Study On The Growth Of Nitrogen-Polar High-Resistance GaN Film By MOCVD

As the third-generation semiconductor material,GaN has many advantages such as large band gap,high breakdown voltage,and high saturation electron drift speed.It is an ideal material for preparing high-frequency and high-power electronic devices.GaN materials have two polarities:metal-polarity and nitrogen-polarity.When the Ga-N bond parallel to the c-axis along the epitaxial growth direction is directed from the Ga atom to the N atom,the polarity of the GaN is the metal-polarity,and the direction of the bond is the[0001]direction.On the contrary,if the Ga-N bond parallel to the c-axis along the epitaxial growth direction is directed from N atoms to Ga atoms,then the polarity of the GaN is nitrogen-polarity,and the direction of the bond is the[0001]direction.At present,Group-? nitride high electron mobility transistors(HEMT)are mostly based on metal-polar GaN-based materials.However,compared with metal-polar materials,nitrogen-polar GaN-based materials have their unique advantages in HEMT preparation.Nitrogen-polar GaN/AlGaN HEMT has lower source and drain ohmic contact resistance,and there is a natural back barrier at the same time.Therefore,nitrogen-polar materials are suitable for the preparation of high-performance HEMT devices.However,the nitrogen-polar GaN has poor surface morphology,is prone to cracks,and has a high background electron concentration,which hinders the development and application of nitrogen-polar nitride devices.In order to solve the above problems,this paper uses MOCVD technology to carry out the epitaxial growth of crack-free high-resistance nitrogen-polar GaN film.The specific research contents are as follows:1.Study on the epitaxial growth of nitrogen-polar GaN film.Experiments have found that the surface of the epitaxial nitrogen-polar GaN film is prone to cracks.According to the distribution of cracks on the surface of the epitaxial film,we analyze that the occurrence of cracks is related to the unevenness of the heating wire temperature zone,that is,the internal stress state of the nitrogen-polar GaN film is more sensitive to the temperature zone.On this basis,we fine-tune the heating wire temperature zone,and finally realize the epitaxial growth of the crack-free nitrogen-polar GaN film on the sapphire substrate.2.Study on the epitaxial growth of nitrogen-polar high-resistance GaN film.The influence of growth kinetics on the electrical properties of nitrogen-polar GaN film is systematically studied.The experimental results show that with the decrease of the growth temperature,the resistance of the nitrogen-polar GaN film will gradually increases.However,the growth temperature cannot be too low,because the surface of the nitrogen-polar GaN film will be very rough at low temperatures and cannot be used for device preparation.In addition,as the growth pressure decreases,the change trend of the resistance value of the nitrogen-polar GaN film is consistent with the trend of temperature on the resistance value of the nitrogen-polar GaN film,that is,the resistance value increases with the decrease of the growth pressure of the GaN film,and the surface morphology gradually gets worse.We also optimize the V/III ratio during the growth of nitrogen-polar GaN film.The study finds that the resistance of nitrogen-polar GaN film gradually increases with the decrease of the growth ?/? ratio,and the surface morphology is also improved.Regarding the influence of growth parameters on the resistance of nitrogen-polar GaN film,we analyze from the perspective of C impurity incorporation.Through the control of growth kinetics,we have achieved the epitaxial growth of nitrogen-polar high-resistance GaN film with a sheet resistance of 2.1×105 ?/?.