Absorption of Light

Source: Little Scientists · Auf Lager

Understanding Photon Absorption in Semiconductors

When photons with energy equal to or greater than the band gap of a material interact with the material, they can excite an electron into the conduction band. This process generates both minority and majority carriers, forming the basis of photovoltaic energy production.

Interaction of Photons with Semiconductors

Upon hitting the surface of a semiconductor, photons can be reflected, absorbed, or transmitted. In the context of photovoltaic devices, reflection and transmission are considered loss mechanisms since only absorbed photons can generate power. The likelihood of absorption depends on the energy of the photon, with only photons with sufficient energy exciting electrons into the conduction band.

Photon Energy and Semiconductor Band Gap

Photon-semiconductor interactions are categorized based on the energy relationship between the photon and the semiconductor band gap:

• When photon energy is less than the band gap (Eph < EG), photons pass through the semiconductor weakly.
• Photon energy equal to the band gap (Eph = EG) efficiently creates electron-hole pairs upon absorption.
• Photon energy greater than the band gap (Eph > EG) leads to strong absorption, but excess energy is wasted in photovoltaic applications.

Impact on Carriers in Semiconductors

Photon absorption results in the generation of both majority and minority carriers. In doped solar cells, the number of majority carriers far exceeds the light-generated carriers, while the number of minority carriers is significantly increased by absorbed photons. This increase in minority carriers contributes to the overall performance of the illuminated semiconductor in photovoltaic applications.

Source: Khan Academy