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 InGaN show an optical memory effect.
