Dependence of InGaN Quantum Well Thickness on the Nature of Optical Transitions in LEDs.

Mateusz Hajdel,Krzesimir Nowakowski-Szkudlarek,Mikolaj Chlipała,Henryk Turski,Czeslaw Skierbiszewski,Paweł Wolny,Marcin Siekacz,Anna Feduniewicz-Żmuda,Grzegorz Muziol

doi:10.3390/ma15010237

Mateusz Hajdel, Krzesimir Nowakowski-Szkudlarek + Show 7 more

Open Access

https://doi.org/10.3390/ma15010237

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Abstract

The design of the active region is one of the most crucial problems to address in light emitting devices (LEDs) based on III-nitride, due to the spatial separation of carriers by the built-in polarization. Here, we studied radiative transitions in InGaN-based LEDs with various quantum well (QW) thicknesses—2.6, 6.5, 7.8, 12, and 15 nm. In the case of the thinnest QW, we observed a typical effect of screening of the built-in field manifested with a blue shift of the electroluminescence spectrum at high current densities, whereas the LEDs with 6.5 and 7.8 nm QWs exhibited extremely high blue shift at low current densities accompanied by complex spectrum with multiple optical transitions. On the other hand, LEDs with the thickest QWs showed a stable, single-peak emission throughout the whole current density range. In order to obtain insight into the physical mechanisms behind this complex behavior, we performed self-consistent Schrodinger–Poisson simulations. We show that variation in the emission spectra between the samples is related to changes in the carrier density and differences in the magnitude of screening of the built-in field inside QWs. Moreover, we show that the excited states play a major role in carrier recombination for all QWs, apart from the thinnest one.

Highlights

We investigated the radiative transitions in light emitting devices (LEDs) with a single quantum well (QW) varying its thickness from 2.6 nm to 15 nm
The InGaN LEDs were grown by plasma assisted molecular beam epitaxy (PAMBE)
In the case of LED with 6.5 nm QW we observe that the initial peak starts to emit at λ = 565 nm and strongly blue shifts

Summary

Introduction

It was shown experimentally that with the increasing thickness for QW, the photoluminescence intensity drops [22,23] This originally led to the usage of thin QW as an active region in nitride LEDs [20,23]. We showed that the reason behind the high efficiency of the wide QWs lays in the screening of the built-in electric field by carriers occupying the ground states and radiative transition through exited states with high wavefunction overlap [30]. We present evidence for emission from excited states in the case of LEDs with sufficiently wide QWs. We investigated the radiative transitions in LEDs with a single QW varying its thickness from 2.6 nm to 15 nm. We performed LED operation simulations to give a comprehensive understanding of the role of the ground and excited states

Samples and Methods

Simulation

Conclusions