i v characterstics of pn junction diode and zener diode

International Journal of Research, 2017

Zener diode –voltage regulator when it undergoes reversed bias and a normal diode in forward bias. Purpose to study the characteristics of zener diode

Zener diode is a P-N junction diode specially designed to operate in the reverse biased mode. It is acting as normal diode while forward biasing. It has a particular voltage known as break down voltage, at which the diode break downs while reverse biased. In the case of normal diodes the diode damages at the break down voltage. But zener diode is specially designed to operate in the reverse breakdown region. Working Principle of zener diode : The basic principle behind the working of a zener diode lies in the cause of breakdown for a diode in reverse biased condition. Normally there are two types of breakdown-Zener and Avalanche. Zener Breakdown This type of breakdown occurs for a reverse bias voltage between 2 to 8V. Even at this low voltage, the electric field intensity is strong enough to exert a force on the valence electrons of the atom such that they are separated from the nuclei. This results in formation of mobile electron-hole pairs, increasing the flow of current across the device. Approximate value of this field is about 2*10 7 V/m. This type of break down occurs normally for highly doped diode with low breakdown voltage and larger electric field. As temperature increases, the valence electrons gain more energy to disrupt from the covalent bond and less amount of external voltage is required. Thus zener breakdown voltage decreases with temperature. Avalanche breakdown This type of breakdown occurs at the reverse bias voltage above 8V and higher. It occurs for lightly doped diode with large breakdown voltage. As voltage increases, the kinetic energy (velocity) of the electrons also increases. With this high velocity when minority charge carriers (electrons) flow across the device, they tend to collide with the electrons in the covalent bond and cause the covalent bond to disrupt. One electron after collision forms one electron-hole pair. These free electron and hole during their travelling again collide with another immobile ion and breaks the covalent bond forming two electron-hole pairs. This is a multiplication process and forms large number of free carriers. The avalanche breakdown voltage increases with temperature.

What makes a difference between the usual P/N semiconductor diode and the power diode? The response is basically: the need to withstand high voltages in the reverse bias condition; this need will pose some constraints on the device structure.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1997

The switching time of silicon diodes has been reduced from 1000 ns to less than 200 ns by introducing ion induced defects into the n-region of silicon junction diodes. These diodes were made on 250 pm thick silicon wafers without adopting a gold diffusion process. The junction was located at a distance of around 60 pm from the surface of the p-region. ln these diodes since the thickness of the p-side is relatively small as compared to that of the n-region, the switching characteristics of the diodes are controlled mainly by the charge carriers of the n-region. In the present work, the lifetime of minority carriers in the n-region has been reduced by creating defects through heavy ion irradiation. The diodes were irradiated from the n-side with 100 MeV silicon ions, 70 and 80 MeV oxygen ions and 65 MeV boron ions covering a fluence range from 10" to lOI ions/cm*. In this way, defects could be induced at different locations in the n-side covering a range from 35 to 140 pm away from the surface of the n-side. It has been observed that the defects produced near the junction are more effective in reducing the turn-off time t, as compared to those produced near the surface. On comparing the values of t, for different diodes, it has been found that the defects induced by 65 MeV boron ions are most effective because even for a large decrement in the t,. the corresponding increment in the forward voltage drop, Vr , was marginal. For other ions, though the decrease in t, was effective, it was followed by a large increment in the Vr. In all the ion irradiated diodes, the increase in the forward voltage drop could be recovered partially after annealing the diodes at 45O"C, which however was followed by a small increment in t,. Furthermore, almost all the ion induced defects could be annealed out at 600°C. Results of this study indicate that heavy ions can be used effectively to control switching parameters of diodes with a much better trade-off between Vr and t, as compared to those exposed to Co-60 gamma rays or made with gold diffusion.

The conductivity of a semiconductor is dependent upon the small number of electrons in the conduction band and holes in the valence band.

In the previous tutorial we saw how to make an N-type semiconductor material by doping a silicon atom with small amounts of Antimony and also how to make a P-type semiconductor material by doping another silicon atom with Boron. This is all well and good, but these newly doped N-type and P-type semiconductor materials do very little on their own as they are electrically neutral. However, if we join (or fuse) these two semiconductor materials together they behave in a very different way merging together and producing what is generally known as a " PN Junction ". When the N-type semiconductor and P-type semiconductor materials are first joined together a very large density gradient exists between both sides of the PN junction. The result is that some of the free electrons from the donor impurity atoms begin to migrate across this newly formed junction to fill up the holes in the P-type material producing negative ions. However, because the electrons have moved across the PN junction from the N-type silicon to the P-type silicon, they leave behind positively charged donor ions (ND) on the negative side and now the holes from the acceptor impurity migrate across the junction in the opposite direction into the region where there are large numbers of free electrons. Related Products: PIN | Varactor As a result, the charge density of the P-type along the junction is filled with negatively charged acceptor ions (NA), and the charge density of the N-type along the junction becomes positive. This charge transfer of electrons and holes across the PN junction is known as diffusion. The width of these P and N layers depends on how heavily each side is doped with acceptor density NA, and donor density ND, respectively.

conductors 5.7 Hole Current 5.8 Intrinsic Semiconductor 5.9 Extrinsic Semiconductor 5.10 n-type Semiconductor 5.11 p-type Semiconductor 5.12 Charge on n-type and p-type Semiconductors 5.13 Ma= ority and Minority Carriers 5.14 pn = unction 5.15 Properties of pn-= unction 5.16 Applying D.C. Voltage across pn-= unction or Biasing a pn-= unc-tion 5.17 Current Flow in a Forward Biased pn-= unction 5.18 Volt-Ampere Characteristics of pn = unction 5.19 Important Terms 5.20 Limitations in the Operating Conditions of pn-= unction

Journal of Physics D: Applied Physics, 2000

The prebreakdown spatial current stabilization of the Townsend discharge in an ionization cell with a high-resistivity semiconductor plate, a gap thickness of 20 µm and gas pressures of 200 and 10 −3 Torr is studied. It has been found, for the first time, that the substitution of one of the metallic electrodes in an ionization cell by a semiconductor electrode leads to the occurrence of a current of 10 −6-10 −5 A, while in the case of two metallic electrodes a current above 10 −7 A is not observed. It is shown that the generation of carriers by a gas discharge establishes a positive feedback. A qualitative discussion of this effect is given, which includes avalanche formation in a system having a high-resistivity semiconductor for the Townsend discharge region. The recording of the current-voltage characteristic between parallel-plane electrodes is realized.