Graded Index Separate Confinement Heterostructures have been grown by MOVPE using ( (\mathrm{Zn}, \mathrm{Cd}) \mathrm{Se}) and (\mathrm{ZnSe}) wide bandgap semiconductors. These structures are composed of a deep (\mathrm{Zn}{1-x} \mathrm{Cd} d{x} \mathrm{Se}(x<0.23 %)) central well embedded between two thick ( (\mathrm{Zn}, \mathrm{Cd}) \mathrm{Se}) graded layers within which the cadmium composition varies from 0 up to (10 %) on one side of the well, and from 10 down to (0 %) on the other side. Both carriers and photon confinement occur in such structures making them suitable for blue-green stimulated emission.
Reflectance and photoreflectance data, taken at (2 \mathrm{~K}) on a series of samples of different designs allowed us to observe excitonic transitions up to the third quantum number. The structures exhibit a strong photoluminescence line due to the recombination of the carriers in the quantum well. The photoluminescence intensity is analyzed as a function of the temperature and displays a strong thermal quenching. This quenching is due to an increase of the non-radiative recombinations through defects at low temperature and to the thermal escape of the carriers above (40-60 \mathrm{~K}). The value of the activation energy for thermal escape shows that this mechanism is unipolar and concerns the heavy holes.
(c) 1995 Academic Press Limited