g_q - Experimental Problem Determination of energy band gap...

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1 Experimental Problem Determination of energy band gap of semiconductor thin films I. Introduction Semiconductors can be roughly characterized as materials whose electronic properties fall somewhere between those of conductors and insulators. To understand semiconductor electronic properties, one can start with the photoelectric effect as a well-known phenomenon. The photoelectric effect is a quantum electronic phenomenon, in which photoelectrons are emitted from the matter through the absorption of sufficient energy from electromagnetic radiation (i.e. photons). The minimum energy which is required for the emission of an electron from a metal by light irradiation ( photoelectron ) is defined as " work function" . Thus, only photons with a frequency higher than a characteristic threshold, i.e. with an energy h ( h is the Planck s constant) more than the material s work function, are able to knock out the photoelectrons. Figure 1. An illustration of photoelectron emission from a metal plate : The incoming photon should have an energy which is more than the work function of the material. In fact, the concept of work function in the photoelectric process is similar to the concept of the energy band gap of a semiconducting material. In solid state physics, the band gap g E is the energy difference between the top of the valence band and the bottom of the conduction band of insulators and semiconductors. The valence band is completely filled with electrons, while the conduction band is empty however electrons can go from the valence band to the conduction band if they acquire sufficient energy (at least equal to the band gap energy).The semiconductor's conductivity strongly depends on its energy band gap. Figure 2. Energy band scheme for a semiconductor. Conduction band Unfilled band Filled bands E Energy Band Gap Valence band
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2 Band gap engineering is the process of controlling or altering the band gap of a material by controlling the composition of certain semiconductor alloys. Recently, it has been shown that by changing the nanostructure of a semiconductor it is possible to manipulate its band gap. In this experiment, we are going to obtain the energy band gap of a thin-film semiconductor containing nano-particle chains of iron oxide (Fe 2 O 3 ) by using an optical method. To measure the band gap, we study the optical absorption properties of the transparent film using its optical transmission spectrum. As a rough statement, the absorption spectra shows a sharp increase when the energy of the incident photons equals to the energy band gap. II. Experimental Setup You will find the following items on your desk: 1. A large white box containing a spectrometer with a halogen lamp. 2.
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This note was uploaded on 11/08/2011 for the course PHYS 0000 taught by Professor Na during the Spring '11 term at Rensselaer Polytechnic Institute.

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g_q - Experimental Problem Determination of energy band gap...

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