In recent years, AlGaN/GaN multiple quantum wells (MQWs) have been taken as the most promising material for infrared photodetectors. The devices can be operated in a wide region at ultrafast speed due to the large conduction band and strong electron-phonon interaction. As the only material that can realize ultraviolet and infrared double band detectection on the same wafer, it opens inspiring prospects for important applications in the military. For infrared photodetectors based on intersubband transitions, in order to effectively make response, it is necessary to find some way to change the energy flow of normal incident source. However, few efforts have been made on enhancing the optical coupling of AlGaN/GaN quantum well infrared photodetector (QWIP) in the atmospheric window of 3-5 μm. Although the direction of energy flow of normal incident source can be changed via surface plasmon resonance excited by one-dimensional as well as two-dimensional metallic grating, the mechanism responsible for the enhanced infrared absorption has not been clearly explained and the optical coupling efficiency is still unsatisfactory.
To solve the problems mentioned above, Wang Shuai et al. from Wuhan National Laboratory for Optoelectronics proposed a new kind of grating, quasi-one-dimensional gold grating to enhance the optical coupling in AlGaN/GaN QWIP under the guidance of Professor Chen Changqing and Associate Professor Dai Jiangnan. The quasi-one-dimensional gold grating not only provides more surface plasmon excitation source but also higher charge density on the gold surface. As a result, the optical coupling efficiency of 85% has been obtained.
These promising results indicate that the square of effective electric field norm in MQWs region shows 2 times and 1.3 times increase compared with that obtained via a one-dimensional gold grating and a two-dimensional gold grating, respectively. The focal plane arrays based on AlGaN/GaN quantum well infrared photodetectors will be potentially realized via the quasi-one-dimensional gold grating.
This work was supported by the National Basic Research Program of China (Grant No. 2012CB619302, 2010CB923204), the National Natural Science Foundation of China (Grant No. 60976042, 51002058, 10990102), the Science and Technology Bureau of Wuhan City (Grant No. 2014010101010006). It is published in Optics Express (2015 Vol. 23, Iss. 7, pp. 8470-8478).
Fig. Effective electric field in AlGaN/GaN MQWs region with three different metallic gratings.