ZnSe-ZnS应变超晶格的Raman散射

本文报导了Znse—ZnS应变超晶格的Raman光学声子谱.我们观测到,随着应变大小的改变,ZnSe和ZnS的纵向光学声子发生频移.ZnSe层中纵向光学声子可发生较大的蓝移,也可发生较小的红移;ZnS层中的纵向光学声子发生较大的红移.这些现象为“应变场下的光学模理论”所解释.文中还报导了在波数为110cm-1处观测到一很强的散射峰,并把它归结为超晶格表面层单斜Se所引起的散射;在其它地方还观测到非晶态Se、三角Se引起的散射峰.

RAMAN SPECTRA OF ZnSe-ZnS STRAINED LAYER SUPERLATTICES ON CaF2 AND GaAs SUBSTRATES

Raman backscattering techniques have been used to measure the phonon spectra of ZnSe-ZnS strained layer superlattices (SLSs) on CaF2 (111) and GaAs (100) substrates grown by atmospheric pressure metal-organic chemical vapor deposition. CaF2 is a transparent substrate for visible region, and is a good substrate for Raman scattering measurement.In part 1 of the paper, we briefly review the development of Raman scattering of semiconductor superlattices. In part 3, we describe the Cerdirs’s theories2] about the calculation of the frequency of longitudinal optical (LO) phonons and transverse optical (TO) phonons of ZnSe and ZnS layers which are under biaxial stress. With Eq.1, we can calculate the frequencies of LO phonons if the effective spring constants p and q are known. In part 3, it can be observed that the energy of ZnS LO phonon in ZnSe-ZnS SLS on CaF2 is 23cm-1 which is lower than that in bulk ZnS, and the peak is very sharp with dominant strength while the peak of ZnSe LO phonons is very weak in Raman spectra of ZnSe-ZnS SLS on CaF2 (111), shown in Fig.4. In Raman spectra of ZnSc-ZnS SLS on GaAs (100) shown in Fig.3, we found that energy of ZnSe LO phonons in SLS is 35cm-1 which is larger than that in bulk ZnSe, and there is a peak with wave number of 110cm-1. We think that the 110cm-1 peak results from Raman scattering of amorphous Se in the surface of ZnSe-ZnS SLS. In conclusion, the energy of LO phonon of a semiconductor material under biaxial compressive strain will shift towards the blue, while the energy of the LO phonons of a semiconductor material under biaxial expanded strain will shift towards the red. Our experiment spectra agree with the Cerdira’s theories in principle.