Doped Layer Thickness Research Articles

Enhanced terahertz ISBT in GaAsBi/AlGaAs quantum well: impact of doping modulation

One of the pivotal characteristics of quantum wells (QW) designed for applications in filters or modulators is its absorption coefficient. This study investigates the combined influence of doping and active layer thickness on the absorption coefficient in GaAsBi/AlGaAs quantum wells. The self-consistent coupling between Schrödinger and Poisson equations was employed for this purpose. A comprehensive analysis of conduction band structure, energy levels, potentials, and densities is presented. This analysis discerns the effects of doping on intersubband transitions (ISBTs) in the terahertz (THz) frequency domain. An introduction of a donor impurity into the system greatly influenced the intersubband absorption coefficient, increasing its intensity and causing the optical response to shift toward the lowest frequency. The obtained resonant peak energies, situated within the terahertz spectrum, hint at promising applications for GaAsBi-based devices within this frequency band.

Dielectric performance improvement of polypropylene film by hierarchical structure design for metallized film capacitors

In this paper, hierarchical structure design method is proposed for improving the dielectric performance of polypropylene (PP) for metallized film capacitors. The results show that the composite film with 0.02 wt% terephthalaldehyde doping and functional layer thickness occupying 25% shows the best dielectric properties. The leakage conductivity declines by 89.0%–94.3%, the DC breakdown strength grows by 15.6%–19.7% and the discharged energy density improves by 50.6%–53.4%. Terephthalaldehyde doping introduces sites that could capture free holes, thereby blocking the carrier migration path. The hierarchical structure design results in the holes accumulating in the functional layer and the reverse electric field formed suppresses the charge injection from the anode. Furthermore, the probability of intrinsic charge excitation due to the band gap width reduction is greatly reduced. The method provides a reference for improving the dielectric performance of PP films from the perspective of regulating the charge transmission behavior.

The effects of thickness and doping concentration on the solar efficiency of GaN/p-Si based solar cells

In this study, we used the PC1D simulator to demonstrate the performance analysis of a solar cell model based on gallium nitride (GaN). It has been discovered that when the layer thickness of the GaN substrate grows, the efficiency of solar cells decreases. This was found by comparing the doping concentration and layer thickness on the GaN and silicon substrates. As the thickness of the p-doping Si layer rises, cell efficiency increases just modestly. The optimal doping concentrations for GaN and p-silicon are 1x1018 cm-3 and 1x1017 cm-3 , respectively. In compared to other designs, GaN/p-silicon solar cells have the highest efficiency of 25.26%.

