Line spectrum of the interstitial iron donor in silicon

Photothermal ionization spectroscopy and infrared transmission measurements have been carried out on iron‐doped silicon. A series of sharp lines in the range from 6100 to 6400 cm⁻¹ was observed with both techniques. Photoionization cross‐section spectra were determined by photothermal ionization spectroscopy and photoelectron paramagnetic resonance, and it is concluded that the lines originate from electronic transitions to excited shallow donor states at the interstitial iron impurity in the neutral charge state Fe⁰_i. The lines and the Fe⁰_i ‐related electron paramagnetic resonance signal annealed out together at approximately 170 °C. The line spectra are analyzed in terms of three overlapping donor series and the origins of these are discussed.