AFORS-het

什么是AFORS-HET AFORS-HET (Automat FOR Simulation of HETerostructures) is a numerical simulation tool, which allows to model/simulate heterojunction semiconductor devices. An arbitrary sequence of semiconducting layers can be modelled, specifying layer properties and interface properties, i.e. the defect distribution of states (DOS). At the boundary, voltage or current controlled metal-semiconductor contacts (MS contacts) or a metal-insulator-semiconductor contact (MIS contact) can be chosen. Sub-bandgap photon absorption can be simulated by specification of optical capture cross sections. The program solves the one dimensional semiconductor equations using Shockley-Read-Hall recombination statistics, (1) for thermodynamic equilibrium, (2) for steady-state conditions under an external illumination and/or bias voltage (3) for small additional sinusoidal perturbations of the applied bias/illumination. Thus the internal cell characteristics (band diagrams, local generation, recombination, currents, carrier densities and phase shifts within the device) can be calculated for various external boundary conditions.. Furthermore, a variety of common characterisation techniques can be simulated, i.e. current-voltage (C-V), quantum efficiency (IQE, EQE), impedance (IMP), voltage and temperature dependant capacitance (C-V, C-T), intensity and field dependant surface photovoltage (SPVi, SPVv), photo- and electro-luminescence (PEL), electron beam induced current (EBIC), electrical detected magnetic resonance (EDMR). Also analytical forms describing a measurement can implemented and compared to the numeric ones (IQEanalytic) A user-friendly interface allows to visualise, store and compare all aspects within your simulations. Furthermore, general parameter variations can be performed. New numerical modules and new measurements may be added by external users (open-source on demand). 如何获得帮助 We tried to equip this software with a user-friendly interface, that is mostly self explaining. We hope, that there is no need for reading the online help, since most program options are obvious, if you have already used similar programs like PC1D or SCAPS. If you are however confused anywhere in the program press F1 to gain context sensitive help for the current program window. What‘s new? version 2.0: ?calculation mode transient was included ?several major and minor bugs fixed version 1.2: ?It is now possible to perform a multidimensional parameter fit on measurement curves ?External circuits can now be applied ?The program now distinguishes between several calculation modes (Eq, DC, AC) ?several major and minor bugs fixed version 1.1: ?You can now customise the program by choosing different optical and numerical calculation models ?In front and behind the cell, optical layers can be defined, that influence the generation rate inside the structure, as multiple coherent/incoherent reflections can be calculated, choosing the optical model multiple reflections and coherence. It can be selected in the settings window. ?the sequence of grid points is now editable by the user via the settings window ?Optical properties of the structure are now defined by nk-files and not anymore by alpha-files. When loading structures created with program version 1.0 be sure to check that all layers have the right optical files associated. ?New measurents IQE analytic, SPV intensity, PES and EDMR are introduced, the old ones have been improved. New measurement methods can be added by an external user (open source on demand). ?AC calculation now is not only available during some measurements. AC voltage and frequency can be applied anytime as external parameters ?Thermionic-Emission and Drift-Diffusion, are now not interface properties, but different numerical models. ?hetero structure files (*.het) and graphical output files (*.res, *.rac, *.iv, *.qe, *.iqean, *.adm, *.imp, *.cv, *.ct, *.spvs, *.spvv, *.spvi, *.ebic, *.pel, *.edmr, *.var, *.spek) can be opened directly from the Windows Explorer when the file type is associated with AFORS-HET. ?The handling of complex graphs has been improved ?several major and minor bugs fixed ?compatibility: unfortunately all graphical output files of program version 1.0 cannot be loaded with the new program version, due to improvements made to the file format. Known issues and planned improvements We are well aware that the program still needs a lot of development work. The following improvements and bugfixes are being developed at the moment: New developments: - a periodic modulation of the light intensity will be available - correlated dangling bond defect distributions will be implemented - a numerical model for Schottky-Bardeen contacts will be implemented - Fermi-Dirac statistics will be implemented - the defect-pool model to treat a-Si:H layers will be implemented 0 bugfixes: -​ phase shifts in the AC-voltage cell results should be continuous and not distracted by +-180?phase jumps (minor bug) Numerical Models AFORS-HET builds a discrete set of gridpoints at which the semiconductor equations are being solved. There are 4 different types of gridpoints (bulk point, interface point, first interface point and last interface point). Even if a gridpoint is called an interface point, it is never located exactly at the interface, but always a very small distance away from it. This distance can be specified within the numerical_settings. So for an heterojunction interface, there are actually two interface points belonging to that interface, one at each side of the heterojunction. For each of these different types of gridpoints different differential equations / boundary conditions and eventually modified routines for solving the resulting discrete equations have been implemented. A set of those routines is called numerical model. By applying a different numerical model to a point you change the way the program calculates at this point. You can choose the models, in the windows for editing layers and interfaces (first, last or any other). New numerical models may be added by an external user (open source on demand). At the moment the following models are implemented: bulk numeric models: There are two numerical models for a bulk gridpoint: Standard: Within this numerical model, Poissons equation and the electron/hole equation of transport is stated in a discritized form, together with (1) the partial derivatives of these equations, (2) a routine to solve locally for the resulting discrete