The Richardson constant depends on the effective mass of the emitting material. In case of Metal to vacuum one uses the effective mass of the metal as the metal is the radiating substance in the vacuum. IN case of M-S contact the Richardson consatnt will be that of the semicondcutor because the emission occurs from semicondcutor. This concept can be applied on and heterojunction with thermionic emission. The material which controls the emission is the material which imposes the the effective mass in the Richardson consatnt.

To see the origin of the Richardson constant please see the book in the book in the link: Book Electronic Devices

Best wishes

I am not experienced with this topic but I am guessing that it is similar to the concept of a work function. If so, then the appropriate constant depends on both materials. In the context of a work function, we can assign one to each material if it refers to that material adjacent to a vacuum. We take the difference between these two work functions when the work function refers to one material adjacent to the other, so the work function depends on both materials when it refers to one adjacent to the other. But, like I said, I am not familiar with the Richardson constant so this is only a guess.

Question is not clearly defined. Before explaining reply of question, brief about the heterojunction grown on which substrate. Is ZnO / NiO layer grown on Si substrate?

 Dear Sir Gadkari, I am ver sorry for the uncleared question. Actually, ZnO thin film is grown on Si substrate by sol-gel method and ZnO/Si heterojunction diode is fabricated.

To calculate the I-V characteristics of this diode using Thermionic emission model, should I consider the Richardson constant of ZnO of Si?  

Bhaskar Parida

Regarding Richardson constant, you read the paper attached herewith, which will help you to know about this constant.

Refer  also book:  by S M Sze- Physics of semiconductor Devices,  PART III : INTERFACE AND THIN-FILM DEVICES,  Chapter- Metal-Semiconductor Devices. 

If you need additional help, send what you required.

 Dear L.D Edmonds, Thank you very much for your answer.

Dear Sir Gadkari, Thank you very much for your help and nice suggestions. However, I am still not clear about the Richardson constant. When a Schottky contact is made between metal/semiconductor (Ex: Au/ZnO), then we use the Richardson constant of the semiconductor to calculate the I-V characteristics using Thermionic emission model. What about ZnO/Si heterojunction? In some papers, the Richardson constant of ZnO is used and in some other papers, the Richardson constant of Si is used. I can't understand, why the Richardson constant of ZnO is used to calculate the I-V characteristics of a ZnO/Si heterojunction diode using Thermionic emission model. Would you please help me to understand this.

Bhaskar Parida

                 In my opinion, it might depend on fabrication of Schottky junction on substrate (sapphire, glass, Si etc.). Related your query, some new e-papers published in 2017 have been listed below. These e-papers will clear your understanding of the Richardson constant. But Richardson is a constant of material, which is independent of temperature. A* is the Richardson constant and was theoretically calculated (A* = 4πqk2m*/ h3) , where m* is effective mass of the material used and it is assumed constant value with the varying temperature. However, verify the similarity of your experiment (not known to us) used to fabrication of the Schottky diode (heterojunction) from the paper, which would clear your doubt.

 1) Halil Ozerli et.al.- Journal of Alloys and Compounds 718 (2017) 75e84, -- Electrical and  photovoltaic properties of Ag/p-Si structure with GO doped NiO interlayer in dark and  under light illumination.

2) Abdullah G.- Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 180 (2017) 110–118, --Composite CuFe1−xSnxO2/p-type silicon photodiodes

3) Halla Lahmar - Journal of Alloys and Compounds 718 (2017) 36e45, -- On the     electrochemical synthesis and characterization of p-Cu2O/n-ZnO heterojunction

4) F. Ynineb- Thin Solid Films 628 (2017) 36–42, --Morphological and optoelectricalstudy of ZnO:In/p-Si heterojunction prepared by ultrasonic spray pyrolysis

5) G. Turgut -Materials Science and Engineering B 206 (2016) 9–16, --A study of Eu  incorporated ZnO thin films: An application ofAl/ZnO:Eu/p-Si heterojunction diode.

6) Mustapha Amine Kadaoui- Superlattices and Microstructures 82 (2015) 269–286, -- Electrical parameters of Au/n-GaN and Pt/n-GaN Schottky diodes

7) See our papers on ResearchGate

The Richardson constant depends on the effective mass of the emitting material. In case of Metal to vacuum one uses the effective mass of the metal as the metal is the radiating substance in the vacuum. IN case of M-S contact the Richardson consatnt will be that of the semicondcutor because the emission occurs from semicondcutor. This concept can be applied on and heterojunction with thermionic emission. The material which controls the emission is the material which imposes the the effective mass in the Richardson consatnt.

To see the origin of the Richardson constant please see the book in the book in the link: Book Electronic Devices

Best wishes

I am searching the Richardson's constant of GeO2. Anybody can help me?

how can we calculate the n-type Cu2O semiconductor Richardsons constant value?