Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping

Electrical and physical properties of a metal-oxide-semiconductor [MOS] structure using atomic layer-deposited high-k dielectrics (TiO2/Al2O3) and epitaxial GaAs [epi-GaAs] grown on Ge(100) substrates have been investigated. The epi-GaAs, either undoped or Zn-doped, was grown using metal-organic chemical vapor deposition method at 620°C to 650°C. The diffusion of Ge atoms into epi-GaAs resulted in auto-doping, and therefore, an n-MOS behavior was observed for undoped and Zn-doped epi-GaAs with the doping concentration up to approximately 1017 cm-3. This is attributed to the diffusion of a significant amount of Ge atoms from the Ge substrate as confirmed by the simulation using SILVACO software and also from the secondary ion mass spectrometry analyses. The Zn-doped epi-GaAs with a doping concentration of approximately 1018 cm-3 converts the epi-GaAs layer into p-type since the Zn doping is relatively higher than the out-diffused Ge concentration. The capacitance-voltage characteristics show similar frequency dispersion and leakage current for n-type and p-type epi-GaAs layers with very low hysteresis voltage (approximately 10 mV)

Functionalized Graphene-Incorporated Cupric Oxide Charge-Transport Layer for Enhanced Photoelectrochemical Performance and Hydrogen Evolution

The production of hydrogen (H2) through photoelectrochemical water splitting (PEC-WS) using renewable energy sources, particularly solar light, has been considered a promising solution for global energy and environmental challenges. In the field of hydrogen-scarce regions, metal oxide semiconductors have been extensively researched as photocathodes. For UV-visible light-driven PEC-WS, cupric oxide (CuO) has emerged as a suitable photocathode. However, the stability of the photocathode (CuO) against photo-corrosion is crucial in developing CuO-based PEC cells. This study reports a stable and effective CuO and graphene-incorporated (Gra-COOH) CuO nanocomposite photocathode through a sol-gel solution-based technique via spin coating. Incorporating graphene into the CuO nanocomposite photocathode resulted in higher stability and an increase in photocurrent compared to bare CuO photocathode electrodes. Compared to cuprous oxide (Cu2O), the CuO photocathode was more identical and thermally stable during PEC-WS due to its high oxidation number. Additionally, the CuO:Gra-COOH nanocomposite photocathode exhibited a H2 evolution of approximately 9.3 µmol, indicating its potential as a stable and effective photocathode for PEC-WS. The enhanced electrical properties of the CuO:Gra-COOH nanocomposite exemplify its potential for use as a charge-transport layer

Protein Encapsulated Covellite CuS Nanospheres for the Efficient Oxidative Degradation of Organic Dyes in Wastewater

The existence of toxic, non-biodegradable organic pollutants in wastewater has become an indisputable and global remark for environmental problem. Interesting works have been performed on engineering/designing novel nano-catalyst to replace well-known Fe-fenton system in the degradation of such pollutants where the residual iron limits their wide application. Alternatively, Cu based materials have been explored in waste-water management mainly due to their ease of availability, cost-effectiveness, and efficient oxidative catalytic activity. However, synthesis of such pure phase water-soluble monodispersed Cu-based nanoparticles is challenging. In this study, we reported the synthesis of monodispersed covellite bovine serum albumin functionalized - copper sulfide (BSA-CuS) nanoparticles by simple thermal decomposition process. As-synthesized nanoparticles were characterized through advanced techniques such as UV-Visible spectra, XRD, FT-IR, HR-TEM and XPS. Finally, their potential for enhanced oxidative catalytic performance was investigated through experimental and theoretical studies for the degradation of wide range of dyes such as anionic dye, cationic dye, and industry effluent, which are commonly present in wastewater as contaminant

Defect analysis of sputter grown cupric oxide for optical and electronics application

We have studied the defect density and defect level of sputter grown cupric oxide (CuO) for optical and electronic applications. A deep level transient spectroscopy (DLTS) technique has been employed to study the defect density in the CuO thin film deposited by sputtering. The DLTS studied showed that the defect density significantly reduced for the film grown at a high working pressure. It has also been shown that doping density increases for the film grown at a high working pressure. Transmission electron microscopy analysis revealed the improvement of the crystal quality of the CuO thin film prepared at the high working pressure. The band gap of sputter grown CuO was found to be ~1.4 eV with an absorption coefficient of ~104 cm−1. From a photoelectron spectroscopy measurement, it was found that the work function for CuO was ~5.2 eV. The present work reveals the importance of CuO for optical and electronic device applications

