Energy dependence of quantum dot formation by ion sputtering

Abstract

Ordered quantum dot patterns are generated on GaSb and InSb surfaces due to a surface instability induced by Ar ϩ -ion sputtering at normal incidence. The characteristic length of the generated patterns scales with the square root of the ion energy over the energy range of 75-1800 eV. This energy dependence is compared to the solutions of the isotropic Kuramoto-Sivashinsky equation and allows the determination of the lateral width of the energy distribution deposited by the incident ions in the very-low-energy range. We show that the observed energy dependence is in agreement with the linear continuum theory under the assumption that the dominant smoothing process is due to effective ion-induced diffusion without mass transport on the surface. The controlled fabrication of semiconductor nanostructures remains a key requirement for the development of future optoelectronic and electronic devices. Although electron-beam lithography enables the fabrication of structures with nanometer dimensions, the low throughput of serial lithographic methods represents a severe bottleneck. Therefore alternative methods based on self-organization to form large arrays of well-defined quantum dots ͑QD's͒ have attracted extensive attention in the past. Up to now most of the work was based on the spontaneous growth of selforganized QD's on semiconductor surfaces in the StranskiKrastanov ͑SK͒ growth mode.1 Very recently, low-energy ion sputtering at normal incidence has been demonstrated to be an attractive alternative to SK growth, opening a promising route for the parallel fabrication of uniform semiconductor QD's ordered in a hexagonal array.2 This self-organized formation of periodic arrays of QD's during ion sputtering is based on a surface instability, i.e., the interplay between surface roughening induced by sputtering and smoothing processes on the surface. The basic mechanism has been related to physical principles underlying the formation of periodic ripple structures during ion sputtering of surfaces at oblique angles of incidence.3 These ripple patterns have been observed on different surfaces of semiconductors, 4-8 metals, 9,10 and glass. 11 The formation of ripple patterns has been investigated experimentally and theoretically in great detail 12 while the formation of regular dot arrays is not yet fully reconnoitered.In order to control the formation process for the QD's induced by ion sputtering a quantitative understanding of the formation mechanism is required. For the description of the dot formation mechanism a continuum model has been developed, which is related microscopically to the distribution function of the energy deposited by the incident ions, 3 and allows the derivation of the wavelength of the pattern. Other microscopic models relate the formation of nanostructures to the formation of surface defects and adatoms and their diffusion on the surface. 10,13 However, quantitative predictions are difficult to extract from these models. Here we report on the investigation of the energy dependence of the dot evol...

Continuum modeling of particle redeposition during ion-beam erosion

“…The remaining defects dissolve for longer simulation times and the surface converges to a perfect hexagonal arrangement. Besides the qualitative similarity of the resulting pattern in comparison with experimentally observed dot morphologies, we can also notice a quantitative agreement: the aspect ratio has a value of = 0.76 (A = 6.62 and L = 8.74) and is therefore comparable to the dot morphologies found on binary compounds [6][7][8][9][10][11] and by irradiation with heavy Bi-(cluster)-ions [12][13][14][15][16][17]. Since we had to use the same scales forĥ and x in (46), the aspect ratio is a characteristic quantity of the model equation (47), which cannot be adjusted by rescaling the height or the lateral extent.…”

“…While the first experiments can be dated back to 1962 [5], a new impetus was given in 1999, when Facsko et al discovered the self-organized formation of hexagonally arranged nanodot structures on semiconductor surfaces by lowenergy ion-beam erosion at normal incidence [6]. Since then, numerous experiments have been carried out which can essentially be categorized into three groups: (i) lowenergy erosion of III-V semiconductor compounds [6][7][8][9][10][11]; (ii) erosion of Ge with heavy ions or ion clusters [12][13][14][15][16][17] and (iii) low-energy erosion of Si with additional metal co-deposition [18][19][20][21].…”

Continuum modeling of sputter erosion under normal incidence: Interplay between nonlocality and nonlinearity

“…During the last five years, however, spectacularly novel experimental results have been reported by Facsko et al 4,5,6,7 showing that GaSb and InSb semiconductor targets eroded by Ar + ions under normal incidence can develop into a rather well ordered surface morphology with basically hexagonally arranged dot structures. Similar results have been subsequently reported by Gago et al 8 for Si targets under normal incidence and, more generally, by Frost et al 9,10,11 for rotated InP, InSb and GaSb targets under oblique incidence (where as function of the inclination angle a variety of other patterns have also been observed).…”

nm- andμm-Scale Surface Roughness on Glass with Specific Optical Scattering Characteristics on Demand

“…As described in a review article by Valbusa et al [8], subsequently, many groups picked up these investigations-not only with (reactive) ion-beam machines, but also with (reactive) ion etching (RIE). Those investigations were usually not performed with amorphous glass, but rather for semiconductors or even metals [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The phenomenon observed and described in all of these publications is self-organization due to two compensating effects, which together stabilize the surface profile: first a tendency of surface structure shrinkage due to a preferred etch erosion at oblique flanks and secondly diffusion of the eroded particles into the etched depressions 2 Advances in OptoElectronics and adsorption.…”