Direct Energy, 2018a

6 PHOTOVOLTAICS 137
6.3. The gure in the previous problem shows the energy level diagram
for a semiconductor pn junction.
(a) If this pn junction is used in an LED, what will be the wavelength
in nm of the light emitted by the LED?
(b) If this pn junction is used as a solar cell, what range of wavelengths
of light will be absorbed by the solar cell?
6.4. A semiconductor is used to make an LED that emits red light at
λ = 630 nm.
(a) Find the energy gap in eV of the semiconductor.
(b) Find the energy in joules of a photon emitted.
(c) Find the energy in joules for Avogadro constant number of these
photons.
6.5. The gure belowshows the energy level diagram for a gallium arsenide
LED.
(a) Find the energy gap.
(b) Find the energy of a photon emitted by the LED.
(c) Find the frequency in Hz of a photon emitted by the LED.
0.5
Energy in eV
1.0
1.5
E f
2.0
2.5
3.0
Position