Fig. 3: Improving the robustness of electrical pumping.
a Current-voltage characteristics of the LEDs presented in this study. Each group of curves represents four cycles from 0 V to 2 V and back to 0 V. Yellow: LED presented in Fig. 1, before extensive characterization. Red: LED presented in Fig. 1 shortly before failure. Gray: LED presented in Fig. 3, before extensive characterization. Blue: same as yellow, but after extensive characterization. b Schematic of the LED operating with an a-Si spiral. The different layers are the same as before, except that Au has been replaced by a-Si. c Scanning electron microscope image of an a-Si spiral on top of the TiO2 electron injection layer (tilted view). As before, the very central part of the spiral is omitted to allow for proper electrical injection. d Experimental phase of the EL measured with four interferometric devices. e Experimental EL dispersion relation at 10 V (negative values of k///k0) compared to the experimental dispersion relation in photoluminescence (positive values of k///k0). The photoluminescence data have been obtained by pumping the center of the device with a focused laser spot. f Cross-section of the EL dispersion relations for the LEDs operating with an Au spiral (top) and a-Si (middle). The bottom panel represents a cross-section of the dispersion relation of the photoluminescence emitted by a device operating with a-Si, but without the bottom electrode (the full characterization of this device is plotted in Supplementary Fig. 8). These cross-sections have been evaluated at wavelengths close to the maximum of luminescence (1405 nm for the Au pattern and 1330 nm in the case of a-Si).
