Benjamin Pinkie

Numerical Simulation of Third-Generation HgCdTe Detector Pixel Arrays

In this paper, we present a physics-based full 3-D numerical simulation model of third-generation infrared (IR) detector pixel arrays. The approach avoids geometrical simplifications typical of 1-D and 2-D models that can introduce errors which are difficult to quantify. We have used a finite-difference time-domain technique to compute the optical characteristics including the reflectance and the carrier generation rate in the device. Subsequently, we employ the finite-element method to solve the drift-diffusion equations on a mixed-element grid to compute the electrical characteristics including the I(V) characteristics and quantum efficiency. Furthermore, we have used this model to study HgCdTe two-color detectors that operate in the medium-wave to long-wave IR and photovoltaic pixel arrays employing a photon-trapping structure realized with a periodic array of pillars that operate in the medium-wave IR.

Physics-based simulation of the modulation transfer function in HgCdTe infrared detector arrays

We have developed a numerical technique for performing physics-based simulations of the modulation transfer function (MTF) of infrared detector focal plane arrays. The finite-difference time-domain and finite element methods are employed to determine the electromagnetic and electrical response, respectively. We show how the total MTF can be decomposed to analyze the effect of lateral diffusion of charge carriers and present several methods for mitigation of such effects. We employ our numerical technique to analyze the MTF of a HgCdTe two-color bias-selectable infrared detector array.

Direct and phonon-assisted indirect Auger and radiative recombination lifetime in HgCdTe, InAsSb, and InGaAs computed using Green's function formalism

Direct and phonon-assisted (PA) indirect Auger and radiative recombination lifetime in HgCdTe, InAsSb, and InGaAs is calculated and compared under different lattice temperatures and doping concentrations. Using the Greens function theory, the electron self energy computed from the electron-phonon interaction is incorporated into the quantum-mechanical expressions of Auger and radiative recombination, which renders the corresponding minority carrier lifetime in the materials due to both direct and PA indirect processes. Specifically, the results of two pairs of materials, namely, InAs0.91Sb0.09, Hg0.67Cd0.33Te and In0.53Ga0.47As, Hg0.38Cd0.62Te with cutoff wavelengths of 4 μm and 1.7 μm at 200 K and 300 K, respectively, are presented. It is shown that for InAs0.91Sb0.09 and Hg0.67Cd0.33Te, when the lattice temperature falls below 250 K the radiative process becomes the limiting factor of carrier lifetime in both materials at an n-type doping of 1015 cm−3, while at a constant temperature of 200 K, a high n...

Numerical Simulation of Spatial and Spectral Crosstalk in Two-Color MWIR/LWIR HgCdTe Infrared Detector Arrays

The sequential two-color Hg1−xCdxTe architecture has emerged as a key technology in the development of third-generation infrared detectors. Due to the expense required to manufacture these devices, it is imperative to create numerical models which can predict the electrical and optical behavior of the technology as well as evaluate design concepts prior to exhaustive development. We have developed a three-dimensional simulation model which fully accounts for the optical phenomena that become increasingly important in small pixels and uses a drift–diffusion approach to determine the electrical behavior of the device. In particular, we employ a finite-difference time- domain method to solve Maxwell’s equations and a finite-element method to evaluate the solutions of the coupled Poisson and carrier continuity equations. We apply our simulation model to simulate the dynamic resistance and current density versus voltage characteristics of this detector architecture. The quantum efficiency is then determined for both spectral bands while observing the effects of variable pixel pitch and detector geometry. Finally, we use a spatially finite Gaussian beam to analyze the crosstalk and perform a simulated spot scan.

Negative Differential Resistance in Dense Short Wave Infrared HgCdTe Planar Photodiode Arrays

A novel room-temperature negative differential resistance (NDR) effect is proposed, theoretically analyzed, and quantitatively modeled for short-wave infrared (SWIR) HgCdTe photodiode detectors in dense double-layer planar heterostructure arrays with a 2.5 μm cutoff at 300 K. The predicted NDR results from nonequilibrium minority carrier suppression-with associated Auger suppression and negative luminescence-imposed by dense array geometry under uniform reverse bias. Using three-dimensional quantitative modeling, we evaluate representative dark current-voltage characteristics at different array pitch values. The predicted dark current and NDR resulting from structural variations in junction radius are consistent with the analytic dense array lateral diffusion current suppression model. The NDR effect and its relation to geometric parameters should be considered when attempting to minimize dark current in high-temperature SWIR HgCdTe photodiode arrays.

