Our main focus is the analysis of point-defects in Wide Band Gap semiconductors. We first study them from first principles through the use of ab initio methods based on Density Functional Theory, and then utilize other means of analysis for finding possible applications in the realm of nanoelectronics (defect-free Al2O3/AlGaN capacitors) or Quantum Technologies (point-defects in 4H- and 3C-SiC having a large decoherence time). E.g., after a defect’s model Hamiltonian ab initio calibration, we shed light on the coherent dynamics of such systems (in the bulk or confined in 3D nanostructures). The defects’ atomic structures are well-characterized and optimized during the calibration phase by using the Quantum Espresso code. Silicon Carbide and Gallium Nitride are the Wide Band Gap semiconductors we study from the point of view of Quantum Technologies and nanoelectronics, respectively. For what concerns nanoelectronics, we examine the deleterious effect Frenkel defects could play in Al2O3/AlGaN junctions. Al2O3/AlGaN Metal Oxide Semiconductor capacitors show a hysteretic behavior in their Capacitance vs Voltage characteristics, often attributed to near-interface traps deriving from defects within the oxide layer. The origin as well as the structural/electronic properties of such defects are still strongly debated in the literature. In our research we use ab initio molecular dynamics and the climbing-image nudged elastic band method to show that Aluminum Frenkel defects give rise to bistable trap states in disordered and stoichiometric Al2O3. Based on these results, we propose a calibrated polaron model representing a distribution of individually interacting energy levels with an internal reconfiguration mode and coupled to continuous bands of carriers to explain the hysteresis mechanism in Al2O3/AlGaN capacitors. As for Quantum Technology, we propose a defect whose experimental identification is yet to be accomplished, i.e. the neutral silicon vacancy in 3C-SiC. We study the silicon vacancy (SiV) in 3C-SiC as a promising color center, modeling it as an electron spin (behaving as a qubit in appropriate conditions) magnetically interacting with the SiC nuclear spin bath containing Si-29 and C-13 nuclei in their natural isotopic concentration. We calculate the energetics of the neutral and charged SiV with ab initio methods, identifying its neutral charge state as the most favorable for p-doped 3C-SiC systems. Magnetic properties are calculated as well for the neutral SiV in 3C- and 4H-SiC, both in the k and h crystal sites, and the results are compared. We thereby evaluate the Free Induction Decay and the Hahn-echo sequence of control pulses on the electron spin interacting with the nuclear spin bath. We shed light on the Electron Spin Echo Envelope Modulation phenomenon and the decoherence effect by means of the Cluster Correlation Expansion theory. We find a non-exponential coherence decay, which is a typical feature of solid-state qubits. We extend the outlined analysis to silicon vacancies in different 3C-SiC nanoparticles for Quantum Sensing applications. We apply the Hahn-echo sequence to the electron spin interacting with the nuclear spin bath and use the Cluster Correlation Expansion theory (by assumption) to calculate the coherence of the total system. We analyze several nanoparticle shapes as environments for the qubit. We apply the thermodynamic Wulff construction, both the original and the modified one, to determine the proper 3C-SiC nanoparticle shape in thermodynamic equilibrium and after a particular growth process has been followed, respectively. We modify Masullo’s Kinetic Crystal Shape until we find two visibly different structures. Furthermore, we show that in a pyramidal nanoparticle the qubit behaves differently far from the tip as opposed to near it. We find that the qubit within the most peaked nanoparticles is more sensitive to the bath configuration with respect to the other shapes.
