Low-threshold lasing of optically pumped micropillar lasers with Al$_{0.2}$Ga$_{0.8}$As/Al$_{0.9}$Ga$_{0.1}$As distributed Bragg reflectors

TL;DR

This paper demonstrates low-threshold micropillar lasers using AlGaAs/AlGaAs DBRs with a broad optical pumping window, improving efficiency and thermal stability compared to traditional structures.

Contribution

It introduces a novel design with AlGaAs/AlGaAs DBRs that enable efficient optical pumping over a wide wavelength range, significantly reducing lasing thresholds.

Findings

Increased pump efficiency within the 700-820 nm window.

Lasing threshold reduced by over an order of magnitude when switching pump wavelength.

Enhanced thermal stability of the micropillar lasers.

Abstract

We report on the design, realization and characterization of optically pumped micropillar lasers with low-absorbing Al$_{0.2}$Ga$_{0.8}$As/Al$_{0.9}$Ga$_{0.1}$As dielectric Bragg reflectors (DBRs) instead of commonly used GaAs/AlGaAs DBRs. A layer of (In, Ga)As quantum dots (QDs) is embedded in the GaAs $\lambda$-cavity of as an active medium. We experimentally study the lasing characteristics of the fabricated micropillars by means of low-temperature photoluminescence with varying pump laser's wavelength between 532 nm and 899 nm. The incorporation of 20% Al content in the DBRs opens an optical pumping window from 700 nm to 820 nm, where the excitation laser light can effectively reach the GaAs cavity above its bandgap, while remaining transparent to the DBRs. This results in a substantially improved pump efficiency, a low lasing threshold, and a high thermal stability. Pump laser wavelengths outside of the engineered spectral window lead to low pump efficiency due to strong absorption by the top DBR, or inefficient excitation of pump-level excitons, respectively. The superiority of the absorption-free modified DBRs is demonstrated by simply switching the pump laser wavelength from 671 nm to 708 nm, which crosses the DBRs absorption edge and drastically reduces the lasing threshold by more than an order of magnitude from (363.5 $\pm$ 18.5) $\mu$W to (12.8 $\pm$ 0.3) $\mu$W.