To be a viable platform for colour-tunable electrically pumped lasers, the quantum-dot LEDs must be modified to withstand the extended, high-current-density operation needed to achieve population inversion. This requirement necessitates a quantum-dot LED design that incorporates robust charge transport layers. Amorphous inorganic semiconductors as robust charge transport layers demonstrate devices capable of operating at current densities exceeding 3.5 A cm2 with peak brightness of 1,950 Cd m2 and maximum external electroluminescence efficiency of nearly 0.1%, which represents a 100-fold improvement over previously common Leds.

The current reported record for QD-LED performance is 18%, by Mashford et al. (10.1038/nphoton.2013.70).

They employ a 40nm sol-gel ZnO electron injection layer, which in my view is a typical thickness for such a film.

As you know, an lot of efforts have been working towards a current driven QD-laser. It turns out that it is limited on many levels, most importantly by Auger-recombination, which should be significantly stronger in a current driven device (compared to an optically pumped laser: 10.1038/NNANO.2012.61).

Best of luck!

Quantum-dot light-emitting diode current–voltage characteristics Current density versus voltage log–log plot for the QD-LED is found on Fig. 1a. of the paper "Colloidal quantum-dot light-emitting diodes with metal-oxide chargetransport layers" published by J. M. CARUGE et al. Three different regimes of conduction are clearly visible. At low voltages the device shows space-charge-limited conduction. At 3 V, the slope of the J–V plot increases as both holes and electrons are injected into the QD, and the onset of EL is observed at 3.8 V. At higher V, the J–V behaviour tends to ohmic conduct

Thanks everyone.

But I wish to know the optimum resistivity of the hole transport and electron transport layers separately and not the device as a whole.

Charge transport in an electron-hole plasma driven by high-field terahertz (THz) pulses is strongly influenced by electron-hole interactions, as has been shown in a recent publication [P. Bowlan , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.107.256602 107, 256602 (2011)]. We introduce a picture of high-field THz transport which accounts for the roles of both types of carriers including their interactions. While holes make a negligible contribution to the current, they are heated by absorbing energy from the driving THz field and introduce a friction force for the electrons over a period of about 500 fs. Our model uses an extended version of the loss-function concept to calculate the time-dependent friction. The local field that drives the electrons differs from the incident THz field by screening due to Coulomb correlations in the plasma. We illustrate how spatial correlations between charged particles (electrons, holes, impurities) create a significant local-field correction to the THz driving field. The dominant contribution stems from Coulomb-correlated heavy-hole wave packets, which are strongly polarizable via inter-valence-band transitions.

Bowlan, P.; Kuehn, W.; Reimann, K.; Woerner, M.; Elsaesser, T.; Hey, R.; Flytzanis, C.

2012-04-01