Norbert Kwietniewski

Technology and characterization of 4H-SiC p-i-n junctions

Silicon Carbide (SiC) photodiodes have been proposed in recent years for ultraviolet (UV) light detection because of their robustness even in harsh environments, high quantum efficiency in all the UV range (200nm-400nm), excellent visible and infra-red blindness excluding UV filters implementation, low dark current and high speed. 4H-SiC has a bandgap three times larger (3.26eV) than Si and, thus, SiC detectors should have much higher sensitivity than Si detectors. In this paper, we present an overview of results on 4H-SiC p-i-n junctions fabrication and characterization. We used implantation technique to obtain p-region of the investigated structure. The ohmic contacts were formed using evaporation, etching and lift-off. Current-voltage, contact resistance and electroluminescence are the main characteristics of the presented devices. All the diodes showed excellent rectification with leakage current density of less than 10-9A/cm2.

Measurements of Planar Metal–Dielectric Structures Using Split-Post Dielectric Resonators

Split-post dielectric resonators were used for the measurement of the complex permittivity and the complex permeability of planar, uniaxialy anisotropic, low- and medium-loss metamaterials at microwave frequencies. Several metamaterials with different metal patterns deposited on dielectric substrates by plasma deposition were investigated, including edge-coupled and broadside-coupled split-rings and circles. It has been shown that, depending on the type of metal pattern and their surface resistance, the metamaterials may exhibit various magnetic and dielectric properties. Several small metamaterial samples were scanned in the cavity electromagnetic field by moving them inside the split-post dielectric resonator. This allowed us to identify loss mechanisms in the samples and to distinguish between their electric and magnetic properties. Our measurements were confirmed by modeling the transmission/reflection characteristics of virtual waveguides containing real metamaterial samples and homogenous samples with the same effective electromagnetic properties as those obtained from the split-post dielectric resonator method using a finite-difference time-domain electromagnetic simulator software package.

Effect of Sample Elevation in Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF PECVD) Reactor on Optical Properties and Deposition Rate of Silicon Nitride Thin Films

In this paper we investigate influence of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) process parameters, which include gas flows, pressure and temperature, as well as a way of sample placement in the reactor, on optical properties and deposition rate of silicon nitride (SiNx) thin films. The influence of the process parameters has been determined using Taguchi’s orthogonal tables approach. As a result of elevating samples above the electrode, it has been found that deposition rate strongly increases with distance between sample and the stage electrode, and reaches its maximum 7 mm above the electrode. Moreover, the refractive index of the films follows increase of the thickness. The effect can be observed when the thickness of the film is below 80 nm. It has been also found that when the deposition temperature is reduced down to 200 °C, as required for many temperature-sensitive substrate materials, the influence of the substrate material (Si or oxidized Si) can be neglected from the point of view of the properties of the films. We believe that the obtained results may help in designing novel complex in shape devices, where optical properties and thickness of thin plasma-deposited coatings need to be well defined.

Large-area transparent in visible range silicon carbide photodiode

This paper describes the construction, fabrication and properties of large-area ultra violet detector that is transparent in the visible range. The device was made on n-type 4H SiC substrate with a double epitaxial layer in which aluminum was implanted to form a p-n junction close to the surface, and a SiO2 layer was formed for passivation, without a guard ring. The design of the top and bottom electrodes of 4mm diameter UV sensitive area allows not less than 20% visible range transmission. This transmission was measured across sensitive area of examined devices and was only 5% lower than that of the substrate before implantation and electrodes deposition.

Fabrication and characterization of epitaxial 4H-SiC pn junctions

This paper provides an overview of the process of 4H-SiC pn junction fabrication and characterization. The samples used in this study were fabricated in a resistively heated horizontal hot-wall Chemical Vapor Deposition reactor. The homo-epitaxial layers were grown on commercially available 4H-SiC substrates (Cree). In order to obtain p-type epilayers, they were intentionally doped with aluminum. In this work, we present our recently developed 4H-SiC pn junctions fabrication and characterization results. The ohmic contacts were formed using evaporation, etching, lift-off and high temperature annealing. Current-voltage characteristics of the devices were demonstrated.

