Doped Region Research Articles

МОДЕЛИРОВАНИЕ И РАСЧЕТ СПЕКТРА ФОТОЛЮМИНЕСЦЕНЦИИ ГЕТЕРОСТРУКТУРЫ С КВАНТОВОЙ ЯМОЙ НА ПРИМЕРЕ ALGaAS/GaAS

This research aims to improve the available means for characterizing the emission properties of quantum well heterostructures by modeling and calculating the absorption and photoluminescence spectra using the GaAs/AlGaAs heterostructure as an example. Research is conducted based on multilayer heterostructures and heterostructures with quantum wells to develop detectors and emitting elements in the infrared frequency range, pulsed solid-state generators in the millimeter and submillimeter-wave ranges. The study of radiating properties of heterostructures with a quantum well on A3B5 compounds has become widespread [1-3]. It is possible to control the heterostructure's emission frequency by selecting the optimal composition of the wideband semiconductor layer, the level and type of its doping, the doping region, and the quantum well layer width, which is of applied importance for the development of optoelectronic devices. Technologies for manufacturing such heterostructures are labor-intensive, time-consuming, and expensive processes, which contribute to developing methods for modeling and calculating the characteristic frequencies of radiation and absorption of radiation. Based on such calculations, radiating elements of the submicronic wavelength range can be developed based on heterostructures with a quantum well on the A3B5 type compounds. [4]

Electrical crosstalk suppression for a compact optical segmented modulator.

Advanced coding formats can improve the spectral efficiency in optical transmission systems, while the generation can be expensive and power hungry when electrical digital-to-analog converts (DACs) are utilized. Optical segmented modulators can supersede electrical DACs with the merits of low cost and power efficiency. However, due to their compact size, the leakage current between the adjacent segments results in considerable electrical crosstalk, which impairs the linearity of the modulators and distorts the modulated signal. Here, we propose and demonstrate an electrical crosstalk suppression scheme for optical segmented modulators by introducing a complementary doped region as an insulator. Two depletion regions with high impedances are formed, resulting in the decrease in leakage current and crosstalk. Qualitative and quantitative analysis are performed, and experimentally, in a ring based segmented modulator, more than 5 dB crosstalk improvement is successfully achieved within the 30 GHz range.

Spectromicroscopy and imaging of photoexcited electron dynamics at in-plane silicon pn junctions.

The ultrafast spatiotemporal imaging of photoexcited electrons is essential to understanding interfacial electron dynamic processes. We used time- and energy-resolved photoemission electron microscopy (PEEM) to investigate the photoexcited electron dynamics at multiplex in-plane silicon pn junctions. We found that the measured kinetic energy of photoelectrons from n-type regions is higher than that from p-type regions owing to different work functions. Interestingly, the kinetic energy of outer n-type regions is higher than that of inner n-type regions, which is caused by the reverse bias induced by photoemission. Time-resolved PEEM results reveal different evolution rates of hot electrons in different doping regions. The rise time of the n-type (outer n-type) regions is faster than that of the p-type (inner n-type) regions. So, closed doping patterns can influence the electron spectra and dynamics at the micro-nano scale. These results help us to understand the ultrafast dynamics of carriers at in-plane interfaces and optimize optoelectronic integrated devices with complex heterojunctions.

Carrier depletion type PIN phase shifter in silicon MZM for 200 Gbps operation

Silicon-based photonic modulators are a primary choice for on-chip optical devices with CMOS fabrication compatibility. The phase shifter in a silicon photonics modulator plays a significant role in determining the efficiency of the modulator to meet the optical data communication's future demands. Obtaining high extinction ratio (ER) and with acceptable bit error rate (BER) at low voltage and low loss was kept as the primary objective for the proposed PIN phase shifter in an unbalanced silicon Mach-Zehnder modulator. The phase shifter length was kept at 2 mm, and the carrier doping region was reduced to decrease the carrier absorption loss. The concentration of P and N in the phase shifter was set to 7 × 1017 cm−3 and 5 × 1017 cm−3, and the intrinsic gap was varied (50, 100, 150, 200, 250, 300, 350 and 450 nm) for the study to obtain the optimum gap to meet the objective. For 200 Gbps, the proposed modulator with intrinsic gap 150 nm obtained 18.68 dB ER having VπL = 0.8 V.cm. Insertion loss obtained for the phase shifter was 3.421 dB/cm. The proposed design is expected to enhance the performance of silicon optical modulators for commercial applications, and also other applications such as optical switches, delay lines, and optical interconnect.

