.08 V, respectively. However, the short-circuit current of the solar cells grown on the PSS showed an improvement of 27.6% compared with that of the cells grown on the CSS. Such observation could be attributed to low edgedislocation density and the increase in the light-absorption path by the scattering of interface incident light between the substrate and the epitaxial layer for the solar cell grown on the PSS
Articles you may be interested inInfluence of stress on structural properties of AlGaN/GaN high electron mobility transistor layers grown on 150 mm diameter Si (111) substrate Ductile relaxation in cracked metal-organic chemical-vapor-deposition-grown AlGaN films on GaN 300ϫ 300 m 2 crack-free GaN / AlN multilayers of 2 m in thickness have been successfully grown on the Si͑111͒ substrate patterned with the Si x N y mesh by metal-organic chemical-vapor deposition. The in-plane stress exhibits a U-shape distribution across the "window" region, supported by the Raman shift of the GaN E 2 ͑TO͒ mode. This indicates a stress relaxation abruptly occurring near the edge of the window region due to the freestanding surface ͑1101͒ or ͑1122͒. The in-plane stress is almost relaxed at the corner of the window region due to three freestanding surfaces ͑1101͒, ͑1122͒, and ͑1011͒. The maximum in-plane stress is located near the surface of the multilayers at the center of the window region, supported by the Raman measurements and the failure observations. The role of the Si x N y mesh in the stress relaxation is discussed.
In this study, a 3-μm-thick AlGaN film with an Al mole fraction of 10% was grown on a nanoscale-patterned sapphire substrate (NPSS) using hydride vapor phase epitaxy (HVPE). The growth mechanism, crystallization, and surface morphology of the epilayers were examined using X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy at various times in the growth process. The screw threading dislocation (TD) density of AlGaN-on-NPSS can improve to 1–2 × 109 cm−2, which is significantly lower than that of the sample grown on a conventional planar sapphire substrate (7 × 109 cm−2). TEM analysis indicated that these TDs do not subsequently propagate to the surface of the overgrown AlGaN layer, but bend or change directions in the region above the voids within the side faces of the patterned substrates, possibly because of the internal stress-relaxed morphologies of the AlGaN film. Hence, the laterally overgrown AlGaN films were obtained by HVPE, which can serve as a template for the growth of ultraviolet III-nitride optoelectronic devices.
The band gap shift in the 80×80μm2 crack-free GaN∕AlN multilayers on the mesh-patterned Si(111) has been characterized by cathodoluminescence (CL) and Raman techniques. The GaN band gap derived from CL spectra depends on the spatial point inside a mesh, which changes from 3.413eV (at center) to 3.418eV (at edge) and to 3.426eV (at corner). The band gap shift is attributed to the variation of tensile stress inside the mesh, confirmed by Raman mapping. The shift of GaN band gap per unit stress is determined to be 0.03eV∕GPa.
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