Introduction to Inorganic Chemistry/Electronic Properties of Metals, Superconductors, and Semiconductors

Chapter 10: Electronic Properties of Materials: Superconductors and Semiconductors   10.1 Metal-insulator transitions   10.2 Superconductors   10.3 Periodic trends: metals, semiconductors, and insulators   10.4 Semiconductors: band gaps, colors, conductivity and doping   10.5 Semiconductor p-n junctions   10.6 Diodes, LED's and solar cells   10.7 Amorphous semiconductors   10.8 Discussion questions   10.9 Problems thumb|500px1. The structure of a high temperature superconductor containing barium, europium, copper, and oxygen is shown at the right. What is the stoichiometry of the compound? This structure is actually closely related to perovskite, ABO3. Mark the positions of the missing atoms that would be found in a perovskite. 2. VO2 can exist in insulating or metallic form, depending on temperature and pressure. Which form would be stabilized by increasing the pressure? Explain your answer. 3. Offer a brief explanation of why bandgaps for octet p-block semiconductors (1) decrease with increasing average principal quantum number, and (2) increase with increasing electronegativity difference. 4. Indicate the type of conduction (n or p) in the following: (a) Zn-doped GaAs, (b) In1+xAs1-x, where x << 1, (c) Li0.05Cu0.95O, (d) WO2.999 5. Using 1 eV = 1240 nm, predict the colors of ZnO (Eg = 3.2 eV), AlP (2.5 eV), ZnSnP2 (2.1 eV), CdGeP2 (1.8 eV), and InP (1.27 eV). 6. Pure Ge is much more conductive than pure Si. Given their bandgaps (0.74 and 1.15 eV, respectively), estimate the ratio of their conductivities at room temperature. 7. Sketch a silicon p-n junction, showing the depletion region, band bending, and the Fermi level in the absence of light or applied potential. In the dark, the p-n junction acts as a rectifier. Which way does current flow with an applied bias? In the light, the junction acts as a photodiode. Which way does current flow in this case?