Electrochemical Tuning of GaN Porosity for Advanced Photonics Applications

The nanoporous GaN from electrochemical process have mainly found roles as strain-free template for light-emitting diodes1, laser diodes2, Bragg reflectors3 and for photonic and optoelectronic applications4.Based on previous researches, a complete review exists on GaN electrochemical and photo-electrochemical etching5: it shows the impact of different parameter on pores morphology and its physical properties. However, according to our knowledge, no literature depicts a systemic pure electrochemical study enabling fine-tuning of porosification process.Our work proposes a three electrodes set up to study the porosification reactions by dynamic electrochemical methods such as cyclic voltammetry (CV) and chronoamperometric (CA) to understand and control the GaN anodic oxidation. It aims to highlight the influence of crucial parameters, relative to both electrochemical and semi-conductor contribution, on the electrochemical signal and on the physico-chemical characteristic of the obtained porous GaN. The main objective is to have a new diagnostic tool for GaN porosification mechanism to better tune the final porous structure.Therefore, the impact of dopant concentration and the influence of thickness of the doped GaN layer was studied by CV analyses and CA method. Coupling the electrochemical curves with SEM analyses enables to define four regimes in the electrochemical charge-transfer: pre-breakdown, porosification zone, a transition phase and electropolishing (figure 1).Moreover, this work show that higher is the doping rate, thinner is the space charges region (SCR): as a result, the conductivity of the n-GaN working electrode increases, and the passage of electrons through the SCR requires lower electric field. This lead to a shift of the CV curves to lower potentials. On the other hand, the range of porosification potentials reduces.The pore morphologies are directly related to the thickness of the space charge region (SCR) which depend on the doping rate and the applied potential:- The nucleation zone corresponds to low potentials region. In this range, dislocations and v-pits control the pores formation. At the tips of these impurities, the radius curvature becomes small enough that a low electric field is sufficient to move electrons through the SCR. In the non-peak areas of the defects, the thickness of SCR is larger and the electric field in the nucleation zone is not sufficient for the electrons passage. Hence the low porosity.- In porosification zone, the electric field is sufficient to accelerate the electrons passage through the SCR, which favors the propagation of nanopores in GaN. The result is the formation of pores on the entire surface, the higher the imposed potential, the higher the pore density and the porosity.The effect of the doped GaN layer thickness was also inspected with CV and CA. The CV curves show that the intensity of the current peaks increases with increasing doped layer thickness because the quantity of available charges is higher. The current drop results from charge consumption in the doped layer.The kinetics of the electrochemical charge transfer reaction between GaN and the electrolyte depends on several parameters. On the semiconductor side, it depends on the doping rate and the quantity of available charges; these two parameters control the creation of holes at the SC/electrolyte interface. On the electrolyte side, it depends on the concentration and the composition of the electrolyte, which control the diffusion of anions towards the SC/electrolyte interface.The cyclic voltammetry curves obtained on different types of electrolyte show that depending on the concentration and the nature of the electrolyte, the charge transfer regime could be diffusional which influences the rate of porosification and thus the pore morphology.The SEM images complete the electrochemical study and confirm that the porosification of GaN depends on:- The doping rate in the semiconductor, which controls the thickness of the SCR in the SC.- The concentration and nature of the electrolyte, which controls the diffusion of material from the electrolyte to the SC/electrolyte interface.- The applied potential, which controls the rate of the charge transfer reaction between the SC and the electrolyte. 1 K.J. Lee, S.-J. Kim, J.-J. Kim, K. Hwang, S.-T. Kim, and S.-J. Park, Optics Express 22, A1164 (2014). 2 S.-M. Lee, S.-H. Gong, J.-H. Kang, M. Ebaid, S.-W. Ryu, and Y.-H. Cho, Opt. Express, OE 23, 11023 (2015). 3 G.-Y. Shiu, K.-T. Chen, F.-H. Fan, K.-P. Huang, W.-J. Hsu, J.-J. Dai, C.-F. Lai, and C.-F. Lin, Scientific Reports 6, 29138 (2016). 4 S.H. Park, G. Yuan, D. Chen, K. Xiong, J. Song, B. Leung, and J. Han, Nano Lett. 14, 4293 (2014). 5 P.H. Griffin and R.A. Oliver, Journal of Physics D-Applied Physics 53, 383002 (2020). Figure 1

Effect of Ultra-Low Expansion Quartz Glass Layer on the Enhancement Performance of Quartz Optical Fiber

In this paper, the prefabricated rod of quartz fiber was prepared by MCVD method. A thickness of ultra-low expansion(ULE) quartz glass was deposited in the wall of quartz tube, and then quartz and its dopants were deposited. Finally, the prefabricated rod of quartz fiber preform containing doped TiO2 layer was successfully prepared by high temperature dehydroxylation treatment. The strength of quartz fiber obtained by wire drawing for the prefab rod is significantly improved. The experimental results showed that the quartz glass layer with TiO2 doped has a lower thermal expansion coefficient, the doped of TiO2 is amount 5wt%, and the doped layer thickness is 4%, the optical fiber has the best enhancement. The maximum tensile strength of the organic coating is up to 75.5N, which is higher (6.34%) than that of the commercial optical fiber (71N).

