| The detection of infrared radiation, which is in the window that human eyes can not see, requires special detector. It is very important for the military, civilian safety, gas detection, medicine, astronomy, and other applications. The commercially available infrared detectors are bulk InSb photodetectors, Mercury Cadmium Telluride (MCT) photodetectors, and quantum well infrared photoconductors (QWIP). All of these photodetectors operate at cryogenic temperature, which require additional coolers to lower the temperature to 77K. The bulk InSb photodetectors have limited cut-off wavelength around 7 micron at 77K so that it is mainly used for the mid-wavelength infrared (MWIR) detection. For the long-wavelength infrared (LWIR) detection, the MCT photodetector is the primary one but it is limited by the uniformity in large area growth. The primary problem QWIPs are facing is low quantum efficiency. Because of all these limitations, an alternative material system, which has the flexibility of tailoring cut-off wavelength, excellent uniformity over large area, potential to operate at higher temperature, high quantum efficiency, and compatibility for multifunction, is required.;Since it was proposed by the Nobel laureate Leo Esaki in 1970s, the InAs/GaSb type-II superlattice (T2SL) has demonstrated its great imaging capability in infrared detection from short-wavelength infrared (SWIR) to very-long-wavelength infrared (VLWIR) regimes, and has been moving towards multi-spectral detection. Because InAs and GaSb are closely lattice matched to each other, they offer great flexibility of designing devices for optical and electrical applications. In recent years, promising performance photodiodes have been achieved because of the development of material quality, the innovative design of device structure, the surface leakage current suppression technique, and its unique band structure engineering capability. Therefore, T2SL has been considered to be a potential alternative of the current state-of-the-art HgCdTe imaging technology.;Despite this rapid development, there is still a discrepancy between the theoretical capabilities of this system and the experimental result of the minority carrier detectors. This is probably due to the following two reasons. The first one is the residual carrier background, which determines the minority carrier concentration and minority carrier life time, and strongly affects their electrical and optical performances. The other one is the surface leakage current, especially in long wavelength infrared regime (LWIR), which generates very high dark current and reduces the quantum efficiency. Therefore, this PhD thesis focuses on realizing the following goals: 1. Investigate the dependence of residual background carrier concentrations as well as activation energy on the superlattice design and their influence on T2SL photodetector's performance. 2. Demonstrate a technique, the gating technique, which can completely eliminate the surface leakage, provide much deeper understand of the surface leakage phenomenon, and can be adaptable to photodetectors with different designs and cut-off wavelengths. At the end, this technique should be able to be applied for FPA (product level).;Capacitance-voltage (C-V) measurement is the characterization technique for free carrier concentration in semiconductor devices. Combining C-V measurement and quantum efficiency analysis, a residual background type change is discovered when the monolayers (MLs) of InAs increases while the MLs of GaSb is kept constant. Moreover, the total concentration and the activation energy of shallow level defect are found to be dependent on the InAs layer thickness.;The gating technique first demonstrates its great potential to completely eliminate the surface leakage current in MWIR photodetector and shows that the surface leakage current is also one of the limiting factors for MWIR photodetector, which originally is ignored. The gating technique increases the detectivity from 7 x 1013 Jones to 2.5 x 1014 Jones at 110K, enables closer evaluation of the bulk current in the Type-II SL p-pi-M-n photodiode, and proves that the electron accumulation on the mesa sidewall causes the surface leakage current.;In the LWIR, where the surface leakage current is more severe, the gating technique also effectively suppresses the surface leakage current generated by the SiO2 passivation layer. By minimize the SiO2 passivation layer thickness, the origin of the surface leakage current is confirmed from fix charges at the SiO2/T2SL interface or the very thin SiO2 passivation layer near the surface, and thicker SiO 2 passivation layer will not further affect the surface leakage. By applying thin SiO2 passivation layer with the gating technique, the gated diode at -4.5 volt saturated gate bias exhibits RA-100mV of 3071 Ohmic.cm2, and detectivity of 7 x 1011 Jones at 77K. Most importantly, different surface leakage mechanisms (surface tunneling and surface generation-recombination) and different surface regimes have been disclosed.;In order to develop the gating technique from single element photodetector level to FPA level and further investigate the effect of surface leakage current on both the electrical and optical characteristics, a high-k dielectric, both Y2O3 and SiO2-Y2O3 hybrid passivation techniques have been developed. The Y2O 3 passivated gated photodetector array decreases the saturated gate bias by 3 times compared to the SiO2 passivated gated photodetector array. The SiO2-Y2O3 hybrid passivation improved the quantliy of Y2O3, resulting in much higher dielectric constant and improvement of fabrication yield, which realized the 27 micron pitch gated array and further suppressed the VG,sat to -7 volt. From backside illumination configuration, the gating technique reveals the fact that the surface recombination can reduce the quantum efficiency. The evolution of QE with different pixel sizes, VG, and VOP exhibits different surface recombination mechanisms and carrier life time in the surface depletion region. Thanks to the gating technique to suppress the surface recombination, at 77K, the QE of the 57micron size detectors was improved by 18.9%. At VG,sat (VG = -7 volt), the 57micron gated diode array exhibits J-200mV of 1.2 x 105 A/cm2, RA-200mV of 2.8 x 104 Ωcm 2, a 63% quantum efficiency, and a detectivity of 2.3 x 10 12 Jones. This gated photodetector array shows BLIP temperature of 110K, demonstrating a strong potential for FPA application. |
