V_n equaion question on PN junction

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Discussion Overview

The discussion revolves around the formula for the potential V_n in the context of a PN junction, exploring different interpretations and applications of the equation. Participants are examining the relationship between energy levels and voltage, as well as practical issues related to measurements using a Keithley system.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant asserts that the formula for V_n should be V_n=(E_f-E_i)/q, referencing high school teachings, but questions the alternative expression V_n=(E_f-E_i)/kT.
  • Another participant clarifies that V_n=(E_f-E_i)/kT is dimensionless and relates to energy levels in the energy band diagram, suggesting a misunderstanding of the terms involved.
  • A different participant challenges the dimensionality of V_n=(E_f-E_i)/kT, proposing it represents a dimensionless ratio of V/V_T, where V_T is the thermal voltage.
  • Several posts discuss practical confusion regarding the use of a Keithley system for four-probe measurements, specifically about the relationship between current and voltage inputs when measuring sheet resistivity.
  • One participant expresses urgency in resolving their confusion regarding the measurement setup and the implications of varying voltage inputs on sheet resistivity.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the dimensionality and interpretation of the formula for V_n. The discussion on the Keithley system also reveals confusion and a lack of consensus on the measurement process and its implications.

Contextual Notes

Participants mention specific assumptions about the context of the equations and measurement setups, but these assumptions remain unresolved. The relationship between voltage, current, and sheet resistivity is also noted as potentially dependent on specific conditions.

Who May Find This Useful

This discussion may be useful for individuals interested in semiconductor physics, electrical engineering, and experimental measurement techniques, particularly those working with PN junctions and four-probe measurement systems.

nhrock3
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the formula for Vn should be
V_n=(E_f-E_i)/q

field divided by charge in the potential
like i was taught in high school
but why
the write it
V_n=(E_f-E_i)/KT

k in the boltsman constant
t is the temprature

there multiplication cannot be the charge

?
 
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Hello nhrock3,

There is a small misconception here.

When we write V_n=\frac{E_f-E_i}{kT}, E for energy; specifically the energy level in the energy band diagram. In such sense the term V_n is dimensionless.

If I'm getting you wrong, could you please reference your equation or state the full equation so I can get a better understanding.

Regards
 
nhrock3 said:
the formula for Vn should be
but why
the write it
V_n=(E_f-E_i)/KT
No that does not have dimensions of voltage. You would have to show the context in which it's used but I would assume it is the dimensionless ratio of V/V_T, where V_T is the temperature dependent "constant" kT/q_e (approx 26 mV at room temperature).
 
I am using a keithley system for my four probe measurements.I am getting confused with th
 
I am using a keithley system for my four probe measurements.I am getting confused with the curre
 
I am using a keithley system for my four probe measurements.I am getting confused with the current from outer two probes .Since we require a constant current source for that.My problem is that as we are forcing current from outer two probes the system is asking for voltage input.How can it be possible to set any voltage as we are targeting to force current and want to measure from inner two probes.Also if we enter different voltages in that coloumn we are different sheet resistivity.But to the best of my knowledge sheet resisitivity of a material is fixed.

Please help me urgently on this
as i have to complete my project on time
 

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