Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
In-situ probing of near and below sputter-threshold ion-induced nanopatterning on GaSb(1 0 0)
Introduction
Bottom-up, parallel processing techniques are beginning to rival other nanolithography approaches to nanopatterning [1]. However, much work remains in understanding scaling from short-range to long-range ordering as device features continue to decrease beyond sub-20 nm size. Device feature size introduces limits on ion-beam sputtering (IBS) nanopatterning conditions such as incident particle energy given the penetration range 1–4 nm for energies between 0.05 and 2 keV Ar+ irradiation. Therefore as device functionality require dimensions approaching 1–5 nm, understanding nanopatterning at these scales become more important. Applications of quantum dot confinement also introduce scaling limits and motivate systematic study of dot characteristic size against IBS parameters (e.g. ion energy, angle, ion-target interaction, etc.). Correlating in-situ surface composition and sputter erosion evolution to nanostructure synthesis could elucidate on self-organization mechanisms such as the balance between physical sputtering and surface diffusion.
In this work we present a systematic study of near and below sputter-threshold energies between 50 and 200 eV Ar+ irradiation at normal incidence of GaSb to examine in-situ the role of surface concentration on nanopatterning. In particular, we conduct in-situ surface characterization of ion-irradiated surfaces during early stage growth (e.g. 1015–1017 cm−2) of ion-induced nanostructures.
XPS and LEISS studies of GaSb irradiated by energetic ions are sparse. W. Yu et al. studied GaSb, InSb and CdSe surfaces with LEISS and XPS; however these were irradiated with Ar+ at energies above 3 keV [2]. Another study of GaSb by Möller et al. [3] assessed the role of surface oxides, which for this particular paper it is relevant since the incident particle energy is below 0.2 keV and the implantation is ultra-shallow (<1.0 nm) where oxide coverage needs to be assessed when investigating early stage (low fluence) growth of ion-induced nanostructures on GaSb. The work by LeRoy et al. indicated two possible mechanisms for growth of ion-induced nanostructured pillar features from flat surfaces of Ga–Sb. In particular for GaSb, the segregation of Ga during sputtering as a shield in Ga–Sb erosion. However, Ga and Sb erode near identically due to similar heats of sublimation. In fact for an energy of about 1 keV Ar+ on GaSb, the corresponding sputter yields are about: YGa = 1.28 and YSb = 1.25 according to SRIM. Our work elucidates on the important early stages of growth with the strong segregation of Ga to the surface primarily due to the reduction of surface oxide followed by a sharp decrease in Ga at the ion-induced amorphous layer with a steady-state Sb-dominant region.
Section snippets
Experimental setup
All in-situ modification and characterization was performed at the Particle and Radiation Interaction with Hard and Soft Matter (PRIHSM) facility at Purdue University. PRIHSM is an ultra-high vacuum (UHV) surface science facility with in-situ ion-beam modification and characterization capabilities. Modification is carried out with a gridded broad-beam non-reactive ion source with current densities of up to 40 μA/cm2 and energies from 10 to 200 eV. In-situ characterization techniques are carried
Results and discussion
Fig. 1 shows the low-energy ion-scattering spectroscopy (LEISS) data for the case of 50 and 100 eV irradiation of GaSb (1 0 0) at normal incidence over the course of irradiation to a cumulative fluence of about 1018 cm−2. Both spectra show a strong backscattering ion signal at pre-irradiation and early stage nanopatterning growth up to about 1016 cm−2 indicative of surface oxide. This is consistent with XPS core level data of Ga 2p3/2 and Sb 3d3/2 and Sb 3 d5/2 for similar fluence level. In Fig. 1c
Conclusions
Nanopatterning of GaSb(1 0 0) has been studied with in-situ surface characterization during irradiation with Ar+ at energies near and below sputter threshold energy regimes between 50 and 200 eV at normal incidence. Early stage growth examined with the combination of monolayer-sensitive LEISS data and sub-surface XPS data elucidates on the composition-dependent evolution during irradiation and consequent pattern formation. Enrichment of Sb at the first monolayer is driven by ion-induced
Acknowledgments
This work is in part supported by the Department of Energy’s Early Career Award and the NRC Faculty Development grant. B. Heim, A. Cimaroli, D.L. Rokusek, E.K. Walker, and D. Zigon are acknowledged for assistance with LEISS and XPS analysis and experimental runs.
References (8)
Surf. Sci.
(1996)Appl. Surf. Sci.
(2005)- Javier Muñoz-Garcia et al. (2009) Self-Organized Surface Nanopatterning by Ion Beam Sputtering. In Z.M. Wang (Ed.),...
- et al.
Phys Rev B
(2001)
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