Zener effect
Encyclopedia
The Zener effect is a type of electrical breakdown in a reverse biased P-N junction
diode
in which the electric field
across the diode breaks some of the covalent bonds
of the semiconductor
atoms
leading to a large number of free minority carriers
, which suddenly increase the reverse current
. Zener breakdown is employed in a Zener diode
.
expands leading to a high strength electric field across the junction. This electric field acts to break covalent bonds of the semiconductor atoms which liberates a large number of free minority carriers. This suddenly increases the reverse current and give rise to the high slope resistance of the Zener diode (i.e. the voltage across the diode stays very close to a well defined and constant value, with increasing current).
which involves minority carrier electrons
in the transition region which are accelerated by the electric field to energies sufficient to free electron-hole pairs via collisions with bound electrons. Either the Zener or avalanche effect may occur independently, or both may occur commensurately. In general, diodes junctions that breakdown below 5V are caused by the Zener effect, while junctions that experience breakdown above 5 V are caused by the avalanche effect. Intermediate breakdown voltages (around 5V) are usually caused by a combination of the two effects.
This Zener breakdown voltage is found to occur at electric field intensity of about .
Zener breakdown occurs in heavily doped junctions (p-type semiconductor moderately doped and n-type heavily doped), which produces a narrow depletion region. The avalanche breakdown occurs in lightly doped junction, which produces a wider depletion layer. Temperature increases in the junction decreases Zener breakdown and increases the contribution of avalanche breakdown.
P-n junction
A p–n junction is formed at the boundary between a P-type and N-type semiconductor created in a single crystal of semiconductor by doping, for example by ion implantation, diffusion of dopants, or by epitaxy .If two separate pieces of material were used, this would...
diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
in which the electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
across the diode breaks some of the covalent bonds
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
of the semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
atoms
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
leading to a large number of free minority carriers
Charge carriers in semiconductors
There are two recognized types of charge carriers in semiconductors. One of them is electrons, which carry negative electric charge. In addition, it is convenient to treat the traveling vacancies in the valence-band electron population as the second type of charge carriers, which carry a positive...
, which suddenly increase the reverse current
Current
- Science and Mathematics :* Electric current* Current , including** Ocean currents** Air currents** Current - currents in rivers and streams* Current density, mathematical concept unifying electric current, fluid current, and others...
. Zener breakdown is employed in a Zener diode
Zener diode
A Zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage" or "Zener...
.
Mechanism
Under a very high reverse voltage, the p-n junction's depletion regionDepletion region
In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region or the space charge region, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have diffused away, or have been forced away by an...
expands leading to a high strength electric field across the junction. This electric field acts to break covalent bonds of the semiconductor atoms which liberates a large number of free minority carriers. This suddenly increases the reverse current and give rise to the high slope resistance of the Zener diode (i.e. the voltage across the diode stays very close to a well defined and constant value, with increasing current).
Relationship to the avalanche effect
The Zener effect is distinct from avalanche breakdownAvalanche breakdown
Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. It is a type of electron avalanche...
which involves minority carrier electrons
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
in the transition region which are accelerated by the electric field to energies sufficient to free electron-hole pairs via collisions with bound electrons. Either the Zener or avalanche effect may occur independently, or both may occur commensurately. In general, diodes junctions that breakdown below 5V are caused by the Zener effect, while junctions that experience breakdown above 5 V are caused by the avalanche effect. Intermediate breakdown voltages (around 5V) are usually caused by a combination of the two effects.
This Zener breakdown voltage is found to occur at electric field intensity of about .
Zener breakdown occurs in heavily doped junctions (p-type semiconductor moderately doped and n-type heavily doped), which produces a narrow depletion region. The avalanche breakdown occurs in lightly doped junction, which produces a wider depletion layer. Temperature increases in the junction decreases Zener breakdown and increases the contribution of avalanche breakdown.