Key Takeaways & Executive Findings
- •• • p-type 2D BiOBr FETs achieve a hole mobility of 26.28 cm2 V−1 s−1 and on/off ratio >10^4, providing a much-needed high-performance p-type counterpart for CMOS integration where p-type 2D semiconductors are scarce. • • n-type 2D BiOBr FETs exhibit an electron mobility of 59.59 cm2 V−1 s−1, exceeding most reported n-type 2D FETs and enabling high-speed, low-power n-channel devices. • • Conduction polarity is switched solely by modulating oxygen chemical potential during CPMCVD, eliminating extrinsic doping and its associated mobility degradation and interface defect generation. • • DFT calculations identify bismuth vacancies (under high oxygen chemical potential) as the origin of p-type conductivity and oxygen vacancies (under low oxygen chemical potential) as the origin of n-type conductivity, providing a predictive defect-engineering framework.
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Abstract
Two-dimensional (2D) BiOBr has attracted considerable attention for optoelectronic applications, yet reported 2D BiOBr predominantly exhibits n-type conductivity. The absence of high-quality p-type 2D BiOBr impedes the development of complementary metal oxide semiconductor (CMOS) integrated circuits. This study reports the synthesis of large-scale, high-quality p-type 2D BiOBr single crystals via chemical potential modulation chemical vapor deposition (CPMCVD). By precisely modulating the oxygen chemical potential during growth, the conduction polarity of 2D BiOBr is controllably switched between p-type and n-type. Density functional theory calculations reveal that high oxygen chemical potential promotes bismuth vacancy formation, yielding p-type conductivity, whereas low oxygen chemical potential favors oxygen vacancies, resulting in n-type BiOBr. Field-effect transistors (FETs) fabricated from the p-type crystals exhibit a hole mobility of 26.28 cm2 V−1 s−1 and an on/off ratio exceeding 10^4. The n-type FETs demonstrate an electron mobility of 59.59 cm2 V−1 s−1, surpassing most reported n-type 2D FETs. This CPMCVD approach enables precise polarity control without extrinsic doping, offering a scalable route for integrating 2D BiOBr into CMOS technology.
1. Introduction
Silicon field-effect transistors face escalating short-channel effects, thermal dissipation limits, and manufacturing cost barriers as scaling approaches atomic dimensions. Two-dimensional (2D) semiconductors offer ultra-high carrier mobility, tunable bandgaps, and superior electrostatic control, positioning them as credible channel materials for post-Moore electronics. However, the commercial deployment of 2D CMOS is throttled by a stark imbalance: the vast majority of reported 2D semiconductors are n-type, while high-quality p-type counterparts remain scarce. This disparity originates from strong electron doping by interfacial charge impurities and intrinsic structural defects, which pin the Fermi level near the conduction band.
Existing polarity-control strategies—atomic doping, electric-field modulation, and mechanical strain—often degrade carrier mobility and impede electron injection at atomic interfaces. Chemical potential modulation during synthesis presents a more elegant alternative, yet few material systems have achieved polarity control solely through this route. This work demonstrates that by tuning the oxygen chemical potential in chemical vapor deposition, 2D BiOBr single crystals can be grown as either p-type or n-type without extrinsic dopants. The resulting p-type FETs deliver a hole mobility of 26.28 cm2 V−1 s−1 and on/off ratio >10^4, while n-type FETs reach an electron mobility of 59.59 cm2 V−1 s−1, establishing a scalable, doping-free pathway for 2D BiOBr in CMOS technology.
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YANG Yulong, FENG Liping, JIA Lingfeng, LIU Pengfei, ZENG Hui, PAN Haixi, WEN Yao (2025). Control of Conduction Polarity of BiOBr Single Crystal via Chemical Potential Modulation Chemical Vapor Deposition. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3571-y
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Frequently Asked Questions
What is the root cause of the mobility degradation typically observed when controlling polarity via extrinsic doping, and how does CPMCVD avoid it?
Extrinsic doping introduces ionized impurity scattering centers and interfacial defects that reduce carrier mobility and hinder electron injection. CPMCVD avoids these by modulating the oxygen chemical potential during growth, which selectively promotes bismuth vacancies (p-type) or oxygen vacancies (n-type) without adding foreign atoms. The resulting p-type FETs retain a hole mobility of 26.28 cm2 V−1 s−1 and on/off ratio >10^4, while n-type FETs achieve 59.59 cm2 V−1 s−1, demonstrating that polarity control is decoupled from mobility degradation.
How stable are the p-type and n-type BiOBr FETs under prolonged bias stress or ambient exposure?
The paper does not report bias-stress or long-term ambient stability data. However, the defect-engineering mechanism—bismuth vacancies for p-type and oxygen vacancies for n-type—suggests that stability depends on the thermodynamic stability of these vacancies under operating conditions. Future work must quantify threshold-voltage shifts and mobility degradation over time to assess commercial viability.
Can the CPMCVD process be scaled to wafer-level production while maintaining precise control over oxygen chemical potential?
The study demonstrates synthesis of large-scale 2D BiOBr crystals, but the paper does not provide wafer-scale uniformity data. Scaling CPMCVD requires precise spatial and temporal control of oxygen partial pressure across the growth substrate. The reported mobilities (26.28 and 59.59 cm2 V−1 s−1) were obtained from individual FETs; wafer-level uniformity and reproducibility remain unverified and represent a critical engineering hurdle.
What are the cost and throughput implications of CPMCVD compared to conventional doping or exfoliation methods for 2D semiconductors?
CPMCVD eliminates the need for extrinsic dopant sources and post-growth doping steps, potentially reducing process complexity and cost. However, the paper does not provide a techno-economic analysis. The throughput depends on reactor design and precursor delivery; current laboratory-scale CVD typically yields limited quantities. Cost parity with silicon CMOS will require demonstration of high-volume, roll-to-roll compatible growth.
How do the reported mobilities compare to state-of-the-art p-type and n-type 2D FETs, and what are the limiting scattering mechanisms?
The p-type hole mobility of 26.28 cm2 V−1 s−1 is competitive with other p-type 2D FETs, while the n-type electron mobility of 59.59 cm2 V−1 s−1 surpasses most reported n-type 2D FETs. Limiting scattering mechanisms likely include phonon scattering, charged impurity scattering from residual defects, and interface roughness. The paper does not provide temperature-dependent mobility data to isolate these contributions, which is necessary for further optimization.
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