Heavily-doped Semiconductor Research Articles

Probing the photocurrent in two-dimensional titanium disulfide

Generating photocurrent in a condensed matter system involves the excitation, relaxation, and transportation of charge carriers. As such, it is viewed a potent method for probing the dynamics of non-equilibrium carriers and the electronic band structure of solid state materials. In this research, we analyze the photoresponse of the mechanically exfoliated titanium disulfide (TiS2), a transition metal dichalcogenide whose classification as either a semimetal or a semiconductor has been the subject of debate for years. The scanning photocurrent microscopy and the temperature-dependent photoresponse characterization expose the appearance of a photovoltaic current primarily from the metal/TiS2 junction in an unbiased sample, while negative photoconductivity due to the bolometric effect is observed in the conductive TiS2 channel. The optoelectronic experimental results, combined with electrical transport characterization and angle-resolved photoemission spectroscopy measurements, indicate that the TiS2 employed in this study is likely a heavily-doped semiconductor. Our findings unveil the photocurrent generation mechanism of two dimensional TiS2, highlighting its prospective optoelectronic applications in the future.

The crucial role of defect structure in understanding the electrical properties of spark plasma sintered antimony doped barium stannate

The influence of structural defects in spark plasma sintered BaSn1-xSbxO3 (BSSO, x = 0.00 and 0.08) ceramic samples on their electrical properties was investigated in the temperature range of 300–4 K. X-ray photoelectron spectroscopy (XPS) revealed the presence of point defects, primarily oxygen vacancies (VO) and mixed oxidation states of tin (Sn2+/Sn4+) in both samples. As a result, the undoped BSSO sample exibited a non-standard semiconductor behavior, retaining its temperature-dependent resistivity. The electrical resistivity of the doped samples was two orders of magnitude lower than that of the undoped sample. The presence of structural defects such as VO, mixed oxidation states of the constituent elements, and significant amounts of O− species make the electrical resistivity of the doped sample constant in the temperature range of 300–70 K, indicating heavily-doped semiconductor behavior.

Fabrication of Cu-doped molybdenum oxide for bifunctional SERS and photothermal conversion

Heavily-doped semiconductor materials have attracted great attentions owing to their tunable localized surface plasmon resonance (LSPR) in the visible or near-infrared (NIR) range, which is expected to own excellent performance comparable to that of precious metals. However, the current strategies of doping MoO3 are usually tedious and not environmental-friendly, and the synergistic effects of oxygen vacancies and metal ion doping on the LSPR are rarely investigated. Herein, we report a facile supercritical CO2-assisted method to synthesize Cu-doped MoO3 nanoparticles (Cu–MoO3-x NPs) with tunable LSPR properties, and the morphology, doped Cu ion concentration and oxygen vacancies density can be modulated as the control of supercritical CO2 pressure from 10 to 16 MPa. Moreover, the Cu–MoO3-x NPs possess outstanding surface enhanced Raman spectroscopy (SERS) performance (with the enhancement factor of 3.48 × 107 and the limit of detection of 10−9 M) and relatively high photothermal conversion efficiency (62.4%). This work provides an efficient route for the fabrication of heavily-doped metal oxide semiconductors with superior LSPR performance in various light utilization fields.

Single Gyrotropic Particle as a Heat Engine

We demonstrate that the system composed of a gyrotropic particle out of thermal equilibrium with vacuum can be regarded as a heat engine. Such a particle, initially at rest, will experience a fluctuation-induced torque and start to rotate, producing mechanical work out from the temperature difference of the particle and its environment. We rigorously prove that the efficiency of the heat engine is tightly bound by the Carnot efficiency. We also predict that, such an engine can be constructed using a heavily-doped semiconductor nanoparticle under magnetic field, and moreover the particle can reach at a steady-state rotating frequency in the order of terahertz solely due to thermal fluctuations.

