Binh Minh Nguyen

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.

High operating temperature midwave infrared photodiodes and focal plane arrays based on type-II InAs/GaSb superlattices

The dominant dark current mechanisms are identified and suppressed to improve the performance of midwave infrared InAs/GaSb type-II superlattice photodiodes at high temperatures. The optimized heterojunction photodiode exhibits a quantum efficiency of 50% for 2 μm thick active region without any bias dependence. At 150 K, R0A of 5100 Ω cm2 and specific detectivity of 1.05×1012 cm Hz0.5/W are demonstrated for a 50% cutoff wavelength of 4.2μm. Assuming 300 K background temperature and 2π field of view, the performance of the detector is background limited up to 180 K, which is improved by 25 °C compared to the homojunction photodiode. Infrared imaging using f/2.3 optics and an integration time of 10.02 ms demonstrates a noise equivalent temperature difference of 11 mK at operating temperatures below 120 K.

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.

Minority electron unipolar photodetectors based on type II InAs/GaSb/AlSb superlattices for very long wavelength infrared detection

We present a hybrid photodetector design that inherits the advantages of traditional photoconductive and photovoltaic devices. The structure consists of a barrier layer blocking the transport of majority holes in a p-type semiconductor, resulting in an electrical transport due to minority carriers with low current density. By using the M-structure superlattice as a barrier region, the band alignments can be experimentally controlled, allowing for the efficient extraction of the photosignal with less than 50 mV bias. At 77 K, a 14 μm cutoff detector exhibits a dark current 3.3 mA/cm2, a photoresponsivity of 1.4 A/W, and the associated shot noise detectivity of 4×1010 Jones.We present a hybrid photodetector design that inherits the advantages of traditional photoconductive and photovoltaic devices. The structure consists of a barrier layer blocking the transport of majority holes in a p-type semiconductor, resulting in an electrical transport due to minority carriers with low current density. By using the M-structure superlattice as a barrier region, the band alignments can be experimentally controlled, allowing for the efficient extraction of the photosignal with less than 50 mV bias. At 77 K, a 14 μm cutoff detector exhibits a dark current 3.3 mA/cm2, a photoresponsivity of 1.4 A/W, and the associated shot noise detectivity of 4×1010 Jones.

Type-II M structure photodiodes: an alternative material design for mid-wave to long wavelength infrared regimes

In this work, an AlSb-containing Type II InAs/GaSb superlattice, the so-called M-structure, is presented as a candidate for mid and long wavelength infrared detection devices. The effect of inserting an AlSb barrier in the GaSb layer is discussed and predicts many promising properties relevant to practical use. A good agreement between the theoretical calculation based on Empirical Tight Binding Method framework and experimental results is observed, showing the feasibility of the structure and its properties. A band gap engineering method without material stress constraint is proposed.

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.

Background Limited Performance of Long Wavelength Infrared Focal Plane Arrays Fabricated From M-Structure InAs–GaSb Superlattices

The recent introduction of a M-structure design improved both the dark current and R0 A performances of type-II InAs-GaSb photodiodes. A focal plane array fabricated with this design was characterized at 81 K. The dark current of individual pixels was measured between 1.1 and 1.6 nA, 7 times lower than previous superlattice FPAs. This led to a higher dynamic range and longer integration times. The quantum efficiency of detectors without antireflective coating was 74%. The noise equivalent temperature difference reached 23 mK, limited only by the performance of the testing system and the read out integrated circuit. Background limited performances were demonstrated at 81 K for a 300 K background.