Surface Recombination Investigation in Thin 4H-SiC Layers

Abstract

n- and p-type 4H-SiC epilayers were grown on heavily doped SiC substrates. The thickness of the p-type layer was 7 µm and the doping level around 10¹⁷ cm ³, while the n-type epilayers were 15 µm thick and had a doping concentration of 3 - 5*10¹⁵ 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 (S₂) and the deeper interface between the epilayer and the SiC substrate i. e. (S₁ = S₂). The other model is simulated assuming that SRV in the epilayer/substrate (S₁) interface is constant while in the passivation layer/epilayer (S₂) interface SRV can be varied S₂ < S₁. Empirical nomograms are presented with various parameters sets to evaluate S₂ values. We found that on the investigated 4H-SiC surfaces S₂ ranges from 3x10⁴ to 5x10⁴ assuming that the bulk lifetime is 4 (µs. In Ar⁺ implanted surfaces S₂ is between (10⁵ - 10⁶) cm/s.

http://dx.doi.org/10.5755/j01.ms.17.2.479