Il nostro obiettivo principale è l'analisi dei difetti di punto nei semiconduttori a larga banda. Li studiamo dapprima da principi primi attraverso l'uso di metodi ab initio basati sulla teoria del funzionale densità, quindi utilizziamo altri mezzi di analisi per trovare possibili applicazioni nel reame della nanoelettronica (condensatori Al2O3/AlGaN privi di difetti) o tecnologie quantistiche (difetti di punto in 4H- e 3C-SiC aventi un tempo di decoerenza elevato). Ad esempio, dopo la calibrazione ab initio del modello hamiltoniano di un difetto, siamo riusciti a far luce sulla dinamica coerente di tali sistemi (nel bulk del materiale o confinati in nanostrutture 3D). Le strutture atomiche dei difetti sono ben caratterizzate e ottimizzate durante la fase di calibrazione utilizzando il codice Quantum Espresso. Il Carburo di Silicio e il Nitruro di Gallio sono i semiconduttori a larga banda che studiamo rispettivamente dal punto di vista delle Tecnologie Quantistiche e della nanoelettronica. Per quanto riguarda la nanoelettronica, esaminiamo l'effetto deleterio che i difetti di Frenkel potrebbero avere nelle giunzioni Al2O3/AlGaN. I condensatori basati sul dispositivo metallo-ossido-semiconduttore Al2O3/AlGaN mostrano un comportamento isteretico nelle loro caratteristiche di capacità vs voltaggio, spesso attribuito a trappole vicine all'interfaccia derivanti da difetti all'interno dello strato di ossido. L'origine e le proprietà strutturali/elettroniche di tali difetti sono ancora fortemente dibattute in letteratura. Nella nostra ricerca utilizziamo la dinamica molecolare ab initio e il metodo Nudged Elastic Band (NEB) arrampica-immagine per mostrare che i difetti di Frenkel di alluminio danno origine a stati trappola bistabili in Al2O3 disordinato e stechiometrico. Sulla base di questi risultati, proponiamo un modello polaronico calibrato che rappresenta una distribuzione di livelli di energia interagenti individualmente con un modo di riconfigurazione interna e accoppiato a bande continue di portatori per spiegare il meccanismo di isteresi nei condensatori Al2O3/AlGaN. Per quanto riguarda la tecnologia quantistica, proponiamo un difetto la cui identificazione sperimentale deve ancora essere effettuata, ossia la vacanza di silicio neutra in 3C-SiC. Studiamo la vacanza di silicio (SiV) in 3C-SiC come un promettente centro di colore, modellandolo come uno spin elettronico (che si comporta come un qubit in condizioni appropriate) che interagisce magneticamente con il bagno di spin nucleari in SiC contenente i nuclei Si-29 e C-13 nella loro naturale concentrazione isotopica. Calcoliamo l'energetica della SiV neutra e carica con metodi ab initio, identificando il suo stato di carica neutro come il più favorevole per i sistemi 3C-SiC drogati p. Vengono anche calcolate le proprietà magnetiche per la SiV neutra in 3C- e 4H-SiC, sia nei siti cristallini k che h, e i risultati vengono confrontati. Valutiamo quindi il Free Induction Decay e la sequenza Hahn-echo degli impulsi di controllo sullo spin elettronico che interagisce con il bagno di spin nucleari. Facciamo luce sul fenomeno Electron Spin Echo Envelope Modulation e sull'effetto di decoerenza mediante la teoria Cluster Correlation Expansion. Troviamo un decadimento della coerenza non esponenziale, che è una caratteristica tipica dei qubit a stato solido. Estendiamo l'analisi delineata alle vacanze di silicio in diverse nanoparticelle 3C-SiC per applicazioni in Quantum Sensing. Applichiamo la sequenza Hahn-echo allo spin elettronico che interagisce con il bagno di spin nucleari e usiamo la teoria Cluster Correlation Expansion (per ipotesi) per calcolare la coerenza del sistema totale. Analizziamo diverse forme di nanoparticelle come ambienti per il qubit. Applichiamo la costruzione termodinamica di Wulff, sia quella originale che quella modificata, per determinare rispettivamente la corretta forma delle nanoparticelle 3C-SiC in equilibrio termodinamico e dopo che è stato seguito un particolare processo di crescita. Modifichiamo la Kinetic Crystal Shape di Masullo et al. finché non troviamo due strutture visibilmente diverse. Inoltre, mostriamo che in una nanoparticella piramidale il qubit si comporta in modo diverso lontano dalla punta rispetto a come si comporta vicino ad essa. Troviamo che il qubit all'interno delle nanoparticelle più appuntite è più sensibile alla configurazione del bagno rispetto alle altre forme.
