Semiconductor Physics - Assignment 2 PDF

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Summary

Consider a bar of n-type silicon that is uniformly doped to a value of Nd = 2 x 1016 cm−3
at
T = 300 K. The applied electric field is zero. A light source is incident on the end of the
semiconductor as shown in figure below. The steady-state concentration of excess carriers

Description

Assignment 2 (Please submit online to the drop box. Deadline: Nov. 29, 23:59)

Use the following parameters for your calculation is need. Physical parameter for Si Bandgap Effective density of states for electron, Nc Effective density of states for hole, Nv

Value 1.12 eV 2.80×1019 cm−3 1.04 ×1019 cm−3

Q1. The value of p0 in silicon at T = 300 K is 2 x 1016 cm−3. (a) Determine EF − Ev. (b) Calculate the value of Ec − EF. (c) What is the value of n0? (d) Determine EFi − EF.

Q2. Silicon atoms, at a concentration of 7 x 1015 cm−3, are added to gallium arsenide. Assume that the silicon atoms act as fully ionized dopant atoms and that 5 percent of the concentration added replace gallium atoms and 95 percent replace arsenic atoms. Let T = 300 K. (a) Determine the donor and acceptor concentrations. (b) Is the material n type or p type? (c) Calculate the electron and hole concentrations. (d) Determine the position of the Fermi level with respect to EFi.

Q3. The steady-state electron distribution in silicon can be approximated by a linear function of x. The maximum electron concentration occurs at x = 0 and is n(0) = 2 x1016 cm−3. At x = 0.012 cm, the electron concentration is 5 x 1015 cm−3. If the electron diffusion coefficient is Dn = 27 cm2/s, determine the electron diffusion current density. Q4. In GaAs, the donor impurity concentration varies as n = Nd0 exp (−x / L) for 0 ≤ x ≤ L, where L = 0.1 μm and Nd0 = 5 x 1016 cm−3. Assume μn = 6000 cm2/V-s and T = 300 K. (a) Derive the expression for the electron diffusion current density versus distance over the given range of x. (b) Determine the induced electric field that generates a drift current density that compensates the diffusion current density to make the total electron current Jn = 0.

Q5. Consider a bar of n-type silicon that is uniformly doped to a value of Nd = 2 x 1016 cm−3 at T = 300 K. The applied electric field is zero. A light source is incident on the end of the semiconductor as shown in figure below. The steady-state concentration of excess carriers generated at x = 0 is δp(0) = δn(0) = 5 x 1014 cm−3. Assume the following parameters: μn =1200 cm2 /V-s, μp = 400 cm2 /V-s, τn0 = 1x10−6 s, and τp0 = 5 x 10−7 s. Neglecting surface effects. (a) Starting from Ambipolar Transport Equation to determine the steady-state excess electron and hole concentrations as a function of distance into the semiconductor. (b) Calculate the steady-state electron and hole diffusion current densities as a function of distance into the semiconductor.

n-type...