Laser Characteristic and Strain Distribution Dependence on Embedding Layer Thickness of Quantum Dots Laser Diodes Grown on InP(311)B Substrate

Herein, 14 layer-stacked quantum dots laser diodes (QD-LDs) are fabricated with different thicknesses of embedding layers grown on InP(311)B substrate, and the lowest threshold current (I-th) of 21.6 mA is demonstrated in an as-cleaved ridge-structured QD-LD with 13 nm-thick embedding layers. I-th has the minimum value when the thickness is 13 nm. The factors unique to QDs grown on an InP(311)B substrate are assumed as the overlap integral of the wavefunction of electrons and holes and the decrease in gain owing to the formation of a miniband. According to the simulation results of the local strain profile in the embedding and QD layers, the strain in the QD and embedding layer is higher in the case of 7 nm thickness than in the case of 20 nm thickness. As a result of the large strain, because the thickness of the embedding layer decreases, a large internal electric field tends to be generated, causing the wavefunctions to become largely separated and localized. Therefore, the overlap integral of the wavefunction becomes smaller, and because of the decrease in the radiation recombination probability, the internal quantum efficiency also decreases, causing the characteristic of I-th on the thickness of the embedding layer.