Electron Mobility Values Research Articles

Enabling 2D Electron Gas with High Room-Temperature Electron Mobility Exceeding 100cm2 Vs-1 at a Perovskite Oxide Interface.

In perovskite oxide heterostructures, bulk functional properties coexist with emergent physical phenomena at epitaxial interfaces. Notably, charge transfer at the interface between two insulating oxide layers can lead to the formation of a 2D electron gas (2DEG) with possible applications in, e.g., high-electron-mobility transistors and ferroelectric field-effect transistors. So far, the realization of oxide 2DEGs is, however, largely limited to the interface between the single-crystal substrate and epitaxial film, preventing their deliberate placement inside a larger device architecture. Additionally, the substrate-limited quality of perovskite oxide interfaces hampers room-temperature (RT) 2DEG performance due to notoriously low electron mobility. In this work, the controlled creation of an interfacial 2DEG at the epitaxial interface between perovskite oxides BaSnO3 and LaInO3 is demonstrated with enhanced RT electron mobility values up to 119 cm2 Vs-1-the highest RT value reported so far for a perovskite oxide 2DEG. Using a combination of state-of-the-art deposition modes during oxide molecular beam epitaxy, this approach opens up another degree of freedom in optimization and in situ control of the interface between two epitaxial oxide layers away from the substrate interface. Thus this approach is expected to apply to the general class of perovskite oxide 2DEG systems and to enable their improved compatibility with novel device concepts and integration across materialsplatforms.

Bis‐Indeno‐Fused Tetraazaanthracene Hybrids: Straightforward Synthesis and Studies of Optical and Electronic Properties

The synthesis and the studies of optical and electronic properties of new bis‐indenone‐fused tetraazaanthracene isomers as electron accepting materials are reported. TD‐DFT calculations have been also undertaken and corroborate experiments. Organic field effect transistors demonstrated unipolar n‐type characteristics and average electron mobility values.

Hybrid Modeling of Miniaturized 50 W Annular Hall Thruster

A 50-W-class annular Hall thruster is studied with a hybrid axial–radial two-dimensional model. Ions are described by a kinetic approach, whereas fluid conservation equations are solved for electrons. In such models, additional (anomalous) contributions must be added to the momentum-transfer electron collision frequency to obtain realistic values of the cross-field electron mobility. First, a parametric study is performed, where anomalous transport is described with a simple two-region model based on constant empirical parameters. The simulated global performance is subsequently compared with experimental measurements. Then, laser-induced fluorescence ion velocity measurements are employed to infer a continuous profile of the anomalous electron collision frequency along the channel centerline. The model reproduces the performance, the acceleration structure, the current oscillations, and the doubly charged ion fraction of the laboratory thruster. Measurements of the ion velocity distribution function highlight the presence of a slow ion population in the near plume. The production of the slow ions and their growth for increasing distances from the thruster channel exit is qualitatively reproduced by the model. The results obtained suggest that the generation and dynamics of the observed slow ions can be attributed to the presence of energetic electrons in the plume.

New Electron‐Transporting Materials Based on Pyrimidine and Thiazolopyridine Moieties for High‐Efficiency Organic Light‐Emitting Diodes

Using the pyrimidine moiety with electron‐accepting capability and the thiazolopyridine moiety, commonly used as a moiety with an electron‐withdrawing group in organic semiconductors, for the first time 2‐(3‐(4,6‐di(phenanthren‐9‐yl)pyrimidin‐2‐yl)phenyl)thiazolo[5,4‐b]pyridine (DPPTP) is designed and synthesized to enhance electron transport capabilities compared to the conventional electron‐transporting layer, tris(8‐hydroxyquinoline)aluminum (Alq3). The photoluminescence maxima in solution and film states are observed at 391 and 410 nm, respectively. Although the photoluminescence quantum yield is relatively low at 2% in the solution state, it increases to 28% in the film state. The measured electron mobility values from the fabricated device range from 1.46 × 10−5 to 2.0 × 10−5 cm2 V−1 s−1, ≈5.7 times faster than the electron mobility of Alq3. In a fluorescent blue device utilizing the newly synthesized DPPTP as the electron‐transporting layer, the current efficiency is 4.36 cd A−1, and the external quantum efficiency is 3.76%, representing a 1.3‐fold improvement in efficiency compared to Alq3 devices.

