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High operating temperature mid-wave infrared HgCdTe photodiode design

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2019
Yurtseven, Eray
Infrared focal plane arrays are critical components in many of the military and civilian applications for advanced imaging systems. HgCdTe is one of the most widely used infrared detector material. An important issue with this material for thermal imaging system is the operating temperature as it determines cryocooler crucial characteristics, namely power comsumption and device lifetime. Therefore, there is an effort towards to operate at higher temperatures, but performance characteristics need to be carefully designed. Increasing operating temperature causes to increase diode current due to thermal generation and also is associated with 1/f noise. Furthermore, number of defective diodes increases at high operating temperatures. High quality material is the first requirement to maintain the same diode characteristic at higher temperatures. This can be achieved by using Molecular Beam Epitaxy (MBE) method that provides ultra-high vacuum condition and ultra-pure materials (Hg, CdTe, Te). Further way to improve diode characteristics at higher temperatures is applying design modifications. For instance, adjusting absorber layer parameters such as thickness, cadmium mole fraction and doping level or adding some extra layers to diode structure. Barrier detectors, auger suppression structures and photon trapping structures are the major high operating temperature (HOT) infrared detector configurations. Within the scope of this thesis, a new HgCdTe MWIR photodiode is designed by interpreting HOT Infrared focal plane arrays are critical components in many of the military and civilian applications for advanced imaging systems. HgCdTe is one of the most widely used infrared detector material. An important issue with this material for thermal imaging system is the operating temperature as it determines cryocooler crucial characteristics, namely power comsumption and device lifetime. Therefore, there is an effort towards to operate at higher temperatures, but performance characteristics need to be carefully designed. Increasing operating temperature causes to increase diode current due to thermal generation and also is associated with 1/f noise. Furthermore, number of defective diodes increases at high operating temperatures. High quality material is the first requirement to maintain the same diode characteristic at higher temperatures. This can be achieved by using Molecular Beam Epitaxy (MBE) method that provides ultra-high vacuum condition and ultra-pure materials (Hg, CdTe, Te). Further way to improve diode characteristics at higher temperatures is applying design modifications. For instance, adjusting absorber layer parameters such as thickness, cadmium mole fraction and doping level or adding some extra layers to diode structure. Barrier detectors, auger suppression structures and photon trapping structures are the major high operating temperature (HOT) infrared detector configurations. Within the scope of this thesis, a new HgCdTe MWIR photodiode is designed by interpreting HOT structures which are mentioned above. With the designed structure, it was observed that the dark current improved at all temperatures between 100 K and 300 K. The quantum efficiency decreased by 3.1% at -0.1 V due to barrier layer in the designed structure. However, this reduction was reduced to 1.2% by photon trapping structure. This structure also provided an improvement of about 18.2% in the dark current. This improvement is consistent with volume reduction in the photodiode. The surface component of the dark current was not included in the simulations. Therefore, during the fabrication of the designed structure, passivation of the mesa walls need to be done well to prevent large surface leakage current.