Nature of an electron - Coursework Example

?QUESTION ONE Photoelectric effect Photoelectric effect is the process by which electrons are emitted from the surface of a photosensitive material when hit by light incidents. The intensity of the light energy determines the kinetic energy of the produced photoelectrons. This is described in a classical wave model of light; which states that light properties that are similar to any wave. For instance, light experiences reflection and refraction in the same manner that any other wave would experience interference. In addition, light experiences the Doppler effect the same way any other wave would experience Doppler effect. However, the prediction of the quantum model shows that frequency or wavelength of the incident of the incident light only affects the photoelectric current. where E- is the energy that the quantum light produces, Kmax is the maximum kinetic energy of the photoelectrom emitted , where as Wo is the work function of the of the energy needed to innitiate the emision of photoelectrons from the metal surface. In an experiment to demonstrate the photoelectric effect, the following apparatus are required: a digital voltmeter to be used to measure the reverse voltage reading, a photodiode connected with an amplifier, monochromatic light source to produce light beams to irradiate the photo cathode, and a filter to neutrally vary the intensity of light. Generally the quantization energy of the electromagnetic radiation in light is given in the relation, where the radiation energy, is a constant known as the Plank’s constant and is given as (6.63?10^-34Js), and - is the frequency of the light incident energy. The validity of the equation is based on the photoelectric effect experiment. There are four aspects that need to be taken into consideration when conducting the photoelectric effect experiment. These facts include: the minimum frequency; when the frequency of the incident light is less than the minimum frequency required, no photoelectrons can be emitted despite the intensity of the light. The value of minimum frequency varies from metal to metal. Secondly, as the frequency of the incident light increases, the kinetic energy of the photoelectrons increases. However, the intensity of the light is independent of the kinetic energy of the electron emitted. And lastly, the emission of photons is effectively instantaneous. (physics 242 laboratory manual) The photoelectric effect experiment consists if a high intensity lamb, a phototube, and batteries. The photodiode tube is the central element of the apparatus. The window in the diode gives way for light into the tube to the clean metal surface at the cathode. The diode is completely evacuated to avoid any collision of air molecules and the electrons. When beams of light hit the surface of the metal plate at the cathode, electrons are emitted by the metal plate. The photodiode has an in-built capacitance developing a voltage during the charging process by the electrons emitted. When the stopping potential of the cathode is reached, the difference in voltage across the two poles, that is, cathode and anode stabilizes. A very sensitive amplifier is used to measure the stopping potential. The amplifier aids in the establishment of the small number of photoelectrons emitted. A voltmeter is used to measure the output voltage of the between the batteries and the output ground terminals. A number of different monochromatic light beams are used for the experiment. A glass tube consisting of mercury vapor produces light when discharged electrically. The glasses envelop filters out the ultraviolet light that can be harmful. The mercury light produces five thin spectral lines that are: yellow, green blue, violet, and ultraviolet in the visible region. These lines can be spatially separated by diffraction. The wavelength desired is selected using a collimator, and the intensity of the selected wavelength is varied using a density filter The mercury lamb is switched on. On the front reflective mask of the lamb box, yellow, green, and tiny rays of blue spectral lines can be seen when viewed at different angles. A digital voltmeter is connected to the output terminal of the photodiode. The photodiode is then pushed to zero to enable shorting out of any charges accumulated on the electronics. In the absence of light, he output shuts. The voltage on the output of the photodiode is recorded which gives the measurement of the stopping potential. For yellow and green mercury lights, yellow and green filters are used. The filters remove ambient room light and block high frequency lights and any ultraviolet light. The graph of the stopping potential against various light intensities can e plotted. The nature of wave electrons The particle properties of light were considered to a phenomenon of the wave length in the photoelectric effect, Louis DeBroglie therefore sought to find out whether electrons and other particles may exhibit wave properties. The hypothesis supporting this wave properties of electrons are the discrete atomic energy levels and the diffraction of electrons from crystal planes in concrete materials. In the bohr model of atomic energy levels, the electron waves is seen wrapping around the perimeter of the electron orbit such that they experience constructive interference. Thomas young coined the term interference to explain the generation of dark and bright fringes in the region on the observation plane where the light provided by the two openings was superimposed. This became a paradigm for proving the wave nature of any physical phenomenon Debroglie notes that an experiment revealing the occurrence of a super position is called an interference experiment. Elements such as atoms, neutrons and large molecules are said to have wave properties. The properties of electrons are that they have to be brought into play to explain the actions of electrons when restricted to elements on the classification of the size of the atom. The experiment in this case is that done by Thompson on which independently by Davisson and Gerner demonstrated the Debroglie hypothesis regarding the existence of electron waves. The interference effects normally are observed when an incoming beam is split into two coherent parts which are consequently made to superimpose on a detector. The realization of the interference test is based on the accessibility of an electro-optical bench and a devise for beam splitting. The wavelength value of a baseball was explored and was found out that the Debroglie wavelengths are small. In comparison to the power of ten, it was found out that the wavelength of ordinary objects are much smaller to a nucleus and therefore, for ordinary objects, one will never see their wavelength nature and consequently. For practical purposes, they are considered as particles. The wavelength associated with particles is calculated from the multiplication of mass and velocity (Solymar & Walsh, 2009). The hypothesis of Debroglie on diffraction as demonstrated by the experiments of Germer, Thomson and Davisson, an electron beam diffracts when crossing a single crystal, this is so because, the coherent patch on the beam of electrons exceeds the distance between the lattice planes of the crystal, the spots