A comparative investigation on <0001> direction and <11–20> direction 4H-SiC impact avalanche transit time devices working at D-band frequencies

We report on a numerical simulation on <;0001> direction and <;11-20> direction p+/n/n-/n+ (single drift region) 4H silicon carbide (4H-SiC) Impact-Ionization-Avalanche-Transit-Time (IMPATT) diodes for operation at D-band frequencies. Results show that the output performance of 4H-SiC IMPATT diode is sensitive to the crystal direction of the one-dimensional current flow. The <;0001> direction 4H-SiC IMPATT diode exhibits larger breakdown voltage and higher de-to-rf conversion efficiency (η) due to its lower electron and hole ionization rates and higher ratio of drift zone voltage drop (V_D) to breakdown voltage (V_B) compared with those for <;11-20> direction 4H-SiC IMPATT diode. Higher dc-to-rf conversion efficiency and larger breakdown voltage in <;0001> direction 4H-SiC IMPATT diode imply its millimeter wave power output higher than <;11-20> direction 4H-SiC IMPATT diode.