Wavelength‐Emission Tuning of ZnO Nanowire‐Based Light‐Emitting Diodes by Cu Doping: Experimental and Computational Insights

Abstract

The band‐gap engineering of doped ZnO nanowires is of the utmost importance for tunable light‐emitting‐diode (LED) applications. A combined experimental and density‐functional theory (DFT) study of ZnO doping by copper (Zn2+ substitution by Cu2+) is presented. ZnO:Cu nanowires are epitaxially grown on magnesium‐doped p‐GaN by electrochemical deposition. The heterojunction is integrated into a LED structure. Efficient charge injection and radiative recombination in the Cu‐doped ZnO nanowires are demonstrated. In the devices, the nanowires act as the light emitters. At room temperature, Cu‐doped ZnO LEDs exhibit low‐threshold emission voltage and electroluminescence emission shifted from the ultraviolet to violet–blue spectral region compared to pure ZnO LEDs. The emission wavelength can be tuned by changing the copper content in the ZnO nanoemitters. The shift is explained by DFT calculations with the appearance of copper d states in the ZnO band‐gap and subsequent gap reduction upon doping. The presented data demonstrate the possibility to tune the band‐gap of ZnO nanowire emitters by copper doping for nano‐LEDs.

Role of defects in one-step synthesis of Cu-doped ZnO nano-coatings by electrodeposition method with enhanced magnetic and electrical properties

“…It has a wide direct band gap of 3.37 eV (at room temperature) and a large exciton binding energy of 60 meV [16][17][18]. In recent years, reports on nanostructured ZnO with native defect states and their control with doping have drawn attention of scientific community due to their exceptionally tunable optical, electrical, and magnetic properties [2,18]. However, the discussion over the origin of ferromagnetism in ZnO is still under debate [19].…”

“…However, the discussion over the origin of ferromagnetism in ZnO is still under debate [19]. Some of the literature claims that the FM nature in TM-doped ZnO is due to the presence of external impurities like magnetic clustering and precipitations of metal ions [13][14][15][16][17][18][19][20]. To nullify the external effects, non-magnetic materials like metal Cu, metal Zn, ZnO, Cu 2 O, and bulk CuO were doped to produce intrinsic DMS materials [24][25][26].…”

“…Among metal oxides, ZnO is widely used in optoelectronic and spintronic applications [12][13][14][15]. It has a wide direct band gap of 3.37 eV (at room temperature) and a large exciton binding energy of 60 meV [16][17][18]. In recent years, reports on nanostructured ZnO with native defect states and their control with doping have drawn attention of scientific community due to their exceptionally tunable optical, electrical, and magnetic properties [2,18].…”

Stimulated electroluminescence emission from n-ZnO/p-GaAs:Zn heterojunctions fabricated by electro-deposition

“…These results were found to be in agreement with the studies carried out earlier. 38,39 The NBE emission is ascribed to the recombination of electrons at the bottom of the conduction band with holes at the top of the valance band within the active ZnO film. The green emission peak centered at 520-538 nm can be attributed to the electron-hole recombination from the V O to the valance band (VB) (E Vo − E VB = 2.38 − 2.53 eV) or the recombination from Zn i to V O energy level.…”

Photoassisted fabrication of zinc indium oxide/oxysulfide composite for enhanced photocatalytic H2evolution under visible-light irradiation

“…Therefore, the loss of indium widens the bandgap of vacancy-rich ZIO. Furthermore, since Cu doping narrows the bandgap by introducing Cu 3d levels above the VB of ZIO [35], it can be concluded that the Cu concentration was low in the vacancy-rich ZIO. …”