Silicon nitride (SiNx) plasma deposition on optical fiber sensors: coating symmetry perspective

This paper discusses the influence of coating long-period gratings with a silicon nitride thin overlay on the grating’s spectral response. The overlays have been obtained with a radio frequency plasma enhanced chemical vapor deposition method. During the experiment, the structures were positioned on various heights over the electrode using specially developed sample holder. The results of the experiment show that the investigated long period grating structures have increased their sensitivity to variations of external medium refractive index in the range of nD=1.33 to 1.43 RIU. The relation between the height at which the long period grating was placed over the electrode and the deposited overlay symmetry is discussed. The highest sensitivity of 2080 nm/RIU has been observed for the grating placed at the highest positions of the holder out of the examined range of 3 to 8 mm over the electrode. This overlay also shows the highest symmetry around the fiber.

Oxidation Process of SiC by RTP Technique

The kinetics of 4H-SiC thermal oxidation by RTP technique and the properties of thin thermal oxide was reported. The thickness of the thermal oxide was determined by spectroscopic ellipsometry and confirmed by electrical measurements. The conductance method was applied to analyse the surface states parameters. The lifetime, density and cross-section of the surface traps were extracted for as-fabricated MOS capacitors and after thermal annealing processes.

Planarization of Epitaxial SiC Trench Structures by Plasma Ion Etching

In this work, we present a planarization concept for epitaxial SiC trench structures involving reactive ion etching (RIE) and inductive coupled plasma (ICP) dry etching. The general idea is to transfer the flat surface from spun-on BCB/photo-resist layers to deposited silicon dioxide and finally to bulk SiC by applying process conditions with the same etch rate for the different materials. In this way several microns of unwanted material can be removed and planar SiC surfaces are obtained. With this method trench structures filled by epitaxial re-growth can be planarized with smooth surfaces and good homogeneity over the wafer. Cost-efficient device manufacturing can be achieved by using standard semiconductor process equipment. This technology makes it possible to manufacture advanced epitaxial SiC material structures for devices such as trench JBS diodes and double-gate trench JFETs.

Reactive impulse plasma ablation deposited barium titanate thin films on silicon

Thin (100 nm) nanocrystalline dielectric films of lanthanum doped barium titanate were produced on Si substrates by means of reactive impulse plasma ablation deposition (IPD) from BaTiO3 + La2O3 (2 wt.%) target. Scanning electron microcopy and atomic force microscopy showed that the obtained layers were dense ceramics of uniform thickness with average roughness Ra = 2.045 nm and the average grain size of the order of 15 nm. Measurements of current-voltage (IV) characteristics of metal-insulator-semiconductor (MIS) structures, produced by evaporation of metal (Al) electrodes on top of barium titanate films, allowed to determine that the leakage current density and critical electric field intensity (EBR) of investigated layers ranged from 10-12 to 10-6 A cm-2 and from 0.2 to 0.5 MV cm-1, respectively. Capacitance-voltage (C-V) measurements of the same structures were performed in accumulation state showing that the dielectric constant value (εri) of films is of the order of 20.

Selective deep wet etching of fused silica optical fibers for sensing applications

In the paper we discuss crucial aspects of selective deep wet etching technology of fused silica optical fibers. The technology includes preparation of the fiber, photolithography aiming to create a mask for etching, wet etching process and photoresist removal. We also discuss the influence of removing polyimide layer from the fiber, photoresist type, thickness of the photoresist and etching time. The developed technology allows for obtaining periodic variations in the fiber diameter resulting in formation of corrugated long-period grating (LPG). Introduction of strain induces appearing of attenuation peak in the transmission spectrum of the fiber. The developed technology can be also applied for fabrication of other optical fiber devices.