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We report on the development of mesa-processed InGaAs/InAlAs avalanche photodiodes (APDs) for short-wave infrared (SWIR) imaging applications with demand for high gain and low breakdown voltage. Devices are designed with separate absorption, grading, charge, and multiplication (SAGCM) layers. Special attention has been paid to the charge layer in order to optimize the structure for low band discontinuities and an appropriate electric field distribution. Hereof, a combination of a p-type grading layer and charge layer is presented. Band-edge profile calculations as well as electro-optical characterization results of the APDs will be discussed in this article. Our optimized APD structures reveal low punch-through and low breakdown voltage of V-pt approximate to 8.5 V and V-bd approximate to 2.3 V, respectively. A maximum gain of M > 300 in the linear operation mode is demonstrated at room temperature and M = 10 has been measured at 20 V bias

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Short-wavelength infrared (SWIR) detection systems are increasingly in demand for surveillance, reconnaissance, and remote sensing applications. Eye-safe SWIR lasers can be utilized for active imaging systems with high image contrast and long detection range. The gated-viewing (GV) technique using short-pulse lasers and fast-gated cameras in the nanosecond range enables utilizing the distance information in addition to the signal intensity of the acquired images. The InGaAs material system is very well suited for the fabrication of high-performance SWIR photodetectors providing a typical cutoff wavelength of 1.7 μm, which covers the emission lines of available laser sources at typical telecom wavelengths around 1.55 μm. However, the usually short integration times needed for GV leads to very small photosignals. We report on the development of SWIR avalanche photodetector (APD) arrays with 640 × 512 pixels and 15 μm pixel pitch based on the InGaAs material system. The InGaAs-APD focal plane arrays have been successfully integrated into SWIR cameras which yield gain values of M ≈ 10 on camera level at a reverse bias voltage around 21 V and are the first InGaAs-based SWIR cameras worldwide providing a 640 × 512 image format and utilizing avalanche gain for signal amplification. The camera performance is demonstrated by SWIR laser GV sample images.

For surveillance and reconnaissance applications in the short-wave infrared (SWIR) spectral range, the imaging sys-tems 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 consi-derations, 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-multi-plication 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 ?m 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