Quantum-dot microlasers based on whispering gallery mode resonators.

The subject of this paper is microlasers with the emission spectra determined by the whispering gallery modes. Owing to the total internal reflection of light on the sidewalls, a high Q-factor is achieved until the diameter is comparable to the wavelength. The light emission predominantly occurs in the plane of the structure, which facilitates the microlaser integration with other elements. We focus on microdisk lasers with various types of the In(Ga)As quantum dots (QDs). Deep localization of charge carriers in spatially separated regions suppresses the lateral diffusion and makes it possible to overcome the undesirable effect of non-radiative recombination in deep mesas. Thus, using conventional epitaxial structures and relatively simple post-growth processing methods, it is possible to realize small microlasers capable of operating without temperature stabilization at elevated temperatures. The low sensitivity of QDs to epitaxial and manufacturing defects allows fabricating microlasers using III-V heterostructures grown on silicon.

Electrically pumped InGaAs/GaAs quantum well microdisk lasers directly grown on Si(100) with Ge/GaAs buffer.

In this work we report, to the best of our knowledge, the first quantum well electrically-pumped microdisk lasers monolithically deposited on (001)-oriented Si substrate. The III-V laser structure was epitaxially grown by MOCVD on silicon with an intermediate MBE-grown Ge buffer. Microlasers with an InGaAs/GaAs quantum well active region were tested at room temperature. Under pulsed injection, lasing is achieved in microlasers with diameters of 23, 27, and 31 µm with a minimal threshold current density of 28 kA/cm2. Lasing spectrum is predominantly single-mode with a dominant mode linewidth as narrow as 35 pm.

Mode selection in InAs quantum dot microdisk lasers using focused ion beam technique.

Optically pumped InAs quantum dot microdisk lasers with grooves etched on their surface by a focused ion beam are studied. It is shown that the radial grooves, depending on their length, suppress the lasing of specific radial modes of the microdisk. Total suppression of all radial modes, except for the fundamental radial one, is also demonstrated. The comparison of laser spectra measured at 78 K before and after ion beam etching for a microdisk of 8 µm in diameter shows a sixfold increase of mode spacing, from 2.5 to 15.5 nm, without a significant decrease of the dominant mode quality factor. Numerical simulations are in good agreement with experimental results.

Control of emission spectra in quantum dot microdisk/microring lasers.

Focused ion beam is applied to quantum dot based microresonators to form pits or groove on their surface. The emission spectra of the resonators based lasers are significantly thinned out after the ion beam milling, and one or two modes become dominant instead of a group of modes having comparable intensities. The linewidth of the lasing mode is kept unchanged, whereas the lasing threshold demonstrates an insignificant growth.