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This analysis applies to a quasi-neutral region of uniformly doped semiconductor material. The objective is to solve for the current density in terms of the carrier density and the electric potential boundary values. It is shown that the combined effects of drift and diffusion can be calculated by assuming the current density to obey Ohm's law, but with modified electric potential boundary values.
The state-of-art power semiconductor devices require a thorough understanding of the thermal behavior for these devices. Traditional thermal analysis have (1) failed to account for the thermo-electrical interaction which is significant for power semiconductor devices operating at high temperature, and (2) failed to account for the thermal interactions among all the levels involved in, from the entire device to the gate micro-structure. Furthermore there is a lack of quantitative studies of the thermal breakdown phenomenon which is one of the major failure mechanisms for power electronics. This research work is directed towards addressing. Using a coupled thermal and electrical simulation, in which the drift-diffusion equations for the semiconductor and the energy equation for temperature are solved simultaneously, the thermo-electrical interactions at the micron scale of various junction structures are thoroughly investigated. The optimization of gate structure designs and doping designs is then addressed. An iterative numerical procedure which incorporates the thermal analysis at the device, chip and junction levels of the power device is proposed for the first time and utilized in a BJT power semiconductor device. In this procedure, interactions of different levels are fully considered. The thermal stability issue is studied both analytically and numerically in this research work in order to understand the mechanism for thermal breakdown.
In this contribution, we show that Ga-hyperdoped poly-Si/SiOx contacts are realized by pulsed laser annealing and post-hydrogenation. The motivation behind this work is to improve the inferior performance of boron-doped poly- Si/SiOx contacts when compared to the phosphorus-doped contacts. Here we used Ga as a novel p-type dopant to replace B, as B is known to accumulate at the interface between the oxide and the crystalline silicon and cause recombination. Due to a high diffusivity of Ga in oxide and a much higher segregation coefficient (Si:SiOx), Ga is shown to be immune to the oxide pileup phenomenon. However, Ga has a low solid solubility limit in Si (5x10^19 cm-3), which is not enough to form a low resistivity contact. To overcome this problem, we explored pulsed laser annealing via excimer laser by varying the laser energy densities and pulses. The passivation and electrical properties are studied systematically using photoluminescence (PL), secondary ion mass spectrometry (SIMS), and Van der Pauw-Hall measurements. We show an active Ga doping concentration above 1x10^20 cm^-3, which is above the solid solubility limit of Ga in Si. Good passivation quality is demonstrated with the highest implied Voc (iVoc) of 721 mV on single side polished samples. Furthermore, a low diode contact resistivity of ~22 m..omega.. cm^2 is obtained using Ti/Ag contacts, with minimal metal-to-semiconductor contact resistivity of 0.9 m..omega.. cm^2.
Titanium inserted in silicon by diffusion or during Czochralski ingot growth is electrically active to a concentration level of about 4 x 10 to the 14th per cu cm. It is reported that Hall measurements after diffusion show conversion of lightly doped p-type Si to n-type due to a Ti donor level at E sub c -0.22 eV. In addition, in DLTS measurements of n(+)p structures this level shows as an electron (minority carrier) trap at E sub c -0.26 eV with an electron capture cross section of about 3 x 10 to the -15th per sq cm at 300 K. Finally, a Ti electrically active concentration of about 1.35 x 10 to the 13th per cu cm in p type Si results in a minority carrier (electron) lifetime of 50 nsec at 300 K.
Long viewed as passive elements, antiferromagnetic materials have emerged as promising candidates for spintronic devices due to their insensitivity to external fields and potential for high-speed switching. Recent work exploiting spin and orbital effects has identified ways to electrically control and probe the spins in metallic antiferromagnets, especially in non-collinear or non-centrosymmetric spin structures. The rare-earth nickelate NdNiO 3 is known to be a non-collinear antiferromagnet in which the onset of antiferromagnetic ordering is concomitant with a transition to an insulating state. In this work, we find that for low electron doping, the magnetic order on the nickel site is preserved, whereas electronically, a new metallic phase is induced. We show that this metallic phase has a Fermi surface that is mostly gapped by an electronic reconstruction driven by bond disproportionation. Furthermore, we demonstrate the ability to write to and read from the spin structure via a large zero-field planar Hall effect. Our results expand the already rich phase diagram of rare-earth nickelates and may enable spintronics applications in this family of correlated oxides.
