Pierre Yves Delaunay

Very high quantum efficiency in type-II InAs∕GaSb superlattice photodiode with cutoff of 12μm

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).

Near bulk-limited R0A of long-wavelength infrared type-II InAs∕GaSb superlattice photodiodes with polyimide surface passivation

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.

Background limited long wavelength infrared type-II InAs/GaSb superlattice photodiodes operating at 110 K

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.

Passivation of type-II InAs∕GaSb double heterostructure

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.

High differential resistance type-II InAs∕GaSb superlattice photodiodes for the long-wavelength infrared

Type-II InAs∕GaSb superlattice photodiodes with a 50% cutoff wavelength ranging from 11to13μm are presented. Optimization of diffusion limited photodiodes provided superlattice structures for improved injection efficiency in direct injection hybrid focal plane array applications. Photodiodes with a cutoff wavelength of 12.9μm exhibit an R0A of ∼7Ωcm2 and a Johnson-limited detectivity of 4.03×1010cmHz1∕2W−1 operating at 77K. Quantum efficiency measurements indicate minority carrier diffusion lengths exceeding 3μm.

Band edge tunability of M-structure for heterojunction design in Sb based type II superlattice photodiodes

We present theoretically and experimentally the effect of the band discontinuity in type II misaligned InAs∕GaSb superlattice heterodiodes. Calculations using the empirical tight binding method have shown the great flexibility in tuning the energy levels of the band edge in M-structure superlattice as compared to the standard InAs∕GaSb superlattice. Through the experimental realization of several p-π-M-n photodiodes, the band discontinuity alignment between the standard binary-binary superlattice and the M-structured superlattice was investigated via optical characterization. The agreement between the theoretical predictions and the experimental measurement confirms the capability of controlling the M-structure band edges and suggests a way to exploit this advantage for the realization of heterostructures containing an M-structured superlattice without bias dependent operation.

Surface leakage reduction in narrow band gap type-II antimonide-based superlattice photodiodes

Inductively coupled plasma (ICP) dry etching rendered structural and electrical enhancements on type-II antimonide-based superlattices compared to those delineated by electron cyclotron resonance (ECR) with a regenerative chemical wet etch. The surface resistivity of 4×105 Ω cm is evidence of the surface quality achieved with ICP etching and polyimide passivation. By only modifying the etching technique in the fabrication steps, the ICP-etched devices with a 9.3 μm cutoff wavelength revealed a diffusion-limited dark current density of 4.1×10−6 A/cm2 and a maximum differential resistance at zero bias in excess of 5300 Ω cm2 at 77 K, which are an order of magnitude better in comparison to the ECR-etched devices.Inductively coupled plasma (ICP) dry etching rendered structural and electrical enhancements on type-II antimonide-based superlattices compared to those delineated by electron cyclotron resonance (ECR) with a regenerative chemical wet etch. The surface resistivity of 4×105 Ω cm is evidence of the surface quality achieved with ICP etching and polyimide passivation. By only modifying the etching technique in the fabrication steps, the ICP-etched devices with a 9.3 μm cutoff wavelength revealed a diffusion-limited dark current density of 4.1×10−6 A/cm2 and a maximum differential resistance at zero bias in excess of 5300 Ω cm2 at 77 K, which are an order of magnitude better in comparison to the ECR-etched devices.

Demonstration of midinfrared type-II InAs/GaSb superlattice photodiodes grown on GaAs substrate

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.

Beryllium compensation doping of InAs∕GaSb infrared superlattice photodiodes

Capacitance-voltage measurements in conjunction with dark current measurements on InAs∕GaSb long wavelength infrared superlattice photodiodes grown by molecular-beam epitaxy on GaSb substrates are reported. By varying the beryllium concentration in the InAs layer of the active region, the residually n-type superlattice is compensated to become slightly p type. By adjusting the doping, the dominant dark current mechanism can be varied from diffusion to Zener tunneling. Minimization of the dark current leads to an increase of the zero-bias differential resistance from less than 4to32Ωcm2 for a 100% cutoff of 12.05μm

The effect of doping the M-barrier in very long-wave type-II InAs∕GaSb heterodiodes

A variation on the standard homodiode type-II superlattice with an M-barrier between the π-region and the n-region is shown to suppress the dark currents. By determining the optimal doping level of the M-superlattice, dark current densities of 4.95mA∕cm2 and quantum efficiencies in excess of 20% have been demonstrated at the moderate reverse bias of 50mV; allowing for near background-limted performance with a Johnson-noise detectivity of 3.11×1010cmHz∕W at 77K for 14.58μm cutoff wavelength for large area diodes without passivation. This is comparable to values for the state-of-the-art HgCdTe photodiodes.