Energy band gap of pn junction diode pdf

Light emitting diode led working, construction and. A steadystate balance of carriers is achieved at the junction where diffusive flux of the carriers is balanced by the drift flux. Electrons and holes reach an equilibrium at the junction and form a depletion region. Experimental estimation of the band gap in silicon and. Energy band diagram at thermal equilibrium at thermal equilibrium energy band diagram of a pn junction in thermal equilibrium while in thermal equilibrium no external voltage is applied between the ntype and ptype material, there is an internal potential, f, which is caused by the workfunction difference between the ntype and ptype pn. A complete treatment of the problem shows that io is proportional to the factor f given by 2 where e g is the energy gap to be determined in this experiment. Semiconductor, silicon, pn junction, forward bias, reverse bias, diode.

Band gap in a semiconductor diode the band gap is one of the most important characteristics in a semiconductor. The temperature dependence of the band gap energy in silicon. A diode is a simple device, which can be implemented by a pnjunction, as well as other heterojunction structures. The concentration of these carriers is dependent upon the energy band gap. Because when reversed biased the band gap increases to its maximum size there is no conduction possiblenow it will require some energy to break this band gap and allow conduction through this insulator, which is basically the energy gap of dio. Valence band p n forming a pn junction electrons continue to diffuse across the junction. Insert the thermometer and the diode inside the holes of the over, where the pn junction diode is kept. It is the width of this energy gap that makes a semiconductor a semiconductor. The cathode emits electrons and the anode will attracts the emitted electrons when it is supplied by positive potential q.

Review, pn junctions, fermi levels, forward bias prof j. E v to be positive if e v,n diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity. A method for determining the band gap in germanium and silicon at 0 k based upon the temperature dependence of the electrical conductivity of a pn junction is described. The diode consists of two electrodes one is cathode and another is anode. The term band gap refers to the energy difference between the top of the valence outer electron band and the bottom of the conduction free. The band gap of a semiconductor is the minimum energy required to excite an electron that is stuck in its bound state into a free state where it can participate in conduction.

In this video, i go over the band diagram of the pn junction, which will allow us to find the electric field and the pn junction width through what is called the builtin potential vbi. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. A pn junction is formed when two types of semiconductors, n type excess electrons and p type excess holes, come into contact. Consider the silicon pn junction diode below, maintained at 300k with a forward bias. A pnjunction diode is formed when a ptype semiconductor is fused to an ntype semiconductor creating a potential barrier voltage across the diode junction the effect described in the previous tutorial is achieved without any external voltage being applied to the actual pn junction resulting in the junction being in a state of equilibrium. Forward bias current flows reverse bias no current flow. These two characteristics of the schottky diode make it very useful in highspeed switching power circuits. Energy engineering courses at the undergraduate and postgraduate levels. The band gap of a semiconductor is the minimum energy required to excite an electron that is stuck in its bound state into a free state where it can participate in. The electrical conductivity of all materials, whether insulators, semiconductors or conductors. What is the currentvoltage characteristic for the pn junction diode. Pdf estimating pn diode bulk parameters, bandgap energy and. Band diagram of a heterojunction pn diode under flatband conditions the flatband energy band diagram of a heterojunction pn diode is shown in the figure below. The region on the left is ptype with an acceptor density n a, while the region on the right is ntype with a donor density n d.

Doped semiconductors ntype materials ptype materials diodes and transistors. Schottky diode can switch on and off much faster than the pn junction diode. Why diode is reverse biased in determining the energy gap. The pn junction is an important element of most electronic devices, from a simple diode to a transistor. In this experiment you will use the temperaturevoltage curve of a diode under constant current to determine the band gap for the diode material. The dopants are assumed to be shallow, so that the electron hole density in the ntype ptype region is approximately equal to the donor acceptor density. Energy band gap apparatus containing micrometer, voltmeter, temperature controlled electric oven to heat up the diode, pn junction. For a pn junction at equilibrium, the fermi levels match on the two sides of the junctions. The electric field results from the deviation from charge neutrality in the vicinity of the junction.