Carrier transport in bulk and two-dimensional Zn2(V,Nb,Ta)N3 ternary nitrides.

Density functional theory-based simulations are applied to study the electronic structures, carrier masses, carrier mobility and carrier relaxation times in bulk and two-dimensional (2D) Zn2(V,Nb,Ta)N3 ternary nitrides. Bulk Zn2(V,Nb,Ta)N3 possess moderate band gap sizes of 2.17 eV, 3.11 eV, and 3.40 eV, respectively. Two-dimensional Zn2(V,Nb,Ta)N3 have slightly higher band gap sizes of 2.77 eV, 3.33 eV, and 3.23 eV, respectively. Carrier mass, carrier mobility and carrier relaxation time are found to be anisotropic in all the studied structures. Bulk and 2D samples show an order of magnitude higher electron mobility compared to hole mobility. The highest electron mobility in bulk Zn2NbN3 and Zn2TaN3 is about ∼103 cm2 V-1 s-1. Importantly, for 2D Zn2NbN3, an abnormally high electron mobility of 1.67 × 104 cm2 V-1 s-1 is observed, which is not inferior to the highest known electron mobility values in 2D materials. Such a high electron mobility in 2D Zn2NbN3 can be attributed to a strong delocalization of the conduction band minimum, which is responsible for electron transport. Therefore, this work opens up new materials for high performance nanodevices, such as tandem solar cells and field-effect transistors. This study also provides deep physical insights into the nature of carrier transport mechanisms in bulk and 2D Zn2(V,Nb,Ta)N3 ternary nitrides.

Exceptional electron transport characteristics of naphthalene diimide-based materials for perovskite photovoltaic devices

Some electron transporting layers (ETLs) were designed for perovskite solar cells (PSCs) and contained NDIID (N,N′-bis(1-indanyl) naphthalene-1,4,5,8-tetracarboxylic diimide) core, in which R groups were attached to phenyl rings, where R = H (NDIID), SiF3, SiCl3, SiBr3, SiCN3, SiH3, SiMe3, SiOH3, SiOMe3, SiSH3, SiSMe3, Si(NH2)3, and Si(NMe2)3. Density functional theory (DFT) computations were conducted to investigate structural, electronic, and optical features of NDIID-based ETLs. The LUMO levels of all ETLs could be positioned lower compared to that of CH(NH2)2PbI3-xBrx perovskite after their coupling in the assembled PSCs to efficiently inject electrons from the CH(NH2)2PbI3-xBrx towards the Al electrode. Furthermore, the HOMO levels of all ETLs had much deeper energies (changing in the range of −5.54 to −6.94 eV) than that of CH(NH2)2PbI3-xBrx, validating stopped backward hole transfer toward the valence band of perovskite (−5.4 eV). The hole mobilities of all samples were very much smaller than their related electron mobility values. The NDIID-SiMe3 ETL revealed utmost calculated electron mobility of 229.459 cm2V−1s−1, displaying a larger value compared to 202.510 cm2V−1s−1 for NDIID reference ETL. All calculated power conversion efficiencies (PCEs) of PSCs were very comparable (PCEs were about 22.5–23.7 %) so that four NDIID-Si(NH2)3, NDIID-SiMe3, NDIID, and NDIID-Si(NMe2)3 ETLs displayed largest PCEs of 23.726, 23.710, 23.682, and 23.663 %, respectively, illustrating their exceptional efficacy.

