Roxann Larcia

 WIDE BANDGAP SEMICONDUCTOR About What is WIDE BANDGAP SEMICONDUCTORS? -WIDE BANDGAP SEMICONDUCTORS (WBGS) are semi conductor materials which have a relatively large band gap compared to typical semiconductors.They are semi conductor materials that permit devices to operate at much higher voltages, frequences and temperatures than conventional semi conductor materials like silicon and gallium arsenide.They are the key component used to make green and blue- LEDs and lasers,and are also used in certain radio frequency applications,notably military radars. ULTRA- WIDE BANDGAP SEMICONDUCTOR (UWBGS) materials are a subset of WBGS and are defined as those WBGS materials which have a bandgap above that of GaN,which is 3.4 eV. This includes materials such as diamond,gallium oxide,Algan and AIN. UBWGS materials have the potential to support the realization of devices with even higher levels of performance than that the devices based on Si, GaAs,SiC or GaN. What is BANDGAP? -BANDGAP refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. Importance WIDE BANDGAP SEMICONDUCTORS operate at high temperatures, frequencies and voltages helping to eliminate up to 90 percent of the power issues in electricity conversion compared to current technology.This in return means that power electronics can be smaller because they need fewer semi-conductor chips, and the technologies -like electric vehicle chargers, consumer appliances and LEDs, will perform better be more efficient and cost less. It’s materials have superior electrical characteristics compared with Si. Some of these characteristics are tabulated for the most popular wide bandgap semiconductors. What are the important wide bandgap Semiconductors? 1. Silicon carbide Silicon Carbide also known as caborundum, is a semiconductor containing silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. 2. Silicon dioxide Silicon Dioxide also known as Silica, is an oxide of silicon most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. 3. Aluminum nitride Aluminum Nitride is a nitride of aluminum. It’s wurtzite phase is a wide band gap semiconductor material, giving it potential application for deep ultraviolet optoelectronics. 4. Gallium nitride Gallium Nitride is a binary III/V direct bandgap semiconductor commonly used in light-emmiting diodes since the 1990s. The compound is a very hard material that has a wurtzite crystal structure. 5. Boron nitride Boron Nitride is a heat and chemically resistant refractory compound of boron and nitrogen with the chemical formula BN. It exists in various crystalline forms that are isoelectronic to a similarly structured carbon lattice. 6. Diamond Diamond is a metastable allotrope of carbon atoms are arranged in variation of the face- centered cubic crystal structure called diamond lattice. What Is the advantage of band semiconductor? -Wide Band Gap Semiconductors over Si, in power electronics include lower losses for higher efficiency, higher switching frequencies for more compact designs, higher operating temperature ( far beyond 150degree celsius , the approximate maximum of Si) robustness in harsh environments, and high breakdown voltages. WHAT IS DIRECT AND INDIRECT BAND GAP SEMICONDUCTOR? 1.DIRECT band-Gap semiconductor (dbg) A DBG semiconductor is one in which the maximum energy level of the valence band aligns within the minimum energy level of the conduction band with respect to momentum. In DBG semiconductor, a direct recombination takes place with the release of the energy equal to the energy difference between the recombining particles. The efficiency factor of a DBG semiconductor is higher. Thus, DBG conductors are always preferred over IBG for making optical sources. Example: Gallium Arsenide ( GaAs) 2. Indirect band-gap semiconductor ( ibg) An Indirect band-gap(IBG) semiconductor is one in which the maximum energy level of the conduction band are misaligned with respect to momentum. In case of a IBG semiconductor, due to relative difference in the momentum, first, the momentum is conserved by released of energy and only after the both the momentum align themselves, a recombination occurs accompanied with the release of energy. The probability of a radiative recombination is comparatively low. The efficiency of the IBG semiconductor is lower. Example: Silicon and Germanium Applications High power applications The high breakdown voltage of wide band-gap semiconductors is a useful property in high power applications that require large electric fields. Devices for high power and high temperature applications have been developed. Both gallium nitride and silicon carbide are robust materials well suited for such applications. Due to its robustness and ease of manufacture, semiconductors using silicon carbide are expected to be used widely, creates simplier and higher efficiency charging for hybrid and all electric vehicles, reduced energy loss and longer life solar and wind energy power converters and elimination of bulky grid substation transformers. Cubic boron