Optoelectronic performances on different structures of Al‐doped ZnO

Abstract

ZnO films and Al‐doped ZnO (AZO) films were deposited on p‐Si substrate by magnetron sputtering to investigate its chemical composition, structural and photoelectric properties. XRD and FTIR show that Al ions can enter into the substitutional and interstitial site of ZnO crystal, and O atoms in AZO films are more abundant. Three different structures of Al‐doped ZnO (substitutional Al, interstitial Al, and O‐rich Al‐doped ZnO) were built using first‐principles method based on experimental results, charge density difference, and density of States (DOS) illustrate that there are strong ionic interactions between Al and O atoms in substitutional Al‐doped ZnO, moreover, substitutional and interstitial Al doping both are beneficial to N type, but oxygen‐enriched ZnO is not conducive to N type. Furthermore, the optical properties of 3 different Al‐doped ZnO structures were investigated respectively. Compared with pure ZnO, the real and imaginary part of dielectric function of O‐rich and interstitial Al have a significant increase and move to lower energy (red shift), the reflectivity of O‐rich is 3 times of pure ZnO and substitutional Al‐doped ZnO. The results are hoped to be helpful to study AZO thin film and predict the properties of Al‐doped ZnO.

Study on the Effect of Thermal Shock on Al‐Doped ZnO Films

“…The results show that the bandgaps from 0 to 50 shocks are 0.531, 0.615, 0.587, 0.610, 0.634, and 0.617 eV, respectively, the simulated bandgaps are much smaller than the experimental value, which may be caused by the lower exchange‐correlation between electrons generated by GGA function, but this does not affect the qualitative research in this paper. [ 5 ] All move to a higher energy direction (blue shift) after thermal shock, showing the shocked samples still maintain a wide bandgap and exhibit good endurance. Compared with the AZO without thermal shock, the bandgaps of shocked AZO increase slightly and fluctuate with the increase of thermal shock times.…”

“…After the thermal shock, the charges of Al atom in all AZO are about 1.54e, and the charge of Zn increases, which means the electron interactions between Zn and O are stronger due to Zn robbing O atoms related to Al‐O bonding, that is to say, oxygen contributes more to the Zn—O bond of AZO after thermal shock. Moreover, the O atom was proved to be the acceptor defect, [ 5 ] which could narrow the bandgap.…”

“…2 × 2 × 2 supercell AZO was constructed and as shown in Figure based on our previous work. [ 5 ] The scissors correction (2.573 eV) was adopted in this paper because of the lower exchange correlation caused by the GGA function. The simulations of the thermal shock process were performed by molecular dynamics calculations using the Forcite module in Materials Studio.…”

“…After the thermal shock, the bandgaps of AZO film become smaller, indicating that the film quality decreases, and the bandgaps fluctuate within a certain range, which can be attributed to the effect of oxygen in the air under thermal shock based on XPS results. The O atom was proved to be an acceptor defect, [5,34,41] which could narrow the bandgap and degenerate optical properties. Furthermore, the Zn 2p binding energy of shocked AZO is maintained in a certain range with the increase of thermal shock times, so the degradation trend of optical properties is fluctuating after shock.…”

“…[1][2][3] AZO is constantly being used as a window layer or front electrode and is widely used in micro/nano/optoelectronic devices such as solar cells, photodetectors, sensors, hydrogen generation by hydrolyzation and lithium-ion battery. [4,5] AZO films could be obtained through many methods including sol-gel, [6] magnetron sputtering, [7] spray pyrolysis, [8] pulsed laser deposition, [9] atomic layer deposition, [10] metal-organic vapor phase epitaxy [11] and chemical bath deposition. [12] Compared with other processes, magnetron sputtering technology has many advantages and is considered to be the most suitable technology for industrialization.…”