Dopant Diffusion Research Articles

Influence of irradiation wavelength during laser-assisted doping of 4H-silicon carbide in liquid phase

Laser-assisted doping of silicon carbide (SiC) substrates is challenging due to the low diffusion coefficient of dopant atoms and the chemically inert nature of SiC. Single crystal intrinsic 4H-SiC substrate is irradiated with neodymium-doped yttrium aluminium garnet (Nd3+):YAG laser with wavelengths of 1064, 355 and 266 nm, and krypton fluoride (KrF) excimer laser with the wavelength of 248 nm under liquid phase dopant sources. Different liquid solutions were used as dopant sources for aluminium (Al) and phosphorus (P). SiC was transparent to 1064 and 355 nm due to low absorption coefficients, while 266 and 248 nm showed better coupling due to higher absorption coefficients and led to the diffusion of atoms. The electrical resistance of the substrates was measured to be lower than 1000 kΩ after diffusion. Dispersive X-ray spectroscopy (EDS) studies showed that both laser wavelengths of 248 nm and 266 nm resulted in doping of Al and P, with the surface concentrations ranging from 0.5 to 1.5 at.% and from 0.24 to 0.6 at.%, respectively. Two-dimensional thermo-temporal simulation of the laser pulse interaction in the liquid phase revealed that unlike in air, during irradiation with 266 nm laser under liquid, the surface temperature of the substrate was slightly lower. However, the subsurface temperature increased along the depth by a few microns. Similarly, simulation studies with longer pulse irradiation also show that high temperature was maintained for a longer time, indicating improved dopant diffusion into the 4H-SiC substrate.

Low Contact Resistance WSe2 p-Type Transistors with Highly Stable, CMOS-Compatible Dopants.

High contact resistance has been a bottleneck in developing high-performance transition-metal dichalcogenide (TMD) based p-type transistors. We report degenerately doped few-layer WSe2 transistors with contact resistance as low as 0.23 ± 0.07 kΩ·μm per contact by using platinum(IV) chloride (PtCl4) as the p-type dopant, which is composed of ions compatible with the complementary metal-oxide-semiconductor (CMOS) fabrication process. Top-gated devices with a gate length of 200 nm showed good switching behaviors, implying that the dopant diffusion into the gate stack is not significant. The devices showed nearly identical performance after being kept in air for 86 days without any encapsulation while retaining the degenerately doped states at 78 K with pressure lower than 10-5 Torr, highlighting the stability of the dopants. The presented method sets forth the availability of highly stable methods for pattern doping the transistors with a thinned Schottky barrier width for low contact resistance devices.

Modification of the Spectral Absorption Characteristics of ZnGeP2 in the THz and IR Wavelength Ranges Due to Diffusion Doping with Impurity Atoms of Mg, Se, Sn, and Pb

This study demonstrates that diffusion doping of ZGP single crystals with impurity atoms (Mg, Se, Sn, Pb) leads to a decrease in the specific conductivity of the samples. Consequently, this results in reduced absorption in the terahertz frequency range (150–1000 μm). It has been shown that doping ZGP samples with selenium (Se) and lead (Pb) atoms reduces absorption in the infrared region from 0.3–0.6 cm−1 to 0.06–0.09 cm−1. Doping with tin (Sn) leads to a decrease in absorption only in the wavelength region near 2.1 μm from 0.2 cm−1 to 0.05 cm−1. The proposed mechanism for the decrease in infrared absorption is a reduction in zinc vacancies due to doping with impurity atoms. This research lays the groundwork for a technology that produces ZGP crystals with minimal absorption within the 2–8 μm wavelength range, eliminating the need for fast electron beam irradiation technology. This advancement will facilitate the fabrication of ZGP crystals with arbitrary apertures.

Low-Temperature Selective Si:As Epitaxy

A selective low-temperature Si:As (LT-SiAs) process is presented which utilizes cyclic deposition-etch (CDE) at <450oC. Selectivity against SiN and SiOx dielectrics and crystallinity are confirmed on gate-all-around (GAA) patterned structures. Hall measurements on blanket wafers show a resistivity minimum of 0.42 mΩ-cm at ~1.7% As for selective LT-SiAs. Secondary-ion mass spectroscopy (SIMS) profiles of P and As diffusion into intrinsic Si (i-Si) for LT-SiP/LT-SiAs/i-Si and LT-SiP/i-Si stacks show >2× benefit of using LT-SiAs spacers to minimize dopant diffusion for as-deposited, soak-annealed and spike-annealed samples. Improvement is attributed to relatively limited diffusivity of As in Si versus P and the lower As concentration needed for LT-SiAs layer to achieve minimum resistivity relative to LT-SiP (~3%). Lastly, a comparison of LT-SiAs and high-temperature Si:As (HT-SiAs) shows a ~2× reduction of As diffusion into i-Si for LT-SiAs at length scales of >10nm.

