Study On The Growth And Properties Of Diamond Thin Films And Related Heterojunction

Diamond is widely recognized as the ultimate semiconductor for high power devices,radiation detectors and UV solar-blind detectors due to its superior physical properties like wide bandgap,high carrier mobility and extreme breakdown field.On the other hand,with the rapid development of quantum control technologies,solid-state single photon source based on diamond nitrogen-vacancy(NV)color center,due to its good stability at room temperature,longer decoherence time,and readable state of quantum state,has become a research hotspot in the fields of solid-state quantum information.Especially,when combined it with optical microcavity or other high quality factor semiconductor micro/nano structure,quantum key distribution system with higher quality can be constructed.At the same time,the p-type diamond film is combined with other n-type wide bandgap semiconductors to form a heterogeneous pn junction,which has high research value in the field of high temperature and high power electronic devices.This thesis is mainly based on experimental fabrication,supplemented by the first-principles calculation method based on density functional theory.The effects of different growth parameters on the epitaxial quality of diamond films,nitrogen and oxygen-nitrogen impurities on the regulation of diamond NV center are studied.We have also investigated the preparation and characterization of large-size ZnO-based nanodiamonds and electrical and optical properties of ZnO/CNT core-shell nanostructures.The main research accomplishments are included as follows:1.High-quality diamond films were successfully synthesized by microwave plasma chemical vapor deposition.A variety of material characterization methods were used to analyze the effects of different methane concentrations,different microwave powers and oxygen on the quality of diamond films.The results show that the increase of methane concentration leads to an increase in the deposition rate of diamond film,while the quality of the film decreases.Meanwhile,the growth crystal orientation of the diamond film also changes significantly.The increase of the microwave output power is beneficial to the increasing deposition rate of the diamond film,and the film quality is also slightly improved.In addition,adding a certain amount of oxygen during the deposition is also beneficial to the quality improvement of the diamond film.2.High-quality homo-epitaxial diamond films were successfully synthesized.The effect of boron and nitrogen doping on the growth rate,growth quality and surface morphology of diamond films were also studied.The results show that low concentration of methane is beneficial to the formation of'high-quality single crystal diamond.High concentration of boron inhibits the growth of diamond film,and etching pits related to boron plasma appear on diamond surface.The N-induced increase in the growth rate is caused by the effective activation of the surface by enhancing H desorption.With the increase of nitrogen concentration,the width of surface "step" gradually decreases.3.The effects of nitrogen on the regulation of near-surface NV center in diamond films were investigated.The results show that the intensity of NV centers is the net result of the competition between the increasing PL intensity caused by the formation of NV centers and the quenching PL intensity induced by the degradation of crystalline quality of the as-grown diamond films with higher nitrogen contents.The increase of nitrogen concentration is benifical to the enhancement of the luminescence intensity of diamond NV centers.Meanwhile,it also leads to the obvious aggregation phenomenon of the distribution of NV centers.The rapid galvanometer confocal test system shows that the luminescence region of diamond NV color center is mainly concentrated near the "step" where it grows,and the luminescence intensity reaches the peak at the edge of the "step".4.Aiming at the luminescence aggregation phenomenon of diamond NV centers caused by the higher concentration of nitrogen,the regulation role of oxygen on diamond NV centers was studied.The results show that the introduction of oxygen into diamond lattice can efficiently regulate the luminous intensity and distribution of diamond NV centers.The lower oxygen concentration can improve the quality and promote the formation of diamond NV centers.However,under the condition of higher oxygen concentration,the quality of diamond thin films decreases significantly.The "small steps" formed by the catalytic role of nitrogen are firstly etched by oxygen,resulting in a reduced luminescence intensity and a more discrete distribution of NV color center.The first-principles calculation results indicate that oxygen exists mainly in the form of interstitial or substitutional atoms in the diamond NV center system.With oxygen concentration increasing,the formation energy decreases first and then increases.The effects of oxygen concentration on the formation of diamond NV center are explained from the microscopic atomic point of view.The proposed method combined further with electron beam lithography technique may provide an alternative platform for designing a range of stable,room-temperature single photon source with controllably intensity and spatial distribution.5.The heterojunction device made up of p-type diamond and n-type ZnO is an ideal electric injection device,and the high thermal conducitivity of diamond can provide a feasible solution to the self-heating problem of wide bandgap semiconductors(such as ZnO).For the strong etching effect of hydrogen plasma on the ZnO substrate during the growth of diamond film,a two-step growth method was proposed.We first insert a thin silicon buffer layer on the ZnO substrate and then start to the growth of nanodiamond film.Studies have shown that the inserted silicon buffer layer can effectively alleviate the etching effect of hydrogen plasma during the growth of diamond film,and silicon film will first form a thin SiC layer in the H2/CH4 plasma,which in turn acts as a nucleation layer of subsequent nano-diamond films.This study can provide a feasible technical reference for the subsequent growth and device fabrication of large-size ZnO or GaN-based diamond heterojunctions.6.For the photoelectric performance of ZnO and carbon-based heterojunction device,the electrical and optical properties of the one-dimensional(1D)ZnO@CNT core-shell nanostructure were studied by using the first-principles calculation method based on density functional theory.Metal-and semiconductor-type CNT and ZnO core-shell nanostructure systems were constructed.The stability and electrical performance of metal CNT@ZnO core-shell structure were analyzed with different CNT size and applied strains.It is found that the ZnO nanowire encapsulated in(9,9)-CNT is the most stable structure from the view of formation energy.The interaction between the inner ZnO nanowire and the outer(9,9)CNT belongs to a weak van der Waals type.The complex structure is found to possess metallicity for the outer(9,9)CNT and maintain the wide band gap nature for the inner ZnO nanowire.Under the different external strains,the charge redistribution between inner ZnO nanowire and outer CNT caused by electron tunneling leads to the shift of Dirac point and the band narrowing of inner ZnO nanowire.A specific insulator-to-semiconductor transition occurs for the inner ZnO nanowire in the complex structure.This research can provide some inspiring ideas for the application of future nanodevices and designing new types of functional nanodevices.