Catálogo de publicaciones - revistas

<jats:p>As a common impurity in 4H silicon carbide (4H-SiC), hydrogen (H) may play a role in tuning the electronic properties of 4H-SiC. In this work, we systemically explore the effect of H on the electronic properties of both n-type and p-type 4H-SiC. The passivation of H on intrinsic defects such as carbon vacancies (V<jats:sub>C</jats:sub>) and silicon vacancies (V<jats:sub>Si</jats:sub>) in 4H-SiC is also evaluated. We find that interstitial H at the bonding center of the Si–C bond (<jats:inline-formula> <jats:tex-math><?CDATA ${{\rm{H}}}_{{\rm{i}}}^{{\rm{bc}}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi mathvariant="normal">i</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">bc</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_31_5_056108_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) and interstitial H at the tetrahedral center of Si (<jats:inline-formula> <jats:tex-math><?CDATA ${{\rm{H}}}_{{\rm{i}}}^{{\rm{Si}}-{\rm{te}}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi mathvariant="normal">i</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">Si</mml:mi> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">te</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_31_5_056108_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>) dominate the defect configurations of H in p-type and n-type 4H-SiC, respectively. In n-type 4H-SiC, the compensation of <jats:inline-formula> <jats:tex-math><?CDATA ${{\rm{H}}}_{{\rm{i}}}^{{\rm{Si}}-{\rm{te}}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi mathvariant="normal">i</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">Si</mml:mi> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">te</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_31_5_056108_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> is found to pin the Fermi energy and hinder the increase of the electron concentration for highly N-doped 4H-SiC. The compensation of <jats:inline-formula> <jats:tex-math><?CDATA ${{\rm{H}}}_{{\rm{i}}}^{{\rm{bc}}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi mathvariant="normal">i</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">bc</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_31_5_056108_ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> is negligible compared to that of V<jats:sub>C</jats:sub> on the p-type doping of Al-doped 4H-SiC. We further examine whether H can passivate V<jats:sub>C</jats:sub> and improve the carrier lifetime in 4H-SiC. It turns out that nonequilibrium passivation of V<jats:sub>C</jats:sub> by H is effective to eliminate the defect states of V<jats:sub>C</jats:sub>, which enhances the carrier lifetime of moderately doped 4H-SiC. Regarding the quantum-qubit applications of 4H-SiC, we find that H can readily passivate V<jats:sub>Si</jats:sub> during the creation of V<jats:sub>Si</jats:sub> centers. Thermal annealing is needed to decompose the resulting V<jats:sub>Si</jats:sub>–<jats:italic>n</jats:italic>H (<jats:italic>n</jats:italic> = 1–4) complexes and promote the uniformity of the photoluminescence of V<jats:sub>Si</jats:sub> arrays in 4H-SiC. The current work may inspire the impurity engineering of H in 4H-SiC.</jats:p>

<jats:p>The knowledge of interfacial thermal conductance (ITC) is key to understand thermal transport in nanostructures. The non-equilibrium molecular dynamics (NEMD) simulation is a useful tool to calculate the ITC. In this study, we investigate the impact of thermostat on the prediction of the ITC. The Langevin thermostat is found to result in larger ITC than the Nose–Hoover thermostat. In addition, the results from NEMD simulations with the Nose–Hoover thermostat exhibit strong size effect of thermal reservoirs. Detailed spectral heat flux decomposition and modal temperature calculation reveal that the acoustic phonons in hot and cold thermal reservoirs are of smaller temperature difference than optical phonons when using the Nose–Hoover thermostat, while phonons in the Langevin thermostat are of identical temperatures. Such a non-equilibrium state of phonons in the case of the Nose–Hoover thermostat reduces the heat flux of low-to-middle-frequency phonons. We also discuss how enlarging the reservoirs or adding an epitaxial rough wall to the reservoirs affects the predicted ITC, and find that these attempts could help to thermalize the phonons, but still underestimate the heat flux from low-frequency phonons.</jats:p>

