Nanofaceting and alloy decomposition: From basic studies to advanced photonic devices

Most of the modern epitaxial structures for semiconductor lasers serving the needs of optical storage and fiber pumping are grown on misoriented GaAs(0 0 1) substrates. It has been found in metal-organic vapor-phase epitaxy that surface misorientation helps to achieve better epitaxial quality of the alloy layers. On the other hand, these misoriented or, in other definition, high-index surfaces are known to undergo phase transformations, depending on the misorientation angle, from nanofaceting (like (3 1 1)A, (3 1 1)B, (3 3 1), (2 1 1)B GaAs surfaces) to arrays of step bunches (like (7 7 5) GaAs, etc.). In the present paper, we consider growth-related effects during growth of both standard and advanced laser structures on GaAs (11¯8) substrates which are typically used for growth of 650 nm GaAlInP devices. We show that the active region of the laser structures represents a corrugated superlattice with a ∼25 nm in-plane periodicity, while the surrounding layers are natural superlattices with a ∼5 nm vertical periodicity. Corrugated superlattice used as an active region manifests itself through a strong modification of optical properties. Strong in-plane polarization evidences the formation of arrays of quantum wires. Both standard and advanced red laser have been grown and processed. The advanced lasers have demonstrated a vertical beam divergence of only 7–8° full-width at half-maximum (FWHM). The advanced lasers with 10 μm-wide stripes demonstrate continuous wave (CW) power up to ∼200 mW and the lateral beam divergence of 4°, and those with 4 μm-wide stripes show CW power up to ∼120 mW and the lateral beam divergence of 6.5°. No facet passivation has been applied and the power is limited by the catastrophic optical mirror damage (COMD). 20 W pulsed power has been achieved in 100 μm-wide stripes for the advanced design and 6 W has been obtained for the standard design. The advantage comes from the design optimization of the laser waveguide using the concept of the longitudinal photonic bandgap crystal. We believe that also the optimization of the active region with better utilization of the nanofaceting effects may enable, in addition, a dramatic extension of the emission wavelength towards bright red (620–630 nm) and, probably, yellow (∼580 nm) spectral ranges.