Dispositivos a nanoescala dopados eléctricamente que utilizan el enfoque del primer principio:una encuesta exhaustiva

Trabajos de investigación a nivel molecular basados ​​en el dopaje eléctrico

El dopaje eléctrico a nivel molecular juega un papel importante en la nanoelectrónica. Los investigadores están muy interesados ​​en introducir este procedimiento de dopaje en el procedimiento de diseño de dispositivos a nanoescala. El efecto de este dopaje ayuda a interactuar entre diferentes niveles moleculares de alineación. Este proceso no solo es útil para estudiar el nivel molecular de heterouniones orgánicas, sino que también es aceptable para materiales inorgánicos. Este dopaje ayuda a la formación de la interfaz con la ayuda de un dipolo y un movimiento equivalente en la posición comparativa de la interfaz molecular. Por lo tanto, este proceso de dopaje eléctrico es aceptable para la alineación de la interfaz molecular.

La miniaturización de dispositivos electrónicos convencionales es el área de investigación más emergente en la actualidad. Hay varios enfoques que llevan a motivar a los investigadores a investigar y estudiar la naturaleza de los dispositivos a nanoescala. Uno de los enfoques más importantes es diseñar y simular nanoestructuras analíticas. Se pueden diseñar muchos dispositivos importantes utilizando este procedimiento de simulación y analizar los resultados obtenidos [47, 55, 56]. Según el resultado, los investigadores pueden modificar los distintos parámetros de simulación, así como los diferentes aspectos del modelo analítico a nanoescala. Entre estos métodos de simulación, el enfoque del primer principio es el proceso más eficaz y popular. La modernización de los dispositivos electrónicos anima a los investigadores a innovar los dispositivos convencionales en una versión modificada. Por ejemplo, los dispositivos semiconductores tradicionales se pueden diseñar utilizando biomoléculas. En el caso de las biomoléculas en general, se han considerado bases nucleicas como la adenina, timina, guanina y citosina, que se conocen como los componentes básicos del ADN [47, 55]. Es muy común construir dispositivos semiconductores inorgánicos convencionales en el campo de la nanotecnología. Sin embargo, es difícil construir dispositivos electrónicos orgánicos que utilicen principalmente biomoléculas. Estos semiconductores se caracterizan en función de las propiedades de dopaje. Si el semiconductor no tiene impurezas dopadas, entonces se denomina semiconductor intrínseco o puro. Por otro lado, si el semiconductor está dopado con átomos o moléculas extrañas, entonces se le conoce como semiconductor extrínseco o impuro [55,56,57,58,59,60].

Hoy en día, el diseño de dispositivos a nanoescala es un aspecto desafiante para los investigadores. Diodos, transistores, puertas lógicas ya se han implementado a nivel molecular. Existe otro ámbito para que los investigadores implementen dispositivos nanobiosemiconductores a nivel molecular. Algunos de estos dispositivos biomoleculares ya se han introducido en el campo de la biomedicina. El diseño teórico de estos nanodispositivos se ha implementado utilizando el kit de herramientas Atomistix y el simulador de software Quantumwise basado en el laboratorio virtual Nano (ATK-VNL) versión 13.8.0 [69,70,71,72,73,74,75,76] . Incluso la lógica de Quantum Cellular Automata (QCA) se puede implementar teóricamente utilizando el enfoque del primer principio basado en DFT y NEGF [77]. Se pueden diseñar varias puertas lógicas utilizando biomoléculas, y los resultados obtenidos de estas implicaciones teóricas también se han validado utilizando Multi-Sim o SPICE u otros simuladores [70]. El proceso de dopaje eléctrico es la característica clave que se introduce para obtener una corriente óptima. La corriente de túnel a través del canal molecular se ve afectada por varios factores como el efecto de retrodispersión, etc. Al implementar este proceso de dopaje, podemos evitar los problemas relacionados con el proceso de dopaje convencional. El modelo de combinación de dipolos para el ajuste de la barrera de Schottky también se sugiere en la interfaz metal-semiconductor a nivel molecular [78]. El enfoque del primer principio también es aplicable a la unión de túnel magnético, y se han analizado sus propiedades electrónicas cuánticas [79]. Para calcular la corriente de fuga a través de SiO ₂ y SiO _x N _y basado en MOSFET, los investigadores utilizaron el enfoque de primer principio basado en DFT y NEGF [80]. Este modelado ab-initio se aplica para modelar el ajuste de la altura de la barrera de Schottky utilizando la interfaz de escala atómica de itrio y siliciuro de níquel [81]. La tunelización directa de banda a banda en nanocintas de unión p – n de MOS2 con polarización inversa se puede describir utilizando DFT y NEGF [82]. El efecto de la incorporación de átomos dopantes de polaridades opuestas en el nanoalambre exhibe propiedades eléctricas como el diodo Zener [83]. El efecto de filtrado de doble giro se puede ver en el nitrito de itrio semimetálico YN ₂ [84]. La investigación de la FET biomolecular heteroestructura se puede observar utilizando esta técnica de dopaje eléctrico. El transporte balístico cuántico se puede observar utilizando este fenómeno de dopaje eléctrico a nivel molecular [85]. Utilizando este enfoque teórico, el interruptor biomolecular dopado eléctricamente se diseña cuando se utilizan nanotubos de carbono de pared simple (SWCNT) como electrodos [86]. Los formalismos NEGF ayudan a diseñar un diodo túnel resonante anti-punto basado en grafeno [87]. Las características atomísticas de las uniones p – n bidimensionales de silicio se han demostrado utilizando el enfoque del primer principio [88]. Los diodos y los transistores son los componentes básicos de cualquier circuito electrónico. Las puertas lógicas también se pueden implementar utilizando diodos y transistores. Por lo tanto, cualquier lógica puede implementarse usando formalismos de primer principio.

