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1. 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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2. Selective phosphorus doping of polycrystalline silicon on glass using self-assembled monolayer doping (MLD) and flash anneal

   https://doi.org/https://doi.org/10.1016/j.matlet.2021.130780  

   Glenn Packard; Carolyn Spaulding; Alex Taylor; Karl Hirschman; Scott Williams, Santosh Kurinec (August 2021, Materials letters)

   Aldo R. Boccaccini (Ed.)

   We report doping of thin (~60 nm) amorphous silicon (a-Si) on glass substrate to form n + polycrystalline silicon on glass in selective regions using Monolayer doping (MLD) via Flash Lamp Annealing (FLA). The phosphorus monolayer was formed on the exposed regions of SiO2 patterned a-Si, through functionalization with chemically bound Diethyl vinylphosphonate (DVP) dopant molecules. The samples were capped with SiO2 and annealed using a single xenon flash pulse (5.0 J/cm2, 250 μs) to simultaneously crystallize a-Si, incorporate and activate phosphorus dopants. SIMS results show an average concentration of 8x1019 cm−3 in the 60 nm of thin silicon on glass. Electrical results show a resistivity of ~6.60x10−2 Ω.cm in doped regions. N-channel field effect transistor devices are successfully demonstrated using this MLD-FLA technique. 

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3. Silicon-doped β -Ga2O3 films grown at 1 µ m/h by suboxide molecular-beam epitaxy

   https://doi.org/10.1063/5.0139622  

   Azizie, Kathy; Hensling, Felix_V_E; Gorsak, Cameron_A; Kim, Yunjo; Pieczulewski, Naomi_A; Dryden, Daniel_M; Senevirathna, M_K_Indika; Coye, Selena; Shang, Shun-Li; Steele, Jacob; et al (April 2023, APL Materials)

   We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow β-Ga2O3 at a growth rate of ∼1 µm/h with control of the silicon doping concentration from 5 × 1016 to 1019 cm−3. In S-MBE, pre-oxidized gallium in the form of a molecular beam that is 99.98% Ga2O, i.e., gallium suboxide, is supplied. Directly supplying Ga2O to the growth surface bypasses the rate-limiting first step of the two-step reaction mechanism involved in the growth of β-Ga2O3 by conventional MBE. As a result, a growth rate of ∼1 µm/h is readily achieved at a relatively low growth temperature (Tsub ≈ 525 °C), resulting in films with high structural perfection and smooth surfaces (rms roughness of <2 nm on ∼1 µm thick films). Silicon-containing oxide sources (SiO and SiO2) producing an SiO suboxide molecular beam are used to dope the β-Ga2O3 layers. Temperature-dependent Hall effect measurements on a 1 µm thick film with a mobile carrier concentration of 2.7 × 1017 cm−3 reveal a room-temperature mobility of 124 cm2 V−1 s−1 that increases to 627 cm2 V−1 s−1 at 76 K; the silicon dopants are found to exhibit an activation energy of 27 meV. We also demonstrate working metal–semiconductor field-effect transistors made from these silicon-doped β-Ga2O3 films grown by S-MBE at growth rates of ∼1 µm/h. 

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4. Epitaxial growth of α-(Al x Ga1− x )2O3 by suboxide molecular-beam epitaxy at 1 µm/h

   https://doi.org/10.1063/5.0170095  

   Steele, Jacob; Azizie, Kathy; Pieczulewski, Naomi; Kim, Yunjo; Mou, Shin; Asel, Thaddeus_J; Neal, Adam_T; Jena, Debdeep; Xing, Huili_G; Muller, David_A; et al (April 2024, APL Materials)

   We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow α-(AlxGa1−x)2O3 films on (110) sapphire substrates over the 0 < x < 0.95 range of aluminum content. In S-MBE, 99.98% of the gallium-containing molecular beam arrives at the substrate in a preoxidized form as gallium suboxide (Ga2O). This bypasses the rate-limiting step of conventional MBE for the growth of gallium oxide (Ga2O3) from a gallium molecular beam and allows us to grow fully epitaxial α-(AlxGa1−x)2O3 films at growth rates exceeding 1 µm/h and relatively low substrate temperature (Tsub = 605 ± 15 °C). The ability to grow α-(AlxGa1−x)2O3 over the nominally full composition range is confirmed by Vegard’s law applied to the x-ray diffraction data and by optical bandgap measurements with ultraviolet–visible spectroscopy. We show that S-MBE allows straightforward composition control and bandgap selection for α-(AlxGa1−x)2O3 films as the aluminum incorporation x in the film is linear with the relative flux ratio of aluminum to Ga2O. The films are characterized by atomic-force microscopy, x-ray diffraction, and scanning transmission electron microscopy (STEM). These α-(AlxGa1−x)2O3 films grown by S-MBE at record growth rates exhibit a rocking curve full width at half maximum of ≊ 12 arc secs, rms roughness <1 nm, and are fully commensurate for x ≥ 0.5 for 20–50 nm thick films. STEM imaging of the x = 0.78 sample reveals high structural quality and uniform composition. Despite the high structural quality of the films, our attempts at doping with silicon result in highly insulating films. 

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5. Vertically aligned carbon nanotubes from premade binary metal oxide nanoparticles on bare SiO2

   https://doi.org/10.1016/j.carbon.2025.120086  

   Hoque, Abdul; Nawarathne, Chaminda P; Alvarez, Noe T (March 2025, Carbon)

   Liu, Chang (Ed.)

   The synthesis of carbon nanotubes (CNTs) requires well-defined catalyst nanoparticles that can influence both diameter and chirality. Herein, catalyst nanoparticles containing both the catalyst and catalyst support material were developed. Bimetallic aluminum oxide–iron oxide (AlOx–Fe2O3) nanorice was synthesized from a mixture containing both aluminum and iron oleate precursors in the solution phase. The nanoparticles were assembled as a monolayer film on a silicon oxide (SiO2) substrate via organic linker molecules to synthesize vertically aligned carbon nanotubes (VA-CNTs). Microscopic and spectroscopic characterization of the premade catalyst nanoparticles and monolayer film assembly revealed the quality of the nanoscale assembly, which facilitated the successful growth of VA-CNTs. The length of the CNTs synthesized using these AlOx–Fe2O3 nanorice catalyst nanoparticles surpassed that of previously reported CNTs grown on bare SiO2 surfaces without oxide buffer layers. In addition, the CNTs appeared to be directly bonded/connected to the SiO2 substrate, suggesting CNT formation via the tip-growth mechanism. The effects of growth temperature and catalyst reduction time were evaluated to obtain high-yield VA-CNTs. 

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