Absorption and Emission Spectra of Silicon and Germanium in the Soft X-Ray Region

The absorption spectra of thin evaporated foils of Si and Ge have been investigated in the soft x-ray region extending from 70 A to 200 A. The thicknesses of the various absorbers ranged from several hundred to several thousand angstroms. The spectral region covers the $L_{2,3}$ and $M_{2,3}$ absorption discontinuities of Si and Ge, respectively. The $L_{2,3}$ edge of Si appears at 123 A, while the $M_{2,3}$ edge of Ge is centered at 101.5 A. The linear absorption coefficients on the high-energy side of the respective edges of Si and Ge are 1.4×${10}^5$ ${\mathrm{cm}}^{-1\mathrm{}}$ and 1.8×${10}^5$ ${\mathrm{cm}}^{-1\mathrm{}}$. The emission spectrum of a Ge target was also studied in the 60 A to 600 A region. Two bands, whose peaks fall at 102.4 A and 104.3 A, have been identified as the $M_2$ and $M_3$ emission spectra, corresponding to transitions from the valence band into the $M_2$ and $M_3$ levels. With the aid of the present measurements and Skinner's data on the $L$ emission bands of Si, it has been possible to arrive at an estimation of the magnitude of the energy gap in each semiconductor on the basis of the observed interval between emission and absorption edges. The range of forbidden energies as determined by the spectroscopic method is found to be 1.0 ev and 0.8 ev for Si and Ge, respectively.