P. Godignon

Field-effect mobility temperature modeling of 4H-SiC metal-oxide-semiconductor transistors

Here a physically based channel mobility model has been developed to investigate the temperature dependence of the field-effect mobility of 4H-SiC metal-oxide-semiconductor (MOS) transistors with thermally oxidized gate insulators. This model has been designed so that it accounts for the high density of traps at the MOS interface. This temperature dependence is a key issue for silicon carbide electronics, as its basic material properties make it the foremost semiconductor for high power/high temperature electronic devices in applications such as spacecraft, aircraft, automobile, and energy distribution. Our modeling suggests that the high density of charged acceptor interface traps, encountered in thermally grown gate oxides, modulates the channel mobility due to the Coulomb scattering of free carriers in the inversion layer. When the temperature increases, the field-effect mobility of these devices also increases, due to an increase in inversion charge and a reduction of the trapped charge. Experimental ...

GaN transistor characteristics at elevated temperatures

The characteristics of different GaN transistor devices characterized at elevated temperatures for power applications are compared in this paper. High temperature characteristics of GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) and GaN high electron mobility transistors (HEMTs) are reported. For MOSFETs, the transconductance current (gm) increases with temperature, while for HEMTs is reduced. Their specific on resistance (Ron) follows the same trend. Specific contact resistivity (ρc) to implanted Si N+ GaN also diminishes with T, whereas for AlGaN/GaN ρc remains practically constant. We bring a more physical insight into the temperature behavior of these GaN devices by means of physics-based modeling in Sec. VI of this paper. The MOSFET’s field-effect mobility increases with T due to interface trap Coulomb scattering. Analogously, the HEMT’s gm decrease with T is attributed to a significant reduction in the two-dimensional electron gas carrier mobility due to polar-optical-phonon scatte...

High frequency characteristics and modelling of p-type 6H-silicon carbide MOS structures

Abstract This paper presents the high frequency electrical characteristics and modelling of Al/SiO 2 / p -type 6HSiC structures. The oxide was thermally grown under dry conditions. Capacitance and conductance vs bias and frequency measurements have been performed in daylight and exposing the capacitors to u.v. light. The experimental C m - V g and G m - V g characteristics show hysteresis effects, which are more important when the samples are exposed to 254 nm u.v. light. This behaviour can be explained in terms of interface traps. The MOS structure modelling is based on an interface trap model in which the interface trap levels are considered to be continuously distributed in the SiC bandgap and only charge exchange between interface trap levels and the SiC bands is allowed. From this formulation and from the G m - f characteristics, the interface state density and the interface trap time constant have been determined.

Low-doped 6H-SiC n-type epilayers grown by sublimation epitaxy

Abstract Sublimation epitaxy has not yet been a technique of prime importance to grow epitaxial 6H-SiC layers because grown layers have always shown a residual net doping level higher than 10 16 cm −3 and a high compensation level. We present here results obtained with an optimized technology of sublimation epitaxial growth, which can be used to obtain structurally perfect layers with a concentration of uncompensated donors as low as 10 15 cm −3 . These layers have been both physically and electrically characterized. Deep level transient spectroscopy indicates that the concentration of deep levels is greatly reduced. As a consequence the hole diffusion length is significantly increased up to about 2.5 μm, as confirmed by electron beam induced current measurements. So these optimized layers are envisaged for the fabrication of high voltage diodes or bipolar transistors.

SiC Materials and Technologies for Sensors Development

Silicon Carbide has proven its strong interest for power and high frequency devices but it also has superior characteristics for application in the sensors and MEMS fields. The characteristic requirements of the starting material are different from that of power devices since the level of defects is not so critical while the layer stress is important especially in 3C-SiC on Si. The keyprocess for MEMS fabrication is the etching, which is progressing thanks to ICP process improvements. A perfect control of the etching step could allow the obtention of nano-resonators in SiC with fairly superior characteristics to the Si ones. Other electrical sensors for high temperature application such as gas sensors or Hall sensors have been also successfully developed taking profit of the deep etching process improvement and high temperature contact developments.

