Cathodoluminescence Study of the Locaal Fluctuation of Band Gaps in AlloySemiconductor Films

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The local fluctuation of the magnitude of the band-gap energy in alloy semiconductor films was studied by cathodoluminescence. The magnitude of band-gap energy of alloy semiconductor film is mainly determined by alloy composition. However, it often fluctuates in a film due to two reasons.One is the fluctuation of alloy composition (DELTAchi) and the other is the local strain due to lattice mismatch(DELTAiota). In the first year of this research, each of these effect was studied independently. The effect of local strain was studied with GaAs/Si films. It was found that the shift of the peak energy of exitonic luminescence of GaAs is very sensitive to the local strain reserved in GaAs layr. The compositional fluctuation was studied with In GaAs/Inp film. The fluctuation of the composition also detected by the peak position of exitonic luminescence. It was concluded that the fluctuation of DELTAchi or DELTAiota was easily detected by the shift of peak positions of luminescence line.In the second year, it was tried to separate DELTAchi from DELTAiota in the films in which these parameters varies spatially. SiGe/Si and In GaAsP/InP films was prepared for this purpose. However, it was difficult to separate DELTAchi from DELTAiota in these specimens due to following reasons.(i)The specimens were not suitable for this purpose, namely DELTAchi >> DELTAiota in the former case, while DELTAchi << DELTAiota in the latter. (ii)The lack of the information of fine structure of the spectra make the separation difficult. Beside this purpose, we found the new luminescent center in GaAsP/InP films which shows metastable behavior against electron beam irradiation. The stability of this center was studied in detail.