Fig. 4: An LED-like device which performs as both an optically pumped single-mode laser and an electrically excited emitter.

a Schematic illustration of an optically pumped multilayered DFB laser employing the same device architecture as a traditional p-i-n QD-LED. b Surface emission spectra on this device as a function of pump fluence display a clear transition to single-mode lasing at 629 nm. c Based on the onset of steep growth of the emitted light intensity, the lasing threshold is 65 µJ cm⁻². Inset displays dramatic increase in emission intensity and line narrowing above the lasing threshold. d The cross-sectional SEM image of the EL device. To study EL, the device shown in a is supplemented by a hole-injecting electrode made of MoO_x (10 nm thickness) followed by Al (100 nm thickness). The scale bar is 200 nm. e The EL spectrum peaks at 621 nm. Inset: a photograph of an operating device, which shows that EL is highly uniform across the active area (0.15 × 0.15 cm²). f Current-density (luminance) versus voltage characteristics of the EL device; shaded area is the range of current densities where the QDs are expected to exhibit optical gain. Inset shows that the turn-on voltage of the EL device is ~2.4 V. g Device EQE as a function of current density indicates a peak EQE of 4.3%; the meaning of the shaded area is the same as in f. Source data are provided as a Source Data file.