Design And Study Of High Speed 850nm Vertical Cavity Surface Emitting Lasers

Vertical-cavity surface-emitting lasers(VCSELs)are widely used in short-reach optical communication links and interconnects,including supercomputer clusters and data centers,because of their low energy consumption,low threshold current,high modulation speed and low fabrication cost.With the development of technologies including mobile internet,streaming media,cloud computing technology,it is urgent to expand the data bandwidth to satisfy the rapid growth of data storage and communications.850 nm is the communication wavelength with low transmission loss,and the epitaxial growth technology of 850 nm VCSEL with high differential gain quantum well structure is mature,hence the 850 nm VCSELs are standard light sources for short-reach optical communication links and interconnects.At present,high speed 850 nm VCSEL with small signal modulation bandwidth above 10 GHz are imported chips.Therefore,it will be improvement for development of high speed VCSEL by studying the physical mechanism of small signal modulation,analysising the limiting factors for high speed performance,and optimizing the design of and the fabrication technology.This dissertation is focused on achieving the high modulation bandwidth of 850 nm of VCSEL and propose a VCSEL with double mesas and coplanar electrode structure,based on the intensive research of the physical mechanism of high-speed modulation and the limitation of high-speed performance.O n the experimental aspect,we fabricated the high speed 850 nm VCSEL and performed static and dynamic characterization tests.The impacts of benzocyclobutene(BCB)planarization technology,mesa etching technique,thermal diffusion of device and oxide aperture diameter on high speed modulation performance of 850 nm VCSEL were analyzed.Small signal modulation bandwidth abo ve 16 GHz was achieved at 5 ?m and 7 ?m oxide aperture diameters.The researches can be summarized as follows:1.The impact of benzocyclobutene planarization technology on high speed modulation performance of 850 nm VCSEL is analyzed.The pad capacitance and parasitic limitation are reduced by using a low-k BCB instead of Si O2 passivation.The pad capacitance calculated using the small signal model is reduced to one-ninth of that for Si O2-passivated VCSELs,and the parasitic cutoff frequency increased from 10.6 GHz to 17.8 GHz.The small signal modulation bandwidth of the low-k BC B planarization VCSELs with a 7 ?m oxide aperture greatly increased compared with the VCSEL with Si O2 passivation,from 9.85 GHz to 15.2 GHz.2.The impacts of wet etching and dry etching on high speed modulation performance is analyzed.Compared to the wet etching process,the oxide capacitance of VCSEL with dry etching is decreased by reduceing the size of oxide layer.The small signal modulation response of the VCSELs fabricated by wet and dry etching process were measured respectively,and the bandwidth of 7 ?m oxide aperture VCSEL with dry etching was increased to 16.1 GHz.3.The impact of thermal diffusion on high speed modulation performance is studied.For the 5 ?m oxide aperture VCSELs with bottom DBR diameter of 34 ?m,38 ?m,42 ?m and 46 ?m,the small signal modulation bandwidth increases with increasing bottom DBR diameter.A small-signal modulation frequency of 16.2 GHz was achieved for the 46 ?m bottom DBR diameter VCSEL with an oxide aperture of 5 ?m.4.The impact of oxide aperture diameter on high speed modulation performance of 850 nm VCSEL is analyzed.Small signal modulation response of the 3 ?m,5 ?m,7 ?m,9 ?m,11 ?m and 13 ?m oxide apertures VCSELs were measured,and the-3d B bandwidth at 5 ?m and 7 ?m oxide aperture diameters exceeded 16 GHz.The D-factor decreases with the increase of oxide aperture from 10.6 GHz/m A1/2 @ 3 ?m to 2.95 GHz/m A1/2 @ 13?m.The results show that the small oxide aperture VCSELs have lower energy consumption,and the large aperture VCSEL could achieve high modulation bandwidth due to the large current injection.