Materials Science Forum Vol. 711

Abstract: This paper reports on results of interface trap analysis of 3C-SiC MOS capacitors fabricated using four different gate materials and two SiO₂ oxide preparation methods. The results indicate that post-deposition annealing in wet oxygen of PECVD deposited SiO₂ samples increases the near-interface or slow trap densities, compared with wet oxygen thermally oxidized samples. It has also been found that the energy distribution, D_it, of electron states at the oxide/SiC interface of MOS capacitors with different sizes depend on the factor R=P/A, where P stands for the gate perimeter and A for the gate area, which is related to the amount of stress under the edge of the metallic gate.

Abstract: In this paper, we deal with the study of Ultra Violet (UV) photodetector device based on SiC material undergoing a p-i-n structure process. Current density-voltage (J-V) measurements in reverse and forward bias, are performed on the UV photodetector device. Due to a very thin p⁺-type doping layer, a high reactivation annealing and the metallic contact deposit, experimental measurements point out Junction Barrier Schottky (JBS) device behaviour in spite of the p-i-n structure device process. To understand this involuntary phenomenon, these experimental characteristics are accompanied with an experimental study by the SIMS analysis.

Abstract: Silicon carbide (SiC) is a wide band gap semiconductor having good thermal conductivity and high break down voltage. Formation of SiO₂ layer in thermal oxidation process completes the set of properties of SiC as a promising material for fabrication of high power and high frequency electronic devices. This picture is perturbed by Near Interface Traps (NIT's) that decrease the surface mobility of charge carriers. The origin of NIT's is still the subject of discussion and there are several candidates for NIT's. One possibility is the formation of carbonic structures during the process of manufacturing of MOS-type structures. The aim of this work was to look for possible carbonic inclusions with Raman spectroscopy. The attention of authors was focused on non-destructive way of application of the experimental technique.

Abstract: This paper presents the high blocking capability of the 4H-SiC tungsten Schottky and junction barrier Schottky (JBS) diodes at room temperature as well as at high operating temperature. First, we present the design of the proposed devices and the process employed for their fabrication. In a second part, their forward and reverse characteristics at room temperature will be presented. Our rectifiers exhibit blocking capability up to 9kV at room temperature. Then, we investigate the reverse current behaviour at 5kV from room temperature to 250°C under vacuum. JBS and Schottky devices that are capable to block 8kV at room temperature, show leakage current inferior to 100µA at 250°C when reverse biased at 5kV. It confirms the capability of Silicon Carbide to produce devices capable of operation at temperatures and voltages above the Silicon limits.

Abstract: This paper demonstrates the parallel and serial association of two SiC light triggered thyristors. Such systems are needed to increase the power handling capacity of SiC switches. The devices and their fabrication are presented. The experiments and their results are detailed, addressing particularly the problem of voltage and current sharing during the switching of the thyristors.

Abstract: 4H-SiC presents great advantages for its use in power electronic devices working at particular conditions. However the development of MOSFETs based on this material is limited by mobility degradation. N-channel SiC MOSFETs were manufactured on p-type epitaxial and p-implanted substrates and the electron mobility in the inversion channels was measured to be correlated with their structural and chemical properties determined by transmission electron microscopy methods. With regard to what was previously discussed in the literature, transition layer formation and carbon distribution across the SiC-SiO₂ interface are considered in relation with the measured low electron mobility of the MOSFETS.

Abstract: We present a nanoscale morphological and structural characterization of few layers of graphene grown by thermal decomposition of off-axis 4H-SiC (0001). A comparison between transmission electron microscopy (TEM) in cross-section and in plan view allows to fully exploit the potentialities of TEM. Such a comparison was used to get information on the number of graphene layers as well as on the rotational order between the layers and with respect to the substrate. Some peculiar structures observed by TEM (wrinkles) could only be systematically measured by atomic force microscopy (AFM). In particular, the density and the height of the wrinkles in the few layers of graphene was investigated.

Abstract: We report on n-type 3C-SiC samples grown by sublimation epitaxy. We focus on the low temperature photoluminescence intensity and show that the presence of a first conversion layer, grown at low temperature, is not only beneficial to improve the homogeneity of the polytype conversion but, also, to the LTPL signal intensity. From the use of a simple model, we show that this comes from a reduced density of non-radiative recombination centers.

Abstract: In this paper, we studied the influence of nitrogen implantation dose on both physical and electrical properties in 3C-SiC grown on Si (100) substrate. Scanning Transmission Electron Microscopy characterizations prove that high dose is responsible for amorphization of the implanted layer and the high defect density after annealing. A high V-shape defect density is still found in the implanted layer after an annealing at 1350°C. By lowering the dose, the layer is less damaged and no amorphization is observed. For the different doses, low Specific Contact Resistances are measured using Ti/Ni contacts. The Specific Contact Resistance value decreases from 8x10^-6 Ω.cm² for the high dose to 3.2x10^­6 Ω.cm² with decreasing the dose. Furthermore, the dopant activation ratio, evaluated by quantitative SSRM measurements, is improved at the same time from 17% (for the high dose) to 60% (for the low dose). This work demonstrates that high activation ratio can be achieved consecutively to a nitrogen implantation at reasonable implantation fluence.

Abstract: We applied a number of time-resolved optical techniques for investigation of optical and photoelectrical properties of cubic SiC grown by different technologies on different substrates. The excess carriers were injected by a short laser pulse and their dynamics was monitored by free-carrier absorption, light-induced transient grating, and photoluminescence techniques in a wide excitation range. Combining an optical and electrical probe beam delay, we found that free carrier lifetimes in differently grown layers vary from few ns up to 20 μs. Temperature dependences of carrier diffusivity and lifetime revealed a pronounced carrier trapping in thin sublimation grown layers. In free-standing layers and thick sublimation layers, the ambipolar mobility was found the highest (120 cm²/Vs at room temperature). A linear correlation between the room-temperature band edge emission and carrier lifetime in differently grown layers was attributed to defect density, strongly dependent on the used growth conditions.