21 October 2016 Advances in the characterization of InAs/GaSb superlattice infrared photodetectors
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This paper reports on advances in the electro-optical characterization of InAs/GaSb short-period superlattice infrared photodetectors with cut-off wavelengths in the mid-wavelength and long-wavelength infrared ranges. To facilitate in-line monitoring of the electro-optical device performance at different processing stages we have integrated a semi-automated cryogenic wafer prober in our process line. The prober is configured for measuring current-voltage characteristics of individual photodiodes at 77 K. We employ it to compile a spatial map of the dark current density of a superlattice sample with a cut-off wavelength around 5 μm patterned into a regular array of 1760 quadratic mesa diodes with a pitch of 370 μm and side lengths varying from 60 to 350 μm. The different perimeter-to-area ratios make it possible to separate bulk current from sidewall current contributions. We find a sidewall contribution to the dark current of 1.2×10-11 A/cm and a corrected bulk dark current density of 1.1×10-7 A/cm2, both at 200 mV reverse bias voltage. An automated data analysis framework can extract bulk and sidewall current contributions for various subsets of the test device grid. With a suitable periodic arrangement of test diode sizes, the spatial distribution of the individual contributions can thus be investigated. We found a relatively homogeneous distribution of both bulk dark current density and sidewall current contribution across the sample. With the help of an improved capacitance-voltage measurement setup developed to complement this technique a residual carrier concentration of 1.3×1015 cm-3 is obtained. The work is motivated by research into high performance superlattice array sensors with demanding processing requirements. A novel long-wavelength infrared imager based on a heterojunction concept is presented as an example for this work. It achieves a noise equivalent temperature difference below 30 mK for realistic operating conditions.
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A. Wörl, A. Wörl, V. Daumer, V. Daumer, T. Hugger, T. Hugger, N. Kohn, N. Kohn, W. Luppold, W. Luppold, R. Müller, R. Müller, J. Niemasz, J. Niemasz, R. Rehm, R. Rehm, F. Rutz, F. Rutz, J. Schmidt, J. Schmidt, J. Schmitz, J. Schmitz, T. Stadelmann, T. Stadelmann, M. Wauro, M. Wauro, } "Advances in the characterization of InAs/GaSb superlattice infrared photodetectors", Proc. SPIE 9987, Electro-Optical and Infrared Systems: Technology and Applications XIII, 99870U (21 October 2016); doi: 10.1117/12.2240949; https://doi.org/10.1117/12.2240949

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