Studio multiscala degli stati elettronici e di spin indotti da difetti di punto in semiconduttori a banda larga e prospettive per le tecnologie quantistiche / Fazio, Tommaso. - (2023 Apr 27).
Studio multiscala degli stati elettronici e di spin indotti da difetti di punto in semiconduttori a banda larga e prospettive per le tecnologie quantistiche
FAZIO, Tommaso
2023-04-27
Abstract
Our main focus is the analysis of point-defects in Wide Band Gap semiconductors. We first study them from first principles through the use of ab initio methods based on Density Functional Theory, and then utilize other means of analysis for finding possible applications in the realm of nanoelectronics (defect-free Al2O3/AlGaN capacitors) or Quantum Technologies (point-defects in 4H- and 3C-SiC having a large decoherence time). E.g., after a defect’s model Hamiltonian ab initio calibration, we shed light on the coherent dynamics of such systems (in the bulk or confined in 3D nanostructures). The defects’ atomic structures are well-characterized and optimized during the calibration phase by using the Quantum Espresso code. Silicon Carbide and Gallium Nitride are the Wide Band Gap semiconductors we study from the point of view of Quantum Technologies and nanoelectronics, respectively. For what concerns nanoelectronics, we examine the deleterious effect Frenkel defects could play in Al2O3/AlGaN junctions. Al2O3/AlGaN Metal Oxide Semiconductor capacitors show a hysteretic behavior in their Capacitance vs Voltage characteristics, often attributed to near-interface traps deriving from defects within the oxide layer. The origin as well as the structural/electronic properties of such defects are still strongly debated in the literature. In our research we use ab initio molecular dynamics and the climbing-image nudged elastic band method to show that Aluminum Frenkel defects give rise to bistable trap states in disordered and stoichiometric Al2O3. Based on these results, we propose a calibrated polaron model representing a distribution of individually interacting energy levels with an internal reconfiguration mode and coupled to continuous bands of carriers to explain the hysteresis mechanism in Al2O3/AlGaN capacitors. As for Quantum Technology, we propose a defect whose experimental identification is yet to be accomplished, i.e. the neutral silicon vacancy in 3C-SiC. We study the silicon vacancy (SiV) in 3C-SiC as a promising color center, modeling it as an electron spin (behaving as a qubit in appropriate conditions) magnetically interacting with the SiC nuclear spin bath containing Si-29 and C-13 nuclei in their natural isotopic concentration. We calculate the energetics of the neutral and charged SiV with ab initio methods, identifying its neutral charge state as the most favorable for p-doped 3C-SiC systems. Magnetic properties are calculated as well for the neutral SiV in 3C- and 4H-SiC, both in the k and h crystal sites, and the results are compared. We thereby evaluate the Free Induction Decay and the Hahn-echo sequence of control pulses on the electron spin interacting with the nuclear spin bath. We shed light on the Electron Spin Echo Envelope Modulation phenomenon and the decoherence effect by means of the Cluster Correlation Expansion theory. We find a non-exponential coherence decay, which is a typical feature of solid-state qubits. We extend the outlined analysis to silicon vacancies in different 3C-SiC nanoparticles for Quantum Sensing applications. We apply the Hahn-echo sequence to the electron spin interacting with the nuclear spin bath and use the Cluster Correlation Expansion theory (by assumption) to calculate the coherence of the total system. We analyze several nanoparticle shapes as environments for the qubit. We apply the thermodynamic Wulff construction, both the original and the modified one, to determine the proper 3C-SiC nanoparticle shape in thermodynamic equilibrium and after a particular growth process has been followed, respectively. We modify Masullo’s Kinetic Crystal Shape until we find two visibly different structures. Furthermore, we show that in a pyramidal nanoparticle the qubit behaves differently far from the tip as opposed to near it. We find that the qubit within the most peaked nanoparticles is more sensitive to the bath configuration with respect to the other shapes.File | Dimensione | Formato | |
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