Fabrication Of Si Submicron Pattern Substrates And Growth Of Low Dimensional Structures

At present,silicon materials can realize most of the key optoelectronic functional devices,but commercial silicon-based optoelectronic devices compatible with CMOS process have not yet been realized.The core problem is that the indirect band gap physical properties of Si limit the light emission of materials.The low-dimensional structure of Ge Si may circumvent this limitation.However,since the self-assembled quantum dots are indeterminate in nucleation position and the size is not uniform,it will lead to non-uniform broadening of the luminescence peak,thereby reducing the photoelectric performance of the low-dimensional structure.The use of a patterned substrate to grow a low-dimensional structure can control the nucleation position and size of a low-dimensional structure,but obtaining a uniform low-cost pattern substrate and extending a high-quality low-dimensional material on a patterned substrate has been a difficult point of research.In this paper,a method for preparing a high-quality sub-micron pattern substrate is proposed for the above problems.The pattern substrate is prepared by laser interference lithography,dry etch and wet etch.This paper focuses on the optimization of submicron patterned substrates preparation and the growth of low-dimensional Ge Si structures on this substrate.The main work is divided into the following aspects:(1)A method of preparing low cost and high quality silicon submicron patterned substrates is proposed.The method combines laser interference lithography,dry etch and wet etch to prepare patterned substrates.The dry etching product is used as a mask layer for wet etch,which avoids film evaporation and pattern reversal,and simplifies the operation process.Inverted pyramid patterns with a period of 450 nm,a size of 240 nm,and V-shaped grooves with a period of 600 nm and a size of 100 nm was successfully prepared.(2)In order to optimize the growth conditions of Ge Si low-dimensional materials,the laws of epitaxial growth of Si layer and Ge Si layer by gaseous source molecular beam were studied.When the growth temperature is lower than 700 °C,the growth rate of Si layer increases rapidly with the increase of growth temperature.When the growth temperature is higher than 700°C,the Si layer growth rate is substantially unaffected by temperature.When the growth temperature is higher than 700 °C,the growth rate of the Si layer and the Ge Si layer is proportional to the gas flow rate.In the growth temperature range of 650 ° C to 780 ° C,the composition of the Ge Si layer is only affected by the flow ratio of Si2H6 and Ge H4,regardless of the growth temperature and gas flow rate.(3)Using the self-made gaseous source MBE to grow Ge Si quantum dots on the inverted pyramid pattern,the morphology evolution of Ge Si quantum dots with different deposition amounts was studied.In this process,the quantum dots are precisely nucleated in the pattern pits,and there are no quantum dots on the(100)plane region between the pattern pits,and the size of the epitaxial quantum dots is uniform.In addition,Ge Si nanowires were grown in the V-shaped grooves.And theoretically calculated the surface chemical potential on the patterned substrate,giving the theoretical analysis and interpretation of the quantum dot preferential nucleation in the inverted pyramid pit and the preferential growth of the nanowire in the V-shaped groove.(4)Analysis of physical properties of bound excitons in Ge Si low-dimensional materials prepared on a patterned substrate under low temperature conditions.The physical properties of the prepared Ge Si quantum dots and Ge Si nanowires were measured at different temperatures using the PL technique.The zero phonon(NP)peak of the Ge Si nanowire is measured,and the intensity of the luminescence peak is higher than that of the Si substrate.This reflects that under quantum confinement,the luminescence must be weakened by the requirement of phonon assistance.This lays the foundation for the future production of silicon-based laser sources.The luminescence peaks of the quantum dots on the patterned substrate are not collected.The reason may be that the quantum dot density is too low,which is three orders of magnitude smaller than the density of self-assembled quantum dots.Subsequent experiments should strive to increase the density of growing low-dimensional quantum dots.