Active region dimensionality and quantum efficiencies of ingan leds from temperature dependent photoluminescence transients

Abstract

Temperature dependent recombination dynamics in c-plane InGaN light emitting diodes (LEDs) with different well thicknesses, 1.5, 2, and 3 nm, were investigated to determine the active region dimensionality and its effect on the internal quantum efficiencies. It was confirmed for all LEDs that the photoluminescence (PL) transients are governed by radiative recombination at low temperatures while nonradiative recombination dominates at room temperature. At photoexcited carrier densities of 3 - 4.5 x 10(16) cm(-3), the room-temperature Shockley-Read-Hall (A) and the bimolecular (B) recombination coefficients (A, B) were deduced to be (9.2x10(7) s(-1), 8.8x10(-10) cm(3)s(-1)), (8.5x10(7) s(-1), 6.6x10(-10) cm(3)s(-1)), and (6.5x10(7) s(-1), 1.4x10(-10) cm(3)s(-1)) for the six period 1.5, 2, and 3 nm well-width LEDs, respectively. From the temperature dependence of the radiative lifetimes, trad tau(rad) alpha T-N/2, the dimensionality N of the active region was found to decrease consistently with decreasing well width. The 3 nm wide wells exhibited similar to T-1.5 dependence, suggesting a threedimensional nature, whereas the 1.5 nm wells were confirmed to be two-dimensional (similar to T-1) and the 2 nm wells close to being two-dimensional. We demonstrate that a combination of temperature dependent PL and time-resolved PL techniques can be used to evaluate the dimensionality as well as the quantum efficiencies of the LED active regions for a better understanding of the relationship between active-region design and the efficiency limiting processes in InGaN LEDs.