Investigation of the activation and diffusion of ion-implanted p-type and n-type dopants in germanium using high-pressure annealing

In this study, we investigate the effectiveness of high-pressure annealing (HPA) compared to microwave annealing (MWA) in activating n-type and p-type dopants in germanium. For phosphorus dopants, HPA at 500 °C significantly enhances the activation level, resulting in a reduction of sheet resistance to 120.1 ohms sq.−1 and a maximum active concentration of up to 5.76 × 1019 P cm−3. Similarly, for boron dopants, HPA at 800 °C reduces the sheet resistance to 80.6 ohms sq.−1 and achieves a maximum active concentration that maintains effective doping profiles. Transmission electron microscopy images reveal that the amorphous layers implanted with phosphorus and boron are significantly reduced, indicating that HPA is more effective in achieving solid-phase epitaxial regrowth compared to MWA. HPA demonstrates superior performance in minimizing dopant diffusion and reducing sheet resistance for both phosphorus and boron dopants, making it a preferable method for high-temperature annealing in germanium-based devices.

Enhanced Activation in Phosphorous-Doped Silicon via Dual-Beam Laser Annealing.

In this study, we conduct a comparative analysis of single-beam laser annealing (SBLA) and dual-beam laser annealing (DBLA) techniques for semiconductor manufacturing. In the DBLA approach, two laser beams were precisely aligned to simultaneously heat a phosphorus-doped silicon (Si) wafer. The main objective was to investigate the impact of the two annealing techniques on the electrical properties, crystalline structure, and diffusion profile of the treated phosphorus-doped Si at equivalent laser powers. Both SBLA and DBLA improved the electrical properties of the phosphorus-doped Si, evidenced by increased carrier concentration and reduced carrier mobility. Additionally, the crystalline structure of the phosphorus-doped Si showed favorable modifications, with no defects and improved crystallinity. While both SBLA and DBLA produced similar phosphorus profiles with no significant redistribution of dopants compared to the as-implanted sample, DBLA achieved a higher activation ratio than SBLA. Although the results suggest improved dopant activation with minimal diffusion, further studies are needed to clearly confirm the effect of DBLA on dopant activation and diffusion.

(Invited) Breakdown Improvement of Mg-Diffused Current Blocking Layer in Ga2O3

The path towards an all-planar highly efficient vertical Ga2O3 transistor requires the construction of a buried gate barrier junction to circumvent the pre-mature breakdown near the gate often seen in lateral structures. An effective selective doping technique is necessary to achieve this. By taking advantage of the high diffusivity of dopants and defects in Ga2O3, we propose the use of diffusion doping as a rapid and non-invasive technique to explore the possibility of an effective current blocking layer (CBL) in vertical Ga2O3 transistors. Unlike ion implantation, diffusion doping does not require an 1100°C annealing for the repair of crystal damage. Thus, the desired Mg doping profile can be maintained by the end of device fabrication, which is the key to achieving a high blocking voltage with Mg-doped CBL. In addition, diffusion doping can easily form a much deeper dope junction and be very useful for high-voltage and super-junction devices.Recently, we have demonstrated the first Ga2O3 vertical-diffused-barrier field-effect transistor (or VDBFET) utilizing a Mg-diffusion doped CBL with a spin-on-glass source. The transistor exhibited excellent FET behavior with decent saturation, enhancement-mode operation, and an on/off ratio of more than 109. However, the breakdown voltage is measured to be only 72V most likely due to the punch-through of the Mg-diffused CBL. This is likely caused by a lower-than-expected Mg doping rendering an inefficient electron blocking. In addition, SIMS analysis indicated the existence of Mg-H complex that deactivated the Mg. Thus, the effective Mg doping is even lower than its chemical concentration. Here we will discuss a new strategy to resolve this problem and showcase the characteristics of the improved CBL with a higher breakdown. This development paves the way for the development of high-voltage Ga2O3 VDBFETs.

