# How to get junction resistance

• posted

Does anyone know how to calculate the junction resistance for a n-Si Schottky diode from the fundamental properties. I know the effective depletion width, the junction area, the doped resistance, and of course the intrinsic resistance of silicon. Obviously I cannot use the doped resistance because the depletion region is just that, depleted. Yet it doesn't seem correct to use the intrinsic resistance because it's doped silicon, no? Any ideas?

I appreciate any help, Paul

• posted

Given the above info, I guess it's impossible to calculate Rj. I calculated the bandgap. Now is it possible to calculate Rj?

Regards, Paul

• posted

First, you need to define the junction resistance. A Schottky diode, like all rectifying diodes, has an extremely nonlinear I(V) characteristic. If what you are looking for is the small-signal equivalent resistance, it is the inverse of the small-signal conductance dI/dV. The full I(V) curve contains all the circuit- relevant information about the diode at dc. If you are looking for an equivalent-circuit model element that has an effect at higher frequencies, then its definition depends entirely on the (never unique) equivalent-circuit model.

- Bill Frensley

• posted

That requires current and voltage measurements to obtain the resistance. I know about the diode modeling equations. I'm talking about calculating the resistance without I & V measurements. Since most of the resistance is in the depletion region, I would settle for Rd. At zero bias, it's often written as Ro. The depletion region is void of mobile carriers, even at zero bias. I'm uncertain if the semiconductors effective resistance while void of mobile carriers is equal to the intrinsic resistance. If not, then how is it calculate?

Paul

• posted

For V=0, the quantity you're looking for is 0.258 V / Is. Calculating Is is the problem. The conventional model is Richardson's thermionic emission theory, which for room temperature gives 1.1E7 A/cm2 (times) exp(-Schottky barrier height/0.258 eV) (times) (diode area). To get one significant figure of accuracy, you need to know the Schottky barrier height to about 0.01 eV. You probably won't do much better than just guessing that Is is 1E-10 A.

By the way, this problem has ->nothing

• posted

Thanks a whole bunch Bill! Your post on the Richardson's thermionic emission theory led to all of the exact mathematical equations for schottky diodes -->