Dopant Redistribution and Activation in Ga Ion-Implanted High Ge Content SiGe by Explosive Crystallization during UV Nanosecond Pulsed Laser Annealing

Explosive crystallization (EC) is often observed when using nanosecond-pulsed melt laser annealing (MLA) in amorphous silicon (Si) and germanium (Ge). The solidification velocity in EC is so fast that a diffusion-less crystallization can be expected. In the contacts of advanced transistors, the active level at the metal/semiconductor Schottky interface must be very high to achieve a sub-10−9 ohm·cm2 contact resistivity, which has been already demonstrated by using the dopant surface segregation induced by MLA. However, the beneficial layer of a few nanometers at the surface may be easily consumed during subsequent contact cleaning and metallization. EC helps to address such kind of process integration issues, enabling the optimal positioning of the peak of the dopant chemical profile. However, there is a lack of experimental studies of EC in heavily-doped semiconductor materials. Furthermore, to the best of our knowledge, dopant activation by EC has never been experimentally reported. In this paper, we present dopant redistribution and activation by an EC process induced by UV nanosecond-pulsed MLA in heavily gallium (Ga) ion-implanted high Ge content SiGe. Based on the obtained results, we also highlight potential issues of integrating EC into real device fabrication processes and discuss how to manage them.

Interpretation of the 1/C2 Curvature and Discontinuity in Electrochemical Capacitance Voltage Profiling of Heavily Ga Implanted SiGe Followed by Melt Laser Annealing

Electrochemical Capacitance Voltage Profiling (ECVP) is one of the most widely used characterization methods in semiconductor industry to measure the activation of dopants in doped semiconductor materials owing to its low-cost and easy-to-use features. Today, there are some specific industrial needs, for instance reduction of the contact resistance in advanced transistors, for which heavily-doped semiconductor materials must be implemented. A clear challenge addressed to ECVP here is that the interpretation of measured data becomes much more complex in such materials because of the appearance of curvatures and discontinuity on the curve given by the inverse of the square of the capacitance within the space charge zone as a function of the applied polarisation voltage. In this paper, we present a case of silicon-germanium doped by heavy gallium ion-implantation and annealed by melt laser annealing, where a metastable dopant activation can be expected. We develop a fitting model with different deep levels, highlighting their possibly different time constants to provide a more reliable interpretation on the measurements.

New accurate approximation of the Einstein Relation for heavily-doped semiconductor devices

The modern electronic devices have been scaled down significantly. The scaling rules would dictate higher doping concentrations which lead us to consider the degeneracy in the calculations. One of the semiconductor device quantities that would be impacted by considering the degeneracy is the Einstein Relation. The commonly used formula of Einstein Relation assumes that it is constant and independent of doping. The doping-independent Einstein Relation would cause serious inaccuracy in the calculations. This paper offers a closed-form solution fordoping-dependent Einstein Relation. The proposed expression employs approximations of Fermi-Dirac Integrals (FDI) needed in the Einstein Relation. The quality and accuracy of the proposed approximations have been determined.

Anomalous plasmon resonance from confined diffusive charges: high quality and tunability from mid to far infrared wavebands.

For heavily-doped semiconductor nanocrystals, a new class of plasmonic materials, the abundant dopants provide sufficient free carriers, but also act as scattering impurities, which have been limiting the merit of localized surface plasmon resonance (LSPR). To resolve this intrinsic contradiction, we propose a core-shell (heavily-lightly doped) semiconductor nanosystem to generate plasmon resonance from the highly mobile diffusive charges rather than the strongly scattered charges. We develop a complete theory to describe the spatial distribution of the diffusive charges as well as their resonance under the light excitation and predict a LSPR tunable from mid to far infrared band with a 15-fold field enhancement near the resonance. Meanwhile, the physical nature of such LSPR, which is different from the bonding and antibonding plasmon mode in typical core-shell structures, was revealed by studying the polarization charge distribution. Hopefully, these results can help realize high quality plasmonic structures for applications in infrared waveband.

Mid-Infrared Sensing Using Heavily Doped Germanium Plasmonics on Silicon Substrates

Heavily-doped semiconductor films are very promising for applications in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work, we investigate, n-type doped Ge epilayers grown on Si substrates. We design and realize Ge nano-antennas on Si substrates demonstrating the presence of localized plasmon resonances, and exploit them for molecular sensing in the mid-infrared.

