Optical studies of surface recombination velocity in 4H-SiC epitaxial layer

Abstract: In this work optical studies of the effect of surface passivation for surface recombination velocity at the interface between 4H-SiC epitaxial layer and various passivation layers are presented. Four samples have been used consisting of three main parts: thin film oxide layer, 4H-SiC epitaxial layer and 4H-SiC substrate. The substrates for all samples are the same, highly doped n-type. The doping and thickness of the epitaxial layers are different; three samples have n-type epilayer, doping around 3-5×1015cm-3and one sample, the thinnest one, has a p-type doping of 1×1017cm-3.Two types of oxide are used as passivation layer: Al2O3on the n-type and p-type with 80 nm thickness, which is prepared by the ALD method, and SiO2– grown layer with 50 nm thickness, which is produced by thermal growth technique at 1250 ºC in N2O ambient for 8 hours. The forth epilayer was bombarded with 30 keV energy argon ion implanted with different doses through a native oxide. Free carrier absorption (FCA) technique was used to extract effective lifetime of excess carriers. The excess carriers are created by a high energy laser (355 nm) pulse, exiting electrons to the conduction band. The decay of these carriers is then studied by a second laser at 861nm. The carriers in the substrate recombine quickly, but in the thin epilayer the lifetime is long enough to be influenced by surface recombination at the epi-passivation layer interface. By fitting the experimental results, the surface recombination velocity (SRV) at the interfaces of epi/oxide can be extracted. The SRV of substrate/epi is assumed constant at 1×106cm/s value. The highest SRV, 5.7×104cm/s, is found in the n-type epitaxial layer with 50 nm SiO2and the slowest value, 1.07 ×103cm/s, is found in the p-type epitaxial layer with 80 nm Al2O3. For the argon implanted sample, we did not find the anticipation results. Although the highest dose gives the most defects, the SRV, 1.41×103 cm/s, was not very different for other doses.