TABLE OF CONTENTS To exceed the limitations imposed by the InTlSb miscibility gap, arsenic can be added to form a quaternary material with an extended photoresponse cutoff wavelength. This work led to the first successful demonstration of InTlAsSb on GaAs substrates with a cutoff wavelength up to 15 ?m at room temperature. These measurements were the first observations of a room temperature band-edge photo-response at such long wavelengths from III-V alloys.
Film deposition was carried out in a horizontal cold wall LP-MOCVD reactor. TMIn, TMSb, CPTl, and 5% AsH 3 were used as precursors of indium, antimony, thallium, and arsenic, respectively. The reactor pressure was 76 Torr for all of the growth and the temperature was around 455 C. The substrates were superclean semi-insulated GaAs (100).
To investigate the bandgap variation due to the As incorporation into InTlSb, IR photoresponse measurements using FTIR were performed. Quaternary sample (b) [(d)] has the same growth conditions with ternary (a) [(c)] except for the As flux. For the InSb sample, an absorption cutoff wavelength at about 5.5 ?m was observed at 77K, which agrees with the PL measurement. The feature around 4.3 ?m is due to the CO 2 absorption in the spectrometer. A clear shift of an absorption cutoff wavelength to a longer wavelength up to 8.5 ?m was obtained for InTlSb, which indicates decrease in the energy gap by Tl incorporation. A further increase in the cutoff wavelength is achieved by incorporating As into the InTlSb alloy.
