Si Ion Implantation Research Articles

Submicron Embedded Air/GaN Diffraction Gratings for Photonic Applications

AbstractThe integration of photonic elements with nitride optoelectronic structures allows control of emitted light properties, which is advantageous for achieving, e.g., a single wavelength lasing. Positioning of the photonic structures on the top surface of GaN‐based devices is problematic, in particular, for deposition of a metal contact to p‐type top layer. In this work, custom‐shaped submicron air channels arranged periodically 150 nm below the sample surface, forming an air/GaN diffraction grating embedded within a volume of the structure is proposed and fabricated. The fabrication process includes selective area Si ion implantation, GaN regrowth using plasma‐assisted molecular beam epitaxy, ultra‐high‐pressure annealing for efficient electrical activation of implanted Si without diffusion, and electrochemical etching for the removal of selectively doped material. Embedded air/GaN diffraction gratings with periodicity of 460 and 631 nm are shown. Width of air channels ranges from 46 to 320 nm. Angle and polarization resolved reflectivity measurements combined with theoretical modeling confirm the designed optical performance of the embedded diffraction gratings in the GaN volume. The presented design and fabrication of custom‐shaped, fully integrated photonic structures buried below the surface paves the way for novel type constructions of optoelectronic devices, such as compact distributed feedback laser diodes

Evaluation of single silicon vacancy centers in nanodiamonds created by ion implantation at cryogenic temperatures

Abstract Silicon vacancy (SiV) centers in diamonds have attracted much attention because of their stability and narrow emission linewidth, and are promising for applications in quantum information technology. SiV-center-encapsulated nanodiamonds have also attracted much attention because of their potential to be coupled to various photonic devices. One efficient way to fabricate nanodiamonds that contain SiV centers is Si ion implantation into nanodiamonds. However, the evaluation of a single SiV center in a nanodiamond produced by this method at low temperatures has not been performed. In this study, we report on the optical properties of a single SiV center in a nanodiamond produced by ion implantation at cryogenic temperatures. The emission spectrum from a single SiV center ( g 2 ( 0 ) = 0.19 ) was observed with four distinct fine splittings of the zero-phonon line (ZPL) at 4 K. At an excitation power of 50 μ W, the full width at half maximum of the ZPL reached the spectrometer resolution limit (0.09 nm). The temperature dependence of the emission peak is consistent with that of the emission coming from an SiV center under high strain. The results obtained in this work suggest that nanodiamonds containing single SiV centers formed using this method will be an important building block for the realization of quantum information applications.

Synthesis of cobalt-oxide nanoparticles embedded in silicon nanotubes via low-energy cobalt implantation

Silicon nanotubes (Si NTs) show a unique structure compared to other silicon nanostructures, such as porous silicon, silicon nanoparticles, and silicon nanowires. Si NTs' well-defined structure in terms of silicon shell thickness, inner diameter, and length with a high surface area makes them useful in myriad applications. In this work, we fabricate Si NTs by using ZnO nanowires as templates; the Si NTs have a shell thickness of ∼13 nm, inner diameter of ∼80 nm, and a length in the range of 1–2 μm with embedded Co3O4 nanoparticles (NPs), which are formed by annealing the cobalt ion-implanted Si NTs. The cobalt ion implantation was carried out at 50 keV with a fluence of 7.5 × 1015 ions/cm2. The morphology and composition of the cobalt-NP decorated Si NTs are characterized by using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), and x-ray photoemission spectroscopy (XPS). TEM, HRTEM, XPS, and Raman spectroscopy studies confirm the formation of Co3O4 nanoparticles in the NTs. The temperature-dependent zero-field-cooled (ZFC), and field-cooled (FC) magnetization for the Co implanted Si NTs before and after annealing is also measured and shows little magnetic response due to the low concentration of cobalt in the nanotubes. The fabrication process is compatible with the current semiconductor industry methods and may find potential applications in magnetic drug delivery and devices.

