In this lecture, i discussed about the energy band diagram of the pn junction in equilibrium. A pn junction consists of two semiconductor regions with opposite doping type as shown in figure 4. A study on the band structure of znocds heterojunction. Electrons and holes reach an equilibrium at the junction and form a depletion region. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone. Valence band p n forming a pn junction electrons continue to diffuse across the junction. Valence band conduction band forming a pn junction once in the ptype they can drop down into the valence band and to fill up one of the hole states. The electric field results from the deviation from charge neutrality in the vicinity of the junction.
Band diagram of pn junction under a equilibrium and b forward bias. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode. Which can be understood from the energy band diagram shown above. The region around m contains the space charge layer scl. This project neglects band gap narrowing due to heavy doping levels. Advanced discussion about pn junction, especially focus on the affect of the depletion region in energy band diagram. A diode is a simple device, which can be implemented by a pnjunction, as well as. There is a builtin voltage at the pn junction interface that prevents penetration of electrons into the pside and holes into the nside. Zero bias no external voltage potential is applied to the pn junction diode. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction.
Within the band structure model, even under the effect of an external electric field, filled. Depending on how the junction is biased, current may easily flow between the diode terminals forward bias, v d v on or the current is essentially zero reverse bias, v d files. Band structure of open circuted pn junction study buddy. I attach a pdf file of one of my lectures where i explain this stepbystep. Energy band diagram of a pn junction a before and b after merging the ntype and ptype regions note that this does not automatically align the fermi energies, e f,n and e f, p. E c and e v are known relative to e f nregion pregion a e f c e c e v e f b e c e f e v e v e c d depletion. A steadystate balance of carriers is achieved at the junction where diffusive flux of the carriers is balanced by the drift flux.
A few factors determine the probability of electrons in the valence band jumping up to. Hence comparing the schematic symbol to the pn junction in figure 4, we see the anode is the ptype semiconductor and the cathode is the ntype semiconductor. While fermi levels line up in equilibrium in the presence of an external. At the left and right boundaries, metal contacts are connected to the gaas semiconductor i. The constant of integration is determined by setting e 0 at xx. Exploring the valenceband structure by ups technique a intensityenergy curve, b energyband diagram. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. At t 00, semiconductor materials have basically the same structure as. For a pn junction at equilibrium, the fermi levels match on the two sides of the junctions.
The band structure is crucial to understanding properties of. The area of the ptype near the junction becomes more. Review, pn junctions, fermi levels, forward bias prof j. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can lower their energy by crossing the junction. Silicon, select a folder for the project, click ok and then open to start the project in the quantumatk main window, click on the icon to open the builder in the builder, go to the stash, click add. Physics stack exchange is a question and answer site for active researchers, academics and students of physics. In this pn junction, the entire band gap offset between gan and aln 2. Energy band diagram of a pn junction in thermal equilibrium. The difference between an insulator and a semiconductor lies in the size of the bandgap. Figure out the movement of charge carriers in a crystal.
The intrinsic carrier concentration nie then is only modeled as a function of temperature as shown below. While in thermal equilibrium no external voltage is applied between thentype andptype material, there is an internal potential,f, which is caused by the workfunction difference between thentype andptype. A pn junction band diagram when the two semiconductors are in contact. 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. Polarizationinduced pn diodes in widebandgap nanowires. The pn junction is the fundamental building block of the electronic age. 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.
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. The upward direction in the diagram represents increasing electron energy. These diagrams help to explain the operation of many kinds of semiconductor devices and to visualize how bands change with position band bending. Energy band diagram of a pn junction a before and b after merging the ntype and ptype regions. The structure is ptype doped from 10 nm to 160 nm and ntype doped from 160 nm to 310 nm. A pn junction of two different materials in the open circuit case. The energy band diagram of the pnjunction duration. Silicon a single silicon atom consists of fourteen negatively. Forming a pn junction doping one side of a piece of silicon with boron a ptype dopant and the other side with phosphorus an ntype dopant forms a pn junction. If we join a piece of p type material to a pieceof n type material such that the crystalstructure remains continuous at the boundary, a pn junction is formed 2. At t 00, semiconductor materials have basically the same structure as insulators. Semiconductors, diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity. Part ii introduction to physical electronics openstax.
Extraction of the eg of zno using the transmittance measurement results a extraction of cutoff wavelength by the linear extrapolation, b location of the maximum first derivative. Open quantumatk and create a new project by clicking on create new. Photocurrent in a silicon pn junction quantumatk q2019. The diffusion forms a dipole charge layer at the pn junction interface. 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. E f is constant at equilibrium e c and e v are smooth, the exact shape to be determined.
Doped semiconductors ntype materials ptype materials diodes and transistors. Transport in a pn junction for b 0 massless dirac hamiltonian with a uniform electric field. Thermal equilibrium, carrier concentrations lecture. Ee lecture handouts pdf format download adobe acrobat to read pdf files. The difference between an insulator and a semiconductor lies in the size of the bandgap eg. On the nside of m, scl has the exposed positively charged donors, whereas on the pside it has the exposed negatively charged. P type and n type semiconductors, takenseparately are of very limited use. Ee lecture notes university of california, berkeley. Diode schematic symbol and actual picture of a common 1n914 diode the black stripe in the picture is the cathode. The figure below shows a simplified structure of a pn junction. Bjt structure and operational modes recall that the semiconductor diode is simply a pn junction.
While the doping in the nepilayer can be uniform, the doping in the pregion is often either gaussian or errorfunction in nature. The area of the ptype near the junction becomes more negative due to the excess electrons while the ntype. Figure 1b shows energy bandedge diagrams for a gaaseras pn junction and a gaasonly pn junction, obtained by numerical solution of poissons equation in one dimension. This large barrier prevents electrons and holes from overshooting the active region, thus providing builtin electron and hole blocking. 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. The circuit schematic symbol of a diode is shown in figure 5. However, the structure of these energy levels is the same for all atoms. Formation of a pn junction diode and its band diagram. Conductivity and structure of eras nanoparticles embedded. 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. The structure can be fabricated by diffusing ptype impurity in the nepilayer grown over an substrate. A silicon pn junction in thermal equilibrium at t 300 k is doped such that e fe fi 0. Band structure of open circuted pn junction youtube.