Type-II Superlattice Heterojunction Photodetector with Optoelectronic Characterization and Analytical/ Numerical Simulation

This chapter focuses on characterization, modeling, and simulation about the type-II superlattices photodetector application. Despite dramatic improvements in type-II superlattices in the past 15 years, challenges still exist in InAs/GaSb and InAs/GaInSb superlattices: The diffusion current, Shockley-Read-Hall (SRH) recombination current, tunneling current, and surface leakage current at elevated temperature. To establish a set of modeling and simulation input parameters, in-depth materials and device characterization at different conditions are carried out for initial materials and device models. Based on input parameters, we will describe the development of analytical and numerical models of InAs/GaSb and InAs/GaInSb type-II superlattice-structured materials and device systems. At the end of this chapter, the fitting of modeled and simulated data will be performed to compare empirical data and modeling results at a set of temperature, which will provide guidance to achieve the higher performance

Circular and linear photogalvanic effects in type-II GaSb/InAs quantum well structures in the inverted regime

The work was supported by the Elite Network of Bavaria (K-NW-2013-247), the DFG priority program SPP1666, the Volkswagen Stiftung Program, the State of Bavaria and the German Research Foundation (Ka2318/4-1). S.A.T. acknowledges support from the RFBR (projects 14-22-02102 and 16-02-00375).We report on the observation of photogalvanic effects induced by terahertz radiation in type-II GaSb/InAs quantum wells with inverted band order. Photocurrents are excited at oblique incidence of radiation and consists of several contributions varying differently with the change of the radiation polarization state; the one driven by the helicity and the other one driven by the linearly polarization of radiation are of comparable magnitudes. Experimental and theoretical analyses reveal that the photocurrent is dominated by the circular and linear photogalvanic effects in a system with a dominant structure inversion asymmetry. A microscopic theory developed in the framework of the Boltzmann equation of motion considers both photogalvanic effects and describes well all the experimental findings.PostprintPeer reviewe

Coherent Phonon Dynamics in Short-Period InAs/GaSb Superlattices

We have performed ultrafast pump-probe spectroscopy studies on a series of InAs/GaSb-based short-period superlattice (SL) samples with periods ranging from 46 \AA to 71 \AA. We observe two types of oscillations in the differential reflectivity with fast ($\sim$ 1- 2 ps) and slow ($\sim$ 24 ps) periods. The period of the fast oscillations changes with the SL period and can be explained as coherent acoustic phonons generated from carriers photoexcited within the SL. This mode provides an accurate method for determining the SL period and assessing interface quality. The period of the slow mode depends on the wavelength of the probe pulse and can be understood as a propagating coherent phonon wavepacket modulating the reflectivity of the probe pulse as it travels from the surface into the sample.Comment: 6 pages, 4 figure

Multispectral Metamaterial Detectors for Smart Imaging

The ability to produce a high quality infrared image has significantly improved since its initial development in the 1950s. The first generation consisted of a single pixel that required a two-dimensional raster scan to produce an image. The second generation comprised of a linear array of pixels that required a mechanical sweep to produce an image. The third generation utilizes a two-dimensional array of pixels to eliminate the need for a mechanical sweep. Third generation imaging technology incorporates pixels with single color or broadband sensitivity, which results in \u27black and white\u27 images. The research presented in this dissertation focuses on the development of 4th generation infrared detectors for the realization of a new generation of infrared focal plane array. To achieve this goal, we investigate metamaterials to realize multicolor detectors with enhanced quantum efficiency for similar function to a human retina. The key idea is to engineer the pixel such that it not only has the ability to sense multimodal data such as color, polarization, dynamic range and phase but also the intelligence to transmit a reduced data set to the central processing unit (neurophotonics). In this dissertation, we utilize both a quantum well infrared photodetector (QWIP) and interband cascade detector (ICD) hybridized with a metamaterial absorber for enhanced multicolor sensitivity in the infrared regime. Through this work, along with some design lessons throughout this iterative process, we design, fabricate and demonstrate the first deep-subwavelength multispectral infrared detector using an ultra-thin type-II superlattice (T2-SL) detector coupled with a metamaterial absorber with 7X enhanced quantum efficiency. We also identify useful versus non-useful absorption through a combination of absolute absorption and quantum efficiency measurements. In addition to these research efforts, we also demonstrate a dynamic multicolor metamaterial in the terahertz regime with electronically tunable frequency and gain for the first time. Utilizing an electronically tunable metamaterial, one can design an imaging system that can take multiple spectral responses within one frame for the classification of objects based on their spectral fingerprint.\u2

The Theoretical Simulation Of Inas/Gainsb And Inasn/Gainsb Strained Layer Superlattice Band Gaps

A superlattice (SL) is a periodic structure of layers of two (or more) materials. They are typically only a few nanometers thick (individual layers), and were discovered in the early 20th century. There are three different types of division for the miniband structures of the SL, type I, type II and type III. Type I heterostructure SL is a heterostructure where the bottom of the conduction band and the top of the valence band are formed in the same semiconductor layer. In type II, the conduction and valence band are staggered in both real and reciprocal space, so that electrons and holes are confined in different spaces. These particular devices are to be used in infrared devices and have been known to be designed in focal plane arrays and other designs for this use. The particular assignment was to find the band gap using simulation through Optel ZB 2011 software that would provide an initial guess on the SL design parameters before the growth was carried out. There were major problems that had to be addressed while simulating certain factors that we looked for in our tested quantum well (QW) and SL systems in GaAs/GaAlAs, InAs/GaInSb, InAs/GaSb and InAsN/GaInSb. Finally a comparison of the simulated and experimental data indicates that the lack of room temperature simulation as well as the inability to incorporate interfacial layers of sub monolayer thicknesses are some of the major limitations of this software

