Doped Region Research Articles

Doped-δ-doped transferred electron device for sustained terahertz signal generation

Abstract The performance of a novel transferred electron device structure aimed at sustaining high-frequency signals in the terahertz (THz) range is investigated. The device uses a highly doped δ-layer to split the n-doped device into two distinct regions, forming a doped-δ-doped configuration. The first region generates high-speed electrons toward the δ-layer, while the second region utilizes negative differential resistance to modulate electron speeds and sustain oscillations. An ensemble self-consistent Monte Carlo model is employed to analyze electron dynamics and THz signal generation in this structure under a constant bias. The design demonstrates superior performance, achieving a fundamental operating frequency of 427 GHz in a 600 nm length InP device, nearly a 50% increase over conventional notch-doped design, while maintaining the current harmonic amplitude. This design achieves higher frequencies without reducing device length and increasing doping density, effectively addressing the trade-off of the Kroemer criterion. The study of the effects of varying doping densities and region lengths on device performance, highlighting the importance of optimizing these parameters to sustain current oscillations and efficiently generate THz signals. This design offers a promising solution for a compact and efficient THz source.

Dynamical control of nanoscale electron density in atomically thin n-type semiconductors via nano-electric pulse generator.

Controlling electron density in two-dimensional semiconductors is crucial for both comprehensive understanding of fundamental material properties and their technological applications. However, conventional electrostatic doping methods exhibit limitations, particularly in addressing electric field-induced drift and subsequent diffusion of electrons, which restrict nanoscale doping. Here, we present a tip-induced nanospectroscopic electric pulse modulator to dynamically control nanoscale electron density, thereby facilitating precise measurement of nano-optoelectronic behaviors within a MoS2 monolayer. The tip-induced electric pulse enables nanoscale modulation of electron distribution as a function of electric pulse width. We simultaneously investigate spatially altering photoluminescence quantum yield at the nanoscale region. We model the extent of electron depletion region, confirming a minimum doping region with a radius of ∼265 nanometers for a 30-nanosecond pulse width. Our approach paves the way for engineering local electron density and in situ nano-optical characterization in two-dimensional materials, enabling an in-depth understanding of doping-dependent nano-optoelectronic phenomena.

Structural Stability and High-Temperature Thermoelectric Performance of LiYPdSn Quaternary Heusler Compound

In this research work, the electronic, mechanical, and thermoelectric properties of the recently discovered Li-based quaternary Heusler compound i.e. LiYPdSn are explored with the help of density functional theory and the Boltzmann transport equations. The LiYPdSn alloy has an indirect band gap of 0.41 eV that confirming its p-type semiconducting features. This material shows the mechanical and dynamical stability along with a maximum recorded ZT (Figure of Merit) of 0.52 at 1200K. The electrical conductivity i.e. ease of electric propagation is calculated as 4.43x106 Ω-1 m-1 at 600K for the p-type doping region, while in the n-type doping region, the maximum recorded value is 2.8x106 Ω-1 m-1, similarly the leading thermoelectric performance i.e. Seebeck coefficient with a maximum value of 531.14 μV/K at 300K, declaring that its properties are awaking the interesting research perspective in future. The paper seems to be an outlet of various research properties and announces the presenting material to have valuable thermoelectric performance and hence the potential applications to manufacture the wired or rolled structural thermoelectric modules in the high-temperature regions.

