Ion-induced formation of regular nanostructures on amorphous GaSb surfaces

Abstract

Crystalline and amorphous GaSb surfaces are compared concerning their response to sputter erosion with low energy Ar ϩ ions under normal incidence. We show that the formation of regular nanostructures on GaSb is basically independent of whether the initial material is crystalline or amorphous. The similarity in the temporal and spatial evolution demonstrates that the dynamics of the morphology evolution is entirely controlled by a thin amorphous surface layer. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1429750͔The large potential of nanoelectronics has stimulated much effort to find new methods for the parallel processing of nanostructures. Promising techniques, like StranskiKrastanov growth of semiconductor heterostructures 1 and self-assembly of semiconductor nanocrystals by colloid chemistry 2 have been exploited. Recently, during the erosion of semiconductor and metal surfaces by ion sputtering, a self-organizing mechanism has been discovered leading to regular patterns of structures with dimensions of some tens of nanometers.3,4 These surface structures can form quantum dots with a high aspect ratio and are therefore particularly attractive for quantum electronic applications.The appearance of periodic ripple patterns on semiconductor and metal surfaces bombarded with ions under offnormal incidence has been known for a long time. 5 In certain metals and III-V semiconductors these ripple patterns transform into hexagonally ordered isolated nanostructures under normal incidence sputtering. 3,4,6 -8 Up to now these observations have only been made in crystalline materials. The main points addressed in this letter concern ͑i͒ the comparison of the pattern evolution from initially crystalline ͑c-GaSb͒ and amorphous GaSb ͑␣-GaSb͒ targets and ͑ii͒ the microscopic structure of the patterned surface. We find that the surface dot patterns generated are independent of the crystallinity of the initial material surface. This independence is explained by the decisive role of a thin amorphous layer that forms during the very first seconds of the sputtering process. Besides the fundamental insight into the sputtering process on semiconductor surfaces, the structuring of amorphous layers deposited on arbitrary materials provides a technologically attractive method of surface nanostructuring.Stochastic nonlinear continuum models have been introduced to explain the temporal and spatial evolution of nanoscale surface patterns during ion sputteringwhere h(x,y) is the surface height function, v 0 is the constant erosion velocity, is the ''negative surface tension,'' ͑͒ is a nonlinear coefficient attributed to the tilt dependent sputter yield with the tilt angle, D is the thermal or ion induced surface diffusion, and denotes a noise term, that describes the stochastic character of the sputtering process. This continuum equation represents an approximation to the surface dynamics because higher order derivatives are not considered. The effect of additional higher order terms in Eq. ͑1͒ is believed to be minor. 10 The m...

Self-organized nanopatterning of silicon surfaces by ion beam sputtering

“…Specifically, the question addressed in this reference was the influence of the crystallinity of the initial surface on the evolution of the pattern. This issue has attracted the interest of many researchers in the field, ever since the earliest reports on nanodot formation on GaSb [106]. For the case of Si [105], both amorphous Si (a-Si) films and crystalline Si(1 0 0) (c-Si) targets were irradiated simultaneously with 1 keV Ar þ ions at normal incidence.…”

Plasma-assisted oxide removal from p-type GaSb for low resistivity ohmic contacts

“…However, at higher ion energies (250 and 325 eV), the ion-induced damage led to the formation of nanodots on the GaSb surface, as depicted in figure 2 and figure 3. The nanodot formation indicates the presence of the Ga rich amorphous layer as has been reported in the literature [17][18][19] that results in high contact resistances. Hence, as can be seen in figure 4, the best contact is obtained for an optimum compromise between oxide removal and ion-induced damage.…”

“…The p-type doping concentration was 2×10 19 cm -3 which is a typical concentration for the laser cap layer 11,12 .…”

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).…”