Ⅱ-Ⅵ compound semiconductor materials

in particular ZnCdSe-ZnSe superlattices have been extensively studied in the past several years due to their potential applications in blue and blue-green laser diode (LD). ZnSe-based LD generally use a single quantum well or multiple quantum wells structure as an active layer where light is emitted. In this paper the stimulated emission is studied in a special kind of superlattice structure-ZnCdSe-ZnSe compound superlattices

in order to try a new structure for the LD’s active layer. The sample used here was grown by a low pressure MOCVD on GaAs(100) substrate. The ZnCdSe-ZnSe compound superlattices have two groups of superlattices SL1 and SL2 with different Cd compositions which separated by a 50nm ZnSe isolating layer. The double superlattices are embedded in an 12μm ZnSe buffer layer and an 150nm ZnSe cap layer. The superlattice SL1 with Cd composition 10% near the buffer layer have 20 periods

well width 5nm and barrier width 6nm

and the superlattice SL2 with Cd composition 7% have 20 periods

well width 3nm

and barrier width 6nm. Photo luminescence and photopumped stimulated emission spectra were excited by the 337.1nm line of a UV-24 N

2

laser working at 10Hz

and the signals were measured at 77K using a SPEX1404 double grating monochromator with a RCA-C31034 cooled photomultiplier. The samples used in the stimulated emission measurement were cleaved in approximately 2mm wide resonators and the Fabry-Perot cavities were formed by the natural facets of the sample bars. Fig.1 and Fig.2 show the emission spectra from the surface emission and the edge emission of the samples

respectively. There are four bands a

SL1

SL2 and L in Fig.1 and Fig2. The band L increased rapidly with increasing the excitation intensity. We can attribute the bands a

SL1 and SL2 to spontaneous emission from ZnSe barrier and superlattices

respectively. We can also attribute the band L to stimulated emission from superlattice SL1.Due to the carrier transfer between the double superlattices

the stimulated emission mainly appeared in the superlattice with wide well. The gain spectrum was shown in Fig.3. According to the dependence of the stimulated emission intensity from the cleaved edge on the strip length of excitation

the magnitude of the optical gain is found to be about 72cm

-1

.