Silicon implantation and annealing in β-Ga2O3: Role of ambient, temperature, and time

Optimizing thermal anneals of Si-implanted β-Ga2O3 is critical for low resistance contacts and selective area doping. We report the impact of annealing ambient, temperature, and time on the activation of room temperature ion-implanted Si in β-Ga2O3 at concentrations from 5 × 1018 to 1 × 1020 cm−3, demonstrating full activation (>80% activation, mobilities >70 cm2/V s) with contact resistances below 0.29 Ω mm. Homoepitaxial β-Ga2O3 films, grown by plasma-assisted molecular beam epitaxy on Fe-doped (010) substrates, were implanted at multiple energies to yield 100 nm box profiles of 5 × 1018, 5 × 1019, and 1 × 1020 cm−3. Anneals were performed in an ultra-high vacuum-compatible quartz furnace at 1 bar with well-controlled gas compositions. To maintain β-Ga2O3 stability, pO2 must be greater than 10−9 bar. Anneals up to pO2 = 1 bar achieve full activation at 5 × 1018 cm−3, while 5 × 1019 cm−3 must be annealed with pO2 ≤ 10−4 bar, and 1 × 1020 cm−3 requires pO2 < 10−6 bar. Water vapor prevents activation and must be maintained below 10−8 bar. Activation is achieved for anneal temperatures as low as 850 °C with mobility increasing with anneal temperatures up to 1050 °C, though Si diffusion has been reported above 950 °C. At 950 °C, activation is maximized between 5 and 20 min with longer times resulting in decreased carrier activation (over-annealing). This over-annealing is significant for concentrations above 5 × 1019 cm−3 and occurs rapidly at 1 × 1020 cm−3. Rutherford backscattering spectrometry (channeling) suggests that damage recovery is seeded from remnant aligned β-Ga2O3 that remains after implantation; this conclusion is also supported by scanning transmission electron microscopy showing retention of the β-phase with inclusions that resemble the γ-phase.

Enhancement of Selectivity for Chemical Mechanical Polishing by Ultra-High-Dose C and Si Ion Implantation

Enhancement of Selectivity for Chemical Mechanical Polishing by Ultra-High-Dose C and Si Ion Implantation

Low donor ionization energy in Si-implanted heteroepitaxial AlN

We obtained high n-type conductivity and low donor ionization energy for an AlN film grown on SiC by Si ion implantation. The room temperature conductivity reaches 0.26 Ω−1 cm−1, and the donor ionization energy is only 112 meV, which is the best result of Si-implanted heteroepitaxial AlN. The lattice damage caused by ion implantation can be almost completely repaired by annealing at 1330 °C for 2 h. X-ray photoelectron spectroscopy (XPS) results show few O impurity in the sample. The low donor ionization energy is attributed to avoiding the introduction of O impurities and the mitigation of self-compensating effect. These results show the great potential of Si-implanted heteroepitaxial AlN for device applications.

High conductivity β-Ga2O3 formed by hot Si ion implantation

This work demonstrates the advantage of carrying out silicon ion (Si+) implantation at high temperatures for forming controlled heavily doped regions in gallium oxide. Room temperature (RT, 25 °C) and high temperature (HT, 600 °C) Si implants were carried out into MBE grown (010) β-Ga2O3 films to form ∼350 nm deep Si-doped layers with average concentrations up to ∼1.2 × 1020 cm−3. For such high concentrations, the RT sample was too resistive for measurement, but the HT samples had 82.1% Si dopant activation efficiency with a high sheet electron concentration of 3.3 × 1015 cm−2 and an excellent mobility of 92.8 cm2/V·s at room temperature. X-ray diffraction measurements indicate that HT implantation prevents the formation of other Ga2O3 phases and results in reduced structural defects and lattice damage. These results are highly encouraging for achieving ultra-low resistance heavily doped Ga2O3 layers using ion implantation.

Depth profiling of E C – 0.26 eV electron traps introduced in homoepitaxial n-type GaN by ultra-low-dose Si-ion implantation and subsequent annealing

Si ions were implanted into homoepitaxial n-type GaN at a peak concentration of 3 × 1014 cm−3 with subsequent annealing, and the associated formation of electron traps was investigated in detail using deep-level transient spectroscopy. A major electron trap was identified as 0.26 eV below the conduction band minimum and this trap concentration increased with increasing post-implantation annealing temperature, to a value of 6–8 × 1015 cm−3. Significant increases in the net donor concentration (N D) were also observed within the implanted region. The profile of the electron trap concentration was correlated with these increases in N D, suggesting that these traps acted as donors.

