SemiconSemiconductor, Diode & its Application

1 Mark Questions

1. The graph shown in the figure represents a plot of current versus voltage for a given

semiconductor. Identify the region, if any over which the semiconductor has a negative resistance. [All India 2013]

Current (mA) Voltage (V)

Ans.Resistance of a material can be found out by the slope of the curve V versus I. Part BC of the curve shows the negative resistance as with the increase in current and decrease in voltage.

1. What happens to the width of depletion layer of a p-n junction when it is

(i)forward biased?

(ii)reverse biased? [All India 2011]

Ans.(i) Width of depletion layer's decreases in forward bias

1. Width depletion layer increases in reverse bias.
2. Why cannot we take one slab of p-type semiconductor and physically join it to another slab of n-type semiconductor to get p-n junction?

-2 V D₁

Ans. In this way, continuous contact cannot be produced at atomic level and junction will behave as a discontinuity for the flowing charge carrier.

1. What is the most common use of photo diode? [All India 2009]

Ans. The photodiode can be used as a photodetector to detect optical signals

1. State the relation between the frequency v of radiation emitted by LED and the band gap energy E, of the semiconductor used to fabricate it.[All India 2009 C] Ans. Zener diode, which is used as a DC voltage regulator.
2. Figure show the I-V characteristics of a given device. Name the device and write where it is used.

† / (m/A)

Reverse bias <math>V_z</math> Forward bias V(volt)

I(mA)

[Delhi 2009]

Ans.

In LED, energy of the photon should be equal to or less than the band gap energy i.e.

<math>h\nu \leq E_g</math>

where, <math>E_g</math> = band gap energy,

<math>v =</math> frequency of emitted photon.

1. State the reason, why GaAs is most commonly used in making of a solar cell. [All India 2008]

Ans.solar radiation is nearly 1.5 eV. In order to have photo excitation, the energy of radiation (hv) must be greater than energy band gap <math>(E_g)</math>. Therefore, the semiconductor with energy band gap about 1.5 eV or lower than it and with higher absorption coefficient is likely to give better solar conversion efficiency. The energy band gap for Si is about 1.1 eV, while for GaAs, it is about 1.53 eV. The GaAs is better inspite of its higher band gap than Si because it absorbs relatively more energy from the incident solar radiations being of relatively higher absorption coefficient.

8.At what temperature would an intrinsic semiconductor behave like a perfect insulator? [Delhi 2008 C]

Ans. At O° K temperature, an intrinsic semiconductor behaves like a perfect insulator