Improved Emission Wavelength Reproducibiliy of InP-Based All Movpe Grown 1.55 μm Quantum Dot Lasers

InAs quantum dots (QD) on InP emitting at 1.55 μm grown by using conventional MOVPE sources were investigated. Aiming at their implementation in 1.55 μm laser structures thermal stability of the QDs during growth of the upper cladding layer was found to be a severe problem most probably due to movement of growth constituents resulting in a marked blue-shift of the emission. This shift was systematically investigated using thermal treatment to simulate cladding growth. The strong dependence of the blue-shift on growth temperature (T_g) of the QDs is believed to be due to defects being incorporated during GalnAsP matrix deposition. The cause for the defects is assumed to be incomplete decomposition of the PH₃ or reduced surface diffusion length at low T_g which support interdiffusion. Above T_g = 510°C stable emission from the QDs independent of regrowth temperature in this range was observed. Application of a QD deposition temperature of 500°C results in laser structures with a QD density of 5-10¹⁰ cm^-2. Excellent laser material quality characterized by J_th ≪ 100 A/cm² per QD layer was achieved.