THE EFFECT OF ALUMINIUM DOPING ON OPTICAL AND ELECTRICAL PROPERTIES OF ZNO THIN FILMS FOR PHOTODETECTOR APPLICATION

• Main Author: Azizah, Ni'matul
• Format: Theses
• Language: Indonesia
• Subjects: Fisika
• Online Access: https://digilib.itb.ac.id/gdl/view/37883
• Institution: Institut Teknologi Bandung

Undoped ZnO and Al-doped ZnO (AZO) thin films with a different concentrations of Al doping were successfully deposited on silicon substrates using direct current-unbalanced magnetron sputtering (DC-UBMS) method. The addition of Al doping with various concentrations on the ZnO thin film were performed to further study and analyse its effect on the optical and electrical properties of the film for photodetector applications. The name of the fabricated thin film samples are ZnO (0 at.% Al), AZO1 (1 at.% Al), AZO3 (3 at.% Al) and AZO5 (5 at.% Al). The optical and electrical properties were characterized using spectrophotometer UV-Vis and I-V measurement using metal-semiconductor-metal (MSM) photodetector configuration structure, respectively. Furthermore, the surface morphology and crystal structure of the films were also investigated using sanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD). The SEM image results present that AZO thin films have more homogeneous morphology with a smaller grain size than undoped ZnO. It indicates that the small quantity of Al dopants was successfully substituted into ZnO lattice which is strengthened by EDX results. Al doping played an important role to uniformly distribute ZnO elemens from the sputtering target to the substrate and it’s contributed to an increased the nucleation number also homogeneity of the films. From the XRD patterns of as-prepared ZnO and AZO thin films on silicon substrates revealed that they were polycristalline thin film. In addition, the full width at half-maximum (FWHM) values of diffraction peaks for AZO thin films were narrower than those of the undoped ZnO thin film. The decreasing of FWHM values followed by the increasing of the peak diffraction intensity. It indicates that the crystalline quality of film is better upon Al doping. Based on the opotical absorbance spectra, Al doping increases the optical band gap of film from 3.25 eV in ZnO film to 3.48 eV in AZO5 film. The shifting band gap towards the larger energy is due to the Burstein-Moss(BM) effect. The ZnO and AZO thin films are showed a high transparency with average transmittance ~ 90%, but the optical transmittance of AZO films decreases with increasing Al doping concentration due to the improvement in thickness of thin films. Furthemore, in order to investigate the electrical properties of film and light detection sensitivity, current versus voltage (I-V) characteristic was measured under the dark and UV light conditions. From I-V cracterization, we found that the films exhibit non-linear I-V curves behavior for both conditions due to the Schottky barrier formation between a metal-semiconductor interface as consequence in applying Ag metal contact on the ZnO or AZO thin films. ZnO thin films is also produces a very higher photocurrent than dark current upon Al doping. It is because Al3+ ions may replace Zn2+ ions and acts as a donor by providing one free electron, then increasing the carrier concentration in ZnO structure so that the photocurrent increase. Beside that, the film shows a higher photo-to-dark-current ratio (Ip/Id) upon Al doping, which is related to the better sensitivity of light detection. The improvement of sensitivity is from 5.8 (ZnO) to 12.5 (AZO5). However, these results clearly demonstrate that the Al doping has a significant role to the modify the properties of ZnO thin film and it is improving light detection performance of the ZnO-based photodetectors.