Germanium Implantation Research Articles

A Study of High Resistivity Semi-Insulating 4H-SiC Epilayers Formed via the Implantation of Germanium and Vanadium

A systematic germanium (Ge) and vanadium (V) study on 4H-SiC epitaxial layers is presented. Electrical results of TLM structures which were fabricated on these layers revealed that highly-doped Ge and V-implanted layers showed extremely low specific contact resistivity, down to 2 x 10-7 Ω.cm2. Current flow in the conducting state of Schottky barrier diodes has been successfully suppressed in some implanted layers, with highly V doped samples showing current density values of approximately 1 x 10-5 Acm-2 at 10 V. DLTS spectra reveal the presence of germanium and vanadium centers in the respective samples as well as novel peaks which are likely related to the formation of a novel GeN center.

Intrinsic color centers in 4H-silicon carbide formed by heavy ion implantation and annealing

We study the generation and transformation of intrinsic luminescent centers in 4H-polytype of silicon carbide via heavy ion implantation and subsequent annealing. Defects induced by the implantation of germanium (Ge) or tin (Sn) have been characterized by photoluminescence (PL) spectra recorded at cryogenic temperatures. We find three predominant but as-yet-unidentified PL signatures (labeled as DI1–3) at the wavelength of 1002.8 nm (DI1), 1004.7 nm (DI2), and 1006.1 nm (DI3) after high dose implantation (> 4 × 1013 cm−2) and high temperature annealing (> 1700°C). The fact that the DI lines co-occur and are energetically close together suggest that they originate from the same defect. Regardless of the implanted ion (Ge or Sn), a sharp increase in their PL intensity is observed when the implantation damage becomes high (vacancy concentration > 1022 cm−3), indicating that the lines stem from an intrinsic defect caused by the damage. By tracking the PL signals after stepwise annealing, we examine how the overall intrinsic defects behave in the temperature range of 500 – 1800°C; the silicon vacancies formed by the implantation transform into either divacancies or antisite-vacancy pairs with annealing at about 1000°C. These spectral signatures are strongly reduced at 1200°C where the so-called TS defects are maximized in luminescence. As a final stage, the DI defects, which are most likely formed of antisites and vacancies, emerge at 1700°C. Our results provide a knowledge on how to incorporate and manipulate the intrinsic luminescent centers in SiC with ion implantation and annealing, paving the way for fully integrated quantum technology employing SiC.

Study of the electrophysical properties of nanostructured porous germanium as a promising material for electrodes of electrochemical capacitors

Electrochemical capacitors (ECC) are a fast charging devices, with high power density, capacity and increased life time. Nanostructured semiconductors are now considered as the promising materials for electrodes of such devices due to its conductive properties and effective surface. One of such materials is the porous germanium which can be used as an electrode in electrochemical capacitors. In this article the novel approach based on the method of ion implantation was developed to grow these structures. This method allows to obtain a structures up to 1 μm thick. The object of this work was the investigation of the electrophysical characteristics of samples of nanostructured porous germanium (Ge) depending on the implantation dose and surface morphology. The scientific novelty of this research lies in the search the structures with the highest effective surface area and electronic conductivity, capable of multiplying the energy capacity and specific power of ECC. Methods: The samples of amorphous Ge were grown on dielectric single-crystal substrates of Al2O3. The thickness of samples was 600 and 1000 nm. The magnetron sputtering and ion implantation methods were used to growth these structures. The irradiation with Ge+ ions produced with an energy of 40 keV and the range of implantation doses varied from 2·1016 to 12•1016 ion / cm2. The study of electrical properties was carried out on the Hall installation HL55PC at the NPP KVANT in Moscow. The following parameters were measured: the sheet concentration of carriers in the near-surface layer, electrical resistance, mobility of the charge carriers, Hall coefficient. As a result, the dependences of carriers concentration and their mobility as the function of the implantation dose and thickness of the samples of nanostructured porous germanium were determined, and the results were analyzed. Results: It was found that ion implantation of single-crystal germanium leads to an increase in the carrier concentration in the near-surface layer. To sum up, the most suitable material as an electrode for ECC is the porous germanium with the maximum dose of ion implantation and the largest thickness. The maximum sheet carrier concentration that was obtained in the study for Ge is 1017 cm-2.

