EC ENGR 121B: Principles of Semiconductor Device Design
Homework #7
Due: Friday Nov 22, 2024 at 11:59pm by Bruinlearn pdf upload
Assume χSi=4.03 eV
1. Short answer. Answer in complete sentences, with a maximum of two sentences for each.
a. Is the forward bias current in an MS diode dominated by majority or minority carriers?
b. List two ways we can achieve an ohmic contact to a semiconductor.
2. For the two ideal MS contacts described below, draw the equilibrium band diagram, state
whether the contact is Ohmic or rectifying, and provide calculations as needed to justify your answer and diagram. Assume the temperature is 300 K. Assume Ei is at mid-gap.
a. Si contact to Al (ΦM=4.1 eV), where the Si has ND = 1017 cm-3.
b. Si contact to Al (ΦM=4.1 eV), where the Si has NA = 1017 cm-3.
3. Consider an indium metal - germanium semiconductor junction. Consider an ideal junction, i.e. there are no surface states to pin the Fermi level. Use the following parameters: indium metal work function ΦM = 4.1 eV, electron affinity in Ge χ = 4.00 eV, relative permittivity is Ge is 16.0, and doping in germanium of NA = 1016 cm-3. Assume Ei is at mid-gap.
a. Sketch the band diagram at thermal equilibrium. Is this a Schottky diode or an Ohmic contact?
b. Which charge carrier (electron or hole) determines the I-V characteristics?
c. Determine the potential barrier at the junction ΦB.
d. Determine the built-in potential Vbi.
e. Calculate Wunder equilibrium conditions.
f. Calculate Emax in the semiconductor under equilibrium conditions.
g. Sketch the I-V curve. Define the voltage as the difference between the metal side and the semiconductor side, i.e. V = Vmetal – Vsemiconductor.
4. You are given an MS diode made with n-type silicon and a metal such that a Schottky barrier is formed. The diode is illuminated, generating electron-hole-pairs inside the semiconductor.
a. Consider the case when the diode terminals are short-circuited during illumination.
Draw the energy band diagram. Include a cartoon of what happens to the photogenerated carriers created in the semiconductor near the MS interface (along the lines of Fig. 14.3 b and c, but with zero applied voltage.) If current flows, indicate its direction.
b. Consider the case when the diode terminals are open-circuited during illumination. Remember that under open-circuit conditions, no current can flow. Draw the energy band diagram. If a potential is dropped across the diode, indicate its polarity.
c. Based on your answers to (a) and (b), sketch the expected shape of the I-V characteristic of the illuminated MS photodiode. Explain the shape.