En la tendencia reciente de la nanotecnología, los investigadores se han interesado en diseñar y caracterizar las diversas características electromecánicas de los dispositivos bioinspirados y semiconductores a escala atómica. Estos dispositivos bioinspirados son altamente biocompatibles y crean un puente entre el área de los semiconductores y el campo de la investigación bi-molecular. La tecnología CMOS ya está saturada. Por tanto, el objetivo de los investigadores es reemplazarlos y crear un puente entre ellos. Los investigadores ya han planteado varias propuestas para unir la tecnología CMOS con tecnología bioinspirada como el ADN o cualquier otra biomolécula. Las partes importantes del ADN son las bases nitrogenadas de adenina, timina, citosina y guanina. Estas bases nitrogenadas han formado compuestos con azúcar ribosa y grupos fosfato para formar oligonucleótidos. Este oligonucleótido tiene grupos fosfato como columna vertebral. Se han mejorado las correlaciones de señales dinámicas para la identificación de biomoléculas y ADN [89]. La translocación del ADN, la transmisión electrónica y el modelado semiempírico a través de nanoporos de grafeno también pueden ser posibles teóricamente utilizando DFT y NEGF [90,91,92,93]. El análisis de ADN también puede ser posible con electrodos de grafeno utilizando modelos semiempíricos [94]. También se ha hecho posible el reconocimiento de pares de bases de ácidos nucleicos utilizando propiedades de transporte transversal [95]. El grupo de investigadores también ha propuesto la conductancia a través del ADN inyectado [96]. También se ha incorporado la mejora electrónica mediante el procedimiento de dopaje a los pares de bases del ADN para mejorar la conductividad [97]. La promoción electrónica también ha sido posible mediante el proceso de transferencia de doble protón [98]. El reconocimiento de nucleótidos por el método de túnel cruzado también ha sido posible utilizando el enfoque del primer principio [99]. Los factores estructurales controlan la conductividad del ADN, y esto también se ha discutido en [100]. Los dispositivos a nanoescala exhiben un enorme fenómeno de transporte cuántico para diferentes tipos de modelado de dispositivos a nanoescala [56, 58, 59, 101,102,103,104,105,106,107]. Estos dispositivos incluyen FET, diodos e interruptores ópticos [60, 68, 108,109,110,111,112,113,114,115,116]. Este trabajo propuesto es un enfoque para hacer un puente entre las biomoléculas con la tecnología de semiconductores III-V. La heteroestructura de biomoléculas y materiales nanocristalinos III-V también se puede diseñar utilizando el enfoque teórico del primer principio. Además, las propiedades eléctricas y ópticas del grafeno codopado con nitrógeno y oro se investigan utilizando formalismos de primer principio. El formalismo de primer principio se utiliza para descubrir el cambio de las características mecánicas cuánticas y la investigación de varias propiedades electrónicas u ópticas de las moléculas orgánicas e inorgánicas. También se puede investigar el grafeno vacante defectuoso y el grafeno dopado con Mn hacia el H ₂ S absorción. La investigación del ferromagnetismo utilizando el enfoque del primer principio para la monocapa de AlN dopada con metales de transición también es una tendencia emergente. Se investiga el efecto de dopaje para MoS ₂ monocapa el uso de DFT para luz visible es un tema importante de discusión. A study of change of electronic properties was demonstrated for Eu-doped phosphorene based on the first-principle approach. Electromechanical quantum transport features are available for these devices [117,118,119,120,121].