nitride is used as well. Most of these are for specialist applications in space programmes and military systems. They have not begun to displace silicon from its leading place in the general power semiconductor market. Light emitting diodes In the near future, white LEDs with the features of more brightness and longer life may replace incandescent bulbs in many situations. The next generation of DVD players ( The Blue-ray and HD DVD formats) uses GaN based blue lasers. Transducers Large piezoelectric effects allow wide band gap materials to be used as transducers. Hemt Very high speed GaN uses the phenomenon of high interface-charge densities. Due to its cost, aluminum Nitride is so far used mostly in military applications. Band gap discontinuity When wide band gap semiconductors are used in heterojunctions band discontinuities formed at equilibrium can be a design feature, although the discontinuity can result in complications when creating ohmic contacts. Thermal properties Silicon and other common materials have a bandgap on the order of 1 to 1.electrovolt (eV), which implies that such semiconductor devices can be controlled by relatively low voltages. However, it also implies that they are more readily activated by thermal energy, which interferes with their proper operation. This limits silicon based devices to operational temperatures below about 100 °C, beyond which the uncontrolled thermal activation of the devices makes it difficult for them to operate correctly. Wide-bandgap materials typically have bandgaps on the order of 2 to 4 eV, allowing them to operate at much higher temperatures on the order of 300 °C. This makes them highly attractive in military applications, where they have seen a fair amount of use. Melting temperatures,thermal expansion coefficients and thermal conductivity can be considered to be secondary properties that are essential in processing, and these properties are related to the bonding in wide bandgap materials. Strong bonds result in higher melting temperatures and lower thermal expansion coefficients. A high  Debye temperature  results in a high thermal conductivity. With such thermal properties, heat is easily removed. Semiconductor devices Semiconductor devices are electronic components that exploit the electronic properties of semiconductor material, principally silicon, germanium and gallium arsenid, as well as organic semiconductors.Semiconductor devices have replaced the thermionic devices (vacuum tubes) in the most applications. They use electronic conduction in the solid state as opposed to the gaseous state of thermionic emission in a high vacuum. Semi conductor devices are manufactured both as single discrete devices and as integrated circuits ( Ics),which consist of a number- from a few (as low as two) to billions-of devices manufactured and interconnected on a single semiconductors substrate, or water. Semiconductor materials are useful because their behavior can be easily manipulated by the addition of impurities, known as doping. Semiconductor conductivity can be controlled by the introduction of an electric or magnetic field, by the exposure to light or heat, or by the mechanical deformation of a doped monocrystalline grid; thus, semiconductors can make excellent sensors. Current conduction in a semiconductor occurs via mobile or free electrons and holes, collectively known as charge carriers. Doping a semiconductor such as silicon with a small proportion of an atomic impurity,such as phosphorus or boron, greatly increases the number of free electrons or holes within the semiconductor. When a doped semiconductor contains excess holes it is called “p-type”, and when it contains excess free electrons it is known as “n-type”, where p (positive for holes) or n (negative for electrons) is the sign of the charge of the majority mobile change carriers. The semiconductor material used in devices is doped under highly consoled conditions in a fabrication facility, or fab, to control precisely the location and concentration of p- and n-type dopants. The junctions which form where n-type and p-type semiconductor join together are called p-n junctions. Diode A semiconductor diode is a device typically made from a single p–n junction. At the junction of a p-type and an n-type semiconductor there forms a depletion region where current conduction is inhibited by the lack of mobile charge carriers. When the device is forward biased (connected with the p-side at higher electric potential than the n-side), this depletion region is diminished, allowing for significant conduction, while only very small current can be achieved when the diode is reverse biased and thus the depletion region expanded. Exposing a semiconductor to light  can generate electro-holes pair, which increases the number of free carriers and thereby the conductivity. Diodes optimized to take advantage of this phenomenon are known as photodiodes. Compound semiconductor diodes can also be used to generate light, as in light-emitting diodes  and laser diodes.