equations. Crystalline-Silicon: Within this numerical model, the standard numerical model is modified within the routine for solving locally for the resulting discrete equations, in order to account for impurity scattering and carrier-carrier scattering within crystalline silicon. That is, the electron/hole mobilities will no longer treated to be constant within a layer, but they will (iteratively) depend on the local electron/hole particle densities within the cell. interface numeric models: There are two numerical models for an interface gridpoint: Drift-Diffusion: The transport across the heterojunction interface is modelled by drift-diffusion, in complete analogy to the bulk. In order to do so, an interface layer is assumed, with the thickness given by the distance of the two interface gridpoints specified in numerical settings. Additional interface states can be specified, which will result in additional interface recombination. Within the interface layer, all the layer properties are linearely transformed from one semiconductor to the second semiconductor. Thermionic emmision: Alternatively, the transport across the heterojunction can be modelled by thermionic emission over the energetic barrier of the heterointerface. Additional interface states can be specified, which will result in additional interface recombination. These interface states can interact with both adjacent semiconductors, thus charge carriers can transverse the heterointerface via defect states from one semiconductor to the other. first interface numeric models: So far, there are two numerical models for the first interface gridpoint: Metal/semiconductor Schottky contact: The front contact is treated as a metal/semiconductor Schottky contact. That is, the difference between the metal work function and the electron affinity of the adjacent semiconductor defines an energetic barrier for the current flow from the semiconductor into the metal. Interface states are not considered, if they are specified, they will be ignored. Metal/insulator/semiconductor MIS contact: The front contact is treated as a metal/insulator/semiconductor contact. Thus there is no current flow into the front contact. The corresponding insulator capacity has to be specified. Additional interface defects can also be specified, resulting in an enhanced interface recombination and also in a modified band banding in thermodynamic equilibrium. last interface numeric models: At the moment, there is only one numerical model for the last interface gridpoint: Metal/semiconductor Schottky contact: This is exactly the same as stated in the first interface gridpoint transient mode: Since version 2.0. AFORS-Het offers a transient calculation mode. Each numerical model has to provide additional functions that solve the problem under transient conditions. For more information on the numerical implementation of the transient mode click here. Defining a structure The first step when starting AFORS-HET is usually to define the structure you want to simulate. A structure always consists of a front contact, a back contact, and a variable number of layers in between (at least 1). Between all these items are interfaces, which are by default disabled (drift diffusion transport across the interface). Since version 1.1 a structure furthermore contains optical layers, which define light absorption, reflection and transmission at the cell contacts. Since version 1.2 external circuits can also be defined, i.e. a serial resistance Rs, a serial capacitance Cs, a parallel resistance Rp and a parallel capacitance Cp. Click on the Button 慏efine Structure?in order to create, load or modify a structure. All the items of the structure (contacts, layers, interfaces, external circuits) are displayed here. By clicking on an item you can change it抯 properties (e.g. click on a layer, if you want to change its properties). The simplest structure possible (1 layer and no interfaces) is offered if you start the program or if you select the button 慛ew Cell? Press the buttons under the label 慉dd Layer?to add new layers. The button labeled 慹lectric?will add a new electric layer. This new layer will be placed between the last layer and the back contact. Now, you either have to specify the material properties manually, or you load a layer that already exists. The same procedure works with the optical layers. Press 憃ptic front?or 憃ptic back?to add an optic layer in front of or behind the structure. Click the optic layers to edit their properties. Since version 1.1 you can also change the sequence of layers by clicking on the arrows in front of the structure. If you have specified the structure click on 慜K?and the program will start calculating the Eq equilibrium state for your structure. Furthermore you have the possibility of saving the structure to a file (*.het) and loading previously saved structures (save/load buttons). There are already some structures included with the program so you might want to load and modify them for your purpose. External Parameters On the left side of the main program window you can see the external parameters. They are divided into 3 subgroups: temperature, illumination and boundary conditions. Each time you start the program, the external parameters are reset to defaults. Illumination First you must decide if illumination should be turned on or off (darkness). If illumination is turned on you can define the incoming light, which consists of two components，that can be individually turned on and off: a spectral component and a monochromatic component. If both components are enabled the incoming light will be the sum of both components. Furthermore you can decide between front side and back side illumination. To view the complete incident spectrum use the 憇pectra?button in the main window . The spectral component can be directly defined by an incident file (*.in), specifying the number of photons at each wavelength of the incident illumination. These numbers will be additionally multiplied with the factor called times you have to enter. The default file 慉M15.in?with the default factor times=1 describes the average incident irradiation of the sun in middle Europe in summer at noon. The generation of electron-hole pairs within the semiconductor-layers will then be calculated using the spectral absorption coefficient alpha [cm^-1] of the layers. Only super-bandgap photons with E>Eg Opt will be absorbed due to the layer parameter alpha and generate electron-hole pairs, photons with E