GROWTH ISSUES FOR BLUE-GREEN LASER-DIODES

Laser device lifetime is linked to electrical dissipation, hence verti cal transport. One significant issue is the resistivity of ZnSe and al loys of ZnSe. The results of our recent studies into the origins of bo th doping level limitations in ZnSe, and the relatively high acceptor activation energies found in wide bandgap alloys of ZnSe, will be revi ewed. The experimental evidence, including the presence or absence of persistent photoconductivity in wide bandgap alloys of p-ZnSe and p-Zn Se:N, points to the presence of deep levels associated with lattice re laxation as the origin of the increased acceptor activation energy. Ke y issues of growth include the evaluation of sticking coefficient for the alloy constituents, and the maintenance of constant substrate temp erature to avoid variations in alloy fraction, The appearance of compo sition modulation in ZnSe alloys will also be discussed. Understanding the degradation of II-VI blue-green laser diodes has become important after the demonstrations of room-temperature continuous-wave operatio n from (Zn,Mg)(S,Se)/Zn(S,Se)/(Zn,Cd)Se separate confinement heterostr ucture (SCH) laser diodes. The observed degradation seems associated w ith the existence of stacking faults originated from the II-VI/GaAs he terovalent interfaces. Segments of these extended structural defects w hich penetrate the active region become sources for the generation of macroscopically dark patches under lasing conditions. Lessons from III -V semiconductor laser device research are consistent with the observa tion that the presence of non-radiative point defects and built-in str ain contribute to the propagation and growth of dislocations. Efforts to reduce the density of stacking faults continue, while the temperatu re dependence of photoluminescence points the way to a reduction in as -grown point defects.