ZnSe-based laser diodes with quaternary CdZnSSe quantum wells as active region:-Chances and limitations-

Abstract

Light emitting devices based on the material system ZnSe provide the unique possibility to produce emission in the blue-green visible spectrum. However, an insufficient lifetime is the main obstacle for commercialization so far, which is connected to the stability of the active region, the Cd-containing quantum well. In this work, ZnSe-based laser diodes with quaternary CdZnSSe quantum wells are investigated.:p:First, the material system ZnSe and the applied experimental techniques are introduced. The third chapter focuses on the degradation mechanism of the devices. A mechanism based on recombination enhanced defect reactions is found to be the dominating process, which is driven by the diffusion of Cd, as well, as the accumulation of heat. Experimental approaches to improve the stability of the quantum well are explored, where the use of tensile strained ZnSSe barriers shows promising results. Under high current injection levels in pulsed-mode, a new degradation mechanism is observed for the first time: catastrophic optical damage.:p:Next, the unique possibilities of CdZnSSe quantum wells are investigated in terms of high Cd contents, which allow light emission around 560 nm and are therefore suitable for plastic optical fibers. Laser diodes with an emission at 560 nm are fabricated for the first time, exhibiting operation in cw-mode and output powers above 1.1 W in pulsed mode. :p:Finally, a novel approach with a fivefold stack of CdSe quantum dots as active region is tested and lasing with a threshold current density of 7.5 kA/cm:sup:2:/sup:, is observed for the first time. A surprisingly high stability of the devices is noted. In pulsed-mode, current densities as high as 20 kA/cm:sup:2:/sup: are sustained, in DC-mode operation at 2.5 kA/cm:sup:2:/sup: with more than 100 h is possible. Degradation experiments indicate a greatly increased stability as compared to quantum well laser diodes emitting in the same spectral region.