POTENTIAL OF SI1-XGEX ALLOYS FOR AUGER GENERATION IN HIGHLY EFFICIENTSOLAR-CELLS

Recent investigation on Si solar cells demonstrated the utility of Aug er generation for the creation of more than merely one electron/hole p air per absorbed photon. The semiconductor Si requires a minimum photo n energy of about 3.4 eV for this internal carrier multiplication. The current of a Si cell is therefore not significantly increased by Auge r generation when the cell is illuminated by an air mass 1.5 spectrum, which contains only few photons with energies above 3.4 eV. Use of Si 1-xGex alloys promises a lower onset energy. Unfortunately, incomplete data on band structures of random Si1-xGex alloys preclude a detailed quantitative discussion of the full potential for these materials. Ne vertheless, (i) analogies to our own quantum efficiency data from pure Si, (ii) the calculated band structure of the hypothetical, ol del ed zincblende type Si0.5Ge0.5 crystal, and (iii) optical data for Si1-xG ex alloys indicate an optimum Ge content of x = 0.6 to x = 0.7.