Understanding asymmetries using integrated simulations of capsule implosions in low gas-fill hohlraums at the National Ignition Facility

Current capsule implosions at the National Ignition Facility (NIF) using high-density-carbon ablators and laser energies close to 2 MJ have shown neutron yields in excess of 50 kJ. Improving on this performance requires understanding of the different degradation mechanisms. For many NIF implosions, nuclear diagnostic signatures have inferred residual hot-spot velocities that correlate with fuel areal density variations consistent with a low-order mode-1 asymmetry. A current working hypothesis attributes these asymmetries to a combination of beam to beam variations in the laser delivery and possibly coupling to target features, such as the diagnostic holes needed for x-ray imaging. Recently, a new source has been identified, thickness variation in the ablator shell. To gain better understanding and eventually mitigate the causes of asymmetries, 3D integrated simulations using the actual delivered laser powers are needed. To capture the effect of the diagnostic holes (DHs) using direct numerical simulation would require significantly large computational resources. Instead, our 3D simulations make use of a subgrid model developed using highly-resolved 2D simulations that include several details of the DH engineering complexity. Simulations of NIF shots using hohlraums without DHs, to isolate the effect of beam-to-beam variations, reproduce fairly well the observed nuclear diagnostic signatures. Similarly, reasonable agreement between data and simulations is also obtained in the presence of diagnostic holes. To account for the remaining discrepancies a sensitivity study of ablator thickness variation showed that 1% thickness asymmetries are comparable in effect to 1% peak drive mode-1 asymmetries. Additionally, this study identified sensitivity to variations in the imbedded doped layer (needed to shield the DT ice from the high energy x-rays generated in the hohlraum) thickness even when the inner and outer surface of the ablator are perfectly spherical.

Numerical study of AgInTe2 solar cells using SCAPS

ABSTRACT The ternary (ABX2) semiconductors have wide optical band gaps range and motilities of carrier, has led to their appearance importance device materials, including solar cells of photovoltaic and light-emitting diodes. In accordance with this, AgInTe2 solar cells have proved to be the next big advancement in the field of solar energy. In this work, different numerical simulations were performed using SCAPS. The doping density and layer thickness are investigated under solar illumination of AM1.5 for optimised performance of solar cell. Thus, starting from J–V curves, we have calculated the short-circuit current density J sc, the open-circuit voltage V oc, the fill factor and the efficiency conversion. This structure can also provide a fundamental solar cell unit for developing very high efficiency solar cell.

Quantum efficiency improvement depending on the oxygen doping density, temperature, and layer thicknesses of an intermediate band solar cell based on ZnTe:O: Numerical analysis

Intermediate band solar cell based on ZnTe:O with an efficiency of 17.46 % has been optimized using solar cell capacitance simulator (SCAPS). The impacts of defect densities in the band gap of the absorber layer, layer thicknesses and temperature variation on the intermediate band solar cell (IBSC) output were widely simulated. Quantum efficiencies of the intermediate band solar cell were simulated at different temperatures above room temperature. The simulation results indicate that the quantum efficiencies of the ZnTe:O devices decrease with the increasing temperature above room temperature.An intermediate band solar based on ZnTe:O showed a significant spectral response of below band gap photons, and demonstrated an increase of more than 100 % in power conversion efficiency in comparison to the ZnTe solar cell without oxygen doping.

An insight into effect of front surface field on the performance of interdigitated back contact silicon heterojunction solar cells

The development of interdigitated back contact silicon heterojunction has been flourishing in the field of solar cells. The front surface field has a decisive influence on the electrical field effect passivation of interdigitated back contact silicon heterojunction solar cells, and the effect of passivation layers on the performance of solar cells needs to be clarified. In this study, the two-dimension TCAD models of the doped n+-a-Si: H layer and SiNx with a fixed charge layer were established by the Sentaurus code, respectively. The space charge density and electric field intensity, carrier transportation, and distribution of current density were numerically analyzed to evaluate the effect of these two front surfaces on the performance of interdigitated back contact silicon heterojunction solar cells. The results show that for SiNx, the root cause of the field passivation is the surface fixed charge density. The combination of the doping concentration and layer thickness directly affects the field passivation of n+-a-Si: H. Based on the intuitive carrier transport vector, the selective transportation of the carrier near the surface is proved by the front surface field, which effectively inhibits the recombination. The current density distribution on the cross-section reveals that a strong front surface field is an effective way to reduce the internal recombination in particular. Considering practical operating conditions, a doping concentration of 1e20 cm−3, in combination with 7 nm layer thickness, potentially improves the front surface field of n+ a-Si: H leading to the maximum conversion efficiency of 27.41%, with the voltage increased by 32.8 mV and the fill factor reaching 86.84%.

