ASELSAN has been developing new generation high operating temperature (HOT) infrared detectors to reduce the power consumption of T2SL detectors. In this paper, recent results for HOT T2SL detectors for mid-wavelength infrared (MWIR) technology at ASELSAN are presented. Performance is shown for 640x512 format 15 µm pitch IDDCA with average noise equivalent temperature (NETD) and pixel operability values of <25 mK (F/4) and >99.5% at 110 K, respectively. These NETD and operability values remain unaffected by temperature between 77 K and 110 K.
ASELSAN has made significant progress on developing its short-wave infrared (SWIR) technology, with a focus on improving dark current, quantum efficiency, and operability. In recent work, shunt current and generation-recombination current have been identified as the predominant dark current mechanisms. Shunt current can be suppressed by reducing the dangling bond count which requires optimizing the focal plane array passivation, and generation-recombination current can be reduced by improving the device design. Extensive work on process optimization employing various passivation schemes combined with theoretical layer design has lowered the SWIR focal plane array pixel dark current values down to < 1 nA/cm2. Furthermore, achieving low dark current without sacrificing high quantum efficiency (exceeding 80%), by building on the previous process and post-process work, has enhanced the sensor’s ability to capture faint signals. 640x512 format and 15 μm pitch SWIR focal plane arrays coupled with ASEL64015CG read-out circuits have consistently reached > 99.9% operability. After maturing the development work, ASELSAN launches its SWIR detector, LEOP-640/15-SW, pioneering the company’s photodetector production. In this paper, the results of the theoretical and experimental R and D work on LEOP photodetector development and production at ASELSAN are presented.
ASELSAN, the largest defense company in Turkey, develops high performance electro-optical systems for various applications. Due to the technical challenges and relatively higher cost associated with MCT technology, there is a search for an alternative material system all over the world, especially for the applications that need relatively low quantum efficiency and high volume production. Research and development activities have been carried out on developing InAs/GaSb T2SL detectors for mid-wavelength infrared (MWIR) technology in ASELSAN. In this paper, recent results for 15μm pitch MWIR T2SL and 10μm pitch MWIR T2SL detectors are presented. InAs/GaSb T2SL epilayers are used for FPA fabrication with mesa pixel structures. Typically, over 99% operability and less than 25 mK NETD values are achieved for 15 μm pitch 640x512 format MWIR T2SL FPAs at IDDCA level (F/4). Besides ongoing efforts on development of FPAs with 15 μm pixel pitch, development activities for pixel pitch reduction are also initiated recently for MWIR T2SL FPAs for improving resolution and promising results are achieved. For this purpose, MWIR T2SL FPAs with 1280x1024/10μm resolution/pixel pitch are fabricated and NETD values less than 25 mK (F/2) with pixel operability of 97% are achieved for the first prototypes.
ASELSAN, the largest defense company in Türkiye, develops high performance electro-optical systems for various applications. Research and development activities have been carried out on developing HgCdTe (MCT) detectors for long-wavelength infrared (LWIR) and mid-wavelength infrared (MWIR). In this paper, recent results for VGA 15μm pitch MWIR MCT detectors at IDDCA level are presented. P-on-n MCT epilayers are used for FPA fabrication with either mesa or planar pixel structures. Typically, over 99% operability and less than 20mK NETD values are achieved for 15μm pitch 640x512 format MWIR MCT FPAs at IDDCA level (F/4) in a repeatable fashion. Thermal cycle, mechanical shock, vibration and environmental tests (such as storage and operation under hot and cold temperatures) were applied to these MWIR MCT IDDCAs and passed successfully. Besides ongoing efforts on development of FPAs with 15μm pixel pitch, development activities for pixel pitch reduction also initiated recently for MWIR MCT and very promising results are achieved.
As the largest defense company in Turkey, ASELSAN A.S. pioneers the development of high performance electro-optical systems. Starting from 2014, significant progress has been made for the mid-wave infrared (MWIR) HgCdTe detector technology including development of Cadmium Zinc Telluride (CZT) substrate, Mercury Cadmium Telluride (MCT) growth and focal plane array (FPA) fabrication as well as Readout Integrated Circuit (ROIC) design. In this paper, recent process optimization studies on MWIR MCT detector technology are presented. p-on-n MWIR MCT layers with Cadmium (Cd) composition of ~0.3 are used for the FPA fabrication. 640x512/15 µm FPAs, which demonstrate the state-of-the-art performances, have been fabricated. Typically, over 99.0% operability and less than 25 mK Noise Equivalent Temperature Difference (NETD) values are attained with a cut-off wavelength of 5 µm at 77K. Among these remarkable results, major improvements have been recorded in pixel uniformity, reliability and reproducibility by revisiting process steps. As a result, process yield has been considerably increased.
Recent advances in short-wave infrared (SWIR) technology including numerous new applications in civil areas, fusion with visible wavelengths, and integration with active imaging systems triggered the SWIR photodetector research at ASELSAN for both passive and active imaging. SWIR focal plane arrays with a 640x512 format and 15μm pitch were developed and coupled with ASEL64015C readout circuits which had been designed at ASELSAN as well. Through extensive research and development dark current density values <10 nA/cm2 (at 20°C) and operabilities >;99% were achieved. This paper reviews the work that has been conducted on SWIR detector development at ASELSAN.
High performance multi-layer MWIR HgCdTe detector design requires detailed analysis considering the interaction between layers and the nonlinear effects. For this purpose, an in-house numerical model is utilized so that electrical and optical parameters are manipulated to eliminate the undesired performance limits. An ideal detector with perfect crystal quality is expected to have diffusion limited dark current. However, for low operating temperatures (<120K), which is usually the case for the high performance applications, SRH mechanism may dominate dark current especially for alternative substrate detectors and low crystal quality resulting in a short SRH lifetime (~200ns). Here, physical sizes, composition and doping profiles are optimized to suppress generation-recombination (GR) dark current so that cooling burden can be minimized. We numerically achieve ~30K (from ~85K to ~115K) increase on the operating temperature without degrading the system performance parameters for the detection of near room temperature object (300K) by placing a wide bandgap layer inside the bandgap.
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