John Österman

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.

Carrier profiling of Al-doped 4H-SiC by scanning spreading resistance microscopy

Epitaxially-grown Al-doped 4H-SiC has been studied by scanning spreading resistance microscopy. The measured current shows good quantitative agreement with the chemical Al concentration in the range 2×1016 to 2×1020 atoms cm−3. Simulations of the sample temperature distribution using finite element calculations predict a maximum temperature exceeding 750 K within 100 nm of the contact region at 7.5 V dc bias for an Al doping of 1020 cm−3. The heating causes a significant increase in the ionization of the dopants relative to that at room temperature. Due to the strong voltage dependence, the effect can be avoided by operating below 5 V dc bias where the temperature rise is shown to be negligible for all dopant concentrations.

Annealing of Al implanted 4H silicon carbide

Al ions were implanted with multiple energies up to 250 keV at elevated temperatures in n-type 4H SiC epitaxial layers to reach a surface concentration of 1 x 10(20) cm(-3). These samples were then ...

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

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.