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1

Two-step etch in n-on-p type-II superlattices for surface leakage reduction in mid-wave infrared megapixel detectors

Ramos David, Delmas Marie, Ivanov Ruslan, Žurauskaitė Laura, Evans Dean, Almqvist Susanne, Becanovic Smilja, Hellström Per-Erik, Costard Eric, Höglund Linda

Opto-Electronics Review

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2023

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Vol. 31, Special Issue

art. no. e144556

EN

This work investigates the potential of p-type InAs/GaSb superlattice for the fabrication of full mid-wave megapixel detectors with n-on-p polarity. A significantly higher surface leakage is observed in deep-etched n-on-p photodiodes compared to p-on-n diodes. Shallowetch and two-etch-step pixel geometry are demonstrated to mitigate the surface leakage on devices down to 10 μm with n-on-p polarity. A lateral diffusion length of 16 μm is extracted from the shallow etched pixels, which indicates that cross talk could be a major problem in small pitch arrays. Therefore, the two-etch-step process is used in the fabrication of 1280 × 1024 arrays with a 7.5 μm pitch, and a potential operating temperature up to 100 K is demonstrated.

2

Quantum simulations of band-to-band tunnelling in a type-II broken-gap superlattice diode

Makowiec Marcin, Kolek Andrzej

Opto-Electronics Review

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2023

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Vol. 31, Special Issue

art. no. e144558

EN

In recent years, type-II superlattice-based devices have completed the offer of the electronic industry in many areas of applications. Photodetection is one of them, especially in the midinfrared wavelength range. It is due to the unique feature of a superlattice material, which is a tuneable bandgap. It is also believed that the dark current of superlattice-based photodetectors is strongly suppressed due to the suppression of the band-to-band tunnelling current in a superlattice material. This argument relies, however, on a semi-classical approach that treats superlattice as a bulk material with effective parameters extracted from the k·p analysis. In the paper, a superlattice device is analysed on a quantum level: the nonequilibrium Green’s function method is applied to the two-band Hamiltonian of the InAs/GaSb superlattice p-i-n diode. The analysis concentrates on the band-to-band tunnelling with the aim to validate the correctness of a semi-classical description of the phenomenon. The results of calculations reveal that in a superlattice diode, the inter-band tunnelling occurs only for certain values of energy and in-plane momentum, for which electronic and hole sub-bands cross. The transitions occurring for vanishing in-plane momentum produce resonances in the current-voltage characteristics - the feature which was reported in a few experimental observations. This scenario is quite different from that occurring in bulk materials, where there is a range of energy-momentum pairs for which the band-to-band tunnelling takes place, and so current-voltage characteristics are free from any resonances. However, simulations show that, while not justified for a detailed analysis, the semi-classical description can be applied to superlattice-based devices for an ‘order of magnitude’ estimation of the band-to-band tunnelling current.

3

Long wavelength type-II superlattice barrier infrared detector for CubeSat hyperspectral thermal imager

Rafol Sir B., Gunapala Sarath D., Ting David Z., Soibel Alexander, Khoshakhlagh Arezou, Keo Sam A., Pepper Brian J., Hill Cory J., Maruyama Yuki, Fisher Anita M., Sood Ashok, Zeller John, Wright Robert, Lucey Paul, Nunes Miguel, Flynn Luke, Babu Sachidananda, Ghuman Parminder

Opto-Electronics Review

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2023

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Vol. 31, Special Issue

art. no. e144569

EN

The hyperspectral thermal imaging instrument for technology demonstration funded by NASA’s Earth Science Technology Office under the In-Space Validation of Earth Science Technologies program requires focal plane array with reasonably good performance at a low cost. The instrument is designed to fit in a 6U CubeSat platform for a low-Earth orbit. It will collect data on hydrological parameters and Earth surface temperature for agricultural remote sensing. The long wavelength infrared type-II strain layer superlattices barrier infrared detector focal plane array is chosen for this mission. With the driving requirement dictated by the power consumption of the cryocooler and signal-noise-ratio, cut-off wavelengths and dark current are utilized to model instrument operating temperature. Many focal plane arrays are fabricated and characterised, and the best performing focal plane array that fulfils the requirements is selected. The spectral band, dark current and 8-9.4 μm pass band quantum efficiency of the candidate focal plane array are: 8-10.7 μm, 2.1∙10ˉ⁵ A/cm², and 47%, respectively. The corresponding noise equivalent difference temperature and operability are 30 mK and 99.7%, respectively. Anti-reflective coating is deposited on the focal plane array surface to enhance the quantum efficiency and to reduce the interference pattern due to an absorption layer parallel surfaces cladding material.

