Sigo Scharnholz

Extreme dielectric strength in boron doped homoepitaxial diamond

The fabrication of Schottky diodes withstanding breakdown voltages up to 10 kV is demonstrated. A corresponding electric field of 7.7 MV/cm at the center of the diode is evaluated with the help of a two-dimensional finite elements software. These properties result from a net shallow acceptor concentration below 10(16) cm(-3) in the first micrometers of an epitaxial film with optimized crystalline quality and a special oxidizing treatment of its surface, allowing the true dielectric strength of bulk diamond to be revealed.

High-Voltage 4H-SiC Thyristors With a Graded Etched Junction Termination Extension

For the first time, a graded etched junction termination extension (JTE) is applied to completed 4H-SiC gate turn-off thyristors. These devices demonstrate the feasibility of nonimplanted high-voltage SiC thyristors. The maximal measured forward breakdown voltage of 7.8 kV corresponds very well to the ideal value of 8.1 kV. This letter explains the conceptual procedure to realize an optimal four-step JTE and compares measurement results with those obtained from finite-element simulations.

Hot carrier-induced photon emission in 6H and 4H–SiC MOSFETs

Abstract We report experimental results of photon emission from silicon carbide MOS transistors. Emission spectra have been measured on 6H and 4H–SiC MOSFETs, in a region below the bandgap energy of the SiC material. The relationship found between light intensity and the substrate and drain currents shows that the origin of photon emission can be ascribed to recombination processes. In both cases we observed a decrease of the emitted light with increasing photon energy. Two distinct peaks are always observed, located around 1.5 and 2.5 eV, respectively.

Modular 50-kV IGBT Switch for Pulsed-Power Applications

In this paper, we describe the development of a modular semiconductor switch, based on the compact IGBT switch, presented at the 14th EML. Using a discrete 18-kV IGBT switching module, we tested first two and then three of these modules connected in series. The goal was to handle 30 kV with two switches and 50 kV with three switches. In order to have safe operating conditions during the experiments, the current was limited by the load resistor and should not exceed 500 A. All the tests were carried out as single-shot tests. To get a safe synchronous switching, it was necessary to have a trigger unit that is capable of creating a signal triggering all the modules at the same time. For this purpose, we used a trigger unit, which was inductively coupled by means of a ferrite core system to the modules, to create the gate signals for all the discrete IGBTs on the board simultaneously. With that experimental setup, we have shown that, by using the modular IGBT-based semiconductor switch, it is possible to handle 50 kV. Depending on the available load resistor, the current which could be handled amounted to 450 A at the maximum.

Passivation of interface traps in MOS-devices on n- and p-type 6H-SiC

Abstract Interface traps in the SiO2-6H-SiC system can be passivated by a high temperature anneal in hydrogen or moistrous atmosphere. The passivation is very effective for deep donor like traps which are reduced towards the 1011 cm−2 eV−1 range. The electrical properties of n-channel MOSFETs show that the gate oxides contain only a low density of fixed oxide charges in the low 1011 cm−2 range for the passivated and the unpassivated state. It is further demonstrated that deep donor-like interface states hardly affect the electrical properties of n-channel MOSFETs on 6H-SiC.

OBIC Measurements on Avalanche Diodes in 4H-SiC for the Determination of Impact Ionization Coefficients

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.

SIMS analyses applied to open an optical window in 4H-SiC devices for electro-optical measurements

4H-SiC vertical bipolar power diodes have been fabricated with bilayer metallic anode contact based on an Al-Ti-Ni ohmic contact and a thick Al over-metallization. An optical window of 100 × 100 μm2 has been created through the anode contact with a SIMS Cameca IMS 4F equipment using Cs+ primary ions at 10 kV and with a beam spot size of 100 nm. The current/voltage characteristics of the diodes show that the SIMS process does not induce an increase of the leakage currents in forward nor in reverse bias. OBIC UV photogeneration occurs under the optical window and not under the contact metal.

Graded Etched Junction Termination for SiC Thyristors

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.

Temperature Dependence of 4H-SiC Ionization Rates Using Optical Beam Induced Current

The behavior of 4H-SiC power devices in severe environment with varying temperature is a key characteristic indicating their reliability. This paper shows the dependence of the ionization rates of 4H-SiC with respect to temperature. Optical Beam Induced Current (OBIC) measurements have been performed on PN junctions to determine the multiplication coefficient for temperature varying between 100 and 450K. That allows extracting the ionization rates by fitting the curves of multiplication coefficient.

600 V PIN Diodes Fabricated Using On-Axis 4H Silicon Carbide

This paper reports the fabrication and electrical characterization of PiN diodes on an on-axis grown epitaxial layer. TCAD simulations have been performed in order to design their architecture. Some of these diodes have a breakdown voltage around 600 V. A comparison is made with similar diodes fabricated on off-cut grown layers. Computer simulations are used to explain lower breakdown voltage than those expected.