| Semiconductor low-dimensional heterostructures have been the cornerstone for structuring high-performance semiconductor light-emitting devices for a long time.The frontier innovations in this field have lasted for decades,but research hotspots have been transferred from early two-dimensional quantum wells and superlattices to the one-dimensional quantum wires(or more general nanowires)and zero-dimensional quantum dots.In particular,novel semiconductor light-emitting devices based on self-organized quantum dots have received particular attention due to their ease of electrical injection,unique performance such as high temperature stability and important application prospects.However,most quantum dot light-emitting devices such as quantum dot lasers rely on molecular beam epitaxy(MBE)growth technique.The progress of metal-organic chemical vapor deposition(MOCVD)growth of quantum dot lasers is greatly delayed and there is a significant gap between MBE and MOCVD growth technique.Only a few foreign research groups have mastered the core technology of MOCVD growth of quantum dot lasers.In view of the advantages of MOCVD in industrialization of semiconductor devices,it is of great significance to carry out in-depth systematic research on MOCVD growth of quantum dot lasers in China.Then,in addition to the laser,another kind of significant light-emitting device based on semiconductor low-dimensional heterostructures is superluminescent diode.As the light source of the fiber optic gyroscope system,the superluminescent diode plays an irreplaceable role in improving the performance of the system.Therefore,the research of superluminescent diode is of great value for practical applications such as fiber optic gyroscopes.In addition,semiconductor low-dimensional heterostructures contain not only the aforementioned integer dimensionalities,in the recent years,the novel concept of energy level dispersion was proposed by our laboratory and then developed into the theory of fractional dimensionality in electron-states-architectures,that is,there are not only the above-mentioned integer dimensionalities:three-dimensional,two-dimensional,one-dimensional,zero-dimensional,but also exist the fractional dimensionalities between these integer dimensions,for example,between two and three dimensionalities,between one and two dimensionalities,and so on.After the theory of fractional dimensionality was put forward,the founder of the theory found that this theory has the potential to be applied in the performance improvement of superluminescent diodes,and this finding has been confirmed by preliminary experiments,so it is urgent to use the theory of fractional dimensionality in electron-states-architectures to guide the design and performance optimization of the active region of the superluminescent diodes.Based on the above scientific cognition,in order to verify the superiority of the theory of fractional dimensionality in electron-states-architectures in the superluminescent diodes,and then use this theory to guide the design and optimization,we firstly need to carry out the fabrication of corresponding typical integer-dimensional superluminescent diode to master the fabrication process of superluminescent diodes,etc.,so as to lay the foundation for further development of fractional-dimensional superluminescent diodes.This paper takes the low-dimensional heterostructures of semiconductor as the starting point,relies on the international cooperation proj ect of the ministry of science and technology and the national natural science foundation of China,was guided by the original theory of fractional dimensionality,and focused on the expansion of III-V quantum wells and quantum dots.The research work of lasers and superluminescent diodes in integer dimensions such as two-dimensional quantum wells and zero-dimensional quantum dots,which has accumulated technical experience for MOCVD growth quantum dot devices,and also laid the foundation for subsequent fractional dimensionalities(such as from two-dimensional to three-dimensional,from zero-dimensional to three-dimensional)superluminescent diodes and other related devices.The research work and main results of this paper have been carried out as follows:1.The variation of density of electronic states in the case of applying different linetypes(exponential linetype and Lorentz linetype)of divergent state permissibility density functions were investigated.The density of electronic states was calculated and analyzed for the two dispersion functions of exponential linetype and Lorentz linetype,and the curves of of density of electronic states were plotted with different energy level dispersion width values,futhermore,the composite dispersion linetypes in the actual situation were expounded,which provides a support for the further development of the fractional dimensionality theory based on energy level dispersion.2.Lasers and superluminescent diodes based on typical quantum wells were fabricated,including 1.3?m-band InP-based quantum wells and 1.1?m-band GaAs-based InGaAs quantum wells,and we have obtained some important experimental results.The fabricated devices laid the foundation for further fabrication of the fractional-dimensional superluminescent diode between two-dimensional and three-dimensional with better performance.