On estimation of maximal value of full diffusion time of infused and implanted dopants

In this paper, we estimate the maximal annealing time of dopant and/or radiation defects during the manufacturing of elements of integrated circuits by dopant diffusion and ion implantation. We introduce an analytical approach to estimate the maximal continuance of the diffusion process. We analyzed the influence of parameters of considered technological processes on the value of their maximal continuance of diffusion process.

Ion diffusion retarded by diverging chemical susceptibility

For first-order phase transitions, the second derivatives of Gibbs free energy (specific heat and compressibility) diverge at the transition point, resulting in an effect known as super-elasticity along the pressure axis, or super-thermicity along the temperature axis. Here we report a chemical analogy of these singularity effects along the atomic doping axis, where the second derivative of Gibbs free energy (chemical susceptibility) diverges at the transition point, leading to an anomalously high energy barrier for dopant diffusion in co-existing phases, an effect we coin as super-susceptibility. The effect is realized in hydrogen diffusion in vanadium dioxide (VO2) with a metal-insulator transition (MIT). We show that hydrogen faces three times higher energy barrier and over one order of magnitude lower diffusivity when it diffuses across a metal-insulator domain wall in VO2. The additional energy barrier is attributed to a volumetric energy penalty that the diffusers need to pay for the reduction of latent heat. The super-susceptibility and resultant retarded atomic diffusion are expected to exist universally in all phase transformations where the transformation temperature is coupled to chemical composition, and inspires new ways to engineer dopant diffusion in phase-coexisting material systems.

Anion Bulk Doping of Organic Single‐Crystalline Thin Films for Performance Enhancement of Organic Field‐Effect Transistors

AbstractChemical doping is a powerful way to enhance the electrical performance of organic electronics. To avoid perturbing the ordered molecular packing of organic semiconducting hosts, molecular dopants are deposited on the surface of highly crystalline organic semiconductor thin films. However, such surface doping protocols not only limit charge‐transfer efficiency but also cause dopant diffusion problems, which significantly reduce charge carrier mobility and device stability. Here, an innovative anion bulk doping strategy is reported that allows effective doping of organic single‐crystalline films (OSCFs) without disrupting molecular ordering to improve the performance of organic field‐effect transistors (OFETs). This method is mediated by anion dopants and can be pictured as an effective charge transfer of dopants with organic semiconductors in liquid phase. The direct introduction of dopant anions overcomes limitations of partial charge transfer while avoiding interference from dopant aggregation with crystallization. Using this method, the average carrier mobility of the OSCFs is boosted by ≈2.5 times. Significantly, low‐voltage OFETs developed from anion‐doped OSCFs exhibit a near‐ideal subthreshold swing of 59.2 mV dec−1 and unparalleled mobility as high as 19.8 cm2 V−1 s−1 together with excellent stability. The concept of anion doping opens new avenues for improving the electrical performance of organic electronics.

On how Doping with Atoms of Gadolinium and Scandium affects the Surface Structure of Silicon

The experimental team has developed a technology of step-by-step low-temperature diffusion doping of gadolinium and scandium into silicon that allows the clusters of impurity atoms to be uniformly distributed throughout the entire bulk of the silicon material. It was shown that, unlike the samples obtained under the high-temperature diffusion doping technology, in the samples obtained under the novel technology the team had detected any surface erosion or formation of alloys and silicide in the near-surface region. The authors have revealed increased thermostability and radiation resistance of silicon samples dotted with clusters of impurity atoms of gadolinium and scandium. The authors have conducted comprehensive studies by using the techniques of tagged atoms, autoradiography, measurement of conductivity and Hall effect, isothermal relaxation of capacitance and current of diffusion, solubility, and electrophysical properties of scandium in silicon under various doping conditions and for a wide temperature range (1100 ÷ 1250 0С). Diffusion parameters, solubility and acceptor nature of scandium in silicon as well as thermal stability of silicon doped with gadolinium and scandium impurity atoms have been established.

The thermal diffusion blocking effect of holes enclosing core fiber

We have developed a variety of optical fibers with holes enclosing the core to increase the service life of fiber optic devices under high-temperature and high-pressure environments by blocking the diffusion of dopants in the core with the help of air holes. Simulation results show that the fiber with uniformly distributed holes enclosing the core, the more the hole number, the smaller the core hole distance, and the larger the hole radius, the more significant the blocking effect on thermal diffusion. By comparing the refractive index distribution of three kinds of holes enclosing core fibers and single-mode fibers after prolonged high-temperature heating treatment, the thermal diffusion blocking effect of the holes enclosing core fiber is verified. Long-period fiber gratings fabricated by periodic refractive index modulation of holes enclosing core fibers can realize the measurement of various physical parameters. The thermal diffusion blocking effect of the holes enclosing core fiber enables the long-period fiber grating devices to work for a long time under high-temperature and high-pressure environments, showing the potential for practical applications in various industrial processes.

