Showing papers on "Cathodoluminescence published in 1968"

Cathodoluminescence of n‐Type GaAs

Abstract: n‐type GaAs specimens with carrier concentration in the range of 4×1016 to 6.8×1018 cm−3 were bombarded with 24‐kV electrons at 4.2°K. The emission spectrum indicates that the radiative transition occurs between donors and residual acceptor states. A simple phenomenological model suggests that most of the donor states are located below the Fermi level. Taking the bottom of a parabolic distribution of states in the conduction band as a reference, the maximum density of donor occurs roughly one‐third of the way to the Fermi level, this Fermi level being already depressed by the tail of states of the conduction band. The same model indicates that the width of the donor band varies as the one‐third power of the donor concentration.

Atomic displacements and the nature of band edge radiative emission in cadmium telluride

Abstract: By combining low temperature luminescence measurements on electron-irradiated samples with reported luminescence data on non-stoichiometric specimens it has been possible to identify the luminescence role and energy levels of a number of defects in cadmium telluride. Cadmium and tellurium vacancies are shown to produce energy levels 0·036 ev and 0·46 ev above the valence band respectively. Using electrons from a Van de Graaff accelerator and observing photoluminescence and cathodoluminescence emission spectra at liquid helium temperatures the displacement energies of tellurium and cadmium have been found to be 7·8 ev and 5·6 ev respectively. The defects introduced by low temperature electron irradiation have been shown to produce emission characteristics which are not observed in specimens grown from the melt. It is suggested that this is the result of the strong perturbation of the electronic wave functions of a cadmium vacancy by the displaced cadmium atom at a nearby interstitial site.

Scanning electron microscope studies of cathodoluminescence in znse single crystals

Abstract: Cathodoluminescence in hexagonal and cubic zinc selenide single crystals at liquid nitrogen temperature has been investigated using a scanning electron microscope. The effects on the luminescence of both stacking faults and twin boundaries have been observed by comparing micrographs taken of the same crystals in a transmission electron microscope and in a scanning microscope. With the latter operating at magnifications up to 40 000 x, luminescence spectra have been observed from very small regions of thicker single crystals. On increasing the current density, a threshold effect was noted in the emission of certain peaks from thin basal plane intergrowths in the hexagonal platelets used. These peaks were identified as arising from cubic regions in the latter by comparison with the cathodoluminescence spectra of cubic crystals observed under similar conditions.

Intrinsic and extrinsic edge luminescence in epitaxial GaP

Abstract: Cathodoluminescence spectra have been obtained from undoped and n-type gallium phosphide crystals at temperatures between 80 °k and 300 °k. The gallium phosphide was grown epitaxially by vapour transport on GaAs substrates, the n-type specimens being doped with either sulphur or tellurium. The crystals showed only weak edge luminescence, and this is interpreted as the radiative recombination of free excitons and free holes at neutral donor centres. The free-exciton recombination bands show a weak no-phonon component and other bands that give evidence of the expected phonon co-operation for indirect band to band transitions. The phonon energies deduced from these bands are in good agreement with those observed in the optical absorption edge and lattice vibration absorption spectra. The luminescence attributed to free-hole recombination at donor centres has enabled values for ED, the donor electron binding energy, to be obtained for the two impurities involved (sulphur, 105±5 mev; tellurium, 90±5 mev). The temperature dependence of the luminescence features is shown to be consistent with the proposed interpretation.