EE 461G Introduction to Electronics

Homework # 6 Due October 12, 1999

Problem 1

For the junction diode below answering the following questions.

  1. How many valance electrons does the impurity on the N side have?
  2. In which direction (N to P or P to N) is it difficult for the current to flow in?
  3. Draw the schematic symbol in the correct orientation with respect to the N and P side of the diode.
  4. Which side (N or P) of the junction is the anode and the cathode?

Problem 2

  1. For a solid, the allowed energy states for electrons form into bands separated by energy gaps. No electron can posses any energy value in the energy gap. For semiconductors the two most important energy bands are the valance band and the conduction band. Which has more energy, an electron in the conduction band or or one in the valance band?
  2. In terms of the valance and conduction bands what is an electron and what is a hole?
  3. When a sample of intrinsic Si is at absolute zero how full are its conduction and valance bands.
  4. When a sample of intrinsic Si is at room temperature
    1. how many holes per cm3 are in the valance band
    2. how many electrons per cm3 are in the conduction band.
  5. Why can bands other than the conduction and valance bands, with energy values below the valance energies, be neglected in the treatment of the electrical behavior of semiconductors?

Problem 3

A sample of silicon is doped with 2.0 1014 phosphorus atoms per cm3.

  1. Is the sample n or p type? What are the majority and minority carriers
  2. What is the concentration of holes and electrons?
  3. Which concentration changes more with temperature, the hole or the electron concentration?

Next, half of the sample is doped with 3.0 1016 boron atoms per cm3.

  1. Is the boron doped half of the sample n or p type? What are the majority and minority carriers in this half of the sample.
  2. What is the concentration of holes and electrons in the boron doped half of the sample?
  3. Plot the electron and hole concentrations from one end of the sample to the other.

Problem 4

For the circuit shown below connect two pulse sources back to back in order to generate a pulse that goes +/- 100V with a pulse width of 100ms and a frequency of 5kHz. The pulse rise and fall times should be 100ns. The resistor value is 1kW.

Simulate the circuit and plot the diode current for

  1. Diode parameters IS = 80nA and n =2.
  2. Diode parameters IS = 80nA, n =2, and tt = 10ms.
  3. Diode parameters IS = 80nA, n =2, tt = 10ms, and cjo = 30pF.
  4. What are values of tend and tstep did you use?
  5. What conclusions can you draw?