The Hall effect

Diffraction, the spreading of waves around obstacles. Diffraction takes place with sound; with electromagnetic radiation, such as light, X-rays, and gamma rays; and with very small moving particles such as atoms, neutrons, and electrons, which show wavelike properties. One consequence of diffraction is that sharp shadows are not produced. The phenomenon is the result of interference (i.e., when waves are superimposed, they may reinforce or cancel each other out) and is most pronounced when the wavelength of the radiation is comparable to the linear dimensions of the obstacle. When sound of various wavelengths or frequencies is emitted from a loudspeaker, the loudspeaker itself acts as an obstacle and casts a shadow to its rear so that only the longer bass notes are diffracted there. When a beam of light falls on the edge of an object, it will not continue in a straight line but will be slightly bent by the contact, causing a blur at the edg...

Quantum mechanics, sciencedealing with the behaviour of matterand light on the atomic and subatomic scale. It attempts to describe and account for the properties of molecules and atoms and their constituents—electrons, protons, neutrons, and other more esoteric particles such as quarks and gluons. These properties include the interactions of the particles with one another and with electromagnetic radiation (i.e., light, X-rays, and gamma rays). The behaviour of matter and radiation on the atomic scale often seems peculiar, and the consequences of quantum theory are accordingly difficult to understand and to believe. Its concepts frequently conflict with common-sense notions derived from observations of the everyday world. There is no reason, however, why the behaviour of the atomic world should conform to that of the familiar, large-scale world. It is important to realize that quantummechanics is a bra...

The Big Bang Theory is the leading explanation about how the universe began. At its simplest, it says the universe as we know it started with a small singularity, then inflated over the next 13.8 billion years to the cosmos that we know today. Because current instruments don't allow astronomers to peer back at the universe's birth, much of what we understand about the Big Bang Theory comes from mathematical formulas and models. Astronomers can, however, see the "echo" of the expansion through a phenomenon known as the cosmic microwave background. While the majority of the astronomical community accepts the theory, there are some theorists who have alternative explanations besides the Big Bang — such as eternal inflation or an oscillating universe. The phrase "Big Bang Theory" has been popular among astrophysicists for decades, but it hit the mainstream in 2007 when a comedy show with the same name premiered on CBS. The show follows the home and...

Zener breakdown: A strong reverse-bias applied to a p-n junction leads to high reverse current. When the increasing reverse bias attains a certain value, the junction breaks down and reverse current rises sharply. This specific value of the reverse bias voltage is called breakdown voltage (v z ). The breakdown voltage depends upon the width of depletion layer, which in turn depends upon the doping concentration. Zener Breakdown: Zener breakdown occurs in heavily doped p-n junction diodes which have strong electric field across a thin depletion region. This field breaks the covalent bonds and generates electrons which are pulled into the conduction band and become available for conduction. Minority carrier thus generated quantum mechanically tunnel through the thin depletion layer. As the number of such free electrons becomes large, the reverse current through the Zener diode is b...

Fabrication of p-n junction: Thermal Oxidation: Thermal oxidation is a technique that uses high temperature (700- 1300 o C) for growing the layer of silicon dioxide (SiO 2 ) on the substrate silicon. In thermal oxidation, silicon substrate is exposed to an oxidizing environment of O 2 or H 2 O at elevated temperature, producing oxide films whose thicknesses range from 60 to 10000 A o . Silicon has a natural inclination to form a stable oxide even at room temperature, as long as an oxidizing ambient is present. The elevated temperature used in thermal oxidation therefore serves primarily as an accelerator of the oxidation process, resulting in thicker oxide layers per unit of time. Thermal oxidation is accomplished using an oxidation furnace or diffusion furnace, since oxidation is basically a diffusion process involving oxidant species. A furnace typically consists of: 1) a cabinet; 2) a heating system; 3) a temperature measurement and control system;...

Molecular Beam Epitaxy: MBE is non-CVD epitaxial process using evaporation at very low pressures. Using it we can grow high-purity epitaxial layers of compound semiconductors. MBE operates at lower temp than CVD, it minimizes auto-doping, facilitates abrupt interfaces and good control of thickness, doping, and composition. It allows complicated doping profiles that have applications in microwave and photonic devices, e.g. linear doping profile for linear C-V of Varactor diodes, which are used as FM modulators. In a highly evacuated chamber, heat a base material (substrate) such as silicon, germanium, or gallium arsenide to 500 – 600°C. Shoot precise beams of atoms or molecules in gas form (suitably heated) at the substrate from guns called effusion cells. A separate effusion cell is needed for each different beam, shooting a different kind of molecule at the substrate, depending on the nature of the crystal t...