Ordered Quantum Dot Formation by Ion Sputtering

Abstract

Ion sputtering with low energy ions at normal angle of incidence represents an alternative method for the self-organized formation of semiconductor quantum dots. Dot patterns are formed spontaneously on GaSb and InSb surfaces during sputtering and exhibit a uniform size distribution and a long-range hexagonal ordering. The diameter of the fabricated dots ranges from 15-80 nm with an aspect ratio of nearly unity and with dot densities of 3 Â 10 11 to 1 Â 10 10 cm --2 . The size and density of the dots can be controlled separately by sputtering time and ion energy, respectively. GaSb quantum dots are prepared by this method through sputtering of GaSb layers in a multilayer sample down to the interface. Numerical integration of the Kuramoto-Sivashinsky equation which describes in a continuum model the dot formation are compared to the experimental findings.Introduction For the preparation and lateral structuring of semiconductor surfaces as well as in mass spectrometry ion sputtering is used extensively for the controlled erosion of the surface. In most cases the change in surface morphology, especially the increase in surface roughness during ion sputtering is a rather undesired side effect. The discovery of the appearance of periodic structures with dimensions in the nanometer regime induced by ion bombardment has attracted growing interest due to the possibility of obtaining a self-organized formation of nanometer structures. At non-normal angles of incidence regular ripple structures have been observed on insulator [1], metal [2] and semiconductor surfaces [3, 4], for elemental [3] and compound materials [4]. Recently, uniform dot structures [5] and hole structures [6] were observed when the angle of incidence is normal to the bombarded surface.The high uniformity and the regular long-range hexagonal ordering of the dot patterns on GaSb surfaces induced by ion sputtering has led to the preparation of GaSb quantum dots (QDs) by this method [5]. As a subtractive method it has some advantages compared to Stranski-Krastanov growth of QDs regarding the relative low technical requirements, the absence of a wetting layer and the possible material combinations.

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.…”

“…whereby the angles α, θ and ϕ have to be evaluated according to equations (3), (7) and (8). The last step in the derivation of our model is the generalization of the single ion impact at r E to a homogeneous irradiation of the whole surface with a constant ion flux J (i.e.…”

“…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 particle redeposition during ion-beam erosion

“…The resulting aspect ratios are in the same order as the experiments on binary compounds [6][7][8][9][10][11] and Ge irradiated by Bi-(cluster)-ions [12][13][14][15][16][17]. Additionally, the negative sign of κ is compatible with the physical interpretation of this parameter.…”

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.…”