We presented an alternative design of type II superlattice photodiodes with the insertion of a mid-wavelength infrared M-structure AlSb∕GaSb∕InAs∕GaSb∕AlSb superlattice for the reduction of dark current. The M-structure superlattice has a larger carrier effective mass and a greater band discontinuity as compared to the standard type II superlattices at the valence band. It acts as an effective medium that weakens the diffusion and tunneling transport at the depletion region. As a result, a 10.5μm cutoff type II superlattice with 500nm M-superlattice barrier exhibited a R0A of 200Ωcm2 at 77K, approximately one order of magnitude higher than the design without the barrier. The quantum efficiency of such structures does not show dependence on either barrier thickness or applied bias.
The utilization of the P+-π-M-N+ photodiode architecture in conjunction with a thick active region can significantly improve long wavelength infrared type-II InAs/GaSb superlattice photodiodes. By studying the effect of the depletion region placement on the quantum efficiency in a thick structure, we achieved a topside illuminated quantum efficiency of 50% for an N-on-P diode at 8.0 μm at 77 K. Both the double heterostructure design and the application of polyimide passivation greatly reduce the surface leakage, giving an R0A of 416 Ω cm2 for a 1% cutoff wavelength of 10.52 μm, a Shot–Johnson detectivity of 8.1×1011 cmHz/W at 77 K, and a background limited operating temperature of 110 K with 300 K background.
Effective surface passivation of type-II InAs∕GaSb superlattice photodiodes with cutoff wavelengths in the long-wavelength infrared is presented. A stable passivation layer, the electrical properties of which do not change as a function of the ambient environment nor time, has been prepared by a solvent-based surface preparation, vacuum desorption, and the application of an insulating polyimide layer. Passivated photodiodes, with dimensions ranging from 400×400to25×25μm2, with a cutoff wavelength of ∼11μm, exhibited near bulk-limited R0A values of ∼12Ωcm2, surface resistivities in excess of 104Ωcm, and very uniform current-voltage behavior at 77K.
The authors report the dependence of the quantum efficiency on device thickness of type-II InAs∕GaSb superlattice photodetectors with a cutoff wavelength around 12μm. The quantum efficiency and responsivity show a clear delineation in comparison to the device thickness. An external single-pass quantum efficiency of 54% is obtained for a 12μm cutoff wavelength photodiodes with a π-region thickness of 6.0μm. The R0A value is kept stable for the range of structure thicknesses allowing for a specific detectivity (2.2×1011cmHz∕W).
We report the growth and characterization of type-II InAs/GaSb superlattice photodiodes grown on a GaAs substrate. Through a low nucleation temperature and a reduced growth rate, a smooth GaSb surface was obtained on the GaAs substrate with clear atomic steps and low roughness morphology. On the top of the GaSb buffer, a p+-i-n+ type-II InAs/GaSb superlattice photodiode was grown with a designed cutoff wavelength of 4 μm. The detector exhibited a differential resistance at zero bias (R0A) in excess of 1600 Ω cm2 and a quantum efficiency of 36.4% at 77 K, providing a specific detectivity of 6×1011 cmHz/W and a background limited operating temperature of 100 K with a 300 K background. Uncooled detectors showed similar performance to those grown on GaSb substrates with a carrier lifetime of 110 ns and a detectivity of 6×108 cmHz/W.
Focal plane array fabrication requires a well passivated material that is resistant to aggressive processes. The authors report on the ability of type-II InAs∕GaSb superlattice heterodiodes to be more resilient than homojunctions diodes in improving sidewall resistivity through the use of various passivation techniques. The heterostructure consisting of two wide band gap (5μm) superlattice contacts and a low band gap active region (11μm) exhibits an R0A averaging of 13Ωcm2. The devices passivated with SiO2, Na2S and SiO2 or polyimide did not degrade compared to the unpassivated sample and the resistivity of the sidewalls increased to 47kΩcm.
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