Mariusz Sochacki

Influence of annealing on reverse current of 4H-SiC Schottky diodes

Abstract In this work, we show results of our measurements of the forward and reverse I–V characteristics of Ni/4H-SiC Schottky rectifiers, which were observed prior and after annealing of devices in various gases (Ar, Ar+H2). We investigate the influence of temperature and atmosphere of annealing on diodes properties. The annealing has no influence on forward I–V characteristics, but the reverse leakage current is reduced as a result of decreasing number of surface states. This phenomenon decreases generation of minority carriers due to reduction of the number of available discrete energy levels in the bandgap of investigated material.

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.

TiAl-based ohmic contacts on p-type SiC

Titanium-aluminum alloys were successfully used to form low resistance ohmic contacts to p-type SiC. This work concerns two Al-Ti alloy compositions. Contacts were prepared by magnetron sputtering of bilayer Al-Ti and trilayer Ti-Al-Ti thin films and rapid thermal annealing at temperatures range 900°C ÷ 1000°C. Using scanning electron microscopy and profiler, an investigation of surface morphology of annealed contacts was conducted. The best resistivity of 5.8·10−5 Ωcm2 was attained on 100nm/26nm Al/Ti metallization of 80% at. Al alloy composition annealed at 1000°C for 2 min. Relatively low roughness of 30 nm was observed on trilayer Ti/Al/Ti metallization.

Dielectric films fabricated in plasma as passivation of 4H-SiC Schottky diodes

Abstract In this report, we propose Al 2 O 3 and AlN films as passivation for high-voltage SiC Schottky barrier diodes. A reactive pulse plasma enhanced chemical vapour deposition method is used to form the layers. The comparison between the Schottky barrier diodes with and without passivation shows the effectiveness of Al 2 O 3 layer on the reverse current decrease as a result of the surface states reduction.

Thermal properties of SiC-ceramics substrate interface made by silver glass composition

In this work, thermal properties of Al<inf>2</inf>O<inf>3</inf>, AlN, SiC as well as some of SiC die attachment materials are characterized by the laser flash method. The thermal diffusivity, specific heat and thermal conductivity were measured or calculated for the systems consisted of Al<inf>2</inf>O<inf>3</inf> or AlN substrates and SiC structures with die-attach layers between them. The experiments for single materials were carried out within wide temperature range of 50°C ÷ 800°C in argon atmosphere. Firstly, the thermal diffusivity and conductivity of Al<inf>2</inf>O<inf>3</inf>, AlN and SiC bulk material were extracted to increase the final results accuracy within full temperature range. Then 8×8 mm² SiC chips were attached to 8×8 mm² Al<inf>2</inf>O<inf>3</inf> or AlN substrates by silver-glass composition. Thermal properties of SiC - ceramics connections were measured from room temperature up to 350°C. The connection quality was investigated by X-ray microtomography. The thermal conductivity of the interfacial silver glass composition between SiC and Al<inf>2</inf>O<inf>3</inf> decreases from 120 W/mK at room temperature to 45 W/mK at temperature of 350°C and between SiC and AlN from 270 W/mK to100 W/mK, respectively. These values strongly depend of interface quality and thickness of interfacial layer.

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.

Mechanisms of carriers transport in Ni/n-SiC, Ti/n-SiC ohmic contacts

A mechanism of carriers transport through metal-semiconductor interface created by nickel or titanium-based ohmic contacts on Si-face n-type 4H-SiC is presented herein. The mechanism was observed within the temperature range of 20 °C ÷ 300 °C which are typical for devices operating at high current density and at poor cooling conditions. It was found that carriers transport depends strongly on concentration of dopants in the epitaxial layer. The carriers transport has thermionic emission nature for low dopant concentration of 5×1016 cm−3. The thermionic emission was identified for moderate dopant concentration of 5×1017 cm−3 at temperatures higher than 200 °C. Below 200 °C, the field emission dominates (for the same doping level of 5×1017 cm−3). High dopant concentration of 5×1018 cm−3 leads to almost pure field emission transport within the whole investigated temperature range.

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.

Influence of Phosphorus Implantation on Electrical Properties of Al/SiO2/4H-SiC MOS Structure

This paper describes the effects of phosphorus implantation into n-type 4H-SiC substrate prior to standard dry oxidation process. Phosphorus incorporation has been reported to be one of the most efficient means of increasing SiC MOSFET field mobility however the physical basis of this phenomenon is still not clear. The aim of this research is to investigate the influence of phosphorus implantation on trap density profile close to conduction band of silicon carbide and to gain understanding of physical processes responsible for observed trap density improvement in phosphorus related oxidation technologies of silicon carbide.

The Influence of Post-Oxidation Annealing Process in O2 and N2O on the Quality of Al/SiO2/n-Type 4H-SiC MOS Interface

The effect of the n-type 4H-SiC (0001) oxidation in wet O2 at temperature of 1175 °C followed by low temperature annealing in N2O at temperature of 800°C for 2 or 4 hours followed by high temperature annealing in nitrogen ambient on nitrogen distribution in silicon dioxide was investigated. It was shown that the oxidation and annealing have a strong impact on the behavior of electrical parameters of MOS capacitors using the oxides as gate dielectric what is probably an effect of nitrogen incorporation. The explanation of the observed electrical properties is included.