Sensor material not valid for this model

Simulation / Configuration Questions
1

Hello experts,

I am wanting to know more about declaring a sensor material for a defined detector. I retrofitted the source measurement example with a larger sensor thickness and changed the sensor_material parameter to "CADMIUM_TELLURIDE". I keep getting a warning of Sensor material cadmium_telluride is not a valid for this model. Is there something wrong in my sensor material declaration? Thank you!

[AllPix]
log_level = "WARNING"
log_format = "LONG"
number_of_events = 1
detectors_file = "detector.conf"
model_paths = ./
multithreading = true
random_seed = 1234

[GeometryBuilderGeant4]
world_material = "air"

[DepositionGeant4]
physics_list = FTFP_BERT_LIV
particle_type = "gamma"
source_energy = 59.5keV
source_position = 0 0 -20mm
source_type = "beam"
beam_direction = 0 0 1
number_of_particles = 1

[ElectricFieldReader]
model="linear"
bias_voltage=-500V
depletion_voltage=-100V

[ProjectionPropagation]
temperature = 293K
charge_per_step = 100
output_plots = true

[SimpleTransfer]
max_depth_distance = 5um
output_plots = true

[DefaultDigitizer]
threshold = 600e
output_plots = true

# [VisualizationGeant4]
# mode = "gui"
# view_style = "wireframe"
# trajectories_color_mode = "generic"
# accumulate = 1
# accumulate_time_step = 2s

[DetectorHistogrammer]
name = "mydetector"
granularity = 100, 100

[ROOTObjectWriter]
include = PixelHit, MCParticle
file_name = "output_source_measurement_59keV.root"


# Reference http://www.sciencedirect.com/science/article/pii/S0168900210012982
type = "hybrid"
geometry = "pixel"

number_of_pixels = 256 256
pixel_size = 55um 55um

sensor_thickness = 2000um
sensor_excess = 1mm
sensor_material = CADMIUM_TELLURIDE

bump_sphere_radius = 9.0um
bump_cylinder_radius = 7.0um
bump_height = 20.0um

chip_thickness = 100um
chip_excess_top = 1610um
chip_excess_bottom = 1610um
chip_excess_right = 10um
chip_excess_left = 10um

[support]
thickness = 1.76mm
size = 47mm 79mm
offset = 0 -22.25mm
material = "g10"
2

Hi @oobie2142

The reason you are seeing this warning has only indirectly to do with your sensor material choice - the cause is the choice of ProjectionPropagation as your propagation module.

The module documentation details that the Jacoboni/Canali mobility model is used for the approximation made for the total drift time. For CdTe this model is likely not suitable because it only parametrizes mobility in Silicon.

Currently we don’t have a mobility model for CdTe implemented - if you have a reference you would like us to add, let us know!
I would suggest using GenericPropagation module along with a custom mobility function - or ignore the warning if the Silicon mobility is close enough to what you expect for your CdTe sensor.

All the best,
Simon

3

Thanks for the reply @simonspa! I see, now I understand what is going on. I think for now I can just use a constant mobility using tabulated values. Is there anything else that must be accounted for using a different material from silicon?

4

Hi @oobie2142

from a technical perspective no, but of course anything you use in terms of recombination model, mobility model, etc. will have a direct impact on your simulation - and I myself have no first-hand experience with CdTe sensors myself. I would suggest trying it out and compare it to data. :slight_smile:

/Simon

1 Like
5

Thank you @simonspa I will take a look!