In operandi observation of dynamic annealing: a case study of boron in germanium nanowire devices Supplementary Material Maria M. Koleśnik-Gray, 1,3,4 Christian Sorger, 1 Subhajit Biswas, 2,3 Justin D. Holmes, 2,3 Heiko B. Weber, 1 and Vojislav Krstić* 1,3,4 1 Department of Physics, Chair for Applied Physics, Friedrich-Alexander University Erlangen-Nürnberg (FAU), Staudtstr. 7, 91058 Erlangen, Germany 2 Materials Chemistry and Analysis Group, Department of Chemistry, Tyndall Institute, University College Cork, Cork, Ireland 3 Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), and AMBER at CRANN, Trinity College Dublin, College Green, Dublin 2, Ireland 4 School of Physics, Trinity College Dublin, College Green, Dublin 2, Ireland *e-mail:vojislav.krstic@fau.de 1
1. Experimental methods 1.1 Nanowire device fabrication As substrates, n ++ As-doped Si wafers covered with 300 nm thermally grown SiO 2 were used and cleaved into 1 1 coupons. The wafers were cleaned with acetone and isopropanol and spin-coated with S1813 Microposit photoresist. Large contact pads and alignment markers were patterned via optical lithography using OEI Mask Aligner and metallized with 10 nm Ti/60 nm Au using Temescal electron-beam evaporator. Following the UV lithography, Ge NWs suspended in isopropanol were drop-cast onto the substrates (10-15 µl) and left to dry. The samples were then covered with MicroChem 950K PMMA A3 e-beam resist. Imaging with dark-field optical microscope allowed for identification of individual nanowires on the grid. Individual four-terminal nanowire devices were patterned using Supra 40 SEM equipped with Elphy Quantum e-beam lithography system. Following developments, electrode materials were deposited using Temescal evaporator. 1.2 Electrical characterization Electrical characterization was carried out using Agilent SMU. The samples were transferred onto ceramic chip-carriers and wire bonded allowing for measurements inside the implantation chamber. 1.3 Ion implantation into Ge NW devices Ion implantation was carried out using a 350 kv Heavy Ion Accelerator (HV Engineering Europa BV) at the pressure of 10-6 mbar. Figure S1. Schematic diagram for ion implantation approach. 2
2. TRIM simulation data for implantation into Ge NWs and associated devices Figure S2. TRIM data implantation profiles of 20 kev B into bulk Ge for ion fluencies in the 10 11 to 5 10 14 cm -2 range. 3. EDX analysis of elemental composition of NWs and devices before and after ion implantation Elemental identification was carried out using an Oxford Inca system equipped with a dry EDX detector (SiLi) with 129 ev resolution. The compositions of clean SiO 2 substrates before implantation and SiO 2 surface after B implantation (cf. Fig. 1(f) in main manuscript) are shown in Table S1. Composition of as-grown and B-implanted Ge NWs is compared in Table S2. The values were averaged among 8 spectra for each material tested. Table S1. EDX analysis of elemental composition of SiO 2 substrates before and after B implantation (darkened halo on chip). Post implantation, an increase in carbon content is observed (revealed by a dark halo on chip, cf. Fig. 1d) which is a consequence of hydrocarbon decomposition under ion beam in the chamber. Element Bare SiO 2 Contamination area C 2.71 3.96 O 34.63 35.27 Si 62.66 60.77 3
Figure S3. Halo on surface of device chip visible after implantation. Table S2. EDX analysis of elemental composition of Ge NW bundles deposited on SiO 2 wafers. Comparison of atomic % for as-grown and implanted with 5 10 14 B cm -2 ions. It should be noted that the EDX is not a very reliable method for quantitative analysis of light species such as B due to the close proximity of B 1s (188 ev) peak close to Ge 3s (181 ev) and the presence of a broad 280 ev C1s peak, however traces of B can be detected in the post-implanted wires. Element Not-implanted wires Wires after implantation B 0.00 13.44 C 24.20 60.73 O 3.23 4.04 Si 66.10 16.91 Ti 0.37 0.51 Ge 2.15 3.04 Au 3.95 1.32 4
4. Current-voltage characteristics of Ge NW devices Figure S 3. Current-voltage characteristics for a 53 nm B-implanted Ge NW. Main plots show device characteristics whereas the insets show four-point NW characteristics. Graphs show the change in I-V curve shape at the beginning (5 10 10 cm -2 ) and end (3 10 14 cm -2 ) of the implantation cycle. Figure S 4. Current-voltage characteristics measured using open-circuit devices before (black lines) and after implantation (blue lines) of boron and phosphorus. The test was carried out to check the potential damage to SiO 2 due to B irradiation. 5
5. Distribution of carrier concentration in Ge NWs used in the study as function of diameter size Figure S5. Distribution of carrier concentrations in Ge NWs used in the study (field-effect measurements, to be published elsewhere). 6
6. TEM images of B-implanted Ge NWs Figure S 6. TEM images of a 23 ± 5 nm thin Ge NW after B implantation. The NW underwent a high degree of damage with clusters of boron (dark centres) embedded into the amorphised Ge matrix. Maximum boron concentration estimated at 8.7 10 20 cm -3. Scale bar: (a) 20 nm, (b) to (d) 2 nm. 7
Figure S 7. TEM images of a 36 ± 3 nm thin Ge NW after B implantation. Slight surface roughness increase is observed along the axis and also boron clusters are visible. The material is highly amorphous as confirmed by the selected area electron diffraction (SAED) pattern (c). Maximum boron concentration estimated at 5.6 10 20 cm -3. Scale bar: (a) 50 nm, (b) 10 nm, (d) 2 nm. 8
Figure S8. TEM images of a 55 ± 5 nm thin Ge NW after B implantation. The NW is highly amorphized, with stacking defects dominating. Boron clusters are visible embedded into the material and significant blistering of the damaged NW and grouping of defects. Maximum boron concentration estimated at 3.6 10 20 cm -3. Scale bar: (a) 0.2 μm, (b) 10 nm, (c) 5 nm, (d) 2 nm. 9
Figure S9. (a-d) TEM images of a 82 ± 3 nm thin Ge NW after B implantation. Boron clusters spread all over the NW diameter are visible, with stacking defects dominating in the weakly amorphized structure. Maximum B concentration estimated at 2.4 10 20 cm -3. Scale bar: (a) 50 nm, (b) to (d) 5 nm. 10