Semiconductor Physics

Informatie over het vak

Het vak wordt onderwezen in de eerste semester door prof. V. Afanasiev. Het examen is gesloten boek.

Examenvragen

30 augustus 2024 (Version ?)

Question 1

• What are the conditions for the conservation of crystal momentum in a semiconductor and why do they almost never apply in metals

Question 2

• Given N_c(T) and N_v(T) calculate the chemical potential in an intrinsic semiconductor.

Question 3

• What physical mechanisms determine the charge carrier dependence of semiconductor optical absorption spectra?

12 januari 2024 (Version 1)

Question 1

• Describe the physical principle of Deep Level Transient Spectroscopy (DLTS). What physical information can be obtained in this way?

Question 2

• Describe the temperature-induced changes of barrier height at the interfaces of a metal with n- and p-type semiconductors. What effect will it have on the current-voltage and capacitance-voltage characteristics?

-> barrier height refers to both phi_ms as to psi_s, thus to the barrier height and to the surface potential/band bending

Question 3

• What physical mechanisms determine the temperature dependence of semiconductor optical absorption spectra?

27 januari 2022 (Versie 1)

Question 1

• Explain why the binding energies of donor/acceptor levels are so much smaller than the bandgap energy. How can we use the hydrogen model explain this and what are the differences?

Question 2

• Consider a PN-junction in equilibrium. At V=0, draw and explain the curves of carrier concentration, charge density, electric potential and electric field.
• Do the same for forward bias.

Question 3

• Explain the exciton optical absorption, the influence of temperature on the spectrum and the physical mechanisms behind this.

27 januari 2022 (Versie 2)

Question 1

• Describe the physical principle of Deep Level Transient Spectroscopy (DLTS). What physical information can be obtained in this way?

Question 2

• Describe the temperature-induced changes of barrier height at the interfaces of a metal with n- and p-type semiconductors. What effect will it have on the current-voltage and capacitance-voltage characteristics?

Question 3

• What physical mechanisms determine the temperature dependence of semiconductor optical absorption spectra?

12 januari 2021 (Versie 1)

Question 1

• Explain why the binding energies of donor/acceptor levels are so much smaller than the bandgap energy. How can we use the hydrogen model explain this and what are the differences?

Question 2

• Consider a PN-junction in equilibrium. At V=0, draw and explain the curves of carrier concentration, charge density, electric potential and electric field.
• Do the same for forward bias.

Question 3

• Explain the exciton optical absorption, the influence of temperature on the spectrum and the physical mechanisms behind this.

12 januari 2021 (Versie 2)

Question 2

• Consider a PN-junction in equilibrium. At V=0, draw and explain the curves of carrier concentration, charge density, electric potential and electric field.
• Do the same for reverse bias.

16 januari 2020

Question 1

• What properties of a semiconductor affect the reverse current of a p-n junction as opposed to the Schottky diode (metal-semiconductor contact)?

Question 2

• What is the physical origin of the difference between the spectral distributions of optical absorption and luminescence in direct-gap and indirect-gap semiconductors?

Question 3

• Describe the effect of acceptor impurity concentration on the capacitance-voltage characteristics of metal/semiconductor and metal/oxide/semiconductor capacitors.

Other exam questions

• Discuss the effective mass concept within the semi-classical model used for describing electrons (charge carriers) within condensed matter.
  • Explain in more detail the meaning of this for a pure parabolic band.
  • What parameters determine the effective mass within the k.p method for a non-degenerate band? Discuss limitations of the effective mass approximation.
• Derive the Einstein formula for electrons describing the relationship between the diffusion constant and the mobility of an electron in a semiconductor. For help: Consider a p-n junction with nc(x) = N(T)exp(-[Ec-e*phi(x)-mu]/kT).
• A free-standing GaAs film of 10 ?m thickness absorbs 50 % of an incident monochromatic light bundle with photon energy hv = 1.65 eV and power density 10 W/cm². Calculate the absorption coefficient.
  • If we assume a carrier generation efficiency of 1 electron-hole pair/photon, at what depth in the film will the generation rate be reduced to 20 % of its value at the surface and calculate the generation rate at this depth. 1 Joule = 6.24x10^18 eV.