Exploitable results
The properties of oxygen in quasi-monoisotopic germanium (Ge) samples have been investigated by infrared and phonon spectroscopies and the attempts of doping germanium by laser annealing have been continued. The main results are summarized below.
Interstitial oxygen (Oi) has been introduced in natural Ge (nGe) by laser annealing in air using either 193 or 249 nm laser wavelengths and a pulse energy density near 1 J/cm2. The Oi concentration introduced exceeds the equilibrium solubility by a factor of about 50.
In Kiev, thermal donors related to oxygen, produced in 74Ge by annealing at 350°C in air have been detected by their IR electronic absorption.
In Paris, annealing in argon of 70Ge at 350C for 170 hours has produced a reduction of [Oi] by a factor of 5. This reduction is mainly due to the precipitation of GeO2 and to a lesser extent to the production of thermal donors.
Small frequency shifts of the position of the Ge2O antisymmetric modes have been observed in Paris between 70Ge and 76Ge on the one hand and nGe in the other hand. The shifts are opposite for 70Ge and 76Ge. They are explained for 70Ge by an increase of the interaction between the Oi mode and the lattice phonon spectrum compared to nGe and to a decrease in the case of 76Ge. This is the first time that such an effect is observed. This effect is due to the shape of the three-phonon density of state of Ge and it should be absent for 17O and 18O. The absorption of 17O has been observed in a nGe sample using a multireflexion geometry at low-temperature, but further measurements require a sample with a lower intrinsic absorption.
In Ge, the rotational motion of Oi at low energy is difficult to figure out. The Ge isotope shift of the phonon resonance lines observed in Stuttgart in qmi Ge samples was unexpected at first sight. It brought an evidence of the coupling of the motion of the Ge lattice to the rotation of Oi. and/or of the participation of the first Ge neighbours to the rotation. The measurement of the phonon resonance rotation spectra of 18O in 18O-implanted nGe samples has allowed to evaluate the 16O-18O rotational isotope shift. This shift is smaller than expected if only Oi would rotate and it seems also to imply the contribution of the first Ge neighbours.
A further outcome of these phonon resonance measurements in qmi Ge has been the detection of excited states of the rotational motion at higher energies. Their fitting to the calculations allows to determine a model potential for the low-energy motion of the Oi centre in germanium.
È in corso la ricerca di dati su OpenAIRE...
Si è verificato un errore durante la ricerca dei dati su OpenAIRE
Nessun risultato disponibile