Reduction of Cu-rich interfacial layer and improvement of bulk CuO property through two-step sputtering for p-CuO/n-Si heterojunction solar cell

Copper-rich interfacial-layer (Cu-rich IL) is formed during sputter deposition of cupric oxide (CuO) layer on silicon (Si). It has significant impact on the performance of p-CuO/n-Si heterojunction solar cells. In this report, CuO films deposited on Si at different RF-power levels using single and two-step RF-sputtering techniques and p-CuO/n-Si heterojunction solar cells have been investigated. Systematic characterization using XPS, AFM, XRD, Raman, and HR-TEM reveal that two-step RF-sputtering technique offers better crystal quality CuO film with thinner Cu-rich IL layer. Photovoltaic (PV) properties with an open-circuit voltage (Voc ) of 421 mV, short circuit current (Jsc ) of 4.5 mA/cm2, and a photocurrent of 8.3 mA/cm2 have been achieved for the cells prepared using two-step sputtering method, which are significantly higher than that for the solar cells fabricated using a single-step sputtering. The PV properties were further improved by depositing CuO films at higher working pressure with nitrogen doping. The efficiency of the best device achieved is approximately 1.21%, which is the highest value reported for p-CuO/n-Si heterojunction based solar cells.Published versio

Impact of deposition parameters on the material quality of SPC poly-Si thin films using high-rate PECVD of a-Si:H

The impact of the deposition parameters such as gas flow (sccm) and RF plasma power density (W/cm2) on the deposition rate of a-Si:H films is systematically investigated. A high deposition rate of up to 146 nm/min at 13.56 MHz is achieved for the a-Si:H films deposited with high lateral uniformity on 30 × 40 cm2 large-area glass substrates. A relationship between the SiH4 gas flow and the RF power density is established. The SiH4 gas flow to RF power density ratio of about 2.4 sccm/mW cm-2 is found to give a linear increase in the deposition rate. The influence of the deposition rate on the material quality is studied using UV-VIS-NIR spectrophotometer and Raman characterisation techniques. Poly-Si thin film with crystal quality as high as 90% of single-crystalline Si wafer is obtained from the SPC of high rate deposited a-Si:H films

Impact of deposition parameters on the material quality of SPC poly-Si thin films using high-rate PECVD of a-Si:H

The impact of the deposition parameters such as gas flow (sccm) and RF plasma power density (W/cm2) on the deposition rate of a-Si:H films is systematically investigated. A high deposition rate of up to 146 nm/min at 13.56 MHz is achieved for the a-Si:H films deposited with high lateral uniformity on 30 × 40 cm2 large-area glass substrates. A relationship between the SiH4 gas flow and the RF power density is established. The SiH4 gas flow to RF power density ratio of about 2.4 sccm/mW cm-2 is found to give a linear increase in the deposition rate. The influence of the deposition rate on the material quality is studied using UV-VIS-NIR spectrophotometer and Raman characterisation techniques. Poly-Si thin film with crystal quality as high as 90% of single-crystalline Si wafer is obtained from the SPC of high rate deposited a-Si:H films

Controlling stress in large-grained solid phase crystallized n-type poly-SI thin films to improve crystal quality

Crystal Growth and Design1531067-107

Optical bandgap widening and phase transformation of nitrogen doped cupric oxide

The structural and optical properties of sputter deposited nitrogen (N) doped CuO (CuO(N)) thin films are systematically investigated. It is found that the incorporation of N into CuO causes an enlargement of optical bandgap and reduction in resistivity of the CuO(N) films. Furthermore, a gradual phase transformation from CuO to Cu2O is observed with the increase in N concentration. The effects of annealing temperature on the structural properties of CuO (N) and its dependence on N concentration are also investigated. It is observed that the phase transformation process from CuO to Cu2O significantly depends on the N concentration and the annealing temperature. Heterojunction solar cells of p-type CuO(N) on n-type silicon (Si) substrate, p-CuO(N)/n-Si, are fabricated to investigate the impact of N doping on its photovoltaic properties.Published versio