The Impact of Polymorphism on Charge Transport Properties for Pyrene-FxTCNQ Cocrystals

Research on the charge transport properties of organic semiconductor materials is crucial for the development of organic sensors. In this paper, we investigated the charge transport properties of pyrene-TCNQ, pyrene-F2TCNQ, and pyrene-F4TCNQ cocrystals using the quantum nuclear tunneling model and Monte Carlo simulations to calculate charge mobility. At room temperature, we observed hole mobility values is 0.658 cm2V-1s-1 and electron mobility values is 1.492 cm2V-1s-1, respectively, for pyrene-TCNQ. As the number of F atoms in TCNQ increases, we observed an increase in both hole and electron mobility. Our results showed that the electron to hole mobility ratio was approximately 2.2 for pyrene-TCNQ, 0.6 for pyrene-F2TCNQ, and 0.5 for pyrene-F4TCNQ. Our findings suggest that the introduction of F atoms causes changes in the TCNQ molecular structure, cocrystal stacking mode, adjacent molecular distance, and intermolecular polarization. These changes lead to a modification of the reorganization energy and transfer integrals, ultimately affecting charge transport. Additionally, our results showed that transport along the π-π direction in the three cocrystals exhibited strong anisotropic characteristics, which were much larger than those observed in the other two directions.

Formation of Highly Conductive Interfaces in Crystalline Ionic Liquid-Gated Unipolar MoTe2/h-BN Field-Effect Transistor.

2H MoTe2 (molybdenum ditelluride) has generated significant interest because of its superconducting, nonvolatile memory, and semiconducting of new materials, and it has a large range of electrical properties. The combination of transition metal dichalcogenides (TMDCs) and two dimensional (2D) materials like hexagonal boron nitride (h-BN) in lateral heterostructures offers a unique platform for designing and engineering novel electronic devices. We report the fabrication of highly conductive interfaces in crystalline ionic liquid-gated (ILG) field-effect transistors (FETs) consisting of a few layers of MoTe2/h-BN heterojunctions. In our initial exploration of tellurium-based semiconducting TMDs, we directed our attention to MoTe2 crystals with thicknesses exceeding 12 nm. Our primary focus centered on investigating the transport characteristics and quantitatively assessing the surface interface heterostructure. Our transconductance (gm) measurements indicate that the very efficient carrier modulation with an ILG FET is two times larger than standard back gating, and it demonstrates unipolarity of the device. The ILG FET exhibited highly unipolar p-type behavior with a high on/off ratio, and it significantly increased the mobility in MoTe2/h-BN heterochannels, achieving improvement as one of the highest recorded mobility increments. Specifically, we observed hole and electron mobility values ranging from 345 cm2 V-1 s-1 to 285 cm2 V-1 s-1 at 80 K. We predict that our ability to observe the intrinsic, heterointerface conduction in the channels was due to a drastic reduction of the Schottky barriers, and electrostatic gating is suggested as a method for controlling the phase transitions in the few layers of TMDC FETs. Moreover, the simultaneous structural phase transitions throughout the sample, achieved through electrostatic doping control, presents new opportunities for developing phase change devices using atomically thin membranes.

Anisotropic Crystal Structure and High Electron Mobility of Novel Ternary Janus P6XY Monolayers (X/Y = S, Se, Te): First‐Principles Examinations

AbstractRecently, by forming a P‐rich P–S system, the P3S monolayer has been predicted to have good resistance to air oxidation, large band gap, high absorption, and superior mobility. Inheriting this prediction, a series of ternary Janus P6XY (X/Y = S, Se, and Te; X ≠ Y) monolayers based on P3X nanosheet are designed and studied. The structures of P6XY monolayers are confirmed to be stable based on the evaluation of calculated results for phonon spectra, ab initio molecular dynamic simulations. It is also found that P6XY compounds possess anisotropic mechanical characteristics. All Janus structures are indirect semiconductors with large energy gaps varying from 2.12 to 2.60 eV calculated by the hybrid functional. Besides, biaxial strain significantly affects the electronic properties of the P6XY monolayers. In particular, the biaxial strains can induce a transition from indirect to direct bandgap in all three P6XY structures. The carrier mobility in the three proposed structures exhibits directional anisotropy and high electron mobility value, up to 1.27 × 103 cm2 V−1 s−1, which are suitable for applications in high‐performance and direction‐dependent nanoelectronic devices.