Mode, dispersion, and loss analysis of a graded-index germanium-doped silicon buried strip waveguide

The mode, loss, and dispersion characteristics of a buried strip waveguide have been calculated for coarse wavelength division multiplexing wavelengths. Process simulation has been used to form the graded-index core by germanium implantation in silicon. Quasivectorial finite-difference method has been used to calculate the number of propagating modes, effective indices, material absorption, mode confinement, and the dispersion parameters. The scattering loss has been determined from the Payne–Lacey model. The zero dispersion for higher-order modes occurs in the O-band, which is suitable for short-reach multimodal applications. The usable waveguide length and number of modes have been characterized and are limited by the mode with highest propagation loss/dispersion and lowest mode confinement, respectively.

Ion Implantation of Germanium Into Silicon for Critical Coupling Control of Racetrack Resonators

Critical coupling control is an important concept used in integrated photonics to obtain functionalities such as single and coupled resonator optical filters and wavelength multiplexers. Realization of critical coupling depends strongly on device fabrication, and reproducibility is therefore an ongoing challenge. Post-fabrication trimming offers a solution for achieving optimal performance for individual devices. Ion implantation into silicon causes crystalline lattice damage which results in an increase of the material's refractive index and therefore creates a platform for realization of various optical devices. In recent years, we have presented results on the development of erasable gratings, optical filters and Mach–Zehnder interferometers using ion implantation of germanium into silicon. Here, we report the design, fabrication and testing of silicon-on-insulator racetrack resonators, trimmed by localised annealing of germanium ion implanted silicon using continuous and pulsed wave laser sources. The results demonstrate the ability to permanently tune the critical coupling condition of racetrack resonators. Compared to the pulsed lasers used for annealing, continuous wave lasers revealed much higher extinction ratio due to improved material quality after silicon recrystallization.

On Investigations of the Optical Absorption Coefficient of Gold and Germanium Implanted Silicon with the Use of the Non-destructive Contactless Photo Thermal Infrared Radiometry

In this paper results of investigations of Au2+ and Ge+ ion-implanted silicon samples with the use of the nondestructive frequency and the space domain photo thermal infrared radiometry (PTR) method are presented. Frequency amplitude characteristics and spatial amplitude distributions of the PTR signal for the implanted silicon samples were measured and analyzed. Measurements have been performed for several wavelengths of the exciting light. The dependence of the amplitude of the PTR signal on the optical and recombination parameters of the implanted layers has been analyzed experimentally and theoretically and discussed. The objective of this work is to present the possibilities of investigations of the influence of the high energy and high dose implantation process into silicon on the optical and recombination parameters of implanted silicon with the use of the frequency and spatial domain PTR method. Observed changes in the measured signal have been explained by simultaneous changes of values of the optical absorption coefficient and carriers lifetime of implanted layers.

Ion Implantation in Silicon for Trimming the Operating Wavelength of Ring Resonators

In recent years, we have presented results on the development of erasable gratings in silicon to facilitate wafer scale testing of photonics circuits via ion implantation of germanium. Similar technology can be employed to control the operating wavelength of ring resonators, which is very sensitive to fabrication imperfections. Ion implantation into silicon causes radiation damage resulting in a refractive index increase, and can therefore, form the basis of multiple optical devices. In this paper, we discuss design, modeling, and fabrication of ring resonators and their subsequent trimming using ion implantation of germanium into silicon, followed by either rapid thermal annealing or localized laser annealing. The results confirm the ability to permanently tune the position of the resonant wavelength to any point inside the free spectral range of the ring resonator, thus, greatly reducing the amount of power required for active tuning of these devices.

