Dopant Distribution Profile Research Articles

Comparison of arsenic and antimony dopant distribution profiles of very high energy implantations

Comparison of arsenic and antimony dopant distribution profiles of very high energy implantations

Impact of ion implantation and laser processing parameters on carrier lifetimes in gold-hyperdoped silicon

In recent years, infrared photodetectors using silicon hyperdoped with deep-level dopants started to demonstrate extended light detection beyond the silicon’s absorption edge. The reported responsivities or external quantum efficiencies, however, are typically low. Focusing on gold-hyperdoped silicon and using time-resolved terahertz spectroscopy, a non-contact photoconductivity measurement, we investigated how hyperdoping parameters affect charge carrier lifetimes. Correlating the observed lifetime characteristics with dopant distribution profiles, we identify factors that impact carrier lifetime most significantly. Specifically, the charge carrier lifetime reduces with increasing gold concentrations, increasing ion implantation energies, and increasing pulsed-laser melting fluences. Both ion implantation energy and laser fluence affect the dopant incorporation depths. The total gold dose implanted and laser fluence affect the carrier distribution profile, particularly the concentration spike toward the surface. Oxide passivation and the number of laser pulses do not impact the carrier lifetime significantly. Our findings benefit future device developments.

Analysis of dopant distribution profiles of very high energy implants

Analysis of dopant distribution profiles of very high energy implants

Carrier lifetimes in gold–hyperdoped silicon—Influence of dopant incorporation methods and concentration profiles

Incorporating ultrahigh concentrations of deep-level dopants in silicon drastically alters silicon’s optoelectronic properties. Photodiodes built from silicon hyperdoped with gold extend light sensitivity into the shortwave infrared region, far beyond the absorption edge of a pristine silicon sample. Deep-level dopants, however, also enhance carrier recombination; even though hyperdoped silicon has great light absorption properties, short charge carrier lifetime limits its applications. In this work, using terahertz spectroscopy, we investigate the charge carrier lifetime of gold–hyperdoped silicon, where the gold dopants are introduced by either film deposition or ion implantation, followed by pulsed laser melting. Using reactive ion etching, we measure how carrier lifetime changes when dopant concentration profiles are altered. Furthermore, using a 1D diffusion and recombination model, we simulate carrier dynamics when electrons are excited by sub-bandgap light. Our results show that the dopant distribution profile heavily influences excited carrier dynamics. We found that etching improves the half-life by a factor of two. In the short-wave-infrared range, the gold dopants are both light absorption centers and recombination centers. Focusing on optoelectronic properties in the short-wave-infrared region, our results suggest that these samples are over doped—etching much of the gold dopants away has little impact on the number of excited electrons at a later time. Our results suggest that dopant profile engineering is important for building efficient optoelectronic devices using hyperdoped semiconductors.

Dopant Activation Depth Profiling for Highly Doped Si:P By Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM)

Heavily n-doped epitaxially grown Si layers are of great importance for source/drain (S/D) application in advanced node nMOS devices. For contact resistivity reduction, the dopant activation level is very important. Various techniques are being used to evaluate dopant activation in Si:P layers. Among these two methods are Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM). SSRM uses an atomic force microscope equipped with a hard conductive probe that is scanned in contact mode on the cross-sectioned sample’s surface and measures spreading resistance. Measured resistance values as a function of depth are converted into resistivity and carrier concentration depth profiles using calibration measurements and conversion relationships. DHEM provides depth profiles of mobility, resistivity and carrier concentration through a semiconductor layer by making successive sheet resistance (Rs) and Hall voltage measurements using Hall effect/Van der Pauw techniques, as the electrically active thickness of the layer is reduced through successive oxidation steps. Controlled oxidation is achieved by electrochemical anodization. Data collected can then be processed to yield the depth profiles. In this contribution we have carried out SSRM and DHEM measurements on Si:P epi layers subjected to different processing conditions including annealing and ohmic contact fabrication. Secondary Ion Mass Spectrometry (SIMS) was used to measure the total (active + inactive) dopant profiles through the films. Effects of these processes on dopant diffusion and activation were studied and the results from DHEM and SSRM were compared.In-situ phosphorus (P) doped Si epi-layers were grown over 300mm diameter boron doped monitor wafers. While one set was kept as the reference, a second set was treated by a spike-annealing process at 1000 °C. In a third set a Ti/TiN contact fabrication process was carried out and the contact was removed before analysis. In the fourth set contact process was applied to the spike annealed wafer before removal of the Ti/TiN layers. Bulk sheet resistance measurements were made using 4-point probe (4PP) for all the samples. SSRM measurements were carried out at IMEC. Cross-shaped Van der Pauw test-patterns were formed on 8mmx8mm areas on the samples and DHEM measurements were performed at ALP. Figure below shows the dopant depth profiles obtained by SIMS and the carrier concentration profiles from DHEM and SSRM techniques for samples D02 (as deposited Si:P) and D03 (spike annealed). One can make some general observations from the data in this figure. The total dopant concentration as measured by SIMS is ~ 1.4E21/cm3. There is only a small difference in the total dopant distribution profiles (SIMS) between the as deposited sample and the spike annealed sample. However, the spike annealed sample shows much higher dopant activation as measured by DHEM. Carrier concentration is ~2.5x higher in sample D03 (~5E20/cm3) compared to sample D02 (~2E20/cm3). Activation levels measured by SSRM, however, are lower for both samples, and the peak carrier concentration value increases only slightly upon spike annealing, going from ~2E20/cm3 in sample D02 to ~2.2E20/cm3 in sample D03. DHEM clearly indicates the sharp interface between the p-type substrate and the n-type epi-layer and its depth calibration agrees well with the expected thicknesses of the epi layers. The tail of the SSRM data is much more graded. Data from other samples will be presented and discussed in the final manuscript. Figure 1