(1)The InGaAsP quantum well layers were used as the active region,and the lasers and superluminescent diodes were fabricated.The threshold current density of the laser with a ridge width of 10?m and a cavity length of 2mm is 0.8kA/cm2,and the superluminescent diode with the same ridge width and length using the bent waveguide has a power of 5.9mW at 350mA and a full width at half maximum(FWHM)of 27nm.(2)The AlGaInAs quantum well layers were used as the active region,and the lasers and superluminescent diodes were fabricated.The threshold current density of the laser with a ridge width of 10?m and a cavity length of 2mm is 460A/cm2,and the superluminescent diode with the same ridge width and length using the bent waveguide has a power more than 30mW,and the FWHM of the spectrum is about 10nm.(3)GaAs-based InGaAs quantum well light-emitting devices was grown and fabricated.The growth of the InGaAs multiple quantum well device structure was carried out by MOCVD,and then the corresponding light-emitting devices were fabricated,and the emission wavelength was around 1.1?m.The threshold current density of laser with a ridge width of 10?m and a cavity length of 2mm was 450A/cm2.In the fabrication of superluminescent devices,we compared the effects of different waveguide shapes(bent,tilted,etc.)on superluminescent diode.The superluminescent diode power of the curved waveguide with a ridge width of 10?m and a length of 2mm is more than 20mW and the FMWHM is around 10nm.3.Lasers and superluminescent diodes based on typical quantum dots were fabricated,and in-depth exploration as well as important progress in optimization of device performance was made,which provided technical support for further fabrication of fractional-dimensional superluminescent diodes between zero-dimensional and three-dimensional.And high-quality multi-layer quantum dots have been grown on the silicon substrate,which lays a foundation for the subsequent use of MOCVD to grow fractional?dimensional devices on silicon substrates.(1)Ga As-based In As quantum dot lasers were grown and fabricated by MOCVD.Firstly,the growth conditions of IrnAs quantum dots were optimized.The effects of single layer/multilayer,InGaAs underlayer/capping layer,?/? on quantum dots were compared.Using the optimized growth conditions,multi-layer quantum dots photoluminescence wavelength closed to 1.3?m were grown,the density was up to 4 × 1010/cm2,then the multi-layer quantum dots were used as active regions of the laser structure and quantum dot lasers were fabricated.We achieved quantum dot lasers that can operate at room temperature under continuous current on both exact and 2° miscut substrates.The lasers have a ridge width of 10?m and a cavity length of 2mm.Due to the excited state lasing,the lasing wavelength of the quantum dot lasers is shorter than 1.3 ?m.The threshold current density of the laser on the exact substrate is 700A/cm2 and the lasing wavelength is 1.19?m;the threshold current density of the laser on the 20° miscut substrate is 950A/cm2 and the lasing wavelength is 1.16?m.(2)Based on MBE technology,we utilized two diferent epitaxial structures of InAs/GaAs quantum dots to fabricate lasers and superluminescent diodes.The lasing wavelength of the laser based on first epitaxial structure was 1.3?m,the threshold current density was as low as 117A/cm2.The superluminescent diode with bent waveguide operated under pulse condition with an emitting wavelength around 1.3?m,a spectral width of above 20nm and an output power above 10mW.The lasing wavelength of the laser based on second epitaxial structure was 1.27?m,the threshold current density was as low as 118/cm2.The superluminescent diode with anti-reflection coating and straight waveguide operated at room temperature under continuous current with an emitting wavelength around 1.27?m,a spectral width of about lOnm an output power above 3mW.(3)InAs/GaAs quantum dot multilayers on the Si substrate were grown.Based on the high-quality Si-based GaAs epitaxial layer,the growth of multilayer quantum dots on Si was optimized by MOCVD equipment.The GaAs/Si "three-step" epitaxial growth technique was combined with the GaAs-based quantum dot multilayer growth technique to grow Si-based hetero quantum dots multilayers with an emission wavelength of 1.3?m,The dots have a good morphology and high density up to 5 X 1010/cm2,which was found by atomic force microscopy,and a good luminescence performance measured by photoluminescence spectrograph. |
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