Ga2O3/GaN-based solar-blind phototransistors fabricated using a thermal oxidation process performed on the GaN p-n junction layers

In this article, β-Ga2O3/GaN-based solar-blind phototransistors are fabricated using a thermal oxidation process performed on the p-GaN layer of a p-GaN/n-GaN junction to form the β-Ga2O3/p-GaN/n-GaN heterostructure. The thermal-oxidized β-Ga2O3 films exhibit a (2̅01)-orientated crystal phase and high-resistivity property. The high-resistivity β-Ga2O3 layer can be converted into an n-type β-Ga2O3 layer through Si ion implantation and a subsequent thermal annealing process. The typical electron concentration and mobility of the Si-implanted β-Ga2O3 are as high as 3.2 × 1020 cm−3 and 177 cm2v−1s−1, respectively. The n-type β-Ga2O3 and unimplanted β-Ga2O3 layers serve as the collector associating with the p-GaN and n-GaN layers, which function as the base and emitter, respectively, to construct the heterojunction phototransistors (HPTs). The HPTs exhibit a distinct cut-off wavelength at around 260 nm, indicating that the photocurrents result from the β-Ga2O3 layers rather than the p-GaN and n-GaN layers. The HPTs also show a significant bias-dependent responsivity in the deep UV (λ < 260 nm) region. This increased responsivity can be attributed to band discontinuity, resulting in the accumulation of photogenerated carriers at the β-Ga2O3/p-GaN interface. The preliminary results suggest that the β-Ga2O3/GaN-based HPTs can be achieved through the thermal oxidation of a p-GaN/n-GaN epitaxial structure.

Si-ion implantation effects on the surface hardness and microstructure of brass alloy

Innovation in materials science is important to provide society with new developments and help engineers deliver more reliable products that are also cost-effective. Brass has a vast range of its applications, while its single-phase structure (α-brass) is more flexible towards modification under ion dose. In this study, the α-brass (64%Cu; 36%Zn) was ion-implanted by 500 keV energy Si-ions, whereas four different doses were used with the main aim of reforming its structural, surface morphological and mechanical properties. SEM analysis revealed that defects were created on the implanted surface in the form of pits, pores, cavities and craters. An obvious decrease occurs in crystallite size and was found dropped from 44.351 to 24.908 nm. The intensity ratio for the plane (2 2 0) was found to be decreased after Si-ion implantation. Whereas for the planes (1 1 1), (2 0 0) and (3 1 1) fluctuating behavior was noted. Hardness of the surface was found higher after Si-ion implantation due to induced defects on the surface. Overall, the Si-ions distorted the surface, induced the strain, reduced the crystalline behavior of brass and improved the hardness.

Increase in net donor concentration due to introduction of donor-like defects by ultra-low-dose Si-ion implantation and subsequent annealing in homoepitaxial n-type GaN

Si ions were implanted at a dose of 1 × 1010 cm−2 into a homoepitaxial n-type GaN layer with a net donor concentration (N D) of 3–8 × 1015 cm−3. The N D in the implanted region increased by 1–3 × 1015 cm−3 after annealing at a temperature greater than 900 °C compared with that for the as-grown homoepitaxial layer. The increase in N D was considerably larger than the peak concentration of implanted Si ions (3 × 1014 cm−3). No increase in N D was observed for an as-grown sample after annealing. These results clearly suggest that donor-like defects were introduced by implantation of Si ions and a subsequent annealing process.

Recessed-Channel WSe2 Field-Effect Transistor via Self-Terminated Doping and Layer-by-Layer Etching.

Effective channel control with low contact resistance can be accomplished through selective ion implantation in Si and III-V semiconductor technologies; however, this approach cannot be adopted for ultrathin van der Waals materials. Herein, we demonstrate a self-aligned fabrication process based on self-terminated p-doping and layer-by-layer chemical etching to achieve low contact resistance as well as a high on/off current ratio in ultrathin tungsten diselenide (WSe2) field-effect transistors (FETs). Damage-free layer-by-layer thinning of the WSe2 channel is repeated up to a thickness of approximately 1.4 nm, while maintaining the selectively p-doped source/drain regions. The device characteristics of the recessed-channel WSe2 FET are systematically monitored during this layer-by-layer recess-channel process. The WSe2 etching rate is estimated to be 2-3 layers per cycle of oxidation and subsequent chemical etching. The self-terminated tungsten oxide (WOX) layer grown through ultraviolet-ozone treatment induces robust p-doping in the neighboring (or underlying) WSe2 through the electron withdrawal mechanism, which remains in the source/drain regions after channel oxide removal. The adopted self-terminated and self-aligned recess-channel process for ultrathin WSe2 FETs enables the realization of a high on/off output current ratio (>108) and field-effect mobility (∼190 cm2/V·s), while maintaining low contact resistance (0.9-6.1 kΩ·μm) without a postannealing process. The proposed facile and reproducible doping and atomic-layer-etching method for the fabrication of a recessed-channel FET with an ultrathin body can be helpful for high-performance two-dimensional semiconductor devices and is applicable to post-Si complementary metal-oxide semiconductor devices.

