Pressure-dependent bandgap study of MBE grown {CdO/MgO} short period SLs using diamond anvil cell
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-12-12 |
| Journal | Applied Physics Letters |
| Authors | A. Adhikari, PaweĆ StrÄ k, P. DĆuĆŒewski, Agata KamiĆska, E. PrzeĆșdziecka |
| Institutions | Polish Academy of Sciences, Institute of High Pressure Physics |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the pressure-dependent electronic properties of short-period {CdO/MgO} Superlattices (SLs) grown via Plasma-Assisted Molecular Beam Epitaxy (PA-MBE), demonstrating effective bandgap tuning using hydrostatic pressure.
- Core Achievement: Successful experimental determination of the pressure coefficient (PC) for the direct bandgap of {CdO/MgO} SLs using a Diamond Anvil Cell (DAC) technique.
- Bandgap Tuning: The direct bandgap was widened from 2.76 eV (ambient) to over 2.87 eV by applying hydrostatic pressure up to 5.9 GPa.
- Pressure Sensitivity: The experimental linear pressure coefficient (PC) for the direct (Gamma-Gamma) transition was found to be 26 meV/GPa, indicating strong pressure sensitivity.
- Theoretical Validation: Density Functional Theory (DFT) calculations (using GGA-1/2 correction) supported the experimental results, yielding a theoretical PC of 32 meV/GPa and a volume deformation potential of -5.05 eV.
- Transition Dominance: Analysis confirmed that the direct (Gamma-Gamma) transition dominates the optical behavior over the indirect (Gamma-L and Gamma-X) transitions in the pressure range studied.
- Application Insight: These findings provide crucial data for bandgap engineering and device optimization, particularly for future applications in optoelectronics and solid-state pressure sensors.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Ambient Direct Bandgap (Experimental) | 2.76 ± 0.002 | eV | {CdO/MgO} SLs (Zero Pressure) |
| Maximum Applied Pressure | 5.9 | GPa | Diamond Anvil Cell (DAC) |
| Bandgap Tuning Range | 2.76 to 2.87 | eV | Over 0 to 5.9 GPa pressure range |
| Direct Bandgap Pressure Coefficient (Experimental) | 26 ± 2 | meV/GPa | Gamma-Gamma transition |
| Direct Bandgap Pressure Coefficient (Theoretical) | 32 | meV/GPa | Ideal SLs (DFT calculation) |
| Volume Deformation Potential (Theoretical) | -5.05 | eV | Calculated for Gamma-Gamma transition |
| Bulk Modulus (B) of SLs (Theoretical) | 156.6 | GPa | Derived from Murnaghan EOS |
| Pressure Derivative of Bulk Modulus (Bâ) of SLs (Theoretical) | 4.75 | N/A | Derived from Murnaghan EOS |
| CdO Bulk Modulus (Literature Range) | 130 to 166 | GPa | Comparison data |
| MgO Bulk Modulus (Literature Range) | 171 to 186 | GPa | Comparison data |
| Linear Pressure Range (Direct Transition) | Up to 4.3 | GPa | Observed linear shift in optical bandgap |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Synthesis: Short-period {CdO/MgO} Superlattices (SLs) were grown on an r-plane (1-102) sapphire substrate using the Plasma-Assisted Molecular Beam Epitaxy (PA-MBE) technique.
- Structural Characterization: High-resolution transmission electron microscopy (HR-TEM) and Energy-Dispersive X-ray (EDX) mapping were used to confirm the layered structure and distinct separation of Cd and Mg elements.
- Ambient Optical Measurement: The zero-pressure direct bandgap was determined using UV-Vis spectroscopy at room temperature, applying Taucâs relation (n=1/2) for direct transition extrapolation.
- High-Pressure Experimentation: Hydrostatic pressure was applied to the SL samples using a Diamond Anvil Cell (DAC) technique, with pressure monitored via ruby luminescence.
- Bandgap Determination under Pressure: Absorption spectroscopy was performed inside the DAC. The direct bandgap was determined by extrapolating the linear portion of the absorption coefficient squared (alpha2) plot to the energy axis.
- Theoretical Modeling (DFT): Electronic band structure calculations were performed using the VASP code within the Density Functional Theory (DFT) framework, employing the modified GGA-1/2 correction method to accurately predict bandgap values.
- Mechanical Parameter Calculation: The bulk modulus (B) and its pressure derivative (Bâ) for the SLs were calculated by fitting the theoretical Pressure-Volume data to the Murnaghan equation of state.
- Deformation Potential Estimation: The hydrostatic volume deformation potential (av) was estimated using the empirical relation ap = -av/B, linking the pressure coefficient and bulk modulus.
Commercial Applications
Section titled âCommercial ApplicationsâThe demonstrated control over the bandgap of {CdO/MgO} SLs via pressure and material design is highly relevant for several advanced technological fields:
- Solid-State Pressure Sensors: The high and positive pressure coefficient (26 meV/GPa) for the direct bandgap transition makes these SLs excellent candidates for designing high-sensitivity, compact pressure sensors based on optical readout.
- Optoelectronics (UV/Blue Range): The ability to tune the bandgap between 2.76 eV and 2.87 eV allows for the fabrication of light-emitting diodes (LEDs) or photodetectors operating in the near-UV to blue visible spectrum.
- Bandgap Engineering: The flexible control over the electronic structure, achieved by alternating wide-bandgap MgO (7.5 eV) and narrow-bandgap CdO (2.23 eV), is fundamental for designing custom semiconductor heterostructures.
- Ultrafast Electronics: As oxide heterojunctions, these materials are foundational for emerging technologies requiring high-speed operation and novel functionalities.
- Quantum Technology: The precise control over electronic band structure in SLs is a key requirement for developing certain quantum devices and components.
View Original Abstract
Semiconductor superlattices (SLs) have found widespread applications in electronic industries. In this work, a short-period SL structure composed of CdO and MgO layers was grown using a plasma-assisted molecular beam epitaxy technique. The optical property of the SLs was investigated by absorption measurement at room temperature. The ambient-pressure direct bandgap was found to be 2.76 eV. The pressure dependence of fundamental bandgap has been studied using a diamond anvil cell technique. It has been found that the band-to-band transition shifts toward higher energy with an applied pressure. The bandgap of SLs was varied from 2.76 to 2.87 eV with applied pressure varied from 0 to 5.9 GPa. The pressure coefficient for the direct bandgap of SLs was found to be 26 meV/GPa. The obtained experimental result was supported by theoretical results obtained using density functional theory calculations. The volume deformation potential was estimated using the empirical rule. We believe that our findings may provide valuable insight for a better understanding of {CdO/MgO} SLs toward their future applications in optoelectronics.