This paper studies the ionizing radiation effects on functionalized single-walled carbon nanotube (SWCNT)/poly(methyl methacrylate) (PMMA) thin-film nanocomposites [SWNT/PMMA]. The functionalized thin-film devices are made of ferrocene-doped SWCNTs, SWCNTs functionalized with carboxylic acid (COOH), and SWCNTs coated/ modified with copper. The nanocomposite was synthesized by the solution blending method and the resulting nanocomposite was spin-cast on interdigitated electrodes (IDEs). A 160 kV X-ray source was used to irradiate the thin film and changes in the electrical resistance of the nanocomposites due to X-rays were measured using a semiconductor device analyzer. Carboxylic acid functionalized and copper-coated SWCNT/PMMA nanocomposite showed a reduced response to X-rays compared to unfunctionalized SWCNT/PMMA nanocomposite. Ferrocene-doped SWCNT showed a higher sensitivity to X-rays at lower dose rates. This is in contrast to a previous study that showed that similar nanocomposites using functionalized multi-walled CNTs (MWCNTs) had demonstrated an improved response to X-rays ionizing radiation compared to unfunctionalized MWCNTs for all dose rates. Electrical measurements were also performed using the Arduino Nano microcontroller. The result showed that a relatively economical, lightweight-designed prototype radiation sensor based on SWCNT/PMMA thin-film devices could be produced by interfacing the devices with a modest microcontroller. This work also shows that by encapsulating the SWCNT/PMMA thin-film device in a plastic container, the effect of ambient humidity can be reduced and the device can still be used to detect X-ray radiation. This study further shows that the sensitivity of SWCNT to X-rays was dependent on both the functionalization of the SWCNT and the dose rate.
As an emerging ultra-wide bandgap compound semiconductor, Ga 2 O 3 has attracted rapidly growing interest due to its unique physical properties for harsh condition applications. Compared to Ga 2 O 3 ’s electrical-characteristic based uses, such as power electronics, photodetectors and solar cells, a much less explored area for Ga 2 O 3 is its promising optical properties and its related scintillation capabilities. Undoped Ga 2 O 3 is a strong scintillator with excellent scintillation characteristics such as fast decay constants and encouraging light yield which is comparable to that of the classic Bi 4 Ge 3 O 12 (BGO) scintillator. The scintillation capability of Ga 2 O 3 can be precisely tuned via a series of approaches including systematic crystal growth control, post-growth annealing, targeted doping, and optimization of operation temperature. Here we summarize exciting progress of Ga 2 O 3 scintillators which have been pursued over the past few years. Our efforts cover a series of growth techniques of Ga 2 O 3 materials as well as discussion of emission mechanisms. Here we dedicate a targeted portion toward the doping strategies to improve the performance of Ga 2 O 3 . A detailed analysis is provided to compare the impact of different dopants. Through these efforts, we hope to provide useful perspectives to help accelerate the development of high performance Ga 2 O 3 scintillators.
We report three lactone-based rigid semiconducting polymers were designed to overcome major limitations in the development of n-type organic thermoelectrics, namely electrical conductivity and air stability. Experimental and theoretical investigations demonstrated that increasing the lactone group density by increasing the benzene content from 0% benzene (P-0), to 50% (P-50), and 75% (P-75) resulted in progressively larger electron affinities (up to 4.37 eV), suggesting a more favorable doping process, when employing (N-DMBI) as the dopant. Larger polaron delocalization was also evident, due to the more planarized conformation, which is proposed to lead to a lower hopping energy barrier. As a consequence, the electrical conductivity increased by three orders of magnitude, to achieve values of up to 12 S/cm and Power factors of 13.2 μWm -1 K -2 were thereby enabled. These findings present new insights into material design guidelines for the future development of air stable n-type organic thermoelectrics.
The quantum anomalous Hall (QAH) effect combines topology and magnetism to produce precisely quantized Hall resistance at zero magnetic field. We report the observation of a QAH effect in twisted bilayer graphene aligned to hexagonal boron nitride. The effect is driven by intrinsic strong interactions, which polarize the electrons into a single spin- and valley-resolved moiré miniband with Chern number C = 1. In contrast to magnetically doped systems, the measured transport energy gap is larger than the Curie temperature for magnetic ordering, and quantization to within 0.1% of the von Klitzing constant persists to temperatures of several kelvin at zero magnetic field. Electrical currents as small as 1 nanoampere controllably switch the magnetic order between states of opposite polarization, forming an electrically rewritable magnetic memory.
