Optical And Electrical Properties Of Silicon-rich Silicon Nitride Thin Films

With the continuous scaling of the COMS technology,the integration level of integrated circuits becomes higher and higher,which will make the signal propagation via metal lines for intra-chip interconnection an unacceptable bottleneck for device performance.An optimum solution is the use of silicon-based optoelectronics to substitute present electrical signals with optical signals.However,Si is intrinsically unable to emit light efficiently due to its indirect bandgap,so the efficient silicon-based light emitting devices have been pursued.Recently,silicon-rich silicon nitride(SiN_x,x＜4/3)has received enormous interest because of its potential applications in optoelectronics devices.Due to its fabrication compatible with COMS technology, strong light emission and lower potential barriers for carriers injection than silicon oxide,SiN_x has been intensively investigated.In this thesis,SiN_x thin films have been grown by Plasma Enhanced Chemical Vapor Deposition(PECVD).The photoluminescence(PL)and electroluminescence (EL)properties of SiN_x have been systematically investigated subsequently.The main results are summarized as follows:(1)Both photoluminescence and electroluminescence of SiN_x thin films come from the electronic transitions of the defect states.With the change of Si concentration the PL peak position shifts,and the lifetime of photoluminescence is on the order of nanoseconds.With the increasing annealing temperature the PL intensity of SiN_x sharply decreases due to the formation of silicon quantum dots,which reduces the silicon dangling bond(radiative recombination centers)density.On the other hand,the EL peak of SiN_x thin film MIS devices(ITO/SiN_x/p-Si/Al)remains at 600nm,which originates from the electronic transitions of E_C→≡Si^-.(2)SiN_x thin film MIS devices have a good rectifying property.At high intensity of electric fields the electrons can be injected into SiN_x via Fowler-Nordheim tunneling and trap assisted tunneling,while at low intensity of electric fields the electrons can be injected via Poole-Frenkel conduction.Long period of electron tunneling causes the devices heat,which will impact seriously on the stability of the devices.(3)NH₃ plasma pretreatment of Si substrate has no effect on the PL intensity and the peak position of SiN_x,but has a great effect on its EL intensity.The EL intensity of the pretreated samples enhances dramatically after annealing at a proper temperature.It is the reducing of the interface state densities by NH₃ plasma pretreatment and subsequent annealing at a proper temperature that resulted in the enhancement of the EL intensity.(4)N₂O plasma post treatment of SiN_x thin film can increase the EL intensity due to the introduction of N atoms to SiN_x to passivate the nonradiative recombination centers.Subsequent annealing causes the atomic rearrangement(breaks off Si-N bond and then produces N=O bond),and leads to the decrease of the EL intensity.(5)Introducing SiO₂ electron accelerating layer to SiN_x thin film MIS devices increases the EL intensity significantly due to the impact ionization processes of the high energy electrons.