The Study Of The Characteristics Of InGaAs Grown On Si Substrates And Thermal Stress Of Silicon-based Laser

Due to the rapid growth of cloud-based application and data centers,the demand for high capacity and compact optical links is significantly increasing.Si-based optoelectronic integrated technology is expected to meet such needs due to its potential prospects for the integration of optoelectronic devices with the mature Si-based microelectronic technology.However,reliable,low-cost,and efficient integrated Si-based light sources for the integration at telecommunication wavelengths of 1550 nm are not yet available.Although wafer-bonding techniques have been extensively investigated for ?-?/Si integration,there are still issues of yield and scalability.The direct epitaxial growth of ?-? materials on Si substrates is considered as one of the most promising methods to provide Si-based lasers for future integration.At present,InP and InGaAs materials are mainly used to achieve the Si-based 1550 nm light source.Direct epitaxy of InP on Si(8%lattice mismatch)usually leads to high density defects.Several strategies such as buffer layer and strained-layer superlattice(SLS)are usually used to reduce dislocation density,which leads to a complicated structure for InP-Si structure lasers and is not suitable for subsequent device preparation and integration.Low-composition InGaAs materials can be utilized to extend the emission wavelength of InAs/(In)GaAs QDs to 1550 nm.The lattice mismatch between the low-composition InGaAs material and Si substrates is small,and the threading dislocations can be reduced by simple methods such as two-step method.In addition,QDs are capable of bending or pinning the threading dislocations because of their large strain field.With such technique,highly efficient and integrated 1550 nm InAs/(In)GaAs QD lasers on Si substrates are expected soon.Therefore,epitaxial growth of InGaAs/Si is an important step towards the achievement for the high-performance long-wavelength Si-based III-V lasers.However,direct epitaxial growths of ?-? materials on Si substrates encounter three major challenges,which are large lattice mismatch,polarity difference,and thermal expansion mismatch,leading to threading dislocations(TDs),antiphase boundaries(APBs),and microthermal cracks,respectively.APBs caused by the difference of polarity can be solved by using offcut substrates or V-groove-patterned substrates.For the problem of TDs,researchers have found various approaches to counter this problem including buffer layer,selective-area growth and two-step method.There are few studies on the stress problems caused by the difference of thermal expansion coefficient.And most of these studies are completed by means of Raman spectroscopy,photoluminescence spectroscopy and XRD.A few theoretical study works are to study the thermal stress of two-layer material structure through simple numerical calculation.There is a lack of studies about the thermal stress distribution in device structure,especially Si-based laser device structures.In fact,stress free is desirable for the heteroepitaxy of the films,since the stress not only affects the quality of thin films due to the formation of cracks,but also deteriorates the performance and lifetime of devices fabricated on the epilayers.In addition,the stress distribution of the device with patterned substrate structure is far different from that of the planar substrate structure.Understanding the thermal stress distribution of patterned substrate structure will help us design the laser device structure.This thesis is focused on the growth of InGaAs on Si substrates by metal organic chemical vapor deposition(MOCVD).At the same time,thermal stress in V-groove-patterned laser array has been studied by finite-element method.The main achievements are listed below.1.Achieved the growth of the InGaAs/Si with low-temperature trinary InxGa1-xAs nucleation layer using low-pressure metalorganic vapor phase epitaxy.The influence of the In composition and the thickness of low-temperature nucleation layer on high-temperature InGaAs epilayer have been studied.The results indicate that with appropriate In composition and optimum thickness of 20 nm,the InGaAs nucleation layer can efficiently release the misfit strain between the high-temperature InGaAs epilayers and substrates and prevent threading and misfit dislocations from propagating to the upper InGaAs epilayer,leading to a high-crystallinity InGaAs/Si.2.Established the structure model of Si-based V-groove-pattened laser array using the finite element method and examine the reliability of the procedure and simulation results.The results show that the simulation results are reliable.3.Studied the thermal stress distribution of Si-based V-groove-patterned laser array structure.The results are futhrer compared with that of Si-based planar structure.The results show that the top of the InGaAs layer and most of the region of the InP cap layer are subjected to compression,which is different from the stress distribution in Si-baesd planar structures.4.Studied the mechanism of the coalesce of the Si-based V-groove-patterned laser array structure on the thermal stress.The results show that the width of InGaAs and InP of the unclalesced laser array are much smaller than that of the substrate,resulting in compressive stress in InGaAs active layer and InP cap layer.5.Studied the mechanism of the parameters of V-groove on the stress distributon of the Si-based V-groove-patterned substrate structure.The effect of V-groove parameters such as the V-groove height,the SiO2 mask height and width on the thermal stress distribution of the Si-based V-groove-patterned substrate structure was investigated.It is found that the height of the V-groove and the SiO2 mask have a great influence on the thermal stress distribution,while the width of the SiO2 mask has little effect on the thermal stress distribution.