Reduced Junction Leakage by Hot Phosphorus Ion Implantation of NiGe-Contacted Germanium n+/p Shallow Junction

Effects of hot phosphorus (P) implantation on the NiGe-contacted Ge n+/p junction are studied in this work. At an adequately high ion-implantation temperature (150°C), the P depth profiles of the hot-implanted samples are similar to that of the room-temperature implanted ones. Hot P implantation is demonstrated effectively in reducing ion implantation induced defect formation and suppressing nickel atoms diffusion. Therefore, hot P implantation is efficient in lowering junction leakage and excellent junction characteristics exhibiting $\sim 1\times 10^{6}~{J}_{ \mathrm{\scriptscriptstyle ON}}/{J}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio is achieved.

Reduction in number of crystal defects in a p+Si diffusion layer by germanium and boron cryogenic implantation combined with sub-melt laser spike annealing

To reduce the number of crystal defects in a p+Si diffusion layer by a low-thermal-budget annealing process, we have examined crystal recovery in the amorphous layer formed by the cryogenic implantation of germanium and boron combined with sub-melt laser spike annealing (LSA). The cryogenic implantation at −150 °C is very effective in suppressing vacancy clustering, which is advantageous for rapid crystal recovery during annealing. The crystallinity after LSA is shown to be very high and comparable to that after rapid thermal annealing (RTA) owing to the cryogenic implantation, although LSA is a low-thermal-budget annealing process that can suppress boron diffusion effectively. It is also shown that in the p+Si diffusion layer, there is high contact resistance due to the incomplete formation of a metal silicide contact, which originates from insufficient outdiffusion of surface contaminants such as fluorine. To widely utilize the marked reduction in the number of crystal defects, sufficient removal of surface contaminants will be required in the low-thermal-budget process.

Quantification of germanium-induced suppression of interstitial injection during oxidation of silicon

The oxidation of silicon is known to inject interstitials, and the presence of silicon–germanium (SiGe) alloys at the Si/SiO2 interface during oxidation is known to suppress the injection of silicon self-interstitials. This study uses a layer of implantation-induced dislocation loops to measure interstitial injection as a function of SiGe layer thickness. The loops were introduced by a 50 keV 2 × 1014 cm−2 P+ room-temperature implantation and thermal annealing. Germanium was subsequently introduced via a second implant at 3 keV Ge+ over a range of doses between 1.7 × 1014 cm−2 and 1.4 × 1015 cm−2. Results show that upon oxidizing at 850 °C for 3 h or 900 °C for 70 min to condense the germanium at the Si/SiO2 interface, where if forms a Si0.5Ge0.5 alloy. Upon subsequent oxidations of 850 °C for 6 h or 900 °C for 2 h, partial suppression of interstitial injection can be observed for sub-monolayer doses of germanium, and more than three monolayers of Si0.5Ge0.5 (1.4 × 1015 cm−2) are necessary to suppress interstitial injection below the detection limit during oxidation. These results show that low-energy implantation of germanium can be used to eliminate or modulate injection of oxidation-induced interstitials.

Elimination and Quantification of Oxidation Induced Interstitial Injection via Ge Implants

The presence of Silicon-Germanium (SiGe) alloys at the Si/SiO2 interface during oxidation is known to suppress the injection of silicon self-interstitials that normally accompanies silicon oxidation and lead to observed effects such as Oxidation Enhanced Diffusion (OED) and stacking fault growth. This study uses a layer of implantation induced dislocation loops to measure interstitial injection as a function of SiGe layer thickness. The loops were introduced by implanting phosphorus and thermal annealing, and Germanium was subsequently introduced via a second implant at 3 keV over a range of doses between 1.7 x1014 cm-2 and 1.4 x1015 cm-2. Results show that partial suppression of interstitial injection can be observed for sub-monolayer doses of germanium, and that more than three monolayers of SiGe are necessary to fully suppress interstitial injection below our detection limit during oxidation. They further show that low energy implantation of germanium opens up possibilities to eliminate or modulate injection of interstitials during thermal processing of future devices.