Lasing characteristics of highly bend compensated large mode area ytterbium doped modified hybrid multi trench fiber

In this article, lasing characteristics of a newly designed ytterbium-doped modified hybrid multi trench fiber (YDMHMTF) has been numerically investigated for strongly pumped conditions. The designed YDMHMTF is maintained single-mode condition with an effective mode area of 1300μm2 at the wavelength of 1064 nm for the compact bending radius of 7.5 cm. The radius of doped region is varied up to a maximum core size of ~19 µm through numerical simulations to achieve maximum conversion efficiency for the straight and bending cases. The effective signal overlap factor is ensured by introducing a high-index arc in the inner trench of fiber along with a maximum doped core region. A 1.5 m length of highly bend LMA YDMHMTF shows slope efficiency of 74% and conversion efficiency of 75% when pumped with a laser source of 975 nm. Further, the high slope efficiency of 81% and conversion efficiency of 80% are achieved with aid of a 2 m length YDMHMTF for the straight and practical bending conditions. Therefore, the proposed YDMHMTF can be utilized to develop an efficient compact laser system suitable for industrial lasing applications. Moreover, the fabrication feasibility of our proposed YDMHMTF becomes easier than the photonic crystal fiber and Bragg fiber based designs.

Distinct pairing symmetries of superconductivity in infinite-layer nickelates

We report theoretical predictions on the pairing symmetry of the newly discovered superconducting nickelate Nd$_{1-x}$Sr$_{x}$NiO$_{2}$ based on the renormalized mean-field theory for a generalized model Hamiltonian proposed in [Phys. Rev. B \textbf{101}, 020501(R)]. For practical values of the key parameters, we find a transition between a gapped ($d+is$)-wave pairing state in the small doping region to a gapless $d$-wave pairing state in the large doping region, accompanied by an abrupt Fermi surface change at the critical doping. Our overall phase diagram also shows the possibility of a ($d+is$)- to $s$-wave transition if the electron hybridization is relatively small. In either case, the low-doping ($d+is$)-wave state is a gapped superconducting state with broken time-reversal symmetry. Our results are in qualitative agreement with recent experimental observations and predict several key features to be examined in future measurements.

Double-gate tunnel field-effect transistor with inner doping and spacer regions

In this study, a tunnel field-effect transistor (FET) with source-side inner doping and a drain-side spacer is proposed to obtain high current drivability and reduced gate-to-drain capacitance, simultaneously. The effects of the inner doping region (regioninner) are investigated with various lengths (L ID) and concentrations (N ID). As the N ID increases, the more source-to-regioninner tunneling is added to conventional source-to-channel tunneling and thus the total tunneling current is enhanced. Moreover, with a wider L ID, the on-current is reduced by the wider source-to-regioninner tunneling width and the source-to-regioninner tunneling is generated at a lower gate voltage by the L ID-induced limitation of energy band bending. Also, the impact of the inner spacer is evaluated with various inner spacer lengths (L IS). By introducing the inner spacer, the gate-to-drain capacitance can be significantly reduced. Consequently, the proposed tunnel FET has a reduced gate-to-drain capacitance as well as an increased tunneling current, which leads an improvement in switching delay.

