# Materials & Photogeneration Rate at 1550 nm

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