DEVELOPMENT OF MULTIPLY PHOTO-ASSISTED MOVPE FOR FABRICATION OF SEMICONDUCTOR BLUE LASER DIODES

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A new multiply photo-assisted MOVPE system suitable for both growth and p-type doping of widegap II-VI compound semiconductors has been developed in this work. Two laser beams, i.e., Ar-ion laser and He-Ne laser, were used as light sources for photo-assistance and optical probing, respectively. Further, in some cases, an Ar ion laser beam was splitted into two beams and they are used for both photo-assistance and optical probing. As for the in-situ optical probing method, so-called RD (reflectance difference) and SPI (surface photo-interference) methods were adopted. With using this MOVPE system, both epitaxial growth and p-type doping processes in MOVPE of ZnSe layrs on GaAs when using DMZn, DMSe, H_2Se and tBNH_2 were investigated, and following results were obtained.First, it has been found that oscillations with monolayr periodicity in both RD and SPI signal traces have been successfully detected for the first time in MOVPE of ZnSe. On the basis of these optical signal traces observed during growth, the surface-structure during growth was found to be greatly dependent on the used source materials and photoirradiation. Further it was found that (1) when using H_2Se as the Se-source, tBNH_2 molecules are selectively adsorbed on the "Zn-terminated" surface and not on the "Se-terminated" surface, while (2) they can be adsorbed on both surfaces when using DMSe as the Se-source.On the basis of these results, both selective nitrogen-doping on "Zn-terminated" surface in ALE growth mode and photo-assisted doping of nitrogen in conventional photo-assisted MOVPE mode were investigated ; it has been found that the ZnSe layrs can be effectively doped with nitrogen in both cases, though thermal annealing is still effective to improve both electrical and optical properties of the epitaxial layrs.