Surface Recombination Investigation in Thin 4H-SiC Layers

n- and p-type 4H-SiC epilayers were grown on heavily doped SiC substrates. The thickness of the p-type layer was 7 mu m and the doping level around 10(17) cm(-3), while the n-type epilayers were 15 mu m thick and had a doping concentration of 3-5x10(15) cm(-3). Several different surface treatments were then applied on the epilayers for surface passivation: SiO2 growth, Al2O3 deposited by atomic layer deposition, and Ar-ion implantation. Using collinear pump - probe technique the effective carrier lifetimes were measured from various places and statistical lifetime distributions were obtained. For surface recombination evaluation, two models are presented. One states that surface recombination velocity (SRV) is equal on both the passivation/epi layer interface (S-2) and the deeper interface between the epilayer and the SiC substrate (S-1), i.e. (S-1 = S-2). The other model is simulated assuming that SRV in the epilayer/substrate (S-1) interface is constant while in the passivation layer/epilayer (S-2) interface SRV can be varied S-2 < S-1. Empirical nomograms are presented with various parameters sets to evaluate S-2 values. We found that on the investigated 4H-SiC surfaces S-2 ranges from 3x10(4) to 5 x 10(4) assuming that the bulk lifetime is 4 mu s. In Ar+ implanted surfaces S-2 is between (10(5)-10(6)) cm/s.