Numerical Simulation of the Modulation Transfer Function in HgCdTe Detector Arrays

In this work, we develop a method for simulating the modulation transfer function (MTF) of infrared detector arrays, which is based on numerical evaluation of the detector physics. The finite-difference time-domain and finite element methods are used to solve the electromagnetic and electrical equations for the device, respectively. We show how the total MTF can be deconvolved to examine the effects of specific physical processes. We introduce the MTF area difference and use it to quantify the effectiveness of several crosstalk mitigation techniques in improving the system MTF. We then apply our simulation methods to two-thirds generation mercury cadmium telluride (HgCdTe) detector architectures. The methodology is general, can be implemented with commercially available software, has experimentally realizable analogs, and is extendable to other material systems and device designs.

Modulation Transfer Function Consequences of Planar Dense Array Geometries in Infrared Focal Plane Arrays

Finite-difference time-domain and finite element method simulations are used to evaluate two-dimensional spot-scan profiles of p-on-n double-layer planar heterostructure (DLPH) detector arrays with abrupt p-type diffusions. The modulation transfer function (MTF) is calculated from the spot-scan profiles. An asymmetric dark and photo current collection mechanism is identified and explained as a result of electric field bunching through the corners of polygonal diffusions in DLPH arrays. The MTF consequences of the asymmetric collection are studied for triangular, square, and hexagonal diffusions in square and hexagonal arrays. We show that the placement and shape of the diffusion relative to the pixel can modify the MTF by several percent. The magnitude of the effect is largest for diffusions with fewer degrees of rotational symmetry.

Numerical simulation of InAs nBn infrared detectors with n-type barrier layers

This paper presents one-dimensional numerical simulations and analytical modeling of ideal (only diffusion current and only Auger-1 and radiative recombination) InAs nBn detectors having n-type barrier layers, with donor concentrations ranging from 1.8×1015 to 2.5×1016 cm-3. We examine quantitatively the three space charge regions in the nBn detector with an n-type barrier layer (BL), and determine criteria for combinations of bias voltage and BL donor concentration that allow operation of the nBn with no depletion region in the narrow-gap absorber layer (AL) or contact layer (CL). We determine the quantitative characteristics of the valence band barrier that is present for an n-type BL. From solution of Poisson’s equation in the uniformly doped BL, we derive analytical expressions for the valence band barrier heights versus bias voltage for holes in both the AL and the CL. These expressions show that the VB barrier height varies linearly with the BL donor concentration and as the square of the BL width. Using these expressions, we constructed a phenomenological equation for the dark current density versus bias voltage which agrees reasonably well with the shape of the J(V) curves from numerical simulations. Our simulations suggest that the nBn detector should be able to be operated at or near zero-bias voltage.

Multiscale modeling of photon detectors from the infrared to the ultraviolet

Due to the ever increasing complexity of novel semiconductor systems, it is essential to possess design tools and simulation strategies that include in the macroscopic device models the details of the microscopic physics and their dependence on the macroscopic (continuum) variables. Towards this end, we have developed robust multi-scale modeling capabilities that begin with modeling the intrinsic semiconductor properties. The models are fully capable of incorporating effects of substrate driven stress/strain and the material quality (dislocations and defects) on microscopic quantities such as the local transport coefficients and non-radiative recombination rate. Using this modeling approach we have extensively studied UV APD detectors and infrared focal plane arrays. Particular emphasis was placed on HgCdTe and InAsSb arrays incorporating photon trapping structures as well as two-color HgCdTe detectors arrays.

Full-band structure modeling of the radiative and non-radiative properties of semiconductor materials and devices (Presentation Recording)

Understanding the radiative and non-radiative properties of semiconductor materials is a prerequisite for optimizing the performance of existing light emitters and detectors and for developing new device architectures based on novel materials. Due to the ever increasing complexity of novel semiconductor systems and their relative technological immaturity, it is essential to have design tools and simulation strategies that include the details of the microscopic physics and their dependence on the macroscopic (continuum) variables in the macroscopic device models. Towards this end, we have developed a robust full-band structure based approach that can be used to study the intrinsic material radiative and non-radiative properties and evaluate the same characteristics of low-dimensional device structures. A parallel effort is being carried out to model the effect of substrate driven stress/strain and material quality (dislocations and defects) on microscopic quantities such as non-radiative recombination rate. Using this modeling approach, we have extensively studied the radiative and non-radiative properties of both elemental (Si and Ge) and compound semiconductors (HgCdTe, InGaAs, InAsSb and InGaN). In this work we outline the details of the modelling approach, specifically the challenges and advantages related to the use of the full-band description of the material electronic structure. We will present a detailed comparison of the radiative and Auger recombination rates as a function of temperature and doping for HgCdTe and InAsSb that are two important materials for infrared detectors and emitters. Furthermore we will discuss the role of non-radiatiave Auger recombination processes in explaining the performance of light emitter diodes. Finally we will present the extension of the model to low dimensional structures employed in a number of light emitter and detector structures.