Study Of The Formation Of Double Layer Atomic Steps On On-Axis Si(001)Surfaces

Silicon-based optoelectronic technology can combine the advantages of high bandwidth,low power consumption and high speed of photonic technology with the mature processing technology of microelectronics to realize photoelectric integration,which has the advantages of low cost,high integration degree and high reliability.At present,the Si based photodetectors,silicon-based optical modulator and Si based optical waveguide have been successfully applied,but there are still some shortcomings in silicon-based lasers.Although there are commercial silicon-based optoelectronic integrated chips based on wafer bonding technology,wafer bonding has some problems such as high cost and cannot be produced on a large scale.The technology of silicon-based direct epitaxy III-V semiconductor materials can maximize the use of mature microelectronic processing technology to achieve low-cost and large-scale production.GaAs is one of the most commonly used III-V semiconductor materials.However,there are differences in lattice constant,thermal expansion coefficient and polarity between Si and GaAs.The growth of GaAs material with polar zinc blende structure on Si(001)substrates with non-polar diamond structure leads to the formation of antiphase boundary(APB)defects.The traditional methods to solve the problem of reverse domain usually use off-axis Si(001)substrates tilted by 4°?6° towards[110]direction or Si(211)plane as substrate to suppress APBs.However,these methods are not compatible with CMOS technology which uses on-axis Si(001)as substrate.In order to solve the problem of APBs,people have made unremitting efforts.The researchers found that APBs can be suppressed by annealing Si substrate at high temperature,which is low cost and simple.Several growth techniques without reverse domain epitaxial have been proposed for this method.However,there are still many problems in the current technique of APBs suppressing,such as the high annealing temperature and the need for intermediate buffer layer(GaP,Si,AlGaAs).The high annealing temperature may destroy the structure of microelectronic chips,it also has a negative impact on the integration of microelectronics and optoelectronics,which puts forward higher requirements for industrial production equipment that leads to the increasing of production cost.Adding buffer layers makes the process become complex,for example,the growth of Si buffer layer needs a specific growth chamber.The fundamental reason for the formation of APBs is the single-layer atomic steps on the surface of Si(001).If the single-layer atomic step phase on Si(001)surface is transformed into double-layer atomic step phase,APBs can be eliminated fundamentally.Therefore,it is urgent to study the formation of double-layer atomic step phase on the surface of on-axis Si(001)and optimize the growth process with APB-free.In this paper,theoretical calculation and experimental study on the formation of double-layer atomic step phase on on-axis Si(001)surface have been carried out.First,the thermodynamic stability of different Si(001)surface step phase structures in different gas environments is calculated with the using of first principles.Then,APB-free GaAs on on-axis Si(001)epitaxial sample was obtained by experiments.The main research contents and achievements are as follows:(1)Firstly,the models of on-axis Si(001)with different step structures are established,and then the surface energy of different step phase structures is analyzed and compared by first principles method.It can be seen that the energy of SA step is the lowest under the vacuum environment,and the energy of double-layer atomic step phase(DA and DB)is higher than that of single-layer atomic step phase(SA and SB).From the aspect of thermodynamics single-layer atomic steps can not spontaneously form double-layer atomic steps under the vacuum environment.Under the H2 environment,when the chemical potential of H is greater than-3.2 eV,the energy of double-layer atomic steps DB is the lowest,which is most conducive to the formation of double-layer atomic step phase on on-axis Si(001)surfaces.Under the AsH₃ environment,when the As chemical potential is greater than-5ev,SB,DA and DB steps have the lowest surface energy,nearly the same value.The surface phase transition does not tend to form double-layer atomic steps under the AsH₃ environment,because it has no energy selectivity for SB,DA and DB from the aspects of thermodynamics.From the macroscopic point of view,double-layer atomic steps cannot be dominant on on-axis Si(001)surfaces.The surface energy of different step phase structures on on-axis Si(001)surface under P,Ga,In and Al chemical potentials is calculated respectively.It is concluded that it is not easy to form double-layer atomic step phase on on-axis Si(001)surface under these chemical potentials.(2)The effect of hydrogenated annealing and annealing under the AsH₃ environment on the formation of double-layer atomic step phase on on-axis Si(001)surface was studied by metal-organic chemical vapor deposition(MOCVD)technology.First,by comparing the experimental results of off-axis Si(001)substrates tilted by 4° towards[110]direction and nominal on-axis Si(001)substrates annealed under the AsH₃ environment,our simulation analysis is verified that there is no energy selectivity for the single-layer atomic step phase and double-layer atomic step phase on on-axis Si(001)surface under the AsH₃ environment,and the conversion between single-layer atomic step phase and double-layer atomic step phase can not be realized.Then,the effect of annealing temperature on APB density of GaAs epitaxial on on-axis Si(001)substrate in H2 environment was investigated.The experimental results are explained in terms of kinetics and thermodynamics.Finally,the best annealing conditions were obtained:H2 environment,pressure 800 mbar,temperature 800?,annealing time 10 min.Under this annealing condition,double-layer atomic step phase is formed on on-axis Si(001)surfaces.