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1. Electrical and optical properties of nickel-doped Ge2Sb2Te5 films produced by magnetron co-sputtering

   https://doi.org/10.1117/12.2320843  

   Guo, Pengfei; Sevison, Gary; Agha, Imad; Sarangan, Andrew; Burrow, Joshua; Sakdinawat, Anne E.; Attias, André-Jean; Panchapakesan, Balaji; Dobisz, Elizabeth A. (September 2018, Proceedings of SPIE, Nanoengineering: Fabrication, Properties, Optics, and Devices XV)

   A magnetron co-sputtering system was used for producing nickel-doped Ge2Sb2Te5 (GST-Ni) thin films. The nickel content in the thin film was adjusted by the ratio of the plasma discharge power applied to the GST and nickel targets, as well as a physical shuttering technique to further control the nickel deposition rate. The doping concentration of the film was con firmed using Energy Dispersion Spectroscopy (EDS) technique. Results from a four-point probe measurement indicate that the nickel doping can reduce the resistivity of GST in the amorphous state by nearly three orders of magnitude. The dopant's influence on crystallization behavior was studied by analyzing X-Ray Diffraction (XRD) patterns of the pure GST and GST-Ni at different annealing temperatures. To examine the structural changes due to the nickel dopant, the thin films were investigated with the aid of Raman scattering. Additionally, we extracted the optical constants for both the amorphous and crystalline states of undoped-GST and GST-Ni films by ellipsometry. The results indicate that at low doping concentrations nickel does not appreciably affect the optical constants, but dramatically improves the electrical conductivity. Therefore, nickel-doping of GST a viable method for designing optical devices for lower operating voltages at higher switching speeds. 

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2. High‐Efficiency Ion‐Exchange Doping of Conducting Polymers

   https://doi.org/10.1002/adma.202102988  

   Jacobs, Ian_E; Lin, Yue; Huang, Yuxuan; Ren, Xinglong; Simatos, Dimitrios; Chen, Chen; Tjhe, Dion; Statz, Martin; Lai, Lianglun; Finn, Peter_A; et al (August 2021, Advanced Materials)

   Abstract Molecular doping—the use of redox‐active small molecules as dopants for organic semiconductors—has seen a surge in research interest driven by emerging applications in sensing, bioelectronics, and thermoelectrics. However, molecular doping carries with it several intrinsic problems stemming directly from the redox‐active character of these materials. A recent breakthrough was a doping technique based on ion‐exchange, which separates the redox and charge compensation steps of the doping process. Here, the equilibrium and kinetics of ion exchange doping in a model system, poly(2,5‐bis(3‐alkylthiophen‐2‐yl)thieno(3,2‐b)thiophene) (PBTTT) doped with FeCl₃and an ionic liquid, is studied, reaching conductivities in excess of 1000 S cm⁻¹and ion exchange efficiencies above 99%. Several factors that enable such high performance, including the choice of acetonitrile as the doping solvent, which largely eliminates electrolyte association effects and dramatically increases the doping strength of FeCl₃, are demonstrated. In this high ion exchange efficiency regime, a simple connection between electrochemical doping and ion exchange is illustrated, and it is shown that the performance and stability of highly doped PBTTT is ultimately limited by intrinsically poor stability at high redox potential. 

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3. Enhanced carrier transport by transition metal doping in WS 2 field effect transistors

   https://doi.org/10.1039/d0nr01573c  

   Liu, Maomao; Wei, Sichen; Shahi, Simran; Jaiswal, Hemendra Nath; Paletti, Paolo; Fathipour, Sara; Remškar, Maja; Jiao, Jun; Hwang, Wansik; Yao, Fei; et al (August 2020, Nanoscale)

   null (Ed.)

   High contact resistance is one of the primary concerns for electronic device applications of two-dimensional (2D) layered semiconductors. Here, we explore the enhanced carrier transport through metal–semiconductor interfaces in WS 2 field effect transistors (FETs) by introducing a typical transition metal, Cu, with two different doping strategies: (i) a “generalized” Cu doping by using randomly distributed Cu atoms along the channel and (ii) a “localized” Cu doping by adapting an ultrathin Cu layer at the metal–semiconductor interface. Compared to the pristine WS 2 FETs, both the generalized Cu atomic dopant and localized Cu contact decoration can provide a Schottky-to-Ohmic contact transition owing to the reduced contact resistances by 1–3 orders of magnitude, and consequently elevate electron mobilities by 5–7 times. Our work demonstrates that the introduction of transition metal can be an efficient and reliable technique to enhance the carrier transport and device performance in 2D TMD FETs. 

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4. Shallow Si N + P junction diodes realized via molecular monolayer doping

   https://doi.org/10.1016/j.mee.2018.02.008  

   Astha Tapriya, Brian Novak (January 2022, Microelectronic engineering)

   Lanza, Mario (Ed.)

   A conformal and controlled semiconductor doping is needed for applications in next generation nanoscale devices,low contact resistivity metal semiconductor junctions such as selective emitters in solar cells. Molecular monolayer doping (MLD) in silicon is a novel technique based on the formation of self-assembled monolayer of dopant – containing molecules on surface of crystalline silicon, followed by rapid thermal anneal. The technique is capable of forming ultra-shallow junctions with high atomic accuracy and minimum defects in silicon. A container and process was developed which successfully doped 6 in. diameter silicon wafers using MLD for the in-house CMOS fabrication facility. The phosphorus monolayer is grafted on hydrogen terminated p-type silicon followed by rapid thermal anneal. Average sheet resistance ~670 Ω/sq. and junction depth ~25 nm are achieved. N + P junctions are fabricated using MLD and current-voltage characteristics are measured and analyzed using unified diode model. 

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5. Introducing gallium in silicon and thin film polysilicon using self assembled monolayer doping

   https://doi.org/https://doi.org/10.1016/j.matlet.2022.132839  

   Carolyn Spaulding; Alex Taylor; Scott Williams; Glenn Packard; Gabriel Curvacho; Santosh Kurinec (October 2022, Materials letters)

   Aldo R. Boccaccini (Ed.)

   Monolayer Doping (MLD) is a technique involving the fmmation of a self-assembled dopant-containing layer on the substrate. The dopant is subsequently incorporated into the substrate by annealing, fmming a diffused region. Following MLD, samples were capped with silicon dioxide and rapid the1mal annealed (RTA). In this work, gallium doping using MLD has been demonstrated. Gallium containing compound Tris (2,4 pentanedionato) gallium(III) was synthesized, and shown to be suitable for monolayer doping silicon subsa-ates and deposited thin film polysi!icon. Seconda1y ion mass spectroscopy (SIMS) and spreading resistance probe (SRP) measurements were performed to determine the dopant profiles and dopant elecu-ical activation. TI1ese results showed that a dose of l.6*1015 atoms/cm2 was received, and the gallium dopant produced a 0.2 µm junction in 11-type silicon. For polysilicon, tlle entire 0.4 µm film was evenly doped, witll a concenu-ation greater than 1019 atoms/cm3 tllroughout. 

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