The radiative recombination of free excitons in diamond has been previously reported by Dean et al. /l/. They showed that the valence band splitting due to spin-orbit interaction must be taken into account for a good understanding of their line shape. Their experiments were performed a t high temperature (T > 77 K) and with a relatively low resolution.In our experiments we used a cathodoluminescence apparatus, working in pulsed mode, described in preceding publications /2, 3/. The main characteristics are briefly recalled: 2 z < 1 n s for 0 < I < 2 A/cm , rise time: pulse length 8 : 10 n s < 8 < 1000 ns, acceleration voltage U: 20 kV < U < 100 kV.We worked generally with the following experimental conditions: 2 I * 1.6 A/cm , U = 50 kV, repetition rate f = 800 Hz.High injection r a t e s can be reached, so that we could observe the free exciton luminescence a t low temperature, down to about 4.2 K. The intensity of this line decreases very quickly below 77 K. We worked with a sample of "natural diamond", type I1 b.On Fig, 1 is reported the main emission line of free excitons a t 80 K. The maximum is situated a t 5.275 eV, as previously observed by Dean et al. /l/.The width a t half height is much l a r g e r than predicted when the valence band split off by the spin-orbit interaction is neglected.

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Using a time-resolved cathodoluminescence technique, we have investigated the radiative recombination in highly doped (Ga, Al)As epitaxial layers (the dopant was Si or Ge). We have realized in homogeneous Si-doped epitaxial (Ga, Al)As layers the conditions of large luminescence efficiency and great decay time usually observed in L.E.D. obtained by double liquid phase epitaxy of (Ga, Al)As on GaAs substrate. The phenomena are well explained if we consider the effect of charge impurity fluctuations in compensated semiconductors on the density of state tails at the edges of the band-gap

Nous étudions deux défauts dans le diamant naturel semiconducteur. La raie d'émission du premier, située à 3,158 eV à 4 K, est attribuable à une transition entre le niveau excité 4T1 et le niveau de base 4A2 du centre ND 1. Le second est positionné entre 3,8 et 4,581 eV et est caractérisé par un couplage privilégié avec un mode local de vibration d'énergie 236 meV : son spectre a été noté 5 RL par Wight [7]. Nous proposons l'identification à un complexe lacune de carbone-accepteur

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