Evaluation of DSRD-based pulsers for a Dielectric Wall Accelerator

Silicon (Si) drift step recovery diodes (DSRD) are opening switches that form the basis for nanosecond-scale high voltage (HV) pulsers. These pulsers are crucial to the operation of a dielectric wall accelerator (DWA), a compact particle accelerator design for proton beam radiation therapy. For the DWA to operate properly, the pulser must generate HV pulses with fast rise times and widths on the order of 1 ns at an operating frequency above 1 kHz. Several pulser designs are available that can optimally drive DSRDs. The purpose of this study is to investigate the capabilities of two DSRD-based pulsers in the context of the DWA and the required pulse parameters. The first pulser is based on a magnetic saturation transformer (MST) and a DRSD. The second pulser considered is a multi-module MOSFET-DSRD-based pulser. Additionally, Sentaurus TCAD simulations are used to study the influence of the Si DSRD doping profile on the output pulse shape. The MST-DSRD-based pulser is able to generate higher amplitude pulses than the MOSFET-DSRD-based pulser with a single module (9645 V and 1807 V, respectively). However, the multi-module MOSFET-DSRD-based pulser achieves the maximum pulse amplitude (10.9 kV) compared to MST-DSRD-based pulser (9645 V). The MOSFET-DSRD-based pulser also generates pulses with shorter pulse widths compared to the MST-DSRD-based pulser (minimum of 3 ns vs. minimum of 8.36 ns, respectively). With no compression stage, the MOSFET-DSRD-based pulser (with more than one module) generates pulses with consistently faster rise times (≤3.06 ns) compared to the MST-DSRD-based pulser (≤4.31 ns). With a compression stage, the rise times were comparable between the two pulsers (MOSFET-DSRD: 1.66 ns and MST-DSRD: 1.48 ns). Both pulsers are able to operate at 1 kHz and the MOSFET-DSRD-based pulser up to 10 kHz. Parasitic capacitance and coupling between modules of the MOSFET-DSRD-based pulser affect the pulse through their influence on the forward and reverse pumping duration. Simulations show that the p region of the DSRD should be larger than the n doped region. Simulations including a parasitic capacitance, modelling the electrical connections to the DSRD, reduce the pulse amplitude. Simulations of the pulsers incorporating SiC DSRDs show a reduction in the pulse amplitude and a widening of the pulse width in comparison to the Si DSRDs.

High-performance single crystal Ni-rich cathode with regulated lattice and interface constructed by separated lithiation and crystallization calcination

Incorporating high valence dopants, such as W6+ and Mo6+ has been verified to be effective for tuning the microstructure and grain boundary of polycrystal Ni-rich cathode. However, the hindered consolidation of primary particles induced by dopants during lithiation calcination limits the utilization of those dopants to crystalize single-crystal Ni-rich cathodes with stabilized lattice and surface. Herein, high performance single crystal LiNi0.84Co0.11Mn0.05O2 cathode with Al3+ and W6+ regulated lattice and boundary phase was construed based on commercial process with two-step calcination process containing separated lithiation and crystallization. The introduction of appropriate amount of Al3+ in the first lithiation calcination of 6 h endows the bulk of crystalline with enhanced lattice stability, while the incorporation of W6+ with stoichiometrical LiOH in the secondary crystallization calcination of 6 h renders uniformly distributed surface layer without hampering the growth of single-crystal. With the Al3+ doped bulk lattice, W6+ doped subsurface region and hetero-epitaxially grown Li2WO4, the cathode infused by two-step calcination exhibits high discharge capacity, rate performance, and cycling stability. Specifically, the modified LiNi0.84Co0.11Mn0.05O2 exhibits exceptional capacity retention, maintaining 88.98% of its initial capacity after 200 cycles at a rate of 1 C within a voltage window of 2.7–4.3 V at a temperature of 25 °C in half-cell. This performance is markedly superior to the capacity retention of 72.96% observed for pristine cathode. Even when subjected to a stringent test after 200 cycles at the same rate, the modified cathode sustains an impressive capacity retention of 82.41% at an elevated cut-off voltage of 4.5 V and a temperature of 30 °C.

Investigation of BPD Faulting under Extreme Carrier Injection in Room vs High Temperature Implanted 3.3kV SiC MOSFETs

Implantation process for high Al dose p+ contact layers in SiC MOSFETs can generate new basal plane dislocations (BPDs). Such BPD faulting under high carrier injection was investigated in SiC MOSFET layers designed for 3.3kV operation with either room temperature (RT) or high temperature (HT) implantations performed for their high dose p+ contact layer. For excess carrier injection levels of ~1x1018 cm-3 implant induced BPDs faulted from the termination regions of the MOSFETs in the case of RT samples, while the HT samples show no BPD faulting because there were no implant-induced BPDs. However, in the active region of the device no BPDs faulted for both the RT as well as HT samples even at a higher carrier injection of ~1x1019 cm-3. Technology computer-aided design (TCAD) simulations show that the lower doped p-well region below the p+ contact in the active area of the device prevents the minority electron density in the p+ contact layer to below 10x the hole density, which limits BPD faulting even when they are present in that layer as in the case of RT implanted samples.

