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 H

2

cavity can increase the volume of active material included in the cavity.Moreover

comparing to H

2

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.