Semiconductor Flashcards
What is energy band
Energy level with continuous energy variation is energy band
What is conduction band
Energy band above valence band is called conduction band
Define energy band gap
Gap between top of valence band and bottom of conduction band is called energy band gap
What is hole
Vacancy with the effective +ve charge is called a hole
State properties of intrinsic semiconductors
1 No. of free e- is equal to no of hole
2an intrinsic semiconductor will behave as insulator at T =0K
What is the necessity of extrinsic semiconductor
Conductivity of intrinsic semiconductors depends on its temp at room temp it’s conductivity is very low
No important devices can be developed using these semiconductors so their is need of improving their conductivity
Define extrinsic semiconductor
Small amount of impurity when added to the pure semiconductor it’s conductivity is increased manifold. Such material are known as extrinsic semiconductor
What is doping
Addition of a desirable impurity is called doping
What are dopants
The impurity atoms that are added in doping are dopants
What is donor impurity
Pentavalent dopant is donating one extra e- for conduction and hence is known as donor impurity
Why minority charge carriers can be destroyed
Because of abundance of majority current carriers the minority carriers produced thermally have more chance of meeting majority carriers and thus getting destroyed
Although Sn is a group 4 element it is considered as metal . Why ?
Because the energy gap in its case is 0 eV
How diffusion current is produced in p-n junction
During the formation of p-n junction due to the concentration gradient across p and n side hole and e- diffuses . This motion of charge carriers gives rise to diffusion current
Define depletion region
Space-charge region on either side of junction is known as depletion region
What is drift
The motion of charge carriers due to the electric field is called drift
How is p-n junction formed
Initially , diffusion current is large and drift current is small . As the diffusion continues the space charge region on either side of the junction extended thus increase in electric field and hence drift current . This process continues until the diffusion current equals the drift current hence a p-n junction is formed
What is a diode
P-n junction with metallic contacts at the ends for the application of an external voltage
Define forward bias
When an external voltage is applied across a semiconductor diode such that p side is connected to the +ve terminal of the battery and n-side to -ve terminal it is called said to be forward bias
What is minority carrier injection
Due to applied voltage e- from n-side cross the depletion region and reach p-side . This process is known as minority carrier injection
Define reverse bias
When an external voltage is applied across the diode such that n-side is +ve and p-side is -ve it is said to be reverse biased
Define breakdown voltage
Current under reverse bias is essential voltage independently upto a critical reverse bias voltage known as breakdown voltage
Define threshold voltage
After the characteristics voltage the diode current increase significantly even for a very small increas in the diode bias voltage . This voltage is called the threshold voltage
Define reverse saturation current
For the diode in reverse bias the current is very small and almost remain constant with change in bias . Is is called reverse saturation current
What is rectifier
If an alternating voltage is applied across a diode the current flows only I that part of the cycle when the diode is forward biased . This property is used to rectify alternating voltage and the circuit used for this purpose is called a rectifier
