Hpht Synthesis And Impurities Research Of Boron And Nitrogen Co-doped Diamonds

As the development of artificial diamond technology,people began to obtain doped diamond with corresponding properties by doping.Boron doping is the most typical one among many kinds of synthetic diamond doped with different elements.As the boron impurity in diamond is a kind of shallow level acceptor with an ionization energy of 0.37ev,boron doped diamond is a kind of p-type semiconductor superhard material,which has great research value and market potential in the fields of high temperature,high frequency and high power electronic devices,and has been paid attention by researchers for a long time.However,up to now,there are still some limitations in the application of diamond in the field of semiconductor.The main reason is the lack of n-type semiconductor.As we know,boron is the third main group element,as a shallow level acceptor,it absorbs a valence electron of carbon atom,thus producing holes,so boron doped diamond is a p-type semiconductor.Unfortunately,nitrogen,the most common impurity element in diamond,is a kind of deep level donor,whose ionization energy is 1.7eV,which can not provide free electrons at room temperature.In addition,P and S have been also proved deep level donors.After a large number of experiments by researchers,it is almost impossible to get an ideal n-type semiconductor diamond with single element doping.Therefore,the fabrication of n-type semiconductor diamond materials is expected to be co-doping.In recent years,the preparation of synthetic co-doped diamond has attracted much attention.Some of the B-H and B-O complex impurities show the properties of shallow level donors in experiments.However,this n-type conductivity is not stable and occurs on the diamond surface.In addition to the above two complex impurities,B-N complex impurities are also considered to be a shallow level donor after calculation.Moreover,boron and nitrogen impurities have high solubility in diamond,thus the property change caused by boron nitrogen complex impurities will not be limited to the surface of diamond.Therefore,it is necessary to study and understand the interaction between boron and nitrogen impurities in diamond.In this paper,we have compared the doping effect of two kinds of boron source.According to the different characteristics of metal catalyst,nitrogen rich boron doped diamond single crystal was synthesized by using NiMnCo catalyst and boron nitrogen co-doped diamond single crystal with high boron content was synthesized by using FeNi.The high temperature and high pressure annealing of nitrogen rich boron doped diamond was studied.We have observed in detail the changes of impurities and optical and electrical properties of the crystals,the innovative results are as follow:1.We found that the growth rate of diamond increases with the increase of boron content.When the boron additive of the system reaches 20 wt.%,the diamond crystal with high quality can still be synthesized,but its Raman spectrum does not show a peak of500cm^-1.When the content of amorphous boron reaches 4wt.%,the Raman spectrum of synthesized diamond shows a peak of 500cm^-1.The peak at 500cm^-1is considered to be related to the boron impurity pair,which is a sign of the heavy doping of boron doped diamond.We find that amorphous boron has better doping effect than crystal boron.2.Boron/nitrogen co-doped diamond single crystal with high boron concentration were synthesized by using FeNi catalyst.The infrared spectrum shows that with the incorporation of nitrogen impurity,the photoionization spectrum of boron doped diamond weakens,which indicates that the concentration of neutral boron impurity in diamond decreases.The reason lies in the compensation of nitrogen to boron and the inhibition of boron entering diamond lattice.Boron/nitrogen co-doped diamond has higher mobility than boron doped diamond,which may be related to the decrease of the acceptor concentration.3.Nitrogen rich boron doped diamond single crystal with relatively high nitrogen content was synthesized in NiMnCo catalyst alloy.With the introduction of boron impurity,the concentration of C-center and total nitrogen in nitrogen rich diamond decreased obviously,and the absorption peak of A-center gradually weakened to disappear.On the contrary,the concentration of N⁺?isolated nitrogen with positive charge?increased obviously,which indicated that the compensation effect of N and B occurred in the crystal.The carrier mobility of the crystal decreases with the increase of boron doping,which is related to a large number of N⁺scattering centers in diamond.4.The nitrogen-rich boron-doped diamond synthesized by NiMnCo catalyst was annealed at high temperature and high pressure.The high temperature increased the movement of impurities in the diamond lattice,enhanced the compensation effect of nitrogen and boron,and produced more N⁺impurities.The Raman spectrum shows that the width of diamond peak becomes narrow after annealing,which indicates that the crystal has better crystallinity.5.PL spectra of nitrogen-rich boron-doped diamond before and after annealing were measured at room temperature.The“band-A”near 483.3nm was found in the 325nm excitation PL spectrum when the boron additive of system reached 5 wt.%.The PL spectra of 532 nm excitation show that the incorporation of boron impurities gradually reduces the luminesence intensity of NV^-color center.After annealing,PL spectra show that a large number of Ni-N and Co-N related optical centers are produced in the process of annealing,even at room temperature,there are still strong zero phonon lines.The correlation optical centers of Ni-N and Co-N in boron-doped nitrogen-rich diamond are greatly reduced to disappear as boron increases.The N⁺impurities in diamond do not participate in the formation of Ni-N and Co-N.