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In recent decades, infrared (IR) detection technology has been widely used in many fields such as weather monitoring, environmental protection, medical diagnostics, security protection, etc. With the progress and mature of the technologies, more attention has been paid to the imaging detections of weak IR signals. So the higher efficiency of the device is required. Moreover the next-generation IR photodetection technology focuses on large-scale, high-speed and low-dark-current imaging. The mechanical bonding between infrared detector chip and silicon readout circuit inevitably causes a thermal mismatch problem. Up-conversion IR photodetectors can solve the problem about the performance deterioration of photodetector and the thermal mismatch with silicon-based readout circuit, hence they have great advantages in realizing large-format focal plane array detection.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 to improve the device efficiency. In this paper, surface microstructures with micro-pillar morphology are designed and fabricated on quantum-cascade up-conversion IR photodetectors. The effect on the up-conversion efficiency is investigated by enhancing the light extraction efficiency.Firstly, by the optical ray retracing method, the influence of surface microstructure on light extraction efficiency is studied when considering different morphology parameters, and optimized surface microstructure is designed to possess a pillar base length of 150 nm, height of 105 nm and side wall angle of 75.Then based on the results of simulation, up-conversion IR photodetectors with surface microstructures are fabricated using polystyrene nanospheres as mask. The self-assembled monolayer nanospheres are first etched to a proper size by using O2 plasma, then the patterns are transferred to SiNx film, which acts as an ICP dry etching mask of the micro-pillars. Finally, the up-conversion device and a silicon detector are together loaded on a cold finger of a cryogenic dewar. The characteristics of the up-converter and up-conversion system are evaluated using a blackbody source.The experimental results show that the devices with and without surface microstructure exhibit similar IR responses and dark currents, while the emission of device with microstructure is obviously increased. Taking into consideration other factors related to external quantum efficiency, the light extraction efficiency of the device with micro-pillar structure on surface can be increased by up to 130%. Therefore it can be concluded that this method is an efficient way to improve the efficiency of up-conversion IR photodetector. The finding in this paper can also be applied to other semiconductor device with light extraction efficiency.

Infrared (IR) photodetectors have been widely used in the fields of both civil and military applications such as environmental monitoring, medical diagnostics, satellite remote sensing and missile guidance, etc. In conventional large scale focal plane array (FPA) IR imaging, the thermal mismatch between IR photodetectors and silicon readout circuits will inevitably lead to the degradation of the device performance. An up-conversion IR photodetector, which converts IR photons to short-wavelength photons for Si-CCD-based imaging, can avoid thermal mismatch caused by hybridization with silicon readout circuits, resulting in a low-cost way for large array IR imaging. The operation principle of the semiconductor up-conversion IR photodetector is based on electron transitions and carrier transportation in different functional sections including absorption section, transportation section and emission section, hence the carrier distribution in the device structure has a crucial influence on the device performance. In order to achieve low dark current, carriers are expected to be non-uniformly distributed in the up-conversion device structure. Designing and optimizing the carrier-blocking structure are usually the key issues to acquire inhomogeneous carrier distribution. In this paper, up-conversion infrared photodetectors with various hole-blocking structures are investigated both theoretically and experimentally. Firstly the carrier distributions are calculated by self-consistently solving the Schr?dinger equation, Poisson equation, current continuity equation and carrier rate equation. Then the influence of the carrierblocking structure on the device performance is analyzed by electroluminescence measurements on the corresponding epitaxial structures. According to the theoretical and experimental results, it is found that a 2-nm-thick AlAs barrier layer can block holes effectively without hampering the electron transportation, which is necessary for the up-conversion infrared photodetectors. However, other attempts to block holes, such as light n-doping in the transportation section or lowering the injection barrier, do not work well. In addition, the influences of the thickness and height of the blocking barrier and the operation temperature on the carrier distributions are also studied. When the thickness of the blocking barrier is less than 2 nm, the thicker or the higher is the barrier, the better is the blocking effect. However, when the thickness of the blocking barrier is larger than 2 nm, the blocking effect is not persistently enhanced with increasing thickness because the tunneling process is almost fully suppressed. Furthermore, with the same blocking barrier parameters, lowering the operation temperature can lead to better blocking effect. This work demonstrates the utilization and effect of carrier-blocking structures in semiconductor devices which deamnd an inhomogeneous carrier distribution.

The design and fabrication of multilayer antireflection (AR) coating based on plasma enhanced chemical vapor deposition (PECVD) is studied for its applications in optoelectronic devices. Deposition conditions for obtaining SiO2/SiNx thin films with large refractive index difference is determined through systematic study of factors influencing the refractive index of deposited SiNx. Four-layer SiO2/SiNx AR coating is designed to exhibit a reflectivity of less than 10-4 over 70 nm bandwidth. Reflectivity of the thin film structure at the center wavelength of 1550 nm remains less than 5×10-4 when the thickness deviation of any single layer is within ±5 nm from the designed value. Based on the simulation results, SiO2/SiNx multilayer AR coating is deposited on the end facet of a Fabry-Perot laser. By analyzing the output spectra of the laser, the residual reflectivity of the AR coating is determined to be on the order of 10-4 over the wavelength range of 1535—1565 nm.

In this paper, GaN films are grown by metal organic vapor phase epitaxy. Different N2 carrier gas percentages were used in the high-temperature growth process of the bulk GaN, and the dependence of sheet resistance on N2 carrier gas percentage is studied. It is found that the sheet resistance of the GaN film increases dramatically with N2 carrier gas percentage. When N2 carrier gas percentage is 50%, the sheet resistance of the GaN film is 1.1×108Ω/sq, and the surface root-mean-square roughness is as small as 0.233 nm. Secondary ion mass spectroscopy measurements reveal that the concentration of carbon and oxygen impurities is almost the same in the samples with different N2 carrier gas percentage. The density of edge-dislocation-related defects increases with N2 carrier gas percentage, while the density of screw-dislocation-related defects shows no obvious difference for all the samples. Our results indicate that the increase of the sheet resistance of GaN film is mainly due to the increase of edge threading dislocations, which act as acceptor centers in the GaN material.

Precise measurement and control of GaN-film thickness is very important for GaN-based material epitaxy and device fabrication. However, GaN-films heteroepitaxially grown on large-mismatch substrates, such as sapphire, SiC and Si, etc., usually show a mosaic structure, which causes great difficulty to the GaN-film thickness measurement. Combining the advantages of Williamson-Hall plot method and diffraction profile shape analysis method, a new strategy was presented to effectively distinguish the X-ray diffraction broadening factors of finite crystallite size and inhomogeneous strain, which can be used to precisely and reliably determine the thickness of epitaxial films. The thickness of a series of GaN films grown on sapphire substrates in the range of 0.7—4.2 μm were measured by this method. Comparing with the thickness obtained from spectroscopic ellipsometry measurements, the difference was found to be within 4%, which shows the excellent performance of this method.

In this work, the abnormal double-peak in the electroluminescence spectra of In xGa1-xN/GaN multiple quantum wells (MQWs) light emitting d iode s tructure materials with high indium contents was studied under different injecti on currents. The results show that the screening of internal electric field by i njection current plays an important role in the radiation recombination process of InxGa1-xN/GaN-MQWs materials.