| With the innovation and development of Internet technology,the exchange of information has reached an unprecedented level.At the same time,they also drive the rapid development of storage technology.Higher demands for storage are put forward by all walks of life.In order to meet the different requirements of various systems,the development of new-type memory with large capacity,high speed,and low power consumption has become one of the focuses of current scientific research.Phase-change random access memory(PCRAM)has been widely used in the field of storage due to its advantages of high integration,high read-write speed,low working voltage,and low power consumption.Phase-change materials are the core of PCRAM,mainly including GeSb,SbTe,GeTeAsSi,GeBiTe,GeTeAs,AsSbTe,and GeSbTe.Among various phase-change materials,Ge-Sb-Te family is the most widely used materials.In particular,Ge2Sb2Te5 has been considered as the most outstanding one for PCRAM application.However,the major shortcoming of Ge2Sb2Te5 is the relatively short data retention time because of its low crystallization temperature.In comparison with the commonly researched Ge2Sb2Te5,GeTe binary compound alloy has also been intensely exploited for PCRAM application because of its simple composition and excellent phase-change performances including higher crystallization temperature,longer data retention time,and better amorphous stability.In order to further accelerate the practical application of GeTe phase-change materials,it is necessary to conduct effective and effective research on the controllable preparation,growth mechanism,and related structural properties of GeTe phase-change materials.In this dissertation,GeTe thin films and GeTe nanowires were studied from the aspects of preparation method,structure,and properties,in order to provide the experimental reference to the preparation of GeTe phase-change materials with higher quality,higher storage density,and lower power consumption,also in order to provide better phase-change materials for the next generation of non-volatile phase-change memories.The specific contents of the dissertation were as follows:Firstly,high quality GeTe phase-change films were prepared on Si substrates by pulsed laser deposition(PLD).The controlled annealing temperature was between 225℃-375℃,and its structure and optical properties were analyzed.X-ray diffraction(XRD)measurements revealed that the GeTe films deposited at room temperature were amorphous,and the crystallization temperature of the films was about 250℃.With the increase of annealing temperature,the 2θ position of(202)peaks shifted to the low angle direction,and the(202)lattice plane distance increased gradually,which may be related to the large compressive stress in the crystallized films.Optical reflectivity measurements revealed that the GeTe films possessed a high reflectivity contrast between the crystalline and amorphous states.The above results suggest that the PLD deposited GeTe films have a good potential for application in optical date storage.Then,considering that one-dimensional nanowire phase-change materials were beneficial to the decrease of device power consumption and the increase of storage density,growth of diameter-controlled GeTe phase-change nanowires on Si substrates was demonstrated by a Au catalyst-assisted chemical vapor deposition(CVD)technique.Besides Au catalyst size,GeTe source powder amount,an uncommon growth parameter,was also employed to control the diameter of GeTe nanowires.The diameter of GeTe nano wires showed an obvious increase with the increase of both Au catalyst size and GeTe powder amount.The measured average diameters of GeTe nanowires were 150 nm,230 nm,and 270 nm when Au catalyst sizes are 5 nm,20 nm,and 60 nm,respectively.The measured average diameters of GeTe nanowires were 160 nm,230 nm,and 280 nm when the amounts of GeTe source powders are 0.01 g,0.10g,and 1.00 g,respectively.Therefore,the diameters of GeTe nanowires can be tunable in a wide range of 150 nm to 280 nm by effectively controlling the Au nanoparticle size and GeTe powder amount.Based on the vapour-liquid-solid(VLS)growth model and Gibbs-Thomson effect,the effects of the Au nanoparticle size and GeTe powder amount on the diameter of GeTe nanowires were also revealed in terms of supersaturation detailedly.The preparation of diameter-controlled GeTe nanowires lays a material foundation for their size-dependent storage performance research and low-power and high-density storage application. |
