(a) Schematic illustration of the InAs/In0.53Al0.22Ga0.25As QDot heterostructure. (b) 1 × 1 μm2 AFM image of the open dots on top of the 4 ML QDot sample.
(a) Schematic illustration of the InAs/In0.52Al0.48As QDash heterostructure. (b) 1 × 1 μm2 AFM image of a 6 ML QDash sample without cap layer.
(a) Low temperature PL spectrum of 4 ML InAs/In0.53Al0.22Ga0.25As QDots featuring the QDot PL at 0.885 eV (1.401 μm), the barrier emission at 1.142 eV (1.085 μm) and the substrate emission at 1.425 eV (0.870 μm). The solid line (red) is the PL measured using a YAG laser (2.33 eV) of 4 W/cm2 and the solid filled (blue area) is the PL recorded under the excitation power of 180 W/cm2 using He-Ne laser (1.95 eV). (b) Low temperature PL spectrum of 4 ML InAs/In0.52Al0.48As QDashes measured in a similar way using the YAG laser (2.33 eV) of 4 W/cm2 (the solid red line) and using He-Ne laser (1.95 eV) of 180 W/cm2 (the solid filled green area) featuring the QDash PLat 1.005 eV (1.233 μm) as well as emission from the WL (1.377 eV; 0.900 μm), substrate (1.425 eV; 0.870 μm) and barrier (1.53 eV; 0.810 μm).
(a) Low temperature PL spectra of InAs QDots of 4 and 6 ML nominal thickness. (b) Temperature dependent PL spectra of 4 ML QDots at T = 10, 20, 40, 70, 100, 140, 170, 200, and 250 K under low power non-resonant excitation (7 W/cm2). The “dips” at about 0.89 eV in the 4 ML QDot spectra are due to the OH− absorption in the fibers used for these measurements. (c) Integrated PL intensities of 4 and 6 ML InAs QDots displayed as a function of inverse temperature. The fit curves (black solid lines) were obtained using Eq. (1) . The dashed line corresponds to the line calculated by Eq. (1) with the fixation of the coefficient B 1 = 0.
(a) Low temperature PL spectra of InAs QDashes of 3 to 6 ML nominal thickness. (b) Temperature dependent PL spectra of 4 ML QDashes at T = 10, 50, 80, 100, 120, 140, 180, 240 and 293 K under low power non-resonant excitation (13 W/cm2). (c) Integrated PL intensities of the 3, 4 and 6 ML InAs QDashes displayed as a function of inverse temperature. The fit curves (black solid lines) were obtained using Eq. (1) . The dashed line represents the line calculated using Eq. (1) by fixing B 1 = 0.
Activation energies of QDots and QDashes as a function of their number of MLs (height); blue diamonds represent the QDashes, red circles the QDots. The blue (red) solid line represents the multiplication of νi with ΔEi (ΔEi = the energy separation between the QDash (QDot) PL and the WL (barrier) PL, deduced at high temperatures including the additional PL peak shift described below in Sec. ??? ).
Schematic illustration of the thermal escape and charge carrier redistribution model exemplifying two QDs of different size and GS energy and the related thermally activated carrier escape and tunneling processes between QDs, as well as the common features CES, barrier (for QDot samples) and WL (for QDash samples).
(a) Temperature dependence of the 4 ML QDot PL obtained from Gaussian fits to the spectra (Fig. 4 ). The two parallel dashed lines are calculated using Eq. (4) (α = 0.27 meV/K and β = 94 K). 57 (b) Temperature dependence of the 4 ML QDot PL FWHM obtained from Gaussian fits to the spectra. (c) Temperature dependence of the 4 ML QDash PL extracted from Gaussian fits to the spectra (Fig. 5 ); displayed in the same way as in (a). (d) Temperature dependence of the 4 ML QDash PL FWHM.
(a) Time-resolved PL of 4 ML QDots as a function of temperature (4, 140, and 220 K) under low power non-resonant excitation (25 W/cm2). The transients were obtained by spectrally binning the data between 1.3–1.5 μm, 1.325–1.525 μm, and 1.350–1.550 μm, respectively. The solid lines are the results of single-exponential fits. The horizontal dashed lines are guide to the eyes to show the offset noise level. (b) Temperature dependence of the decay time, the solid line represents the resultant fit to the higher temperature data points obtained by Eq. (9) .
(a) Schematic illustration of a 190 nm sized mesa and the corresponding secondary-electron microscope (SEM) image with a 24° taper angle, a height of 230 nm and a top diameter of 100 nm. (b) Low temperature (4 K) excitation power dependence of μ-PL spectra of few no. of 4 ML QDots embedded in a mesa of top diameter of 100 nm. With increased excitation power emission from excited states is also taking place. (c) Low temperature (4 K) excitation power dependence of high resolution μ-PL spectra of single 6 ML QDashes embedded in a 190 nm mesa, featuring emission lines from a few individual QDashes emitting near the telecommunication C band. The FWHM is Lorentzian and found around 140 μeV.
Activation energies and fitting coefficients.
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