利用纳米球提高红外波长上转换探测器效率

在红外波长上转换探测器氮化硅(SiN_x)钝化层制作单层六角密排的二氧化硅(SiO_2)纳米球阵列,以提高红外波长上转换探测器的整体效率.采用自组装的方法在器件钝化层上制备了直径分别约为300,450,750和1000 nm的SiO_2纳米球,并与无表面微纳结构器件进行对比测试.结果表明:钝化层附着SiO_2纳米球能有效地提高红外波长上转换器的光提取效率;当SiO_2纳米球直径为750 nm时的光提取效率最优,是无表面微纳结构器件的2.6倍,可实现低成本制作高效率红外波长上转换探测器.

Improvement in the efficiency of up-conversion infrared photodetector by nanospheres

In recent years, infrared (IR) photodetector has been extensively used and played an important role in environmental control, medical diagnostics, and satellite remote sensing. Therefore, the priority should be given to how to stimulate the development of imaging detection of weak IR signal. Up-conversion IR photodetector has an ability to detect quite weak IR signal in the large plane array focal plane, so it has civil and military significance. However, the poor light extraction efficiency due to total reflection severely restricts the overall efficiency of the up-conversion device, which has become one of the bottlenecks in improving the device efficiency.#br#In this work, we propose that the light-extraction efficiency of up-conversion IR photodetector can be improved by a self-assembled monolayer of SiO₂ sphere. Thereby, the up-conversion efficiency can be enhanced. The up-conversion IR photodetector emits the light mainly from the silicon nitride (SiN_x) passivation layer. And the hexagonal closely-packed SiO₂ sphere monolayer is formed on the SiN_x layer. In order to study the effect of the size of nanosphere on the light-extraction efficiency, we prepare the SiO₂ spheres with diameters of 300, 450, 750, and 1000 nm respectively.#br#Results indicate that the devices with and without SiO₂ nanospheres exhibit similar IR responses and dark currents, while the emission of device with SiO₂ spheres obviously increases. And the light extraction efficiency increases up to an optimal level when the average size (750 nm) of SiO₂ sphere approximates to the wavelength (770 nm) of light source. Taking into consideration other factors relating to external quantum efficiency, the light extraction efficiency of the device with 750-nm-sized SiO₂ spheres on surface increases 2.6 times. In order to explain the physical mechanism for the light-extraction enhancement, we carry out the three-dimensional finite difference time-domain simulation, thereby calculating the transmission spectrum of the device with 750-nm-sized SiO₂ spheres. Simulation results show that the incident light beyond critical angle can be partly extracted when the surface of up-conversion IR photodetector has a SiO₂ sphere monolayer, leading to an enhanced light-extraction efficiency. So the SiO₂ sphere monolayer acts as a two-dimensional diffraction grating, which behaves as a light scattering medium for the light propagating in a waveguiding mode within the up-conversion IR photodetector. Therefore it can be concluded that this is a simple and cost-effective method of improving the efficiency of up-conversion IR photodetector. The finding in this paper can also be applied to improving the light extraction efficiency of other semiconductor devices.