Quantum Efficiency Analysis of Near-Ultraviolet Emitting AlGaN and AlInGaN Structures

The quantum efficiency of c-plane Al x Ga1-x N and Al x In y Ga1-x-y N structures (x = 0.06–0.21, y = 0.015–0.05) emitting in the UV spectral range between 320 and 350 nm was analyzed using temperature-dependent and polarization-resolved photoluminescence measurements. We found increasing bandgap fluctuation and charge carrier localization in case of higher aluminum or higher indium content. Improved suppression of nonradiative recombination was observed only in case of indium incorporation. The light polarization changed from E⊥c to E∥c with increasing aluminum content in AlGaN. It switched back to E⊥c by the incorporation of indium in AlInGaN. Light polarization significantly contributes to the photoluminescence intensity measured from the top, and the degree of light polarization decreases with increasing temperature. Thus, temperature-dependent photoluminescence measured via the c-plane surface was found to depend both on internal quantum efficiency and on extraction efficiency.