In the year of 1987, Destefanis proposed the electrical doping of HgCdTe using ion implantation and heat treatment method. To increase a large number of pixels into the focal plane array devices, infrared photovoltaic detectors were required. The use of ion implanting HgCdTe was increasing this interest of manufacturers. In this type of manufacturing of photovoltaic infrared detectors, the electrical doping process was introduced. It was revealed that the effect of electrical doping into HgCdTe appeared significantly as the intrinsic properties of diodes were directly related to it [122]. Electrical was also proposed for enhancement of plasmonic absorption on Au-PbS core–shell nanocrystals. This method of doping was implemented using the intra-particle charge transfer method. In this experiment, colloidal nanocrystals were used to be the basic building blocks for solar cells, photo-detectors, etc. In this approach, researchers investigated the electronic properties of colloidal nanocrystalline materials and they also proposed a novel approach to electrical doping to these nanocrystalline solids using intra-particle charge transfer method [123]. The process flow for this simulation work is shown in Fig. 3.

Working flowchart diagram of Quantumwise ATK-VNL [76]

Simulation Methods of Electrical Doping

The analytical design of these molecular devices requires constant innovation and improvement in the field of material science. Density functional theory (DFT) and non-equilibrium Green’s function (NEGF) are the two key formalisms behind the analytics for the modeling of these nanoscale devices. The first-principle approach combines these two formalisms to describe theoretically these types of nanodimension devices. Extended Hückel theory (EHT) is another key factor to accelerate the design procedure of these atomistic devices [126, 127]. These theoretical modeling procedures help to prevent various problems regarding the nanoscale design like hazards during doping of foreign particles, generation of THz operating frequency, etc. Another aim of this nanoscale design procedure is to operate the device by keeping the electronic temperature at 300 K, i.e., room temperature. III–V semiconductors are optically sound semiconductor material that can be used for the design of various electronic devices. After silicon technology, III–V semiconductor technology is one of the emerging and most desirable areas to be fit in the nanoscale semiconductor technology. Biomolecules (like adenine, thymine, guanine and cytosine) have been introduced to form different nanoscale electronic devices. These biomolecules also exhibit their optical exposure whenever they are simulated at near-UV region (mid-UV-B). In this proposed work the electronic characterization has been made for the simulated nanoscale devices using the first-principle approach. This semiempirical modeling is carried out using EHT for obtaining faster simulation. We aim to design and characterize the III–V materials along with biomolecules using DFT- and NEGF-based first-principle formalisms. This semiempirical design of this bioinspired nanodevices has been carried out using the Quantumwise software simulation package.

To include electrical doping into the molecular devices, the same but opposite charge is to be provided to the two ends of the molecular interface. The electrical doping concentration is calculated using the following procedure:

Let us assume the electrodes are about 1 nm long and with 0.5 nm × 0.5 nm cross-sectional area. For simplification of calculation, we have taken those values. In the script editor, we have located the section for the electrodes calculator and assigned the charge =  + 0.01 and − 0.01. For this theoretical study, the Atomistic Tool Kit-Virtual Nano-laboratory (ATK-VNL) software package has been used. This software uses density functional theory (DFT) and non-equilibrium Green’s function (NEGF)-based first-principle approach. This value is being calculated using the following formula:

• Effective doping concentration = doping/volume [1, 70, 71]

• Assume, doping charge =  ± x V

• Assume that, volume = length (a ) × width (b ) × height (c ) = a × b  × c

• Volume = (a  × 10 ^–7 ) × (b  × 10 ^–7 ) × (c  × 10 ^–7 ) cm ⁻³  = abc  × 10 ^–21 / cm ³

• Effective doping = \(\frac{x}{{abc \times 10^{ - 21} }}\) = abc  × 10 ²¹ / cm ³ [as we have consider the dimension in nm unit]

The volumes of the electrodes remain constant so from Fig. 4, it can be observed that the doping concentration is directly proportional to the applied bias voltage. This is another reason that we have kept constant the electrode’s size. The little change in electrodes’ size leads to a large change in electrical doping concentration. So by changing the little amount of bias voltage we can be able to generate very high electrical doping into the system using the first-principle approach.

