Download ARPIT 2019 Physics Of Semiconductors And Devices Creation Question Paper

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Question Paper Name: 5263Physics of Semiconductors and Devices30th June 2019 Shift 1

Subject Name: Physics of Semiconductors and Devices

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Creation Date: 2019-06-30 13:01:44

Duration: 180

Total Marks: 100

Display Marks: Yes

Physics of Semiconductors and Devices

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Group Number: 1

Group Id: 489994190

Group Maximum Duration: 0

Group Minimum Duration: 120

Revisit allowed for view?: No

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Revisit allowed for edit?: No

Break time: 0

Group Marks: 100

Physics of Semiconductors and Devices

Section Id: 489994246

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Section Number: 1

Section type: Online

Mandatory or Optional: Mandatory

Number of Questions: 100

Number of Questions to be attempted: 100

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Section Marks: 100

Display Number Panel: Yes

Group All Questions: No

Sub-Section Number: 1

Sub-Section Id: 489994264

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Question Shuffling Allowed: Yes

Question Number: 1 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

A beam of monochromatic light with intensity I₀ falls on a substrate of thickness d_s. A detector on the backside measures a transmitted intensity 0.5I₀. If a_l and a_s are the absorption coefficients for the semiconductor layer and the substrate, respectively, which of the following statements is correct?

A. a_ld_l + a_sd_s = ln(2)

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B. a_ld_l + a_sd_s = ln(1/2)

C. a_ld_l + a_sd_s = 1/2

D. None of these

Options:

1. 1

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2. 2

3. 3

4. 4

Question Number: 2 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

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The reverse saturation current in a p-n diode is 10 fA. What will be its ideality factor at a forward bias of 0.9 V if the forward current at that bias is 20 µA?

A. 1.6

B. 3.2

C. 2.1

D. 2.6

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Options:

1. 1

2. 2

3. 3

4. 4

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Question Number: 3 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

If the non-radiative lifetime is 1 ns and the radiative lifetime is 1 ms, then the IQE is approximately equal to

A. 0%

B. 1%

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C. 100%

D. Undefined

Options:

1. 1

2. 2

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3. 3

4. 4

Question Number: 4 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

For index (n=2.50) the critical angle at the GaN/air interface is 23º. Because of this:

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A. Photons are self-channelled into the sides.

B. The metal contact has to be aligned to cover the 23º cone at the centre of the chip to allow maximum current injection in this region.

C. The internal efficiency is affected due to photon recycling.

D. There is a narrow escape cone for light travelling from the semiconductor to air, causing low external quantum efficiency.

Options:

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1. 1

2. 2

3. 3

4. 4

Question Number: 5 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

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Correct Marks: 1 Wrong Marks: 0

A Bloch electron in an Eigen state characterized by band index, n, and wave vector k,

A. Is stationary.

B. Starts with a velocity, v_n = (2p/h)?_kE_n(k) but stops after a while.

C. Starts with a velocity, v_n = (2/h)?_kE_n(k) and continues forever without degradation.

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D. Has a random velocity.

Options:

1. 1

2. 2

3. 3

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4. 4

Question Number: 6 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

A solar cell uses p type silicon which has resistivity 2 ohm-cm at 300K. Given the mobility of holes is 300 cm²/V-sec, what is the doping concentration N_a in units of per cm³? Assume there are no donors (N_D =0) and all acceptors are ionized at 300K (N_A = N_a). Choose the option with value close to your calculation.

A. 1 x 10¹⁶

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B. 5 x 10¹⁵

C. 1 x 10¹⁵

Options:

1. 1

2. 2

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3. 3

Question Number: 7 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

For GaN is doped p-type with Mg dopant with concentration N_a = 10¹⁹/cm³. It is given that donor concentration N_D = 0. Measurements show that the Fermi level is E_F = 0.1 eV above the valence band edge E_V.

Given that effective density of valence band states is 10¹⁹/cm³ at 300 K, what is the ionization energy E_A - E_V of the acceptors in units of eV? You may use the concentration of ionized acceptors to be given by N_A = N_a/[1+4 exp (E_A-E_F)/KT], where E_F is the Fermi energy. Tick a box closest to your estimate below.

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A. 0.1

B. 0.2

C. 0.3

Options:

1. 1

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2. 2

3. 3

Question Number: 8 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

Shown below are schematics of E-k diagrams of conduction band of three different semiconductors A, B and C. Consider all the semiconductors are high purity. Which semiconductor will have the highest density of states at a given energy?

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a. A

b. B

c. C

Options:

1. 1

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2. 2

3. 3

Question Number: 9 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

The mobility µ_n of electrons in high purity silicon is 1400 cm²/V-sec at 300K The electron mass in conduction band of silicon is 0.26m₀. Given, m₀ = 9.1 x 10^-31 Kg. What is the Diffusion coefficient of electrons in high purity silicon at 300 K in units of cm²/sec? Choose the option close to your answer.

