Preparation And Properties Of GaN Films By Plasma Enhanced Atomic Layer Deposition

Gallium nitride(GaN),one of the third-generation wide bandgap semiconductor materials,due to its unique opto-electronic properties,has been widely used in electronic and optoelectronics applications,such as ultraviolet photodetector,light-emitting diode,high electron mobility transistor and 5G radio frequency devices.Plasma enhanced atomic layer deposition(PEALD)is a newly-developed technique for thin film growth with the advantages of low-temperature process,accurate thickness controllability and high uniformity.Therefore,it is expected that the low temperature epitaxial growth of high-quality GaN films can be realized by PEALD,which may broaden the application of GaN films in flexible optoelectronic devices.GaN films were deposited by PEALD in this thesis.The main factors affecting the growth of GaN films were systematically studied,and the growth mechanism of GaN films was revealed.Atomic layer epitaxy of high-quality GaN was realized by in situ N plasma treatment of substrate surface.High-quality GaN epilayer was further improved by rapid thermal annealing.The main contents of the thesis are as following:(1)The growth of GaN films on Si(100)substrates by PEALD was optimized,and the growth mechanism of GaN films was proposed.The effects of growth parameters on growth rate,crystal structure and surface morphology of GaN films were systematically studied,including growth temperature,N₂/H₂plasma duration,N₂/H₂ plasma flow rate and plasma RF power.The results show that the growth mechanism of GaN films varies with the parameters of PEALD.During the initial stage,GaN films follows“island growth mode”.With the increase of plasma RF power,GaN films change from“island growth mode”to“layered growth mode”.With optimized growth parameters of 320?,30 s of N₂/H₂plasma duration,30 sccm of N₂/H₂flow rate and 180 W of plasma RF power,GaN films with the highest crystalline quality are realized.The optimized GaN films exhibit preferred(002)growth direction with full width at half maxima(FWHM)of the(002)peaks of 0.593°.(2)High-quality GaN heteroepitaxy was realized by in situ N plasma treatment of substrate surfaces.After N plasma treatment on Si and sapphire substrates respectively,the interface state was effectively improved,and the crystal quality and photoelectric properties of the GaN films were significantly improved.The GaN films on sapphire substrate grow along the(002)orientation with FWHM of the(002)peaks of 0.410°,and the contents of C and O impurities of the films are as low as 1.4 at%and 3.8 at%,respectively.The films are n-type with an electron mobility of?13.04 cm²·V^-1·s^-1.(3)Rapid thermal annealing was used to improve the crystal quality.It has been found that the quality of GaN films grown on sapphire substrate is better than that of Si substate due to the lower lattice mismatch.Under the annealing temperature of 750?and N₂ atmosphere,the GaN/sapphire films grow highly along the preferred orientation of(002).The FWHM of(002)and the strain of the films are as low as 0.238°and 0.0015,respectively.Ga and all the N elements form GaN with Ga-N bonds,and the Ga/N atomic ratio is 1.03.The content of C and O impurities are as low as 1.2 at%and 3.6 at%,respectively.The carrier concentration and the mobility of GaN films are 6.895×10¹⁶ cm^-3 and 151.8 cm²·V^-1·s^-1,respectively.