We report high quantum efficiency (QE) MWIR barrier photodetectors based on the InAs/GaSb/AlSb type II superlattice (T2SL) material system. The nBp design consists of a single unipolar barrier (InAs/AlSb SL) placed between a 4 μm thick p-doped absorber (InAs/GaSb SL) and an n-type contact layer (InAs/GaSb SL). At 80K, the device exhibited a 50% cut-off wavelength of 5 μm, was fully turned-ON at zero bias and the measured QE was 62% (front side illumination with no AR coating) at 4.5 μm with a dark current density of 8.5×10-9 A/cm2 . At 150 K and Vb=50 mV, the 50% cut-off wavelength increased to 5.3 μm and the quantum efficiency (QE) was measured to be 64% at 4.5 μm with a dark current of 1.07×10-4 A/cm2 . The measurements were verified at multiple AFRL laboratories. The results from this device along with the analysis will be presented in this paper.
KEYWORDS: Resistors, Sensors, Temperature metrology, Field effect transistors, Mid-IR, Superlattices, Infrared sensors, Signal to noise ratio, Interference (communication), Infrared radiation
Type-II Strained Layer Superlattice (T2SLS) infrared photodetectors have been in ongoing development over the last decade with the goal of achieving lower dark currents and higher operating temperatures when com- pared to mercury cadmium telluride (MCT) detectors. The theoretically longer Auger recombination lifetime of T2SLS has potential to lower dark current but the presence of Shockley-Read-Hall (SRH) defects limits the recombination lifetime far below the Auger-limit. In order to reduce SRH-recombination, unipolar barriers have been incorporated into the energy bands of T2SLS materials in different forms, such as nBn, to improve performance. Here, noise spectra are presented for varyingly sized, near 90% quantum efficiency, nBn mid-wave infrared (MWIR) detectors with superlattice absorbing layers grown by MBE. Noise spectrum measurements are used to evaluate device performance and reveal mechanisms contributing to low frequency noise that often exceeds predictions based on ideal shot noise. Voltage and temperature dependent noise spectra were taken using an external trans-impedance amplifier with an internal, cooled impedance converter and feedback resistor.
Midwave infrared (MWIR) photodetectors that do not require cryogenic cooling would significantly reduce the complexity of the cooling system, which would lead to a reduction in the size, weight, and cost of the detection system. The key aspect to realize high operating temperature (HOT) photodetectors is to design device structures that exhibit significantly lower levels of dark current compared to the existing technologies. One of the most attractive material systems to develop HOT photodetectors is InAs/GaSb Type II Strained layer Superlattice (SLS). This is due the ability of Type II SLS materials to engineer the band structure of the device, which can be exploited to make devices with unipolar barriers. It has been shown that, compared to the traditional homojunction SLS devices, band-gap engineered unipolar barrier SLS devices can obtain significantly lower levels of dark current. In this work, we report on the design, growth, and fabrication of mid wave infrared detectors based on type-II InAs/GaSb strained layer superlattice for high operating temperatures. The device architecture is the double-barrier heterostructure, pBiBn design. Under an applied bias of -10 mV and an operating temperature of 200 K, the tested devices show a dark current density of 4 x 10-3 A/cm2 and a quantum efficiency of 27%. At 4.5 μm and 200 K, the devices show a zero-bias specific detectivity of 4.4 x 1010 Jones.
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