Impact of channel doping engineering on the high-frequency noise performance of junctionless In0.3Ga0.7As/GaAs FET: A numerical simulation study

Abstract In this paper, the channel doping engineering is proposed to improve the benchmarking parameters of the analog/radio frequency and the high frequency noise performance of the junctionless (JL)-In0.3Ga0.7As/GaAs device. The proposed structure is called shell doped of channel-JLFET (SDCh-JLFET). The sub-gate doped layer thickness (D) and middle of channel impurity concentration (Nmiddle) are considered as additional factors to improve the analog/radio frequency parameters and high frequency noise performance of device. The SDCh-JLFET with a channel length of 10 nm, D = 1 nm, and Nmiddle = 2 × 1017cm−3 showed the transconductance of Gmmax = 3mS/um, unity gain cut-off frequency of fT = 700 GHz, the minimum noise figure of Nfmin = 0.84 db and available associated gain of Gass = 28.5 db. The Gmmax, fT, Nfmin and Gass parameters of the SDCh-JLFET device are improved by 76%, 36%, 35% and 26%, respectively, compared to JL-In0.3Ga0.7As/GaAs device without shell doping (JLFET) but with similar dimensions. The SDCh-JLFET device proposed in this paper can be a reasonable candidate for analog/radio frequency applications and high frequency noise.

Efficient green organic electroluminescent devices based on thermally activated delayed fluorescence emitter by constructing supplementary light-emitting layer

In this work, we reported the high performance green organic electroluminescent (EL) devices based on thermally activated delayed fluorescence (TADF) emitter by constructing supplementary light-emitting layer (EML) to broaden recombination zone and balance the distribution of holes and electrons. Due to the relatively low-lying energy levels of emitter, (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) doped 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPy) film served as the predominant EML, while 4CzIPN doped 4,4′,4″-tris(carbazole-9-yl)triphenylamine (TcTa) film functioned as the supplementary EML, which is instrumental in trapping the superfluous electrons in predominant EML. By optimizing the doping concentration and layer thicknesses, a series of EL devices were fabricated and measured. Finally, the optimized double-EMLs device with the maximum brightness, external quantum efficiency, current efficiency and power efficiency up to 40,571 cd/m2, 17.8%, 53.79 cd/A and 50.61 lm/W, respectively, was achieved. Even at the practical brightness of 1000 cd/m2, external quantum efficiency and current efficiency as high as 14.9% and 47.18 cd/A, respectively, can still be retained.

Tailored deep blue OLEDs characteristics with doping engineering in fluorescent dyes based on DMPPP: towards manufacturable solid-state lighting building blocks

We report on a deep blue OLED paradigm where the typical electrical and optical characteristics can be tailored with doping engineering. The devices are fabricated with a representative structure of ITO/m-MTDATA (20 nm) NPB (10 nm)/DMPPP:BCzVBi (d nm, x wt%)/Bphen (30 nm)/Cs2CO3:Ag2O (20 wt%, 1 nm)/Al (100 nm). Complementary studies are performed on the properties of deep blue OLEDs with specific doping concentrations (x = 2, 5, 8 and 10) and various doping layer thicknesses (d = 3, 5, 15 and 20). High luminance and efficiency deep blue OLEDs are obtained with tailored energy transfer between the host and the guest in the emissive layer when the x and d was 8 and 15, respectively. The developed device demonstrate a maximum current efficiency of 3.53 cd/A with a maximum luminance of 16,570 cd/m2. The CIE coordinates of the device are well within the deep blue region when the voltage is changed from 6 to 11 V. The CIEx,y is (0.155, 0.128) at the maximum luminance. Our systematic studies and complementary engineering investigations upon highly efficient deep blue OLEDs open new opportunities towards innovative applications in an industrial level available with optimized device integration among performance, dimension and cost in a variety of fields, e.g., flat panel display, smart wearable devices and human–machine interfaces lighting.

