Research Of Passivation Property Of A-Si:H And A-SiO_x:H For Silicon Wafer Prepared By HWCVD

The passivation of silicon wafer surface is one of the key technologies to achieve high conversion efficiency for a-Si:H/c-Si heterojunction solar cells.hydrogenated amorphous silicon（a-Si:H）and hydrogenated amorphous silicon sub-oxide（a-SiO_x:H）are normally used as the passivation layers.At present,the key control parameters of the films are still not known enough for the passivation,which made us be puzzled in the process improvement.In this paper,a-Si:H and a-SiO_x:H films with different microstructure and passivation effect were prepared by hot wire chemical vapor deposition（HWCVD）.the microstructure and dielectric function of the films were analyzed by ellipsometry spectrometer,Fourier infrared and Lifetime tester.The main conclusions are as follows:（1）The relationship between high frequency dielectric functionε_1∞and refractive index of a-Si:H network structures isε_1∞=n²_∞,（when k=0）.The higher value of refractive index means a denser microstructure.Combined with the peak fitting analysis of infrared spectrum,it is found that the film microstructure factor R^*(C_SiH2/C_SiH+C_SiH2)has the minimum value when the n_∞value is the largest in each series of samples with different process parameters in the HWCVD deposition process.small value of R^*indicates a low proportion content of SiH₂ in the films,which present a dense network structure.So,the value ofε_∞can be used to character the dense of a-Si:H.（2）By changing the deposition pressure and T_s（substrate temperature）,we found that the process parameters have a linear relationship with the optical band gap E_g and the peak value ofε₂.In the series of samples with deposition pressure,the E_g and peak value ofε₂ decreases linearly with the increase of deposition pressure.And in the series of samples with T_s,the Eg reduces with T_s increases,the value ofε₂ peak increases with T_s increases.It shows that there is a strongly correlated between E_g and the value ofε₂peak.（3）The refractive index n_bulk（632.8nm）reduces with increasing content of Si H₂in a-Si:H film.In this study,the values of the two factors have a linear relationship.（4）The maximum lifetime of the sample with a-SiO_x:H thin film deposited by HWCVD is 2539μs,and the maximum lifetime of the sample with a-Si:H thin film is1154μs,the R^*of these two films is 0.11 and 0.25 respectively,which the value is neither the minimum nor the maximum of the samples in each series.It indicates that the content of SiH₂ is not the smaller the better.,it should be in the suitable range.The above results show a strong regular association in theε₁,ε₂ peak,n_bulk（632.8nm）with the R^*and passivation effect of the two thin films.It can provide effective means to optimize the film materials and deposition process.