Doped silicon nanoparticles. A review

Doped silicon nanoparticles combine availability and biocompatibility of the material with a wide variety of functional properties. In this review, the methods of fabrication of doped silicon nanoparticles are discussed, the prevalent of those being chemical vapor deposition, annealing of substoichiometric silicon compounds, and diffusion doping. The data are summarized for the attained impurity contents, in the important case of phosphorus it is shown that impurity, excessive with respect to bulk solubility, is electrically inactive. The patterns of intraparticle impurity distributions are presented, that were studied in the previous decade with highly-informative techniques of atom probe tomography and solid-state NMR. Prospective optical and electrical properties of doped silicon nanoparticles are reviewed, significant role of the position of the impurities is exemplified with plasmonic behavior.

Study of infrared quenching in silicide-silicon-silicide structures

Infrared quenching (IR Q) in silicide-silicon-silicide and silicide-silicon-metal structures has been studied. Silicides are obtained through the process of diffusion doping of silicon with manganese atoms. Infrared quenching was detected in the irradiation energy range of 0.31-0.75 eV when illuminated with local light hv≥Eg. Attachment levels for electrons were found: Ec-0.31 eV, Ec-0.38 eV, Ec-0.51 eV. The long-wave limit of photoconductivity (PC) was established to be 0.38 eV by studying the spectral characteristics of silicide-silicon-silicide structures.

Low-Temperature Growth of InGaAs Quantum Wells Using Migration-Enhanced Epitaxy.

The growth of InGaAs quantum wells (QWs) epitaxially on InP substrates is of great interest due to their wide application in optoelectronic devices. However, conventional molecular beam epitaxy requires substrate temperatures between 400 and 500 °C, which can lead to disorder scattering, dopant diffusion, and interface roughening, adversely affecting device performance. Lower growth temperatures enable the fabrication of high-speed optoelectronic devices by increasing arsenic antisite defects and reducing carrier lifetimes. This work investigates the low-temperature epitaxial growth of InAs/GaAs short-period superlattices as an ordered replacement for InGaAs quantum wells, using migration-enhanced epitaxy (MEE) with low growth temperatures down to 200-250 °C. The InAs/GaAs multi-quantum wells with InAlAs barriers using MEE grown at 230 °C show good single crystals with sharp interfaces, without mismatch dislocations found. The Raman results reveal that the MEE mode enables the growth of (InAs)4(GaAs)3/InAlAs QWs with excellent periodicity, effectively reducing alloy scattering. The room temperature (RT) photoluminescence (PL) measurement shows the strong PL responses with narrow peaks, revealing the good quality of the MEE-grown QWs. The RT electron mobility of the sample grown in low-temperature MEE mode is as high as 2100 cm2/V∗s. In addition, the photoexcited band-edge carrier lifetime was about 3.3 ps at RT. The high-quality superlattices obtained confirm MEE's effectiveness for enabling advanced III-V device structures at reduced temperatures. This promises improved performance for applications in areas such as high-speed transistors, terahertz imaging, and optical communications.

A multi-core fiber coupler without a central core

An efficient method for fabricating multi-core fiber couplers based on the thermal diffusion technique is proposed to realize the connection of single-mode fibers to multi-core fibers without a central core. The fabrication efficiency of the multi-core fiber coupler is improved by fiber-loaded hydrogen. The simulation results show that the single-mode fiber and the multi-core fiber can be coupled stably and efficiently by using the designed double-clad fiber to connect the single-mode fiber and the multi-core fiber. Double-clad fiber and multi-core fiber were loaded with hydrogen to enhance the dopant diffusion rate. Three-dimensional refractive index measurements of the multi-core fiber coupler show that the dopant diffusion rate and the diffusion zone length of the hydrogen-loaded fiber are significantly increased compared to the original fiber. These enhancements contributed to the shorter fabrication time of multi-core fiber couplers. The multi-core fiber couplers fabricated by thermal diffusion technology have the advantages of high coupling efficiency, high integration, simple manufacture, and high mechanical strength. Enhancing the diffusion rate of optical fibers by using the hydrogen loading method will increase the application potential of multi-core optical fiber couplers prepared by thermal diffusion technology, and accelerate the translation of multi-core fibers toward optical communication and optical fiber sensing.

