Active and passive short-wave infrared (SWIR) detection systems for surveillance and remote sensing applications are mostly required to detect extremely low photon fluxes. This can be achieved by utilizing the internal signal gain as provided by avalanche photodiodes (APDs). We report on our current development activities of SWIR photodetectors based on InGaAs/InAlAs/InP APDs, covering detector design, epitaxial growth, process technology, and electro-optical characterization results of single-element detectors and fanout hybrids. For the first time, the operation of an InGaAsbased SWIR camera with 640 × 512 pixels utilizing APDs for signal amplification is demonstrated for operating temperatures of 180 K and even 260 K.
For surveillance and reconnaissance applications in the short-wave infrared (SWIR) spectral range, the imaging systems have to cope with usually very low photon flux densities. Thus, dark-current and noise characteristics of the focal plane array (FPA) are demanding. On the other hand, the challenge of detecting extremely low photocurrents can be mitigated by utilizing an internal gain as provided by avalanche photodiodes (APDs). Fraunhofer IAF has recently started the development of InGaAs-based SWIR detectors. We report on the current development status covering design considerations, epitaxy, process technology and electro-optical characterization. Detector structures based on both, classical InGaAs PIN homojunction diodes as well as InGaAs/InAlAs APDs in separated-absorption-grading-charge-and-multiplication layer heterostructures, have been grown by molecular beam epitaxy on InP. Diodes structures were fabricated with a dry-etch mesa process and a subsequent dielectric passivation of the mesa sidewalls. High-resolution FPAs with 640 x 512 pixels and a 15 μm pixel pitch based on PIN diodes have been assembled to a SWIR camera system in cooperation with AIM Infrarot-Module GmbH. Design variations, in particular for the APDs, were assisted by band-edge-profile simulations. APD test structures as well as fan-out hybrids have been characterized, revealing gain values larger than 300 at room temperature.
We report on the development and optimization of mesa-processed InGaAs/InAlAs avalanche photodiodes (APD)
for short-wave infrared applications with demand for high gain and low breakdown voltage. The APDs were
grown by molecular beam epitaxy. Dark and photo current measurements of fully processed APDs reveal high
dynamic range of 104 and gain larger than 40 for 25 V reverse bias voltage and cooled operation at 140 K. A
maximum gain larger than 300 is demonstrated for room temperature as well as 140 K. Two different approaches
to determine the gain of the APD structures are discussed.
Fraunhofer IAF can look back on many years of expertise in developing high-performance infrared photodetectors. Since
pioneering the InAs/GaSb type-II superlattice detector development, extensive capabilities of epitaxy, process
technology, and device characterization of single element detectors and camera arrays for the mid- and longwave
infrared (MWIR and LWIR) have been established up to the level of small-scale production. Bispectral MWIR/MWIR
and MWIR/LWIR cameras based on type-II superlattices or HgCdTe are key topics at Fraunhofer IAF. Moreover, the
development of InGaAs-based short-wave infrared (SWIR) photodetectors for low-light-level applications has recently
been initiated.
In this contribution, we report on the status of recent photodetector development activities at IAF, covering detector
design, epitaxial growth, process technology, and most recent electro-optical characterization results of focal plane
arrays as well as single element detectors especially for the SWIR based on InGaAs material system.
We report on materials and technology development for short-wave infrared photodetectors based on InGaAs p-i-n and avalanche photodiodes (APDs). Using molecular beam epitaxy for the growth of thin layers with abrupt interfaces, which are required for optimized APD structures, excellent crystalline quality has been achieved for detector structures grown on 3-inch InP substrates. For the fabrication of focal plane detector arrays, we employed a mesa etching technology in order to compare the results with the commonly utilized planar technology. Camera detector arrays as well as test structures with various sizes and geometries for materials and process characterization are processed using a dry-etch mesa technology. Aspects of the process development are presented along with measured dark-current and photo-current characteristics of the detector devices.
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