Tunability of the dielectric function of heavily doped germanium thin films for mid-infrared plasmonics

Heavily-doped semiconductor films are very promising for application in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work we investigate heavily n-type doped germanium epilayers grown on different substrates, in-situ doped in the $10^{17}$ to $10^{19}$ cm$^{-3}$ range, by infrared spectroscopy, first principle calculations, pump-probe spectroscopy and dc transport measurements to determine the relation between plasma edge and carrier density and to quantify mid-infrared plasmon losses. We demonstrate that the unscreened plasma frequency can be tuned in the 400 - 4800 cm$^{-1}$ range and that the average electron scattering rate, dominated by scattering with optical phonons and charged impurities, increases almost linearly with frequency. We also found weak dependence of losses and tunability on the crystal defect density, on the inactivated dopant density and on the temperature down to 10 K. In films where the plasma was optically activated by pumping in the near-infrared, we found weak but significant dependence of relaxation times on the static doping level of the film. Our results suggest that plasmon decay times in the several-picosecond range can be obtained in n-type germanium thin films grown on silicon substrates hence allowing for underdamped mid-infrared plasma oscillations at room temperature.

Theoretical investigation of the heavily-doped semiconductor aspect of ultra-dilute GaAsN

The model of GaAs1−y N y (y = 0.001) as a heavily-doped semiconductor in the ultra-dilute region is attentively examined. The model enables GaAsN to be viewed as a disordered assembly of three-dimensional quantum dots (potential wells) caused by random potential fluctuations from nitrogen pairs in the system. Consequently, Feynman’s path-integration technique is applied in order to quantify the density of states (DOS) in the vicinity of the conduction band edge. The obtained DOS tail, even though overestimated, still clearly shows a much shorter tail than that the experimental result does. This shows that the heavily-doped semiconductor viewpoint is not proper for GaAsN, not even in the ultra-dilute region. Furthermore, this also suggests that the impurity wave function overlap is not a basic mechanism of band gap reduction.

Thermoelectric Properties of p-Type La1−z Pr z Fe4−x Co x Sb12 Skutterudites

p-Type La1−zPrzFe4−xCoxSb12 skutterudites were prepared by encapsulated melting, quenching, annealing, and hot pressing. The skutterudite phase was successfully synthesized but small amounts of FeSb2 and (La,Pr)Sb2 secondary phases were also observed, especially for the Co-substituted specimens. Carrier concentration decreased with increasing Pr and Co content. Electrical conductivity decreased with increasing temperature, showing that all specimens were heavily-doped semiconductors. Electrical conductivity also decreased with increasing Pr and Co content. The Hall and the Seebeck coefficients revealed that all specimens had p-type characteristics. Seebeck coefficients increased with increasing temperature, with maximum values occurring between 723 and 823 K. The maximum power factor (PF) was 3.1 m Wm−1 K−2, at 823 K and 723 K for La0.75Pr0.25Fe4Sb12 and La0.75Pr0.25 Fe3.75Co0.25Sb12, respectively. Thermal conductivity decreased with increasing Pr and Co content, and increased because of bipolar conduction at temperatures above 723 K. For a fixed Co content, lattice thermal conductivity decreased with increasing Pr content; this may be attributed to a larger contribution from Pr than from La to the decrease in lattice thermal conductivity. The dimensionless figure of merit (ZT) had maximum values of 0.83 at 823 K for La0.75Pr0.25Fe4Sb12 and 0.81 at 723 K for La0.75Pr0.25Fe3.75Co0.25Sb12.

Computational and experimental study of copper–gold nitride formation

This work investigates the formation of a Cu3Au-nitride alloy using experimental and computational methods. For this purpose, we prepared a custom-made Cu–Au target and then hit it with argon ions in the presence of molecular nitrogen that produced a film on Corning glass. This film was analyzed using spectroscopic and diffraction techniques. The four-point-probe method and Tauc plots were applied to determine the electrical and optical properties of this thin film. Using first principle calculations a structural model was constructed that validated our observations. The crystalline system that we used was cubic (Pm3m space group) with half the sites filled with Au randomly. The composition was close to Cu3Au0.5N. In agreement with the electrical measurements and calculations, the Cu3Au0.5N band structure was highly affected by the Au incorporation since the electrical resistance and carrier density were in the 10−3Ωcm and 1022cm−3 ranges, respectively, and the optical gap decreased 0.61eV with respect to the Cu3N. The material was a pseudo-gap conductor with conductance as good as a heavily-doped semiconductor at room temperature; this should give it great potential for use in the optoelectronics industry.

Doping of wide-bandgap titanium-dioxide nanotubes: optical, electronic and magnetic properties.

Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO₂) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications.

Microwave Detection Properties of Asymmetrically Narrowed YBa2Cu3O7–x Structures

Results of our research demonstrate possibilities of detection of microwaves radiation by means of asymmetrically narrowed YBa 2 Cu 3 O 7- x oxygen-rich ( x ≤ 0.2) and oxygen-decomposed ( x > 0.5) in the necked region at temperatures higher than the critical temperature of the superconductor T c at which superconductor exhibits properties of a heavily-doped semiconductor. Both types of structures, mounted into a 10 GHz waveguide, generate sub-linearly increasing amplitude of detected voltage with increase of incident power of pulsed 10-GHz-frequency microwave radiation. The voltage sensitivity S x ≤ 0.2 ≥ 1.3 mV/W of oxygen-rich and S x > 0.5 ≥ 9 mV/W of oxygen-decomposed structure were measured at room temperature. Asymmetrical shape of nonlinear current-voltage dependences depend s on oxygen content x in the necked region and temperature of the tested structure. Our results show that the asymmetrically narrowed structure with a necked region down to 10 μ m m made of partially deoxygenated YBa 2 Cu 3 O 7– x superconductor can be used as a nonsuperconducting, nonlinear on-chip element (detector of MW power) in the YBa 2 Cu 3 O 7– x chip operating at temperatures below critical temperature T c of the chip superconductor. DOI: http://dx.doi.org/10.5755/j01.ms.20.2.6320

Heavily-doped colloidal semiconductor and metal oxide nanocrystals: an emerging new class of plasmonic nanomaterials

The creation and study of non-metallic nanomaterials that exhibit localized surface plasmon resonance (LSPR) interactions with light is a rapidly growing field of research. These doped nanocrystals, mainly self-doped semiconductor nanocrystals (NCs) and extrinsically-doped metal oxide NCs, have extremely high concentrations of free charge carriers, which allows them to exhibit LSPR at near infrared (NIR) wavelengths. In this tutorial review, we discuss recent progress in developing and synthesizing doped semiconductor and metal oxide nanocrystals with LSPR, and in studying the optical properties of these plasmonic nanocrystals. We go on to discuss their growing potential for advancing biomedical and optoelectronic applications.

Plasmonics in heavily-doped semiconductor nanocrystals

Heavily-doped semiconductor nanocrystals characterized by a tunable plasmonic band have been gaining increasing attention recently. Herein, we introduce this type of materials focusing on their structural and photo physical properties. Beside their continuous-wave plasmonic response, depicted both theoretically and experimentally, we also review recent results on their transient, ultrafast response. This was successfully interpreted by adapting models of the ultrafast response of gold nanoparticles.

The Diffusivity-Mobility Relationship of Heavily Doped Semiconductors Exhibiting a Non-Parabolic Band Structure and Bandgap Narrowing

A relationship between the mobility and diffusivity of semiconductors exhibiting bandgap narrowing has been presented. The relationship is general and applicable to both non-degenerate and degenerate semiconductors under an applied bias. It is suitable for the investigation of the electrical transport in heavily doped semiconductors.

Impact of heat treatment on resistivity of ohmic contacts in GaAs p-type monocrystals

The paper is devoted to inquiries in resistivity of ohmic contacts with heavily-doped semiconductor (2´1018 cm–3) made of p-type GaAs, in the case of many-layer structure of the contact — Au/TiBx/Ti. As shown by measurements, this ohmic system is competitive enough and has some advantages over other ohmic structures.

Energy band alignment of injector/insulator heterojunctions

Heterojunction energy band analysis is employed to elucidate the energy band structure of injector (i.e. a metal or heavily-doped semiconductor)/insulator (i.e. an insulator or semi-insulating wide-bandgap semiconductor) heterojunctions. Although both blocking and injecting contacts are considered, the primary focus is to clarify the energy band nature of injecting contacts. An important aspect of this work is the invocation of spatial truncation of the insulator region as a means of obtaining a physically realistic energy band picture of the interface in real devices, thereby avoiding confusion associated with insulator bulk boundary conditions in mathematical device physics models. The topic of insulator injecting contacts is perceived to be one of current interest, since such contacts appear to play a critical role in the operation of transparent thin-film transistors and perhaps other transparent electronics devices.