High-resolution, background-free spectroscopy of shallow-impurity transitions in semiconductors with a terahertz photomixer source

Abstract

We report on a method which enables background-free spectroscopy of the narrow absorption lines of shallow impurity transitions in low-doped and high-purity semiconductors, providing a much better spectral resolution than standard Fourier-transform spectrometers. To achieve this, we combined high-resolution continuous-wave terahertz spectroscopy based on a photomixer system with a bandgap excitation scheme for varying the concentration of neutral impurities. For the minority doping species, the lifetime of the excited states can be directly inferred from such a measurement by analyzing the line shape with respect to the width of the lifetime-related Lorentzian contribution. For a germanium sample with residual impurity concentrations of the order 1012 cm−3, we obtained lifetime values of 110 and 130 ps for the 2Γ8− excited state of the acceptors B and Al, respectively. The method complements time-domain pump-probe measurements for moderately and highly doped samples.

Combination of ultrafast time-resolved spectroscopy techniques for the analysis of electron dynamics of heliumlike impurity centers in silicon

“…Furthermore, high-quality crystal growth and precise doping of natural and isotopically enriched Si crystals by shallow donors as well as refined steady-state spectroscopy have led to high-quality spectral data. Nearlifetime-broadened (Lorentzian-shaped) absorption lines were shown [6][7][8] and appear to be in good agreement with the time-domain measurements [7]. In contrast to substitutional atoms in Si, magnesium (Mg, group-IIA) atoms are usually incorporated into the Si lattice by diffusion and occupy interstitial positions.…”