Elimination and Quantification of Oxidation Induced Interstitial Injection via Ge Implants

The presence of Silicon-Germanium (SiGe) alloys at the Si/SiO2 interface during an oxidation is known to suppress the injection of silicon self interstitials that normally accompanies silicon oxidation and leads to observed effects such as Oxidation Enhanced Diffusion (OED) and stacking fault growth. To measure interstitial injection, a layer of implantation induced dislocation loops was introduced and the interstitial fluxes measured via quantitative plan-view TEM. Germanium was introduced via a second implant at 3keV over a range of doses between 1.7 x1014 cm-2 and 1.4 x1015 cm-2. We show that partial suppression can be observed for sub-monolayer quantities of germanium, and that more than three monolayers of SiGe are necessary to suppress interstitial injection below the detection limit during oxidation. This study shows that low energy implantation of germanium can be used to eliminate or modulate injection of interstitials. Additional results suggest the mechanism is related to stopping interstitial formation, not migration. Figure 1

Ion-beam induced atomic mixing in isotopically controlled silicon multilayers

Implantation of germanium (Ge), gallium (Ga), and arsenic (As) into crystalline and preamorphized isotopically controlled silicon (Si) multilayer structures at temperatures between 153 K and 973 K was performed to study the mechanisms mediating ion-beam induced atomic mixing. Secondary-ion-mass-spectrometry was applied to determine concentration-depth profiles of the stable isotopes before and after ion implantation. The intermixing is analytically described by a depth-dependent displacement function. The maximum displacement is found to depend not only on temperature and microstructure but also on the doping type of the implanted ion. Molecular dynamics calculations evaluate the contribution of cascade mixing, i.e., thermal-spike mixing, to the overall observed atomic mixing. Calculated and experimental results on the temperature dependence of ion-beam mixing in the amorphous and crystalline structures provide strong evidence for ion-beam induced enhanced crystallization and enhanced self-diffusion, respectively. On the other hand, the former process is confirmed by channeling Rutherford backscattering analyses of the amorphous layer thickness remaining after implantation, the latter process is consistently attributed to the formation of highly mobile Si di-interstitials formed under irradiation and in the course of damage annealing. The observed ion-beam mixing in Si is compared to recent results on ion-beam mixing of Ge isotope multilayers that, in contrast to Si, are fully described by thermal-spike mixing only.

Boron diffusion layer formation using Ge cryogenic implantation with low-temperature microwave annealing

It is shown that a low-sheet-resistance p-type diffusion layer with a small diffusion depth can be fabricated efficiently by cryogenic boron and germanium implantation combined with low-temperature (400 °C) microwave annealing. Compared with the conventional annealing at 1000 °C, a much smaller diffusion depth is obtained at the same sheet resistance. The low sheet resistance at 400 °C is due to microwave absorption in the surface amorphous layer, which is formed by cryogenic germanium implantation. However, the pn junction leakage was worse than that in conventional annealing, because crystal defects remain near the amorphous/crystal interface after microwave annealing. It is found that the pn junction leakage is improved greatly by cryogenic germanium implantation. These results show that a suitable combination of cryogenic implantation and microwave annealing is very promising for p-type diffusion layer technology.

Locally Erasable Couplers for Optical Device Testing in Silicon on Insulator

Wafer scale testing is critical to reducing production costs and increasing production yield. Here we report a method that allows testing of individual optical components within a complex optical integrated circuit. The method is based on diffractive grating couplers, fabricated using lattice damage induced by ion implantation of germanium. These gratings can be erased via localised laser annealing, which is shown to reduce the outcoupling efficiency by over 20 dB after the device testing is completed. Laser annealing was achieved by employing a CW laser, operating at visible wavelengths thus reducing equipment costs and allowing annealing through thick oxide claddings. The process used also retains CMOS compatibility.

Multiple implantation and multiple annealing of phosphorus doped germanium to achieve n-type activation near the theoretical limit

Full activation of n-type dopant in germanium (Ge) reaching to its solid solubility has never been achieved by using ion implantation doping technique. This is because implantation of dopants always leaves defects such as vacancy and interstitials in the Ge crystal. While implantation-induced defects are electrically neutral for the most of semiconductor materials, they are electrically positive for Ge resulting in compensation of n-type dopants. In this Letter, we verified that 5 × 1019 P/cm3 is the maximum active concentration, which can be fully activated in germanium “without leaving implantation damage” per implantation/annealing cycle. The repetition of implantation and annealing of phosphorous (P) with the concentration of 5 × 1019 cm−3 leads to the activation of 1 × 1020 P/cm3 close to its solid solubility limit of 2 × 1020 P/cm3.

