RF reactive sputter deposition and characterization of transparent CuAlO ₂ thin films

Abstract

CuAlO 2 thin films have been prepared on quartz glass and sapphire substrates by radio-frequency (RF) reactive sputtering using a CuAlO 2 ceramic target. The deposition process was optimized by varying the sputter parameters, such as the substrate temperature and the oxygen flow. In addition a post-growth annealing has been carried out. X-ray diffraction (XRD) revealed that the as-sputtered films are amorphous, and crystallize in the delafossite-type CuAlO 2 or in a phase mixture of CuAlO 2 and CuAl 2 O 4 after annealing in air at 1100°C. The surface morphology of the films was characterized by scanning electron microscopy (SEM). The as-grown films are nearly stoichiometric in terms of Cu to Al ratio and have good depth homogeneity as examined by Rutherford backscattering spectroscopy (RBS) and secondary ion mass spectroscopy (SIMS), respectively. The optical bandgap of the films was estimated by wavelengthdependent transmission measurements at room temperature, which revealed a direct bandgap of 3.38 and 3.80 eV for the as-sputtered and post-growth annealed CuAlO 2 films, respectively.

Fabrication of a n ‐type ZnO/p ‐type Cu–Al–O heterojunction diode by sputtering deposition methods

“…1(c). This result indicates that HWPS can deposit CuAlO 2 films of good lattice coherency at lower growth temperatures than other methods, such as RF magnetron sputtering [3,4], DC magnetron sputtering [7], and pulsed laser deposition [10]. However, a p-n heterojunction diode could not be fabricated using CuAlO 2 , since these films showed semi-insulating property.…”

“…CuAlO 2 is a candidate for use in transparent transistors, UV-visible light emitting diodes, and solar cells consisting of a transparent p-n junction, since its indirect and direct bandgap energies have been reported to be approximately 1.8 and 3.5 eV [2], respectively. CuAlO 2 films have been deposited by a variety of methods, including RF magnetron sputtering [3,4], DC magnetron sputtering [5][6][7][8], chemical vapor deposition [9], pulsed laser deposition [1,10], and wet oxidation [11] techniques. Sputtering methods are most desirable because they can deposit large-area films with well-controlled compositions economically.…”

Helicon‐wave‐excited plasma sputtering deposition of CuAlO2 thin films

“…3(b). This result indicates that HWPS can grow CuAlO 2 films of good lattice coherency at lower growth temperatures than other methods such as RF magnetron sputtering [5,6], DC magnetron sputtering [9], and pulsed laser deposition [12]. The XRD patterns of CuAlO 2 films are shown in Fig.…”

“…CuAlO 2 is also a candidate for use in transparent transistors, UV light emitting diodes, and solar cells composed of transparent p-n junction, since its direct bandgap energy has been reported to be ∼3.5 eV [4]. CuAlO 2 films have been deposited by a variety of methods, including RF magnetron sputtering [5,6], DC magnetron sputtering [7][8][9][10], chemical vapor deposition [11], pulsed laser deposition [1,12], and wet oxidation [13] techniques. The sputtering methods are most desirable because they can economically deposit large-area films with well-controlled compositions.…”

Deposition of cupric oxide thin films by spin coating

“…Despite this there have been relatively few studies on its use as a photovoltaic material, with most groups focussing instead on cuprous oxide (Cu 2 O). Copper oxides are also a key component of the more successful p-type transparent conductive oxides [4][5][6] (TCOs) due to the ability of copper ions to delocalise holes from oxide sites 6,7 . Therefore in order to gain a better understanding of the conduction mechanisms and to look for ways of increasing the conductivity of p-type TCOs, characterisation of the copper oxides is important.…”