Quantum dot lasers: Theory and experiment

Abstract

Using of structures with size quantization in all three directions, or quantum dots (QD’s) allows exciting possibilities in device engineering. Semiconductor heterostructures with self-organized QDs have experimentally exhibited properties expected for zero-dimensional systems. When used as active layer in the injection lasers, these advantages help to strongly increase material gain and differential gain, to improve temperature stability of the threshold current, and to provide improved dynamic properties. Optimization of deposition parameters can ensure that the self-organized islands are small (∼10 nm), have a similar size and shape and form dense arrays. Saturation material gain as high as 150000 cm−1 as compared to QW values of about 3000 cm−1. Maximum differential gain reported for QD lasers approaches 10−12 cm2 and exceeds the QW laser values by about three orders of magnitude. Direct observation of relaxation oscillations reveals present cutoff frequencies close to 10 GHz. High internal (>96%) and differential (70%) efficiencies at 300 K are realized for QD lasers emitting in the 0.94–1.15 μm range. GaAs-based lasers for the 1.3 μm range with low Jth(80 A/cm2, cavity length 1.9 mm) at room temperature (RT) are realized using InAs/InGaAs/GaAs QDs obtained by activated spinodal decomposition. Differential efficiency is 55% and internal losses are 1.5 cm−1. 3W CW operation at RT is achieved. 1.3 μm GaAs-based QD VCSELs (300 K, Ith=1.8 mA, ηdiff>40%) are realized.