Doped bottom-contact organic field-effect transistors

The influence of doping on doped bottom-gate bottom-contact organic field-effect transistors (OFETs) is discussed. It is shown that the inclusion of a doped layer at the dielectric/organic semiconductor layer leads to a significant reduction in the contact resistances and a fine control of the threshold voltage. Through varying the thickness of the doped layer, a linear shift of threshold voltage VT from −3.1 to −0.22 V is observed for increasing thickness of doped layer. Meanwhile, the contact resistance at the source and drain electrode is reduced from 138.8 MΩ at VGS = −10 V for 3 nm to 0.3 MΩ for 7 nm thick doped layers. Furthermore, an increase of charge mobility is observed for increasing thickness of doped layer. Overall, it is shown that doping can minimize injection barriers in bottom-contact OFETs with channel lengths in the micro-meter regime, which has the potential to increase the performance of this technology further.

Improvement in ultra-thin hydrogenated amorphous silicon solar cells with nanocrystalline silicon oxide

Ultra-thin a-Si:H p-i-n solar cell has been proposed as advance to form three-dimensional structures on nano-structured substrates for achieving optically thick and electrically thin solar cells. However, over the years, although extensive studies have been carried out, no high efficiency was achieved yet. We found that not only the short circuit current density (Jsc) decreases, but also the open circuit voltage (Voc) and fill factor (FF) decreases with the reduction of i-layer thickness, which is opposite to the expectation. We investigated the possible root-causes for this unusual phenomenon and speculated the direct recombination of the electrons in the n-layer and the holes in the p-layer by tunneling through the thin i-layer is the main reason for the reduced Voc and FF in ultra-thin solar cells. Furthermore, the absorption in the doped layers is the most critical limitation for ultra-thin silicon solar cell efficiency because the doped layer thickness becomes comparable to the intrinsic layer. To resolve this issue, we used nanocrystalline silicon oxide (nc-SiOx:H) doped layers with a wide bandgap to reduce the parasitic absorption in the doped layers and the highly asymmetric conductivity improves the carrier collection and made a significant improvement in the cell efficiency. We achieved 8.79%, 7.65%, and 5.32% efficiencies with the i-layer thickness of only 70nm, 50nm and 20nm, respectively, which are the highest ones in ultra-thin silicon solar cells.

A new type of gas sensor based on the thermovoltaic effect in zinc oxide inhomogeneously doped with mixed-valence impurities

We propose a new type of potentiometric gas sensor operating on the basis of the thermovoltaic effect in uniformly heated (without temperature gradients) ZnO/ZnO–Fe sandwich structures obtained by the sol–gel method. It is established that a significant contribution to the gas responsivity of sensors is related to the thickness of the upper doped layer of the structure.

Comparative Study of Single and Double Quantum Well AlGaN/GaN HEMT Structures for High Power GHz Frequency Application

The aim of this work is to simulate and analyze the performance of single and double quantum well AlGaN/GaN HEMT (High Electron Mobility Transistor) structures for high power GHz frequency application with the variation of gate length, spacer layer thickness and doping layer thickness. To study the effect of these variations we use Atlas Tcad-Silvaco numerical simulation software. The drift-diffusion model has been taken for simulating the proposed device. We use sapphire as a substrate for this structure. We have performed the comparative characterization study of 2-DEG (Two Dimensional Electron Gas), threshold voltage (Vth) and transconductance (gm) of the double quantum with single quantum well HEMT structure. As a result of this comparison the double quantum well HEMT structure has been seen to exhibit more sensitive to these parameters. Thus, optimization of the gate length, donor layer thickness and spacer layer thickness of double quantum well HEMT structure is crucial.