Phosphorus precursors reactivity versus hydrogenated Ge surface: towards a reliable self-limited monolayer doping

Three different phosphorus compounds are tested as precursors for monolayer formation on Ge (100) surface to be used as the nanoscale-controlled dopant source. By applying different deposition methodologies, the role of several deposition parameters is evaluated employing X-ray Photoelectron Spectroscopy and Grazing Incidence Extended X-Ray Absorption Fine Structure Spectroscopy. The self-limiting physisorption or chemisorption process has proved to be strongly influenced by deposition ambient conditions for phosphonates or phosphonic acids, while the adsorption of allyl-phosphine occurs through a competitive oxidation reaction instead of hydrogermylation process, even in ultra-dry conditions. The produced phosphine oxide monolayer is structurally characterized, and an explanation of its formation is presented, based on the chemical features of both the hydrogenated Ge surface and P-based molecule. The ability of the adsorbed layers in releasing P to dope Ge is tested, revealing strong thermal stability of the deposited layers that is disclosed to be directly associated with the adsorption chemistry. However, the use of the Pulsed Laser Melting technique allows achieving a homogeneous fully active doped region with a high concentration level, thus pointing to allyl-diphenyl phosphine as the best precursor used here for Ge doping purposes for a n+/p junction formation.

Inverse Design of a Graphene-Based Quantum Transducer via Neuroevolution

We introduce an inverse design framework based on artificial neural networks, genetic algorithms, and tight-binding calculations, capable to optimize the very large configuration space of nanoelectronic devices. Our non-linear optimization procedure operates on trial Hamiltonians through superoperators controlling growth policies of regions of distinct doping. We demonstrate that our algorithm optimizes the doping of graphene-based three-terminal devices for valleytronics applications, monotonously converging to synthesizable devices with high merit functions in a few thousand evaluations (out of $\simeq 2^{3800}$ possible configurations). The best-performing device allowed for a terminal-specific separation of valley currents with $\simeq 96$\% ($\simeq 94\%)$ $K$ ($K'$) valley purity. Importantly, the devices found through our non-linear optimization procedure have both higher merit function and higher robustness to defects than the ones obtained through geometry optimization.

Study of the Drain Leakage Current Behavior in Graded-Channel SOI nMOSFETs Operating at High Temperatures

The theoretical and experimental study of drain leakage current behavior in Graded-Channel ( GC ) SOI nMOSFETs operating at high-temperatures ( up to 300oC ) is analyzed and discussed here. Through the studies it was noticed that drain leakage current depends strongly on the ratio between the length of the lowly doped region and the mask channel length. Also, it was observed that the drain leakage behavior is similar to the conventional SOI nMOSFETs which effective channel length being equal in both structures when the GC SOI nMOSFETs has the same channel doping level in the higher doped region. Numerical bidimensional simulations and experimental data were used in order to compare and discuss all the results.

SiC Trenched Schottky Diode with Step-Shaped Junction Barrier for Superior Static Performance and Large Design Window

A novel silicon carbide (SiC) trenched schottky diode with step-shaped junction barrier is proposed for superior static performance and large design window. In the proposed diode, to improve tradeoff between specific on-resistance and surface peak electric field, the shape of the trenched-junction is modified to stair-step, without extra fabrication process. To investigate the performances of the SiC step-shaped trenched junction barrier schottky (SSTJBS) diode, numerical simulations are carried out through Silvaco TCAD. The results indicate that the proposed diode can accommodate highly doped drift region with no degradation of its reverse blocking characteristic. In comparison with the conventional SiC trenched junction barrier schottky (TJBS) diode, the proposed SiC SSTJBS diode shows a larger design window of drift region doping concentration from 7.9×1015cm-3 to 9.5×1015cm-3. In the design window, the specific on-resistance and surface peak electric field can be reduced by 12.9% and 11%, respectively.

Transient Overshoot Voltages During VF-TLP Pulses for Bipolar Devices in the Presence of Lowly Doped Regions

The transient overshoot behavior of bipolar devices is investigated by means of very fast transmission line pulses (VF-TLP). All devices under investigation, a forward biased diode, an open base transistor and a SCR comprise a lowly doped region (LDR). Measurements have been done for rise times of 0.3ns and 1ns. To separate the voltage drop inside the device from parasitic contributions TCAD simulations have been performed. The analysis shows that for a fixed length of LDR the effect of the lowly doped region depends on the type of the device and is linked to the charge carrier distribution inside the LDR. In addition, the effect of the length of the LDR on transient voltage overshoot is compared for a forward biased diode and an SCR.