Dependence of effective electrical doping on an applied bias voltage

The electrical doping in this case totally depends on two parameters mainly. They are (1) effective doping charge (charge applied at the two ends of the electrodes) and (2) volume of the nanoscale device. Therefore, the formula of calculating electrical doping is mentioned as doping/volume, so if the length, height or breadth or anyone of the parameter is changed, then the doping concentration is definitely changed. For this type of device structure, volume is a function of length, height, width [70].

Both the temperature and thickness affect the performance of these nanoscale devices. Self-heating effect along with thermal noise generated heat also makes changes in quantum-ballistic transport phenomenon of these devices at this low dimension. Therefore, temperature plays an important role in the device performance. On the other hand, as thickness is related to the volume of the device and effective doping is directly related to volume, thickness also affects device performance. If thickness is changed, then accordingly volume changes which result in changes of doping concentration. Doping concentration is related directly to device performance like channel conductivity, current–voltage characteristics, etc., for these nanoscale devices. Therefore, doping is changed due to thickness changed that will definitely change device performance [70].

Evolution of Electrical Doping

Doping means the addition of explicit impurity atoms to the semiconductor. Doping is the intentional addition of atoms to the intrinsic semiconductor to modulate the electrical properties of intrinsic semiconductors. The electrodes sizes are inserted within the script editor, where we assigned the length of the electrode as 1 nm and cross section 0.5 nm × 0.5 nm. Thus, the nominal charge, i.e., ± 0.01, is set for the two electrodes. This script is processed through the job manager, and the calculated doping value for the electrodes is obtained. For this calculation we pursue the following steps:

• Open the New Calculator and select “ATK-SE:Extended Hückel (Device).”

• Uncheck “No SCF iteration.”

• Keep mesh cutoff to 10 Hartree.

• Under “Poisson Solver” set the “Neumann” boundary conditions along A(X) and B(Y) directions.

Figure 5 shows the consolidated form of the comparative study between electrical doping and conventional doping process (using Fe and Ni). This analytical experiment is observed for the thymine nanotube structure which is an example of electrical doping [70]. Fe and Ni atoms are chosen to dope the thymine nanotube, and on the other hand, the molecule is electrically doped [70]. All these results show that amount of electrical doping is much more when compared with conventional doping for little amount of applied bias. Some example works of electrical doping along with its some advantages over conventional doping are discussed in Table 2. It gives a comparative study of electrically doped devices with the existing device modeling which follows the conventional doping method. There are several types of doping, and dopants are available, for example, conventional doping (by adding impurity), electrical doping, co-doping. Generally, two types of dopants are available for conventional doping process, p-type dopants and n-type dopants. They are often called as acceptor and donor impurity atoms. These external impurities are added to the semiconducting materials to enhance their electrical properties mainly conductivity. In the case of the electrical doping process, mainly for analytical modeling using the ATK-VNL approach, we do not proceed with the addition of foreign atoms. Instead of these explicit atom doping, we focus on the change of potential difference at the two ends of the device (mainly at the ends of electrodes). The doping of a semiconductor along with another substance is known as co-doping. For example, when Co and N both are added to MoO₂ nanowires, it will increase the electronic performance of this nanowire [128,129,130]. Various properties like electronic, optical and morphological characteristics of p-doped polyfuran (PF) molecular thin films were investigated by the researchers using a wide range of doping ratios using the electrical doping method. When the doping concentration is ≤ 2%, then it increased the short-circuit current of this PF-based photovoltaic device significantly [44].

Comparative diagram at various electrical dopings along with conventional Fe- and Ni-doping

If we take a close look at the doping concentration from Fig. 6, we can observe that before the year 2000, doping concentration was high, but after that, it becomes lower. Therefore, it can be emphasized that though the device performance has been enhanced, doping concentration is reducing very fast [124, 128, 134,135,136].

