Passivation effect of hydrogen and oxygen on the carrier capture of vacancies in 4H-SiC

Unintentional dopants, such as hydrogen and oxygen, are unavoidable in the epitaxial growth of semiconductors, significantly impacting the device performances by acting as traps for interstitials and passivation. Herein, hybrid functional was adopted to systematically investigate the charge transfer of vacancies altered by hydrogen and oxygen passivation in 4H-SiC. Overall, both of them stabilize the formation of vacancies to prevent the diffusion and recombination effectively. Especially, the more the hydrogen passivated, the lower the formation energies. The number of passivated hydrogens shows huge impacts on the hole capturing of carbide vacancy (V-C), while the effect is small on carbon dangling bonds to capture electron both k and h site, of which the transition level epsilon (0/-1) always locates around E-C - 0.3-0.6 eV. Silicon vacancy (V-Si) primarily acts as an electron acceptor, with its transition level epsilon (0/-1) showing limited response to hydrogen passivation, while the effectiveness of electron capture is determined by the passivation process. Comparing divacancy (VCVSi) with single V-C and V-Si, there is an enhanced ability for hole capturing by silicon dangling orbitals. Once all dangling bonds are passivated, V-C, V-Si and VCVSi always keep neutral state. For oxygen passivation, V-C turns to a donor with one oxygen passivation and a neutral defect with fully passivated. V-Si is regulated from an acceptor to a bipolar dopant with one and two oxygen passivation. Our calculations unveil the underlying mechanism for hydrogen and oxygen passivation effects on the process of carrier captures of vacancies, which can further explain the relative defect signal in experimental characterizations.