Thickness effects of Al0.5Ga0.5N barriers on the optical properties of δ-AlGaN-inserted GaN-coupled multiquantum wells

Abstract

Coupled multiquantum well structures, GaN(10 angstrom)/AlGaN(5 angstrom)/GaN(20 angstrom) bounded by Al0.5Ga0.5N barriers whose thickness varied from 20 to 100 A, are characterized by photoluminescence and cathodoluminescence measurements. As a result of these measurements, main emission lines are redshifted with increments of the Al0.5Ga0.5N barrier thickness. The main emission line of photoluminescence for the barrier thickness of 20 A is centered at 3.188 eV. This value is redshifted with respect to the GaN excitonic emission line by an amount of 290 meV. An additional redshift centered at 2.96 eV is observed with the barrier thickness of 100 angstrom. As the excitation power increases, the main emission lines of the photoluminescence are blueshifted significantly and then saturated. This behavior is explained by the partial screening of the piezoelectric field by the photoexcited electron-hole pairs. From the results of cathodoluminescence measurements, the GaN excitonic emission line as well as the quantum well emission line for the barrier thickness of 20 A is also observed. (C) 2005 American Institute of Physics.