Well-Balanced Ambipolar Charge Transport of Diketopyrrolepyrrole-Based Copolymers: Organic Field-Effect Transistors and High-Voltage Logic Applications.

A poly (3,6-bis(thiophen-2-yl)-2,5-bis(2-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione-co-(2,3-bis(phenyl)acrylonitrile)) (PDPADPP) copolymer, composed of diketopyrrolopyrrole (DPP) and a cyano (nitrile) group with a vinylene spacer linking two benzene rings, is synthesized via a palladium-catalyzed Suzuki coupling reaction. The electrical performance of PDPADPP in organic field-effect transistors (OFETs) and circuits is investigated. The OFETs based on PDPADPP exhibit typical ambipolar transport characteristics, with the as-cast OFETs demonstrating low field-effect hole and electron mobility values of 0.016 and 0.004cm2 V-1 s-1 , respectively. However, after thermal annealing at 240°C, the OFETs exhibit improved transport characteristics with highly balanced ambipolar transport, showing average hole and electron mobility values of 0.065 and 0.116cm2 V-1 s-1 , respectively. To verify the application of the PDPADPP OFETs in high-voltage logic circuits, compact modeling using the industry-standard small-signal Berkeley short-channel IGFET model (BSIM) is performed, and the logic application characteristics are evaluated. The circuit simulation results demonstrate excellent logic application performance of the PDPADPP-based ambipolar transistor and illustrate that the device annealed at 240°C exhibits ideal circuit characteristics.

Newly efficient designed benzothiadiazole (A-D-A-D-A topology) based materials for organic photovoltaics: DFT Study

A series of fifteen small-donor molecules (R1- R15) based on acceptor-donor-acceptor-donor-acceptor (A-D-A-D-A) topology has been designed and investigated theoretically, by introducing three different cores (benzodithiophene, [1,2,5] thiadiazole and [3,4] quinoxaline) and π-spacers (cyclopentadithiophene, 2-(thiophene-2-yl)− 1 H-pyrrole and 2, 5-bithiazole) in the reference molecule (R). Computational analysis is based on the DFT and TD-DFT levels of theory. Herein, our findings confirmed that molecules having [3,4] quinoxaline core unit along with various π-spacers bithienyl (R3), cyclopentadithiophene (R7), 2-(thiophene-2-yl)− 1 H-pyrrole (R11) 2, 5-bithiazole (R15) exhibited narrow energy gap value 1.37, 1.23, 1.34 and 1.56 eV, respectively. Moreover, their absorption spectra are shifted towards UV-Visible and NIR regions at 885 nm, 972 nm, 885 nm, and 791 nm, respectively. Almost all donors display extraordinarily enhanced spectral responses and yield good hole (λh) and electron (λe) transporting values range from 0.132 to 0.231 and 0.162–0.275 eV, respectively. The predicted electron and hole mobility values for R7 are μe= 6.4 × 10-3 and μh= 1.18204 cm2/Vs, respectively. The Voc value ranges from 0.43 V to 1.62 V and the predicted power conversion efficiency PCE value of designed donors ranges from ∼2% - ∼13%. Interestingly, the R15 molecule shows an impressive PCE of over 13%. Thus, our computational studies provide a deep insight to confirm that among all R1, R2, R3, R5, R6, R7, R9, R10, R11, R13, R14, and R15 show extraordinary results than R. Hence, they would be a promising candidate on the base of orbital energy levels, λmax, PCEs values and photo physical properties which has been compared with the suggested PCBM acceptor for OSCs.