Enhanced broadband reflection properties of PSCLCs films supported by electrospun nanofiber networks loaded with Cs0.33WO3 nanoparticles

ABSTRACT The introduction of nanoparticles into cholesteric liquid crystals has long provided inspiration for innovative device materials. A novel material design strategy was demonstrated to achieve a broadband reflection of polymer-stabilised cholesteric liquid crystals (PSCLCs) based on Cs0.33WO3 nanoparticles and the polymer nanonetworks in the PSCLCs. Through the adjustment of nanoparticle and chiral dopant (C6M) concentrations and meticulous control of polymerisation conditions, an appropriate pitch gradient distribution was achieved in the polymer-stabilised cholesteric liquid crystals (PSCLCs). This was attained by striking a delicate balance between the polymerisation speed and chiral dopant diffusion rate, resulting in optimal PSCLCs optical properties. Modification of Cs0.33WO3 nanoparticles by oleic acid was successfully accomplished as confirmed by IR spectroscopy. SEM and EDS analyses further demonstrated the distribution of nanoparticles in the spun fibre film. Moreover, POM observations showed that liquid crystals with nanofiber networks maintained the planar texture and temperature stability. The prepared broadband reflective film opens an avenue towards developing the reflection bandwidth in the PSCLCs, essential for intelligent windows and infrared shielding devices.

Synthesis and Photocatalytic Activity of Zinc and Tungsten Co-Doped Barium Titanate Perovskite for Methylene Blue Degradation under Solar Irradiation

This research delves into the properties of x% ZW-BT compounds (x=3% and 7%), synthesized using a solid-state reaction approach. Utilizing X-ray diffraction, the crystal structure of the x% ZW-BT compositions is confirmed, showcasing a distinct tetragonal symmetry devoid of any parasitic phases. With increasing dopant concentrations, slight reductions in lattice parameters are observed, signifying the even diffusion of dopant (Zn2+ and W6+) ions. Moreover, the validation of metal-oxygen bonding vibrations is achieved through Fourier-transform infrared spectroscopy (FTIR) analysis. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) reveals consistent granular arrangements and clear elemental signatures in both compositions. Notably, photocatalytic experiments highlight remarkable degradation rates; within 100 minutes, 3% and 7% ZW-BT achieve degradation levels of 78.04% and 88.9% respectively. These findings underscore the significant potential of these compounds for environmentally friendly photocatalytic applications.

Diffusion doping of analgesics into UHMWPE for prophylactic pain management.

Pain management after total joint arthroplasty is often addressed by systemic delivery of opioids. Local delivery of non-opioid analgesic drugs directly in the joint space from the UHMWPE component of the prosthesis would be highly beneficial to increase the efficacy of the drugs, decreasing the overall side effects and the risk of opioid addiction. It has been shown that effective concentrations of local analgesics can be achieved by eluting from analgesic-blended UHMWPE; however, this approach is limited by the decrease in mechanical properties resulting from the extent of phase separation of the blended drugs from the polymeric matrix. Here we hypothesized that mechanical properties could be maintained by incorporating analgesics into solid form UHMWPE by diffusion as an alternative method. Lidocaine or bupivacaine were diffused in solid form UHMWPE with or without radiation crosslinking. The loaded drug content, the spatial distribution of the drugs and their chemical stability after doping were characterized by FTIR and NMR spectroscopy, respectively. Drug release kinetics, tensile mechanical properties and wear rates were assessed. The results showed that diffusion doping could be used as a promising method to obtain a therapeutic implant material without compromising its mechanical and structural integrity.

Periodically-Poled Lithium Tantalate Ridge Waveguides for Efficient Nonlinear Frequency Conversion in the Near UV

Optical damage resistant ridge waveguides for blue and near UV wavelengths have been fabricated using high-temperature Zr and Zn diffusion doping and vapor transport equilibration (VTE) of congruent LiTaO3 crystals. For both dopants high optical damage thresholds &gt;10 MW/cm2 for 532 nm light were demonstrated at room temperature, which can be increased by a factor ~3 when heating the samples to ~150°C. Ridge waveguides with low optical losses of ~0.4 dB/cm were fabricated using diamond-blade dicing. First-order periodic poling with grating periods of ~3 μm can be used for efficient nonlinear frequency conversion for both SHG (800 nm pump) or SPDC (400 nm pump) processes.