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Applied Physics Letters

Population inversion and far-infrared emission from optically pumped silicon

Heinz‐Wilhelm Hübers, Karsten Auen, Sergei G. Pavlov, Ekaterina E. Orlova, Roman Kh. Zhukavin, V. N. Shastin

Published May 3, 1999• 30 citations
Publisher

Abstract

A mechanism for the generation of population inversion and far-infrared emission in Si with shallow donors is investigated. By optically pumping a phosphorus doped Si crystal with a CO2 laser it was possible to achieve population inversion between the metastable 2p0 state and the 1s(E) and 1s(T) states. Spontaneous emission from these transitions was detected. Frequency measurements of this emission are in agreement with the expected transition frequency. Absorption measurements with a far-infrared probe laser confirm the existence of population inversion between the 2p0 state and the 1s(E) and 1s(T) states.

DOI
10.1063/1.123928

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A mechanism for the generation of population inversion and far-infrared emission in Si with shallow donors is investigated. By optically pumping a phosphorus doped Si crystal with a CO2 laser it was possible to achieve population inversion between the metastable 2p0 state and the 1s(E) and 1s(T) states. Spontaneous emission from these transitions was detected. Frequency measurements of this emission are in agreement with the expected transition frequency. Absorption measurements with a far-infrared probe laser confirm the existence of population inversion between the 2p0 state and the 1s(E) and 1s(T) states.
Two mechanisms of the inverse population of shallow impurity states in silicon under optical pumping have been proposed and analyzed, using a procedure allowing to reduce the number of required matrix elements of transitions. The first mechanism is based on the resonance interaction of the 2p0 state in Si:Bi with optical phonons. The other one is based on the suppression of acoustic-phonon-assisted relaxation from the 2p0 state in Si:P due to the momentum conservation law. Spontaneous emission was registered from shallow donors in Si:P under photoionization by a CO2 laser. The dependence of the spontaneous emission intensity on the intensity of pumping radiation confirms the possibility of amplification on impurity transitions.
The observation of far-infrared stimulated emission from shallow donor transitions in silicon is reported. Lasing with a wavelength of $59\ensuremath{\mu}\mathrm{m}$ due to the neutral donor intracenter ${2p}_{0}\ensuremath{\rightarrow}1s(E)$ transition in Si:P pumped by CO2{\mathrm{CO}}_{2}CO2​ laser radiation is obtained. Populations of D0{D}^{0}D0 and ${D}^{\ensuremath{-}}$ center states and the balance of the radiation absorption and amplification are theoretically analyzed.
We report on an optically pumped laser where photons are simultaneously generated by population inversion and by stimulated Raman scattering in the same active medium, namely crystalline silicon doped by bismuth (Si∶Bi).The medium utilizes three electronic levels: ground state [j1i: 1sðA 1 Þ in Si∶Bi], upper [j3i: 2p Æ ] and lower [j2i: 1sðEÞ] laser levels.The j1i ↔ j3i and j2i ↔ j3i transitions are optically allowed and the j1i ↔ j2i transition is Raman active.Lasing based on population inversion occurs between the states j3i and j2i, while Raman scattering benefits from the Raman-active transition.At high pump power the inversion-based stimulated emission j3i → j2i disappears, because electronic scattering from j1i to j2i via a virtual state dominates and the electrons are excited into j2i rather than into j3i.Starting as population inversion-based lasing, it ends as stimulated Raman scattering.Our model shows that such a competition occurs on the timescale of the 10-ps-long pump pulse.
Abstract The relaxation rates of lower excited states 1s(T), 2p0, 2s, 3p0, and 2p± of arsenic donors in a germanium crystal are calculated upon the interaction with long-wavelength acoustic phonons depending on the uniaxial stress in the crystallographic direction [111]. The populations of states under optical excitation are estimated for calculated times. It is shown theoretically that optical excitation of the medium forms an inverse population of arsenic donor levels and leads to the possibility of the implementation of a four-level laser scheme with the radiative transition between 2p states and the 1s triplet state at zero strain. The estimated value of the expected gain in the medium under optical excitation conditions by CO2 laser radiation in the medium at a donor concentration of 2 × 1015 cm–3 is ~0.35 cm–1 at a frequency of 1.98 THz if the laser transition is 2p± → 1s(T) and 1.25 THz if the laser transition is 2p0 → 1s(T).
Abstract The results of experiments aimed at the observation of split 1s states in Mg-doped Si are reported. From the results, it is possible to determine the chemical shift and exchange interaction energy of a neutral Mg donor in Si. The position of the 1s(E), 1s(T2), and 2s(A1) parastates determines the possibility for attaining population inversion and the specific mechanism of stimulated Raman scattering. The energy of the 1s(T2) parastate is determined from the position of the Fano resonances in the photoconductivity spectrum of Si:Mg at T = 4 K, and the energies of the 1s(T2) and 1s(E) orthostates from the transmittance spectra at elevated temperatures. On the basis of the experimental data, the relaxation rates are estimated, and the possible mechanisms of stimulated emission are analyzed.