Below is a figure that depicts the potential energy of an electron (a finite square well), as well as the energies associated with the first two wave-functions. a) Sketch the first two stationary wavefunctions (solutions to the Schrődinger equation) for an electron trapped in this fashion. Pay attention to detail! Use the two dashed lines as x-axes. U(x) E2 E1 b) If the potential energy were an infinite square well (not finite well as shown above), what would the energy of the first two allowed energy levels be (i.e., E1 and E;). Write the expressions in terms of constants and a (the width of the well) and then evaluate numerically for a = 6.0*10*10 m. [If you don't remember the formula, you can derive it by using E = h°k² /2m, together with the condition on À = 2a/n.) c) Let's say I adjust the width of the well, a, such that E1 = 3.5 ev. In that case, calculate the wavelength (in nanometers) of a photon that would be emitted in the electron's transition from Ez to E1. [Remember: hc = 1240 eV nm] b) In this same infinite square well (from part c), how many states (or energy levels) are there below an energy ceiling of 200 eV? Given the Pauli exclusion principle, how many electrons would fit into those states?

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Below is a figure that depicts the potential energy of an electron (a finite square well), as well as the
energies associated with the first two wave-functions.
a) Sketch the first two stationary wavefunctions (solutions to the Schrődinger equation) for an electron
trapped in this fashion. Pay attention to detail! Use the two dashed lines as x-axes.
U(x)
E2
E1
b) If the potential energy were an infinite square well (not finite well as shown above), what would the
energy of the first two allowed energy levels be (i.e., E, and E2). Write the expressions in terms of
constants and a (the width of the well) and then evaluate numerically for a = 6.0*1010 m. [If you don't
remember the formula, you can derive it by using E = h*k*/2m, together with the condition on à =
2a/n.)
c) Let's say I adjust the width of the well, a, such that E1 = 3.5 ev. In that case, calculate the wavelength
(in nanometers) of a photon that would be emitted in the electron's transition from Ez to E1.
[Remember: hc = 1240 eV nm]
b) In this same infinite square well (from part c), how many states (or energy levels) are there below an
energy ceiling of 200 ev? Given the Pauli exclusion principle, how many electrons would fit into those
states?
Transcribed Image Text:Below is a figure that depicts the potential energy of an electron (a finite square well), as well as the energies associated with the first two wave-functions. a) Sketch the first two stationary wavefunctions (solutions to the Schrődinger equation) for an electron trapped in this fashion. Pay attention to detail! Use the two dashed lines as x-axes. U(x) E2 E1 b) If the potential energy were an infinite square well (not finite well as shown above), what would the energy of the first two allowed energy levels be (i.e., E, and E2). Write the expressions in terms of constants and a (the width of the well) and then evaluate numerically for a = 6.0*1010 m. [If you don't remember the formula, you can derive it by using E = h*k*/2m, together with the condition on à = 2a/n.) c) Let's say I adjust the width of the well, a, such that E1 = 3.5 ev. In that case, calculate the wavelength (in nanometers) of a photon that would be emitted in the electron's transition from Ez to E1. [Remember: hc = 1240 eV nm] b) In this same infinite square well (from part c), how many states (or energy levels) are there below an energy ceiling of 200 ev? Given the Pauli exclusion principle, how many electrons would fit into those states?
The formula for the contact potential of a pn-junction diode is given by the formula:
apo = "in ().
NaNa
kT
a) This contact potential ensures that the net current across the junction is zero. Which side is higher
in electron potential energy – the n or the p-side? Briefly explain your answer.
b) Even though there is no net current across the pn-junction in equilibrium with no applied voltage
(V=0), there are two individual currents associated with electrons that add to zero (and two more
associated with holes) – drift and diffusion current. Explain what they are (and how they arise), and
give their direction (for electrons).
c) Which of the two types of current is independent of A$o? Briefly explain why.
d) Arguing from the formula above for A$o, give a conceptual reason for the fact that germanium (Ge)
diodes have about half the contact potential compared to silicon (Si) diodes, all else being equal
(same doping concentrations and temperature). For a photodiode (PV cell), would you choose Si or
Ge, and why?
Transcribed Image Text:The formula for the contact potential of a pn-junction diode is given by the formula: apo = "in (). NaNa kT a) This contact potential ensures that the net current across the junction is zero. Which side is higher in electron potential energy – the n or the p-side? Briefly explain your answer. b) Even though there is no net current across the pn-junction in equilibrium with no applied voltage (V=0), there are two individual currents associated with electrons that add to zero (and two more associated with holes) – drift and diffusion current. Explain what they are (and how they arise), and give their direction (for electrons). c) Which of the two types of current is independent of A$o? Briefly explain why. d) Arguing from the formula above for A$o, give a conceptual reason for the fact that germanium (Ge) diodes have about half the contact potential compared to silicon (Si) diodes, all else being equal (same doping concentrations and temperature). For a photodiode (PV cell), would you choose Si or Ge, and why?
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