Germanium undoped

In traditional semiconductors such as silicon, germanium, or Ga2As3 the conductivity is between, say, 10 to 10 cm In an undoped solid, the concentration of free charge carriers is determined by n = where Aeff is... 

For stacked junction solar cells, one would like to tailor the optical properties so that the active material in the first junction has a wide band gap, and the active layers in other junctions have progressively narrower band gaps (see Section 8). As mentioned earlier, either carbon or nitrogen alloying can be used to open the optical gap, while alloying with tin or germanium can reduce the optical gap. Representative optical data for undoped a-Si C H and a-Si Ge H films are shown in Fig. 2. 

Hamers and coworkers showed that undoped diamond (001) surfaces undergo [2 + 2] cycloaddition reactions with a prototypical alkene, cyclopentene [95]. The (001) surfaces of diamond, silicon, and germanium share a similar bonding motif in which pairs of atoms can bond to each other via a strong a bond and a weaker tt bond forming a dimer. Normally, the formation of dimers on the diamond surface is prevented by hydrogen chemisorption however, the diamond (001) surface was made reactive for the addition reaction by heat treatment in the UHV at 1375 K. At these temperatures, the surface is cleaned of impurities and surface hydrogen desorbs. This leads to the formation of carbon atoms paired into C=C dimers with a partial 7t bond [95]. This surface is essentially an extended array of alkene-like C=C... 

Most fibers have a core which consists of silica doped with oxides of germanium or phosphorus to raise the refractive index. The cladding usually consists of pure, undoped silica... 

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