Laser-Assisted Growth and Analysis of Crystalline Organic Semiconductor Multiple Layer Structures for Optoelectronic Applications

最近，研究人员已经证明，由两个结晶有机半导体的非常薄(10A)交替的层组成的多量子阱结构可以通过有机分子束外延(OMBE)的超高真空新工艺生长。X射线和双折射数据表明，这些结构在堆叠方向上以及在水面上都是高度有序的。因此，这种生长被认为是“准外延”的，因为这种有序性即使在两个有机晶格材料不相称。晶体织构的控制受到分子表面迁移率对温度的依赖关系的强烈影响。例如，在拟议的工作中，对于冷却到低于100K的衬底，观察到最高的结晶有序度，研究人员将使用激光和他们的OMBE系统在生长过程中对冷却的衬底进行局部加热，从而创造出高度限定的有序和无序生长区域。这种对两层顺序的精细控制，以及已经证明的生长非常薄的薄膜的能力，应该允许他们理解，从而在很大程度上控制生长过程。这种控制将被用来制造几种光学器件，如光栅和波导。此外，通过制造由非常薄(10A)、深层(100周期)的多层堆叠组成的结构，它们或许能够打破晶体半导体的中心对称性特征。反过来，它们应该会导致显著的二阶非线性光学响应。因此，它们将生长这种结构，并使用与激光相同的激光系统来探测它们的线性和非线性光学性质。辅助性生长实验。

Recently, the investigators have demonstrated that multiple quantum well structures consisting of very thin (10A) alternating layers of two crystalline organic semiconductors can be grown by the new ultrahigh vacuum process of organic molecular beam epitaxy (OMBE). X-ray and birefringence data indicate that the structures are highly ordered both in the stacking direction, as well as across the water surface. Thus, the growth is considered to be "quasi-epitaxial" in that this ordering occurs even though the lattices of the two organic materials are incommensurate. Control of the crystalline texture is strongly influenced by the dependence of molecular surface mobility on temperature. For example, the highest degree of crystalline ordering is observed for substrates cooled to less than 100 K. In the proposed work, the investigator will use a laser in conjunction with their OMBE system to locally heat the cooled substrate during growth, thus creating highly defined regions of both ordered and disordered growth. This fine control of both layer order, as well as the already demonstrated ability to grow very thin films, should allow them to understand, and hence control the growth processes to a high degree. This control will be utilized to fabricate several optical devices such as gratings and waveguides. Futhermore, by making structures consisting of very thin ( 10 A), deeply layered ( 100 period) multi-layered stacks, they may be able to break the centrosymmetry characteristic of crystalline semiconductors. They, in turn, should lead to a significant second-order non-linear optical response. Thus, they will grow such structures and probe their linear and non-linear optical properties using the same laser system employed for the laser- assisted growth experiments.