0
A semiconductor has an energy band (a range of energy levels) that is forbidden -- ideally void of charged particles at all temperatures. Practically, at low temperatures (T < 40 K for silicon), the probability of finding a free charge carrier outside the forbidden gap is nearly nil. When the temperature is increased, the probability of finding a free charge carrier outside the forbidden gap increases, but the net charge is still zero (negative charge exactly cancels positive charge). However, an intrinsic semiconductor (pure or undoped) is just a resistor of little importance (other materials are cheaper and better-controlled than a semiconductor).
When we introduce foreign atoms into a semiconductor (the process is called doping), we change its electrical properties -- it has a lot more free charge carriers than an intrinsic semiconductor, although again, the net charge is zero. The total charge of free carriers is balanced by immobile ions of equal and opposite total charge. For example, boron and indium will be used to dope silicon p-type; phosphorus and arsenic will be doping silicon n-type. I am quoting boron, phosphorus, and silicon as examples from hereon.
p-type doping is a process where a silicon atom in the lattice is replaced by a boron atom. A Boron atom has 3 electrons in the outer shell, compared with an electron occupancy of 4 for a silicon atom. So a Boron atom provides a vacancy for any free electrons to occupy with a little effort, when an electron chances to be nearby (the four boron-silicon covalent bonds needs 8 electrons to be stable, but only 7 are provided). The net charge of the material is still zero. More about from where the free electron is coming.
n-type doping is using a phosphorus atom to replace a silicon atom. A phosphorus atom has 5 electrons in the outer shell. So a phosphorus atom provides an electron that can be freed with a little effort (the four phosphorus-silicon covalent bonds only need 8 electrons to be stable, each atom needing only to contribute four electrons; the 9th electron will be loosely bound). The net charge of the material is still zero. Where can the electron go?
Magic happens when a p-type silicon is brought in contact with an n-type silicon to form a pn junction. The excess electron vacancies (holes) in p-Si now can exchange with the excess electrons in n-Si, but the net charge of the p-n silicon entity is still zero. However, microscopically, a depletion region is formed at the pn junction, where excess carriers can cross over to the other side. In the p-Si, excess electrons from the n-Si start filling up the holes (the lack of the 8th outer-shell electron to form the four stable boron-silicon covalent bonds) and negatively-charged boron atoms are formed. In the n-Si, excess holes from the p-Si start swallowing up the loosely-bound electrons (the 9th electron in the outer shell) of phosphorus atoms and positively-charged phosphorus atoms are formed. Once formed, and in the absence of an electric field, the depletion region now presents an energy barrier to any further carrier movement and a steady state results -- no net current in the pn junction.
Add your answer:
Earn +20 pts
Explain the formation of depletion layer in pn junction diode?
hey dear, in p-n junction p-type material has more positive charged called holes and n-side having e-in majority... when we apply negative biasing then negative terminal is connected to p terminal then holes are attracted by negative terminal and e's are attracted by positive terminals.....and minority carries are forced towards junction, then at junction electron and hole pair generation occurs. after this at junction charge is accumulated by attraction and junction is get wider by a small amount that is called as depletion layer...... now you can understand how depletion layer is created..
What causes depletion region across P-N junction?
The presence of mobile and bound charges on either sides of the pn junction causes the depletion layer. A pn junction is formed when a semiconductor is dopped with a pentavalent impurity on one side and a tri-valent impurity on the other side.on one side electrons will be more in number and on the other side holes will be more in number.At the junction the electrons combine with holes and there will be no charge carriers(i.e. electrons and holes) in that region.That region which is free from charge carriers is called depletion region.
How do you control PN-junction?
When a pn junction is direct polarized, the height of the depletion layer is reduced and majority charge carriers now have sufficient energy to cross the junction and when it is revers polarized the height of the depletion layer is increased and the number of majority charge with sufficient energy to cross the junction is cut sharply.
What is difference between early effect and punch through in BJT?
When we apply reverse bias voltage to input and output sides of a BJT, then the width of the depletion layer at emitter-base and base-collection got increased. Due to which the effective base width got decreased. This phenomenon of reduction in the base width is called Early effect. And if we go on increasing the Reverse bias voltage then at a time instant the width of the base becomes zero and this effect is called punch through effect and that reverse bias voltage is called punch through voltage.
Difference between avalanche and zener breakdown?
A: There is no difference except for a zener its breakdown is known and predictable. Avalanche breakdown is not predictable and usually happens at hi voltage and because of it if the current is not limited it self destroy the device
How does doping effect the depletion layer in semiconductor?
Width of depletion layer is given by x = (2*ebsylum*Vb).5/(qN) x = width Vb = potential barrier q = charge of electron N = doping concentration. Thus increase in doping will reduce width of depletion layer.
Where does the charge concentrate in a semiconductor?
In a semiconductor, the charge concentrates at the bounds of the space charge region(depletion layer).
What effect of depletion layer by biasing?
on forward biasing width of the depletion layer decreases whereas on reverse biasing the width of depletion layer increases.
What is the thickness of the depletion layer in a semiconductor?
The thickness of the depletion region or depletion layer (and there are other terms) varies as the design of the semiconductor. The layers in a semiconductor are "grown" (usually by deposition), and this can be controlled. The typical depletion region thickness in an "average" junction diode is about a micron, or 10-6 meters. Junction "construction" presents major engineering considerations to those who design and make semiconductors as there are many different kinds. A link is provided to the section on the width of depletion regions in the Wikipedia article on that topic.
What are the effect of depletion of ozone layer on man?
Depletion of ozone layer causes:Suppression of immune systemSkin cancerEye cataract.
How temperature effects depletion layer width?
As temperature increases, the depletion layer width in a semiconductor decreases due to the increased thermal energy disrupting the balance of charges within the material. This disrupts the formation of the electric field that maintains the width of the depletion layer, causing it to shrink. Conversely, at lower temperatures, the depletion layer tends to widen as charges are less mobile and the electric field is more pronounced.
What is the causes and effect of depletion in the ozone layer?
Depletion of ozone has many causes and effects. The UV entering is the main.
What is the depletion layer in a semi conductor?
in correct sense it is not the layer but the region around the metallurgical junction which is depleted of charge carriers .in this region an internal electric field exist which counter balance the diffusion of electron and hole around the junction . basically the main reason for the formation of depletion region is the concentration gradient across metallurgical junction of p-n semiconductor.
How is the greenhouse effect the cause of the ozone layer depletion?
The greenhouse effect causes ozone depletion. Greenhouse doesn't let the heat escape, causing problems for ozone.
Which layer of the atmosphere is affected the most during Diwali?
The stratosphere. there's a theory call stratospheric ozone depletion that causes the greenhouse effect and global warming and depletion if the ozone layer
Is the depletion of ozone layer related with greenhouse effect?
The depletion of the ozone layer and the greenhouse effect are related but separate issues. The depletion of the ozone layer allows more ultraviolet radiation to reach Earth's surface, leading to increased skin cancer rates and other health problems. The greenhouse effect, on the other hand, refers to the trapping of heat in Earth's atmosphere by greenhouse gases like carbon dioxide, which contributes to global warming. Both issues are important environmental concerns.
How ozone layer is damaged by greenhouse effect?
Global warming causes greenhouse effect. It then causes ozone depletion.
