# Absorption Profile AlGaAs GaAs Structure Example¶

In :
import matplotlib.pyplot as plt
import numpy as np
from solcore.absorption_calculator import calculate_absorption_profile
from solcore import material, si
from solcore.structure import Structure, Layer


First we defined a couple of materials, for example, GaAs and AlGAs

In :
GaAs = material('GaAs')(T=300)
AlGaAs = material('AlGaAs')(T=300, Al=0.3)


Now, let's build the structure

In :
my_structure = Structure([
Layer(si(30, 'nm'), material=AlGaAs),
Layer(si(3000, 'nm'), material=GaAs),
Layer(si(300, 'um'), material=GaAs),
])


We want to calculate the absorption profile of this structure as a function of the position and wavelength

In :
wl = np.linspace(400, 1000, 200)
out = calculate_absorption_profile(my_structure, wl, steps_size=1, z_limit=3000)


Finally, we plot the absorption profile. Note that absorption at short wavelengths take place near the surface of the structure, in the AlGaAs layer and top of the GaAs layer, while longer wavelengths penetrate more. Wavelengths beyond the GaAs band edge are not absorbed.

In :
plt.figure(1)
ax = plt.contourf(out['position'], wl, out['absorption'], 200)
plt.xlabel('Position (nm)')
plt.ylabel('Wavelength (nm)')
cbar = plt.colorbar()
cbar.set_label('Absorption (1/nm)')


We can also check what is the overall light absorption in the AlGaAs and GaAs epilayers as that represents the total light absorption in our solar cell and therefore the maximum EQE (light absorbed in the thick substrate lost). The absorption is mostly limited by the reflexion in the front surface. Clearly, this solar cell needs an AR coating.

In :
A = np.zeros_like(wl)

for i, absorption in enumerate(out['absorption'][:]):
A[i] = np.trapz(absorption, out['position'])

In :
plt.figure(2)
plt.plot(wl, A)
plt.xlabel('Wavelength (nm)')
plt.ylabel('Absorption')

plt.show()