光子晶体对nc-Ge/Si岛发光增强的模拟

在Si基集成光电子学的发展中,高效的Si基光源是人们不懈追求的目标。但是Si材料的间接带隙特性导致其发光效率低,更谈不上受激发射。于是人们探索了多种Si基材料体系来提高Si材料的发光效率,并在不同程度上取得了重要的进展。在众多的Si基发光材料体系中,Ge/Si量子点材料,不仅生长工艺与标准的CMOS工艺有很好的兼容性,而且发光波长能够覆盖重要的光通信波段即1.3~1.55μm,因此成为实现Si基发光器件的重要途径之一。但是目前这种材料的发光效率仍很低,所以提高其发光效率自然成为人们关注的焦点。如果将光子晶体引入到nc-Ge/Si材料中,它不仅可以改变材料本身的自发发射特性,而且可以改变发射的光子的提取效率,从而使材料的发光效率得到增强。提出了在Ge/Si量子点材料中引入光子晶体结构来提高其发光效率,包括光子晶体点缺陷腔结构和带边模式工作的完整光子晶体结构,并从理论上分析了发光效率提高的原理。针对发光波长在1.5μm附近的材料结构,模拟出了相应的光子晶体的结构参数。从模拟结果可以看出,对于缺陷腔的光子晶体结构,采用单点缺陷微腔很好地实现了单模运作,但是微腔内有源材料的体积很小,因此得到的发光效率很低。而采用耦合缺陷腔的结构和H₂腔都增加了腔内有源区的体积。但是耦合腔与H₂腔相比,谐振腔模减少,主谐振模式的峰值强度增加,更容易实现单模发光。因而更适用于提高nc-Ge/Si的发光效率。而带边模式工作的光子晶体结构,尺寸较大,不需引入缺陷,工艺上更容易实现。

Theoretical Simulation of Enhanced Luminescence from nc-Ge/Si Islands by Photonic Crystal

In the development of silicon-based integrated optoelectronics,high efficient silicon-based light source is always the desired goal,however,the emission efficiency of silicon is very poor due to its indirect bandgap,saying nothing of stimulated emission.Then,many kinds of silicon-based materials system are explored to improve the emission efficiency of silicon, several important progresses have been made.Among the numerous silicon-based emission system,Ge/Si quantum dots is one of the approaches realizing siliconbased light-emitting devices due to its compatibility with standard CMOS processing and its wavelength covering the optical communication waveband,i.e,1.3~1.55μm.However,the emission efficiency of this material is very low,more and more attention is paid to improve its emission efficiency.If a photonic crystal is introduced into the nc-Ge/Si material,not only the spontaneous emission of this material but also the extraction efficiency of photons can be changed, resulting in a greatly enhanced emission efficiency.In this paper,two types of photonic crystal structures including point defect cavity and band-edge perfect photonic crystal are introduced to the Ge/Si quantum dots to enhance its efficiency,and the principle of the emission enhancement is analyzed from(theory.) For the 1.5 μm wavelength material,some structure parameters of photonic crystal are obtained.It can be seen from the simulated results that single point defect cavity can achieve single-mode operation very well,but the volume of active material within this kind of cavity is very small,the emission efficiency is very low,too.Coupled defect cavity and H₂ cavity can increase the volume of active material included in the cavity.Moreover,comparing to H₂ cavity,the number of resonant cavity modes reduces and the peak intensity of main mode increases for coupled defect cavity,which is more apt to improve the emission efficiency of Ge/Si(quantum) dots.Band-edge photonic crystal is more easily fabricated because its size is large and no defects are introduced.