Study of effective coupling between charge degrees of freedom in low dimensional hole-doped quantum antiferromagnets

Expressions for the generalized charge stiffness constant at zero temperature are derived corresponding to low-dimensional hole-doped quantum antiferromagnets, describable by the t–J-like models, with a view to understanding fermionic pairing possibilities and charge couplings in itinerant antiferromagnetic systems. A detailed comparison between spin and charge correlations and couplings are presented for the strong and weak coupling limits in one (1D) and two (2D) dimensions. The result highlights that the charge and spin couplings show very similar behaviour in the over-doped region in both dimensions, whereas they show a completely different trend in the lower doping regimes. A qualitative equivalence of the generalized charge stiffness constant with the effective Drude weight and Coulomb interaction is established based on the comparison with other theoretical and experimental results. The fall in charge stiffness with increase in doping then implies a reduction in magnitude of the effective Coulomb repulsion between the mobile carriers. This leads to an enhanced possibility of fermionic pairing with an increase in doping concentration, in the possible presence of some other attraction-producing mechanism from a source outside the t–J-like models. Moreover, under certain conditions in the optimal doping region, the t–J-like models themselves are able to produce an attractive interaction for pairing.

Crystal Growth of Epitaxial 3C-SiC Thin Film on Si Substrate by Chemical Vapor Deposition using Single Precursor of Vinylsilane

We have examined the formation of 3C SiC thin films on Si substrates by chemical vapor deposition (CVD) method using vinysilane as a single precursor. The epitaxial 3C-SiC film was successfully grown on Si(111) substrate at a lower temperature of 1000 °C. In addition, in-situ phosphorus doping for polycrystalline 3C-SiC was achieved using tri-ethyl-phosphorus as a dopant source. The active dopant concentration as high as 8.2×1019 cm−3 and the resistivity as low as 1.9×10−2 Ωcm was obtained. This resistivity value is comparable to the epitaxial 3C-SiC film formed on Si substrate ever reported at the same dopant concentration region. The fact that resistivity as low as single crystalline films can be obtained at a low temperature of 900°C promises that CVD-grown 3C-SiC films using a single precursor of vinylsilane is a suitable material for a wide range of applications.

Energy band adjustment of 808 nm GaAs laser power converters via gradient doping

The gradient doping regions were employed in the emitter layer and the base layer of GaAs based laser power converters (LPCs). Silvaco TCAD was used to numerically simulate the linear gradient doping and exponential gradient doping structure, and analyze the transport process of photogenerated carriers. Energy band adjustment via gradient doping improved the separation and transport efficiency of photogenerated carriers and reduced the total recombination rate of GaAs LPCs. Compared with traditional structure of LPCs, the photoelectric conversion efficiency of LPCs with linear and exponential gradient doping structure were improved from 52.7% to 57.2% and 57.7%, respectively, under 808 nm laser light at the power density of 1 W/cm2.

Self-aligned local contact opening and n+ diffusion by single-step laser doping from POx/Al2O3 passivation stacks

Laser doping is a promising route to realise industrially compatible processing of local contacts for high-efficiency solar cells, especially when the same film acts as both dopant source and passivation layer. In this work we demonstrate simultaneous local contact opening and n+ laser doping of silicon from positively charged POx/Al2O3 thin-film stacks, which also provide outstanding passivation of n-type silicon surfaces. Local n+ doped regions with sheet resistance ranging from 35 to ~540 Ω/□ are formed using single nanosecond laser pulses with varying fluence. ECV profiling shows net n-type doping in all cases, confirmed by SIMS profiling to be due to phosphorus from the POx layer. J0 of metallised laser-doped regions is consistent with values achieved for state-of-the-art furnace diffusions with similar sheet resistance, confirming that laser-induced recombination-active defects are avoided. A minimum J0 of 540 fA cm−2 is obtained for metallised laser-doped regions formed from POx/Al2O3 passivation stacks having J0 of 2.5 fA cm−2. The combination of outstanding passivation of uncontacted n-type regions offered by POx/Al2O3, with self-aligned formation of locally-diffused contact openings via single-step laser processing, opens up exciting possibilities for simplified fabrication of high-efficiency cell structures.

