Semiconductor Diodes - theoretical Introduction
Main topics:
- the p-n junction
- characteristics and basic parameters of semiconductor diodes
- the operating point of the diode
- photodiode
The p-n junction
A p-n junction is a structure of a single crystal semiconductor, e.g. silicon or germanium, consisting of two adjacent p-type and n-type layers, which are formed as a result of doping:
In the n-type layer, the majority of the charge carriers are electrons. In contrast, in the p-type layer, the majority of the charge carriers are holes. In a p-n junction, we have two p- and n-layers pushed together, which causes the diffusion of electrons from the n-layer to the p-layer and holes from the p-layer to the n-layer. Similarly, as a result of the diffusive flow of holes in the boundary region of the p-layer, uncompensated negative charges of stationary acceptor centers remain.
The formation of uncompensated positive and negative charges of stationary centers causes the boundary layer to generate an electric field that counteracts the diffusion of charge carriers. Such an area is called the depletion layer. And the voltage generated in this area is called the potential barrier or diffusion voltage. When an external source is connected with the positive pole with the n layer and the negative pole with the p layer (reverse polarization), the potential barrier will increase by the value of the external voltage. The width of the barrier layer will increase - the diffusion components of the currents will decrease:
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However, when an external source is connected with the positive pole with the p layer and the negative pole with the n layer (forward polarization), then the potential barrier decreases by the value of the external voltage, which reduces the width of the barrier layer. The component of electron and hole diffusion current increases.
Source of image: https://ecstudiosystems.com/discover/textbooks/basic-electronics/diodes/pn-junction-operation/