Hi Juan,
To model the AC behaviour of photodetectors, one typically perturbs (SSAC) or pulses (transient) a carrier generation term corresponding to some illumination profile
Since all the AC examples only involves going through the device contacts, I’m wondering if there is any proper practice to do this before going down the rabbit hole 
Hi,
devsim is capable of the Impedance Field Method. Which is used to perturb sources inside of the device, and results in an external current. Is that the type of transfer function you need? You end up with a transfer function from each node to an external contact current. This transfer function is at a given frequency.
I have used this method for noise simulation of both generation-recombination and diffusion. It can also used it for variability, including random dopant fluctuations.
It seems like it would be a fit to your application, and I would be very interested in hearing if that is being used in the photodetector simulation.
Hi @simbilod,
for my simulations I attach an extra generation term to SRH to emulate optical generation. It might not be best practice but it works for my transient simulations.
Modify SRH Equation:
def CreateSRHOptical(device, region):
"""
Modified SRH model to include constant carrier generation, used to emulate optical generation
:param device:
:param region:
:return:
"""
# init optical generation to 0.0 on all nodes
ds.set_parameter(device=device, name="OptScale", value=0.0)
ds.node_solution(device=device, region=region, name="OptGen")
xpos = ds.get_node_model_values(device=device, region=region, name="x")
optical_generation = [0.0] * len(xpos)
ds.set_node_values(device=device, region=region, name="OptGen", values=optical_generation)
USRH = "(Electrons*Holes - n_i^2)/(taup*(Electrons + n1) + taun*(Holes + p1))"
Gn = "-ElectronCharge * (USRH - OptGen * OptScale)"
Gp = "+ElectronCharge * (USRH - OptGen * OptScale)"
CreateNodeModel(device, region, "USRH", USRH)
CreateNodeModel(device, region, "ElectronGeneration", Gn)
CreateNodeModel(device, region, "HoleGeneration", Gp)
for i in ("Electrons", "Holes"):
CreateNodeModelDerivative(device, region, "USRH", USRH, i)
CreateNodeModelDerivative(device, region, "ElectronGeneration", Gn, i)
CreateNodeModelDerivative(device, region, "HoleGeneration", Gp, i)
Change OptGen Term to some value on all mesh points within a circle. Constant values in z-Direction in this examples:
def OpticalGenerationCircular(device, region, center: tuple = (0, 0), radius: float = 1.0,
genrate: float = 0.0) -> None:
"""
Define constant cylindrical illumination profile
"""
xpos = ds.get_node_model_values(device=device, region=region, name="x")
ypos = ds.get_node_model_values(device=device, region=region, name="y")
zpos = ds.get_node_model_values(device=device, region=region, name="z")
optical_generation = [0.0] * len(xpos)
for i in range(len(xpos)):
if (xpos[i]*1e4 - center[0]) ** 2 + (ypos[i]*1e4 - center[1]) ** 2 <= radius ** 2:
value = float(genrate)
optical_generation[i] = value
ds.set_node_values(device=device, region=region, name="OptGen", values=optical_generation)
With this you can now modify the global ‘OptScale’ Parameter to switch the light on and off:
//On
ds.set_parameter(device=self.device, name="OptScale", value=0.0)
//Off
ds.set_parameter(device=self.device, name="OptScale", value=1.0)
Thank you both! The global turn-on turn-off parameter is very clever, I will give it a shot.
Hello @GLuek
I’m trying to implement your solution in my code. However, I can’t get a transient illumination. Could you give a working code, please?
have a nice day
This is a quick and dirty copy/paste job but it runs and the output current is reacting to the optical generation parameters.
# Copyright 2013 DEVSIM LLC
#
# SPDX-License-Identifier: Apache-2.0
from devsim import *
from devsim.python_packages.simple_physics import *
import devsim.python_packages.Klaassen as kla
import diode_common
def CreateSRHOptical(device: str, region: str):
"""
Modified SRH model to include constant carrier generation, used to emulate optical generation
:param device:
:param region:
:return:
"""
# init optical generation to 0.0 on all nodes
set_parameter(device=device, name="OptScale", value=0.0)
node_solution(device=device, region=region, name="OptGen")
xpos = get_node_model_values(device=device, region=region, name="x")
optical_generation = [0.0] * len(xpos)
set_node_values(device=device, region=region, name="OptGen", values=optical_generation)
USRH = "(Electrons*Holes - n_i^2)/(taup*(Electrons + n1) + taun*(Holes + p1))"
Gn = "-ElectronCharge * (USRH - OptGen * OptScale)"
Gp = "+ElectronCharge * (USRH - OptGen * OptScale)"
CreateNodeModel(device, region, "USRH", USRH)
CreateNodeModel(device, region, "ElectronGeneration", Gn)
CreateNodeModel(device, region, "HoleGeneration", Gp)
for i in ("Electrons", "Holes"):
CreateNodeModelDerivative(device, region, "USRH", USRH, i)
CreateNodeModelDerivative(device, region, "ElectronGeneration", Gn, i)
CreateNodeModelDerivative(device, region, "HoleGeneration", Gp, i)
def print_currents(device, contact):
"""
Print out contact currents
"""
ece_name = "ElectronContinuityEquation"
hce_name = "HoleContinuityEquation"
contact_bias_name = GetContactBiasName(contact)
electron_current= get_contact_current(device=device, contact=contact, equation=ece_name)
hole_current = get_contact_current(device=device, contact=contact, equation=hce_name)
total_current = electron_current + hole_current
if contact in ["top", "bot"]:
voltage = get_circuit_node_value(solution='dcop', node=f"n{contact}")
else:
voltage = get_parameter(device=device, name=GetContactBiasName(contact))
data = (voltage, electron_current, hole_current, total_current)
print(f"{contact:10}{voltage:+.3e}\t{electron_current:+.3e}\t{hole_current:+.3e}\t{total_current:+.3e}")
return data
def print_all_currents():
"""
Prints all currents to console and returns outmap of values. !Currently only functional when all contacts are
silicon contacts!
