AIP ADVANCES 8, 085222 (2018)

Deep levels induced optical memory eﬀect
in thin InGaN ﬁlm
B. B. Wang,1,2 J. J. Zhu,1,3,a D. G. Zhao,1,3,b D. S. Jiang,1 P. Chen,1 Z. S. Liu,1J. Yang,1 W. Liu,1 F. Liang,1 S. T. Liu,1 Y. Xing,1 L. Q. Zhang,4 and M. Li5
1 Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors,Chinese Academy of Sciences, Beijing 100083, China

2 College of Materials Science and Opto-Electronic Technology, University of Chinese Academyof Science, Beijing 100049, China

3 School of Electronic, Electrical and Communication Engineering, University of Chinese

Academy of Sciences, Beijing 100049, China

4 Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences,Suzhou 215125, China

5 Microsystem & Terahertz Research Center, Chinese Academy of Engineering Physics,

Chengdu 610200, China(Received 25 June 2018; accepted 23 August 2018; published online 30 August 2018)

An optical memory effect is found in a 20 nm InGaN ﬁlm. With increasing illumination time, photoluminescence (PL) intensity of InGaN rises at ﬁrst and then falls.
We present that this effect is caused by carriers capture in deep levels near interfaces
between GaN and InGaN. Firstly, carriers captured by deep levels near the interfaces
reduces the band inclination in InGaN. This cause the rise of PL intensity. Secondly, more and more captured carriers may form anti-shielding, which enhances band
inclination and results in the decrease of PL intensity. Carriers captured in previous illumination can remain for a long time after illumination is blocked, which make InGaNshow an optical memory effect. © 2018 Author(s). All article content, except whereotherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/1.5045811

InGaN materials are widely used as active regions in light emission devices, such as lightemission diodes (LEDs) and laser diodes (LDs).1–3 However, due to the lack of a comprehensive
understanding of their luminescence properties, some phenomena still cannot be explained very well.4
Optical memory effect is one of these. This effect has been observed in AlN, GaN, and InGaN.5–7
It is a phenomenon where photoluminescence (PL) intensity changes with increasing illumination
time and this variation depends on previous illumination history. In InGaN, PL intensity may rise
gradually to the maximum or fall exponentially within tens of seconds of an optical illumination.
Such different behaviors of PL variation depends on the InGaN samples are excited by 365 nm or by
405 nm laser.7 However, there are hardly any report of this effect in InGaN with 325 nm excitation.
We have tested the PL of an InGaN ﬁlm with 325 nm laser excitation and then found an interesting
optical memory effect behavior. The PL intensity rises gradually to the maximum at ﬁrst and thenfalls slowly in the range of hours rather than change monotonously.
Some researchers proposed that optical memory effect is somehow related to a blinking or quantum jump phenomenon in InGaN quantum dot.7–9 Tsutsumi et al speculated that adsorbed moleculeson the surface of the sample cause both optical memory effect and blinking.10 However, most likely
there are different mechanisms between them according to the largely different time scales of PLvariation between them (most periods of blinking in InGaN are near several milliseconds, but for
optical memory effect the PL rising or falling can last for more than several minutes).10,11 Morediscussions about the mechanism of optical memory effect are necessary. Our analysis suggestsabElectronic mail: jjzhu2007@sinano.ac.cn.
Electronic mail: dgzhao@red.semi.ac.cn.

2158-3226/2018/8(8)/085222/5

8, 085222-1© Author(s) 2018