ROOM-TEMPERATURE II-VI LASERS WITH 2.5 MA THRESHOLD

Buried-ridge II-VI laser diodes operating at 511 nm at room temperatur e were fabricated from separate-confinement heterostructures. The laye rs consisted of a pseudomorphic CdZnSe quantum well and lattice-matche d ZnSSe light-guiding and MgZnSSe cladding layers. Stripe gain-guide l asers fabricated from similar wafers exhibited threshold current densi ties as low as 630 A/cm2 and threshold voltages less than 9 V. The bur ied-ridge devices operated in single lateral and transverse modes unde r pulsed excitation at room temperature. Threshold currents as low as 2.5 mA and 50% duty cycles at room temperature were demonstrated with these structures. A conventional model for the threshold currents was used in an initial attempt to fit the thresholds as functions of cavit y length and temperature (100-325 K); excitonic mechanisms were not in cluded. The electron lifetime in the light-guiding layer was the only adjustable parameter in the model. Good agreement between measurement and theory was obtained with the electron lifetime taken as 42 ps; thi s value also agrees well with independent lifetime measurements. All r eports of II-VI diode lasers to date indicate very short device lifeti mes at room temperature. Electroluminescence topography and TEM studie s were carried out on both LEDs and stripe lasers in order to gain ins ight to the failure mechanisms and to study their evolution. Two types of dark line defects (along the [100] and [110] directions) and patch es with extremely large densities (10(10) cm-2) of a dislocation netwo rk consisting of elongated dislocation segments were observed in degra ded devices. This work represents the first detailed study of II-VI de vice failure and indicates that the rapid failure is due to the format ion of dark defects at the high current densities required for lasing.