Background Limited Detectivity Research Articles

Mid-infrared detectors in the 3–5 μm band using bound to continuum state absorption in InGaAs/InAlAs multiquantum well structures

Medium wavelength infrared (MWIR) detectors in the 3–5 μm band are demonstrated using bound to continuum state intersubband absorption in lattice-matched InGaAs/InAlAs multiquantum well (MQW) structures. Photodetectors with responsivity peaked at 4 μm wavelength showed low dark current giving a background-limited detectivity D*BL =2.3×1010 cm(Hz)1/2 /W at temperatures up to 120 K.

Chromium concentrations, depth distributions, and diffusion coefficient in bulk and epitaxial GaAs and in Si

Implantation of 200-keV chromium fluences from 4.5×1012 to 1.0×1015 cm−2 and SIMS profiling were used to measure the atom densities and depth distribution of Cr in bulk GaAs (Cr), in undoped liquid-phase epitaxial GaAs grown on a GaAs(Cr) substrate, and in Si. The Cr atom density in both GaAs(Cr) substrates was ∼1.6×1017 cm−3. The background-limited detection sensitivity of SIMS for Cr in GaAs was ⩽3×1015 cm−3. Chromium outdiffused into the epitaxial layer during growth at 800 °C. The diffusion coefficient for CR at 800 °C in GaAs was determined to be 6.7×10−12 cm2/sec. Channeling tails were observed for the Cr implanted in Si and in the undoped epitaxial GaAs, but not in the bulk GaAs(Cr). Ranges, range straggles, and other Pearson IV moments for the implanted Cr distributions are given.

Monolithic HgCdTe charge transfer device infrared imaging arrays

This paper compares the advantages of charge-injection-device (CID) and charge-coupled-device (CCD) technologies for the development of monolithic HgCdTe infrared image sensors for the 3-5- µm-wavelength band. Both technologies perform some signal processing before signal is transferred from the HgCdTe monolith to a silicon signal-processing chip. Line multiplexing may be performed by the CID. Both time-delay-and-integration (TDI) and multiplexing (MPX) may be performed by the CCD. Both the CID and CCD utilize the same HgCdTe material and MIS fabrication technologies. Electrical and infrared response data are given for an 8 × 8 CID matrix with background-limited performance with a 4.45-µm-long-wavelength cutoff. Previous data on 8- and 16-stage CCD linear shift registers are reviewed. New data on 32-stage linear CCD devices and a 16-TDI × 4-MPX area array are presented. The 32-stage CCD has been operated as an infrared sensor with TDI enhancement of sensitivity and background-limited detectivity for a 4.5-µm-long-wavelength cutoff.

Low-capacitance PbTe photodiodes

Thin-film PbTe photodiodes have been operated at 80 K with significantly reduced capacitance. The technique is based upon limitation of the voltage-induced change of the depletion-layer volume by the presence of an insulating substrate. Capacitances as low as 64 pF for a 9-mil-square diode and 35 pF for a 28-mil-square diode have been achieved with retention of background-limited detectivities, which were typically about 1.7×1011 cm Hz1/2 W−1 for peak wavelength near 5 μm.

High-performance 8—14- µm Pb1-xSnxTe photodiodes

Photovoltaic detectors of Pb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Te, sensitive in the 8- 14-µm spectral region, with near-theoretical performance characteristics, have been fabricated by a surface inversion technique. These detectors have exhibited quantum efficiencies of up to 45 percent limited by surface reflection), zero-bias resistance-area products of 21 Ωċcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and background-limited detectivities of 1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> cm ċ Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W. A theoretical model consistent with experimental results is presented. Such high-performance devices are useful in guidance, reconnaissance, surveillance, ranging, and communication systems.