P-type Doping Effect Research Articles

P-type doped AlxGa1-xAs nanowire photocathode: A theoretical perspective on structural and optoelectronic properties

In this work, the effect of p-type doping on the structural, electronic, and optical properties of AlxGa1-xAs nanowires are investigated by first-principles calculations. Different doping elements (Be, Mg, Zn), doping methods (interstitial and substitution doping) and doping concentration are considered. The calculations of formation energy suggest that the structural stability of p-type AlxGa1-xAs nanowires is gradually weaken as the rise of doping concentration and Al composition. Besides, the difficulty of forming substitution doping for different doping elements obeys the following order: Be<Mg<Zn. In addition, the substitution doping atom tends to replace Ga atom rather than Al atom to form substitution doping structure. After substitution doping, all energy bands shift to higher energy region due to the orbital hybridization of electronic states induced by impurity atom and nanowire atoms. Moreover, the substitution doping leads to the Fermi level entering into the valence band, resulting in obviously p-type conductivity. The p-type modulation doping is indeed effective in the axial type AlxGa1-xAs nanowires with p-type carrier concentration varying between 1.85×1020 cm-3 and 4.42×1020 cm-3, and the conductivity will be further enhanced with increasing substitution doping concentration or Al composition. Finally, the optical absorption of AlxGa1-xAs nanowire photocathodes can be effectively enhanced through BeGa doping. Our findings not only present a comprehensive understanding of p-type doping mechanism of AlxGa1-xAs nanowires, but also provide a theoretical basis for preparing AlxGa1-xAs nanowire based photoelectric devices with p-type properties.

Investigation of electronic, optical and thermoelectric properties in orthorhombic perovskite SmFeO3

In this work, we have investigated the electronic, optical, and thermoelectric properties of orthorhombic perovskite SmFeO3 using density functional and Boltzmann transport theories, for renewable energy applications. The modeling of the exact electron exchange-correlation has been carried out using both Generalized Gradient Approximation (GGA) and a functional modified with Hubbard interactions. The spin-polarized calculations show that SmFeO3 adopts a G-type antiferromagnetic configuration. The studied compound's electronic band structure and density of states analysis reveal its p-type semiconductor behavior. Furthermore, the optical properties such as real ε1(ω) and imaginary ε2(ω) components of the dielectric function as well as other conventional optical parameters, were investigated. The results show that SmFeO3 is a promising material for optoelectronic applications. The calculated transport properties including the Seebeck coefficient (S), the electrical conductivity (σ/τ), the electronic thermal conductivity (k0/τ) and the electronic figure of merit (ZTe) show significant results. The studied perovskite is also a potential candidate for thermoelectric applications, due to its high Seebeck coefficient, reaching 2388 μV/K, and the large electronic figure of merit which is close to 1 at room temperature. To improve the thermoelectric performance of SmFeO3 material, we have studied the effect of both p-type and n-type doping on its thermoelectric behavior at different temperature values.

Advanced doping method for highly conductive CNT fibers with enhanced thermal stability

Abstract Due to the inherent limitations of metals, such as their poor performance at high temperatures caused by thermo-oxidation and expansion, carbon nanotube yarns (CNTFs) have emerged as promising alternatives because of their high electrical conductivity and thermal stability. Doping of CNTFs has been widely studied because it significantly increases electrical conductivity through a simple process. Despite these advantages, doped CNTFs are not suitable for extreme environments, especially high temperatures. This is due to the weak interaction between dopants and CNTFs, along with the low thermal stability of the dopants themselves, leading to dopant decomposition and oxidation at high temperatures. Herein, we present doped CNTFs that are covalently functionalized with a nitrogen compound composed of imide and nitro groups, which are renowned for good thermal stability. The electron-withdrawing effect of this nitrogen compound polarizes the CNTFs to a positive charge, inducing p-type doping effects and enhancing electrical conductivity from 2989 to 4008 S cm−1. The strong covalent bonding between the nitrogen compound and CNTFs, along with the thermal stability of the dopants, ensures that the electrical conductivity of our doped CNTFs is maintained even after annealing at 300 °C for 12 h. Our proposed doped CNTFs offer a guideline for expanding the practical applications of doped CNTFs to a wider range of high-temperature environments.

