We now seek to understand how different materials respond and interact with light. Photogeneration is the rate at which electrons are created through the absorption of light.
A program is built in ATLAS TCAD to simulate a beam incident on a block of material. A PN junction is used, similar to previous iterations. An example of the code for the Photogeration Simulator will be provided at the end of this article.
The subject of photogeneration certainly can see a more thorough examination that is provided here. Consider this as an introduction and initial exploration.
GaAs-InP-GaAs PN Junction

Here we see that a cross section of this unintentionally doped InP region, sandwiched between a GaAs PN junction exhibits a level of photogeneration, while the GaAs regions do not.
Adding more layers of other materials, as well as introducing a bias of the structure, we notice that the InP region still exhibits the highest (only) level of photogeneration of the materials tested in this condition. Interestingly, this structure emits light under the conditions tested.

Also consider that a photogeneration effect may not be sought. If, for instance, a device is supposed to act as a waveguide, there will be no benefit to having a photogeneration effect, let alone losses in the beam that result from it.
InGaAsP-InP-InGaAs Heterostructure
A common set of materials for use in Photodetectors is InGaAsP, InP and InGaAs. This particular structure features a simple, n-doped InGaAsP, unintentionally doped InP and p-doped InGaAs. The absorption rate of InP was already demonstrated above. InGaAs proves also to exhibit absorption at 1500 nm.

go atlas
Title Photogeneration Simulator
#Define the mesh
mesh auto
x.m l = -2 Spac=0.1
x.m l = -1 Spac=0.05
x.m l = 1 Spac=0.05
x.m l = 2 Spac =0.1
#TOP TO BOTTOM – Structure Specification
region num=1 bottom thick = 0.5 material = GaAs NY = 20 acceptor = 1e17
region num=3 bottom thick = 0.5 material = InP NY = 10
region num=2 bottom thick = 0.5 material = GaAs NY = 20 donor = 1e17
#Electrode specification
elec num=1 name=anode x.min=-1.0 x.max=1.0 top
elec num=2 name=cathode x.min=-1.0 x.max=1.0 bottom
#Gate Metal Work Function
contact num=2 work=4.77
models region=1 print conmob fldmob srh optr fermi
models region=2 srh optr print conmob fldmob srh optr fermi
models material=GaAs fldmob srh optr fermi print \
laser gainmod=1 las_maxch=200. \
las_xmin=-0.5 las_xmax=0.5 las_ymin=0.4 las_ymax=0.6 \
photon_energy=1.43 las_nx=37 las_ny=33 \
lmodes las_einit=1.415 las_efinal=1.47 cavity_length=200
beam num=1 x.origin=0 y.origin=4 angle=270 wavelength=1550 min.window=-1 max.window=1
output band.param ramptime TRANS.ANALY photogen opt.intens con.band val.band e.mobility h.mobility band.param photogen opt.intens recomb u.srh u.aug u.rad flowlines
method newton autonr trap maxtrap=6 climit=1e-6
#SOLVE AND PLOT
solve init
SOLVE B1=1.0
output band.param ramptime TRANS.ANALY photogen opt.intens con.band val.band e.mobility h.mobility band.param photogen opt.intens recomb u.srh u.aug u.rad flowlines
outf=diode_mb1.str master
tonyplot diode_mb1.str
method newton autonr trap maxtrap=6 climit=1e-6
LOG outf=electrooptic1.log
solve vanode = 0.5
solve vanode = 1.0
solve vanode = 1.5
solve vanode = 2.0
solve vanode = 2.5
save outfile=diode_mb2.str
tonyplot diode_mb2.str
tonyplot electrooptic1.log
quit