Why does it not act like a voltage source? There are +ve and -ve charges present. Isn't it like an electric dipole?anorlunda said:Because the voltage is there only when a current flows. The voltmeter won't cause a significant current flow.
cnh1995 said:Why does it not act like a voltage source? There are +ve and -ve charges present. Isn't it like an electric dipole?
That's what I read somewhere but didn't understand fully. Could you please elaborate? What exactly is the contact potential?marcusl said:A more precise answer is because the contact potentials at the p-metal and n-metal junctions exactly counteract the built-in potential.
Did you hear already about a Schottky diode? This a junction between metal and semiconductor - and exactly such a junction exists (necessarily) caused by the contact material at both ends of the pn diode. And the diffusion voltages at these junctions compensate the diffusion voltage across the internal pn junction.cnh1995 said:That's what I read somewhere and didn't understand fully. Could you please elaborate?
The built-in voltage of a pn junction diode is the voltage that exists across the junction when it is in equilibrium. This voltage is caused by the diffusion of charge carriers from the p-type region to the n-type region, creating a depletion region with an electric field that prevents further diffusion.
The built-in voltage of a pn junction diode can be calculated using the following equation: Vbi = (kT/q)ln(Nd*Nd/ni^2), where Vbi is the built-in voltage, k is Boltzmann's constant, T is temperature, q is the charge of an electron, Nd and Na are the doping concentrations of the n-type and p-type regions, and ni is the intrinsic carrier concentration.
The built-in voltage of a pn junction diode is affected by factors such as temperature, doping concentrations, and the material properties of the semiconductor used. Higher temperatures and higher doping concentrations result in a larger built-in voltage, while different materials have different intrinsic carrier concentrations and bandgap energies that can affect the built-in voltage.
The built-in voltage of a pn junction diode plays a crucial role in its behavior. It determines the direction of current flow, with forward bias allowing current to flow and reverse bias blocking current. It also affects the diode's capacitance, as the depletion region acts as a dielectric material. Additionally, the built-in voltage affects the diode's breakdown voltage, which is the maximum reverse voltage the diode can withstand before breaking down.
The built-in voltage of a pn junction diode is primarily determined by the properties of the semiconductor material and the doping concentrations used. However, it can be altered to some extent by changing the temperature or applying an external electric field through forward or reverse biasing. This can affect the width of the depletion region and therefore the built-in voltage. However, the intrinsic properties of the diode cannot be changed significantly.