Homoepitaxial growth of (100) Si-doped β-Ga2O3 films via MOCVD

Homoepitaxial growth of Si-doped β-Ga2O3 films on semi-insulating (100) β-Ga2O3 substrates by metalorganic chemical vapor deposition (MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in (100) β-Ga2O3 films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga2O3 film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the (400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 1015 – 1.74 × 1020 cm−3. Hall measurements demonstrate a high electron mobility value of 51 cm2/(V·s), corresponding to a carrier concentration of 7.19 × 1018 cm−3 and a high activation efficiency of up to 61.5%. Transmission line model (TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10-4 Ω·cm2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 1019 cm−3, confirming the effective Si doing in the MOCVD epitaxy.

Effect of Substituents with the Different Electron-Donating Abilities on Optoelectronic Properties of Bipolar Thioxanthone Derivatives.

The synthesis and optoelectronic properties of four simple-structure thioxanthone derivatives employing thioxanthone as an acceptor unit, coupled with moieties having very different electron-donating abilities such as phenoxazine, 3,6-di-tert-butylcarbazole, 3,7-di-tert-butylphenothiazine, or 2,7-di-tert-butyl-9,9-dimethylacridane, are reported. The compounds form molecular glasses with glass transition temperatures reaching 116 °C. Ionization potentials of the compounds estimated by photoelectron emission method range from 5.42 to 5.74 eV. Thioxanthone derivatives containing 3,6-tert-butylcarbazole or 2,7-di-tert-butyl-9,9-dimethylacridane moieties with weak electron-donating strengths were characterized by bipolar charge transport with relatively close hole and electron mobility values of 6.8 × 10-5/2.4 × 10-5 and 3.1 × 10-5/4.6 × 10-6 cm2/(V s) recorded at 3.6 × 105 V/cm. The other compounds demonstrated hole-transporting properties. The films of thioxanthones containing phenoxazine or 2,7-di-tert-butyl-9,9-dimethylacridane moieties showed efficient thermally activated delayed fluorescence with a photoluminescence quantum yield of up to 50% due to the solid-state luminescence enhancement. Organic-light-emitting diodes containing the synthesized compounds as emitters showed very different external quantum efficiencies (0.9-10.3%) and blue, sky blue, green, or yellow electroluminescence colors, thus reflecting the effects of donor substituents.

Ambipolar Columnar Self-assembled Organic Semiconductors based on Heteroatom bay-Annulated Perylene Bisimides.

Highly electron-deficient heteroatom (N, S, Se) bay-annulated PBIs exhibiting ordered columnar phase over a wide mesomorphic range including ambient temperature are reported in this manuscript. These compounds with six peripheral n-decyloxy chains exhibited absorption spectra with high molar extinction coefficients, electron-deficient nature and self-assembling behaviour. A detailed comparison with the PBIs bearing six peripheral n-decyl chains was also carried out to get the valuable insights on the structure-property relations in this important class of organic semiconductors. Both of the PBI series were tested for their charge carrier mobility by space charge limited current method and found that they exhibit ambipolar conductivity. This is in contrary to the vast body of literature, where most of the PBI based semiconductors exhibit electron transport behaviour. In general, PBIs derived from tri-n-alkyl anilines exhibit higher mobility values than the PBIs derived from tri-n-alkoxy anilines. Especially, the ambipolar S-annulated PBI derived from tri-n-alkyl aniline exhibited highest hole (8.39×10-3 cm2 /V.s) and electron (1.5×10-2 cm2 /V.s) mobility values and promising for the application in organic electronics.

Designing of Thiophene [3, 2-b] Pyrrole Ring-Based NFAs for High-Performance Electron Transport Materials: A DFT Study.