:return:
"""
print("\nSolution:")
print("{0:10}{1:15}{2:12}{3:12}{4:10}".format("Contact", "Voltage", "Electron", "Hole", "Total"))
print(" Current Current Current")
device_list = get_device_list()
for device in device_list:
contact_list = get_contact_list(device=device)
outmap = {}
for contact in contact_list:
outmap[contact] = print_currents(device, contact)
print_circuit_solution()
return outmap
def print_circuit_solution():
print('Circuit Solution')
nodes = get_circuit_node_list()
for node in get_circuit_node_list():
r = get_circuit_node_value(solution='dcop', node=node)
print("%s\t%1.15e" % (node, r))
set_parameter(name="debug_level", value="info")
#set_parameter(name="threads_available", value=8)
#set_parameter(name="threads_task_size", value=1024)
set_parameter(name="extended_solver", value="True")
set_parameter(name="extended_model", value="True")
set_parameter(name="extended_equation", value="True")
device="diode3d"
region="Bulk"
diode_common.Create3DGmshMesh(device, region)
# this is the devsim format
write_devices (file="gmsh_diode3d_out.msh")
diode_common.SetParameters(device=device, region=region)
set_parameter(device=device, region=region, name="taun", value=1e-3)
set_parameter(device=device, region=region, name="taup", value=1e-3)
v_source_top = circuit_element(name="VSourceTop", n1="ntop_res", n2="GND", value=0.0)
v_source_bot = circuit_element(name="VSourceBot", n1="nbot_res", n2="GND", value=0.0)
r_source_top = circuit_element(name="RSourceTop", n1="ntop_res", n2="ntop", value=1.0)
r_source_bot = circuit_element(name="RSourceBot", n1="nbot_res", n2="nbot", value=1.0)
c_source_top = circuit_element(name="CSourceTop", n1="ntop", n2="GND", value=1e-12)
#c_source_bot = circuit_element(name="CSourceBot", n1="nbot", n2="GND", value=1e-17)
circuit_node_alias(node="ntop", alias="top_bias")
circuit_node_alias(node="nbot", alias="bot_bias")
####
#### NetDoping
####
node_model(device=device, region=region, name="Acceptors", equation="1.0e18*step(0.5e-5-z);")
node_model(device=device, region=region, name="Donors", equation="1.0e18*step(z-0.5e-5);")
node_model(device=device, region=region, name="NetDoping", equation="Donors-Acceptors;")
node_model(device=device, region=region, name="AbsDoping", equation="abs(NetDoping)")
node_model(device=device, region=region, name="logDoping", equation="log(AbsDoping)/log(10)")
diode_common.InitialSolution(device, region, circuit_contacts=["top", "bot"])
####
#### Initial DC solution
####
solve(type="transient_dc", absolute_error=1e-10, relative_error=1e-12, maximum_iterations=30)
###
### Drift diffusion simulation at equilibrium
###
diode_common.DriftDiffusionInitialSolution(device, region, circuit_contacts=["top", "bot"])
kla.Set_Mobility_Parameters(device, region)
kla.Klaassen_Mobility(device, region)
solve(type="transient_dc", absolute_error=1e-10, relative_error=1e-9, maximum_iterations=50)
# init optics
CreateSRHOptical(device=device, region=region)
xpos = get_node_model_values(device=device, region=region, name="x")
# set generation parameters, use set_parameter(device=device, name="OptScale", value=X) in a loop to ramp optical
# generation up or down if required
optical_generation = [1e18] * len(xpos)
set_node_values(device=device, region=region, name="OptGen", values=optical_generation)
set_parameter(device=device, name="OptScale", value=1.0)
solve(type="transient_dc", absolute_error=1e-10, relative_error=1e-9, maximum_iterations=50)
v = -0.1
while v > -3.01:
circuit_alter(name="VSourceTop", value=v)
solve(type="transient_bdf1", absolute_error=1.0, relative_error=1e-09,
maximum_iterations=100, tdelta=1e-8, charge_error=1.0)
print_all_currents()
v -= 0.1
print("\n\n\nSteady State: -----------------------------------------------------------")
for i in range(50):
solve(type="transient_bdf1", absolute_error=1.0, relative_error=1e-09,
maximum_iterations=30, tdelta=1e-8, charge_error=1.0)
print_all_currents()
thanks a lot for your reply =)