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LASER DIAGNOSTICS AND SPECTROSCOPY
LD-O-11
High-Speed GalnAsSb/GaAlAsSb Photodetectors for Precision Diode Laser Spectroscopy
E.V. Kunitsyna1, I.A. Andreev1, G.G. Konovalov1, A.A. Pivovarova1, N.D. Il inskaya1, Yu.P. Yakovlev1, Ya.Ya. Ponurovskii2, A.I. Nadezhdinskii2, A.S. Kuz'michev, D.B. Stavrovskii2, M.V. Spiridonov2
Diode laser spectroscopy (DLS) is one of the most dynamically developing fields of laser physics as applied to the challenges of analytical chemistry and gas analysis [1]. Recent advances in the technology of IR optopairs "diode laser - photodetector" and high-sensitivity IR absorption spectrometry result in a new generation of gas analytical systems. These systems are characterized by record spectral resolution and high operating speed.
Registration of laser radiation in the near- and mid-IR spectral ranges is one of the most important problems of laser physics. Photodetectors based on lead chalcogenides usually demonstrate the time constant of 100-400 ^s. They are hardly applicable for operating with diode lasers that require significantly higher speed. Other widely applied IR photodetectors are InSb-based photodiodes [2]. However, cooling to 80-200 K is required for the effective operation of most InSb-based devices.
The uncooled high-speed photodetectors based on n-GaInAsSb/p-GaAlAsSb heterostructures have been developed for precision DLS. These heterostructures were LPE grown on n-GaSb(100) substrates doped with tellurium to a carrier concentration of (1-5)x 1017 cm-3. The active region was the epitaxial layer of the narrow-gap GaIn0 22AsSb solid solution (Eg = 0.53 eV). The GaAl034AsSb epitaxial layer (Eg =1.1 eV) was used as a "wide-gap window". Chips with diameters of the photosensitive area of 1.0 mm and 2.0 mm were made from the grown heterostructures by contact photolithography and liquid chemical etching. To protect the lateral surface of the mesa and p-n junction, anodic oxide was formed in the electrolyte solution (0.3% tartaric acid/ethyleneglycol in the ratio 1:2). The thickness of the oxide obtained at U = 60 V and j = 5 mA/cm2 was ~0.3 ^m. The Cr/Au/Ni/Au system and a galvanic Au layer were used as a contact system to the Al-containing epitaxial p-layer. The contact enhancement makes it possible to assemble photodiodes at elevated solder temperatures of 200-230°C. The contact to the n-GaSb(100) substrate was formed by sputtering the Cr/Au/Ni/ Au system with subsequent sputtering of an additional Cr/Au layer.
The spectral sensitivity range of photodetectors with a photosensitive area diameter of 1.0 mm and 2.0 mm is 1.0-2.4 ^m at T=300 K. The long-wavelength boundary of the spectral sensitivity is determined by the band-gap energy of the GaInAsSb active region. The sensitivity gradually decreases in the shorter wavelength part of the spectrum towards short wavelengths, which is associated with absorption at indirect-gap transitions in the layer of the Al-containing solid solution. So, the short-wavelength spectral sensitivity boundary is determined by the band-gap energy of the "wide-gap window". The current monochromatic sensitivity at the wavelength of 2.1 ^m has a value of 1.0 A/W without bias. The capacity reaches 375 pF with a photosensitive area diameter of 1.0 mm and 800-5000 pF with 2 mm. The operating speed of the developed photodetectors is 30-45 ns with a diameter of 1 mm and 100-770 ns with a diameter of 2 mm. It is demonstrated, that these values are sufficient for operation of photodetectors as part of DL gas analyzers.
The modern gas analyzers based on diode lasers and developed GaInAsSb/GaAlAsSb photodetectors for medical screening diagnostics by analyzing the gas compositions of exhaled air, for control of impurity gases in the process of rectification of inorganic hydrides, control of methane leaks in gas pipelines, as well as for registration of exhaust gases of a moving car are presented.
[1] Ya.Ya. Ponurovskii, A new generation of gas analysis systems based on diode lasers, Analytics, vol.9(1), pp.68-74 (2019).
[2] B. W. Jia, K. H. Tan, W. K. Loke, S. Wicaksono, K. H. Lee, S. F. Yoon, Monolithic integration of InSb photodetector on silicon for mid-infrared silicon photonics, ACS Photonics, vol.5, pp. 1512-1520 (2018).
1- Ioffe Institute, 26 Politekhnicheskaya str., 194021 St. Petersburg, Russia 2 - A.M. Prokhorov General Physics Institute of Russian Academy of Science, 38 Vavilov str.,
119991 Moscow, Russia kunits@iropt9.ioffe.ru
