Long wavelength mercury cadmium telluride photodiodes and focal plane arrays

Aşıcı, Burak
This thesis reports the fabrication and characterization of long wavelength infrared mercury cadmium telluride (Hg1-xCdxTe) photodiodes and 128x128 focal plane arrays grown on lattice matched cadmium zinc telluride (Cd1-yZnyTe) substrates by metal organic vapor phase epitaxy (MOVPE). The dark current modeling of 33x33 mm2 Hg1-xCdxTe photodiodes has shown the dark current is dominated by trap assisted tunneling under small reverse bias voltages typically used to bias these detectors. The dominant dark current mechanisms under high reverse bias and low forward bias are bandاtoاband tunneling and generationاrecombination, respectively. The photodiodes have yielded a peak 77 K detectivity of 3.2x1010 cm?Hz/W with a cut-off wavelength (50%) of 10.92 mm. It has also been found that the 1/f noise current of the detectors at 1 Hz is related to the trap-assisted tunneling current through the empirical relation in=?TAT(ITAT)β with ?TAT=7.0 x 10-5 and β=0.65. In the course of the focal plane array (FPA) fabrication process development work, ohmic contact formation on p-type Hg1-xCdxTe and mesa wet etch were studied in detail. Contacts with chromium, gold, platinum and copper on p-type Hg1-xCdxTe resulted in bad ohmic contacts, which did not seem to improve with annealing. On the other hand a HgTe cap layer on p-type Hg1-xCdxTe resulted in good ohmic contact with acceptably low resistance. Among the etchants studied for mesa etching of the diode structures, Br2/HBr solution yielded the best performance. After developing all of the steps of FPA processing, 128x128 Hg1-xCdxTe FPAs were successfully fabricated and tested in a thermal imager. While thermal imaging was performed with the FPAs, high nonuniformity of the material and low R0A product of the pixels did not allow high sensitivity imaging.


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Quantum well infrared photodetectors (QWIP) utilize quantum wells of large bandgap materials to detect infrared radiation. When compared to conventional low bandgap LWIR photodetectors, the QWIP technology offers largest format thermal imagers with much better uniformity. The theoretical part of this study includes the development of a QWIP ensemble Monte Carlo simulator. Capture paths of electrons to quantum wells are simulated in detail. For standard AlGaAs/GaAs QWIPs, at medium and high E-fields L valley...
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Özer, Selçuk; Beşikci, Cengiz; Department of Electrical and Electronics Engineering (2005)
InAsxSb1-x (Indium Arsenide Antimonide) is an important low bandgap semiconductor whose high quality growth on GaAs or Si substrates is indispensible for low cost, large format infrared focal plane arrays (FPAs). Quantum well infrared photodetector (QWIP) technology, relying on mature semiconductors, is also promising for the above purpose. While AlGaAs/GaAs has been the standard material system for QWIPs, the search for alternative materials is needed for better performance. This thesis reports a detailed ...
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Arslan, Yetkin; Beşikci, Cengiz; Department of Electrical and Electronics Engineering (2009)
Quantum Well Infrared Photodetectors (QWIPs) are strong competitors to other detector technologies for future third generation thermal imagers. QWIPs have inherent advantages of mature III-V material system and well settled fabrication technology, as well as narrow band photo-response which is an important property facilitating the development of dual-band imagers with low crosstalk. This thesis focuses on the development of long/mid wavelength dual band QWIP focal plane arrays (FPAs) based on the AlGaAs/Ga...
Photovoltaic Properties of Poly(Triphenylamine-Thiazolo[5,4-d] Thiazole) Copolymer Dye in Bulk-Hetorojunction Organic Solar Cells
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In this study, the photovoltaic properties of poly(triphenylamine-thiazolo[5,4-d]thiazole) alternating copolymer dye in bulk heterojunction polymer solar cells were examined. The copolymer is a red colored dye material with high thermal stability, good solubility and low-band gap energy. The band gap energy of the polymer was determined as 1.36 eV. The conductivity of the polymer thin film was measured as 1.5x10(-5) S/cm. The polymer solar cells were fabricated using the different ratios of the blends of th...
Electrically controlled terahertz spatial light modulators with graphene arrays
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Gate-tunable high-mobility electrons on atomically thin graphene layers provide a unique opportunity to control electromagnetic waves in a very broad spectrum. In this paper, we describe an electrically-controlled multipixel terahertz light modulators. The spatial light modulator is fabricated using two large-area graphene layers grown by chemical vapor deposition and transferred on THz transparent and flexible substrates. Room temperature ionic liquid, inserted between the graphene, provides mutual gating ...
Citation Formats
B. Aşıcı, “Long wavelength mercury cadmium telluride photodiodes and focal plane arrays,” M.S. - Master of Science, Middle East Technical University, 2005.