Influence of the Cl2_2 etching on the Al2_2O3_3 /GaN metal–oxide–semiconductor interface

International audienceControlling the plasma etching step involved in metal-oxide-semiconductor high-electron-mobility-transistor (MOSHEMT) GaN fabrication is essential for device performance and reliability. In particular, understanding the impact of GaN etching conditions on dielectric/GaN interface chemical properties is critically important. In this work, we investigate the impact of the carrier wafers (Si, photoresist, SiO 2 , and Si 3 N 4 ) used during the etching of GaN in chlorine plasma on the electrical behavior of Al 2 O 3 /n-GaN metal–oxide–semiconductor (MOS) capacitors. X-ray Photoelectron spectroscopy (XPS) analyses show that the Al 2 O 3 /GaN interface layer contains contaminants from the etching process after the Al 2 O 3 deposition. Their chemical nature depends on the plasma chemistry used as well as the chemical nature of the carrier wafer. Typically, Cl and C are trapped at the interface for all substrates. In the particular case of Si carrier wafer, a significant amount of SiO x is present at the Al 2 O 3 /GaN interface. The capacitance–voltage (C–V) characteristics of the MOS capacitors indicate that the presence of Si residues at the interface shifts the flat band voltage to negative values, while the presence of Cl or C at the interface increases the hysteresis. We demonstrate that introducing an in situ plasma cleaning treatment based on N 2 /H 2 gas, before the atomic layer deposition, allows the removal of most of the residues except silicon and suppresses the hysteresis

A facile hydrothermal approach for the density tunable growth of ZnO nanowires and their electrical characterizations

Abstract Controlling properties of one-dimensional (1D) semiconducting nanostructures is essential for the advancement of electronic devices. In this work, we present a low-temperature hydrothermal growth process enabling density control of aligned high aspect ratio ZnO nanowires (NWs) on seedless Au surface. A two order of magnitude change in ZnO NW density is demonstrated via careful control of the ammonium hydroxide concentration (NH4OH) in the solution. Based on the experimental observations, we further, hypothesized the growth mechanism leading to the density controlled growth of ZnO NWs. Moreover, the effect of NH4OH on the electrical properties of ZnO NWs, such as doping and field-effect mobility, is thoroughly investigated by fabricating single nanowire field-effect transistors. The electrical study shows the increase of free charge density while decrease of mobility in ZnO NWs with the increase of NH4OH concentration in the growth solution. These findings show that NH4OH can be used for simultaneous tuning of the NW density and electrical properties of the ZnO NWs grown by hydrothermal approach. The present work will guide the engineers and researchers to produce low-temperature density controlled aligned 1D ZnO NWs over wide range of substrates, including plastics, with tunable electrical properties

Influence of substrate biasing on structural, chemical and electrical properties of Al 2 O 3 thin films deposited by PEALD

International audienceAbstract High- k materials are needed to minimise the gate leakage current in high-speed and high-power switching applications. In this regard, aluminium oxide (Al 2 O 3 ) deposited by plasma enhanced atomic layer deposition (PEALD) is gaining extensive attention to be used as high- k material in microelectronics. In this work, we studied the effect of substrate biasing during the oxidizing plasma step on physical, chemical and electrical properties of Al 2 O 3 thin films grown by PEALD on silicon substrate. We show that the structural and electrical properties such as the flat band voltage, and chemical composition can be tuned with the applied substrate bias. Indeed, we highlight that the dielectric constant of the MIS capacitor decreases from 8.5 to 6.5 and the charge polarity of the film is modulated from negative to positive when the applied substrate bias is increased. Using morphological and structural characterisations, we show that the substrate bias significantly affects the chemical composition of Al 2 O 3 thin film layer. Moreover, we highlight by cross-sectional transmission electron the presence of an interfacial layer between Si and Al 2 O 3 which could significantly influence the electrical properties of the deposited thin film. The chemical composition of this interfacial layer can be controlled by the applied substrate bias. Using a series of energy dispersive x-ray experiments, we further confirm the formation of aluminosilicate under low substrate bias condition while silicon oxide is formed under high bias. These findings show that the substrate biasing plays a critical role in defining physical, chemical as well as electrical properties of the PEALD Al 2 O 3 thin films

Photoluminescence Study of the Influence of Additive Ammonium Hydroxide in Hydrothermally Grown ZnO Nanowires

International audienceWe report the influence of ammonium hydroxide (NH4OH), as growth additive, on zinc oxide nanomaterial through the optical response obtained by photoluminescence (PL). A low-temperature hydrothermal process is employed for the growth of ZnO nanowires (NWs) on seedless Au surface. A more than two order of magnitude change in ZnO NW density is demonstrated via careful addition of NH4OH in the growth solution. Further, we show by systematic experimental study and PL characterization data that the addition of NH4OH can degrade the optical response of ZnO NWs produced. The increase of growth solution basicity with the addition of NH4OH may slowly degrade the optical response of NWs by slowly etching its surfaces, increasing the point defects in ZnO NWs. The present study demonstrates the importance of growth nutrients to obtain quality controlled density tunable ZnO NWs on seedless conducting substrates

A New Simulation Approach for Performance Prediction of Vertically Integrated Nanogenerators

International audienceThe vertically integrated nanogenerator (VING) is one of the most used designs in mechanical energy harvesting using piezoelectric nanowires, dueto its easiest manufacturing process. Here, a new modeling approach is presented in order to reduce the computation time of a whole VING finiteelement simulation. In this work, the effect of the polymer layer (Parylene C), in which nanowires are immersed, on the electromechanical behavior of the whole VING is taken into account. The active part of the VING (nanowires–polymer composite) is considered as a 1–3 piezocomposite. It isformed with ZnO piezoelectric nanowires; however, this study can be applied to any type of piezoelectric nanowires (PZT, GaN, PVDF, etc.) and matrix materials (PDMS, PMMA, Al2O3, etc.). The present method relies on the finite element method applied to a single nanowire-composite cell in open-circuit condition, combined with an analytical modeling of the full VING. This approach allows the computation time to be drastically reduced without inducing significant approximation errors. The expected maximum power, internal capacitance, and optimum resistance can be deduced thanks to this efficient modeling tool, offering wide perspectives for the optimization of such VING devices