The build-in voltage, Vbi, has a specific value for each pn junction at thermal equilibrium: around 0.7V ... 0.9V. (Vbi ~ kT/q * ln (NA * ND / ni2))
Using a voltmeter between anode and cathode, it injects current thru terminals, so that the equilibrium don't still occur.
For zero currents, a zero voltage is measured.
How can we simultaneously capture zero currents (for equilibrium conditions) and real Vbi that is non-null.
The difference of the built-in potential between cathode and anode is roughly equal to the "knee-voltage" in the diode characteristic, as this is the potential that needs to be surmounted to make the p-n junction conductive.
Couldn't we use Mott-Schottky plot( 1/C2 - V) of a reverse biased diode for an estimate of the same?
There is a difference between built-in voltage and the knee-voltage for a pn junction. They are two model parameters distinct, which belong to two different models of current I-V.
The Mott-Schottky plot (1/C2 - V) could provide Vbi but in approximation of abrupt doping concentration (for this reason appears the exponent "2" in 1/C2 )- that is not in agreement with real case.
I think both solutions are suitable at a first iteration, to have an idea about the magnitude.
good point above by Cristtian. Plot log(C) vs. log(V) - slope will tend to be 1/2 for epitaxial diodes and 1/3 for linearly graded - most diffused junctions.
then plot either 1/C2 - V or 1/C3 - V to get VB
Hello,
Traditionally, there has been no direct way to obtain the values of the built-in potential difference and the doping profile exponent for a PN junction from its depletion capacitance versus reverse bias voltage difference curve. All the methods of which I am aware require you to guess the value of one of the two parameters and solve for the other. I have developed a method wherein a plot of the integral of CdV versus C^2/(dC/dV) yields a straight line, from which the slope and y-intercept can be used to obtain the built-in potential difference and the doping profile exponent. The derivation of the proof of this method, together with a demonstration using real data, can be found on my page on ResearchGate. The document is titled: Extraction of Parameters from Depletion Capacitance versus Reverse Bias Curves.
Regards,
Tom Cuff
You can use Kelvin probe force microscopy to measure the contact difference of the potential of a pn junction under thermal equilibrium.
Please refer to the link:https://www.researchgate.net/post/Is_the_contact_potential_difference_of_a_pn_junction_measured_with_kelvin_probe_force_microscopy_KPFM_equal_to_its_electrostatic_surface_potential
May the the method of C-V measurement under relatively low reverse bias such that the diode current is negligibly small, is the most easiest method to measure the contact difference of potential. Since there is injection the n and p sides remain in equilibrium where will be no injection. Also the transition regions remains more or less in equilibrium since the net current is more or less zero pointing out the balance between the diffusion and drift current which is the condition at thermal equilibrium.
This may be the justification that the C-V measurement at reverse bias is a suitable method for measuring the contact difference of potential.
Best wishes
- Badges
- Science topic
- Similar topics
- Biological Science
- Molecular Biology
- Molecular Methods
- Cloning