Постоперационный контроль технологических параметров процесса ионной имплантации методом вольт-фарадных характеристик

Studies of structures, including a hole-conducting epitaxial layer, doped with boron (KDB – 12), and an electron-conducting layer, doped with phosphorus (KEF – 4,5), are presented. A dielectric layer of silicon dioxide SiO2, from 97 nm to 117 nm thick, as measured using ellipsometry, was grown on the wafers. Then, the subsurface layer was doped with phosphorus or boron using ion implantation, with conductivity type corresponding to the substrate. The postoperative control of dopant atoms dose, embedded by ion implantation, was carried out using the capacitance-voltage characteristics. Dopant distribution profiles for the same sample, as well as for different samples with the same implanted dopant dose differed insignificantly. The relative error of the measurements, as compared to the preassigned dose, was no higher than 10 %. The dose parameter deviation higher than 5 % was observed in samples with the preassigned ion dose close to the maximum detectable dose of implanted ions, allowed for this method.

Implanted Layer Characterization

<p>In modern semiconductor process technology, ion implantation has become the most important technique to introduce dopant atoms into semiconductor materials. The main advantage of ion implantation technique is its high controllability of process parameters, which influencing dopant distribution profile. This research was intended to characterize the product of ion implantation machine NV-3204.</p><p>Ion implantation characterization successfully produced and evaluated pn-junction diode characteristics. PN-junction diode was fabricated using 100 keV energy and 5x1013 cm-3 dose of phosphorus on a silicon wafer type N<111>. For all measured area, pnjunction diode has junction depth Xj = 1 um, breakdown voltage -45V, built-in voltage 0.8V, and dopant concentration 5x1018 cm-3. Comparing the simulation, this result exhibited that output of ion implantation machine was well controlled.</p>

Contributed Review: A review of the investigation of rare-earth dopant profiles in optical fibers.

Rare-earth doped optical fibers have captivated the interest of many researchers around the world across the past three decades. The growth of this research field has been stimulated primarily through their application in optical communications as fiber lasers and amplifiers, although rare-earth doped optical fiber based devices are now finding important uses in many other scientific and industrial areas (for example, medicine, sensing, the military, and material processing). Such wide commercial interest has provided a strong incentive for innovative fiber designs, alternative glass compositions, and novel fabrication processes. A prerequisite for the ongoing progress of this research field is developing the capacity to provide high resolution information about the rare-earth dopant distribution profiles within the optical fibers. This paper constitutes a comprehensive review of the imaging techniques that have been utilized in the analysis of the distribution of the rare-earth ion erbium within the core of optical fibers.

Dopant in Near-Surface Semiconductor Layers of Metal–Insulator–Semiconductor Structures Based on Graded-Gap p-Hg0.78Cd0.22Te Grown by Molecular-Beam Epitaxy

Peculiarities in determining the dopant concentration and dopant distribution profile in the near-surface layer of a semiconductor are investigated by measuring the admittance of metal–insulator–semiconductor structures (MIS structures) based on p-Hg0.78Cd0.22Te grown by molecular beam epitaxy. The dopant concentrations in the near-surface layer of the semiconductor are determined by measuring the admittance of MIS structures in the frequency range of 50 kHz to 1 MHz. It is shown that in this frequency range, the capacitance–voltage characteristics of MIS structures based on p-Hg0.78Cd0.22Te with a near-surface graded gap layer demonstrate a high-frequency behavior with respect to the recharge time of surface states located near the Fermi level for an intrinsic semiconductor. The formation time of the inversion layer is decreased by less than two times, if a near-surface graded-gap layer is created. The dopant distribution profile in the near-surface layer of the semiconductor is found, and it is shown that for structures based on p-Hg0.78Cd0.22Te with a near-surface graded-gap layer, the dopant concentration has a minimum near the interface with the insulator. For MIS structure based on n-Hg0.78Cd0.22Te, the dopant concentration is more uniformly distributed in the near-surface layer of the semiconductor.

