Undercut ridge structures: a novel approach to 1.3/1.55 /spl mu/m vertical-cavity lasers designed for continuous-wave operation

Until now, long-wavelength (1.3/1.55 /spl mu/m) vertical-cavity lasers with two dielectric mirrors have suffered from too low an injection efficiency (which is the result of lateral current injection) and a high thermal resistance (induced by the low thermal conductivity of the dielectric materials). A novel structure for such devices is proposed, which has improved both thermal and electrical characteristics: an undercut InGaAsP layer enables one to define a diaphragm which funnels current paths towards the centre of the cavity and confines the optical mode, thus increasing injection efficiency. Thermal behaviour is improved by realisation of a mesa-like top structure embedded in electrolytic gold. For these lasers, the temperature-dependent threshold condition is first determined theoretically, and some simple design rules are established using efficient simulation softwares. Such devices including two (SiO/sub 2//Si) dielectric mirrors were fabricated and operate at 1.3 /spl mu/m in the continuous-wave regime up to -15/spl deg/C with threshold currents of 8 mA for 6 /spl mu/m wide diaphragms.