Influence Mechanism Of Nitrogen Impurity And Radiation Damage On Thermal Conductivity Of Diamond Wafer

Among the currently known materials,diamond has the highest thermal conductivity and hardness.It is considered an ideal substrate heat dissipation material and has broad application prospects in the field of high-temperature and high-power devices.In the process of preparing high-quality diamond films,nitrogen impurities are often introduced unintentionally.Therefore,it is necessary to study the influence mechanism of nitrogen impurities on the thermal conductivity of diamond films.In addition,as a heat dissipation material,diamond films often are used in the harsh environment of high temperature,high energy,and high radiation such as the outer space.Cosmic rays can cause radiation damage to diamond films and make the heat dissipation performance worse.Therefore,studying the effect of radiation damage on the thermal conductivity of diamond films is also of important research significance.Laser Raman spectroscopy is used in this paper to study the influence of nitrogen impurities,electron irradiation,annealing temperature,and test temperature on the thermal conductivity of diamond films.The mechanism of the influence of nitrogen impurities on the thermal conductivity of diamond films has been revealed,and the mechanism of the influence of radiation damage on the thermal conductivity of diamond films has been elucidated.Provide technical support and theoretical guidance for the preparation and performance control of high-performance diamond heat sink films.The results are as follows:(1)The thermal conductivity of high-purity diamond films conforms to the K ∝ T-1 in the range of 120～270 K,which is caused by the generation and annihilation of phonons.The thermal conductivity of nitrogen-doped diamond films in the range of 120-250 K conforms to the K=CT-1+A(B1/T)T5/2,which is caused by the synergistic effect of phonons and carriers.When the concentration of nitrogen impurities in the diamond film is low,due to the different vibration frequencies of the nitrogen atoms and carbon atoms,an anharmonic effect occurs during the transmission of phonons,resulting in a significant decrease in the thermal conductivity of the diamond film with the temperature increases.As the concentration of nitrogen impurities increases,nitrogen atoms gradually replace carbon atoms,phonons will transfer between nitrogen atoms,and the anharmonic effect disappears.At this time,the decline of thermal conductivity with increasing temperature tends to be flat,and shows a slight upward trend.When the nitrogen impurity concentration is high,the thermal conductivity controlled by phonons still shows a decreasing law with the increase of temperature,while the thermal conductivity controlled by electronic control increases with the increase of temperature and gradually tends to a constant.(2)After high-purity diamond films are irradiated with 200 keV electrons,the GR1,615 cm-1 and 1933 cm-1 Raman peaks appear in the Raman spectrum,and the GR1 is caused by a neutral single vacancy defect.By studying their test temperature,excitation power dependence and distribution in the depth direction of the film,it is proved that the Raman peaks of 615 cm-1 and 1933 cm-1 are caused by intrinsic interstitial atoms.When annealing below 500℃,the Raman spectrum does not change significantly,which means that the defect structure and distribution in the film does not change significantly,and the thermal conductivity remains unchanged;When annealing in the range of 600℃ to 800℃,the Raman peaks of 615 cm-1 and 1933 cm-1 gradually weaken and disappear,which means that the interstitial atomic defects can move freely to the vacancies and recombine with vacancies,making the radiation damage gradually repair.The remaining vacancies can move freely to be bound by nitrogen impurities,and the thermal conductivity of the film rises rapidly;As the temperature continues to rise,the thermal conductivity of the film no longer increases.The thermal conductivity is maintained at 82%of the thermal conductivity of the film before irradiation annealing,which indicates that there is still irreparable radiation damage in the film.