“Simulation Studies on Photo conductive semiconductor materials: CdS & CdSe”

Z. B. Pathan* and Sajid Naeem Department of Electronic Science,AKI’s Poona College of Arts, Science and Commerce, Camp-Pune;Pune-411001 (India)Email: zabk@rediffmail.com

AbstractAn intensive studies on material are carried out to increase the solar conversion efficiency to develop a better solar-cell, CdS and CdSe are the most potential semiconductor material to be used in fabrication of solar-cell. Here an attempt is made to study the characteristics of these photoconductive materials using MATLAB simulation tool.

1. Introduction:Photo conductive materials such as CdS and CdSe are much used and potential material in the fabrication of solar-cells. The studies of optical properties of these materials are of much significance to the user of these materials; such as absorption coefficient and spectral response.

Here an attempt is made to study these optical properties by using simulation tools such as MATLAB.

2. Photon absorption coefficient:

A semiconductor material is subjected to incident light energy, the photons may be absorb or may prorogate through the semiconductor, depending on the photon energy and the band gap energy of the material.

2.1 Case 1: Photon energy less than band gap energy :In this case the light is transmitted through the material and the semiconductor appears to be

transparent.2.2 Case 2: Photon energy equal to or greater than band gap energy.

The absorption process begins and the valance electron will get sufficient energy to jump into conduction band. The access energy may be given to electron or hole to acquire additional kinetic energy which will be dissipated as heat in the semiconductor.

3. Empirical Mathematical Relation:An important technique for the measurement of energy band gap of semiconductor is the absorption of incident photon (light) by the material. The absorption occurs when incident photon energy (hυ) is greater than the band gap energy (Eg).From literature, it is well known that the intensity of light transmitted through a sample thickness ’x’ will be given by

It = I0 exp (-αx) ------------------------ (1)Where,

It = Intensity of light transmitted I0 = maximum incident light intensity

α = absorption coefficient (1/cm) x = thickness of the material

The Energy gap of a material is given by

4. MATLAB Simulation:Flow Chart

5. Simulaton Study: Case 1: Photo conductive semiconductor material: CdS

Eg =2.6 eV λ0 = 475 nm

Case 2: Photo conductive semiconductor material: CdSe

Eg =1.74 eV λ0 = 531nm

6. Result and Discussion:

400 450 500 550 600 6500.86

0.88

0.9

0.92

0.94

0.96

0.98

1

Wavelength

Rel

ativ

e A

bsor

banc

e

Absorption Spectrum of CdS

400 450 500 550 600 6500.94

0.95

0.96

0.97

0.98

0.99

1

Wavelength

Rel

ativ

e A

bsor

ban

ce

Absorption Spectrum of CdSe

Sr. No.

Colour Wavelength λ(nm)

Absorbance

1 Voilet 400 0.97452 Indigo 445 0.99603 Blue 475 14 Green 510 0.99465 Yellow 570 0.96086 Orange 590 0.94317 Red 650 0.8731

Sr. No.

Colour Wavelength λ(nm)

Absorbance

1 Voilet 400 0.94102 Indigo 445 0.97413 Blue 475 0.98894 Green 510 0.99845 531 16 Yellow 570 0.99467 Orange 590 0.98778 Red 650 0.9510

Start

Initializations of Parameters

α = α0 exp (1- λ/ λ0)2

Stop

λ0 = 475 for CdS , λ0 = 475 for CdSe

Enter the Values of Wavelength Matrix

Plot Relative Absorbance v/s Wavelength

7. References:ÿ Semiconductor Physics & Devices- Donald A Neamen, 3rd edition TMcG Hills 2007ÿ Principle of Electronic Material & Devices. S.O. Kasap.ÿ Sold State Electronic Devices- Ben G Streetman., PHI, 1997ÿ Introduction to MATLAB 7 for engineers. - W J Palm III, McGraw Hill International edition.ÿ Studies on fritted thick films of photoconducting CdS- L A Patil, etal,

Material Chemistry & Physics, 55(1998) 79- 83. ÿ Photoconductivity of semiconducting CdS nanowires. Jonathon Milam etal.

Nanoscape, Vol. 2 Issue 1, spring 2005.ÿ Photoconductivity- its application in photometry – S K Guha,

Journal of Physics E : Scientific instrument 1972 vol. 5ÿ Characterization and optical properties of cdse nano-crystalline thin films

R. S. Singh*, S. Bhushan, A. K. singh, S. R. DeoShri shankaracharya engineering college bhilai, durg-490020 (c.g.), india Digest Journal of Nanomaterials and Biostructures (Vol.6 No 2, April-June 2011, p. 403-412)

ÿ Effect of Quantum Confinement on The Wavelength of CdSe, ZnS And GaAs Quantum Dots (Qds) By Chukwuocha, E.O, Onyeaju, M.CInternational journal of scientific & technology research volume 1, issue 7, August 2012

ÿ Energy Band Gap Studies of CdS NanomaterialsDinu Patidar, K.S. Rathore, N.S. Saxena, Kananbala Sharma, T.P. SharmaJournal of Nano Research (Volume 3) October, 2008.

8. Acknowledgment:

The authors are grateful to the management of AKI, Mumbai and Principal Dr. G.M. Nazeruddin to provide necessary facilities in the Electronic Science Department of Poona College, Pune.

9. Annexure: MATLAB programming1. MATLAB Program for CdS:

%********************************************************************% Simulation Studies on Photo Conductive Semiconductor Materials: CdS%********************************************************************% Prof. Z.B.Pathan (zabk@rediffmail.com)% Prof. Sajid Naeem (sne.sajid@gmail.com)% Parameters: % Lamda_V = 400 ; % Voilet Wavelength in nm% Lamda_I = 445 ; % Indigo Wavelength in nm% Lamda_B = 475 ; % Blue Wavelength in nm% Lamda_G = 510 ; % Green Wavelength in nm% Lamda_Y = 570 ; % Yellow Wavelength in nm% Lamda_O = 590 ; % Orange Wavelength in nm% Lamda_R = 650 ; % Red Wavelength in nm% Alpha = Alpha_Max (exp (1-(Lamda /Lamda_Max)))^2Lamda_Max = 475; % Maximum WavelengthLamda = input ('Enter the value of Wavelength = ');Lamda_Ratio = Lamda / Lamda_Max; L = (1-Lamda_Ratio)^2;Alpha_Ratio = 1 / exp(L); % Formula A = Alpha_Ratio;disp ('Enter "A" to calculate the Alpha_Ratio');% Plot Absorbance v/s WavelengthX = [400 445 475 510 570 590 650];Y = [0.9754 0.9960 1 0.9946 0.9608 0.9431 0.8731];plot(X,Y, '-*r');xlabel('Wavelength');ylabel('Relative Absorbance');title('Absorption Spectrum of CdS');grid on;

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2. MATLAB Program for CdSe:

Lamda_Max = 531; % Maximum WavelengthLamda = input ('Enter the value of Wavelength = ');Lamda_Ratio = Lamda / Lamda_Max; L = (1-Lamda_Ratio)^2;Alpha_Ratio = 1 / exp(L); % Formula A = Alpha_Ratio;disp ('Enter "A" to calculate the Alpha_Ratio');

% Plot Absorbance v/s WavelengthX = [400 445 475 510 531 570 590 650];Y = [0.9410 0.9741 0.9889 0.9984 1 0.9946 0.9877 0.9510];plot(X,Y, '-*r');xlabel('Wavelength');ylabel('Relative Absorbance');title('Absorption Spectrum of CdSe');grid on;

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