Regulating the electronic and crystal structure of Na3V2(PO4)3 by pillar ionic substitution and p-type doping effects

Currently, low intrinsic conductivity seriously affects the development and large-scale application of Na3V2(PO4)3 (NVP). Herein, the binary K+/Mn2+ co-substituted Na2.96+xK0.04 V2-xMnx(PO4)3 (x = 0.005, 0, 0.01, 0.04) with enwrapped carbon nanotubes (CNTs) are synthesised. The incorporation of CNTs can form an effective conductive framework and provide more conductive paths, thus reducing the resistance of electron and ion migration thereby increasing the overall conductivity. Notably, replacing Na+ by pillar ion K+ with a larger radius can effectively strengthen the crystal structure of NVP, thus increasing the cycling stability of the battery. Besides, due to the differences in atomic radius and electronic structure between Mn2+ and V3+, this substitution can change the local environment of Na+ in the crystal, thus affecting its migration behaviour. Because of the larger ionic radius of Mn2+, it helps to increase the inter-facial distance in the crystal structure, which is favourable to promote the migration of Na+. Meanwhile, divalent Mn2+ occupying V3+ site can generate p-type doping effects, which introduces more hole carriers, thus increasing the intrinsic conductivity of the material. Accordingly, the optimized NVP/C@KMn0.01 achieves a capacity of 106.4 mAh g−1 at 1C, and maintains 98.1 mAh g−1 with a retention rate of 92.19 % after 230 cycles. At 15C, it reveals 106.1 mAh g−1 and keeps 82.5 mAh g−1 after 5800 cycles, corresponding to a capacity retention of 77.76 %. Furthermore, NVP/C@KMn0.01//CHC full cell delivers a high value of 155.0 mAh g−1 and enables to lighten the LED bulbs, indicating its excellent practical application prospects. The improved crystal structure of NVP/C@KMn0.01 is further verified by post-cycled XRD/SEM/XPS measurements.

Conductive three-layer-stacked polycrystalline graphene intercalated with FeCl3

Graphene has attracted attention as a new transparent conductive film (TCF) because of its transparency, stability, strength, and versatility. However, it has a higher resistance than conventional TCFs. Recently, vapor transport intercalation with doping effect materials has been investigated to reduce the resistivity of graphene. Studies have revealed a correlation between the stacking structure and the intercalation efficiency, which favors smaller interactions between the graphene layers. In this study, polycrystalline graphene, which consists of small domains, grown by chemical vapor deposition is stacked in three layers using a layer-by-layer method, and the graphene layers are intentionally randomly stacked to suppress the interlayer interactions. Intercalation of FeCl3, which has p-type doping effects, into randomly stacked three-layer graphene (3LG) significantly reduces the sheet resistance (Rs) of 3LG from 500 to 41 Ω/sq. Interestingly, Raman mapping of the G peak shift of FeCl3 intercalated into randomly stacked 3LG indicates that in-plane intercalation proceeds homogeneously, even though strong interlayer interactions such as AB stacking are observed in some parts of 3LG. This study reveals that a randomly stacked polycrystalline graphene layer is advantageous for intercalation.

A Multiscale Simulation on Aluminum Ion Implantation-Induced Defects in 4H-SiC MOSFETs

Aluminum (Al) ion implantation is one of the most important technologies in SiC device manufacturing processes due to its ability to produce the p-type doping effect, which is essential to building p–n junctions and blocking high voltages. However, besides the doping effect, defects are also probably induced by the implantation. Here, the impacts of Al ion implantation-induced defects on 4H-SiC MOSFET channel transport behaviors are studied using a multiscale simulation flow, including the molecular dynamics (MD) simulation, density functional theory (DFT) calculation, and tight-binding (TB) model-based quantum transport simulation. The simulation results show that an Al ion can not only replace a Si lattice site to realize the p-doping effect, but it can also replace the C lattice site to induce mid-gap trap levels or become an interstitial to induce the n-doping effect. Moreover, the implantation tends to bring additional point defects to the 4H-SiC body region near the Al ions, which will lead to more complicated coupling effects between them, such as degrading the p-type doping effect by trapping free hole carriers and inducing new trap states at the 4H-SiC bandgap. The quantum transport simulations indicate that these coupling effects will impede local electron transports, compensating for the doping effect and increasing the leakage current of the 4H-SiC MOSFET. In this study, the complicated coupling effects between the implanted Al ions and the implantation-induced point defects are revealed, which provides new references for experiments to increase the accepter activation rate and restrain the defect effect in SiC devices.

