Dear All,
Where to put effective surface recombination velocity in the case of an npp+ solar cell? And is it different from surface recombination velocity at the back/front contact?
In many papers, it is written that the surface recombination velocity depends on different factors (like p and p+ layer acceptor density, p+ region diffusion length, minority carrier lifetime and p+ region width). Those papers mentioned, "effective surface recombination velocity S_eff at p/p+ homojunction/heterojunction...". But while going for simulation (using SCAPS 1D), there is no such option in the p/p+ interface panel, the only place I found for "surface recombination velocity" is at the front/back contact (generally it is taken as 10^5 or 10^7 cm/sec). Should I put the calculated effective surface recombination velocity at the contact profile or it is not necessary to give it as input while simulating?
Kindly help me to understand this.
Thank you in advance.
this increases the voltage of a solar cell. Extra heavy doping at the rear establishes a field that keeps minority carriers (in this case, electrons) from the highly recombining rear surface. The reduction in recombination increases the electron concentration in the base and so the solar cell's voltage.
Dear Santu Mazumder ,
welcome!
Any semiconductor layer has a volume and a surface. The volume is characterized by a volume density Nt of traps acting as recombination center. The volume traps are affecting the volume excess recombination rate by limiting the their recombination lifetime Tau= 1/ sigma vth Nt , where sigma is the capture cross section, vth is the thermal velocity.
On the other side the surface is characterized by surface density of the states of the traps Nts/ cm^2. These surface traps acts as recombination sink for the minority carriers at the surface. The most suitable description of their effect is to consider the recombination current at the surface as Isr= A q n vss where
A is the surface area, q is the electronic charge, n is the excess electrons at the surface, and vss is the surface recombination velocity.
The surface recombination velocity vss is related to Nts by the relation:
vss = Nst vth sigma.
So, whenever you have a volume of a semiconductor you describe its recombination parameter by the lifetime Tau when ever you a semiconductor surface you describe it recombination parameter by vss. This the conceptual answer to your question.
If you have a homojunction then there is no surface recombination at it. Only when you have heterojunction or an int3erface between two different materials then you have a surface recombination velocity vss.
I would like that you follow the paper in the link:Article M. Abdelnaby, A. Zekry, F. Elakkad and H. F. Ragaie, “ Depen...
Best wishes
Dear Hadi Jabbar Alagealy and Abdelhalim abdelnaby Zekry sir,
Thank you so much for your kind help on this matter. I am using a homojunction for my pp+ junction. The information you give suggests me to give Vss in terms of capture crossection, tau and Vth as input in the simulation, if there be any Vss input is unavailable. Correct me if I am wrong sir.
Thank You again Sir,
Yours sincerely
Santu Mazumder
Dear Santu Mazumder ,
I am very astonished that you did not recommend my answer and recommended the other answer in spite of its usefulness for you. My answer gives you a precise reply on your question. I expected that you will mark my question as the best answer as it is directly answer your question.
You must know that it is irrelevant for me but your behavior is disappointing.
Dear Abdelhalim abdelnaby Zekry Sir,
I am very sorry for the inconvenience. And I apologize for the same sir. I have already recommended your answer before I send the last message, it is showing here that your reply is recommended by me. I do not know whether it is visible to you or not. I must say that your answer really helped me a lot. And this is not the first time that you are answering my questions, I must say thank you for that. It is my fault that I could not give the best answer mark, which I should do. Thank you again for your kind support.
Thanking You,
Yours Sincerely,
Santu Mazumder
Dear Santu Mazumder ,
Please never mind my critic. The most important thing for me is the usefulness of my work to my colleagues and the young researchers.
Now I will come to your second question in commenting my first post.
Yes if vss is not available you can calculate it from the given formula by knowing Nst, sigma and vth. In simulations you can even assume a range of vss to see how massive vss can affect the performance of the device.
But i would like to pay your attention as I said before if you have PP+ junction which is homogenous you do not need to consider that there is a surface recombination at the junction. Only the volume trap concentration can change because of the doping change such that Nt in the P+ region is higher than that in the P-region.
Best wishes.
Dear Santu Mazumder ,
Merry Christmas and happy new year!
I would like to add a comment to your question which may clear your doubt.
I think that it is the low high junction P-P+ which is called the back surface field contact . The electric field in this junction us so that it repels the electrons injected from the pn junction and reflect them back to it preventing them from reaching the metal semicondcutor interface at the P+ surface.
So, the surface recombination current will be reduced by reducing the minority carrier concentration (the electrons here) at the surface of the P+ layer but the surface recombination velocity will remain unaltered by introducing the P+ region.
We can consider effectively that one reduced the surface recombination velocity.
This means that if you substitute the P+ region + the metal semicondcutor interface by a lower vss at the surface of the P-region.
Mathematically explained:
with P+ layer
Iswith = surface current= q nswith vss
without P+ Iswithout = q nwithout vss
nwithout >> nwith
If one wants to consider the combined effect of the P+ -layer while considering that they they are equivalent to a recombination current at the surface of the P-layer then one can formally have:
Iswith equivalent= q nwithout vss*
where vss * is the equivalent surface recombination velocity.
As you see one has to effectively reduce the surface recombination velocity in order to take into consideration the P+ layer.
Best wishes
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