Based on the three-dimensional Schrödinger equation and hot-carrier effects, a physical model to clarify how the source–drain voltage affects the energy needed for the emission or absorption of a ...photon in GaN heterojunctions is proposed. The proposed model predicts that the energy needed for the emission or absorption of a photon in GaN heterojunctions will be linearly reduced by the square of the source–drain voltage and the device temperature. Thus, they will shift the emission or absorption spectrum of emission or absorption. The results of voltage and temperature-dependent spectrum noted in the Raman and photoluminescence experiments support the predicted results by the proposed model. Additionally, temperature-dependent spectral broadening observed in experiments can be described by the proposed model. It suggests that quantum coupling should be considered in GaN devices because of the hot-carrier effects, which denote that the energy of channel electrons can be very high. It is also essential for accurately measuring temperature by Raman measurement.
A new current equation for graphene/semiconductor or graphene/metal junctions in graphene-based electronic devices is proposed based on the thermionic emission theory. Temperature-dependent current ...density predicted by the proposed model agrees well with those experimental data reported in the literature. It can also explain the electric field and temperature-dependent effective Schottky barrier height observed in experiments. This is because a high drift velocity in graphene and its dependence on temperature can lead to a change in the effective Schottky barrier height. Due to the nonlinearity between current and temperature, the Richardson’s law will be broken down. The proposed model will benefit to better understand the current transport mechanism in graphene-like materials and graphene-based electronic devices.
After the contribution of hot carriers to the current in solar cells has been considered, a physical and analytical model of open-circuit voltage is proposed. A variety of experiments on the ...temperature-dependent open-circuit voltage in solar cells that is one critical factor to determine their overall efficiency are successfully modeled based on the consideration of hot carriers. While previous modeling studies focused on numerical techniques, a physical and analytical model of the open-circuit voltage has been developed. Such a study is an important step toward a quantitative model of solar cells, leading to a deeper understanding of the physical effects in these materials. The analysis of the open-circuit voltage reveals how it depends on temperature, the acceptor density, the light-generated current density, the donor density, the bandgap, the effective mass, and the dielectric constant. A material parameter variation is performed to understand its effects on the open-circuit voltage. It will benefit to optimize the device performance by tuning material parameters through the simplicity and analytic nature of the proposed model. It is also helpful to characterize the material properties using the open-circuit voltage.
Monte Carlo simulations show that, as temperature increases, the average kinetic energy of channel electrons in a GaN transistor first decreases and then increases. According to the calculations, the ...relative energy change reaches 40%. This change leads to a reduced barrier height due to quantum coupling among the three‐dimensional motions of channel electrons. Thus, an analysis and physical model of the gate leakage current that includes drift velocity is proposed. Numerical calculations show that the negative and positive temperature dependence of gate leakage currents decreases across the barrier as the field increases. They also demonstrate that source–drain voltage can have an effect of 1 to 2 orders of magnitude on the gate leakage current. The proposed model agrees well with the experimental results.
Based on the energy and momentum balance equations and three-dimensional Schrödinger equations, a physical model of the quantum coupling and electrothermal effects on the electron transport in GaN ...transistors is proposed. Quantum coupling and electrothermal effects in GaN transistors cause a reduction in the barrier height, changes in the quantised energy levels of the two-dimensional electron gas, and a decrease in the electron density and source–drain current. This model predicts that the current collapse in GaN transistors can occur under channel electrons with large transverse energy and it can be alleviated by optimising the physical device parameters. The gate length-dependent resistance predicted by the proposed model agrees well with the experimental data reported in the literature. Not only the physical mechanism but also the possibility to improve the reliability of high-electron mobility (HEMT) GaN transistors by optimising its physical parameters has been given in this model due to its analytic nature.
•A physical model of kink in GaN devices was proposed.•This model describes the relation between kink and gate voltage.•It gives how the physical parameters of GaN devices affect the kink.•It can ...explain the kink phenomenon in experiments.