4

InAs/InAsSb superlattice infrared detectors

Ting David Z., Soibel Alexander, Khoshakhlagh Arezou, Keo Sam A., Rafol Sir B., Fisher Anita M., Hill Cory J., Pepper Brian J., Maruyama Yuki, Gunapala Sarath D.

Opto-Electronics Review

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2023

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Vol. 31, Special Issue

art. no. e144565

EN

Mid-wavelength infrared detectors and focal plane array based on n-type InAs/InAsSb type- II strained layer superlattice absorbers have achieved excellent performance. In the long and very long wavelength infrared, however, n-type InAs/InAsSb type-II strained layer superlattice detectors are limited by their relatively small absorption coefficients and short growth-direction hole diffusion lengths, and consequently have only been able to achieve modest level of quantum efficiency. The authors present an overview of their progress in exploring complementary barrier infrared detectors that contain p-type InAs/InAsSb type-II strained layer superlattice absorbers for quantum efficiency enhancement. The authors describe some representative results, and also provide additional references for more indepth discussions. Results on InAs/InAsSb type-II strained layer superlattice focal plane arrays for potential NASA applications are also briefly discussed.

5

High performance type-II InAs/GaSb superlattice infrared photodetectors with a short cut-off wavelength

Delmas Marie, Ramos David, Ivanov Ruslan, Žurauskaitė Laura, Evans Dean, Rihtnesberg David, Almqvist Susanne, Becanovic Smilja, Costard Eric, Höglund Linda

Opto-Electronics Review

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2023

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Vol. 31, Special Issue

art. no. e144555

EN

This work investigates the potential of InAs/GaSb superlattice detectors for the shortwavelength infrared spectral band. A barrier detector structure was grown by molecular beam epitaxy and devices were fabricated using standard photolithography techniques. Optical and electrical characterisations were carried out and the current limitations were identified. The authors found that the short diffusion length of ~1.8 µm is currently limiting the quantum efficiency (double-pass, no anti-reflection coating) to 43% at 2.8 µm and 200 K. The dark current density is limited by the surface leakage current which shows generation-recombination and diffusion characters below and above 195 K, respectively. By fitting the size dependence of the dark current, the bulk values have been estimated to be 6.57·10ˉ⁶ A/cm² at 200 K and 2.31·10ˉ⁶ A/cm² at 250 K, which is only a factor of 4 and 2, respectively, above the Rule07.

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Electro-optical performance and anisotropic transport study of a Ga-free type-II superlattice barrier structure

Bouschet Maxime, Arounassalame Vignesh, Ramiandrasoa Anthony, Perez Jean-Philippe, Péré-Laperne Nicolas, Ribet-Mohamed Isabelle, Christol Philippe

Opto-Electronics Review

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2023

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Vol. 31, Special Issue

art. no. e144549

EN

In the past ten years, InAs/InAsSb type-II superlattice has emerged as a promising technology for high-temperature mid-wave infrared photodetector. Nevertheless, transport properties are still poorly understood in this type of material. In this paper, optical and electro-optical measurements have been realised on InAs/InAsSb type-II superlattice midwave infrared photodetectors. Quantum efficiency of 50% is measured at 150 K, on the front side illumination and simple pass configuration. Absorption measurement, as well as lifetime measurement are used to theoretically calculate the quantum efficiency thanks to Hovel’s equation. Diffusion length values have been extracted from this model ranging from 1.55 μm at 90 K to 7.44 μm at 200 K. Hole mobility values, deduced from both diffusion length and lifetime measurements, varied from 3.64 cm²/Vs at 90 K to 37.7 cm²/Vs at 200 K. The authors then discuss the hole diffusion length and mobility variations within temperature and try to identify the intrinsic transport mechanisms involved in the superlattice structure.