Investigation of AlGaN UV emitting tunnel junction LED devices by off-axis electron holography

Here we use off-axis electron holography combined with advanced transmission electron microscopy techniques to understand the opto-electronic properties of AlGaN tunnel junction (TJ)-light-emitting diode (LED) devices for ultraviolet emission. Four identical AlGaN LED devices emitting at 290 nm have been grown by metal–organic chemical vapour deposition. Then Ge doped n-type regions with and without InGaN or GaN interlayers (IL) have been grown by molecular beam epitaxy onto the top Mg doped p-type layer to form a TJ and hence a high quality ohmic metal contact. Off-axis electron holography has then been used to demonstrate a reduction in the width of the TJ from 9.5 to 4.1 nm when an InGaN IL is used. As such we demonstrate that off-axis electron holography can be used to reproducibly measure nm-scale changes in electrostatic potential in highly defected and challenging materials such as AlGaN and that systematic studies of devices can be performed. The LED devices are then characterized using standard opto-electric techniques and the improvements in the performance of the LEDs are correlated with the electron holography results.

Correlation of dopant solution on doping mechanism and performance of F4TCNQ‐doped P3HT

AbstractUnderstanding the doping mechanism between the dopants and the conjugated polymers (CPs) is crucial for efficiently utilizing the doping process in a controllable manner. In this work, we doped the poly(3‐hexylthiophene) (P3HT) films with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) from a chlorobenzene/acetonitrile (CB/AN) solvent blend and pure AN solvent by using the common sequential doping method. We found that the dissolution ability of the dopant solvent to P3HT and the concentration of the dopant solution were two critical factors to determine the doping process (solution doping or sequential doping) and the doping region (the amorphous or the crystalline phase). When the concentration of the dopant solution was low, solution doping was dominant in the P3HT film doped with F4TCNQ CB/AN solution, and the amorphous regions were doped in the P3HT film doped with F4TCNQ AN solution. With the increase of the dopant solution concentration, the ratio of ordered integer charge transfer (ICT) species, which formed from sequentially doped crystalline domains in the P3HT precast film, increased. Based on the above doping mechanism, a P3HT film with good electrical and tensile performance could be constructed by doping from F4TCNQ CB/AN solution with a relatively low concentration. Our work indicates that the dissolution or swelling ability of the dopant solvent to CP is an important factor in determining not only the doping mechanism but also the electrical and mechanical performances of doped CP films.

Energy Filtering in Doping Modulated Nanoengineered Thermoelectric Materials: A Monte Carlo Simulation Approach.

Using Monte Carlo electronic transport simulations, coupled self-consistently with the Poisson equation for electrostatics, we explore the thermoelectric power factor of nanoengineered materials. These materials consist of alternating highly doped and intrinsic regions on the scale of several nanometers. This structure enables the creation of potential wells and barriers, implementing a mechanism for filtering carrier energy. Our study demonstrates that by carefully designing the nanostructure, we can significantly enhance its thermoelectric power factor compared to the original pristine material. Importantly, these enhancements stem not only from the energy filtering effect that boosts the Seebeck coefficient but also from the utilization of high-energy carriers within the wells and intrinsic barrier regions to maintain relatively high electronic conductivity. These findings can offer guidance for the design and optimization of new-generation thermoelectric materials through improvements in the power factor.

The synergistic design of 5 V ESD protection applications using two holding voltage improving methods

In this paper, a series of Low Voltage Triggering Silicon-Controlled Rectifier (LVTSCR)-based devices were designed and fabricated in a 0.25 μm Bipolar-CMOS-DMOS (BCD) process. Two distinct methods, the integration of additional doping regions and current paths, are investigated to improve the proposed devices’ holding voltage (Vh). Two-dimensional device simulation is employed to elucidate the working mechanism of these ESD protection devices, complemented by the introduction of a transmission line pulse (TLP) measuring system to assess their ESD protection capabilities. Comparative analysis of TLP results reveals that both methods contribute significantly to the augmentation of holding voltage in LVTSCR ESD protection devices. The refined structure, LVTSCR_BN, with two additional current paths, surface and buried, demonstrated a noticeable increment in holding voltage. With its holding voltage of 7.619 V and trigger voltage of 10.61 V, LVTSCR_BN is proved suitable for the ESD protection of circuits operating at the voltage of 5 V.

Aluminum channeling in 4H-SiC by high-energy implantation above 10 MeV

This study explores high-energy aluminum (Al) implantation above 10MeV as a fabrication process to facilitate the creation of deep doping regions in silicon carbide (SiC). Experimental investigations were conducted to evaluate the technical feasibility of ultra-high energy implantation and high-energy channeling implantation of aluminum into 4H-SiC. Ultra-high-energy Al implantations at 30 and 48MeV were performed, revealing limitations such as increased charge dispersion and decreased current near accelerator technical limits. In contrast, high-energy channeling implantations at 12, 15, and 20MeV demonstrated successful Al channeling implantations into 4H-SiC, emphasizing the importance of precision in crystal orientation and mounting systems. Results indicate that channeling implantations, with precise instrumentation, are a preferred approach over non-channeled ultra-high-energy methods for fabricating deep doping regions in SiC, holding promise for advancing the next generation of high-voltage SiC devices.

