Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session W68: Developments in First-Principles Computations of Defects in Condensed MatterInvited
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Sponsoring Units: DCOMP Chair: John Lyons, United States Naval Research Laboratory Room: Room 420 |
Thursday, March 9, 2023 3:00PM - 3:36PM |
W68.00001: Effects of spin-orbit coupling and very large supercells on the description of acceptors in CdTe Invited Speaker: Anderson Janotti Predicting accurate shallow donor and acceptor levels in semiconductors has been quite challenging using periodic boundary conditions as implemented in current density functional theory codes. The reason is that the wave functions associated with the shallow centers are quite extended and are not fully contained in the supercell (typically with a few hundred atoms) so impurities in the periodically repeated image cells interact with each other. Errors of ~0.1 eV are expected, and these are of the same order of magnitude as the ionization energies themselves. In the case of acceptors in CdTe, this problem is exacerbated by the strong spin-orbit coupling that split the Te-related states at the top of the valence band, making the calculations at least 8 times more expensive. CdTe is an important solar-cell material with record high efficiency of 22%. One of the main limiting factors to increasing the efficiency towards the theoretical limit of ~30% is the often reported very low hole concentration. Pushing to the limit of computational capability by using very large supercells with spin-orbit coupling we report the results of hybrid functional calculations of group-V acceptors in CdTe. We show that extrapolation to the dilute limit leads to an interpretation of the experimental data that is qualitatively different from previous DFT and hybrid functional calculation reports. We find that the group-V impurities indeed behave as shallow acceptors and that the corresponding compensating AX-centers are unstable and do not limit p-type doping. We address the differences between our results and previous theoretical predictions and show that our calculated ionization energies predict hole concentrations that are in excellent agreement with recent temperature-dependent Hall measurements on high-quality single-crystal samples. |
Thursday, March 9, 2023 3:36PM - 4:12PM |
W68.00002: Ab initio calculations of defects at surfaces Invited Speaker: Christoph Freysoldt Charged defects at surfaces and interfaces play an important role in (opto)electronic devices, as these may induce large-scale electric fields, which may be essential or detrimental for device performance. Identifying the relevant defects and characterizing their properties is experimentally difficult. Theoretical calculations within density-functional theory aim at filling this gap. Yet, specific challenges arise in these calculations, not least by the challenge to link small-scale atomistic models to the device-scale electric effects. This becomes even more challenging as we move towards single-layer “2D” materials for future devices. |
Thursday, March 9, 2023 4:12PM - 4:48PM |
W68.00003: Computation-Guided Design And Discovery Of Dopable Thermoelectric Materials: How Well We Can Do And What Is Missing Invited Speaker: Elif Ertekin My presentation will highlight our recent attempts to make the computation-experiment handshake applied to the design and discovery of thermoelectric materials. Focusing on the design space of diamond like semiconductors and ordered vacancy compounds, we will highlight the importance of both intrinsic material properties and dopability in computation-guided search for new materials. We will demonstrate how computational predictions can be directly evaluated by experiment using phase boundary mapping, how computational modeling leads to design principles for identification of candidate dopable thermoelectrics, and patterns between structure, defect chemistry, and material dopability in diamond like and ordered vacancy compounds. Finally, we'll discuss where computational approaches have success and what aspects are missing and should be realized to enable true computation-guided thermoelectric materials design and optimization. |
Thursday, March 9, 2023 4:48PM - 5:24PM |
W68.00004: First-principles study of surface kinetics in β-Ga2O3 Invited Speaker: Mengen Wang Monoclinic β-Ga2O3 is a wide-gap (4.8 eV) semiconductor with a high breakdown field. To achieve high-quality Ga2O3 with n-type conductivity, several challenges still remain, including suboxide desorption that hinders the epitaxial growth rate and understanding the incorporation sites of Al, Si, and Sn in the Ga2O3 lattice for alloying and doping. I will discuss the origin of these challenges by unveiling the role of kinetics during the growth, including surface reconstructions under different growth conditions and adatom diffusion. Indium has been used to achieve a higher growth rate and better crystal quality during the epitaxial growth of Ga2O3. I will show the adsorption of Ga and In adatoms on the Ga2O3 (010) surface and the effect of In on the growth rate [1]. The applications of Ga2O3 in power electronics and field-effect transistors require heterostructures with a larger-gap material. As the bandgap of Al2O3 is larger than Ga2O3, there is a growing need of the epitaxial growth of (AlxGa1−x)2O3 alloys that forms heterojunctions with Ga2O3. I will show the co-adsorption of Al, Ga, and O adatoms on the Ga2O3 (010) surface reveals the role of surface reconstructions and adatom diffusion in the Al incorporation sites in the (AlxGa1−x)2O3 alloys [2,3]. Similarly, I will also discuss how surface kinetics can affect the incorporation sites of Si and Sn in β-Ga2O3, which are usually used as shallow donors that contribute the n-type conductivity of Ga2O3 [4]. |
Thursday, March 9, 2023 5:24PM - 6:00PM |
W68.00005: First-principles calculations on quantum defects in silicon Invited Speaker: Péter Udvarhelyi Silicon is an excellent platform for quantum defects owing to the advanced growth and fabrication techniques readily available in this material, offering an ideal environment for the spin and optical properties of the hosted defects. Moreover, several known emitter defects in silicon operate in the telecommunication wavelengths. The recent experimental advancements in the isolation and manipulation of these defects calls for an in-depth identification using high level first-principles calculations. |
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