As you can see, the valence and conduction bands in the n region are at lower energy levels than those in the p region, but there is a significant amount of overlapping. Chapter 1 semiconductor pn junction theory and applications. Forward and reverse characteristics of a pnjunction diode from sze introduction to radiation detectors and electronics, 01apr99 helmuth spieler ix. The pn junction biasing the pn junction the diode trouble shooting. When light emitting diode led is forward biased, free electrons in the conduction band recombines with the holes in the valence band and releases energy in the form of light. Energy gap of a semiconductor engineering physics viva. Pdf the band gap energy eg in silicon was found by exploiting the linear. Energy band gap kit containing a pn junction diode placed. A junction diode is formed when a ptype semiconductor is in intimate contact with ntype semiconductor. Most semiconductor devices involve regions with two different kinds of doping, so a pnjunction is present in all of them. Also, the schottky diode produces less unwanted noise than pn junction diode.

A pn junction consists of two semiconductor regions with opposite doping type as shown in figure 4. A direct band gap means that the minimum of the conduction is. In solidstate physics of semiconductors, a band diagram is a diagram plotting various key electron energy levels fermi level and nearby energy band edges as a function of some spatial dimension, which is often denoted x. A pn junction is said to be forward biased when pregion is connected to positive terminal and n. That implies that you would have to supply energy to get an electron to go up on the diagram, and supply energy to get a hole to go down. Plug the main lead to the nearest mains socket carrying 230 volts. The pn junction is the basic structure of solar cell, lightemitting diode, and diode laser, and is present. The term pn junction refers to the joint interface and the immediate surrounding area of the two semiconductors. Schematic diagram of the energy band structures in metals, semiconductors and insulators. Smith department of eecs university of california, berkeley. To determine the energy band gap of a semiconductor by using pn junction diode. These diagrams help to explain the operation of many kinds of semiconductor devices and to visualize how bands change with position band bending. Working of pn junction diode if an external potential is applied to the terminals of pn junction, it will alter the potential between the p and nregions. The band diagrams of 1 and 2 by themselves are shown below.

It might seem that io could be determined by a simple measurement with a negative bias applied to the junction. The process of emitting light in response to the strong electric field or flow of electric current is called electroluminescence. To plot characteristics between reverse saturation current and 10 3t and find out the approximate value of energy band gap in pn junction diode apparatus. The pn junction insulator semiconductor conduction band valence band energy gap metal occupied states empty states figure 16. A semiconductor device primer doping and diodes lbnl 11 note that in the diode equation a the band gap does not appear explicitly o nly implicitly. Energy band gap kit containing a pn junction diode placed inside the temperature controlled electric oven, microammeter, voltmeter and connections brought out at the socket, a mercury thermometer to mount on the front panel to measure the temperature of. The two semiconductors are not necessarily the same, e. Once carriers are in the conduction band they can participate in conduction. When a pn junction is reverse biased then current is due to minority. The area of the ptype near the junction becomes more negative due to the excess electrons while the ntype. This potential difference can alter the flow of majority carriers, so that the pn junction can be used as an opportunity for the diffusion of. An energy diagram for a pn junction at the instant of formation is shown in figure a. The gap between conduction band and the valency band is called.

Physics stack exchange is a question and answer site for active researchers, academics and students of physics. Working of pn junction diode with biasing, characteristics. The band structure of a semiconductor gives the energy of the electrons on the yaxis and is called a band diagram. I wanted to know the relationship between the band gap eg of the pn regions in a diode and the built in potential in equilibrium. A diode is also used as a temperature sensor 5, in which the linear relationship between the temperature, and the forward voltage drop across the pn junction, v. The upward direction in the diagram represents increasing electron energy. He is also a consultant to industry where he provides expert advice in the optimisation of renewable energy systems. Here dec is the change in the energy of the conduction band across the junction.