Rigorous Analysis on Ring-Doped-Core Fibers for Generating Cylindrical Vector Beams

We propose a novel active fiber design for selectively generating cylindrical vector beams (CVBs) or cylindrical vector modes (CVMs) which can be applied to conventional fiber lasers. A fiber is designed to have a ring-shaped core refractive index profile which can lead to the best overlap between the active dopant distribution profile and the lowest-order CVM (LCVM) field profile. Therefore, the overlap factor (OVF) of the LCVM becomes even higher than that of the fundamental mode. We emphasize that this condition cannot be satisfied by a conventional step-index core fiber (SICF) but by the ring-doped core fiber (RDCF). Because the lasing threshold is inversely proportional to the OVF, the LCVM can predominantly be stimulated even without going through special procedures to impose extra loss mechanisms to the fundamental mode. We numerically verify that the OVF of the LCVM with the doped ions can significantly exceed that of the fundamental mode if the proposed fiber design is applied. In addition, an RDCF of the proposed fiber design can also operate in a regime containing no higher-order modes besides the LCVM, so that it can selectively and efficiently generate the LCVM without being disrupted by the parasitic lasing of the higher-order modes. We highlight that an optimized RDCF can lead to a >30 % higher OVF ratio than a SICF having the same doped area. The proposed model is expected to be useful for enhancing the efficiency of generating CVBs in an all-fiber format.

Dopant segregation in rare earth doped lutetium aluminum garnet single crystals grown by the micro-pulling down method

Nd, Ho, Er, and Tm doped lutetium aluminum garnet (LuAG) single crystals were grown using the micro-pulling down (μ-PD) method. The crystals were produced from the melts containing 3 mol% of the dopants. The axial and radial dopant distribution were measured by electron probe micro analysis. Nd3+ and Ho3+ ions concentrated in the rim (k0<1) and the radial concentration showed concave curvature. k0 is the segregation coefficient of the dopant with respect to the given host phase. In the case of Er3+ and Tm3+ ions, the k0 value is considered to be nearly 1 and the radial dopant distribution profiles were almost flat.

The radial distribution of dopant (Cr, Nd, Yb, or Ce) in yttrium aluminum garnet (Y 3Al 5O 12) single crystals grown by the micro-pulling-down method

Dopant distribution in yttrium aluminum garnet (YAG:Y3Al5O12) shaped crystal grown via the micro-pulling-down method depends primarily on the distribution coefficient (k0). The solid-favoring dopants (k0>1.0), Cr and Yb, concentrated in the central core of the crystal, while the liquid-favoring dopants (k0<1.0), Nd and Ce, concentrated in the rim. Secondary rare-earth oxide phases were sometimes segregated and crystallized circumferentially with Nd and Ce dopant. The dopant distribution profile was also controlled by the position of the melt entrance hole in the crucible shaper, which was confirmed by SIMPLER calculation. Segregation/distribution coefficients for Cr, Yb, Nd, and Ce in YAG were found to be 1.5, 1.01, 0.1, and 0.01, respectively.

Anomalous effects of dopant distribution in Ge single crystals grown by FZ-technique aboard spacecrafts

The gallium distribution in nine germanium single crystals, all grown with similar heat conditions using the floating zone (FZ) method aboard five unmanned “Photon” spacecrafts (SC), from melts doped from 1×1018 to 1×1020 at/cm3 are studied. For the first time, the strong anomalous concentration dependence of the distribution coefficient (from 0.16 to 0.089, respectively), having no “earth” analogue, was revealed experimentally as a result of comparative studies of space-grown and reference crystals. It also was shown, that the revealed dependence can completely define the longitudinal dopant distribution profile in a single crystal. The hypothesis of the nature of the observed effect was proposed, which consists of an intensification of the mixing processes in the heavily doped molten zone, restricted by free surface, caused by an increase of the surface-active impurity content in reduced gravity.

Strong surface segregation of Sb atoms at low temperatures during Si molecular beam epitaxy

Surface segregation of Sb atoms at low temperatures below 400°C during Si molecular beam epitaxy (MBE) growth is studied by ex situ X-ray reflectivity measurements and secondary ion mass spectroscopy (SIMS). One monolayer of Sb atoms was first deposited at the temperature of 300°C, followed by a 23-nm thick Si overlayer grown at different temperatures of 250, 300, 350, and 400°C. The decay lengths of dopant Sb distribution profiles are obtained to be 0.45, 0.95, 3.5, and >20 nm by simulations of their X-ray reflectivity curves, respectively. A strong surface segregation of Sb atoms is observed at temperatures of 350 and 400°C, which is also confirmed by the SIMS profiles. Surface structure change caused by a high coverage of Sb is suggested to explain such a strong segregation.

