Undoped and doped GaN thin films deposited on high-temperature monocrystalline AlN buffer layers on vicinal and on-axis α(6H)–SiC(0001) substrates via organometallic vapor phase epitaxy

Abstract

Monocrystalline GaN(0001) thin films have been grown at 950 ± C on hightemperature, ഠ100 nm thick, monocrystalline AlN(0001) buffer layers predeposited at 1100 ± C on a(6H)-SiC(0001) Si substrates via OMVPE in a cold-wall, vertical, pancake-style reactor. These films were free of low-angle grain boundaries and the associated oriented domain microstructure. The PL spectra of the GaN films deposited on both vicinal and on-axis substrates revealed strong bound excitonic emission with a FWHM value of 4 meV. The near band-edge emission from films on the vicinal substrates was shifted slightly to a lower energy, indicative of films containing residual tensile stresses. A peak attributed to free excitonic emission was also clearly observed in the on-axis spectrum. Undoped films were too resistive for accurate Hall-effect measurements. Controlled n-type, Si-doping in GaN was achieved for net carrier concentrations ranging from approximately 1 3 10 17 cm 23 to 1 3 10 20 cm 23 . Mg-doped, p-type GaN was achieved with n A -n D ഠ 3 3 10 17 cm 23 , r ഠ 7 V ? cm, and m ഠ 3 cm 2 ͞V ? s. Double-crystal x-ray rocking curve measurements for simultaneously deposited 1.4 mm GaN films revealed FWHM values of 58 and 151 arcsec for deposition on on-axis and off-axis 6H-SiC(0001) Si substrates, respectively. The corresponding FWHM values for the AlN buffer layers were approximately 200 and 400 arcsec, respectively.

Epitaxial Growth and Device Design Optimization of Full-Vertical GaN p-i-n Rectifiers

“…For the growth of GaN on a SiC substrate, AlN grown at high temperature has been shown to be a suitable buffer layer. 2,3 Smooth morphology as well as good x-ray diffraction (XRD) characteristics for subsequent epitaxially grown structures has been demonstrated. This is because SiC-AlN has a relatively small a-axis lattice mismatch of approximately 1%; 2 however, one of the problems with using AlN as a buffer layer is that it is an electrical insulator having a large ionization activation energy of~320 meV for Si donors 4 and wide energy bandgap of 6.2 eV.…”

“…6 The best results for GaN/ SiC epitaxial structures are usually obtained using AlN acting as a wetting agent as well as a buffer layer. 2,3,7 As one of the alternative approaches to overcome the technological barrier, a low Al-composition AlGaN, which can be directly grown on SiC substrates with reasonably conductive characteristics, has been studied. [8][9][10] The growth of the insulating AlGaN nucleation layer on SiC and sapphire substrates has also been reported.…”

Thermal Residual Stress Modeling in AlN and GaN Multi Layer Samples

“…Recent work [1][2][3] has highlighted some of the difficulties and successes with their thin film device fabrication. Processing such devices often relies on the high temperature growth of epitaxial layers on different substrates with different coefficients of thermal expansion.…”

Interfacial Microstructure of Ni/Si-Based Ohmic Contacts To GaN

“…The GaN epilayers were grown on AlN buffer layer on 6Η-SiC(0001) substrates via organometallic vapor phase epitaxy [3]. The metallization in a form of sandwich structures Ni/Mg/Ni/Si and Ni/Si for p-and n-type GaN, respectively, was deposited by e-beam evaporation.…”