Influence of post‐deposition annealing on electrical and optical properties of ZnO‐based TCOs deposited at room temperature

Abstract

212941365 ** The first two authors contributed equally to this work.The post-deposition modification of ZnO-based transparent conductive oxides (TCOs) can be the key to produce thin films with optoelectronic properties similar to indium tin oxide (ITO), but at a much lower cost. Here, we present electrooptical results achieved for post-deposition annealing of Al-Zn-O (AZO), AZO:H, Ga-Zn-O:H (GZO:H), and Zn-O:H (ZNO:H) thin films deposited by RF sputtering at room temperature. These studies comprise results of thermal annealing at atmospheric pressure, vacuum, forming gas, H 2 and Ar atmospheres, and H 2 and Ar plasmas, which lead to significant enhancement of their electro-optical properties, which are correlated to morphological and structural improvements. The post-deposition annealing leads to an enhancement in resistivity above 40% for AZO, AZO:H, and GZO:H, reaching r % 2.6-3.5 Â 10 À4 Vcm, while ZnO:H showed a lower improvement of 13%. The averaged optical transmittance in the visible region is about 89% for the investigated TCOs. Such results match the properties of state-of-art ITO (r % 10 À4 Vcm and transmittance in VIS range of 90%) employing much more earth-abundant materials.

Passivation of Interfaces in Thin Film Solar Cells: Understanding the Effects of a Nanostructured Rear Point Contact Layer

“…Only the light absorbed in the CIGS (termed useful absorption) leads to significant photocurrent. The parasitic light absorption by the solar cell stack that does not translate into photocurrent occurs mainly in: (i) the UV range due to the light absorption in the ZnO-based transparent conductive oxide (TCO) and in the CdS layer, where the low minority carrier lifetime does not allow for current output; (ii) the near-infrared (NIR) range due to both the free carriers light absorption in the TCO layer [55,56] and the absorption of the Mo rear contact. [57,58] These optical losses account for the difference shown in Figure 4b between the light absorption of the CIGS layer and that in the complete solar cell stack.…”

Optical reflectance of solution processed quasi-superlattice ZnO and Al-doped ZnO (AZO) channel materials

“…However, there is an interest in developing metal oxide semi conductors to replace ITO, such as ZnO [15], Indoped ZnO (IZO), In-Ga-Zn-O (IGZO) and Aldoped ZnO (AZO) [16]. For AZO, the composition avoids expensive and resourcecrit ical indium due to the higher relative abundance in the Earth's crust (75 ppm for Zn opposed to 0.16 ppm for In) [17].…”

“…ZnO is also attractive as it can be grown by a multitude of methods such as rf sputtering [18], pulsed laser deposition [20] and solutionprocessed methods [21], providing quite good TFT performance compared to pri mary amorphous oxide semiconductor technologies [22,23]. However, on its own, ZnO does not meet the electrical perfor mance standards set by ITO due to a higher resistivity from a lower majority carrier concentration [17,24], but important advances are being made in postdeposition annealing to sig nificantly improve and control its response [17]. In order to improve its electrical properties and reduce sheet resistance and resistivity, while also maintaining a lowcost, nontoxic and stable material, ZnO can be doped with trivalent elec tron donor metals such as Al or Ga to ensure high freecarrier mobility and transparency via the Burnstein-Moss shift that gives metal oxides their useful attributes [25].…”

“…Currently, the semiconducting material used most in the area of optoelectronics is indium tin oxide (ITO), particularly in flatpanel displays [13]. This is due to its wide band gap…”

Highly-Ordered Growth of Solution-Processable ZnO for Thin Film Transistors

“…(6,7) Zinc oxide is an material of interest in the area of optoelectronics due to its wide band gap (Eg ~ 3.3 eV at 300 K) (8), large exciton binding energy (~66 meV) and especially for the variety of methods by which it can be processed (9). Moreover, ZnO is inexpensive, abundant and readily able to alloy with other metals in the oxide form (10)(11)(12) and has a lattice that can facilitate interstitial doping. (7) This gives ZnO a key role in the area of optoelectronics, metal oxide thin films and thin film transistor (TFT) technologies.…”