<jats:p>The holes induced by ionizing radiation or carrier injection can depassivate saturated interface defects. The depassivation of these defects suggests that the deep levels associated with the defects are reactivated, affecting the performance of devices. This work simulates the depassivation reactions between holes and passivated amorphous-SiO<jats:sub>2</jats:sub>/Si interface defects (HP<jats:sub>b</jats:sub> + h → P<jats:sub>b</jats:sub> + H<jats:sup>+</jats:sup>). The climbing image nudged elastic band method is used to calculate the reaction curves and the barriers. In addition, the atomic charges of the initial and final structures are analyzed by the Bader charge method. It is shown that more than one hole is trapped by the defects, which is implied by the reduction in the total number of valence electrons on the active atoms. The results indicate that the depassivation of the defects by the holes actually occurs in three steps. In the first step, a hole is captured by the passivated defect, resulting in the stretching of the Si–H bond. In the second step, the defect captures one more hole, which may contribute to the breaking of the Si–H bond. The H atom is released as a proton and the Si atom is three-coordinated and positively charged. In the third step, an electron is captured by the Si atom, and the Si atom becomes neutral. In this step, a P<jats:sub>b</jats:sub>-type defect is reactivated.</jats:p>

<jats:p>New characteristics of the Kondo effect, arising from spin chirality induced by the Berry phase in the equilibrium state, are investigated. The analysis is based on the hierarchical equations of motion (HEOM) approach in a triangular triple quantum-dot (TTQD) structure. In the absence of magnetic field, TTQD has four-fold degenerate chiral ground states with degenerate spin chirality. When a perpendicular magnetic field is applied, the chiral interaction is induced by the magnetic flux threading through TTQD and the four-fold degenerate states split into two chiral state pairs. The chiral excited states manifest as chiral splitting of the Kondo peak in the spectral function. The theoretical analysis is confirmed by the numerical computations. Furthermore, under a Zeeman magnetic field <jats:italic>B</jats:italic>, the chiral Kondo peak splits into four peaks, owing to the splitting of spin freedom. The influence of spin chirality on the Kondo effect signifies an important role of the phase factor. This work provides insight into the quantum transport of strongly correlated electronic systems.</jats:p>

<jats:p>Interfacial charge recombination is a main issue causing the efficiency loss of the perovskite solar cells (PSCs). Here, ferroelectric Ba<jats:sub>0.75</jats:sub>Sr<jats:sub>0.25</jats:sub>TiO<jats:sub>3</jats:sub> (BST) is introduced as a polarization tunable layer to promote the interfacial charge transfer of the PSCs. The coexistence of ferroelectric polarization and charge carriers in BST is confirmed by density functional theory (DFT) calculations. Experimental characterization demonstrates the polarization reversal and the existence of domain in BST film. The BST film conductivity is tested as 2.98 × 10<jats:sup>−4</jats:sup> S/cm, which is comparable to the TiO<jats:sub>2</jats:sub> being used as the electron transporting layer (ETL) in PSCs. The calculations results prove that BST can be introduced into the PSCs and the interfacial charge transfer can be tuned by ferroelectric polarization. Thus, we fabricated the BST-based PSCs with a champion power conversion efficiency (PCE) of 19.05% after poling.</jats:p>

<jats:p>We investigate the SU(2) gauge effects on bilayer honeycomb lattice thoroughly. We discover a topological Lifshitz transition induced by the non-Abelian gauge potential. Topological Lifshitz transitions are determined by topologies of Fermi surfaces in the momentum space. Fermi surface consists of <jats:italic>N</jats:italic> = 8 Dirac points at <jats:italic>π</jats:italic>-flux point instead of <jats:italic>N</jats:italic> = 4 in the trivial Abelian regimes. A local winding number is defined to classify the universality class of the gapless excitations. We also obtain the phase diagram of gauge fluxes by solving the secular equation. Furthermore, the novel edge states of biased bilayer nanoribbon with gauge fluxes are also investigated.</jats:p>