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A. 46.3

B. 36.3

C. 56.3

Options:

Question Number: 10 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

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Correct Marks: 1 Wrong Marks: 0

Mobility of electrons in high purity silicon is 1400 cm²/V-sec at 300K. This is the value limited by phonon scattering. Mobility of electrons doped with phosphorus donors at concentration 10¹⁸/cm³ is 280 cm²/V-sec at 300 K. What is the value of impurity scattering limited mobility at 300 K in units of cm²/V-sec? Choose an option close to your estimate.

A. 550

B. 450

C. 350

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Options:

1. 1

2. 2

3. 3

Question Number: 11 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

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Correct Marks: 1 Wrong Marks: 0

Band gaps of some semiconductors at 300 K are as follows: E_G,AlN = 6.2 eV, E_G,GaAs = 1.42 eV, E_G,Si = 1.12 eV, E_{G,Al0.5Ga0.5N}=4.5 eV. Which of these is suitable for making a sun-blind (not sensitive to light of wavelength greater than 300 nm) detector of UV radiation of wavelength 256 nm?

A. AlN

B. GaAs

C. Si

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D. Al_0.5Ga_0.5N

Options:

1. 1

2. 2

3. 3

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4. 4

Question Number: 12 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

Band to band radiative recombination coefficient of silicon is B = 10^-15 cm³/sec. A sample of p-type silicon has doping concentration N_A = 10¹⁶/cm³. Excess electrons and holes are generated in the sample with light at concentration much smaller than N_A. The lifetime of non-radiative Shockley-Read-Hall (SRH) recombination t_NR in this silicon sample is 100 µsec. What is the efficiency ? of light emission? Choose the option close to your estimated value.

A. 10^-2

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B. 10^-3

C. 10^-4

Options:

Question Number: 13 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

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Figure below shows an experiment to measure the drift mobility of carriers. A narrow pulse (of about 1 µsec duration) of minority carriers (holes in this case) is injected by light at point A of n-type Si bar sample. Holes drift towards point B in applied field and are collected at B and seen as broadened pulse signal. Distance L between points A and B is about 0.8 cm and the field applied is 7V/cm. The time t₀ between the application of hole injection at A and arrival of holes at B is 240 µsec. What is the drift velocity of holes in cm/sec? Choose the option close to your result.

A. 3000

B. 3330

C. 3550

Options:

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1. 1

2. 2

3. 3

Question Number: 14 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

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Question Number: 15 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

It is seen in the E-k diagram that the valence maximum consist of a heavy hole band for which the effective mass is m_hh* and a light hole band for which the effective mass is m_lh*. The effective mass of holes for calculating the density of states in the valence band is

A. (m_hh* + m_l)

B. [m_hh*. m_lh*]^½

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C. [(m_hh*)^3/2+(m_lh*)^3/2]^2/3

D. [(m_hh*)^{^(2/3)} + (m_lh*)^{^(2/3)}]^{^(3/2)}

Options:

1. 1

2. 2

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3. 3

4. 4

Question Number: 16 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

Lighting is important in our world today for several possible reasons, for example:

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i. It allows us to work beyond the hours of natural daylight

ii. Electricity is cheaply available today

iii. It allows us to use indoor spaces without natural light

iv. Fossil fuels are depleting and hence we need to shift to renewable energy

Which of the above reasons are correct?

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A. i)

B. i) ii)

C. i) and iii)

D. All of the options i) to iv)

Options:

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1. 1

2. 2

3. 3

4. 4

Question Number: 17 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

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Correct Marks: 1 Wrong Marks: 0

Which of these combinations is NOT a compound semiconductor?

A. Al_0.3Ga_1-xAs

B. YBa₂Cu₃O_7-x

C. ZnMgSSe

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D. InGaN

Options:

1. 1

2. 2

3. 3

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4. 4

Question Number: 18 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

The band gap of gallium phosphide, GaP, is 2.26eV corresponding to about 548 nm, in the green region of the visible spectrum. However, GaP is not used for making bright green LEDs because

A. The material has a monoclinic crystal structure making it difficult to work with

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B. It has an indirect band gap

C. It is too expensive for a commercial technology to be based on it

D. All of the above

Options:

1. 1

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2. 2

3. 3

4. 4

Question Number: 19 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

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The p-dopant most commonly used is

A. Magnesium

B. Zinc

C. Silicon

D. Phosphorus

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Options:

1. 1

2. 2

3. 3

4. 4

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Question Number: 20 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

One of the contributions of Shuji Nakamura was the use of thermal annealing to activate the p-dopants in GaN. The thermal annealing step helped to:

A. Reduce the defects and improve the crystallinity of GaN

B. Redistribute the dopants in the p-type layer

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C. Form nitrogen vacancies in the p-type layer

D. Remove hydrogen atoms that were passivating the acceptor impurities

Options:

