Role of carbon and hydrogen in limiting n-type doping of monoclinic (AlxGa1-x)(2)O-3

Article

关键词: IMPURITIES;    ABSORPTION;    CRYSTAL;    STATE;    THIN;   

DOI  :  10.1103/PhysRevB.105.155201

来源: SCIE

【 摘 要 】

We use hybrid density functional calculations to assess n-type doping in monoclinic (AlxGa1-x)(2)O-3 alloys. We focus on silicon, the most promising donor dopant, and study the structural properties, formation energies, and charge-state transition levels of its various configurations. We also explore the impact of carbon and hydrogen, which are common impurities in metal-organic chemical vapor deposition (MOCVD). In Ga2O3, Si-Ga is an effective shallow donor, but in Al2O3 Si-Al acts as a DX center with a (+/-) transition level in the band gap. Interstitial hydrogen acts as a shallow donor in Ga2O3 but behaves as a compensating acceptor in n-type Al2O3. Interpolation indicates that Si is an effective donor in (AlxGa1-x)(2)O(3 )up to 70% Al, but it can be compensated by hydrogen already at 1% Al. We also assess the diffusivity of hydrogen and study complex formation. Si -cation H complexes have relatively low binding energies. Substitutional carbon on a cation site acts as a shallow donor in Ga2O3, but can be stable in a negative charge state in (AlxGa1-x)(2)O-3 when x > 5%. Substitutional carbon on an oxygen site (C-o) always acts as an acceptor in n-type (AlxGa1-x)(2)O-3, but will incorporate only under relatively oxygen-poor conditions. C-o-H complexes can actually incorporate more easily, explaining observations of carbon-related compensation in Ga2O3 grown by MOCVD. We also investigate C-cation-H complexes, finding they have high binding energies and act as compensating acceptors when x > 56%; otherwise the hydrogen just passivates the unintentional carbon donors. C-H complex formation explains why MOCVD-grown Ga2O3 can exhibit record-low free-carrier concentrations, in spite of the unavoidable incorporation of carbon. Our study highlights that, while Si is in principle a suitable shallow donor in (AlxGa1-x)(2)O-3 alloys up to high Al compositions, control of unintentional impurities is essential to avoid compensation.

【 授权许可】

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