Molecular-beam epitaxial growth and high-temperature performance of HgCdTe midwave infrared detectors |
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Authors: | T J De Lyon J E Jensen I Kasai G M Venzor K Kosai J B de Bruin W L Ahlgren |
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Affiliation: | (1) HRL Laboratories, LLC, 90265 Malibu, CA;(2) Raytheon Infrared Operations, 93117 Goleta, CA;(3) Raytheon Electronic Systems, 90245 El Segundo, CA;(4) California Polytechnic State University, 93407 San Luis Obispo, CA |
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Abstract: | Results are reported on the molecular-beam epitaxial (MBE) growth and electrical performance of HgCdTe midwave-infrared (MWIR)
detector structures. These devices are designed for operation in the 140–160 K temperature range with cutoff wavelengths ranging
from 3.4–3.8 μm at 140 K. Epitaxial structures, grown at 185°C on (211)B-oriented CdZnTe substrates, consisting of either
conventional two-layer P-n configurations or three-layer P-n-N configurations, were designed to examine the impact of device
performance on variation of the n-type base layer (absorber) thickness and the inclusion or omission of an underlying wide-bandgap
buffer layer. Devices were grown with absorber thicknesses of 3 μm, 5 μm, and 7 μm to examine the tradeoff between the spectral
response characteristic and the reverse-bias electrical performance. In addition, 5-μm-thick, wide-bandgap HgCdTe buffer layers,
whose CdTe mole fraction was approximately 0.1 larger than the absorber layer, were introduced into several device structures
to study the effect of isolating the device absorbing layer from the substrate/growth initiation interface. The MBE-grown
epitaxial wafers were processed into passivated, mesa-type, discrete device structures and diode mini arrays, which were tested
for temperature-dependent R0A product, quantum efficiency, spectral response, and the I-V characteristic at temperatures close to 140 K. External quantum
efficiencies of 75–79% were obtained with lateral optical-collection lengths of 7 μm. Analysis of the temperature dependence
of the diode R0A product indicates that the device impedance is limited by the diffusion current at temperatures above 140 K with typical
R0A values of 2×106 Ω cm2 for a detector cutoff of 3.8 μm at 140 K. An alloy composition anomaly at the absorbing-layer/buffer-layer interface is believed
to limit the observed R0A products to values approximately one order of magnitude below the theoretical limit projected for radiatively limited carrier
lifetime. Device electrical performance was observed to be improved through incorporation of a wide-bandgap buffer layer and
through reduction of the absorbing layer thickness. An optimum spectral response characteristic was observed for device structures
with 5-μm-thick absorbing layers. |
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Keywords: | Detectors photodiodes HgCdTe molecular-beam epitaxy (MBE) |
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