Effect of crystal defects on minority carrier diffusion lengths in 6H SiC [solar cells]

Minority-carrier diffusion lengths in n-type 6H-SiC solar cells were measured using the planar electron-beam induced current (EBIC) technique. Experimental values of electron beam current, EBIC and beam voltage were obtained for n-type SIC with a carrier concentration of 1.7E17 cm^-3. This data was fit to theoretically calculated diode efficiency curves, and the diffusion length and metal layer thickness extracted. The extracted hole diffusion length ranged from 0.68 μm to 1.46 μm. The error for these values was ±15%. Additionally, we introduce a novel variation of the planar technique. This “planar mapping” technique measures diffusion length along a linescan creating a map of diffusion length versus position. This map is overlaid onto the EBIC image of the linescan, allowing direct visualization of the effect of crystal defects on minority carrier diffusion length. Diffusion length maps of both n and p-type 6H SiC show that large micropipe defects severely limit the minority carrier diffusion length, reducing it well below 0.1 μm inside large defects