E C Lightowlers

The role of defect interactions in reducing the decay time of H3 luminescence in diamond

The decay time of the cathodoluminescence emission from the H3 centre has been measured for diamonds containing nitrogen concentrations up to 0.15 atomic per cent, the nitrogen being predominantly in the A form. In five diamonds with low nitrogen concentrations, <or approximately=0.01 atomic per cent, the mean decay time was found to be 16.7+or-0.5 ns, and this is considered to be close to the radiative lifetime of the H3 centre. For diamonds in which the width of the zero-phonon absorption line is predominantly controlled by the strain field of the A form of nitrogen, the decay time decreases linearly with the increasing width of the emission line. These results are shown to be consistent with a dipole-quadrupole transfer of energy from the H3 centres to the A form of nitrogen.

Photoluminescence lifetime, absorption and excitation spectroscopy measurements on isoelectronic bound excitons in beryllium-doped silicon

Abstract Photoluminescence lifetime measurements confirm that the intense lines seen in Be-doped Si result from exciton recombination at an isoelectronic binding centre, and in addition reveal that other weaker lines are due to a different isoelectronic binding centre. We suggest that these two binding centres may be related in the same way as are the Group III acceptors and the X-acceptors in Si. A number of excited states of the main isoelectronic bound exciton have been observed in absorption, excitation and luminescence spectra, and the density of the binding centres has been determined.

A new photoluminescence band in silicon lightly doped with copper

Abstract A new photoluminescence band is reported for silicon lightly doped with copper. The spectrum consists of five closely spaced zero-phonon lines, with the lowest energy component at 943.67(5)meV, and a sideband composed of local mode 6.4meV phonon replicas of the zero-phonon lines superimposed on a broad band. The spectrum is always accompanied by, and bears a striking resemblance to, the well-known copper-related spectrum with a zero-phonon line at 1014.7 meV. The relative intensity of the two bands depends strongly on the quench rate following diffusion and on the extent of copper doping. Annealing measurements failed to reveal a direct connection between the two centres.

Bound exciton recombination in beryllium-doped silicon

The low-temperature photoluminescence of beryllium-doped silicon is dominated by a system with sharp no-phonon lines at approximately 1.077 eV with well resolved phonon-assisted replicas at lower energies. The temperature dependence of the relative intensities of the no-phonon lines and of the phonon-assisted structure is similar to that which has been observed for electron-hole recombination at axial isoelectronic traps in gallium phosphide. Using Zeeman spectroscopy the recombination centre in beryllium-doped silicon is shown to have (001) symmetry and is identified with beryllium substitutional-interstitial pairs which are expected to predominate in this material. A weak acceptor-like bound exciton spectrum is also reported.

Fine structure in the cathodoluminescence spectrum from chromium-doped gallium arsenide

It has been reported previously that chromium in gallium arsenide gives rise to two luminescence bands, one centred around 0.80 eV with a no-phonon line at 0.839 eV, the other centred around 0.56 eV. High-resolution cathodoluminescence measurements are reported which show that the line at 0.839 eV consists of nine components, and that there are three no-phonon components at approximately 0.574 eV associated with the lower energy band. Temperature dependence measurements show that there is no shift in the transition energies in the temperature range 4-25K and indicate that splitting occurs in both the initial and final states of the transitions.

Donor bound exciton luminescence and absorption in germanium

High-resolution absorption and luminescence spectra associated with the creation and decay of excitons bound to neutral donors in germanium are analysed in terms of the Kirczenow shell model (1977). Interparticle interactions in the excited state of the bound exciton, previously observed in phosphorus-doped germanium, are shown to exist in arsenic- and bismuth-doped material. In the luminescence spectra, transitions due to electron-hole recombination within bound m=2 multiexciton complexes are identified.

The isoelectronic centre in beryllium-doped silicon. I. Zeeman study

The luminescence associated with exciton decay at an isoelectronic centre in beryllium-doped silicon has been studied by Zeeman spectroscopy. The centre is shown to have a (001) axis of symmetry and has been identified with a pair of beryllium atoms occupying a substitutional site (an interstitialcy). Unlike previous isoelectronic centres described in the literature, there is strong evidence for significant mixing of the Gamma 7 and Gamma 8 valence-band-derived hole states which is considered to be due to the small spin-orbit splitting of the beryllium atom. This, together with the phonon-assisted structure, suggests that the centre can be identified with an isoelectronic donor. However, it also renders the group theoretical formalism used for the analysis of the Zeeman data incompatible with the usual spin Hamiltonian approach. Nevertheless, it has been possible to derive approximate electron and hole g-values of 2.1 and 1.2, respectively.

The 1.045 eV vibronic band in silicon doped with lithium

Li isotope substitution has established that the 1.045 eV luminescence centres in irradiated Si unambiguously contain Li. Hitherto unresolved structure and new transitions are reported.

Bound-exciton luminescence and absorption in phosphorus-doped germanium

High-resolution absorption and luminescence spectra associated with the creation and decay of excitons bound to the neutral phosphorus donor in germanium are reported. The sharp line structure observed is analysed in terms of the Kirczenow shell model, which requires refinement to take account of the interparticle interactions in the excited state of the bound exciton.

Accurate determination of the exciton energy gap and the LA and LO momentum-conserving phonon energies in germanium

Free-exciton absorption measurements in the temperature range 2-20K and corresponding luminescence measurements between 5 and 12K on high-purity germanium are described. Accurate threshold energies have been determined to yield values for the exciton energy gap, the LA and LO momentum-conserving phonon energies and the groundstate splitting of the free exciton.