Fabrication of a nanometer thick nitrogen delta doped layer at the sub-surface region of (100) diamond

In this letter, we report on the proof of a concept of an innovative delta doping technique to fabricate an ensemble of nitrogen vacancy centers at shallow depths in (100) diamond. A nitrogen delta doped layer with a concentration of ∼1.8 × 1020 cm−3 and a thickness of a few nanometers was produced using this method. Nitrogen delta doping was realized by producing a stable nitrogen terminated (N-terminated) diamond surface using the RF nitridation process and subsequently depositing a thin layer of diamond on the N-terminated diamond surface. The concentration of nitrogen on the N-terminated diamond surface and its stability upon exposure to chemical vapor deposition conditions are determined by x-ray photoelectron spectroscopy analysis. The SIMS profile exhibits a positive concentration gradient of 1.9 nm/decade and a negative gradient of 4.2 nm/decade. The proposed method offers a finer control on the thickness of the delta doped layer than the currently used ion implantation and delta doping techniques.

The competitive behavior of exciton reactions in Rubrene doped system

In this work, organic light-emitting diodes (OLEDs) have been fabricated with 1 percent of tetraphenyldiben- zoperiflanthene (DBP) doped into 5,6,11,12-tetraphenylnaphthacene (Rubrene) as active layer, which had excellent properties such as strong electroluminescence, high stability and low threshold voltage. The magneto-eletroluminescence (MEL) curves of this devices have been measured under various injection currents at room temperature. The MEL curves exhibit a complicated line shape: the MEL increases sharply with a tiny amplitude first with increasing magnetic field from 0 mT to 27 mT and then decreases rapidly with a large amplitude until at about 200 mT followed by a slow increase in the high field, and this type of shape shows substantially changes during different currents. The non-monotonic increase and decrease of the MEL suggested that there are abundant exciton reacitons inside the devices, such as singlet-triplet annihilation (STA), triplet-triplet annihilation (TTA, or triplet fusion) and singlet fission (STT). These three reactions could be tuned by changing the injection current. The STA and TTA play the mainly role when the injection current is large enough in the devices, and the exciton reaction gradually changes from TTA to STT when the injection current decreases. Furthermore, The MEL curves have also been measured by altering the thickness and location of the doped layer in the devices. Result shows that the STT increases as the thickness of doped layer decreases while the STA and TTA becomes more dominant when the location of doping layer is more closer to the cathode. In conclusion, this study gives insight into the microscopic evolutions of the interactions between singlet and triplet excitons and provides a feasible pathway to control the competition among STA, TTA and STT in OLEDs.

Semi-insulating GaN:C epilayers grown by metalorganic vapor phase epitaxy using propane as a carbon source

The influence of propane present in a reactor at various stages of GaN growth by metalorganic vapor phase epitaxy (MOVPE) on sapphire substrates on the character of epitaxial process and the properties of epilayers has been studied. Doped GaN epilayers with carbon concentration 5 × 1018 cm–3 characterized by high crystalline perfection, an atomically smooth surface, and electric breakdown voltage above 500 V at a doped layer thickness of 4 μm have been obtained.

Modeling, Design, and Fabrication of Self-Doping Si1−xGex/Si Multiquantum Well Material for Infrared Sensing

The paper presents the study of band distributions and thermoelectric properties of self-doping Si1−xGex/Si multiquantum well material for infrared detection. The simulations of different structures (including boron doping, germanium concentrations, and SiGe layer thickness) have been conducted. The critical thickness of SiGe layer grown on silicon substrate has also been illustrated in the paper. The self-doping Si1−xGex/Si multiquantum well material was epitaxially grown on SOI substrate with reduced pressure chemical vapor deposition. Each layer of the material is clear in the SEM. TheI-Vcharacterizations and temperature resistance coefficient (TCR) tests were also performed to show the thermoelectric properties. The TCR was about −3.7%/K at room temperature in the experiments, which is competitive with the other thermistor materials. The material is a low noise material, whose root mean square noise is 1.89 mV in the experiments.