Analysis of the effect of germanium preamorphization on interface defects and leakage current for high-k metal-oxide-semiconductor field-effect transistor

In this article, the authors analyze the impact of germanium amorphization on the interface defect concentration of state of the art high-k metal gate metal-oxide-semiconductor field-effect transistors. The gate etch is a crucial process step for the high-k gate first integration approach. Germanium implantation is used to amorphize the annealed and, therefore, nanocrystalline hafnium silicon oxide. This ensures a well controlled wet etch removal. The quality of the gate oxide to the channel interface of the transistor samples is monitored by charge pumping. The influence of the damage caused by the germanium implant at the unprotected gate edge is analyzed for different gate stacks by measuring the gate induced drain leakage. The defect concentration at the gate edge can be reduced by adjusting the germanium amorphization energy.

Properties of Phase Change Materials Modified by Ion Implantation

ABSTRACTIon implantation of germanium and carbon ions into thin films of Ge2Sb2Te5 (GST) and GeTe was applied to modify the properties of these phase change materials. It was found that it is possible to amorphize crystalline GST and GeTe using ion implantation for optimized ion doses and energies which depend on the film thickness, ion species and capping layer. A relatively low minimum dose is required for complete amorphization as judged by the absence of diffraction peaks in x-ray diffraction (XRD) scans. It is 4–5×1013 cm−2 for germanium implantation into GST, and slightly higher (1014 cm−2) for germanium implantation into GeTe. The properties of the re-amorphized films depend on ion species, dose and energy. The re-crystallization temperature of re-amorphized GST by ion implantation is comparable or higher than as-deposited amorphous GST. Carbon implantation in particular leads to a large increase in the crystallization temperature Tx. A carbon dose of 1016 cm−2 implanted into 20 nm amorphous GST yielded a crystallization temperature of 300 ºC, much higher than the crystallization temperature of 160 ºC we recorded for as-deposited, amorphous GST. Similarly, high dose carbon implantation into amorphous GeTe leads to large increase in Tx. We recorded a shift in Tx from 195 ºC for as-deposited GeTe to 400 ºC for C-implanted GeTe. Crystalline GeTe re-amorphized by a low dose germanium ion implantation exhibits a re-crystallization temperature below Tx of as-deposited amorphous GeTe and Tx increased with the implanted Ge dose to a crystallization temperature above that of unimplanted GeTe. Ion implantation can be regarded an additional tool to create phase change materials with different and improved switching properties that cannot be achieved by conventional sputter deposition.

Hydrogen Implantation in Germanium

Hydrogen implantation of germanium is a promising technique for layer transfer. However, both the implantation process, and subsequent heat treatment can create defects in the transferred layer, which detrimentally effect the performance of devices fabricated on these transferred layers. In this study, implanted Germanium wafers were given various anneals and analysed optically and by spreading resistance, to gain insight on the nature of such defects. GeOI layers were produced by thermal splitting of implanted germanium wafers bonded to sapphire handle substrates.

Modeling of the long-range interstitial migration of ion implanted boron

Abstract A model for interstitial migration of ion implanted boron during rapid thermal annealing of the silicon layers amorphized by implantation of germanium has been developed. It is supposed that boron interstitials are generated continuously during the whole annealing due to dissolution or rearrangement of the clusters of dopant atoms which are formed in the ion implanted layer with impurity concentration above the solubility limit at the initial stage of the treatment. The local elastic stresses arising due to a small atomic radius of boron also contribute to the generation of boron interstitials. A simulation of boron redistribution during thermal annealing for 60 s at a temperature of 850 °C has been carried out. The calculated profile agrees well with the experimental data thus confirming adequacy of the model proposed. A number of the parameters of interstitial boron diffusion have been derived. In particular, the average migration length of nonequilibrium boron interstitials is equal to 12 nm. It was also obtained that approximately 1.8–2% of the boron atoms became interstitial, participated in the fast interstitial migration, and then became immobile again occupying substitutional lattice sites or forming complexes with the crystal lattice defects.