Among the blended components of a photoactive layer in organic photovoltaic (OPV) cells, the acceptor is of high importance. This importance is attributed to its increased ability to withdraw electrons toward itself for their effective transport toward the respective electrode. In this research work, seven new non-fullerene acceptors were designed for their possible utilization in the OPVs. These molecules were designed through side-chain engineering of the PTBTP-4F molecule, with its fused pyrrole ring-based donor core and different strongly electron-withdrawing acceptors. To elucidate their effectiveness, the band gaps, absorption characteristics, chemical reactivity indices, and photovoltaic parameters of all of the architecture molecules were compared with the reference. Through various computational software, transition density matrices, graphs of absorption, and density of states were also plotted for these molecules. From some chemical reactivity indices and electron mobility values, it was proposed that our newly designed molecules could be better electron-transporting materials than the reference. Among all, TP1, due to its most stabilized frontier molecular orbitals, lowest band gap and excitation energies, highest absorption maxima in both the solvent and gas medium, least hardness, highest ionization potential, superior electron affinity, lowest electron reorganization energy, as well as highest rate constant of charge hopping, seemed to be the best molecule in terms of its electron-withdrawing abilities in the photoactive layer blend. In addition, in terms of all of the photovoltaic parameters, TP4-TP7 was perceived to be better suited in comparison to TPR. Thus, all our suggested molecules could act as superior acceptors to TPR.

A novel citric acid facilitated supramolecular Zinc(II)-metallogel: Toward semiconducting device applications

A fascinating approach for the instantaneous synthesis of citric acid as a low molecular weight gelator and zinc ion based metallogel through one-shot mixing in N,N-dimethyl formamide medium has been achieved at room temperature under ambient condition. The rheological study was applied to investigate the mechanical property of the synthesized metallogel material. The layered structure of the metallogel was envisaged through FESEM and the present elements were characterized through EDX mapping investigations. The possible metallogel formation strategy has been analyzed through FT-IR and Raman spectroscopic study. Slight shifting of the X-ray diffraction peaks of the precursor components indicated the structural changes occurring during the gelation and the resulting layered structure. Thermogravimetric analysis (TGA) revealed the role of the fuel (here citric acid) used in the synthesis, and also indicated the formation of ZnO from citric acid. Differential scanning calorimetry (DSC) revealed a phase transition from gel to solution (gel-to-sol) indicating a dramatic change in viscosity during heating and the process is reversible. Optical band gap estimated from absorption characteristics of the gel which suggested a strong semiconducting nature for the material. The semiconducting nature of the metallogel has been further verified with electronic device characterization and charge career mobility evaluation. These results suggest that this gel has an impressive electron mobility value which may be the highest (by several orders) among the reported mobilities of metallogels.

Novel A-π-D-π-A-type non-fullerene acceptors for solution-processed organic photovoltaic cells: A DFT study

For the evaluation of the effectiveness of an experimental molecule, it must first be prepared, which is quite expensive if you have to test several such molecules. For this purpose, computational studies and many computer-based softwares are being utilized, to save time as well as resources, and to eliminate the molecules that show reduced efficiency even on the computational scale. With this in mind, we have computationally designed five new acceptor molecules (IC1-IC5) of A-π-D-π-A configuration, through the substitution of significant acceptor moieties in the indacenodithiophene donor core of the ICR molecule, along with the insertion of thiophene π-linkers between the core and the newly introduced acceptors. By using density functional theory (DFT) calculations at the B3LYP/6-31G(d,p), optoelectronic characteristics of IC1-IC5 molecules at their excited and ground state were studied theoretically and contrasted to the reference molecule ICR. As opposed to ICR, all modified molecules possessed redshift in their λmax in both gaseous and solvent (dichloromethane) phases. They also exhibited smaller bandgaps, lower excitation energies, and greater oscillator strength than ICR molecule. Moreover, when compared with ICR, all the new computationally designed molecules, except IC1, had better light-harvesting efficiency. The smaller reorganization energy values for electron mobility of all the newly developed molecules demonstrated their enhanced capabilities as electron carriers. Upon the calculation of photovoltaic attributes of ICR, IC1-IC5 acceptors regarding PTB7-Th donor, the IC3 and IC4 molecules exhibited greater open-circuit voltage (VOC), normalized VOC, and fill factor than ICR molecule, making them more efficient acceptors than the previously reported reference molecule. Thus in the future, both these molecules could be utilized for the anticipation of the enhancement in the solar efficiency of various organic photovoltaic devices.