Analytical models of the electric field and carrier transit time in the base of bipolar junction transistors

The conventional theory of the bipolar junction transistor (BJT) does not clarify the electric field and its effect on the carrier transit in the uniformly doped base region, although the electric field is considered to be a second-order effect at high-level injection. In this study, analytical models of the carrier distribution, electric field, and carrier transit time in the base region are developed without making additional assumptions. It is found that the electric field may change direction, from forward to reverse, as long as the injection level reaches a criterion, affecting the carrier transport behavior. The models are based on the renovated p–n junction theory, provide insight into the carrier transit and are able to cover all levels of injection without the need to handle the low- and high-level injection separately. These models hold significance in retrieving the theoretical integrity of bipolar junction devices, and can be useful for further investigation in structure design, capacitance control, and AC performance optimization of the p–n junction-based device.

Design and Growth of Low Resistivity P-Type AlGaN Superlattice Structure.

This work investigated the impact of periodic thickness and doping region on the doping efficiency of the P-type AlGaN superlattice. In this paper, the band structure of the simulated superlattice was analyzed. The superlattice structure of Al0.1Ga0.3N/Al0.4Ga0.6N, and the AlGaN buffer on the sapphire substrate, achieved a resistivity of ~3.3 Ω·cm. The results indicate that barrier doping and low periodic thickness offer significant advantages in introducing a reduction of the resistivity of P-type AlGaN superlattice structures.

Investigation of structural, electronic, mechanical, and thermoelectric properties of the defect chalcopyrite semiconductor ZnIn[formula omitted]Se[formula omitted] from density functional theory

In this study, the detailed structural, electronic, mechanical, and thermoelectric properties of ZnIn2Se4 defect chalcopyrite semiconductor are carried out using density functional theory & semi-classical Boltzmann transport theory. From the band structure analysis, the compound is confirmed to be a direct band gap semiconductor with a band gap of 1.20 eV. The presence of flat valence bands near the Fermi level indicates a higher effective mass of holes. From the elastic and mechanical properties, it has been found that the compound is mechanically stable and revealed to be ductile. The phonon dispersion study of the compounds shows that the compound is dynamically stable with no imaginary phonon modes. The electronic transport properties were studied within a temperature range of 300K to 900K as a function of chemical potential (μ), temperature(T), and carrier concentrations (n). The μ dependent electronic transport properties show enhanced values in the p-type doping region because of the cationic site vacancy. The dependency of electronic transport properties on n and T agrees well with Mott’s relation. The highest ZT is found to be 0.96 at 900K for a low carrier concentration of 1019cm−3. The phonon thermal conductivity of the compound is found to be 2.52 W/mK near room temperature and 0.84 W/mK at 900K using the Slack method. All these results support ZnIn2Se4, a defect chalcopyrite semiconductor, as a favorable candidate for thermoelectric applications.

Relationship between disorder, magnetism and band topology in Mn(Sb1–x Bi x )2Te4 single crystals

We investigate the evolution of magnetic properties as well as the content and distribution of Mn for Mn(Sb1−x Bi x )2Te4 single crystals grown by large-temperature-gradient chemical vapor transport method. It is found that the ferromagnetic MnSb2Te4 changes to antiferromagnetism with Bi doping when x ≥ 0.25. Further analysis implies that the occupations of Mn ions at Sb/Bi site MnSb/Bi and Mn site MnMn have a strong influence on the magnetic ground states of these systems. With the decrease of MnMn and increase of MnSb/Bi, the system will favor the ferromagnetic ground state. In addition, the rapid decrease of T C/N with increasing Bi content when x ≤ 0.25 and the insensitivity of T N to x when x > 0.25 suggest that the main magnetic interaction may change from the Ruderman–Kittel–Kasuya–Yosida type at low Bi doping region to the van-Vleck type in high Bi doped samples.

Effect of Fe Doping Profile on Current Collapse in GaN-based RF HEMTs.

