Large substitutional impurity isotope shift in infrared spectra of boron-doped diamond
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-10-16 |
| Journal | Physical review. B./Physical review. B |
| Authors | D. D. Prikhodko, С.Г. Павлов, С. А. Тарелкин, В. С. Бормашов, М. С. Кузнецов |
| Institutions | Humboldt-Universität zu Berlin, All-Russian Research Institute for Optical and Physical Measurements |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”The research successfully resolved the isotopic splitting of boron (B) intracenter transitions in high-purity, boron-doped diamond (BDD) using high-resolution infrared absorption spectroscopy (IRAS).
- Isotope Splitting Resolved: The spectral lines corresponding to 10B and 11B isotopes were clearly differentiated, exhibiting a constant energy separation (chemical shift) of 0.70 ± 0.03 meV.
- Record Impurity Shift: This measured shift is the largest impurity isotopic shift ever observed in semiconductors doped by hydrogen-like impurity centers.
- Methodology: High-quality single-crystal BDD samples were grown via the High Pressure High Temperature (HPHT) method, utilizing both natural (80% 11B, 20% 10B) and isotopically enriched (up to 99% 11B) dopant sources.
- Line Broadening Analysis: The absorption lines exhibited a quasi-Lorentzian shape, indicating that homogeneous broadening (likely due to effective multi-phonon to impurity interaction) dominates, even at low concentrations (down to 1016 cm-3).
- Excited State Dynamics: Determined linewidths (FWHM) allowed for the estimation of excited state lifetimes (τ) ranging from 1 to 9 ps.
- Quantification of Transitions: Accurate determination of absorption line intensities, integrated cross-sections (σ0), and oscillator strengths (f) was achieved for 25 distinct 11B intracenter transitions originating from the 1Γ8+ ground state.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Isotopic Splitting (10B vs 11B) | 0.70 ± 0.03 | meV | Energy separation of intracenter transitions. |
| Boron Ionization Energy (Ei) | ~372 | meV | Commonly accepted binding energy of the acceptor center. |
| Spin-Orbit (SO) Splitting (Ground State) | ~2 | meV | Splitting between 1Γ8+ and 1Γ7+ ground states. |
| Boron Concentration Range (N) | 7·1015 to 3·1017 | cm-3 | Uncompensated B concentration in samples (40 ppb - 2 ppm). |
| Spectrometer Resolution | 0.03 (0.25) | meV (cm-1) | Resolution used for high-resolution IR spectra. |
| Measurement Temperature | 5 | K | Lowest temperature used to minimize thermal broadening and isolate 1Γ8+ transitions. |
| Excited State Lifetimes (τ) | 1 - 9 | ps | Estimated from FWHM using the uncertainty principle. |
| Hole Effective Mass (m)* | 0.63m0 | - | Value used for calculating oscillator strengths (m0 is free electron mass). |
| Integrated Absorption Cross Section (Max) | 86.8·10-16 | cm | For the strongest transition (State 7, 349.39 meV). |
| Oscillator Strength (Max) | 62.0·10-5 | - | For the strongest transition (State 7, 349.39 meV). |
Key Methodologies
Section titled “Key Methodologies”The study relied on precise material synthesis and high-resolution cryogenic spectroscopy to isolate and quantify the subtle isotopic effects.
- Material Growth (HPHT TGM): Single-crystal boron-doped diamonds (SCBDD) were grown using the Temperature Gradient Method (TGM) under High Pressure High Temperature (HPHT) conditions.
- Isotopic Doping Control:
- Natural Boron: Standard amorphous boron powder (80% 11B + 20% 10B).
- Enriched Boron: Boron oxide (B2O3) enriched up to 99% 11B isotope.
- Sample Preparation: (001)-oriented plates (~300 µm thick) were laser-cut from the crystal top. Plates were double-side polished with a wedge of ~1° to suppress optical interference effects.
- Concentration Determination: Boron concentration was estimated from 300 K absorption spectra using empirical integrated absorption calibration on neutral acceptor density.
- Infrared Spectroscopy: A Bruker Vertex 80vTM Fourier-transform spectrometer was used, equipped with a Janis flow helium cryostat to achieve temperatures down to 5 K.
- Spectral Analysis:
- Spectra were normalized using the two-phonon band of an undoped IIa diamond (270 meV to 330 meV).
- Absorption lines were approximated using a Lorentz function (after initial Voigt fitting confirmed dominant uniform broadening) to accurately determine the Full Width at Half Maximum (FWHM).
- Integrated absorption cross-sections (σ0) and oscillator strengths (f) were calculated using the determined line area integrals and the known boron concentration.
Commercial Applications
Section titled “Commercial Applications”The precise control and characterization of boron acceptor states in diamond are critical for developing high-performance electronic and optoelectronic devices.
- Diamond Electronics (p-type): Boron is the primary p-type dopant in diamond. Accurate knowledge of the energy structure and transition strengths is essential for optimizing conductivity and device performance in high-power and high-frequency applications (e.g., MOSFETs, diodes).
- Optoelectronics and IR Detection: The discrete intracenter transitions (330-376 meV range) are relevant for mid-infrared (MIR) applications. Understanding the line broadening and lifetimes (1-9 ps) is crucial for designing fast, efficient MIR detectors and potentially achieving population inversion for light emission.
- Isotopic Engineering: The ability to resolve and control isotopic shifts (0.7 meV) allows for the use of isotopically pure diamond (e.g., 12C or 11B) to minimize spectral broadening, which is vital for high-coherence quantum applications or high-resolution spectroscopy.
- Fundamental Physics Modeling: The derived experimental data (cross-sections, oscillator strengths, energy levels) provides a necessary impulse for developing accurate theoretical models of the boron acceptor energy structure, which is currently lacking compared to Si and Ge.
View Original Abstract
Isotopic enrichment offers cutting-edge properties of materials opening exciting research and development opportunities. In semiconductors, reached progress of ultimate control in growth and doping techniques follows nowadays the high level isotopic purification. This requires deep understanding of isotopic disorder effects and techniques of their effective determination. Isotopic content of both crystal lattice and impurity centers cause the effects, which can be examined by different optical techniques. While disorder in the host lattice can be straight forward evaluated by inelastic light scattering or by SIMS measurements, determination of isotopic contributions of many orders less presented impurities remains challenging and usually observed in high-resolution photoluminescence or optical absorption spectra. Boron-doped diamonds exhibit complex infrared absorption spectra while boron-related luminescence remains unobserved. Boron, as a most light element acting as a hydrogen-like dopant in elemental semiconductors, has a largest relative difference in its isotope masses, and by this, cause the largest isotopic disorder in semiconductors, including diamond, an elemental semiconductor with the lightest atomic mass of a host lattice. This enables an access to the isotopic constitution of boron in diamond by infrared absorption spectroscopy. By comparison of low-temperature absorption spectra of a natural (20% of 10B and 80% of 11B isotopes) and 11B enriched (up to 99%) doped diamonds we differentiate the intracenter transitions related to 10B and to 11B isotopes. We have found that the isotopic spectral lines of the same boron intracenter transition are separated with the energy of about 0.7 meV. This is the largest impurity isotopic shift ever observed in semiconductors doped by hydrogen-like impurity centers.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 2012 - Handbook of Spectral Lines in Diamond [Crossref]