STUDY OF THE EFFECT OF COPPER (CU) DOPING AND ANNEALING ON A ZINC OXIDE (ZNO) FILM GROWN BY DC MAGNETRON CO-SPUTTERING TECHNIQUE FOR VISIBLE LIGHT PHOTODETECTOR APPLICATIONS

• Main Author: Rati, Yolanda
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/79509
• Institution: Institut Teknologi Bandung

Efforts to modify the structural, optical, and electrical properties of zinc oxide (ZnO) to improve the performance of visible light photodetectors have been conducted by doping copper (Cu). The Cu dopant was chosen due to its high electrical conductivity and its ion radius being close to Zn making atomic insertion easier. Cu-doped ZnO (CZO) films were grown using confocal DC magnetron cosputtering on a silicon (Si) substrate at Cu sputtering power varied (15 and 20 W), while the Zn sputtering power was constant at 80 W. Furthermore, the effect of annealing treatment at a temperature of 600? was also studied after the ZnO and CZO films were deposited. The surface morphology and elemental composition, structural properties, chemical bonds, absorbance and photoluminescence of the ZnO and CZO films were characterized using Field Emission Scanning Electron Microscopy (FE-SEM) and Energy dispersive X-ray (EDX), X-ray Diffraction (XRD) , Fourier transforms-infrared (FT-IR), ultraviolet-visible (UV-Vis), and photoluminescence (PL) spectroscopy. Furthermore, I-V measurements with a metal-semiconductor-metal (MSM) configuration were investigated to determine the electrical properties of ZnO and CZO films as visible light photodetector materials. The FESEM image exhibits changes in the shape and size of the rod particles to become shorter as the Cu sputtering power increases. The annealed film produces a granular shape and is reduced in size and more homogeneous. Cu dopant has been successfully substituted in the ZnO system which was confirmed from EDX analysis. Therefore, Cu influences the characteristics of the ZnO film. The XRD spectrum identifies the ZnO structural phase with the (002) plane crystal orientation direction along the c-axis perpendicular to the substrate. At a Cu sputtering power of 20 W as grown (without annealing) and annealed films, a monoclinic CuO phase with a (202) plane was found. Good crystallinity of CZO film due to the increase in Cu sputtering power and the annealing effect as indicated by high crystallite size also low lattice stress and dislocation density. Identification of chemical bonds from the FT-IR spectrum confirms the strong vibrational bonds of Zn-O and becomes sharper due to the annealing effect. Furthermore, peak shift indicates successful substitution of Cu in the ZnO lattice. The effect of annealing reveals the purity of the film increases without the presence of impurities from carbon C=C. Based on the UV-Vis absorbance spectrum, a redshift occurs due to Cu doping which refers to a decrease in band gap energy due to the Burstein-Moss effect (BM). It also occurs in annealed films. The band gap energy of the ZnO and CZO films after annealing is smaller than without annealing because the band edge absorbance is small. The photoluminescence properties show a decrease in PL intensity as the Cu sputtering power increases, causing a decrease in defects and free excited state energy levels. Moreover, the shift in the emission peak indicates recrystallization due to annealing. Furthermore, the electrical properties of ZnO and CZO in light detection were studied from the I-V (current-voltage) characteristic curve in dark and visible light conditions using a solar simulator. The I-V curve exhibits photocurrent of the Cu-doped ZnO is higher than the undoped ZnO film, both in the annealed and non-annealed films. The increased sputtering power of Cu reveals a high sensitivity twice that of ZnO, and responsivity increases three times at a bias of 5 Volt. The sensitivity and the responsivity of annealed Cu-doped ZnO at sputtering power 20 W produces the highest values of 10.01 and 6.7 mA/W. Also, the low Schottky barrier height plays an important role in electron transport from metals to semiconductors. Therefore, increasing the Cu sputtering power and annealing treatment by modifying the structural and optical properties have succeeded in improving the performance of visible light photodetectors.