on the diffraction pattern will be spatially coherent. The spot size of the primary electron beam that illuminates the crystal figure assures this coherent condition. It plays the role of the small light source, introduced by young in the Grimaldi arrangement. The two openings in the Young experiment perform a division of the light wave front to produce the interfering sources by the use of crystal and the aperture at the BF plane. The crystal acts as a diffraction grating that produces a spot pattern. After the selection of two spots as interfering sources Production of an electron pole pair A natural semiconductor is a pure semiconductor lacking any species that are dopant. A semiconductor is defined as those materials whose electrical property lies between those of the conductors and insulators (Singh, 2012). The semiconductor element is determined by the properties of the material rather than the quantity of impurities and thus explains the figure of charge carrier (Sze, 1981). Therefore, the number of charged electrons and holes are equal, as in, the figure of electrons in the conduction group equals the number of holes in the valence group. An indirect band gap natural semiconductor, is defined as the one in which, the greatest energy of the valence group does occur at a different space wave vector than the least amount of energy in the conduction band, for example, silicon In the normal silicon pattern, if the temperatures are exceeding absolute zero, some electrons in the band group that will be excited into the conduction band and this supports the flow of current. When the electron crosses the band, then an electron hole is created in the normal pattern of silicon. This is so as, when influenced by an external voltage, both the hole and the electron moves across the silicon. Therefore, in the n-type, the intrinsic semiconductor adds extra electrons and in the p- type, the semiconductor produces extra holes which in both cases increase conductivity ( Li, 2006) The p-types semiconductor is obtained by the introduction of pentavalent impurities like phosphorous, and antimony. They are also called acceptor impurities because they give positive carriers because; they create holes which can accept electrons. The n- type semiconductor is obtained by introducing trivalent impurity atoms like indium and gallium. They are also called donor impurities because they donate the excess electrons and therefore called donor impurities. The key to the solid state electronic devices is the p-n junction (Kittel, 2004) The flow of currents through a p-n junction The p-n junction is fashioned by fusing the p and n-type semiconductors as one in close contact. The name junction is the periphery crossing point where the two regions of the semiconductors meet. They are effortlessly created particularly in a crystal of semiconductors by doping. The link of an external electrical energy source to the p-n junction is called the biasing of the p-n junction. There are two main types of biasing a p-n junction, first is the forward bias and second is the reverse bias. The p-n junction is said to be forward biased when the positive terminal is of the peripheral supply is linked to the p region and the negative to the n region. In the forward biased condition, the p-n region offers a very low resistance and a large amount of current flows through it (Salivahanan, Kumar & Vallavaraj, 1998). The p-n junction is said to be reverse biased when the positive terminal of the external supply is connected to the n type and the negative terminal to the p type. In this condition, the p-n region offers very high resistance and therefore a very small amount of current passes through it, At zero bias, the flow of current through the p-n junction, the Fermi levels match on the two sides of the junction. When the holes and electrons meet and reach symmetry at the junction, it forms a depletion region. The depletion region is caused when two layers of positive and negative charges are made and the region near the junction is depleted of charge carriers. The upward direction represents an increase in the energy of electrons meaning that one has to supply energy to get an electron to progress up as demonstrated in the diagram and also supply energy to get a hole to set out downward. The valence and conduction band material of a p- type are slightly higher than that of the n-type. As diffusion occurs, the depletion region forms and the energy levels of the n region conduction band drops, causing alignment of the top of the n region conduction band, and the bottom of the p region conduction band. Here the energy bands are at symmetry. An energy gradient across the depletion region that a n region electron must climb to get to the p region At reverse bias, the p-n junction, the p side is made more negative making it an uphill for electrons moving across the junction meaning that there is an increase in the energy of electrons. while the n side is made more positive making it a downhill for holes moving across the junction. It is worth noting that the conduction direction for electrons in the diagram is right to left as demonstrated in the diagram below At forward bias conditions, the P-n junction, the p side is made more positive such that its a downhill for electron motion across the junction. An electron can move across the junction and fill a hole near the junction. In addition, it can move from hole to hole leftwards towards the positive terminal which in this case is the hole moving right. The direction of conduction for electrons as demonstrated in the diagram is from right to left and the upward direction is a representation of an increase in the levels of electron energy. When the p-n junction is biased forward, the electrons in the n-type material which have been elevated to the conduction band and which have diffused across the junction find themselves at a higher energy than the holes in the p type material. They readily combine with the holes ensuring a continuous current moving forward through the junction. A forward current in a p-n junction involves electrons in from the n-type material moving leftward across the junction and combining with the holes in the p- type materials. The electrons further proceed leftward by jumping from hole to hole and therefore, it can be said that the holes move to the right in this process. The voltage drop in the p-n junction is due to the energy loss in an effort to overcome the barrier potential. References Kittel, Ch. (2004). Introduction to Solid State Physics. John Wiley and Sons. ISBN 0-471-41526- X. Li, S. S. (2006). Semiconductor physical electronics with 230 figures. New York, Springer. http://public.eblib.com/EBLPublic/PublicView.do?ptiID=324556. Salivahanan, S., Kumar, N. S., & Vallavaraj, A. (1998). Electronic devices and circuits. New Delhi, Tata McGraw-Hill. Singh, R. J. (2012). Solid state physics. New Delhi, Dorling Kindersley. http://proquest.safaribooksonline.com/?fpi=9789332514812. Solymar, L., & Walsh, D. (2009). Electrical properties of materials. Oxford, Oxford University Press. http://public.eblib.com/EBLPublic/PublicView.do?ptiID=472176. Sze, Simon M. (1981). Physics of Semiconductor Devices (2nd ed.). John Wiley and Sons (WIE). ISBN 0-471-05661-8. Read More