Nanohole and Nanopillar Arrays on GaAs and GaSb Using Nanosphere Lithography and Bromine Ion Beam Assisted Etching
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Nanohole and Nanopillar Arrays on GaAs and GaSb Using Nanosphere Lithography and Bromine Ion Beam Assisted Etching Xifeng Qian, Jin Li, and William D. Goodhue Photonics Center, Department of Physics and Applied Physics, University of Massachusetts Lowell, 720 Suffolk St., Lowell, MA, 01854 ABSTRACT Nanosphere lithography (NSL) has been successfully used to nanopattern silicon and glass substrate surfaces using a spin process in conjunction with the chemical functionalized polystyrene nanospheres. Here, we report for the first time the formation of periodic arrays of nanohole and nanopillar on GaAs and GaSb substrates using a combination of NSL, electron beam (E-Beam) evaporation and Bromine Ion Beam Assisted Etching (Br-IBAE). When 250 nm diameter nanospheres were used as a template or mask, periodic arrays of approximate 55 nm hexagonal nanoholes and 39 nm hexagonal nanopillars were obtained from double-layer nanosphere templates, while arrays of approximate 65nm triangular nanohole and 53nm triangular nanopillar were obtained from single-layer nanosphere templates. The high uniformity of these nanohole and nanopillar arrays demonstrates the technique’s potential for applications in the fabrication of novel high performance opto- and electronic devices in the important GaAs and GaSb III-V direct bandgap semiconductors. INTRODUCTION Gallium Arsenide (GaAs) and Gallium Antimonide (GaSb) are both important III-V semiconductor materials. With higher electron mobility and breakdown voltages as compared to Silicon (Si), GaAs has shown superior performance in high speed transistors [1]. In addition, as materials with direct bandgaps, GaAs and GaSb have advantages in applications including photodetectors [2], emitters [3] and lasers [4]. To fabricate novel devices such as twodimensional (2-D) gratings and quantum dots (QDs) on these materials, submicron nanopatterning is often required. The well-known top-down techniques to create large area nanostructures with high resolution include electron-beam lithography (EBL) [5], X-Ray lithography (XRL) [6], ion-beam lithography (IBL) [7] and holographic interference lithography [8]. EBL offers high resolution and high fidelity, but the process is serial and time consuming. On the other hand, XRL and IBL require expensive upgrades on the system when the nanopatterning feature size needs to be further reduced while double holographic lithography requires expensive lasers and intricate post-processing. Therefore, a nanopatterning technique with low-cost, high throughput and flexibility in tuning feature size is highly desirable. Nanosphere lithography (NSL) is a bottom-up nanopatterning technique. It uses a 2-D, self-assembled, highly ordered and close-packed nanosphere arrays as the template or mask to transfer the nano-scale pattern to the substrate. The self-assembling process is dominated by capillary force between the spheres [9] and usually results in close-packed hexagonal structures. The size of nanospheres can vary from 20 nm to 2000 nm, offering great flexibil
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