A Study Of Nitride Epitaxy And Properties On Diamond Substrates

As a typical third-generation semiconductor material,the power density of GaN is 10-30 times higher than that of Si and Ga As.Power devices made of GaN materials are known as ideal high-power microwave devices.GaN-based microwave power devices continue to show significant development and application significance in radar,5G communications,aerospace and other fields.With the continuous development of GaN-based microwave power devices,higher output power and frequency are required.At the same time,for higher integration,the size of the device is also reduced.However,with the miniaturization of size and the increase of power,the reliability and stability of the device are greatly challenged.This is due to the increase in power density,the problem of self-heating effect in the active area of the chip becomes serious,resulting in the deterioration of performance under high power.Therefore,the low heat dissipation capability of GaN-based power devices has become an important factor restricting their performance improvement,and the heat dissipation capability is mainly determined by the substrate material of the device.As an ultra-wide bandgap semiconductor material,diamond is currently the substrate with the highest thermal conductivity,with a thermal conductivity of up to 22 W/cm K,which is the highest among sapphire(0.5 W/cm K),silicon(1.5 W/cm K)and carbide.44 times,14.6 times and 5.5 times that of silicon(4 W/cm·K).Compared with the commonly used Si C and Si-based GaN microwave power devices,diamond-based GaN power devices have higher heat dissipation capabilities,and are expected to achieve smaller size and higher power density power devices,thereby promoting future RF power devices and related systems.miniaturization,integration and high power applications.However,diamond is a cubic structure,different from the hexagonal wurtzite structure of GaN,so there is a large lattice mismatch(about 13%)between GaN and diamond.Besides lattice mismatch,thermal mismatch between them(1.0 × 10-6 K-1 and 3.17 × 10-6 K-1,respectively)is also a problem.The stress caused by the large lattice and thermal mismatch can lead to film cracking and deterioration of crystal quality.Therefore,it is extremely difficult to grow GaN directly on diamond.In this paper,the epitaxial growth and properties of nitrides on diamond substrates are investigated by adopting different technical means and optimizing the process conditions.1.First,related process attempts were made on polycrystalline diamond,and the surface of polycrystalline diamond was treated by oxygen plasma treatment and etching under different conditions,and then epitaxial growth was carried out.Compared with single crystal diamond,polycrystalline diamond is larger in size and lower in price.Although the thermal conductivity(10-12 W/cm·K)is lower than that of single crystal,it is sufficient as an excellent heat dissipation substrate to meet the needs of heat dissipation.From an economic point of view,it is indeed an alternative strategy.Growth was carried out by metal organic chemical vapor deposition(MOCVD),and the obtained nitrides were characterized using different tests.The results show that the use of O plasma treatment and etching treatment did not significantly improve the nitride epitaxy on the polycrystalline diamond substrate,and the prepared GaN showed larger grains and poor surface morphology.The nitrides were obtained and analyzed by polycrystalline X-ray diffraction,and the information of different crystal planes was obtained.Although the single crystal of GaN was not successfully prepared,it can still provide reference for the epitaxy of nitrides on polycrystalline diamond.2.Secondly,the two-dimensional material h-BN was transferred on the surface of polycrystalline diamond,and the growth conditions were optimized,and GaN single crystal was successfully prepared.Through high-resolution X-ray diffraction tests,the half-width of the 002-face rocking curve of GaN decreased from 4.67° to 1.98°.By optimizing the temperature of the low-temperature Al N nucleation layer,the half-width of the rocking curve of the 002 surface of the optimal group of GaN is only 1.2°.The optical quality of GaN was characterized and analyzed by photoluminescence and Raman tests,and electron microscopy was used.The surface morphology of the GaN epitaxial layer was tested with atomic force microscopy,and the existence of h-BN was confirmed by transmission electron microscopy and X-ray spectroscopy.Compared with O plasma treatment and etching treatment of polycrystalline diamond surface for epitaxial growth of nitride,the transfer of twodimensional material h-BN makes GaN successfully nucleate and grow,and exhibits better surface morphology and crystal quality,For the successful preparation of GaN single crystal by this method,we have carried out a detailed analysis in this paper.3.Next,in order to further prepare higher-quality GaN thin films,we used 111 single crystal diamond substrate for epitaxial growth,and successfully reduced the half-width of the 002-plane rocking curve of GaN to 0.73° by nitriding.The surface morphology of GaN measured by electron microscope was poor and no film was formed.For the poor surface morphology,we believe that it may be caused by the excessive roughness of the single crystal diamond substrate.Therefore,we tested and characterized the single crystal diamond substrate and found that there are differences between different single crystal diamond substrates.large differences,which in turn introduced new variables to the experiment.Through analysis,we believe that the difficulty of nitride epitaxy on diamond is also related to the lack of highquality diamond substrates with accurate crystal planes,which restricts the development of diamond-based power devices with high heat dissipation capabilities.4.Finally,through the preparation and test analysis of nitrides on single crystal and polycrystalline diamond,the difficulties and challenges faced in the preparation of diamondbased GaN materials and devices are summarized.At the same time,compared with traditional Si-based and Si C Based on power devices,the advantages and development prospects of diamond-based power devices are clarified.