Physics & Astronomy

Event Title

Mid-infrared Optical Constants of InAsSb Alloys and Bulk GaSb

Document Type

Poster Presentation

Location

Indianapolis, IN

Start Date

13-4-2018 2:30 AM

End Date

13-4-2018 4:00 PM

Description

Antimonides are attractive materials for mid-infrared detectors and emitters, because they form a direct band gap, which can be tuned from 0.1 to 0.7 eV. For the design and modeling of such devices, the optical constants of these materials must be known. We present results of Fourier-transform infrared (FTIR) ellipsometry measurements of bulk GaSb and doped and undoped InAsSb alloys with different compositions. GaSb is naturally p-type because of antisite defects. Our GaSb (100) substrate was additionally doped with Zn, leading to a hole concentration near 2.5E18 cm-3 and a mobility of 350 cm2/Vs. The pseudodielectric function for this GaSb substrate is mostly flat from 0.1 to 0.7 eV. The band gap of 0.7 eV and a strong free-carrier response below 0.1 eV are easily seen. The infrared free-carrier response can be modeled with two Drude terms, but a comparison with heavy and light hole conduction is not immediately apparent. Doped and undoped layers of InAsSb alloys were grown on similar GaSb substrates by MOCVD. Their optical constants were determined using two different methods. First, we expanded the dielectric function into a sequence of Kramers-Kronig consistent B-spline polynomials, assuming thicknesses obtained from the growth parameters. Second, we fitted the data as a sum of oscillators representing the free-carrier and interband optical response, which allows a physical interpretation of the results. In the doped layers, a free-carrier reflectance band can clearly be seen in the spectra, while the undoped layers show an absorption increase at the band gap.

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Apr 13th, 2:30 AM Apr 13th, 4:00 PM

Mid-infrared Optical Constants of InAsSb Alloys and Bulk GaSb

Indianapolis, IN

Antimonides are attractive materials for mid-infrared detectors and emitters, because they form a direct band gap, which can be tuned from 0.1 to 0.7 eV. For the design and modeling of such devices, the optical constants of these materials must be known. We present results of Fourier-transform infrared (FTIR) ellipsometry measurements of bulk GaSb and doped and undoped InAsSb alloys with different compositions. GaSb is naturally p-type because of antisite defects. Our GaSb (100) substrate was additionally doped with Zn, leading to a hole concentration near 2.5E18 cm-3 and a mobility of 350 cm2/Vs. The pseudodielectric function for this GaSb substrate is mostly flat from 0.1 to 0.7 eV. The band gap of 0.7 eV and a strong free-carrier response below 0.1 eV are easily seen. The infrared free-carrier response can be modeled with two Drude terms, but a comparison with heavy and light hole conduction is not immediately apparent. Doped and undoped layers of InAsSb alloys were grown on similar GaSb substrates by MOCVD. Their optical constants were determined using two different methods. First, we expanded the dielectric function into a sequence of Kramers-Kronig consistent B-spline polynomials, assuming thicknesses obtained from the growth parameters. Second, we fitted the data as a sum of oscillators representing the free-carrier and interband optical response, which allows a physical interpretation of the results. In the doped layers, a free-carrier reflectance band can clearly be seen in the spectra, while the undoped layers show an absorption increase at the band gap.