Deep-red vertical-cavity surface-emitting lasers(VCSELs) with superlattice active region have been designed and fabricated using AlGaAs system. By studying electrical behaviors as a function of temperature from 80K to 310K, barrier heights and optimum cavity design parameters are obtained. The barrier height for holes between Al0.65Ga0.35As-Al0.3Ga0.7As and AlAs-Al0.65Ga0.35As(Δx = 0.35) is measured to be 77 meV at zero bias for a 780 nm VCSEL. The contribution of electrons to electrical resistance is estimated to be negligibly small compared to that of holes for the structure consisting of Δx = 0.35. For n-mirrors, if one avoids using AlGaAs layers with x< 0.3, one could eliminate the n-mirror resistance to a negligible level even without using intermediate steps or grading between quarter-wave layers of AlGaAs.
For 750 nm VCSELs, cw lasing is observed at low temperatures ranging from 80K to 140K. The threshold current has a broad minimum near 100K. The maximum output power of a VCSEL with a 20 ㎛ square window is ~1.6 mW at 80K. At room temperature, gain peak and Fabry-Perot resonance are estimated to be offset by ~40 nm. The VCSELs designed to lase around 780 nm are lasing around 770 nm at room temperature. But the minimum threshold current and maximum differential quantum efficiency are observed at 200K, which indicate slight mismatch between gain peak and Fabry-Perot resonance at room temperature. For optimum cw performance at room temperature, it is necessary to match the gain peak and the Fabry-Perot resonance and consider the effects of thermal red-shift of 4~5 nm due to ohmic heating above lasing.
Precision etch-depth control is realized using a chemically assisted ion-beam etching system equiped with in situ laser reflectometry. Counting the number of interference fringes, we achieve a controllability of etch-depth within an error range of a quarter-wave thickness. Spatial uniformity of etched depth is about 5% over 1 ㎠ area, which corresponds to one pair over 20 pairs of quarter-wave stacks of AlGaAs/GaAs distributed Bragg reflectors.
For future optical switching and optical computing applications, monolithic NOR and INVERTER active optical logic device arrays are characterized.