Effects of Si ion implantation on the surface and electrical characteristics of epitaxial GaSb

GaSb was grown epitaxially on semi-insulating GaAs (001) substrates using molecular beam epitaxy. The effect of varying ion energy and fluence of Si ion implantation on the structure, topology, chemical composition and electrical characteristics of GaSb epilayers is investigated. Si ion implantation was done with energies of 50, 100, and 150 keV and the fluence ranging between 1 × 1012 - 1 × 1015 ions/cm2. The effects of post-implantation annealing have also been investigated. High-resolution x-ray diffraction ω-2ϴ scans clearly revealed the damage and the recovery post-annealing.The surface morphology observed by atomic force microscopy was found to change significantly only at the highest fluence of 1 × 1015 ions/cm2. Raman spectroscopy was used to determine the implantation-induced disorder as well as the evolution of surface oxides; the latter being also corroborated with x-ray photoelectron spectroscopy. Hall measurement has been used to confirm the doping characteristics in the implanted annealed samples. The morphological variations and the mobility are understood from the displacement per atom induced by the ion beam.

Ion-beam synthesis of InSb nanocrystals at the Si/SiO2 interface

The formation of InSb nanocrystals at the bonding Si/SiO2 interface of silicon-on-insulator structure was obtained as a result of the In and Sb atom diffusion from the ion-implanted SiO2 and Si regions, respectively, toward the interface. After the annealing at 1000 °C, the Raman scattering peaks corresponding to the transverse and longitudinal optical phonon mode in the monocrystalline InSb matrix were obtained. As the annealing temperature grew to 1100 °C, the transverse optical phonon mode vanished and the longitudinal optical phonon mode dominated in the spectrum. This effect is explained by matching InSb and Si lattice constants under ion-beam synthesis conditions.

Doping profiling of beveled Si wafers via UV-micro Raman spectroscopy

Doping profiling methods are required to provide doping monitoring of heavy doped Silicon wafers, widely used in electronic devices, with high concentration sensitivity and spatial resolution. Herein, we demonstrate that ultraviolet (UV) micro-Raman spectroscopy implemented on small-angle beveled surfaces is able to produce a Raman-based doping profile without any further measurements. The reliability of the approach is verified on ion-implanted p-type B-doped single-crystalline Si (100) wafers with shallow (100 nm) doping profile, directly comparing the Raman-based doping profiling results with independent secondary ion mass spectrometry (SIMS) and spreading resistance profiling (SRP) measurements. The Raman-based technique is capable to fully reproduce the doping profile down to 100 nm with excellent doping sensitivity (10 ppm) in the 1018–1020 cm−3 doping concentration range providing high lateral (vertical) resolution of 1μm (10 nm). The technique is comparable to SIMS in terms of resolution and sensitivity down to 1018 cm−3 concentration but requires the beveling process. Instead, it is a better alternative to SRP on bevel due to its higher spatial resolution and avoiding probe contact. The Raman-based doping profiling technique is, therefore, suitable for heavy doped Si with typical shallow doping profiles of state-of-the-art Si-based nanoelectronics.

Molecular dynamics simulation of color centers in silicon carbide by helium and dual ion implantation and subsequent annealing

Atomic and close-to-atomic scale fabrication with high yield for the color centers in silicon carbide is critical in developing its applications. Combined with Wigner-Seitz method and identify diamond structure method to consider the structure around the silicon vacancy (VSi), it is found that He ion implantation is more likely to fabricate a small number of silicon vacancies with complete structure but locating deep, while Si ion implantation is more likely to introduce more silicon vacancies with incomplete structure but a large number and closer to the near surface. Therefore, a method of dual ion implantation is proposed in this paper. By adjusting the ratio of He to Si ion concentration for dual ion implantation, the fabrication yield of color centers with depth below 5 nm can be increased compared with that of He implantation after high temperature annealing. Molecular dynamics (MD) simulation is employed to discover the underlying mechanism of VSi color center and damage evolution by helium ion and dual ion implantation into four-hexagonal silicon carbide (4H–SiC) with subsequent annealing. Density-functional theory (DFT) calculation proves that magnetic-spin polarization enhances the stability of carbon anti-vacancy pair (CSiVC) defect, which indicates CSiVC defects are more stable than VSi defects. The evolution of the VSi color centers of different defect models are also calculated at various temperatures by MD, and the dynamic process of VSi defects to CSiVC defects is demonstrated. It is revealed that the decrease of the VSi color center at high temperature annealing is partly due to the transformation of some silicon vacancies to CSiVC defects.

