Periodic Reporting for period 1 - SPOTTED (Spin Polarized Transport in Transfer Doped Diamond Wafers)
Reporting period: 2023-06-01 to 2025-05-31
Due to advancements in techniques for growing high-purity, single-crystal synthetic diamonds and their unique physiochemical properties, including an ultra-wide bandgap of 5.47 eV, diamonds are now being considered as the next-generation material for a wide range of applications, including high-power, high-temperature, and high-frequency electronics, quantum computing, sensing, and communication. Given the temperature-independent conductivity and the potential to generate high hole carrier concentrations and spin-orbit coupling (SOC) through electron acceptors, it is essential to conduct a systematic investigation into the possibilities of spin-polarized transport in a 2D hole gas (2DHG) formed on transfer-doped hydrogen-terminated diamond surfaces. In our project, we aim to assess the strength of SOC in transfer-doped diamond through magnetotransport and ferromagnetic resonance studies. We also plan to explore the feasibility of spin injection and spin-polarized transport through Hanle measurements and the Rashba-Edelstein Effect. Additionally, we intend to introduce 2D-hBN between the transfer dopants and the diamond surfaces to minimize carrier scattering caused by electron acceptors in close proximity to the 2DHG, which could lead to spin depolarization. Furthermore, to gain insights into the spin asymmetry of the 2DHG during the scattering process, we propose characterizing the samples using time-domain THz spectroscopy at various scattering timescales. These studies are expected to drive extensive research in the future, and the realization of spin-polarized transport in diamond wafers offers a robust materials system for spintronics devices, enabling the development of faster and more efficient microelectronic devices that can operate even in extreme environments.
In the first three months of the project, as proposed, we successfully hydrogenated the single-crystal diamond wafers, creating a 2D hole gas with a hole carrier concentration ranging from approximately 1.8 x 10^13 cm^-2 to 2.5 x 10^14 cm^-2, within the first 10 nm from the diamond surface. This doping was achieved through the exposure of hydrogenated diamond wafers to the atmosphere and a 12 nm-thick deposition (sputtering) of a metal oxide layer, such as Al2O3. We are currently conducting various charge and spin transport studies, including Hall transport measurements from room temperature up to 2K, bilinear magnetoresistance measurements, Ferromagnetic Resonance measurements (FMR), Spin Torque Ferromagnetic Resonance (STFMR), and, last but not least, THz time-domain spectroscopy to examine carrier transport at carrier scattering timescales under the influence of magnetic fields.
The specific objectives and work completed under each category are outlined in the following section:
1. Prepare Hydrogen terminated CVD grown diamond wafers and transfer dope via atmospheric adsorbates and MoO3 and reduce carrier scattering by applying 2D-hBN between diamond surface and electron acceptors
Hydrogenation of single crystal diamond wafers has been successfully completed through plasma CVD approach and were doped by means of exposing the hydrogenated surfaces to atmospheric adsorbates and by depositing metal oxide layer (Al2O3) of 12 nm thickness. Carrier concentration studies are underway. Although the program is ended, we will still be attempting to transfer hBN layer between transfer dopants and hydrogenated diamond surface to study the variation in the carrier mobility there off.
Figure 1. Schematic showing the prepared samples for charge and spin transport studies (a) hydrogenated diamond surface with atmospheric adsorbates (b) Hydrogenated diamond surface with metal oxide film, Al2O3 with 12 nm thicknesses.
2. Estimate and experimentally validate the influence of Dresselhaus and Rashba effect contributions towards the total spin-orbit coupling and examine control and tunability of SOC by a gate electrode via the Rashba effect.
Experiments such as bilinear magnetoresistance, ferromagnetic resonance (FMR) and THz-TDS with and without magnetic field are underway to quantify the strength of SoC in transfer doped diamond and study the possibility of spin injection and transport.
3. Inject spin polarized current via magnetic/spin hall materials, produce spin polarized transport in diamond via
inverse spin galvanic effect (iSGE)/REE and study the spin dynamics of 2DHG via Hanle measurements.
Not attempted yet.
4. Perform magneto-transport measurements at carrier scattering times scales (sub-100 fs) via THz electromagnetic
probes with and without applied magnetic fields.
THz-TDS spectroscopy is performed on pristine diamond, transfer doped diamond wafers (with atmospheric adsorbates and metal oxides as transfer dopant) and B doped bulk diamond for its optical, electrical and electronic properties. Post experiment analysis and comparison studies are underway.
The specific objectives and work completed under each category are outlined in the following section:
1. Prepare Hydrogen terminated CVD grown diamond wafers and transfer dope via atmospheric adsorbates and MoO3 and reduce carrier scattering by applying 2D-hBN between diamond surface and electron acceptors
Hydrogenation of single crystal diamond wafers has been successfully completed through plasma CVD approach and were doped by means of exposing the hydrogenated surfaces to atmospheric adsorbates and by depositing metal oxide layer (Al2O3) of 12 nm thickness. Carrier concentration studies are underway. Although the program is ended, we will still be attempting to transfer hBN layer between transfer dopants and hydrogenated diamond surface to study the variation in the carrier mobility there off.
Figure 1. Schematic showing the prepared samples for charge and spin transport studies (a) hydrogenated diamond surface with atmospheric adsorbates (b) Hydrogenated diamond surface with metal oxide film, Al2O3 with 12 nm thicknesses.
2. Estimate and experimentally validate the influence of Dresselhaus and Rashba effect contributions towards the total spin-orbit coupling and examine control and tunability of SOC by a gate electrode via the Rashba effect.
Experiments such as bilinear magnetoresistance, ferromagnetic resonance (FMR) and THz-TDS with and without magnetic field are underway to quantify the strength of SoC in transfer doped diamond and study the possibility of spin injection and transport.
3. Inject spin polarized current via magnetic/spin hall materials, produce spin polarized transport in diamond via
inverse spin galvanic effect (iSGE)/REE and study the spin dynamics of 2DHG via Hanle measurements.
Not attempted yet.
4. Perform magneto-transport measurements at carrier scattering times scales (sub-100 fs) via THz electromagnetic
probes with and without applied magnetic fields.
THz-TDS spectroscopy is performed on pristine diamond, transfer doped diamond wafers (with atmospheric adsorbates and metal oxides as transfer dopant) and B doped bulk diamond for its optical, electrical and electronic properties. Post experiment analysis and comparison studies are underway.
Although, program is ended early, the proposed experiments were being conducted at JGU, and this section will be populated as appropriate if there is an option available to do so.