Early stage formation of graphene on the C face of 6H-SiC

An investigation of the early stage formation of graphene on the C face of 6H-silicon carbide (SiC) is presented. We show that the sublimation of few atomic layers of Si out of the SiC substrate is not homogeneous. In good agreement with the results of theoretical calculations it starts from defective sites, mainly dislocations that define nearly circular graphene layers, which have a pyramidal, volcanolike shape with a center chimney where the original defect was located. At higher temperatures, complete conversion occurs but, again, it is not homogeneous. Within the sample surface, the intensity of the Raman bands evidences inhomogeneous thickness.An investigation of the early stage formation of graphene on the C face of 6H-silicon carbide (SiC) is presented. We show that the sublimation of few atomic layers of Si out of the SiC substrate is not homogeneous. In good agreement with the results of theoretical calculations it starts from defective sites, mainly dislocations that define nearly circular graphene layers, which have a pyramidal, volcanolike shape with a center chimney where the original defect was located. At higher temperatures, complete conversion occurs but, again, it is not homogeneous. Within the sample surface, the intensity of the Raman bands evidences inhomogeneous thickness.

Characterization of High-k Ta2Si Oxidized Films on 4H-SiC and Si Substrates as Gate Insulator

The main physical and electrical characteristics of the high-k insulator layer produced by the Ta 2 Si deposition and subsequent oxidation on SiC and Si substrates are investigated in this paper. The leakage current of these layers shows an asymmetric behavior with the polarity of the gate bias (gate +V or -V), yielding a leakage current density as low as 10 - 8 A cm - 2 at I MV cm - 1 and 4.5 MV cm - 1 , respectively. To identify the conduction mechanisms, the experimental current-voltage curves have been fitted with a theoretical model accounting for a double hopping and tunnel/Poole-Frenkel conduction mechanism. The dielectric constant obtained for a 4H-SiC metal-insulator semiconductor (MIS) is ∼20 basically independent of the insulator thickness or the oxidation temperature. The dielectric constant obtained for Si MIS capacitors decreases with increasing oxidation temperature, and its value has been measured in the 10-7 range. 4H-SiC metal oxide semiconductor field effect transistors (MOSFETs) have been fabricated using oxidized Ta 2 Si as a gate insulator, demonstrating the feasibility of this insulator and reporting one of the first well-behaved MOSFETs on SiC with high-k gate dielectric. For the MOSFETs fabricated on a p-implanted and annealed region, a peak mobility up to 40 cm 2 /Vs has been extracted, which is higher than mobilities commonly reported for thermal oxidized 4H-SiC MOSFETs.

Benefit of H2 surface pretreatment for 4H-SiC oxynitridation using N2O and rapid thermal processing steps

The effect of H2 surface pretreatment on the density of interface traps in SiO2 films grown on the Si-face of 4H-SiC has been investigated. With respect to the more conventional oxide grown in nitrous oxide gas by rapid thermal processing but without any preannealing step, we find that the interface trap and fixed oxide charge densities have been reduced by, typically, one order of magnitude. The reasons for such improvement in the properties of the SiO2/SiC interface after preoxidation hydrogen annealing are discussed.

GaN metal-oxide-semiconductor field-effect transistor inversion channel mobility modeling

Lateral n-channel enhancement-mode GaN metal-oxide-semiconductor (MOS) field-effect transistors and lateral capacitors have been fabricated on a p-type epi-GaN substrate semiconductor and electrically characterized at different temperatures. A clear positive behavior of the inversion channel mobility with temperature has been obtained. A physics-based model on the inversion charge and charge trapped in interface states characteristics has been used to investigate the temperature dependence of the inversion MOS channel mobility. The field-effect mobility increase with temperature is due to an increase in the inversion charge and a reduction in the trapped charge for a given voltage gate. Then, for larger gate bias and/or higher temperatures, surface roughness effects become relevant. The good fitting of the model with the experimental data leads us to consider that the high density of charged acceptor interface traps together with a large interface roughness modulates the channel mobility due to scattering...

Theoretical evidence for the kick-out mechanism for B diffusion in SiC

In this letter, we analyze by means of first-principles electronic structure calculations the diffusion of B impurities in 3C-SiC. We find, through molecular dynamics, that substitutional B at a Si lattice site is readily displaced by a nearby Si interstitial by the process known as a kick-out mechanism, in agreement with recent experimental results. This is in contrast to the situation in Si, where B has recently been shown to diffuse via an interstitialcy mechanism.