Control of microstructures of silicon nanocrystals by ion implantation and their application for optical devices.

Si离子注入SiO_2以及随后的高温退火热处理可诱导形成嵌入发光的Si纳米晶。研究了快速热退火(RTA)增强发光(PL)和诱导低温形成发光Si纳米晶的潜力。采用硅离子注入技术合成了含过饱和硅的SiO_2样品。注入的样品只被快速退火几分钟。之后，在此之前的一些情况下，使用传统的炉子对样品进行几个小时的退火热处理，以诱导硅的析出。在不同的退火过程中测量了发光光谱。在常规的炉退火之前，用RTA可以强烈地增强发光强度。然而，当RTA经过常规的炉退火后，发光强度降低。研究发现，热处理顺序是影响发光强度的重要因素。对于低剂量的样品，增强也是典型的。此外，还发现，即使在低于1000℃的温度下进行退火，也能观察到可见的光致发光，只有经过快速热处理的样品才能观察到可见的光致发光。在SiO_2基质中由过饱和形成发光Si纳米晶的过程中，分解、偏析、扩散、成核、聚集、生长和晶化过程显然是重要的。在本研究项目中，我们发现，在常规炉退火之前，快速热退火可以显著提高发光强度，而在常规炉退火后，快速热退火会降低发光强度。此外，在炉内退火之前进行注入后快速热退火是实现低温形成发光硅纳米晶的有效方法。

Si ion implantation into Si0_2 and subsequent high temperature anneals induce the formation of embedded luminescent Si nanocrystals. The potentialities of rapid thermal annealing (RTA) to enhance the photoluminescence (PL) as well as those to induce low temperature formation of luminescent Si nanocrystals have been investigated. Si ion implantation was used to synthesize specimens of Si0_2 containing supersaturated Si. The implanted samples were rapidly annealed only for a few minutes. After that, in some cases before that, the samples were annealed for a few hours using a conventional furnace to induce Si precipitation. PL spectra were measured at various steps of anneal processes. The luminescence intensity is strongly enhanced with RTA prior to a conventional furnace anneal. The luminescence intensity, however, decreases when RTA follows conventional furnace annealing. It is found that the order of heat treatment is an important factor in intensities of the luminescence. Enhancement is also found to be typical for low dose samples. Moreover, the visible photoluminescence is found to be observed even after furnace anneal below 1000 ℃, only for RTA treated samples. In forming the luminescent Si nanocrystals in a Si0_2 matrix from supersaturation, decomposition, segregation, diffusion, nucleation, aggregation, growth and crystallization processes are clearly important. As a result of diffusion limited segregation, a number of small aggregates will be formed and they act as a nucleation point.In the present research project, we have found that the luminescence intensity is strongly enhanced with a rapid thermal anneal prior to a conventional furnace anneal and the luminescence intensity decreases with a rapid thermal annealing after a conventional furnace anneal. Moreover, a post implantation rapid thermal anneal prior to a furnace anneal is effective to achieve low temperature formation of luminescent Si nanocrystals.