T. Warren Weeks

GaN thin films deposited via organometallic vapor phase epitaxy on α(6H)–SiC(0001) using high‐temperature monocrystalline AlN buffer layers

Monocrystalline GaN(0001) thin films, void of oriented domain structures and associated low‐angle grain boundaries, have been grown via organometallic vapor phase epitaxy (OMVPE) on high‐temperature monocrystalline AlN(0001) buffer layers predeposited on vicinal α(6H)–SiC(0001) wafers using TEG, TEA, and ammonia in a cold wall, vertical, pancake‐style reactor. The surface morphology was smooth, and the PL spectrum showed strong near‐band‐edge emission with a full width at half‐maximum (FWHM) value of 4 meV. The dislocation density within the first 0.5 μm was ≊1×109 cm−2; it decreased substantially with increasing film thickness. Controlled n‐type Si doping of GaN has been achieved for net carrier concentrations ranging from ∼1×1017 to 1×1020 cm−3. Double‐crystal XRC measurements indicated a FWHM value of 66 arcsec for the GaN(0004) reflection.

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

Monocrystalline GaN(0001) thin films have been grown at 950 °C on high-temperature, ≈ 100 nm thick, monocrystalline AlN(0001) buffer layers predeposited at 1100 °C on α (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 × 10 17 cm −3 to 1 × 10 20 cm −3 . Mg-doped, p -type GaN was achieved with n A −n D ≈ 3 × 10 17 cm −3 , ρ ≈ 7 Ω · cm, and μ ≈ 3 cm 2 /V · s. Double-crystal x-ray rocking curve measurements for simultaneously deposited 1.4 μ m 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.

Large-Area, Device Quality GaN on Si Using a Novel Transition Layer Scheme

The emergence of III-nitride technology and fabrication of high quality GaN based devices is possible due to the advances in the heteroepitaxial growth of III-N thin-films on lattice-mismatched substrates. Typically, the substrate of choice is either SiC or sapphire. We have adopted 100mm Si as our substrate of choice; uniform substrates of high quality are inexpensive and plentiful due to decades of use in the microelectronics industry. Growth of device quality GaN on Si is challenged by the ∼17% lattice mismatch and an additional thermal expansion coefficient (TEC) mismatch of ∼56%. In order to accommodate this strain and TEC mismatch between Si and GaN, a novel transition layer was designed, grown and successfully optimized, ® obviating the need for either a PENDEO based overgrowth process or a SiC interlayer-based process. This growth technique (SIGANTIC®) does not require any wafer conditioning prior to growth and thus reduces the process complexity and maintains the cost effectiveness of the GaN on Si strategy. We will report on this manufacturable 100mm MOCVD heteroepitaxial process that consistently produces device quality AlGaN/GaN heterostructures with two dimensional electron gas (2DEG) mobilities typically around 1400 cm 2 /Vs at room temperature. Structural and electrical properties as determined by optical reflectance, atomic force microscopy, capacitance-voltage and van der Pauw Hall measurements, which are measured across the 100mm wafer, will be presented. Device results will be mentioned to show continuous wave (CW) RF operation at 2 GHz with competitive power output, gain and power added efficiency (PAE).