SIMULATION OF BORON DIFFUSION IN THE NEAR-SURFACE REGION OF SILICON SUBSTRATE

The mechanism of boron-enhanced diffusion from a thin boron layer deposited on the surface in the case of silicon crystal doping is proposed and investigated. It was supposed that lattice contraction occurs in the vicinity of the surface due to the difference between the atomic radii of boron and silicon. This lattice contraction provides a stress-mediated diffusion of silicon self-interstitials from the near-surface region to the bulk of a semiconductor. Due to the stress-mediated diffusion, the near-surface region is depleted of silicon self-interstitials, and simultaneous oversaturation of this species occurs in the bulk. In this way, a strong nonuniform distribution of silicon self-interstitials in the vicinity of the surface is formed without regard to the large migration length of this species. The oversaturation of the bulk of a semiconductor with nonequilibrium self-interstitials allows one to explain the boron-enhanced diffusion of impurity atoms. The strong nonuniform distribution of these point defects also results in a specific form of boron concentration profile in the vicinity of the surface. Good agreement of the calculated boron profile with the experimental data for the entire doped region was obtained within the limit of the proposed model.

Laterally asymmetric channel-based tunnel fieldeffect transistors: design and investigation

ABSTRACT In this paper, we propose and simulate a lateral asymmetrically doped channel-based tunnel field-effect transistor. The impact of laterally asymmetric channel (LAC) on the performance of a Tunnel Field-effect transistor, along with a detailed comparison with a uniformly doped TFET (UD-TFET) has been studied. The proposed TFET has uniformly doped source and drain regions and the asymmetrically doped channel is realised by employing the Gaussian profile doping in the channel. The peak doping (NC) and the standard deviation (σ) of Gaussian doping profile used in the LAC-TFET channel are varied and their impact on the DC and AC performances is studied. It has been observed that the use of laterally asymmetric-doped channel in a TFET enhances its ON current (ION), transconductance (gm ) and the cut-off frequency (fT ), without increasing the OFF state current. At optimum values of NC and σ, the ION, g m and the f T are enhanced by more two order of magnitude in the LAC TFET. Hence, we propose that LAC-TFET can serve as a viable alternative to improve the DC and AC characteristics of TFETs.

Impact of Pocket Doping On the Performance of Planar SOI Junctionless Transistor

In this paper, a novel sturcture of planar Silicon on Insulator Junctionless transistor is proposed with improved ION/IOFF ratio, Short Channel effects (SCEs) and most importantly, it is scaleable. A highly doped pocket (p-type) will form PN junction at its interface with n-type channel and hence referred to as pocket doped Silicon on Insulator Junctionless transistor (PD-SOI-JLT). A highly doped region in the channel helps to produce full depletion in the OFF state. A 2D Calibrated simulation study has shown an ION/IOFF ratio 105 in PD-SOI-JLT device comapred to conventional SOI-JLT device for gate length of 20 nm. Further, the use of PN junction isolation reduces the lateral electric field and hence improves the SCE performance of the proposed device as compared to conventional SOI-JLT. Besides this, the ac analysis has shown that the transconductance and Cutoff Frequency of the proposed device is at par with the conventional device.

Slave-rotor theory on magic-angle twisted bilayer graphene

We investigate the correlated electrons in the magic-angle twisted bilayer graphene by using the slave-rotor mean-field theory. Owing to the extended figure of Wannier orbitals, we study the two-orbital cluster Hubbard model with spin-valley fourfold degeneracy, focusing around half filling of valence bands below the neutrality point. The theory predicts multiple Mott insulator phases at fractional fillings not only for integer charges per moir{\'e} site, and it demonstrates that long-range electron hopping is highly suppressed because multiple-charge excitations are induced. Furthermore, the Kekul{\'e} valence bond order is investigated and is found to extend the Mott insulator phases to occupy a finite doping region. Adjacent to Mott insulator phases, superconducting domes emerges by virtue of spin-valley fluctuations. This work has provided a primal understanding and interesting phenomena of the correlated system, and for its novel interaction the model might produce plenty of possibilities waiting to be explored.