<jats:p>Based on first-principles calculations, the bias-induced evolutions of hybrid interface states in <jats:italic>π</jats:italic>-conjugated tricene and in insulating octane magnetic molecular junctions are investigated. Obvious bias-induced splitting and energy shift of the spin-resolved hybrid interface states are observed in the two junctions. The recombination of the shifted hybrid interface states from different interfaces makes the spin polarization around the Fermi energy strongly bias-dependent. The transport calculations demonstrate that in the <jats:italic>π</jats:italic>-conjugated tricene junction, the bias-dependent hybrid interface states work efficiently for large current, current spin polarization, and distinct tunneling magnetoresistance. But in the insulating octane junction, the spin-dependent transport via the hybrid interface states is inhibited, which is only slightly disturbed by the bias. This work reveals the phenomenon of bias-induced reconstruction of hybrid interface states in molecular spinterface devices, and the underlying role of conjugated molecular orbitals in the transport ability of hybrid interface states.</jats:p>

<jats:p>Superconducting nanowire single-photon detectors (SNSPDs) are typical switching devices capable of detecting single photons with almost 100% detection efficiency. However, they cannot determine the exact number of incident photons during a detection event. Multi-pixel SNSPDs employing multiple read-out channels can provide photon number resolvability (PNR), but they require increased cooling power and costly multi-channel electronic systems. In this work, a single-flux quantum (SFQ) circuit is employed, and PNR based on multi-pixel SNSPDs is successfully demonstrated. A multi-input magnetically coupled DC/SFQ converter (MMD2Q) circuit with a mutual inductance <jats:italic>M</jats:italic> is used to combine and record signals from a multi-pixel SNSPD device. The designed circuit is capable of discriminating the amplitude of the combined signals in accuracy of <jats:italic>Φ</jats:italic> <jats:sub>0</jats:sub>/<jats:italic>M</jats:italic> with <jats:italic>Φ</jats:italic> <jats:sub>0</jats:sub> being a single magnetic flux quantum. By employing the MMD2Q circuit, the discrimination of up to 40 photons can be simulated. A 4-parallel-input MMD2Q circuit is fabricated, and a PNR of 3 is successfully demonstrated for an SNSPD array with one channel reserved for the functional verification. The results confirm that an MMD2Q circuit is an effective tool for implementing PNR with multi-pixel SNSPDs.</jats:p>

<jats:p>A large amount of ultra-low-power consumption electronic devices are urgently needed in the new era of the internet of things, which demand relatively low frequency response. Here, atomic layer deposition has been utilized to fabricate the ion polarization dielectric of the LiPON–Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> hybrid structure. The LiPON thin film is periodically stacked in the Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> matrix. This hybrid structure presents a frequency-dependent dielectric constant, of which <jats:italic>k</jats:italic> is significantly higher than the aluminum oxide matrix from 1 kHz to 200 kHz in frequency. The increased dielectric constant is attributed to the lithium ions shifting locally upon the applied electrical field, which shows an additional polarization to the Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> matrix. This work provides a new strategy with promising potential to engineers for the dielectric constant of the gate oxide and sheds light on the application of electrolyte/dielectric hybrid structure in a variety of devices from capacitors to transistors.</jats:p>

<jats:p>A quasi-vertical GaN Schottky barrier diode with a hybrid anode structure is proposed to trade off the on-resistance and the breakdown voltage. By inserting a SiN dielectric between the anode metal with a relatively small length, it suppresses the electric field crowding effect without presenting an obvious effect on the forward characteristics. The enhanced breakdown voltage is ascribed to the charge-coupling effect between the insulation dielectric layer and GaN. On the other hand, the current density is decreased beneath the dielectric layer with the increasing length of the SiN, resulting in a high on-resistance. Furthermore, the introduction of the field plate on the side wall forms an metal-oxide-semiconductor (MOS) channel and decreases the series resistance, but also shows an obvious electric field crowding effect at the bottom of the mesa due to the quasi-vertical structure.</jats:p>