Comparison of Electrical, Optical, and Structural Properties of RF-Sputtered ZnO Thin Films Deposited Under Different Gas Ambients

Abstract

Transparent conducting ZnO:Al thin films were prepared by rf-magnetron sputtering under different gas ambients at 300 C. The electrical resistivity varied from 1:23 Â 10 À1 to 2:8 Â 10 À4 cm introducing O 2 and H 2 gas with Ar ambient. The minimum sheet resistance of ZnO:Al film is 3.5 /square. The maximum carrier concentration and Hall mobility as estimated from Hall effect measurement of the films were 2:3 Â 10 21 /cm 3 and 44.4 cm 2 V À1 s À1 respectively. Photoluminescence (PL) spectra peaks are mainly in the blue emission region and change from 432 nm (2.87 eV) and 541.5 nm (2.29 eV) with the change of gas ambients. From the X-ray diffraction (XRD) pattern exhibiting only the h002i peak of ZnO, all films were found to be c-axis-oriented. The crystallite size varies from 150 to 288 Å for different films calculated from h002i orientation of XRD data. The characteristic features of ZnO films prepared under Ar þ H 2 ambient are their high carrier concentration, high strain values, high band gap and blue emission compared to the other ZnO films. The structural, electrical, optical properties and surface topography of ZnO thin films using XRD, Hall measurements, PL, UV-visible (vis)-near IR (NIR) spectroscopy and atomic force microscopy (AFM) have been investigated.

Narrow band defect luminescence from Al-doped ZnO probed by scanning tunneling cathodoluminescence

“…1(b), we attribute peaks C (475 nm, 2.62 eV), D (642 nm, 1.95 eV), and E (787 nm, 1.59 eV) to emission from different charge states of V O . The strongest peak at 475 nm is consistent with the blue-green emission reported in ZnO and AZO films and most often attributed to oxygen vacancies, 5,[17][18][19][20] although the specific charge states of V O involved the question of whether an electron is captured from the conduction band or a hole from the valence band, or even of whether V O at all contribute to the characteristic green luminescence remain unresolved issues in the literature. 9 We attribute peak A (329 nm, 3.77 eV) to recombination of electrons at the Fermi level with holes from the valence band (peak A is strongly suppressed in PL due to a laser line filter); this is supported by optical absorption spectroscopy (not shown) which shows that the absorption edge in our films is close to 3.8 eV.…”

“…[5][6][7][8][16][17][18][19][20] Nevertheless, most authors agree on three points: [6][7][8][9] for degenerately doped ZnO oxygen vacancies, V O are thermodynamically favorable; V O are deep donors, and for n-type ZnO are the most stable in the neutral charge state V O ) are well separated within the band gap, due to a large ionic rearrangement around V O resulting in an effective negative-U interaction between localized holes. Based on the consistency of our spectra from site-to-site, we assume that all the observed surface defects are of the same type, and due to the wide distribution of deep-level emission lines, we propose that our STM-CL spectra represent emission from individual V O sites.…”

Merits and Demerits of Transparent Conducting Magnetron Sputtered ZnO:Al, ITO and SnO2:F Thin Films for Solar Cell Applications

“…ion will be replaced by Al 3? ions or Zn-H bond can be formed that contributes in enhancement of free carrier density without disturbance of optical transmission [1,11]. But for ITO and SnO 2 :F thin films more metallic nature is created, so electrical sheet resistance and optical transmission drastically deteriorated due to low binding energy.…”

“…Transparent conductive oxide (TCO) films are most important material from technological point of view mainly for its wide applications in various electronic and optoelectronic devices, such as solar cells, gas sensors, varistors, organic material based microelectronic, polymer electronics and diodes due to their unique materials properties such as high electrical conductivity and high optical transmittance [1][2][3][4][5]. Among them magnetron sputtered fluorine doped tin oxide (SnO 2 :F), indium tin oxide (ITO), and aluminum doped zinc oxide (ZnO:Al) thin films are most attractive materials for their non-toxicity, ease of availability, high sticking co-efficient with substrate materials and unique opto-electronic properties.…”

Effect of Sputtered ZnO Layers on Behavior of Thin-Film Transistors Deposited at Room Temperature in a Nonreactive Atmosphere

“…On the other hand, at high deposition pressures, the particles become scattered due to collisions with each other and the deposition rate decreases. 25 Basically, the mean free path is high for low pressures and low for high pressures. The Keller-Simmons relation predicts this well-known phenomenon.…”