J. Vobecký

Optimum lifetime structuring in silicon power diodes by means of various irradiation techniques

Abstract Application of radiation defects for adjustment of power diode parameters is demonstrated. Local lifetime control (LLC) by proton and alpha-particle irradiation with energies 1.8–12.1 MeV is compared with uniform lifetime killing by 4.5 MeV electrons. The influence of both the techniques on static and dynamic parameters of modified diodes is experimentally established and explained by means of state-of-the-art simulation system. Optimization means and limits of lifetime control by irradiation techniques are discussed, as well.

Accurate simulation of fast ion irradiated power devices

Abstract A new approach to simulation of a device that is subject to low-dose high-energy ion irradiation is presented with regard to different energy magnitudes, dose and temperature of subsequent annealing. The procedure utilizes an ion-implantation process simulator, an expert system based on experiment, and a 1-D device simulator with an improved model of thermal generation/recombination. Measured and simulated spatial distribution of minority carrier lifetime within a GTO thyristor provided rigorous system verification. The results of proton and helium irradiation are compared from the standpoint of the ON-state spatial distribution of excess carriers in a high-power thyristor. The forward voltage drop is shown as a function of dose, energy and annealing temperature. The influence of ion irradiation on the simulated trade-off between voltage drop and reverse recovery time of a high-power diode is likewise discussed considering the soft-factor and the reverse current.

Open circuit voltage decay lifetime of ion irradiated devices

Open circuit voltage decay method for measuring of excess carrier lifetime is shown to be effective for in-process checking of ion irradiated power diodes. 2.5 kV/100 A P-i-N diodes irradiated by helium ions with different irradiation energies and doses were used for presentation of capabilities of this method. Differences in carrier dynamics during the OCVD process between unirradiated and irradiated devices were studied by use of the device simulation in ATLAS.

Defect distribution in MeV proton irradiated silicon measured by high-voltage current transient spectroscopy

Abstract Current transient spectroscopy (CTS) using high relaxation voltages up to 1 kV is shown to be an effective tool for non-destructive characterization of radiation defect profiles in silicon resulting from the MeV ion irradiation. The method was used for profiling of different defect centers produced in low-doped, float zone, n-type silicon by irradiation with 3, 4 and 5.3 MeV protons to a fluence of 5×10 9 and 1×10 10 cm −2 . The results were compared with those obtained from capacitance DLTS and reverse I – V profiling. Electronic properties and introduction rates of dominant defect centers were also established. It is shown that CTS is capable to trace full-depth profiles of dominant radiation defects and provide precise and more accurate data than previously presented by destructive profiling procedures. Measured distributions of vacancy related radiation defects agree well with the distribution of the primary damage received from Monte Carlo simulations with the exception of the peak broadening attributed to vacancy diffusion.

Crossing point current of electron and proton irradiated power P-i-N diodes

Abstract Crossing point current of forward I – V curves ( I Xing ) at 25 and 125°C was measured and simulated for 4.5 kV/320 A silicon power P-i-N diode irradiated by electron, proton and combined electron–proton irradiation. The proton and electron irradiation are shown to decrease the magnitude of I Xing which is beneficial for paralleling of diodes under surge conditions. With increasing irradiation dose this effect saturates. High doses of combined electron–proton treatment can even lead to an increased magnitude of I Xing above that of the unirradiated device. To achieve agreement of electro-thermal simulation with experiment, temperature dependence of the capture cross sections σ n and σ p of the deep level dominant in condition of heavy injection had to be taken into account. With the aid of simulation, the dependencies I Xing vs. dose are explained.

Helium irradiated high-power P–i–N diode with low ON-state voltage drop

Abstract The application of a 300 nm thick platinum silicide (PtSi) layer at the place of the anode contact layer of a soft recovery 2.5 kV/100 A high-power P–i–N diode brought a reduction of the forward voltage drop at several tens percent (for the rating current of 100 A) compared to that of the conventional aluminum and Ti–Ni–Ag layers. This enabled us to greatly improve the trade-off curve between the ON-state and turn-OFF losses of the diode subjected to helium irradiation into the anode and anode junction region. The application of PtSi layers thus opens a new way for the improvement of power devices.

Impact of the electron, proton and helium irradiation on the forward I–V characteristics of high-power P–i–N diode

Abstract 2.5 kV/100 A high-power P–i–N diode was electron, proton and helium irradiated in a wide range of irradiation doses with irradiation energies in the MeV range. The resulting forward I – V curves were registered in the temperature range 30–125 °C to investigate the magnitude of the crossing point current of the I – V curves–– I XING . I XING was found to decrease with increasing irradiation dose and to disappear at high doses for all three irradiation treatments with exception of ion irradiated diodes with defect peaks placed deeply into the anode region. Using a simple model based on the thermal and injection dependence of the carrier lifetime, the explanation of this effect is presented with the support of the non-isothermal 2-D device simulation of helium irradiated devices.

Radiation Defects Produced in 4H-SiC Epilayers by Proton and Alpha-Particle Irradiation

Electronic properties of radiation damage produced in 4H-SiC epilayer by proton and alpha particle irradiation were investigated and compared. 4H-SiC epilayers, which formed the low doped n-base of Schottky barrier power diodes, were irradiated to identical depth with 550 keV protons and 1.9 MeV alphas. Radiation defects were then characterized by capacitance deep-level transient spectroscopy and C-V measurements. Results show that both projectiles produce identical, strongly localized damage peaking at ion’s projected range. Radiation defects have a negligible effect on dynamic characteristic of irradiated 4H-SiC Schottky diodes, however acceptor character of introduced deep levels and their high introduction rates deteriorate diode’s ON-state resistance already at very low irradiation fluences.

Dynamic avalanche in diodes with local lifetime control by means of palladium

The increase of the static breakdown voltage and the reduction of dynamic avalanche in a fast recovery 2.5kV/150A P-i-N diode subjected to the radiation enhanced diffusion of a palladium are discussed. The in-diffusing palladium compensates the doping profile in a lightly doped N-base close to the anode junction. Using a device simulation, the increase of the breakdown voltage and the reduction of the dynamic avalanche are explained by the reduction of peak electric field in the additional low-doped P-type layer created by the compensation effect. This is presented for both a dc and transient device operation and confirmed experimentally as well. An improved technology curve for the static versus recovery losses at a high line voltage has been obtained. A high thermal budget of deep levels and a low leakage current are additional benefits of the method.

Effect of Neutron Irradiation on High Voltage 4H-SiC Vertical JFET Characteristics: Characterization and Modeling

The effect of neutron irradiation on commercial vertical high voltage normally-OFF SiC power N-JFETs was investigated. JFETs were irradiated with 1 MeV neutron equivalent fluences up to 4×1014 cm-2. Measurement showed that fast neutrons introduce deep levels acting mostly as deep acceptor centers. These centers gradually compensate lightly doped channel and drift regions of JFETs. As a result, characteristics are deteriorated, the JFET threshold voltage gradually increases and transconductance is lowered. At fluences higher than 4×1014 cm-2, the low doped n-regions are fully compensated and transistor loses its functionality. The 2D physical model of JFET in ATLAS simulator was developed and calibrated including the neutron irradiation effects. Simulation showed a good agreement with experimental data. This confirmed that carrier removal in the channel and drift region by acceptors centers introduced by neutrons is a dominant reason of SiC JFET degradation.