Growth morphology and electrical/optical properties of Al-doped ZnO thin films grown by atomic layer deposition

Abstract

The authors report electrical and optical characterization of zinc oxide (ZnO) and Al-doped zinc oxide (AZO) films grown by atomic layer deposition (ALD). A detailed analysis of ZnO growth morphology is presented with the help of atomic force microscopy imaging, roughness analysis, and x-ray photoelectron spectroscopy surface chemistry information. Initially the film grew as islands, which coalesced to complete the substrate coverage at 50 ALD cycles. The AZO films to be used as transparent conducting oxides for solar cell applications were grown on single crystalline Si (100) and float-glass substrates at temperatures from 150–325 °C. The amount of aluminum doping was varied from 2 to 8 %. The AZO film with 5% Al exhibited the highest conductivity in the film, which increased as the growth temperature increased. Hall effect measurements of an AZO film of thickness 575 nm doped at 5% on silicon and glass substrates showed a sheet resistance (Rs) of 100 Ω/□, which improved further to 25 Ω/□ after annealing at higher temperatures in an argon-hydrogen environment. The transmittance and reflectance of the films grown on glass substrates were used to calculate the band gap. The band gap of AZO increased with Al-doping level. The transmittance of the films in the entire 0 to 8 % doping range, was found to be 80 to 90 % in the visible region. In addition, the growth rates of ZnO, Al2O3, and AZO films were also studied. The growth rate of the AZO films was 1.95 Å per ALD cycle with a cycle time of 1 s. This growth rate is relatively large for an ALD process. The interface of the AZO-Al2O3-Si(100) imaged using high resolution transmission electron microscopy showed a random texture and a continuous interface.

Aluminum-doped zinc oxide formed by atomic layer deposition for use as anodes in organic light emitting diodes

“…3. This E g widening of AZO film can be explained by the Burstein-Moss effect, 5,7,8,[11][12][13] as shown as follows:…”

“…3,4 Moreover, the conductivity and optical transmittance of ZnO can be controlled by impurity doping with an electron donor from various III metal groups such as gallium, 3 indium, 4 and aluminum. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Of these, Al-doped zinc oxide (AZO) films are considered to be a suitable TCO electrode material for optoelectronic devices.…”

“…[6][7][8] The possibility of TCO electrodes has been successfully demonstrated in optoelectronic device applications such as organic light emitting diodes (OLEDs), 1,4,9 solar cells, 17 and thin film transistors (TFTs). 10 Recently, a novel deposition technique for AZO films was developed using atomic layer deposition (ALD), [12][13][14][15][16][17][18][19] which is a cost efficient, low temperature deposition process. In addition, the electrical and optical properties of thin films deposited via ALD can be modified easily and exactly by controlling the deposition to under several angstroms per cycle.…”

Near-perfect broadband absorption from hyperbolic metamaterial nanoparticles

“…It is well documented that the carrier concentration of AZO is dependent on the ALD deposition temperature, T d , allowing for the absorption of the HNT array to be tuned (24)(25)(26)(27). Using an integrating sphere, Fig.…”

Atomic layer deposition precursor step repetition and surface plasma pretreatment influence on semiconductor–insulator–semiconductor heterojunction solar cell

“…On top of SiO x /Al 2 O 3 layer the typical polycrystalline structure of the Al:ZnO front contact is observed. [38][39][40] The interface between c-Si and SiO x /Al 2 O 3 is very sharp. The interface between SiO x /Al 2 O 3 and Al:ZnO is more diffuse (Fig.…”