Self‐Assembly of Ordered Semiconductor Nanoholes by Ion Beam Sputtering

Abstract

Low-energy-ion bombardment of semiconductors can lead to the development of complex and diverse nanostructures. Of particular interest in these structured surfaces is the formation of highly ordered patterns whose optical, electronic, and magnetic properties are different from those of bulk materials and might find technological uses. [1][2][3][4][5] Compared to the low efficiency of lithographic methods for mass production, this self-organized approach offers a new route for fabrication of ordered patterns over large areas in a short processing time on the nanometer scale, beyond the limits of lithography. [1,4] This technique is based on the morphological instability of a sputtered surface driven by a kinetic balance between roughening and smoothing. [6,7] Thus mechanisms that control the species concentration on the surface can make contributions to structure formation. [3,[7][8][9][10][11][12] It is now established that well-ordered quantum dots can be generated on the surface of semiconductors (Si, Ge, GaSb) under certain irradiation conditions. [1,13,14] For a long time it has been expected that the instability of a surface can also lead to well-ordered hole formation. However, to date experimental observation of such features has been lacking. In this Communication, we report that a hexagonally ordered, honeycomb-like structure of holes 35 nm across and 45 nm apart on the Ge surface can be formed under focused ion beam (FIB) bombardment at normal incidence. The structured Ge fabricated by FIB bombardment shows a high surface area and a considerably blue-shifted energy gap. We found that interplay between ion sputtering, redeposition, viscous flow, and surface diffusion is responsible for ordered pattern formation. Simulations of the evolution of the surface morphology on the basis of the damped Kuramoto-Sivashinsky (DKS) growth model have been performed to facilitate the interpretation of the experimental findings. [15][16][17][18][19] As an indirect energy-gap semiconductor, germanium is a poor light emitter, which makes it challenging to create efficient Ge-based light-emitting devices. Significant effort has been devoted to the development of the optical properties of Ge based on changing the surface morphology.[20] In the work reported here, we focused on the use of ion beam radiation to fabricate nanostructures on the Ge surface.The ion-induced nanostructures were fabricated on commercially available Ge with (100) orientation by FIB bombardment. Under normal bombardment with ion energy greater than 5 keV, worm-like structures were developed on Ge surface with large aspect ratio. When the energy was 5 keV, however, highly ordered hole arrays could be achieved. Figure 1 shows scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of a typical nanohole pattern induced on a Ge(100) surface by 5 keV (Ga þ ) FIB bombardment for 5 min. A perfect hexagonal arrangement of holes is observed within domains of ca. 500 nm. Like polycrystalline structure, there are ''grain boundaries'' separati...

Nanostructures on surfaces by ion irradiation

“…Typically, FIBs are based on liquid-metal ion sources (LMIS) forming Ga + ion beams; because of the very high brightness (>10 6 A/cm 2 sr) and small virtual source size (<100 nm) [139,140] of LIMS, very small spot sizes (~10 nm) and extremely high current densities (>1 A/cm 2 ) can be achieved using suitable electrostatic focusing columns. These irradiation conditions may lead to the formation of quite specific surface structures [137,[141][142][143][144][145][146][147].…”

Controllable fabrication and temperature-resistance characteristics of ordered nanoporous Au and Pt films

“…Most of the published works depend on lithography-based processes such as electronbeam and lift-off [22], focused-ion-beam [23] and deep ultraviolet [24] methods. As an alternative, a bottom-up approach consisting of self-assembly procedures can be chose for the fabrication of nanoporous films [25][26][27]. The anodic aluminum oxide (AAO) is taken into account to serve as a pre-patterned substrate for template-assisted growth of the nanoporous arrays, and this method has the major advantages regarding process simplicity and low cost [6,[28][29][30][31][32].…”

Nano‐scale pattern formation on the surface of HgCdTe produced by ion bombardment

“…According to the Bradley-Harper theory [4], ripples are a result of a surface instability caused by the curvature dependence of the sputter yield. It should be noted that now implantation provides a fast and reproducible means of producing a nano-scale pattern on a semiconductor surface subjected both to normal-and to oblique-incidence ion bombardment in a single process step [5][6][7].…”