1.3-1.5 Mu M Quantum Dot Lasers On Foreign Substrates: Growth Using Defect Reduction Technique, High-Power Cw Operation, And Degradation Resistance

We have performed a systematic study of structural and optical properties of Quantum dot (QDs) lasers based on InAs/InGaAs quantum dots grown on GaAs substrates emitting in the 1.3-1.5 mu m range. 1.3 mu m range QD lasers are grown using GaAs as matrix material. It is shown that the lasers, grown with large number of QD stacks are metamorphic, with plastic relaxation occurring through the formation of misfit dislocations. Thus, 1.3 mu m QD lasers with large number of stacks grown without strain compensation are metamorphic. Another type of defects is related to local dislocated clusters, which are the most dangerous. When proper optimization of the growth conditions is carried out, including a selective thermal etching off of statistically formed dislocated clusters through the defect-reduction technique (DRT), no significant impact of misfit dislocations on the degradation robustness is observed. In uncoated devices a high cw single mode power of similar to 700 mW is realized limited by thermal roll-over, which is not affected by 500 h ageing at room temperature. At elevated temperatures the main degradation mechanism revealed is catastrophic optical mirror damage (COMD). When the facet are passivated, the devices show the extrapolated operation lifetime in excess of 106 h at 40 degrees C at similar to 100 mW cw single mode output power. Longer wavelength (1.4-1.5 mu m) devices are grown on metamorphic (In,Ga,AI)As layers deposited on GaAs substrates. In this case, the plastic relaxation occurs through formation of both misfit and threading dislocations. The latter kill the device performance. Using DRT in this case enables blocking of threading dislocation with growth of QDs in defect-free upper layers. DRT is realized by selective capping of the defect-free areas and high-temperature etching of nano-holes at the non-capped regions near the dislocation. The procedure results in etching of holes and is followed by fast lateral overgrowth with merger of the growth fronts. If the defect does not propagate into the upper layer when the hole is capped, the upper layers become defect-free. Lasers based on this approach exhibited emission wavelength in the 1.4-1.5 mu m range with a differential quantum efficiency of about similar to 50%. The narrow-stripe lasers operate in a single transverse mode and withstand continuous current density above 20 kA cm(-2) without degradation. A maximum continuous-wave output power of 220 mW limited by thermal roll-over is obtained. No beam filamentation was observed up to the highest pumping levels. Narrow stripe devices with as-cleaved facets are tested for 60 degrees C (800 h) and 70 degrees C (200 h) on-chip temperature. No noticeable degradation has been observed at 50 mW cw single mode output power. This shows the possibility of degradation-robust devices on foreign substrates. The technology opens a way for integration of various III-V materials and may target degradation-free lasers on silicon for further convergence of computing and communications.