Materials Science Forum Vols. 821-823

Abstract: Forward J_D–V_D curves of 4H−SiC p−i−n diodes are analyzed by means of an analytical model in order to justify the presence of a crossing−point. The interlacing behaviour occurring in the J_D–V_D curves of 4H−SiC diodes at different temperatures is predicted by a simple formula, which can be used for a first-order design of such devices. Numerical simulation of diodes designed with different epilayer thickness and carrier lifetime values have been used in order to analyze the crossing−point behaviour. Comparisons with experimental data confirm the analytic and simulated results.

Abstract: In this paper we report on the effect of temperature and injection level on the effective lifetime of non-equilibrium charge carriers in p-base of 4H-SiC PiN diodes. Studies were carried out on 1kV drift step recovery diodes (DSRDs) with p⁺-p^--n⁺. The lifetime of non-equilibrium charge carriers in 4H-SiC p⁺-p^--n⁺ structures increases by an average of 6 times from 250ns to 1.4μs with the increase of the samples temperature from 300K to 673K. However, increase of the injection level in the drift region from 2.3·10¹⁶cm^-3 to 5.9·10¹⁶cm^-3 does not affect the lifetime indicating that Shockley-Read-Hall recombination processes are dominating.

Abstract: In this work, we demonstrate the stable operation of 4H-silicon carbide (SiC) p-n diodes at temperature up to 600 °C. In-depth study methods of simulation, fabrication and characterization of the 4H-SiC p-n diode are developed. The simulation results indicate that the turn-on voltage of the 4H-SiC p-n diode changes from 2.7 V to 1.45 V as the temperature increases from 17 °C to 600 °C. The turn-on voltages of the fabricated 4H-SiC p-n diode decreases from 2.6 V to 1.3 V when temperature changes from 17 °C to 600 °C. The experimental I-V curves of the 4H-SiC p-n diode from 17 °C to 600 °C agree with the simulation ones. The demonstration of the stable operation of the 4H-SiC p-n diodes at high temperature up to 600 °C brings great potentials for 4H-SiC devices and circuits working in harsh environment electronic and sensing applications.

Abstract: 4H-SiC (0001) p-n diodes terminated with a floating-field ring were found to emit light at breakdown in the opposite direction to that of substrate misorientation when the diodes were fabricated by aluminum implantation and dry-oxidation passivation. Two-dimensional simulation revealed that such non-uniform breakdown was mainly attributable to the asymmetric lateral straggling of implanted aluminum acceptors, rather than the anisotropic nature of the impact ionization coefficient.

Abstract: Spectral sensitivity measurements versus temperature have been carried out on irradiated SiC p+n photodiodes, fabricated using two different doping processes: Aluminium standard implantation and Boron plasma immersion ion implantation. The spectral sensitivity of Al doped photodiodes increase for incident wavelength higher than 270 nm, and are very stable below. Boron doped irradiated photodiodes show a general increase of the photoresponse for all wavelengths. In both cases, an hysteresis effect is observable when with the temperature. Results are presented and discussed.

Abstract: 4H-SiC p⁺nn⁺ structures fabricated by implantation of Al into a commercial n-type 4H-SiC epitaxial layer doped to (3-5)Ÿ10¹⁵cm^-3 have been studied. Structures with unstable excess forward current were characterized by electron beam induced current (EBIC) and secondary electron (SE) methods and by Auger-electron spectroscopy (AES). Numerous defects were found with a depth which exceed the thickness of the p⁺-layer. Also, it was demonstrated that the concentration of carbon on the SiC surface always exceeds that of silicon, which may be the reason for the initially unstable conductivity via the defects.

Abstract: A novel method for analyzing a decrease in breakdown voltage (V_BD) in the termination of 4H-SiC power devices after reverse-bias stressing on the basis of change in depletion-layer capacitance is proposed. Test PN diodes terminated with a junction-termination extension (JTE) were fabricated on n-type 4H-SiC and analyzed by I-V and C-V measurements. According to the results of the measurements, V_BD after stressing decreases, and the capacitance of the test devices decreases after stressing. Measurements with different chip sizes but the same termination width show that the capacitance decrease occurs in the termination area. The simulated capacitance change, on the supposition that positive charge accumulated at the SiO₂/SiC interface, and the measured capacitance change show the same tendency. These results indicate that the origin of V_BD decrease is positive charge accumulated at the SiO₂/SiC interface of the termination after reverse-bias stressing.

Abstract: In this study, a new robust double-ring junction-termination-extension (DR-JTE) for high-voltage pn-diodes is presented and analyzed using numerical simulations. As figured out, the DR-JTE reduces the electrical field at both, the edge of the single-JTE region and the MESA-transition, respectively. Thereby, due to the reduction of the electrical field, the maximum breakdown voltage is increased to 91.5% of the theoretical, parallel-plane breakdown voltage of 6.5kVand the maximum acceptable deviation of the optimum implantations dose is twice than that of the single-JTE structure. Furthermore, due to the internal ring, the MESA-transition is shielded from the electrical field and therefore the breakdown voltage is much less affected by the angle of the MESA.

Abstract: Silicon Carbide metal-oxide-semiconductor field effect transistor (4H-SiC MOSFET) can be considered as the next revolution in power electronics applications. However, a wide market introduction of 4H-SiC MOSFET requires a special focus on device reliability and simplicity of use to replace Silicon switches in existing applications. This paper describes STMicroelectronics (STM) approach to define methodology and design solutions able to guarantee the end-users and to drive their choice toward 4H-SiC MOSFET as an ideal power component.

Abstract: Long-term degradation of MOS devices has to be avoided in different harsh irradiated environments, especially for aerospace or military applications. In this paper, an overview of the irradiation experiments recently performed on 4H-SiC MOSFETs having an oxynitrided gate oxide is given, with a special focus on the threshold voltage and the effective channel mobility drifts. The general mechanisms taking place during irradiation and post-annealing treatments are described. Finally, new open issues recently observed by performing the temperature measurement on irradiated MOSFETs will be introduced and discussed.