EDC Interview Questions and Answers
In this section, we are going to provide you with the best EDC interview questions that are already asked in the various interview like PSUs, ESE, and many state PSUs interviews.
Que.1 What is the Energy Gap or Forbidden Gap?
Ans:
- To understand this concept we consider the PDF of a single electron (e). If two atoms come closer to each other, then they will interact with each other.
- According to Pauly’s exclusion principle, they can not occupy the same energy level. So the energy levels get splitting.
- As the interatomic distance decrease and results in discrete energy levels.
- So at the equilibrium atomic distance, we gave a set of allowable energy levels separated by bonds of unallowed energy called as Forbidden energy or Energy gap.
Que.2 What is Thermal Voltage?
Ans: It is the voltage equivalent of a temperature. V_T=\frac{\overline K T}{q}. The standard room temperature is equivalent to 26mv.
Que.3 Why Si is preferred over Ge.
Ans:
- Smaller leakage current
- High power capability
- High operating temperature
- Abundance in nature
- Cheapest semiconductor material
Que.4 Why carbon is not considered a semiconducting material?
Ans: (1) Energy Gap of carbon Eg > 5ev. (2) HIgh unstable and unpredictable behavior.
Que.5 What is doping?
Ans: Process of adding impurity to an atom to increase its conductivity in semiconductors.
Que.6 What do you mean by the built-in electric field?
Ans: In the case of non-uniformly doped SC as the charge carrier diffuses to the lower doped side, they leave behind some charge at the highly doped side. This way it creates a potential difference and results in an electric field called a built-in electric field. This field opposes the further then diffusion of charge carriers. Hence net current at equilibrium remains zero.
Que.7 Working of Ge-Si crystals.
Ans: At 0K, it works as an insulator. At room temperature, it works as an intrinsic semiconductor. Its conductivity is small, hence no practical use. It does not have any built-in electric field.
Que.8 Difference between Direct band gap and Indirect band gap SC.
Ans:
| Direct Band Gap | Indirect Band Gap |
|---|---|
| In this, the Conduction band minima and the valance band maxima both occur at the same momentum. | This conduction band minima and the valance band maxima are at different momentum values. |
| This direct transfer is possible and it releases a photon of light. | So indirect transition occurs via intermediate levels and releases heat. |
| The direction and momentum do not change. | The direction and momentum both will change. |
| Examples: GaAs, InP | Example: Ge, Si |
Que.9 What is effective mass?
Ans: It is defined as the mass of the particle by taking into account the forces due to different atoms in the crystal or when the internal forces due to the atom inside the crystal are taken into account, the mass is called the effective mass.
Que.10 What is Fermi’s level of energy?
Ans: It is the energy level beyond which the energy possessed by an electron is 0 at 0K. or It is the maximum energy that an electron can possess at 0K. or Energy possessed by the fastest-moving electron at 0K.
Que.11 What is Hall Effect?
Ans: When a semiconductor is placed under influence of the magnetic field, and a current is passed, an electric field is induced in a direction perpendicular to both I(current) and B(Magnetic field). The direction of filed induced remains the same irrespective of charge carriers. This force is Lorentz force and it results in the accumulation of negative & positive charges on top and bottom surfaces. This results in the induction of a field called as Hall Effect.
The voltage difference between the top and bottom surfaces is called Hall Voltage.
V_H=\frac{I B}{\varrho W}
Que.12 What do you mean by the surface state?
Ans: When a semiconductor is abruptly terminated, the lattice structure of certain atoms consists of some unbounded electron. This electron may occupy the energy states in the forbidden energy gap. These states are called surface states.
Que.13 If we connect a voltmeter across diode terminals, can the built-in voltage be measured?
Ans: No, Meter will not show any reading. Because the algebraic sum of the voltages must be zero and built-in voltage will be compensated due to the ohmic contacts.
Que.14 What is the effect of temperature on the forward bias current in the diode?
Ans: There will be an almost negligible effect on the forward bias current on the diode.
Que.15 Difference between LED and LCD?
Ans:
| LED | LCD |
|---|---|
| Light Emitting Diode | Liquid Crystal Display |
| High power dissipation(mw) | Low power dissipation (uw) |
| Principle: Electroluminescent | Principle: Dynamic scattering of light |
| No backlight | Backlight is visible |
| Longer operating life | comparatively smaller life |
| Costly | Cheaper |
| Faster | Slower |
Que.16 What is Photodiode? Application of photodiode.
Ans:
- The photodiode is a P-N junction diode with reduced doping and light made to fall at the junction which is coated by photo-sensitive material. Photodiode works on the principle of photoconductive effect.
- Output current is proportional to the intensity of light.
- Application: Sensors, optocouplers, photometry, reading of audio track.
\boxed{ \eta = \frac{I}{q} \left [ \frac{h*f}{P_{opt}} \right ]}
\therefore responsivity\; R = \frac{I}{P_{opt}}
Que.17 Difference between sensors and transducers?
Ans:
- Sensor: A circuit that senses or detects the change in its input and produces corresponding output accordingly. for example A thermometer
- Transducers: A device that converts one form of energy into another form. Each transducer uses a sensor at its input. So each transducer uses a sensor but not reverse. I.e Every sensor cannot be a transducer. For example Thermocouple
Que.18 What is a power supply?
Ans: a circuit that supplies power to a load. It converts the AC power into DC power. It consists of Rectifier, filter, and regulator circuit.
Que.19 What is a rectifier?
Ans: It is a circuit that converts pure AC into pulsating DC or bidirectional waveform into unidirectional waveform.
Que.20 Why regulator is used in the power supply?
Ans: Regulator circuits regulate the output DC voltage without changing the output voltage with respect to changing the load variation or changing the input AC voltage.
Que.21 How will you define a Semiconductor?
Answer: Semiconductors are the elements whose conductivity lies between the conductivity of an insulator and the conductivity of a conductor. Moreover, its conductivity can be increased by either increasing temperature or concentration of charge carriers, thus enabling it to work as a switch.
Que.22 What is the absolute temperature in electronic devices?
Answer:
- Absolute temperature- it is the reference temperature or minimum temperature, no semiconductor can have a temperature less than this i.e. temperature cannot be reduced below this.
- This is 0 Kelvin temperature which is equal to -273ocelcius.
Que.23 What is Ambient temperature?
Answer: Surroundings temperature or superficial temperature of electronic devices is known as Ambient temperature. This temperature is most widely used in communication systems. This temperature is 290K.
Que.24 How will you define 1 electron volt?
Answer: 1eV is defined as the energy gained by 1 electron in moving through a potential difference of 1V. It is the practical unit of energy in electronics. It denotes the kinetic energy gained by electrons or potential energy lost by electrons.
Que.25 What does the mobility of the charge carrier determine?
Answer:
- Mobility of charge carriers determines how fast charge carriers will be moving from one point to another point in a material.
- For example the mobility of electrons is always greater than the mobility of holes. Hence electrons always travel faster than holes.
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