N-structure based on InAs/AlSb/GaSb superlattice photodetectors

We have studied the theoretical and experimental properties of InAs/AlSb/GaSb based type-II superlattice (T2SL) pin photodetector called N-structure. Electronic properties of the superlattice such as HH-LH splitting energies was investigated using first principles calculations taking into account InSb and AlAs as possible interface transition alloys between AlSb/InAs layers and individual layer thicknesses of GaSb and InAs. T2SL N-structure was optimized to operate as a MWIR detector based on these theoretical approaches tailoring the band gap and HH-LH splitting energies with InSb transition layers between InAs/AlSb interfaces. Experimental results show that AlSb layers in the structure act as carrier blocking barriers reducing the dark current. Dark current density and R0A product at 125 K were obtained as 1.8 × 10-6 A cm-2 and 800ωcm2 at zero bias, respectively. The specific detectivity was measured as 3 × 1012 Jones with cut-off wavelengths of 4.3 μm at 79 K reaching to 2 × 109 Jones and 4.5 μm at 255 K. ©2014 Elsevier Ltd. All rights reserved

Theoretical investigation of InAs/GaSb type-II pin superlattice infrared detector in the mid wavelength infrared range

In this study, we present the theoretical investigation of type-II InAs/GaSb superlattice p-i-n detector. Kronig-Penney and envelope function approximation is used to calculate band gap energy and superlattice minibands. Variational method is also used to calculate exciton binding energies. Our results show that carriers overlap increases at GaSb/InAs interface on the higher energy side while it decreases at InAs/GaSb interface on the lower energy side with increasing reverse bias due to shifting the hole wavefunction toward to the GaSb/InAs interface decisively. Binding energies increase with increasing electric field due to overall overlap of electron and hole wave functions at the both interfaces in contrast with type I superlattices. This predicts that optical absorption is enhanced with increasing electric field. © 2013 American Institute of Physics

Electronic and optical properties of 4.2 μm"N" structured superlattice MWIR photodetectors

We report on the development of a new structure for type II superlattice photodiodes that we call the "N" design. In this new design, we insert an electron barrier between InAs and GaSb in the growth direction. The barrier pushes the electron and hole wavefunctions towards the layer edges and under bias, increases the overlap integral by about 25% leading to higher detectivity. InAs/AlSb/GaSb superlattices were studied with density functional theory. Both AlAs and InSb interfaces were taken into account by calculating the heavy hole-light hole (HH-LH) splittings. Experiments were carried out on single pixel photodiodes by measuring electrical and optical performance. With cut-off wavelength of 4.2 μm at 120 K, temperature dependent dark current and detectivity measurements show that the dark current is 2.5 × 10 -9 A under zero bias with corresponding R0A resistance of 1.5 × 104 Ω cm2 for the 500 × 500 μm2 single pixel square photodetectors. Photodetector reaches BLIP condition at 125 K with the BLIP detectivity (DBLIP) of 2.6 × 10 10 Jones under 300 K background and -0.3 V bias voltage. © 2012 Elsevier B.V. All rights reserved

Three-color broadband asymmetric quantum well infrared photodetectors in long wavelength infrared range (LWIR)

A theoretical investigation of a GaAs/AlGaAs-material-system-based four quantum well infrared detector structures consisting of ten periods of three asymmetric quantum well units are presented. Each quantum well in the units is sensitive to wavelengths of 8.75, 10, and 11.75 mu m, respectively. The effect of the barrier thicknesses on the responsivity spectra is discussed with respect to barrier transmissions under negative and positive bias voltages. Each detector structure shows voltage-tunable broadband and multicolor features in 8-12-mu m long wavelength infrared range (LWIR)

Tunable long-wavelength broad band asymmetric quantum well infrared photodetector

We present a theoretical investigation of a GaAs/AlGaAs infrared detector consisting of three asymmetric quantum wells. Each well is designed to yield absorption and a photoresponse at peak wavelengths of 8.2 mu m, 9.5 mu m and 10.8 mu m respectively. The device operation is based on an intersubband bound to quasi-bound transition. Asymmetry in the barriers is shown to give rise to the dependence of the spectral line width on applied reverse bias

A new approach to quantum well infrared photodetectors: Staircase-like quantum well and barriers

We present a theoretical investigation of a novel staircase-like quantum well infrared photodetector (QWIP). The proposed structure makes use of quantum wells and barriers with increasing Al content both in the wells and in the barriers forming a staircase-like energy band diagram without applied bias. The detection wavelength is around lambda = 12 mu m at an applied electric field of F = 1.4 x 10(4) V/cm at room temperature. Device operation is based on inter-subband bound-to-bound transition. We have solved the energy band diagram of the structure self-consistently. We have also calculated the absorption coefficient, responsivity, total net quantum efficiency and dark current density at room temperature. The dark current density at the operating field was found to be around 10(-2) A/cm(2). which is lower than the conventional QWIPs in the literature. (c) 2005 Elsevier B.V. All rights reserved

Broadband staircase quantum well infrared photodetector with low dark current

We present a theoretical investigation of a novel staircase-like quantum well infrared photodetector (QWIP). It detects wavelengths between 8.8 mu m and 12.3 mu m at an applied electric field of F= 6 x 10(4) V/cm at room temperature. Device operation is based on inter-subband bound to continuum transition. We also calculated the responsivity at room temperature and dark current density at 77 K. The dark current density was found to be around 10(-8) A/cm(2) at operating bias, which is lower than the conventional QWIPs in the literature. (c) 2005 Elsevier B.V. All rights reserved

Broadband staircase quantum well infrared photodetector: working in long wavelength infrared range (LWIR)

We present a theoretical investigation of a staircase-like quantum well infrared photodetector (QWIP). it detects wavelength between 7.6 mu m and 13.5 mu m range at an applied electric field of F = 1.9x10(4) V/cm at 77 K. The dark current density was found to be around 2x10(-7) A/cm(2) at operating bias, which is lower than the conventional QWIPs in the literature. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Intersubband electron transition across a staircase potential containing quantum wells: light emission

We present a theoretical investigation of a novel staircase-like light emitter based on the GaAs/GaxAl1-xAs material system. The emission wavelength is around 12 mum. The device operation is based on the intersubband bound-to-bound transition. The energy band profile of the structure has been solved self-consistently. We have also calculated the oscillator strength. (C) 2004 Elsevier Ltd. All rights reserved

Gibbs Free Energy Assisted Passivation Layers

Reduction of surface leakage is a major challenge in most photodetectors that requires the elimination of surface oxides on etched mesas during passivation. Engineering the passivation requires close attention to chemical reactions that take place at the interface during the process. In particular, removal of surface oxides may be controlled via Gibbs reactivity. We have compared electrical performance of type-II superlattice photodetectors, designed for MWIR operation, passivated by different passivation techniques. We have used ALD deposited Al2O3, HfO2, TiO2, ZnO, PECVD deposited SiO2, Si3N4 and sulphur containing octadecanethiol (ODT) self-assembled monolayers (SAM) passivation layers on InAs/GaSb p-i-n superlattice photodetectors with cutoff wavelength at 5.1 mu m. In this work, we have compared the result of different passivation techniques which are done under same conditions, same epitaxial structure and same fabrication processes. We have found that ALD deposited passivation is directly related to the Gibbs free energy of the passivation material. Gibbs free energies of the passivation layer can directly be compared with native surface oxides to check the effectiveness of the passivation layer before the experimental study.Wo