Telecom-band lasing in single InP/InAs heterostructure nanowires at room temperature

We demonstrate optically pumped telecom-band lasing in single InAs/InP nanowires at room temperature.


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Supplementary Text Section S1. Calculation of electric field dispersion relationships Section S2. Rate equation analysis Section S3. Strain analysis Fig. S1. Calculation of electric field dispersion relationships for single InP nanowires dispersed on Au/SiO 2 /Si substrate at the wavelength of 1550 nm. Fig. S2. Calculation of electric field dispersion relationships for single InP nanowires dispersed on SiO 2 /Si substrate at the wavelength of 1550 nm. Fig. S3. Rate equation analysis of experimental data. Fig. S4. PL spectra of a nanowire under stimulated emission. Fig. S5. Time-resolved decay of nanowire lasing and system function. Fig. S6. Delay, lifetime, lasing peak line width and shift measured as a function of pumping power. Fig. S7. Lasing spectra recorded at different period (1 week) for a same nanowire. Table S1. Parameters used in rate equation analysis. Table S2. Thickness of a single InAs QDisk versus calculated bandgap energy (without strain) and PL peak range of spontaneous emission (compressively-strain in MQD InP/InAs heterostructure nanowires) at room temperature.

Supplementary Text
Section S1. Calculation of electric field dispersion relationships In our optical characterization experiment, MQD nanowires were dispersed onto SiO2/Si substrates covered with a 200-nm-thickness gold film. The gold film is favorable to suppress the heating effect induced by optical pumping. But the gold film may also cause the plasmonic lasing mode. To clarify the lasing mode, we carried out the following calculation. shown that plasmonic modes can appear when the diameter is smaller than about 600 nm.
The electric modes which were localized in our nanowires were not plasmonic modes, where the electric field magnitude is concentrated near the gold surface, but photonic modes, as the diameter of the nanowire was too thick to support the plasmonic mode. It is found that the mode index is ~3 ( fig. S1d) obtained from the free spectrum range, further suggesting that the electrical mode is fundamental and photonic.
We further carried out optical characterization by using SiO2/Si substrates. We did see lasing from multiple nanowires even using the substrate without gold film, one of which is shown in fig. S4. This is also a direct indicative of photonic mode.

Section S2. Rate equation analysis
Rate equation analysis was used to fit the experimental L-L curve (Fig. 2F) and estimate the spontaneous emission factor, β. The rate equation for the carrier density in the active region, N, and photon density in the cavity mode, S, under optical pumping are as follows The rate equations were numerically evaluated using the parameters shown in table S1.
The curve with β = 0.002 best fits the experimental data ( fig. S3). **The nanowire diameter is 1.2 µm. The nanowire length is 10µm. The active layer region includes 50 layers of InAs quantum disks. Thickness of each active layer is 10 nm.

Section S3. Strain analysis
We analyze the strain situation in our nanowires and discuss the effect on lasing operation below. Because of relatively large diameter (~ 1µm), we consider our MQD InP/InAs nanowire as strained quantum wells with a vertical wire structure. The InP/InAs heterostructure interface exhibits coherent growth despite as high as 3.1% ( ∥ = −3.1%) lattice mismatch, indicating a compressive strain in the growth plane and tensile strain along the growth direction in InAs QDisks. In the case of strain layer grown on <111> Such coherent growth of InAs/InP with 3.1% lattice mismatch is extremely difficult to realize for conventional epitaxial growth with a film structure due to the limitation of critical thickness. Thus the effect of such high strain on quantum well band structure has not been well understood before, both theoretically and experimentally. The nanowire structure enables the growth of mismatch-dislocation-free materials with coherent interface because of its high capability to endure high lattice mismatch. From this point of view, to explore the effect of such high strain on band structure of highly-mismatched