Photoluminescence quenching mechanisms in type II InAs/GaInSb QWs on InAs substrates

We would like to acknowledge the National Science Centre of Poland for support within Grant No. 2014/15/B/ST7/04663.Optical properties of AlSb/InAs/GaInSb/InAs/AlSb quantum wells (QWs) grown on an InAs substrate were investigated from the point of view of room temperature emission in the mid- and long-wavelength infrared ranges. By means of two independent techniques of optical spectroscopy, photoreflectance and temperature-dependent photoluminescence, it was proven that the main process limiting the performance of such InAs substrate-based type II structures is related to the escape of carriers from the hole ground state of the QW. Two nonradiative recombination channels were identified. The main process was attributed to holes tunneling to the valence band of the GaAsSb spacing layer and the second one with trapping of holes by native defects located in the same layer.Publisher PDFPeer reviewe

Non-equilibrium Green's function predictions of band tails and band gap narrowing in III-V semiconductors and nanodevices

High-doping induced Urbach tails and band gap narrowing play a significant role in determining the performance of tunneling devices and optoelectronic devices such as tunnel field-effect transistors (TFETs), Esaki diodes and light-emitting diodes. In this work, Urbach tails and band gap narrowing values are calculated explicitly for GaAs, InAs, GaSb and GaN as well as ultra-thin bodies and nanowires of the same. Electrons are solved in the non-equilibrium Green's function method in multi-band atomistic tight binding. Scattering on polar optical phonons and charged impurities is solved in the self-consistent Born approximation. The corresponding nonlocal scattering self-energies as well as their numerically efficient formulations are introduced for ultra-thin bodies and nanowires. Predicted Urbach band tails and conduction band gap narrowing agree well with experimental literature for a range of temperatures and doping concentrations. Polynomial fits of the Urbach tail and band gap narrowing as a function of doping are tabulated for quick reference

Nonequilibrium Green’s Function Modeling of type-II Superlattice Detectors and its Connection to Semiclassical Approaches

Theoretical investigations of carrier transport in type-II superlattice detectors have been mostly limited to simplified semiclassical treatments, due to the computational challenges posed by quantum kinetic approaches. For example, interband tunneling in broken-gap configurations calls for a multiband description of the electronic structure, and spatially indirect optical transitions in superlattice absorbers require fully nonlocal carrier-photon self-energies. Moreover, a large number of iterations is needed to achieve self-consistency between Green’s functions and self-energies in the presence of strongly localized states not directly accessible from the contacts. We demonstrate an accurate, yet computationally feasible nonequilibrium Green’s function model of superlattice detectors by formulating the kinetic equations in terms of problem-matched maximally localized basis functions, numerically generated from few modes representing the main conductive channels of the nanostructure. The contribution of all the remaining modes is folded in an additional self-energy to ensure current conservation. Inspection of spatially and energetically resolved single particle properties offers insight into the complex nature of carrier transport in type-II superlattice detectors, and the connection to semiclassical approaches enables the interpretation of mobility experiments

Study Of Inas/Ga(In)Sb And Inasn/Ga(In)Sb Superlattices By Mbe For Very Long Wavelength Infrared Photodetectors

Infrared (IR) sensors are extremely important in missile defense as well as in satellite-based infrared detection systems. Long-range ballistic missile defense for incoming missile acquisition, tracking, and discrimination requires space-based infrared technology. Hence long wavelength and very long wavelength infrared regimes are extremely important for such applications. The focus of this work is on the investigation of superlattices (SLs) and in particular dilute nitride based SLs for such applications in this infrared region. A comprehensive study of InAs/GaSb, InAs/GaInSb, InAsN/GaSb and InAsN/GaInSb SLs grown by molecular beam epitaxy (MBE) has been carried out using different characterization techniques. Optimization of the structures with growth parameters such as interfacial layers, layer thickness, and material composition will also be discussed. The judicious selection of the above combination of parameters was abetted by theoretical simulation using OPTEL_ZB software. A systematic and detailed study has been made correlating the structural quality, vibrational modes, scanning transmission electron microscope (STEM) micrographs and optical properties of each of the optimized structure of the SL. All the SLs were defect free with sharp interfaces and well defined sublayers as attested by high resolution x-ray diffraction (HRXRD) and asymmetric reciprocal space mapping (RSM) spectra as well as STEM images. The unique feature of this work is the growth of InAsN/GaSb SL which has not been reported elsewhere to the best of our knowledge. This SL shows promise in that thinner layers of InAsN were used for the same strain balancing effect as thicker InAs. Hence the former would improve optical absorption. Since the N in InAsN reduces the overall lattice constant of the material system it added another degree of freedom in strain balancing the structure to the GaSb substrate. A cut off wavelength of ~20 μm was achieved with the InAsN/GaSb SL