Control of dopant distribution profiles in GaInP laser diodes with Mg- and Se-doped AlInP cladding layers

Abstract High doping levels on either side of a double heterostructure laser are required for optimal performance and temperature stability, especially in the AlGaInP material system. However, in most cases these are accompanied by strong diffusion during growth, shifting the p–n junction and damaging the active zone. We investigated the possibiltity of suppressing the diffusion towards the active zone by introducing thin intermediate layers of different materials and doping levels as well as short-period superlattices. Using SIMS measurements we found that the non indium-containing layers GaP and GaAs are suitable to slow down diffusion of the magnesium on the p-side and produce a rather steep dopant front. On the other hand, the presence of the additional interfaces seems to have a negative influence on the electrical properties of the device, resulting in increased threshold currents and reduced quantum efficiencies. To determine the decisive factors for this behavior, additional optical measurements were done on the samples. In another approach we investigated n-doped AlInP intermediate layers and their influence on the magnesium profile.

Characterization of hafnium oxide films modified by Pt doping

Abstract The Hf/HfO2-Pt electrodes were prepared through galvanostatic platinum deposition from H2PtCl6 solutions followed by potentiodynamic HfO2 growth in 0.5 M H2SO4 solutions. Electron transfer reactions involving a redox couple and impedance investigations were performed in order to obtain information about the electronic conductivity, dielectric properties and thickness of the oxide film as well as the kinetics of the processes taking place on it. X-ray photoelectron spectroscopy (XPS) was used to characterize the composition and dopant distribution profile within the modified film and to correlate the electrochemical behaviour with the structure and composition of the films. A transition from n-type semiconductor to an insulator behaviour was observed at lower Pt content with increase of the final formation potential which is in agreement with platinum distribution through the oxide. At higher Pt content, on the other hand, the oxygen evolution reaction prevails over oxide growth reaction, These results are discussed in terms of a physical model for the system.

Depth profiling of dopants in thin gate oxides in complementary metal– oxide–semiconductor structures by resonance ionization mass spectrometry

The thickness of gate dielectrics for complementary metal–oxide–semiconductor (CMOS) devices with 0.1 to 0.35 μm gate dimensions is typically 4 to 7 nm. Besides serving as an insulator, the dielectric, usually SiO2, also acts as a diffusion barrier between the doped polycrystalline silicon gate material and the Si substrate (channel). Dopant diffusion from the poly‐gate into the device channel may cause undesirable shifts in the transistor threshold voltage. The determination of dopant diffusion through the gate dielectric into the channel region of the transistor is necessary to optimized device processing. This paper reports a method, resonance ionization mass spectrometry (RIMS), to measure dopant distribution profiles near the gate oxide. The pertinent spectroscopy of sputtered B and P atoms is demonstrated. Matrix effects are shown to be diminished. RIMS depth profiles of CMOS test structures show both dopant penetration into the channel and blockage by the gate oxide depending upon annealing conditions.

Gain saturation in three- and four-level fiber amplifiers

Abstract The results of a theoretical study of three- and four-level amplifiers using Er 3+ and Nd 3+ -doped silica fibers are discussed. The analytical expression for the gain factor in case of gain saturation and arbitrary dopant distribution across the fiber waveguide are given. It is shown that in a three-level amplifier (Er 3+ ) constancy of the gain factor with increasing signal power is provided by the accompanying increase in the pump power absorption. In a four-level amplifier (Nd 3+ ) the flatness of the amplitude characteristic of gain can be achieved by a proper choice of the dopant distribution profile, for instance, in the shape of a ring.

Solid‐State film diffusion for the production of integrated optical waveguides

AbstractSolid‐state film ion exchange (Ag+‐Na+) in glass substrates has been investigated for the fabrication of passive, integrated, optical waveguides. A new ion exchange mechanism is proposed which couples the oxidation of silver metal to silver oxide and the diffusion of silver ions into the glass substrate. At high electric fields and/or high temperatures, the growth rate of a silver oxide film limits the formation of mobile silver ions and constrains the diffusion of silver into the glass. This new mechanism is able to predict the dopant distribution profile under those conditions and under conditions where a constant surface concentration is appropriate (infinitely thick oxide film). It also explains the characteristics of the current vs. time curve measured during the ion exchange process. The formation and growth of the silver oxide film were confirmed by X‐ray photoelectron spectroscopy and X‐ray diffraction analysis.

Dopant distribution profile to improve performance of superlattice tunnel diode

We show how it is possible by careful choice of the dopant profile to improve the performance of a superlattice tunnel diode to give negative differential conductance with good current and voltage swings and a low capacitance.