ProjectionPropagation

Description

The module projects the deposited electrons (or holes) to the sensor surface and applies a randomized, simplified diffusion. It can be used to save computing time at the cost of precision.

The diffusion of the charge carriers is realized by placing sets of a configurable number of electrons in positions drawn as a random number from a two-dimensional Gaussian distribution around the projected position at the sensor surface. The diffusion width is based on an approximation of the drift time, using an analytical approximation for the integral of the mobility in a linear electric field. Here, the charge carrier mobility parametrization of Jacoboni [@jacoboni] is used. The integral is calculated as follows, with $\mu_0 = V_m/E_c$:

Here, $\beta$ is set to 1, inducing systematic errors less than 10%, depending on the sensor temperature configured. With the linear approximation to the electric field as $E(s) = ks+E_0$ it is

Since the approximation of the drift time assumes a linear electric field, this module cannot be used with any other electric field configuration.

Depending on the parameter diffuse_deposit, deposited charge carriers in a sensor region without electric field are either not propagated, or a single, three-dimensional diffusion step prior to the propagation of these charge carriers, corresponding to the integration_time is enabled. Charge carriers diffusing into the electric field will be placed at the border between the undepleted and the depleted regions with the corresponding offset in time and then be propagated to the sensor surface.

The charge carrier lifetime can be simulated using the doping concentration of the sensor. The recombination model is selected via the recombination_model parameter, the default value none is equivalent to not simulating finite lifetimes. This feature can only be enabled if a doping profile has been loaded for the respective detector using the DopingProfileReader module. This module only supports doping profiles of type constant. The doping-dependent charge carrier lifetime is determined once and the survival probability is calculated by drawing a random number from an uniform distribution with $0 \leq r \leq 1$ and comparing it to the expression $t/\tau$, where $t$ is the total propagation time of the charge carrier to the sensor surface. Charge carriers which would recombine before reaching the surface are removed from the simulation.

Lorentz drift in a magnetic field is not supported. Hence, in order to use this module with a magnetic field present, the parameter ignore_magnetic_field can be set.

Parameters

• temperature: Temperature in the sensitive device, used to estimate the diffusion constant and therefore the width of the diffusion distribution.
• recombination_model: Charge carrier lifetime model to be used for the propagation. Defaults to none, a list of available models can be found in the documentation. This feature requires a doping concentration to be present for the detector.
• charge_per_step: Maximum number of electrons placed for which the randomized diffusion is calculated together, i.e. they are placed at the same position. Defaults to 10.
• max_charge_groups: Maximum number of charge groups to propagate from a single deposit point. Temporarily increases the value of charge_per_step to reduce the number of propagated groups if the deposit is larger than the value max_charge_groups*charge_per_step, thus reducing the negative performance impact of unexpectedly large deposits. The default value is 1000 charge groups. If it is set to 0, there is no upper limit on the number of charge groups propagated.
• propagate_holes: If set to true, holes are propagated instead of electrons. Defaults to false. Only one carrier type can be selected since all charges are propagated towards the implants.
• ignore_magnetic_field: Enables the usage of this module with a magnetic field present, resulting in an unphysical propagation w/o Lorentz drift. Defaults to false.
• integration_time : Time within which charge carriers are propagated. If the total drift time exceeds, the respective carriers are ignored and do not contribute to the signal. Defaults to the LHC bunch crossing time of 25ns.
• diffuse_deposit: Enables a diffusion prior to the propagation for charge carriers deposited in a region without electric field. Defaults to false.

Plotting parameters

• output_plots : Determines if simple output plots should be generated for a monitoring of the simulation flow. Disabled by default.
• output_linegraphs : Determines if line graphs should be generated for every event. This causes a significant slow down of the simulation, it is not recommended to enable this option for runs with more than a couple of events. Disabled by default.
• output_plots_theta : Viewpoint angle of the 3D animation and the 3D line graph around the world X-axis. Defaults to zero.
• output_plots_phi : Viewpoint angle of the 3D animation and the 3D line graph around the world Z-axis. Defaults to zero.
• output_plots_use_pixel_units : Determines if the plots should use pixels as unit instead of metric length scales. Defaults to false (thus using the metric system).
• output_plots_use_equal_scaling : Determines if the plots should be produced with equal distance scales on every axis (also if this implies that some points will fall out of the graph). Defaults to true.
• output_plots_align_pixels : Determines if the plot should be aligned on pixels, defaults to false. If enabled the start and the end of the axis will be at the split point between pixels.

Usage

[ProjectionPropagation]
temperature = 293K
charge_per_step = 10
output_plots = 1