Efficient inverted quantum-dot (QD) light-emitting diodes (LEDs) are demonstrated by using 15% Mg doped ZnO (Zn0.85Mg0.15O) as an interfacial modification layer. By doping Mg into ZnO, the conduction band level, the density of oxygen vacancies and the conductivity of the ZnO can be tuned. To suppress excess electron injection, a 13 nm Zn0.85Mg0.15O interlayer with a relatively higher conduction band edge and lower conductivity is inserted between the ZnO electron transport layer and QD light-emitting layer, which improves the balance of charge injection and blocks the non-radiative pathway. Moreover, according to the electrical and optical studies of devices and materials, quenching sites at the ZnO surface are effectively reduced by Mg-doping. Therefore exciton quenching induced by ZnO nanoparticles is largely suppressed by capping ZnO with Zn0.85Mg0.15O. Consequently, the red QLEDs with a Zn0.85Mg0.15O interfacial modification layer exhibit superior performance with a maximum current efficiency of 18.69 cd A−1 and a peak external quantum efficiency of 13.57%, which are about 1.72- and 1.74-fold higher than 10.88 cd A−1 and 7.81% of the devices without Zn0.85Mg0.15O. Similar improvements are also achieved in green QLEDs. Our results indicate that Zn0.85Mg0.15O can serve as an effective interfacial modification layer for suppressing exciton quenching and improving the charge balance of the devices.

This work investigates the source-drain (S-D) parasitic resistance (RSD) characteristics of the back-channel-etched (BCE) a-IGZO TFTs with ultra-thin Nb doped TiO2 (TNO) protective layer. It is shown that RSD is strongly related to the thickness of the TNO protective layer although the electrical performances of the BCE a-IGZO TFTs with different TNO thickness are similar to each other. The BCE TFT with 3 nm TNO shows an unusually large RSD value (300 Ω cm). It is suggested that a ~3 nm TNO depletion layer should be formed at the TNO/a-IGZO interface in the S-D region in this case. In addition, RSD of the BCE TFTs with 1 and 5 nm TNO is 11 and 26 Ω cm, respectively. The low RSD of these two devices is caused by much thinner TNO depletion layers in the S-D region. Besides, a moderate RSD of 53 Ω cm for the S-D lift-off device can be ascribed to a lower a-IGZO band bending at the Mo/a-IGZO interface than that of the BCE devices at the TNO/a-IGZO interface.

The electrical and optical properties of direct current and radio frequency (RF) sputtered amorphous indium gallium zinc oxide (a-IGZO) films are compared. It is found that the RF sputtered a-IGZO films have better stoichiometry (In:Ga:Zn:O = 1:1:1:2.5–3.0), lower electrical conductivity (σ < 8 S/cm), higher refractive index (n = 1.9–2.0) and larger band gap (Eg = 3.02–3.29 eV), and show less shift of Fermi level (△ EF ~ 0.26 eV) and increased concentration of electrons (△ Ne ~ 104) in the conduction band with the reduction concentration of oxygen vacancy (VO). Although a-IGZO has intensively been studied for a semiconductor channel material of thin film transistors in next-generation flat panel displays, its fundamental material parameters have not been thoroughly reported. In this work, the work function (φ) of a-IGZO films is tested with the ultraviolet photoelectron spectroscopy. It is found that the φ of a-IGZO films is in the range of 4.0–5.0 eV depending on the VO.Highlights► Amorphous InGaZnO4 (a-IGZO) films were prepared with different sputtering modes. ► Electrical and optical properties of the different films were compared. ► Fermi level (△EF) shift in a-IGZO films were tested by X-ray photoelectron spectroscopy. ► The relation of △EF with the properties of a-IGZO films were discussed. ► Work function was tested by ultraviolet photoelectron spectroscopy.