Simultaneous modification of Na-rich and Ca2+/Ni2+ dual-substitution boosting superior electrochemical performance of Na3V2(PO4)3

The lower intrinsic electronic conductivity of Na3V2(PO4)3(NVP) has seriously limited its further development. Herein, Ca2+/Ni2+ co-doped and carbon nanotubes (CNTs)-coated Na3+x+0.04V1.96-xCa0.04Nix(PO4)3/C@CNTs (CaNi0.07@CNTs) system is presented. Both Ca2+ and Ni2+ are substituted for V3+, triggering charge compensation and producing p-type doping effect, generating abundant hole carriers to improve electronic conductivity. Furthermore, the ionic radius of Ca2+ is significantly larger than that of V3+, so introduction of Ca2+ can support NVP crystal structure and improve the stability. Furthermore, the introduction of Ca2+ can increase the lattice spacing, thus expanding the transport channels for sodium ions. The introduction of Ni2+ reduces the resistance suffered during charge transport and optimizes the chemical properties. Meanwhile, due to low valence of Ca2+ and Ni2+, more Na+ are designed to be introduced to the NVP system for charge balance. The Na-rich strategy induces excess active Na+ participating in the de-intercalation process to supply more reversible capacities. Furthermore, the CNTs wrapped around the active grains serves to buffer deformation of the crystal and to establish a conductive network connecting the particles. The after-cycling XRD/SEM/XPS further confirms the improved crystal stability of CaNi0.07@CNTs. Comprehensively, CaNi0.07@CNTs possess superior sodium storage in half and full cells.

Dual redox reaction of V3+/V4+ and V4+/V5+ with in-situ carbonization of chitosan quaternary ammonium promoting sodium storage property and safety of Na3V2(PO4)3

Na3V2(PO4)3 (NVP) has been limited by the poor ionic and electronic conductivity. Besides, the sole redox pair of V3+/V4+ releases a relatively low capacity. Currently, a simultaneous modification strategy of Fe2+ substitution and chitosan quaternary ammonium (CHACC) in-situ carbonization is proposed to optimize NVP for the first time. Fe2+ substitution can generate a classic P-type doping effect to supply abundant hole carries, effectively enhancing the electronic conductivity. Noteworthily, a new redox reaction of V4+/V5+ is activated after Fe-doping, which releases extra reversible capacities at a high voltage platform of 3.9 V, obviously increasing the active capacity and energy density. Moreover, the reaction mechanism of reversible V4+/V5+ has been deeply explored by ex-situ XPS. Furthermore, Cl− in the CHACC infiltrates into the NVP phase to replace part of (PO4)3−, which can provide a wider migration path and more dedicated space for Na(2) type Na+, improving the ionic conductivity. Moreover, the N element in the CHACC results in vast of active sites and defects in the carbon substrate, which induces the graphitization of hydrogel carbon materials due to the distortion of lattice caused by defects. Comprehensively, the modified NVP/C-CHACC-Fe0.07 shows superior electrochemical and kinetic properties. It reveals a capacity of 121.1 mAh g−1 at 0.1 C. At 30 C and 120 C, it shows capacities of 81.2 mAh g−1 and 70.5 mAh g−1 with retention rates of 72.4 % and 71.2 % after 4000 and 7000 cycles, respectively. Innovatively, temperature monitoring system analyzes the temperature change and safety of the NVP/C-CHACC-Fe0.07 cell, demonstrating that the variate is only 0.8 °C during each cycle. And the temperature remains stable in the long-term operation, suggesting its excellent stability and safety.

Effect of sandwiched YbCl3 layer thickness on exciton dynamics of Yb3+ doped CsPbCl3 perovskite photodetectors

Yb3+ doped CsPbCl3 metal halide perovskite photodetectors (PDs) in the structure of CsPbCl3(50 nm)/YbCl3(x nm)/CsPbCl3(50 nm), in which x ranges from 10 to 40 nm corresponding to the molar ratio from 6.3% to 25.2%, are fabricated by thermal evaporation on Si/SiO2 substrate. Photoresponse from 350 to 980 nm have been achieved with the optimal responsivity (R) of 3959, 5425, 955 A W−1 for the case of 20 nm YbCl3 at the wavelength (λ) of 420, 680 and 980 nm, respectively. A series of photophysical and electrical characterization has been performed and it is found that the remarkably improved photoresponse originates from the combining effects of upconversion and defects passivation from Yb3+. Moreover, the optimal YbCl3 thickness of 20 nm can be ascribed to the balance between upconversion and concentration quenching of Yb3+. The influence of the YbCl3 doping on the CsPbCl3 electronic structure is investigated and downshifting and stabilization of valence band maximum (VBM) can be attributed to the p-type doping and counteracting effect of Yb3+ and Cl−, respectively.

