Electrical and structural characterisation of GaN heterostructure grown on sapphire substrate by MOCVD method

In this thesis, n-type, p-type and undoped GaN structures, which play a critical role in III-Nitride based devices, are grown on c-plane (0001) sapphire substrate by Metal Organic Chemical Vapor Deposition (MOCVD) method. The samples obtained after the growth were characterized by High Resolution X-Ray Diffraction (HR-XRD), Photo-Luminescence (PL), Optical Microscope and Hall Effect Measurement System (HEMS). Considering the 16% lattice mismatch between GaN and sapphire substrate, it was aimed to obtain a structure with uniform, high crystal quality and smooth surface morphology. In order to reduce the defect density, the patterned sapphire substrate (PSS) was used instead of the sapphire substrate and effect of the low V/III ratio which is one of the growth step, on crystal quality was investigated. After the growth, to understand these effects, screw type and mixed type dislocation FWHM values and ratio of yellow luminescence intensity to GaN intensity (IYL/IGaN) were determined by HR-XRD system and PL system. For the best crystal quality, these values were found to be 248 arcsec, 236 arcsec and 0.23, respectively. Since it is difficult to obtain p-type GaN with high hole concentration because GaN behaves like n-type due to the nature of GaN, p-GaN parametric amplification study, one of the other studies, has been tried to determine the flow rate giving the highest doping level by using different Cp2Mg flow rates. After Mg doping, the Mg-H bonds formed in the structure are broken and the Mg atoms are activated by external annealing in a reactor in N2 medium and then with a rapid thermal processor furnace (RTP) at different temperatures. Hole concentration with HEMS system, defect density with PL system and surface morphology with Optical Microscope were investigated for all samples. The Cp2Mg flow was compared with the type of annealing and temperature. The sample with the dopant/III ratio of 0,65 and the annealing temperature of 800°C according to this comparison was determined to be the best sample with both surface quality and carrier density of 5,86E+17 cm-3. In order to obtain n-type GaN at high electron concantration, SiH4 was used as a doping source. After the growths, the electron concentration was determined by HEMS system and effects on the doping levels of different SiH4 flows were observed. As a result, a carrier concentartion of 1,078E+19 cm-3 was obtained with 80 sccm SiH4 flow.