Preparation of Semiconducting Thin Films Essay Example

achieved by the absorption of electromagnetic radiation, if this energy is equal to or larger than Eg.

The excited electrons reaching its new energy level can absorb light according to the equation: hc / ? >= Eg (indicates the absorption of light).

Discussion:

Preparing thin film semiconductor using cadmium sulphide requires the mix of cadmium sulphate, thiourea, and NH3 in hot water bath held at 80oC for 15 minutes.The solution was under constant stirring.

A bright orange-yellow precipitate was observed on half of the glass side. The slide was rinsed with deionized water and then air dried. The obtained wavelength for the reaction was 507 nm from the absorption spectrum. Preparation of zinc sulphide and bismuth sulphide semiconducting films were not required in this experiment.

Questions: 1.

What is the purpose of using thiourea of thioacetamide? Write balanced equations for the reactions that occurs when aqueous NH3 is added to them, and the mixture is heated.To form zinc and cadmium sulfides, thiourea was used. The formation of the bonds between zinc & cadmium atoms and the sulfur atom is through the production of urea, the sulfur atom will be replaced by oxygen atom (aqueous solution, water).

Reactions:

CH4N2S+H2O+ZnSO4+2NH3 CH4N2O+ ZnS+(NH4)2SO4 ? CH4N2S+H2O+CdSO4+2NH3 CH4N2O+CdS+(NH2)2SO4 2. ZnS, CdS and Bi2S3 films absorb in the range of 350, 500 and 950 (nm), respectively. In which regions of the electromagnetic spectrum do these absorptions occur? CdS = visible range (400- 800nm),ZnS = ultraviolet range (10- 400 nm) Bi2S3= infrared range

What are n- and p-type conductors? What’s meant by doping? n-type conductors: When an external (excess of electrons) atom is added to the pure semiconductor, this will result in increase in conductivity of the semiconductor and will result

in the n-type semiconductor. The reason for that is the semiconductor’s valance band is fully filled with electrons and the conduction one is partially filled. The addition will allow the donor band’s electrons to jump and fill the conduction band resulting in a decrease in the band gap.

In sum, the n-type semiconductors are solids doped with atoms that supply electrons to the conduction band.p-type: When external atoms (less than 2n electrons) are added to a pure semiconductor, this will result in an accepter band (empty band) near the valance band. The accepter band will decrease the gap band. This will lead the electrons from the valance band to the accepter band, creating positive spots in the valance one. The positive spots with let the electrons move more freely in the valance band, which will increase the conductivity of the pure semiconductor.

In sum, the p-type semiconductors are solids doped with atoms that remove electrons from the valence band. Doping: additional external electrons carriers which will increase the conductivity of a pure semiconductor.

Conclusion:

The transition of electrons from the valence band to the conduction band can be achieved by the absorption of electromagnetic radiation. Thus the energy absorbed depends on the amount of excited electron. The higher the gap band energy, the lower the conductivity. The energy (Eg) of cadmium sulfide calculated was 3. 2? 10-19J which corresponds to 2. 45 eV.

Reference:

• http://www. veeco.com/learning/learning_lattice. asp
• URFE. " LoveToKnow 1911 Online Encyclopedia. © 2003, 2004 LoveToKnow. http://46.
• 1911encyclopedia. org/U/UR/URFE. htm.
• Experimental Exercises in Introductory Inorganic Chemistry; Department of Chemistry and Biochemistry; Concordia University, Montreal, Canada; Chemistry 241 Wet Labs Manual, p 6-1 to 6-8
• http://en. wikipedia. org/wiki/Cadmium_sulfide
• http://en.wikipedia. org/wiki/Semiconductor