Mathematical Modeling of Drain Current Estimation in a CSDG MOSFET, Based on La2O3 Oxide Layer with Fabrication-A Nanomaterial Approach.

In this work, three-dimensional modeling of the surface potential along the cylindrical surrounding double-gate (CSDG) MOSFET is proposed. The derived surface potential is used to predict the values of electron mobility along the length of the device, thereby deriving the drain current equation at the end of the device. The expressions are used for modeling the symmetric doped and undoped channel CSDG MOSFET device. This model uses Pao-Sah’s double integral to derive the current equation for the concentric cylindrical structure of the CSDG MOSFET. The three-dimensional surface potential estimation is performed analytically for doped and undoped device parameters. The maximum oxidant concentration of the oxide layer is observed to be 4.37 × 1016 cm−3 of the thickness of 0.82 nm for (100) and 3.90 × 1016 cm−3 of the thickness of 0.96 nm for (111) for dry oxidation, and 2.56 × 1019 cm−3 of thickness 0.33 nm for (100) and 2.11 × 1019 cm−3 of thickness 0.49 nm for (111) for wet oxidation environment conditions. Being an extensive analytical approach, the drain current serves the purpose of electron concentration explicitly inside the concentric cylindrical structures. The behavior of the device is analyzed for various threshold conditions of the gate voltage and other parameters.

An Analysis of Mobility Influence in Optoelectronics Parameters in an InGaN/GaN Blue LED

Simulations on mobility influence in optoelectronics parameters from an InGaN/GaN blue LED using the Nextnano++ software arepresented in this paper. These simulations were performed by changing the hole and electron mobility value for the material compounds according to experimental, theoretical, and doping-concentration data already reported in the literature. The power law mobility is used for the current calculation in the quantum drift-diffusion model. The results indicate the lower hole and electron leakage currents correspond to the lowest mobility values for the InGaN alloy, the greatest amount of recombination occurs in the extreme wells within the active layer of the LED and the stable emission is at 3.6 V with peak wavelength λ^LED=456.7 nm and full width at half maximum FWHM~11.1 nm for the three mobilities. Although experimental and theoretical mobility values reach higher carrier density and recombination, the photon emission is broader and unstable. Additionally, the doping-concentration mobility results in lower wavelength shifts and narrows FWHM, making it more stable. The highest quantum efficiency achieved by doping-concentration mobility is only in the breakdown voltage (ηdop−max=60.43%), which is the IQE value comparable to similar LEDs and is more useful for these kinds of semiconductor devices.

Investigation of Electron Effective Mass in AlGaN/GaN Heterostructures by THz Spectroscopy of Drude Conductivity

Terahertz time domain spectroscopy (TDS) of the two-dimensional (2-D) electrons in various commercial AlGaN/GaN heterostructures was performed in the frequency range of 0.1–2.0 THz at selected temperatures of 80 and 300 K. Experimental transmission spectra were analyzed using analytical model derived for the thin conductive layer on dielectric substrate assuming a high-frequency Drude response of electrons. Two-dimensional electron mobility and density values found from the best fit parameters were compared with the results of independent Hall experiment demonstrating good agreement within uncertainty range of 10%. Thermal renormalization of the electron effective mass was revealed in all investigated samples manifesting as the increase of up to 1.45 ± 0.13 fold of nominal value obtained at cryogenic temperatures. Fast method based on measurement of the ratio of transmission spectra at two temperatures (80 and 300 K) was proposed to monitor the renormalization phenomenon in the samples with thin Drude conductivity layer where carrier density is relatively independent on temperature.