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HW4 - the difference of a semiconductor and a metal ay 0 K...

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ECE331 Homework #4 (Due Friday, May 2, 2008) 1. Explain the concept of electron effective mass. At what scenario the effective mass is the actual electron mass? Use equations if necessary. 2. Explain the concept of direct and indirect semiconductors. Use E-K diagram if necessary. 3. A semiconductor such as Si has a band structure with the X minimum along [100] described approximately by E = E 0 – Acos(ak x ) – B[cos(bk y ) + cos (bk z )]. What is the density of states effective mass associated with the X minimum? [hint: cos(2x) = 1-2x 2 for small x.] 4. Sketch the band diagram of semiconductors, metals, and insulators at 0 K. What is
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Unformatted text preview: the difference of a semiconductor and a metal ay 0 K? 5. What are the common dopants for GaAs (n-type and p-type)? If a piece of GaAs is doped with the same number of donors and acceptors with full ionization, is this an intrinsic semiconductor or an extrinsic semiconductor? Why? 6. What are the necessary conditions for optical emission to occur? Which semiconductors will have higher efficiency of optical emission, director semiconductors or indirect semiconductors? Why?...
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