Set 7 Web Solutions LC

8/22/2019 Set 7 Web Solutions LC

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P3000 LON-CAPA Set 7 Sample Solutions

1. pn Junction: From Neamen Sect. 9.2. Calculate the magnitude of the applied reverse-

bias voltage at which the ideal reverse current in a pn junction diode at T = 290 K reaches

81 % of its reverse saturation value. Enter your answer in volts.

Cor r ect , comput er get s: 4. 15e- 02

Hint:


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2. pn Junction: From Neamen Sect. 9.2. Consider an ideal silicon pn junction diode

with the following parameters: tau_n0 = 1.0010-7

s, tau_p0 = 1.0010-7

s, D_n = 30cm^2/s, and D_p=12 cm^2/s. What ratio of acceptor concentration (N_a) to donor

concentration (N_d), is needed so that 55 % of the depletion curent is carried by

electrons? Enter your answer as the value of N_a/N_d.

Corr ect , computer get s: 1. 29e+00

Hint:


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3. Optical Absorption: From Neamen Sect. 12.1. Calculate the maximum wavelength

of a light source that can generate electron-hole pairs in GaAs. Enter your answer in cm.


4. Optical Absorption: From Neamen Sect. 12.1. Photons of energy 1.34 eV are incident

on a thin slab of silicon at a power density (intensity) of 1.0010-2

W/cm^2. Theabsorption coefficient for silicon at this photon energy is 1.5210

2cm^-1. The excess

minority-carrier lifetime is 1.0010-6

s. In the first box, enter the electon-hole generation

rate in units of cm^-3*s^-1. In the second box, enter the steady-state excess carrierconcentration in cm^-3. Neglect surface effects.

Corr ect , comput er get s: 7. 09e+18, 7. 09e+12

Hint: Be very careful with units!


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5. Optical Absorption: From Neamen Sect. 12.1. Photons of energy 1.67 eV are incident

on a slab of GaAs. The absorption coefficient for GaAs at this photon energy is 1.70104

cm^-1. In the first box, enter the thickness, in cm, of GaAs so that 65 % of the energy is

absorbed. In the second box, enter the thickness, in cm, of GaAs so that 65 % of the

energy is transmitted.

Cor r ect , comput er get s: 6. 18e- 05, 2. 53e- 05

Hint: Be very careful with units!


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6. Solar Cells: From Neamen Sect. 12.2. Consider an ideal long n^+p junction GaAs

solar cell at T = 300 K in which excess carriers are uniformly generated. The parametersof the diode area as follows: N_d = 1.2010

19cm^-3, tau_n0 = 5.0010

-8s, tau_p0 =

5.0010-8

s, D_n=225 cm^2/s, D_p = 7 cm^2/s. The generated photcurrent density is J_L

= 31 mA/cm^2. In the first box, enter the reverse saturation current for this diode, in

A/cm^2, assuming that the acceptor concentration density on the p side is 1.0010

16

cm^-3. In the second box, enter the corresponding open-circuit voltage in volts. In the

calculation of minority carrier concentrations, you may use the intrinsic carrier

concentration for GaAs provided in table B4 of your text book.

Cor r ect , comput er get s: 3. 48e- 18, 9. 50e- 01

Hint: You can find an expression for the reverse saturation current of a pn diode in

section 9.2 of your text.


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7. Photodectectors: From Neamen Sect. 12.2. Repeat the previous question assuming an

acceptor concentration density on the p side is 7.001018

cm^-3. In the first box, enter thereverse saturation current in A/cm^2. In the second box, enter the corresponding open-

circuit voltage in volts.

Corr ect , computer gets: 5. 48e- 21, 1. 12e+00

Hint: You can find an expression for the reverse saturation current of a pn diode in

section 9.2 of your text.

8. LEDs From Neamen Sect. 12.3. Consider a silicon PIN diode at T = 300 K illuminated

by an incident photon flux of Phi_0 = 4.001017

cm^-2*s^-1. Assume that the width ofthe intrinsic layer is 1.0010

-2cm. Enter the prompt photocurrent density in A/cm^2.

Assume that the absorption coefficient is 3.00103 cm^-1.


Hint: Be careful with units!


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9. [4pt] From Neamen Sect. 12.4. Consider a pn junction GaAs LED. Assume that

photons are generated uniformly in all directions on a plane to the junction at a distanceof 0.50e-6 m fom the surface. In the first box, enter the fraction, as a percentage, of the

emitted photons that have the potential of being emitted from the semiconductor surface

without undergoing total internal reflection. In the second box, enter the fraction, as a

percentage, of generated photons that can be emitted into air when both total internalreflection and Fresnel loss are taken into account. Neglect absorption losses. Assume that

the index of refraction for GaAs is 3.66.

Cor r ect , comput er get s: 8. 81, 5. 94

Hint: For the total internal reflection part, remember that the problem says that the

photons are emitted in all directions along a plane, not in all directions in 3 dimensions.

For the second part, that the Fresnell loss will be on top of the losses due to total internalreflection.

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Set 7 Web Solutions LC