Advertisements
Advertisements
प्रश्न
In a photo diode, the conductive increases when the material is exposed to light. It is found that the conductivity changes only if the wavelength is less than 620 nm. What is the band gap?
(Use Planck constant h = 4.14 × 10-15 eV-s, Boltzmann constant k = 8·62 × 10-5 eV/K.)
Advertisements
उत्तर
Conductivity of any material increases when the number of free charge carriers in the material increases. When a photo diode is exposed to light, additional electron hole pairs are created in the diode; thus, its conductivity increases. So to change the conductivity of a photo diode, the minimum energy of the incident radiation should be equal to the band gap of the material.
In other words,
Band gap = Energy of the incident radiation
\[\Rightarrow E = \frac{hc}{\lambda}\]
\[ \Rightarrow E = \frac{1242 \text{ eV - nm}}{620 \text{ nm }} = 2.0eV\]
APPEARS IN
संबंधित प्रश्न
What causes the setting up of high electric field even for small reverse bias voltage across the diode?
When a forward bias is applied to a p-n junction, it ______.
With reference to semiconductor devices, define a p-type semiconductor and a Zener diode.
Plot a graph showing variation of current versus voltage for the material GaAs ?
Show on a graph, the variation of resistivity with temperature for a typical semiconductor.
A plate current of 10 mA is obtained when 60 volts are applied across a diode tube. Assuming the Langmuir-Child relation \[i_p \infty V_p^{3/2}\] to hold, find the dynamic resistance rp in this operating condition.
The plate current in a diode is 20 mA when the plate voltage is 50 V or 60 V. What will be the current if the plate voltage is 70 V?
Basic materials used in the present solid state electronic devices like diode, transistor, ICs, etc are ______.
Diffusion in a p-n junction is due to ______.
The drift current in a p-n junction is from the ______.
The expected energy of the electron at absolute zero is called:-
On increasing the reverse biases voltage to a large value in a P – N junction diode-current
In a semiconductor diode, the barrier potential offers opposition to only
Consider an npn transistor with its base-emitter junction forward biased and collector base junction reverse biased. Which of the following statements are true?
- Electrons crossover from emitter to collector.
- Holes move from base to collector.
- Electrons move from emitter to base.
- Electrons from emitter move out of base without going to the collector.
The breakdown in a reverse biased p–n junction diode is more likely to occur due to ______.
- large velocity of the minority charge carriers if the doping concentration is small.
- large velocity of the minority charge carriers if the doping concentration is large.
- strong electric field in a depletion region if the doping concentration is small.
- strong electric field in the depletion region if the doping concentration is large.
Can the potential barrier across a p-n junction be measured by simply connecting a voltmeter across the junction?
Draw V-I characteristics of a p-n Junction diode.
Read the following paragraph and answer the questions that follow.
| A semiconductor diode is basically a pn junction with metallic contacts provided at the ends for the application of an external voltage. It is a two-terminal device. When an external voltage is applied across a semiconductor diode such that the p-side is connected to the positive terminal of the battery and the n-side to the negative terminal, it is said to be forward-biased. When an external voltage is applied across the diode such that the n-side is positive and the p-side is negative, it is said to be reverse-biased. An ideal diode is one whose resistance in forward biasing is zero and the resistance is infinite in reverse biasing. When the diode is forward biased, it is found that beyond forward voltage called knee voltage, the conductivity is very high. When the biasing voltage is more than the knee voltage the potential barrier is overcome and the current increases rapidly with an increase in forward voltage. When the diode is reverse biased, the reverse bias voltage produces a very small current of about a few microamperes which almost remains constant with bias. This small current is a reverse saturation current. |
- In the given figure, a diode D is connected to an external resistance R = 100 Ω and an emf of 3.5 V. If the barrier potential developed across the diode is 0.5 V, the current in the circuit will be:
(a) 40 mA
(b) 20 mA
(c) 35 mA
(d) 30 mA - In which of the following figures, the pn diode is reverse biased?
(a)
(b)
(c)
(d)
- Based on the V-I characteristics of the diode, we can classify the diode as:
(a) bilateral device
(b) ohmic device
(c) non-ohmic device
(d) passive element
OR
Two identical PN junctions can be connected in series by three different methods as shown in the figure. If the potential difference in the junctions is the same, then the correct connections will be:
(a) in the circuits (1) and (2)
(b) in the circuits (2) and (3)
(c) in the circuits (1) and (3)
(d) only in the circuit (1) 
The V-I characteristic of a diode is shown in the figure. The ratio of the resistance of the diode at I = 15 mA to the resistance at V = -10 V is
(a) 100
(b) 106
(c) 10
(d) 10-6
Choose the correct circuit which can achieve the bridge balance.
