P. Hazdra

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.

Optical characterisation of MOVPE grown vertically correlated InAs/GaAs quantum dots

Structures with vertically correlated self-organised InAs quantum dots (QDs) in a GaAs matrix were grown by the low-pressure metal-organic vapour phase epitaxy (MOVPE) and characterised by different microscopic techniques. Photoluminescence in combination with photomodulated reflectance spectroscopy were applied for characterisation of QDs structures. We show that combination of both methods allows detecting optical transitions originating both from QDs and wetting (separation) layers, which can be than compared with those obtained from numerical simulations. On the basis of obtained results, we demonstrate that photoreflectance spectroscopy is an excellent tool for characterisation of QDs structures wetting layers and for identification of spacer thicknesses in vertically stacked QDs structures.

High-power P-i-N diode with the local lifetime control based on the proximity gettering of platinum

We demonstrate for the first time a high-power P-i-N diode with local lifetime control using the proximity gettering of platinum in the FZ silicon. The region of maximal damage resulting from the low-dose helium implantation was decorated by substitutional platinum that diffused from the PtSi anode contact at low temperature (700/spl deg/C) through the P/sup +/-P anode doping at the distance of 70 /spl mu/m. The diodes show very low forward voltage drop with negative temperature coefficient and very low leakage current even at elevated temperatures while keeping the major advantages of the ion irradiated devices like low turn-off losses and soft recovery.

Radiation-Enhanced Diffusion of Palladium for a Local Lifetime Control in Power Devices

Palladium (Pd) diffusion from a surface layer enhanced by defects from a helium (He) irradiation is shown to provide a local lifetime control in a power p-i-n diode annealed between 350degC and 700degC. An open-circuit voltage decay lifetime measurement is used to identify temperature ranges in which one of two lifetime control mechanisms takes part. Spreading resistance measurements show the doping compensation at the anode junction caused by defects after the Pd diffusion below 725degC. Locally modified doping profiles by introduced defects cause significantly lowered dynamic avalanche (DA) during fast reverse recovery compared to the standard He irradiation as confirmed also by device simulation. Advanced shaping of a shallow doping profile, reducing avalanche generation in the area of peaking electric field under a reverse bias, is suggested as an additional method to suppress the DA in power devices. The diffusion at 650degC gives the best static and dynamic parameters. Breakdown voltage and leakage current are those of untreated diode. Turn-off losses close to the SOA limit are also much lower than in the standard He irradiation, and thermal characteristics are better than after the traditional high-temperature diffusion.

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.

Type I–type II band alignment of a GaAsSb/InAs/GaAs quantum dot heterostructure influenced by dot size and strain-reducing layer composition

The aim of this work is to red shift quantum dot (QD) photoluminescence (PL) towards telecommunication wavelengths by engineering the metalorganic vapour phase epitaxy (MOVPE) prepared structure of InAs/GaAs QDs covered by a GaAsSb strain-reducing layer. Our results proved that type I or type II band alignment can be controlled by both GaAsSb composition and QD size. Maintaining type I heterostructure is important for high luminescence efficiency and emission wavelength stability of the QD structure. The simulation of electron structure in InAs QDs covered with a GaAsSb strain-reducing layer as well as experimental results suggest the importance of increasing QD size for obtaining a longer wavelength PL from the type I heterostructure. The PL maximum wavelength 1371 nm was achieved for the MOVPE prepared type I QD structure with 14% of Sb in GaAsSb. This type of structure exhibits seven times higher PL intensity, twice narrower PL peak and 85 meV redshift in comparison with similarly prepared QDs covered by GaAs.

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.