photodiodes
Biology
Cones arte efficiently packed to get a max of light.
Basics
- Energy of a photon : $E = \frac{hc}{\lambda}$
- Photoelectric effect :
Intrinsic effect: - electrons are elevated from valence band to conduction band
- generation of electron hole pairs
- longest possible silicon wavelength is $1.1\mu m$
Phototransduction (in photodiodes)
- A photon of appropriate energy will form electron-hole pairs
- Each generated element will be ywept by the electric field depending where they are generated.
%%🖋 Edit in Excalidraw, and the dark exported image%%
The quantum efficiency can be optimized by applying an anti-reflection coating to the semi-conductor surface to reduce and by generating a thick depletion (also by increasing $Vdt$) region close to the surface.
Photons with larger wavelengths penetrate deeper, because they have less energy and are thus less likely to generate an electron-hole pair at any given location in the material.
Dark current
A background current that is still present in absence of optical stimulation. It is due to large doping concentrations->high conductivity but shite snr.
Photocurrent
Electron hole pairs generated in the depletion region (and within a diffusion length) are more likely to be separated resulting in in a reverse current component called photocurrent.
- Logarithmic response
- Quantum efficiency:
