Novel Infrared Quantum Dot Lasers: Theory and Reality

Abstract

Semiconductor heterostructures with size quantization of carriers in all three directions, or quantum dots (QDs), open a new era in device engineering. An important breakthrough occurred when the self-organised growth approach had been refined to such an extent, that defect-free QDs made with these technique exhibited properties predicted for zero-dimensional structures. Their practical application in devices, first of all lasers, became possible. When used for active layers in injection lasers differential gain is strongly increased potentially providing improved dynamic properties. The cut-off frequencies larger than 10 GHz are presently demonstrated. The saturation material gain is as high as 15 x 10 4 cm -1 as compared to QW values of about 3 x 10 3 cm -1 , The wavelength dependence of gain is best described by Master equations of microstates. High internal (>96%) and differential (70%) efficiencies at 300 K and output power up to 4 W are realized now for QD lasers emitting in the 0.94-1.15 μm range. Transparency current density of 18 A/cm 2 has been recently demonstrated at 1.15 μm. GaAs-based QD lasers emit near 1.3 μm with J th = 70 A/cm 2 (L = 1.9 mm, 300 K) and CW output power of ∼3 W. In narrow (7 μm) stripes almost chirp-free operation and relaxation oscillations at 2.4 GHz (L = 400 μm) are manifested. Differential efficiency is 55% and internal losses are 1.5 cm -1 . 1.3 μm GaAs-based QD VCSELs (300 K, I th = 1.8 mA, η diff > 40%) are realized.