Carrier-mediated ferromagnetism in Mn(II)-doped ZnTe thin films and their optical properties: A first-principles study

We have investigated the opto-electronic and magnetic properties of Mn(II)-doped ZnTe thin films by employing Density Functional Theory (DFT). In the absence of additional carriers, spin-up Mn-ta levels are fully occupied, leading to a super-exchange mechanism. The effect of additional p-type doping on the ferromagnetism is studied by considering the addition of hole carriers, Zn vacancies, and C co-doping, and we found that in all cases, coupling of hole carriers with the spin-up Mn-states causes the stability of the ferromagnetism in the Mn(II)-doped ZnTe thin films. We discovered through the optical study that Mn(II) doping at the Zn site widens ZnTe's bandgap and produces spin-forbidden d-d transition peaks on the low energy side of the bandgap. The p-type defects in Mn(II)-doped films produce absorption peaks in the infrared region and improve the absorption efficiency. In addition, the optical bandgap and spin-forbidden d-d transition of Mn(II) to different modes of spin-spin interactions were correlated, and we found a red shift of d-d intra-band transition peaks as well as an optical bandgap in the FM-coupled Mn(II) ions system and a blue shift in the AFM coupled ions system, supporting the experimental observations.

Selective Surface Modification and Layer Thinning of MoS2 via Ultraviolet-Light Irradiation in an Ionic Solution: Implications for Multifunctional Nanoelectronic Devices

The electrical properties of transition-metal dichalcogenides (TMDs), such as MoS2, are highly dependent on carrier doping and layer thickness. The ability to selectively control these two critical characteristics is of great importance in order to develop TMD-based multifunctional nanoelectronic device applications, which remains challenging. Here, we report a strategy for controllable surface modification and layer thinning of MoS2 via ultraviolet (UV)-light irradiation in a silver ionic (Ag+) solution environment. The results show that, by adjustment of the UV irradiation time, nanostructured Ag ultrathin films (∼2.9 nm) are uniformly deposited on monolayer MoS2 and can lead to a controllable p-type doping effect, while the thickness of MoS2 from few-layer to thick-layer could be thinned to the atomic monolayer limit. Both Ag nanostructure deposition and layer thinning have been evidenced to initiate from the edges of MoS2, independent of the edge type, thus revealing a unique UV-light-assisted defect-induced surface modification and layer-thinning mechanism. Overall, this study provides a simple methodology for the selective control of doping and layer thickness in TMDs, paving the way for developing multifunctional nanoelectronics and integrated optoelectronics.

Tailorable Electronic and Electric Properties of Graphene with Selective Decoration of Silver Nanoparticles by Laser-Assisted Photoreduction.

While graphene shows great potential for diverse device applications, to broaden the scope of graphene-based device applications further, it would be necessary to tune the electronic state of graphene and its resultant electrical properties properly. Surface decoration with metal nanoparticles is one of the efficient doping methods to control the properties of two-dimensional materials. Here, we report the p-type doping effects in single-layer graphene decorated with silver nanoparticles (AgNPs) that were formed area-selectively by the facile one-step photoreduction (PR) process based on focused-laser irradiation. During the PR process, AgNPs were reduced on graphene in AgNO3 solution by laser-driven photoexcitation followed by chemical reactions. Based on scanning electron microscopy analyses, the morphology characteristics of AgNPs were shown to be modulated by the laser dwell time and power controllably. Further, p-type doping effects were demonstrated using graphene-field-effect transistor structures whose graphene channels were selectively decorated with AgNPs by the PR process, as validated by the decrease in channel resistance and the shift of the Dirac point voltage. Moreover, the growth of AgNPs was observed to be more active on the graphene channel that was laser-annealed ahead of the PR process, leading to enhancing the efficiency of this approach for altering device characteristics.