Doping concentration year-wise graph

The optical and electrical doping process was also introduced into the silicon with holmium in the year 1999. Intermolecular hybridization state is also governed by the electrical doping process. It was established that for organic semiconductors, molecular electrical doping was found to be at odds when other methods were proved in this field, for example, the formation of polaron. Therefore, the main objective of this study is to propose a polaron-derived state with decreased ionization energy using ultraviolet photoelectrospectroscopy [134]. The electrical doping profile in ferroelectric film capacitors was investigated by the group of researchers using capacitance–voltage measurement. In this experimental study, profiling effect of electrical doping concentration in ferroelectrics was investigated using the following effects of

• A field and spatially dependent permittivity.

• Domain switching analysis of Schottky profiling [135].

From Fig. 7, we can observe the operating temperature for this type of doping-dependent device operation. Though the graph is a little bit complex, it does not obey any specified rule. Therefore, we can conclude it like that temperature requirement is solely depending on the type of materials that are used for this operation.

Temperature for doping

A new model was proposed for the dissociation of carbon atoms at the copper/silica molecular thin layer interface using catalytically hydrogenated graphene meshes using a semipermanent electrical doping method. This process enables stable electronic doping through C–N bonds. Furthermore, the effect of trap states on the electrical doping for organic semiconductors was also investigated. The direct charge transfer process from the trap state of the host molecules to the dopant molecules raised the electrical effect for organic semiconductors. This type of doping process enhances conductivity. Therefore, trap density and energy are also analyzed using impedance spectroscopy [136].

It is observed clearly from Fig. 8 that the thickness of the wafer layers is reducing year wise. The more the time increasing, the layer thickness reduces, and the performance of the device increases.

The thickness of the wafer

Electrically doped and undoped poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) along with tetrafluorotetracyanoquinodimethane films were composed using photoelectron spectroscopy method and also investigated their current–voltage characteristics. Thus, it can be observed that the depletion region was created for the PFO interface. Therefore, the current was increased subsequently [137, 138]. For high-temperature gas sensors, this method of doping plays an important role. The conductivity and gas sensitivity of Ga₂ O ₃ thin films was investigated. It was observed that this doping concentration influenced the surface sensitivity [138].

From Fig. 9, it is observed that the cutoff wavelength of the devices reduces sharply within a few decades. Hence, device performance enhanced significantly. Table 3 gives a close look at different characteristics of the devices which follow either electrical doping or conventional doping procedure.

The wavelength of the devices reduces

In this survey, we have reviewed the works which were already established using the electrical doping process. In our works, we used the electrical doping process using the Quantumwise software simulation package in the ATK-VNL atmosphere. The version of this software is 13.8.0. This software simulation is based on first-principle formalisms which is again strongly supported by DFT and NEGF formalisms. Quantumwise is a compact set of atomic-scale modeling tools. These tools were developed in the year of 2003 by some software professionals along with academicians. These ATK-VNL simulations engines help us to calculate the electronic structure as well as to formulate intercorrelations of atomic orbitals. This platform helps us to introduce electrical doping into the molecular level.

Conclusión

This report illustrates briefly a comparison between conventional doping and electrical doping process. Though the electrical doping process is not so newer process, the implementation of this process with the help of DFT- and NEGF-based first-principle approach gives a new twist to this phenomenon. Therefore, electrical doping is to be implemented in many molecular modeling approaches to bring a new era in nanoelectronics. This study takes a close look at the electrical doping phenomenon such as why it is important, how it works for the molecular modeling approach, calculation of electrical doping concentration, etc. Hence, we provide a comparative study between electrical doping and conventional doping process for acepromazine molecule. To conclude it is emphasized that in future this is one of the approaches which will prove itself in the field of nanodevice modeling.

Disponibilidad de datos y materiales

All the data and material are available in the manuscript.

Abreviaturas

DFT:

Teoría funcional de la densidad

NEGF:

Non-equilibrium Greens’ function

OPVC:

Organic photovoltaic cell

ATK-VNL:

Atomistix Tool Kit-Virtual Nano-Laboratory

HOMO–LUMO:

Highest occupied molecular orbital–lowest unoccupied molecular orbital

CNT:

Nanotubos de carbono

I–V:

Current–voltage

QCA:

Quantum cellular automata

YN₂ :

Yttrium nitrite

ATK-SE:

Atomistix Tool Kit-Semi-empirical

Transistor de efecto de campo de capacitancia negativa ZrOx con comportamiento de oscilación sub-60 subumbral Fotoluminiscencia y refuerzo del acoplamiento electrón-fonón en nanocables de CdS con concentración variable de dopante Sn (IV)