Role of carbon and hydrogen in limiting $n$-type doping of monoclinic (Al$_x$Ga$_{1-x}$)$_2$O$_3$

Sai Mu; Mengen Wang; Joel B. Varley; John L. Lyons; Darshana Wickramaratne; Chris G. Van de Walle

doi:10.1103/PhysRevB.105.155201

paper

Role of carbon and hydrogen in limiting $n$ -type doping of monoclinic (Al $_{x}$ Ga $_{1 - x}$ ) $_{2}$ O $_{3}$

arXiv:2111.07194 · doi:10.1103/PhysRevB.105.155201

Abstract

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

17 pages, 13 figures

References in corpus (1)

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Abstract

References in corpus (1)

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Role of carbon and hydrogen in limiting $n$ -type doping of monoclinic (Al $_{x}$ Ga $_{1 - x}$ ) $_{2}$ O $_{3}$