Investigation of the Effect of Aluminum Concentration on the Structural, Optical, and Electrical Properties of Al:NiO/PSi Photodetectors
Project no. 32746 · Status: Kapanmış (Yayın bekleniyor) · 2024
Summary
<p>This study aims to investigate how the performance of photodetectors is affected when the structure of nickel oxide (NiO), a significant semiconductor in photodetector technologies, is improved by aluminum (Al) doping and deposited onto porous silicon (PSi) substrates. NiO is frequently preferred in optoelectronic devices sensitive to the UV region due to its wide band gap (~3.6–4.0 eV), chemical stability, and p-type conductivity. However, to overcome the limitations such as low carrier concentration and electrical conductivity in pure NiO, it must be doped with various elements. In this context, it was aimed to improve the regularity of the crystal structure and to enhance the hole carrier concentration through Al doping.</p><p>In the scope of this study, NiO thin films doped with various Al concentrations (0,05 mM, 0,1 mM, 0,5 mM, 1 mM, 3 mM, 5 mM, and 7,5 mM) were synthesized on porous silicon substrates using the electrodeposition method. This electrochemical deposition technique allows for the direct and controlled deposition of films at low temperatures and is especially effective in achieving high homogeneity on porous surfaces. The porous silicon surface is preferred because it provides a large surface area that increases light absorption and are favored for their potential to increase transporter production.</p><p>Structural analyses were conducted using XRD (X-ray Diffraction) and SEM (Scanning Electron Microscopy), revealing that increased Al doping resulted in clear improvements in crystal structure and a reduction in grain sizes. The doping of Al ions into the NiO lattice decreased crystal defects, provided a more homogeneous surface morphology, and improved the overall film quality. Furthermore, XPS (X-ray Photoelectron Spectroscopy) analysis showed that Al doping affected the Ni²⁺/Ni³⁺ ratio, increasing hole carrier concentration and enhancing p-type conductivity.</p><p>According to the optical characterization results, a slight bandgap widening (~from 3,75 eV to ~3,82 eV) was observed in Al-doped NiO films, indicating increased selectivity towards UV light. The high optical transmittance in the visible region also confirmed that Al doping enhanced the transparency of NiO films. Thus, Al-doped NiO films were deemed suitable for UV photodetector applications without requiring additional filters.</p><p>Electrical characterizations included I–V (current-voltage) and I–t (current-time) measurements, which were carried out under various light wavelengths (365 nm, 450 nm, 535 nm, 650 nm, 850 nm) and voltage values (1 V, 3 V, 5 V, 7 V, 9 V). The results showed that as the Al doping ratio increased, the device’s photoresponse improved under illumination. The best performance was obtained with 3 mM Al doping, where the highest responsivity, quantum efficiency (QE), and detectivity values were recorded. While performance was limited at low doping levels such as 0,05 mM, excessive doping at 7,5 mM led to increased recombination events due to overly high carrier concentrations, thereby reducing efficiency. Accordingly, 3 mM was identified as the optimum Al doping concentration.</p><p>This thesis demonstrates that Al doping significantly improves the structural, optical, and electrical performance of NiO/PSi-based photodetectors. Al:NiO structures synthesized via electrodeposition on porous silicon substrates offer high responsivity, broad spectral response range, and low dark current, making them highly suitable and efficient alternatives for photodetection applications. Especially for next-generation optoelectronic devices seeking low-cost, environmentally sustainable, and controllable production techniques, this approach offers notable potential.</p>