Dear Amirhossein,

Welcome, 

The ideal value of the open circuit voltage is the contact difference of potential. The contact difference pf potential between two materials is difference between the work functions of the two materials, that is phi= phi1- phi2,

For the p-n junction assume phi1 is that of the p-type and phi2 is that of the n-type, then the highest possible difference is bounded by the energy gap. Because if the difference is increased beyond the energy gap the material will be metal ike and the barrier will be tunnel able. The practical value achieved for the open circuit voltage is about .6V  because one of the sides of the p-n junction must be moderately doped for effective collection of the generated electron hole pairs and  the real open circuit volatile condition is arrived when the photocurrent is equal to the dark current.

Then the open circuit voltage= nVt Ln ( Iph/ Is),

with n the ideality factor, Vt the thermal voltage. Iph the photo current and Is is the reverse saturation current of he junction.

In case of the Schottky diode solar cell and assuming n-type semiconductor, one can choose a metal such that its phi1 is equal to that of the p-type material. In this way the contact difference of potential is equal in both cases.

However the open circuit condition where the photocurrent is equal to the dark  current will result is a smaller open circuit voltage because the the dark current is a majority carrier current while in the p-n junction it is a minority carrier current.

The formula above for the open circuit holds also for the Schottky diode solar cell with the saturation current controlled by  potential barrier phib from the metal to the semiconductor. Phib= phi1- electron affinity of the semiconductor.Where phi1 is worfunction of the metal.

The presence of surface states at the semiconductor material may limit the potential barrier phib to about two thirds of the energy gap of the semiconductor.

There are some methods developed to increase the barrier hight by ion implanting the surface of the semiconductor to produce a heavily doped surface layer with doping type different from that of the substrate.

In summary,It is the nature of the flow of the dark current that make a difference in the open circuit volatile.

For more information please refer to the BOOK: PHYSICS OF SEMICONDCUTOR DEVICES, S.M. Sze. chapter 14.

Best wishes

Hot carriers Amir , but the metal -semiconductor interface has this effect. When they are fused(bonded) that is metal and semiconductor electrons flow to the metal providing a heavy flow of the carrier (or hot carriers as they are called). They(injected ones) have high kinetic energy effectively give the barrier effect.

The Vth values for hot carriers varies with metal chosen such as gold /chrome etc .

If you want to dig deeper then you can look at metal-semiconductor relations in terms of work function .

Dear Amirhossein,

please look at the attachment I am sending. There I try to explain the formation of junctions in general, both Schottky-Semiconductor  and Semiconductor p-n.

In reference to the attachment then :

1. Schottky interface(contact) is "smaller" than the p-n interface(contact) because the Schottky contact is 1/2 junction (only one majority carriers depletion region), while p-n junction is a full junction (two depletion regions formed by the respective majority carriers).

2. No, in general you can have both Schottky metal-n type semiconductor contact (electron depletion) and/or Schottky metal-ptype semiconductor contact (hole depletion).  But in a way , you are right, Schottky contact involves only one type majority carrier, while the pn contact (junction) involves both the electrons and holes. The fundamental reason for the difference though is the difference of the chemical potential across the interface.

I hope this will help you on the way.

With best regards

Petr

Dear Amirhossein,

Welcome, 

The ideal value of the open circuit voltage is the contact difference of potential. The contact difference pf potential between two materials is difference between the work functions of the two materials, that is phi= phi1- phi2,

For the p-n junction assume phi1 is that of the p-type and phi2 is that of the n-type, then the highest possible difference is bounded by the energy gap. Because if the difference is increased beyond the energy gap the material will be metal ike and the barrier will be tunnel able. The practical value achieved for the open circuit voltage is about .6V  because one of the sides of the p-n junction must be moderately doped for effective collection of the generated electron hole pairs and  the real open circuit volatile condition is arrived when the photocurrent is equal to the dark current.

Then the open circuit voltage= nVt Ln ( Iph/ Is),

with n the ideality factor, Vt the thermal voltage. Iph the photo current and Is is the reverse saturation current of he junction.

In case of the Schottky diode solar cell and assuming n-type semiconductor, one can choose a metal such that its phi1 is equal to that of the p-type material. In this way the contact difference of potential is equal in both cases.

However the open circuit condition where the photocurrent is equal to the dark  current will result is a smaller open circuit voltage because the the dark current is a majority carrier current while in the p-n junction it is a minority carrier current.

The formula above for the open circuit holds also for the Schottky diode solar cell with the saturation current controlled by  potential barrier phib from the metal to the semiconductor. Phib= phi1- electron affinity of the semiconductor.Where phi1 is worfunction of the metal.

The presence of surface states at the semiconductor material may limit the potential barrier phib to about two thirds of the energy gap of the semiconductor.

There are some methods developed to increase the barrier hight by ion implanting the surface of the semiconductor to produce a heavily doped surface layer with doping type different from that of the substrate.

In summary,It is the nature of the flow of the dark current that make a difference in the open circuit volatile.

For more information please refer to the BOOK: PHYSICS OF SEMICONDCUTOR DEVICES, S.M. Sze. chapter 14.

Best wishes