MBE-grown metamorphic lasers for applications at telecom wavelengths

Abstract

We have studied growth phenomena and structural and optical properties of metamorphic (MM) quantum dots (QDs) and QD lasers emitting in the 1.4–1.5 μm range. InAs/InGaAs QDs were grown on top of (In,Ga)As buffer layers deposited on GaAs (1 0 0) substrates. The wavelength of the QDs could be adjusted in the 1400–1600 nm spectral range by changing the composition of the (In,Ga)As matrix layer and by the amount of InAs deposited to form QDs. An additional wavelength shift can be achieved by strained-layer (In,Ga,Al)As overgrowth of the QDs. It is found that high-performance degradation-robust operation of the devices can be achieved through minimization of the defect density in the matrix material and within the QD sheets. A defect-reduction technique involving steps of strain-sensitive overgrowth and selective evaporation of the material in the defect-related areas was applied, leading to both elimination of dislocated clusters and blocking of propagating defects. MM QD lasers exhibited emission wavelength in the 1.4–1.5 μm range with a differential quantum efficiency of about ∼50% and pulsed power up to 7 W, limited by catastrophic optical mirror damage. The narrow-stripe lasers operate in a single transverse mode withstanding continuous wave current densities above 20 kA cm −2 without irreversible degradation. A maximum single mode 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. Single-mode devices with as-cleaved facets are tested for 60 °C (800 h) and 70 °C (200 h) junction temperature. No noticeable degradation has been observed at 50 mW cw single mode output power, clearly manifesting for the first time degradation-free laser diodes on foreign substrates. The technology opens a way for integration of various III–V materials with silicon or germanium substrates for the next generation of microprocessors, optical interconnects and cascaded solar cells.