Epitaxial Growth of Novel II-VI Semiconductor Alloys for Ultraviolet Optical Devices

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The objective of this research is to establish epitaxial growth technique for novel II-VI semiconductor alloys which is to be applied to the optical devices in ultraviolet region. The results are summarized as follows.1. (Zn, Cd) (S,Se) alloys and a ZnCdSSe-ZnSSe double heterostructure (DH structure) were grown on GaP by gas-source (GS) molecular beam epitaxy (MBE). From the ZnCdSSe active layr of the DH structure photoluminescence peaking at around 3.2eV was observed, which suggests that the band structure was type-I and carriers were confined in the active layr in accordance with band-lineup calculation.2.Since the growth rate in GSMBE was quite slow, MBE using an elemental sulfur was investigated. To overcome the high vapor-pressure of an elemental sulfur, a cracking cell was designed, by which sufficient growth rate could be obtained.3.RHEED observation revealed that when ZnS was directly grown on a GaP (100) substrate by MBE,the growth mode was 3-dimensional and many twins were co … More ntained. It was found by optimization of growth conditions that 3-dimensional growth and twin generation were suppressed by a misoriented GaP substrate and a ZnS buffer layr grown at a high temperature, respectively.4.n-type conduction control in ZnS-based alloys was successfully achieved up to 2x10^<18>cm^<-3> by chlorine doping. However, p-type conduction was not obtained by nitrogen doping, unlike ZnSe-based alloys.5.On the basis of the above results, Au/ZnSSe/ZnCdSSe/ZnSSe : Cl MIS structure was fabricated on a misoriented GaP through ZnS buffer layr. Compared with conventional MIS,the MIS in this study is characterized by the ZnCdSSe quantum well. The well is expected to confine carriers and to enhance emission efficiency. Strong ultraviolet emission at 400nm was obtained by current injection at 77K for the first time.These results strongly suggest high potential of (Zn, Cd) (S,Se) alloys on GaP system for the application to ultraviolet optical devices. Further investigation for the improvement of crystallographic quality may contribute to the realization of devices in the spectral region. Less