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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Influence of Spacer Thickness on the Optical Properties of Vertically Stacked InP/AlGaInP Quantum Dot Lasers at the Short Wavelength
摘要： Quantum dot (QD) based semiconductor lasers are the widely used sources in many applications. The unique advantages are their low threshold current density, high characteristic temperature, and high differential material gain, owning to their discrete energy levels. The self-assembled InP QDs in the (AlxGa1?x)0.51In0.49P (AlxGaInP) barriers are of great interests due to the emitting spectrum from 630 nm to 780 nm [1]. However, limited by the low QD density, the low energy state density, and the small optical confinement factor, a single-sheet of QD only can provide a lower optical modal gain in the laser structure, which limits the laser performances. Meanwhile, the weak charge carrier confinement of the AlGaInP material further makes the devices sensitive to the operation temperature. One of the solutions for above issues is to increase the QD density by vertically stacking the QD layers. In the stacked QDs, the spacer thickness between the QD layers is one of the critical parameters needed to be carefully considered [2]. In this report, we investigated the influence of the spacer thickness on the optical properties of the vertically stacked InP/AlGaInP QD lasers at the emitting wavelength around 660 nm. The investigated laser structures (as shown in Fig. 1(a),) were grown by metal-organic vapor-phase epitaxy (MOVPE) on n-doped (100)-GaAs substrate oriented by 6° towards the [111]A direction. The epitaxial growth was performed at the temperature of 710°C and the pressure of 100 mbar with standard precursors. From bottom to top, the laser structure contains a 100 nm-thick GaAs:Si buffer layer, followed by a 50 nm-thick GaInP:Si layer and a 1 μm-thick AlInP:Si optical confinement layer. The InP quantum dot active region was grown and placed in the center of a 2×10 nm thick Al0.10GaInP barrier, surrounded by 2×150 nm Al0.55GaInP waveguide. The p-side layers are similar to the n-side, but the dopant was changed to Zinc. Here, we compared the optical properties of three different active region structures: single QD layer, double QD layers with the spacer of 6 nm and 10 nm. The measured electrically pumped modal absorption spectra of the investigated structures by the segmented contact method are shown in Fig. 1(b). It demonstrated that the thicker spacer introduces additional internal absorption loss due to the Al-based materials of the spacer. Meanwhile, the smaller spacer structure has the higher absorption of the large QD from the upper layer, attributed to the stronger strain effect and the increasing tunnelling rate. At room temperature, it demonstrates that the measured saturated peak net modal gain values (as shown in Fig. 1(c)) are 68.5 cm?1 and 57.8 cm?1 for the 6 nm-spacer structure and 10 nm-spacer structure, respectively, which are 1.56 and 1.32 times higher than the single-layer QD laser. The higher gain value of the smaller spacer structure is also attributed to the higher tunnelling probability and the shorter tunnelling time.
关键词： optical properties,InP/AlGaInP,spacer thickness,Quantum dot,semiconductor lasers
更新于2025-09-12 10:27:22
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Two-state lasing at room temperature in InAs/InP quantum dots
摘要： The two-state lasing conditions at room temperature in InAs/InP quantum dot (QD) lasers under a continuous wave electrical bias current are studied. It is found that excited state (ES) lasing is promoted by moderately decreasing spacer thickness and increasing dot-size dispersion in a QD stack, and the physical origins are due to the increased bottleneck effect and inhomogeneous broadening. Moreover, it is proved theoretically that ground state (GS) lasing with high inhomogeneous broadening may result in high phase and intensity noise at a high bias current. Therefore, an appropriate spacer thickness together with appropriate inhomogeneous broadening is critical to the GS and/or ES lasing, which helps an optimal design of laser geometry.
关键词： two-state lasing,spacer thickness,room temperature,InAs/InP quantum dots,inhomogeneous broadening,dot-size dispersion,intensity noise,continuous wave electrical bias,bottleneck effect,phase noise
更新于2025-09-11 14:15:04