MATERIALIZATION OF ANISOTROPIC CRYSTALLINE SEMICONDUCTORS

点击翻译按钮获取中文摘要

A new semiconductor has been proposed which is featured by showing both the amorphous-like and the single-crystal-like properties. It was materialized and characterized to show new properties. The proposed semiconducting materials are constructed either artificially or naturally so that chemical composition is disordered but physical alignment is sufficiently ordered for epitaxial growth to be possible. Therefore, the semiconductor can be called a anisotropic or disoreded crystalline semiconductor. A disordered superlattice (d-SL) is an example of the anisotropic crystalline semiconductors and possesses disordering along the growth direction and ordering on the surface perpendicular to the growth direction.In this study, the d-SLs were fabricated with AlAs/GaAs. They exhibit the following new properties. (1) Photoluminescence (PL) intensities from the d-SLs are at least 500 times stronger than those from the ordered superlattices (o-SLs) and the bulk alloy (b-AL) at 77K.(2) Non-phonon luminescence is observed from the d-SLs, whereas phonon-assisted luminescence is observed from the o-SLs and the b-AL due to their indirect-band gap structure. (3) Lumine-scence peak of the d-SLs is red-shifted from that of the o-SLs and the b-ALs. (4) PL lifetime of the d-SLs is slower than that of the direct-transition alloy of AlGaAs, but faster than that of the o-SLs and the b-AL.These results show that artificial disordering enhances luminescent capability of semiconductors. This is interprted by the carrier localization effects which create efficient radiative recombination centers.Ths disordering effects can be applied to other indirect-transition semiconductor systems such as AlP/GaP and SiGe/Si. We can expect enhanced luminescence from these indirect-transition semiconductors. The intial stage of research has been already started.