Electrochemical CO 2 reduction is a potential approach to convert CO 2 into valuable chemicals using electricity as feedstock. Abundant and affordable catalyst materials are needed to upscale this process in a sustainable manner. Nickel-nitrogen-doped carbon (Ni-N-C) is an efficient catalyst for CO 2 reduction to CO, and the single-site Ni-N x motif is believed to be the active site. However, critical metrics for its catalytic activity, such as active site density and intrinsic turnover frequency, so far lack systematic discussion. In this work, we prepared a set of covalent organic framework (COF)-derived Ni-N-C catalysts, for which the Ni-N x content could be adjusted by the pyrolysis temperature. The combination of high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure evidenced the presence of Ni single-sites, and quantitative X-ray photoemission addressed the relation between active site density and turnover frequency.
Correlated anion and cation motion can greatly reduce the overall ion conductivity in electrolytes versus the ideal conductivity calculated based on the diffusion constants alone. Using coarse-grained molecular dynamics simulations, we calculate conductivity and the degree of uncorrelated ion motion in salt-doped homopolymers and block copolymers as a function of concentration and interaction strengths. Calculating conductivity from ion mobility under an applied electric field increases accuracy versus the typical use of fluctuation dissipation relationships in equilibrium simulations. In typical electrolytes, correlation in cation-anion motion is often expected to be reduced at low ion concentrations. Yet, for these polymer electrolytes with strong ion-polymer and ion-ion interactions, we find cation-anion motion is more correlated at lower concentrations when other variables are held constant. We show this phenomenon is related to the slower ion cluster relaxation rate at low concentrations rather than the static spatial state of ion aggregation or the fraction of free ions.
Here, we demonstrate a monolithic all-epitaxial resonant-cavity architecture for long-wave infrared photodetectors with substrate-side illumination. An nBn detector with an ultra-thin (t ≈ 350 nm) absorber layer is integrated into a leaky resonant cavity, formed using semitransparent highly doped (n⁺⁺) epitaxial layers, and aligned to the anti-node of the cavity’s standing wave. The devices are characterized electrically and optically and demonstrate an external quantum efficiency of 25% at T ¼ 180 K in an architecture compatible with focal plane array configurations.
Atomic precision advanced manufacturing (APAM) dopes silicon with enough carriers to change its electronic structure and can be used to create novel devices by defining metallic regions whose boundaries have single-atom abruptness. Incompatibility with the thermal and lithography process requirements for gated silicon transistor manufacturing have inhibited exploration of both how APAM can enhance CMOS performance and how transistor manufacturing steps can accelerate the discovery of new APAM device concepts. In this work, we introduce an APAM process that enables direct integration into the middle of a transistor manufacturing workflow. We show that a process that combines sputtering and annealing with a hardmask preserves a defining characteristic of APAM, a doping density far in excess of the solid solubility limit, while trading another, the atomic precision, for compatibility with manufacturing. The electrical characteristics of a chip combining a transistor with an APAM resistor show that the APAM module has only affected the transistor through the addition of a resistance and not by altering the transistor. This proof-of-concept demonstration also outlines the requirements and limitations of a unified APAM tool, which could be introduced into manufacturing environments, greatly expanding access to this technology and inspiring a new generation of devices with it.
Colloidal quantum dots (CQDs) are valuable for their potential applications in optoelectronic devices. However, they are susceptible to thermal degradation during processing and while in use. Mitigating thermally induced sintering, which leads to absorption spectrum broadening and undesirable changes to thin film electrical properties, is necessary for the reliable design and manufacture of CQD-based optoelectronics. Here, low-temperature metal–oxide atomic layer deposition (ALD) was investigated as a method for mitigating sintering while preserving the optoelectronic properties of mercury telluride (HgTe) CQD films. ALD-coated films are subjected to temperatures up to 160 °C for up to 5 h and alumina (Al 2 O 3 ) is found to be most effective at preserving the optical properties, demonstrating the feasibility of metal–oxide in-filling to protect against sintering. HgTe CQD film electrical properties were investigated before and after alumina ALD in-filling, which was found to increase the p-type doping and hole mobility of the films. The magnitude of these effects depended on the conditions used to prepare the HgTe CQDs. With further investigation into the interaction effects of CQD and ALD process factors, these results may be used to guide the design of CQD–ALD materials for their practical integration into useful optoelectronic devices.
