Photoconductivity

When light of sufficient energy is absorbed by a semiconductor, the number of free electrons and holes changes and raises the electrical conductivity of the semiconductor.

Photoconductivity

When light of sufficient energy is absorbed by a semiconductor, the number of free electrons and holes changes and raises the electrical conductivity of the semiconductor. This increase is called photoconductivity and is dependent of the excess electron and hole concentrations and their mobility via the following equation.

${\Delta\sigma=e\cdot(\mu_n\Delta n+\mu_p\Delta p)}\qquad(1)$

In most cases the light pulse is chosen to be long enough to reach a steady state, where re-combination and generation is equal and the photoconductivity can be determined with:

${\Delta\sigma=e\cdot G_{opt}\cdot\tau\cdot (\mu_n+\mu_p)}\qquad(2)$

Gopt is the optical generation rate, which is dependent of the incident light intensity, the light spot on the sample and the wavelength.

$G_{opt}=\alpha\cdot\Phi\cdot(1-R)e^{\alpha x}\qquad(3)$

As it becomes clear in equation 2 the photoconductivity is proportional to the product of life-time t and the mobility µ and there for it is also proportional to the square of the diffusion length L, which is defined as:

$L=\sqrt{D\cdot\tau}=\sqrt{\frac{e}{kT}\cdot\mu\tau}\qquad(4)$

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Photoconductivity

Photoconductivity

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