[填空题]
The energy gap between valence and c,m*c+25p eyogjl7t edonducga2tm-jy d*y 4tion bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band i*jy24-dym gta nto the conduction band? $\lambda \leq$ $ \ \mu\text{m}$
