Two section tunable laser using impurity free intermixing in InGaAsP multiple quantum well structures

We report on controlled group V intermixing in a compressively strained In0.76Ga0.24As0.85P0.15/In0.76Ga0.24As0.52P0.48 multi-quantum well laser structure using different encapsulating layers followed by rapid thermal annealing, and the two-section tunable laser made by using this technique. The sample used is a laser structure with emission wavelength at 1.55mum. The active region consisting of three In0.76Ga0.24As0.85P0.15 quantum wells with In0.76Ga0.24As0.52P0.48 barriers grown by metal organic chemical vapor deposition. At the same thermal treatment, the blueshift of band gap energy was enhanced most efficiently by capping the sample with an InP layer grown at low temperature and less efficiently by a SiO2 film. While the blueshift was suppressed by a Si,N-y film with a refractive index of about 2.1. The suppression effect was independent of the Si,N-y film thickness from 30 nm to 2400 nm. Time of flight secondary ion mass spectra showed that the quantum well intermixing was caused by the interdiffusion of group V atoms between the wells and barriers that have the same group III compositions. A group V interstitial diffusion model was proposed to be responsible for the enhanced intermixing. A 1.55mum two section ridge waveguide laser was fabricated using this technique. The energy transition level of the phase tuning section was tuned to be transparent to the emission wavelength of the active section. A tuning range of about 10 nm can be achieved by simply tuning the bias current for the phase tuning section.