Uwe Zimmermann

Solubility limit and precipitate formation in Al-doped 4H-SiC epitaxial material

Heavily Al-doped 4H-SiC structures have been prepared by vapor phase epitaxy. Subsequent anneals have been carried out in an Ar atmosphere in a rf-heated furnace between 1500 degreesC and 2000 degr ...

Material defects in 4H-silicon carbide diodes

Crystallographic defects revealed by synchrotron white beam x-ray topography, electron beam induced current, optical microscopy, and electroluminescence are correlated with the electrical characteristics of medium-voltage epitaxial 4H-silicon carbide diodes. Diodes that include macroscopic crystallographic defects show a significantly reduced reverse breakdown voltage with typical microplasma current fluctuations under reverse bias. Microplasma current paths are revealed by increased electroluminescence both under forward and reverse bias of the diodes and coincide with the locations of screw dislocations in the epitaxial layers of the diodes. The role of crystallographic imperfections on the formation of stacking faults responsible for the degradation of bipolar silicon carbide components is discussed.

Solubility limits of dopants in 4H-SiC

Epitaxial 4H-SiC structures with heavily boron or aluminium doped layers have been prepared by vapour phase epitaxy. The samples have been annealed in Ar atmosphere in an RF-heated furnace between 1700 and 2000 C for 45 min to 64 h. Secondary ion mass spectrometry has been employed to obtain depth distributions as well as lateral distributions (ion imaging) for boron and aluminium. Transmission electron microscopy has been used to study the crystallinity and determine phase composition. Solubility limits of ∼ 1 × 10 20 Al/cm 3 (1700°C) and < 1 × 10 20 B/cm 3 (1900°C) have been deduced.

Measurements and simulations of self-heating and switching with 4H-SiC power BJTs

Transient measurements and device simulations were performed to investigate self-heating and switching with 4H-SiC BJTs. A current gain decrease was found during self-heating presumably due to reduced electron mobility with increasing temperature. Surface recombination increased the simulated maximum temperature but the current gain decrease during self-heating was similar as for bulk recombination. A fast switching of 0.5 A and 200 V was shown with a voltage rise-time of about 70 ns and fall-time of 50 ns. Turn-off measurements show a noticeably delay time before fall-off of the emitter current, indicating a significant amount of stored carriers in the base.

Simulations of High-Voltage 4H-SiC p+nn+ Diodes Using a Transient Model for the Deep Boron Level

Abstract. Device simulations of B implanted 4H-SiC p nn diodes were performed including transient trapping of carriers in the deep B level. Most traps be com filled at forward current densities above 3000 A/cm 2 thus enabling conductivity modulation by a carrier plasma and a negative resistance in agreement with pulsed forward bias measure ments. Reverse recovery measurements were performed to verify a significant conductivity modulation at 4000 A/cm 2

Recrystallisation and Grain Growth in Batch Annealed Ti-IF Steels

In order to optimize the batch annealing cycles and increase the productivity of this process, the impact of the chemical composition and the processing parameters on the recrystallisation and grain growth kinetics were investigated on different Ti IF steels. A simple model based on an Avrami formulation has been developed for the prediction of the recrystallisation kinetics.

SEM Visibility of Stacking Faults in 4H-Silicon Carbide Epitaxial and Implanted Layers

A strong contrast was observed in a conventional scanning electron microscope resembling the shape of stacking faults in epitaxial 4H silicon carbide layers. This contrast was seen at the location of degradation faults in bipolar diodes as well as far outside the device perimeter on the low n-type doped epitaxial layer. Photoluminescence measurements indicated that the nature of the observed features were stacking faults in the crystalline material. The intersections of the stacking faults with the sample surface was marked by long edges in the pattern of the step-bunching.

Comparison between Implanted and Epitaxial PiN-Diodes on 4H-Silicon Carbide

Two sets of pin-diodes with epitaxially grown anode regions and implanted anode regions, respectively, were processed on the same low-doped n-type epitaxial layer. The designed breakdown voltage fo ...