[Music] hello everyone this is ami patel welcome to online session in this video i am going to discuss about p injention diode ok then let us begin so these are the contents included in this video we will begin our discussion with the types of material then we will discuss the different types of semiconductor material next i will give brief idea about the basic circuit elements like resistor capacitor and inductor then we will see pn junction diode biasing of p-n junction diode and p-n junction diode characteristics so let us begin with the types of material there are the three types of materials that is a metal semiconductor and insulator this figure on screen shows the energy band diagram of this materials it has mainly two bands one is the conduction band and the another one is the valence sign so conduction band is having free electrons whereas the valence band does not or we can see the electrons which are bonded into the covalent bond are said to be in the valence band in metal we see the overlapping of conduction band and the valence band in semiconductor there is a small gap between the conduction and the valence band and at last in insulator you can see there is a large amount of hair between the conduction and the valence band so if we apply some amount of external feed or voltage to the semiconductor material then the electrons bonded in the covalent bond will acquire the external energy and that will get free so semiconductor materials are widely used in the fabrication of the electronic devices because its conductivity can be changed by applying the external voltage external feed and the many other sources like heat or light now we will see what are the types of semiconductor material the first is intrinsic semiconductor it is chemically pure and possesses poor conductivity in intrinsic semiconductor there are equal amount of or equal number of electrons and holes in this type of semiconductor the you can see very small amount of current is flowing and that is due to the thermal agitation second is the extrinsic semiconductor when we are adding impurities it can be trivalent or pentavalent impurity to the intrinsic semiconductor by the process called dopamine it becomes the extrinsic semiconductor the number of electrons and holes in extrinsic semiconductors are not equal next we will see the basic circuit element the first figure is the resistor that is a snapshot of the resistor or other actual resistor the resistor opposes the flow of current or rather it is used to control the current so basically resistor is used in the circuit to control the current this next figure is the symbol of resistor next is the capacitor and capacitor stores the electric charge so next is the symbol of the capacitor next figure is the actual snapshot of an inductor it is also referred as a coil so inductor stores the energy in the magnetic field when the current pass through it so next is the symbol of an inductor so these this is about the basic circuit elements which we are going to use uh frequently in this subject next we will see the pn junction diode this video is about the construction and operation of pn junction diode what is p-n junction diode it is a device which allows the flow of current in one direction whereas it blocks the current in the other direction for example these are the two points so p-n junction diode is a device which will allow the current to flow from here to here and it will block the current from in the opposite direction that is from this point to this point so it is a unique polar device so next figure is the physical construction of the p-n junction diode in which you can see p-type and n-type material or p-type and n-type semiconductor material brought together and joined together rather and it forms the junction that's why it is referred as a pn junction diode now in this the peak side terminal is referred as an anode terminal and the end side terminal is referred as a cathode terminal this is the next that is the symbol of pn junction diode you can see there is a triangular shape and in this this is a symbolic representation which we are regularly using in the circuit so represent the p junction diode in the circuit on paper we are using this particular symbol so in this the flat side of the triangular is the inner terminal and the opposite side is the cathode terminal so next figure shows the printed circuit board and of actual and on that you find the actual components you find number of pn junction diodes onto that which is of black color and at the one terminal you will find silver ring so the terminals are shown in the figure so silver color green is the cathode terminal and the opposite terminal is the anode terminal so when you are having the actual p-n junction diode physical diode then you must be able to identify which are the terminals anode and cathode so silver ring terminal is the cathode one and the other one is the anode terminal now we will see what happened when pn junction forms so when n-type and p-type material brought together then the junction is formed but what is happening when these two different types of semiconductor material materials brought together the electrons which is the majority charge carriers on uh in the n side or n-type semiconductor and holes are the majority charge carrier of p-type semiconductor this carriers will cross the junction this process is called the diffusion so electrons are moving from n side to p side and holes are moving from p side to end side electrons moves from n side to p side so the donor ion on n side becomes positively charged so positive charge build on the n side at the junction and as electrons now reach to the p side and it feels the position of the holes so there the ions becomes negatively charged you can say potential difference is generated at the junction which is having the polarity such that on n side at the junction we are having positive charge and on p side at the junction we are having negative charge near the junction a region created which has ions only and no free carriers this region is called the depletion region or the space charge region that this you can see in the figure over here so ah this is shown in the next figure also the whole process of you can say definition region creation is shown over here in this figure so here the p and n type material brought together electrons and holes are migrated or they are crossing the junction and the depletion region is formed and potential differences being generated now we will see biasing of pn junction diode what is bias application of external dc voltage across the p junction diode is called the bias we can connect the dc source to the p-n junction diode into different manner you can see in the figure that the first one is where we are connecting anode to the positive terminal of the battery and cathode to the negative terminal of the battery so this type of connection is referred as a forward bias or forward biasing of p injection