Experimental and theoretical insights into electronic properties of oxygen-doped MoTe2 field effect transistor

Modulating the electrical and photo-electrical properties is essential to enlighten the potential application in the case of field-effect transistors and other electronic devices. Molybdenum ditelluride (MoTe2), which has a limited energy gap and shows spin-orbit coupling, has piqued curiosity among two-dimensional (2D) transition metal dichalcogenides (TMDCs) and has appeared as a significant material with innovative electronic applications. In this work, we have reported the electrical modulation of multilayer MoTe2-FETs by gas doping under deep ultra-violet (DUV) light. After DUV treatment, the device characteristics were also investigated with oxygen doping. A shift in threshold voltage was observed from negative to positive back-gate voltage (Vbg), revealing a p-type doping effect. This doping effect is further confirmed through the Raman peaks, A1g and E12g were shifted towards higher wavenumbers. For pristine to 30-min doping intervals, the current ON/OFF ratio increased from 104 to 106 and the mobility of the device is enhanced from 22.36 cm2/V.s to 102.43 cm2/V.s. In addition, we used density functional theory (DFT) to investigate the impact of oxygen doping on the electrical and optical properties of MoTe2. The electronic bandgap was determined to be 0.8 eV, which can be a promising material for lower energy devices. The oxygen-doped MoTe2-based field-effect transistors are predicted to be a promising contender for low and high-temperature applications based on the highly intense peak of absorption spectra in the ultra-violet and visible regions of electromagnetic spectra.

Growth of Fe-doped and V-doped MoS2 and their magnetic-electrical effects

Magnetism in two-dimensional (2D) materials has attracted much attention recently. However, intrinsic magnetic 2D materials are rare and mostly unstable in ambient. Although heteroatom doping can introduce magnetism, the basic property especially the electrical-magnetic coupling property has been rarely revealed. Herein, both iron (Fe)-doped and vanadium (V)-doped MoS2 films were grown by chemical vapor deposition. Through studying the structure and electrical property of Fe-doped and V-doped MoS2, it was found that both Fe and V doping would decrease the electron concentration, exhibiting a p-type doping effect. Significantly, V-doped MoS2 displays a p-type conduction behavior. Although the carrier mobility decreases after heteroatom doping, both Fe and V doping could endow MoS2 with magnetism, in which the transfer curves of both MoS2 transistors exhibit a strong magnetic-dependent behavior. It is found that the magnetic response of Fe-doped MoS2 can be tuned from ~0.2 ​nA/T to ~1.3 ​nA/T, with the tunability much larger than that of V-doped MoS2. At last, the magnetic mechanism is discussed with the local magnetic property performed by magnetic force microscopy. The typical morphology-independent magnetic signal demonstrates the formed magnetic domain structure in Fe-doped MoS2. This study opens new potential to design novel magnetic-electrical devices.

Effect of p-type doping on the electronic characteristics of negative electron affinity Al0.5Ga0.5N nanowire photocathodes

Based on the first principles calculation method, we explored the impacts of p-type doping on the electronic characteristics of Al0.5Ga0.5N nanowire. Firstly, Al0.5Ga0.5N nanowires are simulated with different doping elements (Be, Mg and Zn), as well as different doping strategies (interstitial doping and substitutional doping). The estimated formation energies show that the p-type doping of Al0.5Ga0.5N nanowire is an endothermic process. Also, in the substitutional doping process, it is easier for dopant atoms to replace Ga atoms than Al atoms. The substitutional doping of Mg atom drops the nanowire electron affinity obviously, which promotes the transition of surface photoelectrons. Furthermore, it can be concluded that the substitutional doping contributes to the Fermi level cross the valence band and causing the nanowires to exhibit distinct p-type properties. Also, the charge density maps show that for Be and Mg substitutional doping system, the electron density around the dopant significantly decreases, which further verifies the p-type conductivity. Meanwhile, the p-type characteristic of Mg atom substitution doping is the most obvious. This work not only thoroughly explored the impacts of different doping schemes on the electronic characteristics of Al0.5Ga0.5N nanowires but also serves as a significant resource for developing high-quality p-type AlxGa1-xN nanowire photocathodes.

Surface Dangling Bond Effect on Magnetic Property of Mn-doped ZnO Nanowires

We investigate the magnetic properties of Mn-doped ZnO nanowires (NWs) using the local spin density approximation (LSDA) and the LSDA+U approach, where U represents the on-site Coulomb interaction. In carrier-free (Zn,Mn)O NWs, the majority Mn ta states are fully occupied, leading to an antiferromagnetic ground state. We examine the effect of additional p-type doping on the ferromagnetism by considering surface O dangling bonds. Localized hole carriers are generated in the majority ta states and promote a ferromagnetic ordering via double exchange interactions, similar to the trend of bulk (Zn,Mn)O. The ferromagnetic coupling tends to increase with increasing of the hole carrier density.

