Modeling the charge transport mechanism in amorphous Al 2 O 3 with multiphonon trap ionization effect

a b s t r a c t The charge transport mechanism in amorphous alumina, Al 2 O 3 , is investigated both theoretically and experimentally. We found that the experimental current-field-temperature dependencies can hardly be understood based on the commonly used Frenkel effect or the thermally-assisted tunneling model. Instead, we suggest that the charge transport in Al 2 O 3 is related to the ionization of the deep trap by multiphonon tunneling. Excellent agreements between the predicted, the measured data were obtained by using the proposed multiphoton model with the following values of trapping parameters: thermal ionization energy of 1.5 eV, optical ionization energy of 3.0 eV, phonon energy of 0.05 eV, electron effective mass of 0.4m e . The density of electron trap and electron capture cross-section of neutral traps are 2 Â 10 20 cm À3 and 5 Â 10 À15 cm 2 , respectively

A simple figure of merit to identify the first layer to degrade and fail in dual layer SiOx/HfO2 gate dielectric stacks

Understanding the degradation dynamics and the breakdown sequence of a bilayer high-k (HK) gate dielectric stack is crucial for the improvement of device reliability. We present a new Figure of Merit (FoM), the IL/HK Degradation Index, that depends on fundamental materials properties (the dielectric breakdown strength and the dielectric constant) and can be used to easily and quickly identify the first layer to degrade and fail in a bilayer SiO2/HK dielectric stack. Its dependence on IL and HK material parameters is investigated and its validity is demonstrated by means of accurate physics-based simulations of the degradation process. The proposed FoM can be easily used to understand the degradation dynamics of the gate dielectric stack, providing critical insights for device reliability improvement

Multiscale modeling for application-oriented optimization of resistive random-access memory

Memristor-based neuromorphic systems have been proposed as a promising alternative to von Neumann computing architectures, which are currently challenged by the ever-increasing computational power required by modern artificial intelligence (AI) algorithms. The design and optimization of memristive devices for specific AI applications is thus of paramount importance, but still extremely complex, as many dierent physical mechanisms and their interactions have to be accounted for, which are, in many cases, not fully understood. The high complexity of the physical mechanisms involved and their partial comprehension are currently hampering the development of memristive devices and preventing their optimization. In this work, we tackle the application-oriented optimization of Resistive Random-Access Memory (RRAM) devices using a multiscale modeling platform. The considered platform includes all the involved physical mechanisms (i.e., charge transport and trapping, and ion generation, diusion, and recombination) and accounts for the 3D electric and temperature field in the device. Thanks to its multiscale nature, the modeling platform allows RRAM devices to be simulated and the microscopic physical mechanisms involved to be investigated, the device performance to be connected to the material's microscopic properties and geometries, the device electrical characteristics to be predicted, the effect of the forming conditions (i.e., temperature, compliance current, and voltage stress) on the device's performance and variability to be evaluated, the analog resistance switching to be optimized, and the device's reliability and failure causes to be investigated. The discussion of the presented simulation results provides useful insights for supporting the application-oriented optimization of RRAM technology according to specific AI applications, for the implementation of either non-volatile memories, deep neural networks, or spiking neural networks

Improvement of a Solar Cell Performance by Introducing Defects(Amélioration des performances d’une cellule solaire en introduisant des défauts

In this work, we investigated the tunnel oxide passivated contact (TOPCon) solar cell based on ntype Si (p-n-n+ structure), and p-type Si (n-p-p+ structure), respectively. We started by the study of a p-n single junction device. Then, we investigated the p-n-n+ configuration in which an n+ polysilicon layer is added as back-surface field (BSF) layer. Thereafter, the tunnel oxide passivated contact (TOPCon) cell was studied. This latter includes a wide bandgap (nitride or oxide) passivation layer (PL) between the absorber and BSF layers. The carrier transport and tunneling process, in such structure, are mainly ensured by electrons. Under the AM1.5G solar spectrum at ambient temperature, we investigated the BSF and the tunneling layer's effects on the solar cell output parameters. An additional study by changing the tunnel dielectric materials from the conventiona

Miniaturized Transistors, Volume II

In this book, we aim to address the ever-advancing progress in microelectronic device scaling. Complementary Metal-Oxide-Semiconductor (CMOS) devices continue to endure miniaturization, irrespective of the seeming physical limitations, helped by advancing fabrication techniques. We observe that miniaturization does not always refer to the latest technology node for digital transistors. Rather, by applying novel materials and device geometries, a significant reduction in the size of microelectronic devices for a broad set of applications can be achieved. The achievements made in the scaling of devices for applications beyond digital logic (e.g., high power, optoelectronics, and sensors) are taking the forefront in microelectronic miniaturization. Furthermore, all these achievements are assisted by improvements in the simulation and modeling of the involved materials and device structures. In particular, process and device technology computer-aided design (TCAD) has become indispensable in the design cycle of novel devices and technologies. It is our sincere hope that the results provided in this Special Issue prove useful to scientists and engineers who find themselves at the forefront of this rapidly evolving and broadening field. Now, more than ever, it is essential to look for solutions to find the next disrupting technologies which will allow for transistor miniaturization well beyond silicon’s physical limits and the current state-of-the-art. This requires a broad attack, including studies of novel and innovative designs as well as emerging materials which are becoming more application-specific than ever before

Optical and luminiscent properties of terbium / ytterbium doped aluminum oxynitride and terbium doped aluminum nitride thin films

