LATERAL CARRIER DIFFUSION AND SURFACE RECOMBINATION IN INGAAS ALGAAS QUANTUM-WELL RIDGE-WAVE-GUIDE LASERS/

We measured the increase in threshold currents due to lateral carrier diffusion in InGaAs/AlGaAs quantum-well ridge-waveguide laser diodes. The ridge stripes were fabricated by using both in situ monitored pure Cl2 reactive ion etching and selective wet etching to completely elim inate the spreading current in the conductive upper cladding layer whi le keeping the ridge sidewalls straight. After comparing the threshold data with a theoretical model, the ambipolar diffusion coefficient is found to be 22 cm2/s in the population-inverted InGaAs layer. This mo del is based on the calculated optical gain curve and the ambipolar ca rrier transport in the quantum-well and waveguiding layers. The depend ence of carrier lifetime on the local carrier concentration is include d in the calculation. Moreover, from another set of devices with the p ortions of the active layer outside the ridge stripes etched away, the surface recombination velocity is found to be around 1-2x10(5) cm/s.