MONOLITHIC 2-DIMENSIONAL SURFACE-EMITTING DIODE-LASER ARRAYS MOUNTED IN THE JUNCTION-DOWN CONFIGURATION

We report on the first achievement of large area (0.5 cm2) monolithic two-dimensional surface-emitting arrays mounted in the junction-down configuration. Device fabrication involves dry etching of 45-degrees, and vertical micromirrors with +/- 2-degrees tolerances and < 0.2-mu-m RMS smoothness, integration of 100-mu-m-thick current-spreading electrodes for minimizing ohmic loss, large area packaging, and mounting to heat exchangers for long pulse and minimum chirp operation. Uniform lasing is achieved from 0.2 X 0.5 cm2 and 0.5 X 1 cm2 active area junction-down monolithic arrays (120 and 600 emitters, respectively) using 100-mu-s long pulses at a 1% duty cycle. Differential quantum efficiencies of greater-than-or-equal-to 0% and 7% are achieved for rows of 12 emitters, and for 0.2 X 0.5 cm2 active area arrays, respectively. The decrease in efficiency with increased area is found to be due to current leakage, which in turn limits the 2-D array emitted optical-power density to 150 W/cm2. Wavelength chirp in these devices is measured to be < 4 nm at twice the threshold current.