Professor Raid Abdul Wahab Ismail, Head of the Department of Applied Sciences, supervised a postgraduate student in the field of Laser Science and Technology

The doctoral thesis of the postgraduate student, Safaa Abdul Salam Abdul Rahman, was discussed. Her thesis, titled: :
"Preparation of a Thin Nanostructured Cerium Oxide Film by Pulsed Laser Deposition on Silicon for Electro-Optical Applications"
The discussion was held in the hall named after the late Professor Dr. Abdul-Muttalib Ibrahim Al-Sheikh in the department building. The examination committee consisted of

• Professor Alwan Mohammed Alwan Department of Applied Sciences / Laser Science and Technology Branch - Chairman
• Professor Wafa Khalid Khalaf Department of Applied Sciences / Applied Sciences Research Unit - Member
• Assistant Professor Alaa Abdul Jabbar Hussein Department of Applied Sciences / Laser Science and Technology Branch - Member
• Professor Hassan Abdul Sahib Hadi Al-Mustansiriya University / College of Education / Department of Physics - Member
• Professor Haider Abdul Redha Saleh Department of Applied Sciences / Laser Science and Technology Branch - Member
• Assistant Professor Suad Salem Shakir Department of Applied Sciences / Applied Physics Branch - Member
• Professor Muslim Fadel Jawad Department of Applied Sciences / Laser Science and Technology Branch - Member and Supervisor
• Professor Raid Abdul Wahab Ismail Department of Applied Sciences / Laser Science and Technology Branch - Member and Supervisor

Cerium oxide (CeO2) is an attractive semiconducting material that draws attention in optoelectronics and photovoltaics applications. Due to the remarkable progress in photovoltaic technology, enhancing efficiency and minimized the costs have emerged as global challenges for the solar industry. A crucial aspect of this advancement involves the creation of solar cell antireflection coating, which play a significant role in minimizing sunlight reflection on the cell surface. The most crucial issue was the preparation method of Cerium oxide (CeO2) nanostructure films with control of Preparation conditions for the desired application. CeO2 nanostructure films fabricated by pulsed laser deposition (PLD), home-made pulsed laser deposition system used in this work consisted of a Q-switched Nd:YAG laser system and a vacuum chamber. The Nd:YAG laser used to deposit the CeO2 film emitted a laser beam with a wavelength (λ) of 1064 nm, 7 nanoseconds pulse duration, and 6 Hertz  (PRF) a  pulse repetition frequency. The laser beam was focused by a 7-cm conversion lens, and the laser fluence was changed from 63.66 to 101.86 J/cm2 and number of pulses used for film deposition of CeO2 film was changed from 900 to 1200 pulses. This thesis is based on three parts, the first part is the preparation of films under different preparation conditions and their use as anti-reflection coatings that contribute to increasing the efficiency of solar cells. The second part is the use of cerium oxide films prepared under different conditions in terms of laser energy and number of pulses in preparing photodetectors. As for the last part, fabricate high-efficiency CeO2/Si photodetector and study effect of (RTA) rapid thermal annealing on the performance of CeO2/Si photodetector. In the first section, CeO2 thin films have been used as anti-reflection coating (ARC) for Si solar cells. X-ray diffraction measurements showed grown films were crystalline with cubic and hexagonal phases with a preferred orientation along the (111) plane. The degree of crystallinity of the film increases with the increase in the laser fluence. while all peaks can be indexed to a face-centered cubic (fcc) phase of CeO2 fluorite structure for films prepared at different number of laser pulses. Scanning electron microscope (FE-SEM) results reveal that the film’s morphology and film uniformity improved as the laser fluence increases, the film deposited at 63.66 J/cm2 exhibits a surface morphology characterized by densely packed particles with spherical shapes on the film’s surface. The average grain size of the film prepared at 900 pulses was found to be 22 nm, and it increases to 44.7 nm as the number of laser pulses increases to 1200 pulses. Also, nanostructured CeO2 films on a glass substrate exhibit quite uniform, crack-free, and dense. Also, film thickness was measured by (FE-SEM Cross Section). Raman shift of the CeO2 film as a function of laser energy density and number of laser pulses were investigated. The observed peaks at 463 cm−1 can be attributed to CeO2. The room temperature photoluminescence (PL) spectra of CeO2 films deposited on Si substrate with an excitation source of (325 nm) as wavelength showed a wide range of emission, spanning from 350 to 500 nm. This broadband emission is likely attributed to crystal defects, such as oxygen vacancies, which possess electronic energy levels below the 4f band. Photovoltaic properties illustrated that the conversion efficiency of the silicon solar cell increases from 8.37 to 14.04% after deposited with ARC CeO2 film at laser energy density of 76.39 J/cm2. The maximum PCE was 19.27% and fill factor of 87% was obtained after the deposition of silicon solar cell with cerium oxide nanostructured film deposited at 1000 laser pulses. The CeO2 films deposited at 76.39 J/cm2 laser pulse energy density have highest hydrophobicity with the largest water contact angle (WCA) of 117.98°, while at 1000 pulse CeO2 films exhibited highest hydrophobicity with the largest water contact angle (WCA) of 111.90°. In the second section, CeO2 films were deposited on silicon substrates with different laser power densities and different number of laser pulses to fabricate high-performance CeO2/Si photodetectors. Hall effect results confirmed that the Hall coefficient of all films is negative, indicating that the CeO2 film is n-type. Field emission scanning electron microscopy (FE-SEM) results illustrated that the CeO2 film has a spherical grain morphology with an average grain size ranging from 33 to 54 nm, depending on the laser energy density. The film deposited at various numbers of laser pulses also has spherical grains with an average grain size ranging from 32 to 44 nm, depending on the number of pulses. The optical properties of the CeO2 film showed that the optical energy gap of the films decreased from 3.5 to 3 eV as the laser energy density increased from 63.66 to 101.86 J/cm2, and changed from 3.4 to 3 when number of pulses changed from 900-1000 pulse. The I-V characteristics of CeO2/p-Si heterojunctions showed clear rectification characteristics. The CeO2/Si photodetector fabricated at 63.66 J/cm2 showed the highest responsivity of 0.69 A/W at 450 nm, detectivity as high as 1.5 × 1010 Jones at 450 nm, and an external quantum efficiency of 92% when biased to 5 V. Also, photodetector fabricated at 1100 pulse exhibited maximum value of responsivity at wavelength 450 nm and was 0.49 A/W, D* of 1×1010 Jones at 500 nm, and EQE of 61% at 450 nm. The last section of this thesis covers the deposition of cerium oxide films on CeO2/Si silicon substrates prepared by pulsed laser deposition technique at a laser energy density of 63.66 J/cm2 and then studying the effect of rapid thermal annealing (RTA) on the photodetector at different times (2, 4, 6, 8 min) and comparing them with CeO2/Si without annealing. The (I-V) characteristics of the CeO2/p-Si photodetector show good rectification properties after annealing compared to without annealing. The highest responsivity of the photodetector was (0.6 A/W) at an annealing time of 6 min compared to the photodetector without annealing (A/W 0.4), and a detectivity of (3.8×1010) at an annealing time of 6 min while the detectivity of the photodetector without annealing was (3×1010). The maximum photocurrent of the junction was observed when the annealing time was 6 min. The rise and fall times of the photodetector fabricated at 6 min were 0.3 and 0.32 s, indicating that this photodetector has good junction characteristics. The obtained results of this work confirm that the properties of cerium oxide films are suitable for optoelectronic applications.