MATERIALIZATION OF ANISOTROPIC CRYSTALLINE SEMICONDUCTORS

提出了一种具有非晶性和单晶性的新型半导体。它被物化和表征，显示出新的性质。所提出的半导体材料是人工或自然构造的，因此化学成分是无序的，但物理排列是足够有序的，可以实现外延生长。因此，半导体可称为各向异性或无序晶体半导体。无序超晶格（d-SL）是各向异性晶体半导体的一个例子，它具有沿生长方向的无序性和垂直于生长方向表面的有序性。本研究采用AlAs/GaAs制备d-SLs。它们表现出以下新特性。(1)在77K时，d-SLs的光致发光强度至少是有序超晶格（o-SLs）和块状合金（b-AL）的500倍。(2) d-SLs具有非声子发光，而o-SLs和b-AL由于其间接带隙结构而具有声子辅助发光。(3) d-SLs的发光峰与o-SLs和b-ALs的发光峰发生了红移。(4) d-SLs的PL寿命比AlGaAs直接过渡合金慢，但比o-SLs和b-AL快。这些结果表明，人为的无序化提高了半导体的发光性能。这可以用载流子局域化效应来解释，它产生了有效的辐射复合中心。这种无序效应可以应用于其他间接跃迁半导体体系，如AlP/GaP和SiGe/Si。我们可以期待这些间接跃迁半导体的发光增强。初步研究阶段已经开始。

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.