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The spectra of germane enriched up to 99.9 % of 73GeH4 were recorded with a high resolution (0.003 cm − 1 ) at different pressures with the Bruker IFS 125HR Fourier transform spectrometer (Nizhny Novgorod, Russia) in the region of 650–4400 cm − 1 and analyzed in the Dyad and Pentad region. The 9208 transitions belonging to the seven “cold” bands (6987 transitions) of the Dyad and Pentad and to the nine “hot” Dyad–Pentad bands (2221 transitions) were assigned and theoretically analysed in the frame of the effective Hamiltonian model. The obtained set of 68 fitted parameters reproduces the initial 9208 experimental line positions with the d r m s = 2.82 × 10 − 4 cm − 1 .

The spectra of germane 72GeH4 and 73GeH4 enriched up to 99.9 % were recorded with high resolution (0.003 cm − 1 ) at different pressures with the Bruker IFS 125HR Fourier transform spectrometer (Nizhny Novgorod, Russia). The region of 4020–4260 cm − 1 , where the 2ν1(A1) and ν 1 + ν 3 ( F 2 ) bands are located, was theoretically analyzed. The 2025 and 1774 transitions with J max = 21 were assigned to these bands of the 72GeH4 and 73GeH4 species. Rotational, centrifugal distortion, tetrahedral splitting, and interaction parameters of the (2000, A1) and (1010, F2) vibrational states were determined from the fit of experimental line positions of both isotopologues. The obtained sets of 13/13 fitted parameters reproduce the initial 2025/1774 experimental line positions with a d rms = 2.9 × 10 − 4 cm − 1 and d rms = 2.7 × 10 − 4 cm − 1 (for 72GeH4 and 73GeH4, respectively).

We have recently shown that the dramatic reduction in linewidth of many deep luminescence centers in highly enriched 28 Si can lead to the observation of isotopic fingerprints, revealing not only that a specific element is involved in the defect complex, but also the number of atoms of that element. This has led to many surprises regarding the actual constituents of supposedly well known luminescence centers, as well as the discovery of new members of a family of four-atom centers where the constituents can be chosen from Cu, Ag, Au and Li. Obtaining the isotopic fingerprint of Au is problematic, since only 197 Au is stable, but we have now used the relatively long-lived 195 Au to reveal the presence, and the number, of Au atoms in several of these centers. We find a series of four-atom centers containing one Au plus Cu and/or Li. Surprisingly, the Au isotopic fingerprint also reveals a series of five-atom centers containing a single Au plus Cu and/or Li. Further evidence for the ubiquity of these four- and five-atom defects is provided by two previously observed Pt-related centers, with luminescence at 884 and 777 meV, which are present in these samples due to the decay of 195 Au to 195 Pt. In addition to Pt, these centers are found to contain three and four Cu atoms, respectively.

Recent studies have demonstrated remarkable improvements in the spectroscopy of shallow impurities by using highly enriched 28 Si to eliminate the inhomogeneous isotope broadening inherent in natural Si. Here, we show that similar dramatic improvements in the linewidths of electronic transitions of two well-known deep levels can be achieved in highly enriched 28 Si. New fine structure is revealed in the absorption spectrum of the Se double donor, and one of the transitions of Se + becomes so sharp that a splitting due to a hyperfine coupling with the I = 1/2 nuclear spin is revealed for 77 Se + . Under an applied magnetic field, the electronic and nuclear spins can be individually determined leading to the possibility of applications in quantum computing. The photoluminescence transitions of the well-known 1014meV Cu-related luminescence center also sharpen dramatically in 28 Si, allowing fine structure due to Cu isotope shifts to be resolved. Current models disagree as to whether this center contains one or two Cu atoms, but our results clearly demonstrate the involvement of four Cu atoms.

We present a study of excitons bound to sulphur- and copper-related isoelectronic centres in highly enriched 28Si. The S-related centre, which has been shown to have two configurations, SA and SB, was believed to consist of a substitutional sulphur atom paired with an interstitial copper atom. High resolution photoluminescence (PL) emissions from the no-phonon S B 0 transition reveal fine structure not observable in natural silicon. In both 28Si:natS and 28Si:34S, low temperature PL reveals at least 18 distinct components of the S B 0 system, including a triplet splitting seen in natSi:natS by optical detection of magnetic resonance. Investigation of the effect of copper isotopic composition on the S B 0 system shows that the centre contains at least three copper atoms. We also present results of the copper isotope effect on the 943.7 meV *Cu00 system in 28Si and show that three Cu atoms contribute to the Cu isotope shift of *Cu00.

The chalcogen deep double donor sulfur (S) has been studied extensively with optical methods in natural silicon ( Si nat ) . Recently, it was shown that the spectroscopic linewidths of absorption transitions from shallow impurities like boron and phosphorus is limited by inhomogeneous broadening due to a Si isotope effect which is removed with the use of highly enriched 28Si. In this work we extend these results to deep centers and show that the true homogeneous linewidths of many transitions can only be revealed in isotopically enriched Si. The S + 1 s ( T 2 ) Γ 7 transition exhibits a full width at half maximum (FWHM) of only 0.008 cm - 1 in 28Si—more than one order of magnitude sharper than in Si nat , and substantially narrower than the sharpest transitions of B and P in 28Si. Hence, it is the narrowest absorption line ever seen for impurity states in semiconductors. We also report dramatically narrower absorption transitions for the neutral S 0 center, together with higher excited states than previously observed. The isotope shifts of S absorption transitions between Si nat , 28Si and 30Si are also reported.