Polar (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>In</mml:mi></mml:math>,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>Ga</mml:mi></mml:math>)<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mrow><mml:mrow><mml:mi mathvariant="normal">N</mml:mi></mml:mrow></mml:mrow></mml:math>/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mrow><mml:mi>Ga</mml:mi><mml:mi mathvariant="normal">N</mml:mi></mml:mrow></mml:math> Quantum Wells: Revisiting the Impact of Carrier Localization on the “Green Gap” Problem

Abstract

We present a detailed theoretical analysis of the electronic and optical properties of $c$-plane $\mathrm{In}\mathrm{Ga}\mathrm{N}$/$\mathrm{Ga}\mathrm{N}$ quantum-well structures with $\mathrm{In}$ contents ranging from 5% to 25%. Special attention is paid to the relevance of alloy-induced carrier-localization effects to the ``green gap'' problem. Studying the localization length and electron-hole overlaps at low and elevated temperatures, we find alloy-induced localization effects are crucial for the accurate description of ($\mathrm{In}$,$\mathrm{Ga}$)$\mathrm{N}$ quantum wells across the range of $\mathrm{In}$ content studied. However, our calculations show very little change in the localization effects when moving from the blue to the green spectral regime; that is, when the internal quantum efficiency and wall-plug efficiencies reduce sharply, for instance, the in-plane carrier separation due to alloy-induced localization effects changes weakly. We conclude that other effects, such as increased defect densities, are more likely to be the main reason for the green-gap problem. This conclusion is further supported by our finding that the electron localization length is large, when compared with that of holes, and changes little in the $\mathrm{In}$ composition range of interest for the green-gap problem. Thus, electrons may become increasingly susceptible to an increased (point) defect density in green emitters and as a consequence the nonradiative-recombination rate may increase.

Topics & Concepts