When the diode is forward biased, it is found that beyond forward voltage V = V_k, called knee voltage, the conductivity is very high. At this value of battery biasing for p-n junction,the potential barrier is overcome and the current increases rapidly with increase in forward voltage. When the diode is reverse biased, the reverse bias voltage produces a very small current about a few microamperes which almost remains constant with bias. This small current is reverse saturation current.
(i) In which of the following figures, the p-n diode is forward biased.

(ii) Based on the V-I characteristics of the diode, we can classify diode as

(iii) The V-I characteristic of a diode is shown in the figure. The ratio of forward to reverse bias resistance is

(iv) In the case of forward biasing of a p-n junction diode, which one of the following figures correctly depicts the direction of conventional current (indicated by an arrow mark)?

(v) If an ideal junction diode is connected as shown, then the value of the current I is

Rectifier is a device which is used for converting alternating current or voltage into direct current or voltage. Its working is based on the fact that the resistance of p-n junction becomes low when forward biased and becomes high when reverse biased. A half-wave rectifier uses only a single diode while a full wave rectifier uses two diodes as shown in figures (a) and (b) .

(i) If the rms value of sinusoidal input to a full wave rectifier is \(\frac{V_{0}}{\sqrt{2}}\) then the rms value of the rectifier's output is

(ii) In the-diagram, the input ac is actoss the terminals A and C. The output across Band D is

(iii) A bridge rectifier is shown in figure. Alternating input is given across A and C. If output is taken across BD, then it is

(iv) A p-n junction (D) shown in the figure can act as a rectifier. An alternating current source (V) is connected in the circuit. The current (I) in the resistor(R) can be shown by

(v) With an ac input from 50 Hz power line, the ripple frequency is

From Bohr's atomic model, we know that the electrons have well defined energy levels in an isolated atom. But due to interatomic interactions in a crystal, the electrons of the outer shells are forced to have energies different from those in isolated atoms. Each energy level splits into a number of energy levels forming a continuous band.The gap between top of valence band and bottom of the conduction band in which no allowed energy levels for electrons can exist is called energy gap.

(i) In an insulator energy band gap is

(ii) In a semiconductor, separation between conduction and valence band is of the order of

(iii) Based on the band theory of conductors, insulators and semiconductors, the forbidden gap is smallest in

(iv) Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

(v) Solids having highest energy level partially filled with electrons are

Light emitting diode is a photoelectric device which converts electrical energy into light energy. It is a heavily doped p-n junction diode which under forward biased emits spontaneous radiation. The general shape of the J- V characteristics of an LED is similar to that of a normal p-n junction diode, as shown. The barrier potentials are much higher and slightly different for each colour.

(i) The J- V characteristic of an LED is

(ii) The schematic symbol of light emitting diode is (LED)

(iii) An LED is constructed from a p-n junction based on a certain Ga-As-P semiconducting material whose energy gap is 1.9 eV. Identify the colour of the emitted light.

(iv) Which one of the following statement is not correct in the case of light emitting diodes?

(v) The energy of radiation emitted by LED is

A photodiode is an optoelectronic device in which current carriers are generated by photons through photoexcitation i.e., photo conduction by light. It is a p-n junction fabricated from a photosensitive semiconductor and provided with a transparent window so as allow light to fall on its function. A photodiode can turn its current ON and OFF in nanoseconds. So, it can be used as a fastest photo-detector.

(i) A p-n photo diode is fabricated from a semiconductor with a band gap of 2.5 ev' It can detect a signal of wavelength

(ii) Three photo diodes D₁ D₂ and D₃ are made of semiconductors having band gap of 2.5 eV, 2 eV and 3 eV, respectively. Which one will be able to detect light of wavelength 6000 \(\dot A\) ?

(iii) Photodiode is a device

(iv) To detect light of wavelength 500 nrn, the photodiode must be fabricated from a semiconductor of minimum bandwidth of

(v) Photo diode can be used as a photo detector to detect

A silicon p-n junction diode is connected to a resistor R and a battery of voltage V_B through milliammeter (mA) as shown in figure. The knee voltage for this junction diode is V_N = 0.7 V. The p-n junction diode requires a minimum current of 1m. A to attain a value higher than the knee point on the J- V characteristics of this junction diode. Assuming that the voltage V across the junction is independent of the current above the knee point. A p-n junction is the basic building block of many semiconductor devices like diodes. Important process occurring during the formation of a p-n junction are diffusion and drift. In an n-type semiconductor concentration of electrons is more as compared to holes. In a p-type semiconductor concentration of holes is more as compared to electrons.

