Russian Physics Journal, Vol. 61, No. 2, June, 2018 (Russian Original No. 2, February, 2018)
INTERNAL QUANTUM EFFICIENCY OF LED STRUCTURES AT
VARIOUS CHARGE CARRIER DISTRIBUTIONS OVER InGaN/GaN
I. S. Romanov, I. A. Prudaev, and V. V. Kopyev UDC 621.382.2
The results of studying the effect of the thickness of GaN barrier layers in the active region of LED structures
with InGaN/GaN quantum wells on the internal quantum efficiency (IQE) of photoluminescence are presented.
It is shown that a decrease in the thickness of the GaN barrier layers from 15 to 3 nm leads to an increase in
the maximum value of IQE and to a shift of the maximum to the region of high excitation powers. The result
obtained is explained with consideration for the decrease in the Auger recombination rate due to a more
uniform distribution of charge carriers over the active region in structures with a barrier thickness of 3 nm.
Keywords: gallium and indium nitrides, quantum well, internal quantum efficiency, photoluminescence,
tunneling, Auger recombination.
As a rule, quantum efficiency of LEDs with InGaN/GaN quantum wells (QWs) reaches a maximum at a certain
threshold current density j
≈ 1–10 A/cm
, and with a further increase of j, it decreases significantly (this is the
efficiency droop effect). The use of LEDs in the household lighting requires high efficiency of LED heterostructures at
high injection current densities (j ≥ 35A/cm
) . In this regard, the developers often aim to increase the value of j
using various design solutions. Previously, many models have been proposed for explaining the efficiency droop, a brief
review of which is presented in . However, two main and most popular mechanisms can be distinguished: Auger
recombination and electron leakage from the active region [3, 4].
In this paper, we investigated blue LED structures with InGaN/GaN QWs with various thicknesses of the GaN
barrier layers in the active region. Experimental dependences of IQE of photoluminescence on the excitation power are
presented and the influence of the uniformity of the charge carrier distribution over the active region on the internal
quantum efficiency is estimated. Using a simplified quantitative analysis, it is shown that an increase in the uniformity
of the charge carrier distribution over the QW leads to a significant increase in the threshold photoluminescence
excitation power corresponding to the maximum value of IQE.
EXPERIMENT AND ANALYSIS TECHNIQUE
LED structures with InGaN/GaN QWs were grown by metalorganic chemical vapor deposition in an
AIXTRON 2400 system. The samples contained a low-temperature nucleation layer, a buffer i-GaN layer, an n-GaN
layer, an active region based on 5 InGaN/GaN QWs, and a p-GaN layer. The samples with the thicknesses of the GaN
National Research Tomsk State University, Tomsk, Russia, e-mail: firstname.lastname@example.org;
email@example.com; firstname.lastname@example.org. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika,
No. 2, pp. 8–11, February, 2018. Original article submitted December 25, 2017.
1064-8887/18/6102-0211 2018 Springer Science+Business Media, LLC