Papers by Author: Nicolas Dheilly

Abstract: Optical Beam Induced Current (OBIC) measurements have been performed on 4H-SiC avalanche diodes with very thin and highly doped avalanche region. The light source used in this study is an Ar-laser with a wavelength of 351 nm which results in a mixed carrier injection. From these measurements, impact ionization coefficients for 4H-SiC have been extracted in the electric field range from 3 to 4.8 MV/cm. In combination with ionization coefficients in our previous paper extracted from diodes with lowly doped avalanche region, we propose a set of parameters of impact ionization coefficients for 4H-SiC, applicable to a wide electric field range.

Abstract: This paper deals with the pulse capabilities of 4H-SiC optically triggered thyristors. The device structure and the fabrication process are presented. The results of pulse characterizations are shown. Two types of current pulses were used, a short (pulse width of 10 µs) and a long (pulse width of 650 µs). Peak current densities of 17 kA.cm-2 and 4 kA.cm-2 were attained with short and long pulses respectively. The failures and degradation caused by these experiments are also shown in this paper.

Abstract: This paper presents results attained with SiC GTO thyristors terminated by a single step and a graded etched JTE. The comparison of both types of devices reveals no significant difference in the on-state and switching characteristics but a higher blocking capability of some thyristors with the latter kind of termination. The best devices showed a forward breakdown voltage of nearly 6 kV, which is a distinct progress as against previous results of thyristors with a graded etched JTE. Furthermore, such GTO thyristors have been characterized dynamically for the first time.

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: Direct light triggering of 4H-SiC thyristors with a 365 nm UV LED was demonstrated. Two different structures with etched and non etched gate were successfully tested. The current rise time was less than 100 ns and the delay time as short as 1.5 μs. The optical energy density necessary to switch-on a thyristor has been studied for different optical power densities and bus voltages. This work shows that the UV LED technology is becoming sufficiently powerful to switch-on SiC thyristors. Thus, an alternative, less expensive and more compact gate light source than UV laser is now possible. This can be of particular interest for very high voltage and pulse power electronic applications.

Abstract: Avalanche diodes have been fabricated on 4H-SiC substrate. These diodes show an abrupt avalanche voltage of about 59 V which corresponds to the calculated theoretical one using our previously determined impact ionization coefficients. This avalanche voltage increases by as small as 3.7 mV/K over the investigated temperature range (150K-420K).

Abstract: With the aim of investigating the specific process parameters of bipolar semiconductor devices, simple mesa-terminated silicon carbide PiN diodes were designed and fabricated. The expected effect of the mesa height on the reverse behaviour could be investigated as well as the condition of the material surface. It was shown that these simple devices are well suited as test devices.

Abstract: In this paper, we propose a graded etched junction termination extension for SiC thyristors. It has the functionality of a multiple implanted JTE, but is realized by purely etched means. This termination is demonstrated up to 4 kV on a sample with a drift layer thickness of 35 µm. On another sample with a thinner drift layer, similar thyristors have been realized with a low resistive contact, resulting in an on-state voltage drop of 3.2 V at 40 A/cm².

Abstract: This paper reports on the influence of temperature on the electrical carrier lifetime of a 3.3 kV 4H-SiC PiN diode processed with a new generation of SiC material. The Open Circuit Voltage Decay (OCVD) is used to evaluate ambipolar lifetime evolution versus temperature. The paper presents a description of the setup, electrical measurements and extraction fittings. The ambipolar lifetime is found to rise from 600 ns at 30 °C to 3.5 μs at 150 °C.