Bertrand Vergne

Kilovolt, Nanosecond, and Picosecond Electric Pulse Shaping by Using Optoelectronic Switching

This letter describes subnanosecond electric pulse generation and shaping. The optoelectronic switching of silicon semiconductor devices embedded in a frozen wave generator is obtained in the linear regime. Control of the switching delay time, combined with power modulation of the optical gating signals, enables temporal and spectral pulse shaping. In this way, monocycle nanosecond and/or picosecond pulses with balanced or unbalanced positive and negative components and square electrical pulses with adjustable duration are obtained.

A 30-kHz Monocycle Generator Using Linear Photoconductive Switches and a Microchip Laser

We have demonstrated that diode-pumped microchip laser technology can be well adapted for the generation of electrical kilovolt pulses. An ultra-compact system is presented. It delivers a smooth bipolar pulse of 2 ns, a peak-to-peak voltage of 1.3 kV, and a repetition rate of 30 kHz. The required optical energy to achieve a complete switching is as low as 10 muJ. Because of the linear switching regime, this generator still works after half a billion shots. No limitation in terms of life time is currently expected. Nevertheless, heating problems start to occur at a high repetition rate.

AN ULTRA WIDEBAND IMPULSE OPTOELECTRONIC RADAR: RUGBI

An ultra wideband radar system based on a coherent emission of an ultra-wideband antenna array using photoconductive switching devices is proposed. The triggering process is obtained by the excitation of semiconductor samples in linear mode using a picosecond laser source. The emitting antenna system and the receiving antenna developed by the Research Institute XLIM present some specific qualities suitable for radiation and measurement of ultrashort pulses. The optical control of the sources allows to sum the

Optical beam induced current measurements based on two-photon absorption process in 4H-SiC bipolar diodes

Using a pulsed green laser with a wavelength of 532 nm, a duration pulse of ∼1 ns, and a mean power varying between 1 and 100 mW, induced photocurrents have been measured in 4H-SiC bipolar diodes. Considering the photon energy (2.33 eV) and the bandgap of 4H-SiC (3.2 eV), the generation of electron-hole pair by the conventional single photon absorption process should be negligible. The intensity of the measured photocurrents depends quadratically on the power beam intensity. This clearly shows that they are generated using two-photon absorption process. As in conventional OBIC (Optical Beam Induced Current), the measurements give an image of the electric field distribution in the structure under test, and the minority carrier lifetime can be extracted from the decrease of the photocurrent at the edge of the structure. The extracted minority carrier lifetime of 210 ns is consistent with results obtained in case of single photon absorption.

High-Voltage Rectifier Diodes Used as Photoconductive Device for Microwave Pulse Generation

Generation of unipolar and bipolar pulses by using high- and medium-voltage silicon rectifier diodes is achieved. These components are provided by the French Atomic Energy Commission (CEA). Furthermore, these devices work in the linear mode of photoconducting switches. Generation of electrical unipolar pulses with an amplitude of 10.7 kV and a full-width at half-maximum of 300 ps by using only 1.2 mJ of optical power is demonstrated. This energy value is 10-100 times less than usually published during the past decades. Furthermore, the linear mode running of these devices permits to synchronize several generators with a precision as low as 2 ps. This low timing jitter is useful for bipolar generators in order to control their spectrum with high precision, i.e., bipolar pulses of 3 kV peak-to-peak have been generated with a cycle duration of 400 ps and an optical energy of 1 mJ

Pulse Current Characterization of SiC GTO Thyristors

With a focus on pulsed power applications, this paper presents results of the pulse current characterization of GTO thyristors developed and fabricated within a previous ISL funded project. Limited by the pulse current capability of the bonding wire connection, the devices demonstrated to handle a peak current of up to 6 kA/cm2 (about 20 µs FWHM). Pulse tests of Al wires indicate that two 50 µm wires should be sufficient to test a 1 mm2 device up to a peak current of 30 kA/cm2.

Edge Termination Design Improvements for 10 kV 4H-SiC Bipolar Diodes

10 kV class 4H-SiC bipolar diodes have been fabricated. Two different edge terminations (Mesa/JTE or MESA/JTE with JTE rings) with two different junction bend radius have been designed and tested. Measurement results show that the inclusion of JTE rings improve the edge termination efficiency. The measurements indicate also a better reverse performance of diodes with larger bend radius.

High Temperature Capability of High Voltage 4H-SiC JBS

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.

Ultra-Wideband Electrical Pulse Generator Using Photoconductive Semiconductor Switches

We achieved the generation of unipolar and bipolar ultra-wideband electrical pulses by using a photoconductive device. It relies on a doped silicon substrate which is used in the linear mode with less optical energy than usually published. This running mode allows the synchronisation of several sources with a timing jitter less than 5 ps. However it permits to control the low frequency components of the bipolar generator by means of the synchronisation of two photoconductors. So we generated unipolar pulses from 43 ps to 300 ps of duration (full width at half maximum: FWHM) with peak voltage up to 10700 V and bipolar pulses between 200 ps and 450 ps of cycle length with 3000 V of peak voltage.

Determination of 4H-SiC Ionization Rates Using OBIC Based on Two-Photon Absorption

Optical Beam Induced Current (OBIC) measurements are performed on 4H-SiC avalanche diodes with a very thin and a highly doped active region. A pulsed green laser, with a wavelength of 532 nm, illuminates a reverse biased diode leading to generate electron-hole pairs in the space charge region. Comparison between the 4H-SiC bandgap and the incident photon energy shows that single photon absorption process can be neglected and two-photon absorption process dominates in this case. Ionization rates are then extracted from multiplication curve in a high electric field range (3 to 5 MV.cm–1). Results are in good agreement with previous ones obtained on the same diodes using single photon absorption process.