Re: PIN diode newton sec1d problem

[Carlo De Falco]

> On 1 Nov 2017, at 15:17, Tijmen Kroezen <address@hidden> wrote:
> 
> Hello everyone,
> 
> There is some trouble I am having concerning the modeling of a PIN diode 
> (code in the attachments), that would be nice if someone with some more 
> knowledge could help. 
> 
> My approach has been to alter the PN diode code included in the example and 
> let a Newton secs1d solver solve this (I have also tried Gummel, but I was 
> advised that Newton works better for PIN), but unfortunately this hasn't 
> produced any results yet. The PIN diode is supposed to be 180 um long with 
> three segments of 60 um. I don't have a specific doping strength in mind so I 
> took the values 1e16 for both the P and N parts as a start.
> 
> Unfortunately my code still produces the following errors:
> 
> >> newtonPIN
> warning: matrix singular to machine precision
> warning: called from
>     secs1d_dd_newton at line 69 column 11
>     newtonPIN at line 121 column 28
> error: bimu_bernoulli: invalid conversion from NaN to logical
> error: called from
>     bimu_bernoulli at line 45 column 11
>     bim1a_advection_diffusion at line 99 column 13
>     secs1d_dd_newton>residual_jacobian at line 129 column 7
>     secs1d_dd_newton at line 83 column 22
>     newtonPIN at line 121 column 28
> 
> I have tried using a finer mesh, I am starting from zero bias, so I guess the 
> only thing that might be the problem is my initial guess but I don't know 
> what other guess to use. Does anyone have suggestions?
> 
> Thanks so much in advance,
> 
> Best regards,
> 

Hi, Indeed your initial guess is inconsistent.

You are imposing a weak p-type doping in the i region, therefore p = n = ni is 
not correct.
I didn't have time yet to check whether this is the reason for the simulation 
failure.

I also at first sight see some errors in the postprocessing: 
you are de-scaling nout, pout, etc. but your simulation output are called p, n, 
etc.

Finally, if you use secs1d_dd_newton you do not need to compute the current 
densities
by the difference formulas as the simulation already provides them as output 
(you do need to de-scale them though).

Finally hoping to get solutions within a tolerance of 1e-12 sounds a bit 
optimistic in this case, 
I'd rather use something in the order of 1e-4 ~ 1e-6. That is expressed in 
multiples of Vth so that 
means hundreds of microvolts to nanovolts.

HTH,
c.