Using computer-aided design (TCAD) simulation, the impact of the Fe doping profile, including concentration, decay rate, and depth of the doping region on current-collapse magnitude (▵CC) in 0.5-μm gated GaN-based high electron mobility transistors (HEMTs) is systematically investigated. Accurate simulation models are established and developed to facilitate the fabrication of electronics. It is elucidated that the intricate interplay between trapping and de-trapping of Fe-related traps at the gate-drain edge is responsible for current collapse. The concentration and decay rate of the doping region have a more significant impact on current collapse than the depth. Increased trap state density near two-dimensional electron gas (2DEG) channel caused by deep-level acceptors would boost ▵CC. However, a minor dynamic reduction in 2DEG density (nT) induces a relatively small ▵CC. By adjusting the concentration, decay rate, and depth of the doping region, ▵CC of GaN-based Radio Frequency (RF) HEMTs can be reduced by approximately 50.3 %. The optimized distribution of Fe doping discussed in this work helps to prepare GaN-based RF HEMTs with a limited current collapse effect.

Formula omitted]-type doping modulation of double GaAs/AlGaAs quantum wells

Utilizing the FEniCS Project and Python programming, we conduct a comprehensive characterization and analysis of the n-type doped layer in double quantum wells made of GaAs and featuring AlGaAs barriers through self-consistent Schrödinger–Poisson simulations. The main findings reveal that the dimensions of the system and the doping layer significantly influence the electronic properties, energy levels, Fermi energy, wave functions, and electron density. Upon doping the intermediate barrier, electrons exhibit notable migration from the doping region to the quantum well zones, particularly pronounced for thin barriers. Conversely, for large barriers, the emergence of a new well, akin to a real quantum well, imposes constraints on the movement of charge carriers. The electron density varies in accordance with the impurity density, which assumes significant importance as the quantum well and barrier width are reduced. The Fermi energy level, which play a crucial role in semiconductors, rises with a decrease in quantum well width or an increase in doped layer width and n-type doping density, remaining almost unaffected by variations in barrier width.

Beam quality evolution in large-mode-area specially doped laser fiber through bend-induced effective refractive index change

The effect of bending in a specially doped large-mode-area (LMA) gain fiber on the beam quality of the laser and amplifier has been studied through simulation and experimentation. The effect on the overlap between the fundamental mode (FM) and the doping region due to bend-induced refractive index change was studied theoretically by varying the bend radius. Bend radius of the gain fiber in the range of 5–8 cm was used to study the evolution of beam quality at the amplified output. The numerical simulation of the overlap between the FM and the dopant distribution in the core of the gain fiber for different bending radii is well matched to the experimentally measured beam quality of the amplified output for the respective bending of the gain fiber. The master oscillator (having M 2 = 1.1) was successfully amplified to 35 W maintaining the near-diffraction-limited beam quality (M 2 = 1.05) using a confined doped LMA gain fiber with a bend radius of 8 cm. However, the use of a uniform doped LMA gain fiber with similar bend configuration degrades the beam quality (M 2 = 1.37) at the amplified output power of 31.3 W.

Photo-thermoelectric effect-driven detection of optical communication light in graphene/hBN heterostructures

We report on the photodetection properties of high-quality graphene encapsulated by hexagonal boron nitride under illumination with optical communication light. We demonstrate a gate-tunable photocurrent and zero-bias switching cycle operation at RT. Through gate and temperature-dependent photocurrent measurements, we determine that the dominant photoresponse mechanism is the photo-thermoelectric effect. At low temperatures, the photocurrent in finite doping regions correlates with the Seebeck coefficient, while sharp peaks emerge near the charge neutrality point due to an edge-excited photocurrent. Our study provides guidelines for high-performance graphene-based optoelectronic devices.

Bulk fin-type field-effect transistor-based capacitorless dynamic random-access memory with strong resistance to geometrical variations

In this study, a bulk fin-type FET (FinFET)-based capacitorless one-transistor dynamic random-access memory (1T-DRAM) was proposed. The fabrication process of the proposed 1T-DRAM was similar to that of a typical junctionless bulk FinFETs, except that the p-type doped body fin region operated as a charge storage region. The effects of the geometrical variations, such as the fin angle (θ fin) variation and line edge roughness (LER), which are inevitable in fabrication, on the transfer characteristics and memory performance of the proposed 1T-DRAM were studied. θ fin was varied from 90° to 80°, and 200 samples with the LER were analyzed. Results revealed that the transfer characteristics and memory performance were affected by geometrical variations. However, the proposed 1T-DRAM exhibited an excellent retention time in all cases because the charge storage region was separated from the region of operation.