Patterns On Silicon Substrates, Silicon-germanium Quantum Dot Growth

A new scalable approach has been developed for fabricating large-scale pit patterns with controllable periodicity on Si substrates.The fabrication processes start with self-assembling a monolayer of polystyrene(PS) spheres(diameter:1.6 um-100 nm) on hydrogenated Si(001) substrates.A novel net-like mask in combination of the Au pattern thermally evaporated in between the PS spheres and the Au-catalyzed SiO₂ around them is naturally formed.After selective etching of Si by KOH solution, two-dimensionally ordered pits with a periodicity equal to the diameter of the PS spheres in the range from micrometers to less than 100 nm can be obtained.The shape of the pits can be modulated by controlling the chemical etching time.Such pit-patterned Si substrates facilitate the formation of ordered GeSi quantum dot by deposition of Ge using molecular beam epitaxy(MBE).Statistical information on GeSi islands grown on two-dimensionally pit-patterned Si substrates at different temperatures is presented.Three growth regimes on patterned substrates are identified:(ⅰ) kinetically limited growth at low growth temperatures,(ⅱ) ordered island growth in an intermediate temperature range,and(ⅲ) stochastic island growth within pits at high temperatures.A qualitative model based on growth kinetics is proposed to explain these phenomena.It can serve as a guidance to realize optimum growth conditions for ordered islands on patterned substrates.