Conductive nanoporous conformal coatings are important for various applications including touchscreens, displays, and electrochromic windows, though design of such coating with controlled porosity and composition remains challenging. We propose a sequential infiltration synthesis (SIS) method for the fabrication of nanoporous conductive aluminum-doped zinc oxide (AZO) films by infiltrating block copolymer (BCP) templates, specifically polystyrene-block-polyvinyl pyridine (PS-b-P4VP), with diethyl zinc and trimethyl aluminum precursors. Tunability of both porosity and electrical conductivity is achieved by precisely controlling the swelling behavior of the polymer templates and adjusting the number of SIS cycles. Further, our results reveal that porosity levels can reach up to 80 %, with resistivity as low as ~7.83 Ωcm. Using conductive atomic force microscopy (C-AFM) and Hall effect measurements, we show that lower concentrations of aluminum doping relative to zinc (around 1: 17) results in higher conductivity of the AZO films. Additionally, AZO is based on zinc oxide (ZnO) which is cost-efficient, abundant and less toxic than commonly used transparent conductive oxides such as indium tin oxide (ITO) and fluorine-doped tin oxide (FTO). Therefore, this novel approach opens new possibilities for creating highly porous, conformal, conductive AZO coatings with customizable porosity and composition, making them ideal candidates for diverse optoelectronic applications.
A microgyroscope has a baseplate made of the same material as the rest of the microgyroscope. The baseplate is a silicon baseplate having a heavily p-doped epilayer covered by a thick dielectric film and metal electrodes. The metal electrodes are isolated from the ground plane by the dielectric. This provides very low parasitic capacitive coupling between the electrodes. The thick dielectric reduces the capacitance between the electrodes and the ground plane.
In extending the violet and nonreflective cell technology to lower resistivities, several processes limiting output power were encountered. The most important was the dark diffusion current due to recombination at the front grid contacts. After removal of this problem by reduction of the silicon metal contact area (to 0.14 percent of the total area), the electric field enhanced junction recombination current J sub r was the main limitation. Alteration of the diffusion profile to reduce the junction field is shown to be an effective means of influencing J sub r. The remaining problems are the bulk recombination in the n+ layer and the surface recombination at the oxide-silicon interface; both of these problems are aggravated by band-narrowing resulting from heavy doping in the diffused layer. Experimental evidence for the main limitations is shown, where increased diffusion temperature is seen to reduce both the influence of the front grid contacts and the junction electric field by increasing the junction depth. The potential for further significant improvement in efficiency appears to be high.
Magnetoelectric (ME) materials exhibit interesting physics with cross coupling between ferroelectric and magnetic order parameters and thus strong potential to be utilized in memory, spintronics and other multifunctional electronic/magnetic devices. Doping of suitable transition metals in ferroelectrics can induce magnetism and ME coupling and modify the physical properties. Here, we report the structural, electronic, magnetic and ME coupling of 3.5, 5 and 7.5 mol% cobalt doped BaTiO 3 (BTO) ceramics. X-ray diffraction and Raman spectroscopy indicate that the samples are single phase having a tetragonal crystal structure with P4mm symmetry. The tetragonality ratio is found to decrease with increasing cobalt content. We observed a Fano-like asymmetric peak in the [A 1 (LO 1 )] Raman mode at ~173 cm -1 in all the cobalt doped BTO samples. The cobalt dopants are shown to be uniformly distributed throughout the surface of the samples. We observed a lowering of the ferroelectric transition temperature and increasing diffusivity parameter with increasing cobalt concentration. The electrical properties of all the samples have been investigated in detail by impedance spectroscopy and ac conductivity studies before and after the ferroelectric phase transitions. All the samples show hysteretic ferroelectric behavior with a clear saturation state that decreases with increasing cobalt content. The observed ferroelectricity in these samples is intrinsic in nature. The 3.5% cobalt doped BTO sample exhibits paramagnetic behavior whereas the 5 and 7.5% cobalt doped BTO samples show ferromagnetic ordering below 43 K. The 7.5% cobalt doped BTO samples show significant ME coupling.