Abstract
Oxide semiconductors are key materials in many technologies from flat‐panel displays，solar cells to transparent electronics. However, many potential applications are hindered by the lack of high mobility p‐type oxide semiconductors due to the localized O‐2p derived valence band (VB) structure. In this work, the VB structure modulation is reported for perovskite Ba2BiMO6 (M = Bi, Nb, Ta) via the Bi 6s2 lone pair state to achieve p‐type oxide semiconductors with high hole mobility up to 21 cm2 V−1 s−1, and optical bandgaps widely varying from 1.5 to 3.2 eV. Pulsed laser deposition is used to grow high quality epitaxial thin films. Synergistic combination of hard x‐ray photoemission, x‐ray absorption spectroscopies, and density functional theory calculations are used to gain insight into the electronic structure of Ba2BiMO6. The high mobility is attributed to the highly dispersive VB edges contributed from the strong coupling of Bi 6s with O 2p at the top of VB that lead to low hole effective masses (0.4–0.7 m e). Large variation in bandgaps results from the change in the energy positions of unoccupied Bi 6s orbital or Nb/Ta d orbitals that form the bottom of conduction band. P–N junction diode constructed with p‐type Ba2BiTaO6 and n‐type Nb doped SrTiO3 exhibits high rectifying ratio of 1.3 × 104 at ±3 V, showing great potential in fabricating high‐quality devices. This work provides deep insight into the electronic structure of Bi3+ based perovskites and guides the development of new p‐type oxide semiconductors.
Highlights
Oxide semiconductors are being extensively used as key materials in modern optoelectronics technologies including flat panel displays, solar cells, light emitting diodes, and transparent electronics.[1]
X-ray diffraction (XRD) θ–2θ out-ofplane scans in Figure 2a and Figure S1 (Supporting Information) and reciprocal space mapping (RSM) in Figure S2 (Supporting Information) indicate the epitaxial growth of Ba2BiMO6 thin films grown on both SrTiO3 and MgO substrates
Our research reveals the origin of an observed dispersive valence band (VB) and resulted high hole mobility of Ba2BiMO6 perovskites by investigating their bandgap modulation and electronic structure
Summary
Oxide semiconductors are being extensively used as key materials in modern optoelectronics technologies including flat panel displays, solar cells, light emitting diodes, and transparent electronics.[1] Oxides such as ZnO, In2O3, Ga2O3, and SnO2 are typical wide bandgap n-type semiconductors, in which the filled oxygen 2p6 orbitals form the valence band (VB), and the spatially extended metal s orbitals form the conduction band (CB), giving rise to a dispersive CB with a high electron mobility. The development of high mobility p-type oxide semiconductors remains challenging.[2] The lack of p-type oxide semiconductors severely hinders the development of many crucial technologies, e.g., p-channel thin film transistors (TFT) and CMOS inverters for high-resolution energy-saving displays; p-type semiconductor layers for efficient hole transport in photovoltaics and visible-light active photocathodes for solar water splitting.[2a,3]. Li MIIT Key Laboratory of Aerospace Information Materials and Physics College of Science Nanjing University of Aeronautics and Astronautics Nanjing 211106, China
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