Creation of silicon vacancy color centers with a narrow emission line in nanodiamonds by ion implantation

Nanodiamonds containing silicon-vacancy (SiV) centers with high brightness, high photo-stability, and a narrow zero phonon line (ZPL) have attracted attention for bioimaging, nanoscale thermometry, and quantum technologies. One method to create such nanodiamonds is the milling of diamond films synthesized by chemical vapor deposition (CVD). However, this requires post-processing such as acid treatment and centrifugation after the milling process. Therefore, the number of SiV center-containing nanodiamonds made from an initial CVD diamond is small. An alternative method without these problems is the implantation of Si ions into preselected nanodiamonds. This method, however, has an issue regarding the ZPL linewidths, which are more than twice as broad as those in nanodiamonds synthesized by CVD. In order to reduce the linewidth, we employed annealing treatment at high temperatures (up to 1100°C) and high vacuum after the implantation. For an ion fluence of 1013 ions/cm2, a ZPL with a linewidth of about 7 nm at room temperature was observed for a nanodiamond with a median size of 29.9 ± 16.0 nm. This was close to the linewidth for nanodiamonds created by CVD.

Silicon-ion implantation induced doping and nanoporosity in molecular beam epitaxy grown GaSb epitaxial films

This paper reports two specific aspects of Si implantation in the molecular beam epitaxy grown p-type GaSb epilayer, namely, the evolution of nanoporosity and doping characteristics. The implantation is done with 100 keV Si ions at four different fluences, i.e., 5 × 1013, 1 × 1014, 5 × 1014, and 1 × 1015 ions/cm2. A field-emission scanning electron microscope (in-plane and cross-sectional view) shows a smooth nanoporous GaSb with a pore diameter of 10–20 nm for the higher fluences. The thickness of the porous film is enhanced from 235 nm (fluence: 1 × 1014 ions/cm2) to 515 nm (fluence: 1 × 1015 ions/ cm2). Development of smooth uniform porous GaSb using Si ion implantation is discussed from the viewpoint of displacement per atom and distribution of vacancies estimated through Stopping and Range of Ions in Matter simulation tool. Hall measurement shows conversion to n-type behavior after implantation and a variation in the sheet carrier concentration from 2.22 × 1014 to 8.52 × 1014 cm−2. There is a drastic change in the mobility with the onset of void formation by implantation.

On the Formation of Silicide Films of Metals (Li, Cs, Rb, and Ba) During Ion Implantation in Si and Subsequent Thermal Annealing

On the Formation of Silicide Films of Metals (Li, Cs, Rb, and Ba) During Ion Implantation in Si and Subsequent Thermal Annealing

Formation of Si-Rich Interfaces by Radiation-Induced Diffusion and Microsegregation in CrN/ZrN Nanolayer Coating.

A combination of coating deposition and consequent ion implantation could be beneficial in wear-resistant antifriction surface design and modification. In the present paper, the effects of low-energy 60 keV Si-ion implantation on multinanolayered CrN/ZrN grown on a stainless-steel substrate have been investigated. Complementary experimental (X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, secondary ion mass spectrometry) and theoretical (first-principles) methods have been employed to investigate the structure, phase, and composition under a 1 × 10-17 cm-2 irradiation dose. This study has revealed a moderate radiation-tolerance of the CrN/ZrN system, with a 26 nm bilayer period, where the effective ion range after irradiation was below 110 nm. Within the ion range, a decrease in composition homogeneity and structure crystallinity has been found. Si negative ions have been distributed asymmetrically with peak concentrations (10 and 6%) occupying the interfaces between the CrN and ZrN layers. First-principles investigations of the CrN/ZrN(001) heterostructures were carried out to validate the experimental results, which showed that the alignment of Si-rich interfaces closer to chromium layers is a consequence of the lower substitution energy of CrN rather than ZrN. Thus, strong Si-Cr bindings and difference in displacement energies of ZrN and CrN have been attributed as the main factors in Si-rich interface formation. The pin-on-ball tribological test results have exposed the enhancement in wear resistance and the friction coefficient of nanoscale coating via amorphous Si particles descending from interfacial areas and acting as a third-body.