Structural Design And Optimization Of Extended Wavelength In_0.82Ga_0.18 As Infrared Detector

The near-infrared detectors with1-3um spectra have wide applications in spaceremote sensing, atmospheric monitoring, resource exploration and others. Recently,the InGaAs near-infrared detectors emerge as the most promising, as InGaAs cancover1-3um spectra and has many advantages such as high absorption coefficient,high mobility, good uniformity and stability, high detection rate in high temperatureand excellent resistance to space radiation. However, the generated high dark currentrestrict its application in remote sensing and military. The infrared detectors withPIN structure are commonly used in device design due to the manufacture simplicityand high responsivity. The simulation and optimization of the device`s structure andfunction are cost and time effective. In communication, a number of studies havebeen performed on In0.53Ga0.47As detector and InGaAs infrared detector with APDstructure. One simulation is to establish the circuit model using the SPICE to studythe photoelectric properties of photo detectors with different materials and structures.Another method is to use numerical tools to analyze device characteristics based onthe carrier continuity equation and Poisson’s equation. In summary, there is considerable significance to optimize the structures of extended wavelength InGaAsdetector by simulation in order to decrease the dark current and improve the deviceperformance.APSYS was adopted to simulate InGaAs infrared detector. APSYS is a2D/3Dfinite element analysis software, which contains several powerful simulation models,such as hot carrier transport, heterojunction and thermal analysis model. Oursimulation is based on the drift-diffusion model, with solving the Poisson equationand current continuity equation by the self-consistent solution method. Then, a moreaccurate simulation would be obtained to design and optimize devices.After verifying the reliability of APSYS, the simulation of extended wavelengthInGaAs detector was conducted. The material and light illumination were calculatedand analyzed. Moreover, a new composite cap InGaAs infrared detector (i.e. PNNcap InGaAs detector) was designed. The conclusions are the followings:The results showed that each layer can affect the photoelectric performance. Animproved photoelectric performance was observed in the device with GaAs substratecompared with InP. The back illumination was suitable for device with InP substrateand the front illumination was suitable for the device with GaAs substrate. Theincrease in the thickness of absorption layer resulted in a up-regulation of darkcurrent and photo current. The optimal thickness was measured as2um-3um. Inaddition, the energy band of the device can be regulated by the material structure ofbuffer layer. In back illuminated detectors, the thickness of substrate and bufferlayers had significant impact on the device photoelectric performance. The carrierconcentration in buffer layer played a role in device performance and needed to beoptimized while the carrier concentration in substrate had no effect on deviceperformance. To meet the needs in space exploration, In0.82Ga0.18As near-infrared detector withnew structure was developed to reduce dark current, with optimized cap layers usingcombined materials, thickness and carrier concentration. The results indicated thatthe dark current for were4E-6A and2E-6A under bias voltage between0.1V, forPIN structure InGaAs near-infrared detector with InAlAs/InAsP/InGaAs PNN caplayer and InAlAs/InAsP/InAlAs PNN cap layer, respectively. Such values weresmaller by one order of magnitude than that in common PIN structure InGaAsdetector.When the working temperature was lower than280K, the dark current of InGaAsdetector with InAlAs/InAsP/InGaAs PNN cap layer was mainly defect tunnelingcurrent. The dark current was mainly inter-band tunneling current with workingtemperature between280and300K and the current was generation-recombinationcurrent and the diffusion current with working temperature higher than300K.Similarly, the dark current of InGaAs detector with InAlAs/InAsP/InAlAs PNN caplayer was mainly defect tunneling current when the working temperature was lowerthan260K, inter-band tunneling current with working temperature between260and290K and generation-recombination current and the diffusion current withworking temperature between290and320K.