Papers by Keyword: Surface Recombination

Abstract: We present an extended model for the simulation of the effective minority carrier lifetime in 4H-SiC epiwafers after optical excitation. This multilayer model uses measured values (such as doping profile, point defect concentration and capture cross sections, epilayer thickness) as input parameters. The bulk lifetime and the diffusion constant are calculated from the actual time dependent excess carrier profiles, resulting in more realistic transients having different decay regimes than in other models. This enables a better understanding of optical lifetime measurements.

Abstract: The temperature dependence of the carrier lifetime was measured in n-type 4H-SiC epilayers of varying Z1/2 deep defect concentrations and layer thicknesses in order to investigate the recombination processes controlling the carrier lifetime in low- Z1/2 material. The results indicate that in more recently grown layers with lower deep defect concentrations, surface recombination tends to dominate over carrier capture by other bulk defects. Low-injection lifetime measurements were also found to provide a convenient method to assess the surface band bending and surface trap density in samples with a significant surface recombination rate.

Abstract: A new 4H-SiC Bipolar Junction Transistor with Suppressed Surface Recombination structure: SSR-BJT has been proposed to improve the common emitter current gain which is one of the main issues for 4H-SiC BJTs. A Lightly Doped N-type layer (LDN-layer) between the emitter and base layers, and a High Resistive P-type region (HRP-region) formed between the emitter mesa edge and the base contact region were employed in the SSR-BJT. A fabricated SSR-BJT showed a maximum current gain of 134 at room temperature with a specific on-resistance of 3.2 mΩcm2 and a blocking voltage VCEO of 950 V. The SSR-BJT kept a current gain of 60 at 250°C with a specific on-resistance of 8 mΩcm2. To our knowledge, these current gains are the highest among 4H-SiC BJTs with a blocking voltage VCEO more than about 1000 V which have been ever reported.

Abstract: This paper reports a 4H-SiC bipolar junction transistor (BJT) with a breakdown voltage (BVCEO) of 1200 V, a maximum current gain (β) of 60 and the low on-resistance (Rsp_on)of 5.2 mΩcm2. The high gain is attributed to an improved surface passivation SiO2 layer which was grown in N2O ambient in a diffusion furnace. The SiC BJTs with passivation oxide grown in N2O ambient show less emitter size dependence than reference SiC BJTs, with conventional SiO2 passivation, due to a reduced surface recombination current. SiC BJT devices with an active area of 1.8 mm × 1.8 mm showed a current gain of 53 in pulsed mode and a forward voltage drop of VCE=2V at IC=15 A (JC=460 A/cm2).

Abstract: The effect of the different types of passivation layers on the current gain of SiC BJTs has been investigated. Measurements have been compared for BJTs passivated with thermal SiO2, plasma deposited (PECVD) SiO2 and BJTs without passivation. The maximum DC current gain of BJTs with thermal SiO2 was about 62 at IC=20 mA and Vce=40 V. On the other hand, the BJTs with a passivation by PECVD SiO2 had a DC current gain of only 25. The surface recombination current was extracted from measurements with BJTs of different emitter widths. The surface recombination current of BJTs with a thermally grown oxide was about 25 % lower than unpassivated BJTs and 65 % lower than that of PECVD passivated BJTs.

Abstract: This paper reports the fabrication of epitaxial 4H-SiC bipolar junction transistors (BJTs) with a maximum current gain β=64 and a breakdown voltage of 1100 V. The high β value is attributed to high material quality obtained after a continuous epitaxial growth of the base-emitter junction. The current gain of the BJTs increases with increasing emitter width indicating a significant influence of surface recombination. This “emitter-size” effect is in good agreement with device simulations including recombination in interface states at the etched termination of the baseemitter junction.