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Electronic and optical properties of ultrawide bandgap perovskite semiconductors via first principles calculations

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2020-12-07
JournalApplied Physics Letters
AuthorsRadi A. Jishi, Robert J. Appleton, David M. Guzman, Radi A. Jishi, Robert J. Appleton
InstitutionsCalifornia State University Los Angeles, Purdue University West Lafayette
Citations20
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This study uses first-principles calculations to investigate the electronic and optical properties of novel barium-based perovskites, proposing them as candidates for Ultrawide Bandgap (UWBG) semiconductors.

  • Novel UWBG Materials Proposed: Two novel perovskites, Ba2CaTeO6 (double perovskite) and Ba2K2Te2O9 (triple perovskite), are introduced to the UWBG family, expanding beyond traditional Ga- and Al-based materials.
  • High Bandgap Confirmation: Hybrid functional calculations (HSE06) predict bandgaps significantly exceeding the 3.4 eV threshold of GaN, with Ba2CaTeO6 reaching 5.24 eV.
  • Direct Bandgap Advantage: Unlike the reference material BaZrO3 (indirect gap), both novel perovskites exhibit a desirable direct bandgap transition at the Γ-point, enhancing their potential for optoelectronic devices.
  • Deep-UV Capability: All studied materials show strong optical absorption in the deep-UV region, making them suitable for specialized optoelectronic applications.
  • Critical Doping Challenge: A major limitation is identified: holes exhibit a strong tendency toward self-trapping through lattice distortions near oxygen atoms.
  • Self-Trapping Energy Barrier: The calculated hole self-trapping energy (EST) is consistently around 0.25 eV, indicating that achieving enhanced p-type conductivity via traditional chemical doping methods will be highly challenging.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Bandgap (HSE06)5.24eVBa2CaTeO6 (Novel, Direct)
Bandgap (HSE06)4.65eVBa2K2Te2O9 (Novel, Direct)
Bandgap (HSE06)4.90eVBaZrO3 (Reference, Indirect)
Hole Self-Trap Energy (EST)0.247 to 0.256eVEnergy required to stabilize a hole polaron (across all three materials).
Lattice Constant (a)4.19ABaZrO3 (Simple Cubic structure)
Lattice Constant (a)8.3536ABa2CaTeO6 (Face-Centered Cubic structure)
Lattice Constants (a, c)6.047, 16.479ABa2K2Te2O9 (Hexagonal structure)
Valence Band DominanceO-2pOrbitalsUpper valence bands in all three crystals.
Conduction Band ContributionZr-4d or Te-5sOrbitalsLowest conduction band contribution, depending on the material.
VASP Energy Cutoff400eVUsed for hole trapping calculations.

Key Methodologies

Section titled “Key Methodologies”

The electronic, optical, and defect properties were determined using advanced first-principles computational methods:

  1. Electronic Structure Calculation: Calculations were performed using the all-electron, full potential, linear augmented plane wave (FLAPW) method, as implemented in the WIEN2k code.
  2. Potential Selection: The hybrid functional HSE06 (Heyd-Scuseria-Ernzerhof) potential was employed for accurate bandgap prediction, overcoming the limitations of standard PBE (Perdew-Burke-Ernzerhof) potentials.
  3. Wave Function Parameters: Computational convergence was ensured by setting the wave vector cutoff RmtKmax = 7 and expanding the charge density up to Gmax = 12 Ry1/2.
  4. Hole Self-Trapping (Polaron) Study: Hole trapping calculations utilized the HSE06 potential within the VASP code, employing Projector Augmented Wave (PAW) potentials for core-valence interaction.
  5. Supercell Construction: Large, optimized supercells were used to model localized defects (small polarons):
    • BaZrO3: 3x3x3 supercell (135 atoms).
    • Ba2CaTeO6: 80 atoms (doubled conventional unit cell).
    • Ba2K2Te2O9: 2x2x1 supercell (120 atoms).
  6. EST Calculation: The hole self-trapping energy (EST) was calculated by comparing the total energy of a system with a delocalized hole (E1) versus the energy of the system after atomic relaxation around an oxygen atom, stabilizing the localized hole (E2). EST = E1 - E2.

Commercial Applications

Section titled “Commercial Applications”

The predicted properties of these UWBG perovskites make them highly relevant for next-generation high-performance electronic and optoelectronic devices:

  • High-Power RF Electronics: UWBG materials are essential for high-frequency applications, offering superior performance figures of merit (like the Johnson figure of merit) compared to conventional semiconductors.
  • Deep-UV Optoelectronics: The strong optical absorption in the ultraviolet region (bandgaps > 4.5 eV) positions these materials for use in deep-UV light-emitting diodes (LEDs), photodetectors, and sterilization equipment.
  • High-Voltage Power Switching: Due to their wide bandgaps, these materials are candidates for high-voltage, low-loss power switches, leveraging the high Baliga figure of merit.
  • Advanced Semiconductor Doping Research: The identified challenge of hole self-trapping provides a critical focus area for materials engineers developing non-traditional doping techniques (e.g., metal-semiconductor junction assisted epitaxy) necessary to realize functional p-type UWBG devices.
  • Alternative Substrate/Active Layer Materials: These perovskites offer a new class of chemistries and structures, providing alternatives to traditional AlGaN/AlN and Ga2O3 systems for UWBG device fabrication.
View Original Abstract

Recent research in ultrawide-bandgap (UWBG) semiconductors has focused on traditional materials such as Ga2O3, AlGaN, AlN, cubic BN, and diamond; however, some materials exhibiting a single perovskite structure have been known to yield bandgaps above 3.4 eV, such as BaZrO3. In this work, we propose two materials to be added to the family of UWBG semiconductors: Ba2CaTeO6 exhibiting a double perovskite structure and Ba2K2Te2O9 with a triple perovskite structure. Using first-principles hybrid functional calculations, we predict the bandgaps of all the studied systems to be above 4.5 eV, with strong optical absorption in the ultraviolet region. Furthermore, we show that holes have a tendency to get trapped through lattice distortions in the vicinity of oxygen atoms, with an average trapping energy of 0.25 eV, potentially preventing the enhancement of p-type conductivity through traditional chemical doping.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2001 - Nobel Lecture: Quasielectric fields and band offsets: Teaching electrons new tricks [Crossref]
  2. 2015 - The blue LED Nobel Prize: Historical context, current scientific understanding, human benefit [Crossref]
  3. 2013 - History of gallium-nitride-based light-emitting diodes for illumination [Crossref]
  4. 2011 - Solid-state lighting: ‘The case’ 10 years after and future prospects [Crossref]
  5. 2018 - Ultrawide-bandgap semiconductors: Research opportunities and challenges [Crossref]
  6. 1982 - Semiconductors for high-voltage, vertical channel field-effect transistors [Crossref]
  7. 1965 - Physical limitations on frequency and power parameters of transistors [Crossref]
  8. 2012 - Role of self-trapping in luminescence and p-type conductivity of wide-band-gap oxides [Crossref]
  9. 2018 - Self-trapped holes in BaTiO3 [Crossref]
  10. 2019 - Enhanced doping efficiency of ultrawide band gap semiconductors by metal-semiconductor junction assisted epitaxy [Crossref]

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