The effect of DUV-O2 doping on WSe2 FET for sensing applications: Experimental and theoretical approach

Tungsten Diselenide (WSe2) is an emerging electronic material among the TMDCs family exhibiting unique properties, like high surface-to-volume ratio with direct bandgap. Although the external factors contribute majorly on system’s outcome, but the environmental problems can be resolved to achieve the high efficiency of device. Here, to resolve the environmental factors and to improve the efficiency of WSe2 based field effect transistors (FETs), p-type doping effect from (deep ultraviolet light) DUV ​+ ​O2 (oxygen) treatment using mechanical exfoliation method has been employed. By the p-type doping through DUV ​+ ​O2 treatment, the mobility, the ION/IOFF ratio and the charge carrier density enhanced to 68 ​cm2/V, 0.46 ​× ​107 and 4.6 ​× ​1012 ​cm−2 respectively. This doping effect is further confirmed by the negative change of threshold voltage (Vth) as well as Raman peaks at higher wavelength values. Moreover, the structural, optical, and electronic properties of pristine and doped WSe2 by first principal calculations were also investigated. For these theoretical calculations, the full-potential linearized augmented plane wave (FP-LAPW) with Heyd-Scuseria-Ernzerhof hybrid functional (HSE) and generalized gradient approximation (GGA) approach has been utilized to the Quantum espresso and WIEN2k code respectively. For the optical analysis and to examine the behavior of the material before and after doping in the band structure the substitution of oxygen in chalcogenides Se was studied.

Fermi-Level Modulation of Chemical Vapor Deposition-Grown Monolayer Graphene via Nanoparticles to Macromolecular Dopants.

It is critical to modulate the Fermi level of graphene for the development of high-performance electronic and optoelectronic devices. Here, we have demonstrated the modulation of the Fermi level of chemical vapor deposition (CVD)-grown monolayer graphene (MLG) via doping with nanoparticles to macromolecules such as titanium dioxide nanoparticles (TiO2 NPs), nitric acid (HNO3), octadecyltrimethoxysilane (OTS) self-assembled monolayer (SAM), and poly(3,4-ethylene-dioxythiophene):polystyrene sulfonate (PEDOT:PSS). The electronic properties of pristine and doped graphene samples were investigated by Raman spectroscopy and electrical transport measurements. The right shifting of G and 2D peaks and reduction in 2D to G peak intensity ratio (I2D/IG) assured that the dopants induced a p-type doping effect. Upon doping, the shifting of the Dirac point towards positive voltage validates the increment of the hole concentration in graphene and thus downward shift of the Fermi level. More importantly, the combination of HNO3/TiO2 NP doping on graphene yields a substantially larger change in the Fermi level of MLG. Our study may be useful for the development of graphene-based high-performance flexible electronic devices.

Highly Photoluminescent Monolayer MoS2 and WS2 Achieved via Superacid Assisted Vacancy Reparation and Doping Strategy (Laser Photonics Rev. 15(12)/2021)

Monolayer Photoluminescence In article number 2100104 by Weizhen Liu, Haiyang Xu, and co-workers, a novel organic superacid trifluoromethanesulfonic (TFMS) is explored to significantly improve the photoluminescence quantum yield of CVD-grown monolayer MoS2 and WS2 to 14.1% and 56.7%, respectively. Through in-depth study and analysis with scanning transmission electron microscopy and density functional theory calculation, luminescence enhancement mechanism is attributed to a synergistic effect of TFMS-assisted sulfur vacancy repairation and p-type doping.

Tuning the carrier type and density of monolayer tin selenide via organic molecular doping

Utilizing first-principles calculations, charge transfer doping process of single layer tin selenide (SL-SnSe) via the surface adsorption of various organic molecules was investigated. Effective p-type SnSe, with carrier concentration exceeding 3.59 × 1013 cm−2, was obtained upon adsorption of tetracyanoquinodimethane or 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane on SL-SnSe due to their lowest unoccupied molecular orbitals acting as shallow acceptor states. While we could not obtain effective n-type SnSe through adsorption of tetrathiafulvalene (TTF) or 1,4,5,8-tetrathianaphthalene on pristine SnSe due to their highest occupied molecular orbitals (HOMO) being far from the conduction band edge of SnSe, this disadvantageous situation can be amended by the introduction of an external electric field perpendicular to the monolayer surface. It is found that Snvac will facilitate charge transfer from TTF to SnSe through introducing an unoccupied gap state just above the HOMO of TTF, thereby partially compensating for the p-type doping effect of Snvac. Our results show that both effective p-type and n-type SnSe can be obtained and tuned by charge transfer doping, which is necessary to promote its applications in nanoelectronics, thermoelectrics and optoelectronics.