In the present thesis the optical and light emission properties of two systems consisting of Tb3+ and Yb3+ doped amorphous AlOxNy thin films and Tb3+ doped polycrystalline AlN thin films were analyzed. In the two ions system, to obtain an adequate luminescent emission, commonly a significant effort must be made to find a suitable concentration of dopants and elemental composition of the host material. An interesting and highly efficient method is a combinatorial approach, allowing a high velocity screening of a wider range of properties. In the present work a combinatorial gradient based thin film libraries of amorphous AlOxNy:Yb3+, AlOxNy:Tb3+ and AlOxNy:Tb3+:Yb3+ have been prepared by radio frequency co-sputtering from more than one target. In the prepared libraries, the Tb and Yb concentration range spreads along with the oxygen to nitrogen ratio of the host matrix all over the substrate area. Concentrations ranges for each ion were established for producing high emission intensity samples, along with an analysis of the light emission features of Yb3+ ions with Tb3+ ions as sensitizers for cooperative down conversion process. Using different annealing temperatures the activation energy of the rare earth ions and thermal-induced activation mechanisms are evaluated. Here we show that the different oxygen to nitrogen ratios in the host composition affect the light emission intensity. According to experimental results, there is a strong enhancement of the Yb3+ related emission intensity over the Tb3+ emission in codoped films with Tb:Yb concentration ratios near to 1:2, at 850°C. Thus, suggesting the sensitization of Tb3+ ions through an AlOxNy matrix and the cooperative energy transfer between Tb3+ and Yb3+ ions as the driven mechanism for down conversion process with promising applications in silicon solar cells. At the end of this first part, the optimal elemental composition and optimal annealing temperature in the investigated ranges to achieve the highest Yb3+ emission intensity upon sensitization of Tb3+ ions is reported. The second system studied consists of Tb3+ doped AlN layers prepared by reactive magnetron sputtering and analyzed using the conventional one at a time approach. In this work, two types of thermal treatments have been applied: substrate heating during deposition of the films and post deposition rapid thermal annealing, with varying temperature from non intentional heating up to 600°C. The composition, morphology and crystalline structure of the films under different thermal processes and temperatures were investigated along with their optical and light emission properties, with the aim of maximizing the Tb3+ emission intensity. The polycrystalline nature of the films was confirmed by X-ray diffraction under grazing incidence, and the influence of substrate temperature on the crystalline structure was reported. Atomic force microscopy and scanning electron microscopy has revealed the smooth grainy surface quality of the AlN:Tb3+ films. The highest Tb3+ photoluminescence emission intensity was achieved in the film treated with rapid thermal annealing process. For a more detailed study of the post deposition annealing treatments, temperature was further increased up to 900°C, and the influence of annealing temperature on the emission properties was investigated by photoluminescence and photoluminescence decay measurements. An increase in the photoluminescence intensity and photoluminescence decay time was observed upon annealing for the main transition of Tb3+ ions at 545 nm, which was attributed to a decrease of non radiative recombination and increase of the population of excited Tb3+ ions upon annealing. Additionally, using the characterized films as active layer, direct current and alternate current thin film electroluminescence devices were designed and investigated.Tesi

Journal of Telecommunications and Information Technology, 2001, nr 1

kwartalni

Electron transport in semiconducting nanowires and quantum dots

Single electrons confined in electrostatic quantum dots are a promising platform for realizing spin based quantum information processing. In this scheme, the spin of each electron is encoded as a qubit, and can be manipulated and measured by modulating the gate voltages defining each dot. Since each qubit is realized in a single quantum dot, one could imagine scaling up this system by placing many quantum dots together in a tightly packed array. To be truly scalable each qubit must exhibit minimal variation, such that their behavior is consistent across the entire device. Transport through these quantum dots must therefore be explored in detail, to determine the source of these variations and design strategies to combat their effects. In this thesis a study of the transport properties of InAs nanowires and Si quantum dots is presented. In both systems the close proximity of the conduction electrons to defect-prone surfaces or interfaces causes them to be very sensitive to the physical properties of these regions. Through cryogenic transport measurements, and the development of relevant physical models, the effects of surface states, oxide charge traps, and interface defects are explored. In general these defects possess a finite charge, which modifies the electrostatic potential and alters electron transport. These additional changes to the electrostatic potential are detrimental for spin based quantum information processing, which requires precise control of this potential. In addition, the severity of each of these effects can be different in each device, leading to variation which limits scalability. By studying these effects we aim to better understand their properties and origins, such that they can be mitigated. Static defects, such as surface states, are found to be a dominant source of scattering that limits mobility. In InAs nanowires, we find that these effects can be removed through growth of an epitaxial shell that physically separates the nanowire surface from the conducting core. Dynamic defects on the other hand, lead to charge noise that shifts the potential causing instability. This noise originates from charge traps in close proximity to the conduction channel. For nanowires, the native oxide that forms at the surface is a likely location for these traps to occur. Through removal of this oxide and replacement with a defect free dielectric shell, greatly improved stability is observed. To test the viability of these fabrication techniques, nanowires treated with the most promising surface processes are used to fabricate top-gated nanowire field effect transistors. These devices are used to realize electrostatically defined double quantum dots, which show well controlled transport properties and minimal charge noise. In Si, electron transport is studied in a pair of capacitively coupled metal-oxide-semiconductor quantum dots. Here, the capacitive coupling is used implement charge sensing, such that the electrostatic potential of one dot can be measured down to the single electron regime. The pair of dots is also used to implement a novel memristive system which demonstrates current hysteresis. This shows the versatility of this system and its capability to control individual electrons, similar to the requirements needed to implement spin based quantum information processing