(i) If V_B = 5 V, the maximum value of R so that the voltage V is above the knee point voltage is

(ii) If V_B = 5 V, the value of R in order to establish a current to 6 mA in the circuit is

(iii) If V_B = 6 V, the power dissipated in the resistor R, when a current of 6 mA flows in the circuit is

(iv) When the diode is reverse biased with a voltage of 6 V and V_bi = 0.63 V. Calculate the total potential.

(v) Which of the below mentioned statement is false regarding a p-n junction diode?

The electron mobility characterises how quickly an electron can move through a metal of semiconductor when pulled by an electric field. There is an analogous quality for holes, called hole mobility. A block of pure silicon at 300 K has a length of 10 cm and an area of 1.0 cm². A battery of emf 2 V is connected across it. The mobility of electron is 0.14 m² y^-1 s^-1 and their number density is 1.5 x 10¹⁶ m^-3. The mobility of holes is 0.05 m² y^-1 s^-1.
(i) The electron current is

(ii) The hole current is

(iii) The number density of donor atoms which are to be added up to pure silicon semiconductor to produce an n-type semiconductor of conductivity 6.4 \(\Omega\)^-1 cm^-1 is approximately (neglect the contribution of holes to conductivity)

(iv) When the given silicon semiconductor is doped with indium, the hole concentration increases to 4.5 x 10²³ m^-3. The electron concentration in doped silicon is

(v) Pick out the statement which is not correct.

p-n junction is a single crystal of Ge or Si doped in such a manner that one half portion of it acts as p-type semiconductor and other half functions as n-type semiconductor. As soon as a p-n junction is formed, the holes from the p-region diffuse into the n-region and electron from n region diffuse in to p-region. This results in the development of VB across the junction which opposes the further diffusion of electrons and holes through the junction.
(i) In an unbiased p-n junction electrons diffuse from n-region to p-region because

(ii) Electron hole recombination in p-n junction may lead to emission of

(iii) In an unbiased p-n junction

(iv) The potential of depletion layer is due to

(v) In the depletion layer of unbiased p-n junction

The potential barrier in the p-n junction diode is the barrier in which the charge recquires additional force for crossing the region. In other words, the barrier in which the charge carrier stopped by the obstructive force is known as the potential barrier.
When a p-type semiconductor is brought into a close contact with n-type semiconductor, we get a p-n junction with a barrier potential 0.4 V and width of depletion region is 4.0 x 10^-7 m. This p-n junction is forward biased with a battery of voltage 3V and negligible internal resistance, in series with a resistor of resistance R, ideal millimeter and key K as shown in figure. When key is pressed, a current of 20 mA passes through the diode.
(i) The intersity of the electric field in the depletion region when p-n junction is unbiased is

(ii) The resistance of resistor R is

(iii) In a p-n junction, the potential barrier is due to the charges on either side of the junction, these charges are

(iv) If the voltage of the potential barrier is V₀  A voltage V is applied to the input, at what moment will the barrier disappear?

(v) If an electron with speed 4.0 x 10⁵ m s^-1 approaches the p-n junction from the n-side, the speed with which it will enter the p-side is

Solar cell is a p-n junction diode which converts solar energy into electric energy. It is basically a solar energy converter. The upper layer of solar cell is of p- type semiconductor and very thin so that the incident light photons may easily reach the p-n junction. On the top face of p-layer, the metal finger electrodes are prepared in order to have enough spacing between the fingers for the lights to reach the p-n junction through p-layer.
(i) The schematic symbol of solar cell is

(ii) The p-n jqnction which generates an emf when solar radiations fall an it, with no external bias applied,is a

(iii) For satellites the source of energy is

(iv) Which of the following material is used in solar cell?

(v) The efficiency of a solar cell may be in the range

Figure shows the I - V characteristic of an LED designed to emit blue light.

(i) Describe and justify the variation of R of the LED as the potential difference V across the LED is increased from
(a) -1.0 V to 2.6 V
(b) 2.6 V to 3.0 V
(c) 3.0 V to 3.4 V
(ii) A student uses the LED with the characteristic shown in the figure given on the previous page and constructs the circuit as shown below.

R is a resistor used in series with the LED. The electric cell has emf of 1.5 V and negligible internal resistance. The LED fails to emit light when the switch S is closed. Suggest some reason and modify the circuit so that the LED glows on closing the switch.
(iii) Name the material suitable for fabricating LED to emit red light. What minimum voltage is required for it to glow?