IV characteristics of Diode - Reverse Bias


While ploting the reverse characteristics of the pn junction diode, i am not getting the expected result.

basicpnjunction.ldev (5.7 MB)

Also in the charge monitor anode current ,band structure,doping etc are not coming.
Charge and total charge is showing.


Hi @muhamed.shafeeq, in your simulation all the recombination mechanisms are turned off. As a result the reverse bias current is almost zero. The value of the reverse bias current is so small that it is comparable or even lower than the accuracy level of the gummel solver. In such a case the current value at the contact where non-zero bias is applied can be inaccurate. However the current at the contact where the applied bias is zero should be more accurate. So in your present setup the current at the cathode contact would be the accurate one.

When you enable the common recombination mechanisms however, the reverse current is large enough that the solver will give you accurate values at both contacts (you may need to increase the solver accuracy to say 1e-7 as shown below).

Regarding the result in the charge monitor, it is supposed to provide you with the electron and hole density (n and p) only (and total charge if you enable that option). To get other properties you need other monitors for example your bandstructure monitor will give you the band profile. Note that when you have a voltage sweep the bandstructure monitor initially plots a surface plot so you will have to switch to a line plot (shown below). Also shown is how you can look at the band diagram at different voltages (by using the slider).

Unfortunately there is no monitor for doping (you can see the doping profile from the results at the CHARGE solver region).


Thank you Alam ,for clarifying my doubt.
One more problem i faced with the model is at higher voltages, above 1V, Forward characteristics doesn’t shows an exponential relationship.


Hi @muhamed.shafeeq, You can imagine the equivalent circuit of the diode to be a series combination of a diode and a resistance. The diode portion models the behavior of the pn-junction. You can think of it in terms of a dynamic resistance where the resistance of the diode decreases exponentially with bias (therefore you get an exponential I-V). Once the diode is fully turned on, the dynamic resistance becomes very small and the characteristics of the diode gets dictated by the resistance (of the un-depleted regions on both sides of the pn-junction) in series with the diode. This is why at higher bias your I-V becomes a straight line. The slope of the line will give you the value of the series resistance (slope = 1/R).


Thank you @aalam for the clear explanation.