The kink in the source-drain current of GaN devices has been not clarified. Based on the Maxwell-Boltzmann distribution of hot channel electrons, the generation of excess carriers in the L valleys of GaN and the origin of the kink had been modeled. This proposed model can predict how the kink depends on the gate voltage in experiments. It provides the reason why the kink partially disappears or disappears by sweeping the source-drain voltage from high voltage to low voltage, disappears under illumination, is more obvious at a lower temperature, and can be affected by different traps. All above experimental phenomena are associated with excess carriers in the L valleys of gain due to the hot channel carrier via internal transport. This model gives physical insight into how physical parameters of GaN devices affect the kink in the source-drain current. Thus, it can be used to optimize the physical parameters of GaN devices for reducing the kink.
After the carrier drift velocity at the semiconductor / metal interface is considered, current transport in Schottky diodes under a forward electric field is physically modelled. This model reveals ...that the ideality factor can be physically originated from the drift velocity and the drift velocity can also reduce the effective Schottky barrier height. This proposed model predicts that both the ideality factor and the Schottky barrier height depend on temperature, voltage and doping density, which agree well with the experimental results reported in the literature. The proposed diode current model also predicts a linear dependent relation between the reciprocal of the ideality factor and the effective Schottky barrier height, which is validated by experimental results. Such a model is useful to better understand the thermionic emission current physically in semiconductor / metal contact. It is also useful to characterise the material properties by using the ideality factor.
The properties and behavior of a single Au atom supported anatase TiO2(001) surface are calculated using density functional theory (DFT) methods. The structures and energies of adsorbed single Au on ...an anatase TiO2(001) surface with surface oxygen vacancy, as well as subsurface oxygen vacancy, are systematically determined. Initially, the surface threefold coordinated oxygen vacancy adjacent to a single Au atom, rather than the surface two‐fold coordinated oxygen vacancy and subsurface threefold coordinated oxygen vacancy, results in more stability for anatase TiO2(001) surface with an Au adatom. Afterwards, the CO molecule is more strongly adsorbed on the single Au‐supported TiO2(001) surface with surface threefold coordinated oxygen vacancy when comparing to other structures. This is attributed to the more negatively charged Au single‐atom caused by a surface threefold coordinated oxygen vacancy presents concededly active for CO adsorption.
The structures and energies of adsorbed single Au on anatase TiO2(001) surface with various oxygen vacancies are systematically addressed. The surface oxygen vacancy adjacent the adsorbed atomic Au increased the stability of atomic Au and further improved the adsorption of CO molecules. This is attributed to the oxygen vacancy above resulting in the presence of a charge reservoir in atomic Au.
Barrier height of AlGaN/GaN transistor is lowered by the quantum coupling of hot electrons with large transverse energy via electro‐thermal effect. The coupling effectively raises the quantized ...levels of hot electrons, changes the electron density of the two‐dimensional electron gas, and consequently decreases the source drain current of the transistor. Based on the theory of quantum coupling of hot electrons, the current reduction is successfully modeled. The model is able to explain the effect of gate voltage, device temperature, gate length, gate metals, passivation, field‐plate structure, traps, and electron‐phonon interaction on current reduction. It also predicts a relative decrease of 4.6% in the source drain current caused by the quantum coupling at moderately low electron temperature of 1771 K.
The quantum coupling of channel hot electrons effectively raises the quantized levels of hot electrons, changes the electron density of two‐dimensional electron gas, and consequently decreases the source drain current due to its impacts on the barrier height of AlGaN/GaN transistors. Thus, a physical model of the current reduction in AlGaN/GaN transistors is successfully modeled.
However evanescent coupling between acoustic waveguides has been well studied by the mode-matching method in the literature, a proposed physical model based on the tunnelling concept is used to ...explain such coupling. Based on phonons being one type of quasi-particles, the Schrödinger equation for a phonon has been built by introducing a virtual mass and potential for phonons. This proposed model is physically intuitive and analytical. It can well explain the exponential dependence of the coupling length on the guide separation distances and the frequency of acoustic waves reported in the literature. The exponential dependent relationship between the coupling coefficients predicted by the proposed model agrees well with the experimental data reported in the literature. The model provides a new idea for understanding and studying coupling between acoustic waveguides.
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