[填空题]
The energy gap between valence and conduction bands in germxmg;fyw3,l:r0r jf 3a u.d3c yanium is 0.7zimzk1t+i7fzf8z-q u/ 3k,fip d:ypxh;/u x32 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band into the conduction ba:x/3 kf+1xyuiz qhfm7kip3,/z;di zfztu-p8nd? $\lambda \leq$ $ \ \mu\text{m}$