diode and the another ways where we are connecting anode to the negative terminal of the battery and cathode to the positive terminal of the battery so this type of connection is referred as the reverse biasing of p-n junction diode this you can see in the figure on screen you find two figures the upper one is the forward and reverse bias connection of p-n junction diode with the symbolic representation and the another one is the with the semiconductor materials p-type and enzyme so p injection diode is represented in form of p-type and anti-material next we will see the forward biasing of pn junction diode now what happens when we apply the forward bias to the diode so as we are increasing the external voltage it overcomes the depletion region potential barrier you can see in the figure when the supply reaches to volt the depletion region is fully vanishes and the electrons and holes will be able to cross the junction and the current is flowing so when we have not applied any forward bias voltage or any external voltage we are having the deflation region at the junction and it is uh it is having some potential barrier so when we apply the forward bias and we gradually increase the voltage it is used to overcome the potential barrier at the junction due to the depletion region so up to 0.3 volt it is used to overcome the potential barrier of the you can say uh division region so this is the 0.3 volt is for the germanium and if we are using the silicon material to form the pn junction diode then this voltage will be 0.6 or 0.7 so this voltage is referred as the cutting voltage so it is a minimum voltage we need to apply across the pn junction diode in forward bias manner to allow the carriers to cross the junction or to allow the current to flow so this figure figure shows the vi characteristic of pn junction diode for the forward bias condition so here we are plotting the applied voltage across the p injection diode and current flowing through the p-n junction diode you can find as we increase the voltage up to 0.3 volt the current is zero so that is a cutting voltage and as the voltage is increased beyond this cutting voltage the current will increase so this is the forward characteristic of pn junction diode now we will see the reverse bias pn junction diode that what will be the behavior of the injection diode under the reverse mass condition reverse bias condition means we are applying the we are connecting the positive terminal of the battery to inside and negative terminal of the battery to pc now the electrons that is a majority charge carrier of n side or n type material gets attracted towards the p or rather the positive terminal of the battery and similarly the holes which is majority charge carrier of this p type material it gets attracted towards the negative terminal of the battery so you can see in the figure due to this type of attraction the majority charge carrier of both type of material will move away from the junction so they are moving away from the junction and due to that what happens near the junction the region is created which is having just immobile ions and no free carriers or rather the depletion region so this depletion region width is going to increase as you are increasing the reverse bias voltage so in this reverse bias condition there is no current flows the small amount of carriers will be able to cross the junction and that will be the minority carriers only and it will constitute some current and this current is referred as the reverse saturation current this reverse saturation current will be of the order of micro ampere or nano npm so this is about the reverse bias condition of p-n junction diode now next figure shows the all this processes together here the pn junction diode is connected with the external battery through the switch and resist so when switches open that means the diode is not connected to the battery at that time the normal depletion region is generated and the potential barrier is set now when switch is closed and forward bias is applied the majority charge carrier will cross the junction and the current will flow now when the reverse bias is applied and switch is closed definitely then the dimension region width is going to increase and very small amount of current is flowing so this whole process you can see in this figure so next we will see the vi characteristic of p-n junction diode this figure shows the p-n junction diode simple when it is formed using the p-type and n-type material and the v-i characteristic vl characteristic is plotted for the voltage applied across the pn junction diode and the current flowing through the pn junction diode so you find the four quadrant in this characteristic so when forward biasing of p junction diode is done and whatever voltage and current which we are getting is plotted in the first quadrant so we consider the applied voltage is positive and the current which is flowing is also positive so this characteristic you find that as we increase the forward voltage up to the knee voltage there is no current flowing and if we increase the forward voltage beyond the knee voltage the current gradually increases and the knee voltage for the germanium is 0.3 volt and for the silicon it will be 0.6 or 0.7 volt now reverse bias characteristic of pn junction diode is plotted in the third quadrant so here we are changing the polarity of applied voltage that's why we are considering the negative voltage and the flow of current is also the direction of flow of current is also reverse that's why that is considered as a negative so the reverse bias voltage and current both are negative so when we are increasing the reverse bias voltage up to certain limit we find that the current which is flowing is the reverse saturation current which is of the order of micro ampere and so but beyond certain limit we find that this current increases gradually and this reverse bias voltage is called the breakdown voltage and this breakdown will damage the pn junction diode permanently so we are not applying uh a practically we are not applying reverse bias voltage beyond the breakdown voltage so this is about the vi characteristic of tn junction diode next we will see the basic definitions or terms with reference to the pn junction diode so first is the cutting voltage or it is called the knee voltage it is a forward voltage applied across the p-n junction diode at which the current starts flowing through the diode and it is referred as the cutting voltage or the knee voltage the breakdown voltage is the reverse voltage applied across the pn junction diode at which the breakdown occurs and the next is depletion region or space charge region it is a region nearer to the p n junction where there is no free carriers only in mobile ions are present and this region is referred as the depletion region so this is the basic terms these are the basic terms we can say with this i am ending this session over here thank you stay connected thank you