1. 1

2. 2

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3. 3

4. 4

Question Number: 21 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

GaN is typically grown epitaxially on sapphire substrates. The ~33% lattice mismatch between GaN and sapphire is reduced to ~ 14.8% primarily due to

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A. A 30° relative rotation of the unit cell of sapphire w.r.t that of GaN

B. The relative change in lattice constant at the high growth temperature due to the different thermal expansion coefficients

C. The stable high temperature phase of GaN changing from hexagonal to orthorhombic

D. Substitution of oxygen atoms at the sapphire surface by nitrogen atoms

Options:

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1. 1

2. 2

3. 3

4. 4

Question Number: 22 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

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Correct Marks: 1 Wrong Marks: 0

The substrate with the least lattice mismatch to GaN is

A. Silicon (111)

B. Silicon carbide (SiC)

C. Sapphire

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D. Silicon (100)

Question Number: 23 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

A key step in the epitaxial growth of GaN on sapphire is the growth of a buffer layer between the sapphire and the GaN. In MOVPE growth, the main GaN layer is usually grown at ~ 1000-1050 °C. The buffer layer is grown at

A. A temperature higher than that used for the main GaN layer (1100-1150 °C)

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B. The same temperature as the main layer but with much higher ammonia flow

C. A lower temperature (520-550°C)

D. The same temperature as the main layer but at a very low reactor pressure

Options:

1. 1

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2. 2

3. 3

4. 4

Question Number: 24 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

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For blue LEDs the active region consists of quantum wells of

A. InGaN, embedded in GaN barriers

B. GaN, embedded in AlGaN barriers

C. Si-doped AlGaN embedded in GaN barriers

D. Si-doped GaN embedded in InGaN barriers

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Options:

1. 1

2. 2

3. 3

4. 4

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Question Number: 25 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

Which of the metals would form a good Ohmic contact to n-type GaN?

A. Pt

B. Pd

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C. Ti

D. Ni

Options:

1. 1

2. 2

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3. 3

4. 4

Question Number: 26 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

Based on Schottky barrier heights, which metal would form a good Ohmic contact to p-type GaN?

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A. Ti

B. Al

C. W

D. None of the above

Options:

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1. 1

2. 2

3. 3

4. 4

Question Number: 27 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

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Correct Marks: 1 Wrong Marks: 0

The main difficulty in light extraction from a GaN-based LED is

A. The poor internal quantum efficiency of the active region

B. Blockage of light due to the metal contacts

C. Scattering due to rough interfaces and the top surface

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D. A narrow escape cone for light due to the critical angle for light travelling from the semiconductor to air

Options:

1. 1

2. 2

3. 3

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4. 4

Question Number: 28 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

The term efficiency droop in an LED refers to the

A. Reduction of efficiency of light emission due to increasing indium content in the quantum well

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B. Reduction of efficiency of light emission on increasing current density

C. Reduction of efficiency of light emission due to aging of the device

D. Reduction of efficiency of light emission due to an increase in operating voltage

Options:

1. 1

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2. 2

3. 3

4. 4

Question Number: 29 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

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The gap problem in nitride LEDs refers to

A. Recombination at mid-gap defect states in GaN

B. Reduction of efficiency of light emission on increasing indium content in the quantum well when going from blue to green emitting LEDs

C. Environmentally friendly "green" LEDs being more expensive than the typical GaN LEDs

D. Poor performance of green-emitting LEDs due to absorption of green light in the sapphire substrate

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Options:

1. 1

2. 2

3. 3

4. 4

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Question Number: 30 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

The in-built electric polarization field in a GaN crystal

A. Is directed along the c-axis in the (0001) direction

B. Lies in the c-plane, directed along the (1-100) "m" direction

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C. Lies in the c-plane, directed along the (11-20) "a" direction

D. None of the above

Options:

1. 1

2. 2

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3. 3

4. 4

Question Number: 31 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

Nanowire LEDs may solve several of the performance limiting issues in planar LEDs. Which of these statements are correct about NW LEDs? NW LEDs can i) Remove constraints of lattice matching, ii) expose non-polar and semi-polar facets, iii) make p-type doping easier iv) increase reflectivity of the contacts

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A. i} and ii} only

B. i) and iii) only

C. ii), iii) and iv) only

D. All the statements i) to iv)

Options:

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1. 1

2. 2

3. 3

4. 4

Question Number: 32 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

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Correct Marks: 1 Wrong Marks: 0

LEDs may be more advantageous than mercury lamps for disinfection/water purification for the following reasons

A. The operating currents are lower, though the voltages needed are high

B. The operating temperature is lower

C. Large area devices can be made

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D. The wavelength can be tuned to match the absorption peak of DNA in bacteria

Options:

1. 1

2. 2

3. 3

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4. 4

Question Number: 33 Question Type: MCQ Option Shuffling: No Display Question Number: Yes Single Line Question Option: No Option Orientation: Vertical

Correct Marks: 1 Wrong Marks: 0

The colour temperature of an LED is related to

A. The

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