Edward Lloyd Hutchins

Properties of Delta Doped Al 0.25 Ga 0.75 N and GaN Epitaxial Layers

Delta doping (paused growth doping) was investigated as an alternative to uniformly distributing the dopant in the nitride semiconductor layer. In this work, delta doped layers were produced in MOVPE-grown AlGaN and GaN layers at a susceptor temperature of 1220°C by turning off the group III precursors (TMG and TMA) and introducing into the reactor a silicon precursor Si 2 H 6 (disilane) for a fixed period (pause time) before growth was restarted. The compositional and electrical properties as a function of aluminum content and dopant flux were investigated for nitride layers on 2 inch c-plane sapphire substrates. Secondary ion mass spectroscopy (SIMS) measurements revealed a sharp silicon peak with a FWHM of 5.7 ± 0.6 nm for an Al 0.25 Ga 0.75 N sample and 10.0 ± 0.6 nm for a GaN sample with sheet charges of 7.9×10 12 cm −2 and 9.9×10 12 cm −2 ,respectively. Room temperature Hall mobility as high as 265 cm 2 V −1 s −1 for a sheet charge 7.9×10 12 cm −2 was demonstrated for delta doped Al 0.25 Ga 0.75 N layers, but the mobility enhancement saturated and then decreased with increasing sheet charge. Room temperature sheet charge increased with increasing dopant flux for delta-doped AlGaN and GaN layers. Sheet charge density as high as 2.2×10 13 cm −2 and 1.3×10 13 cm −2 was measured at room temperature for Al 0.25 Ga 0.75 N and GaN delta doped layers, respectively. Under identical doping conditions, the Hall sheet charge of the delta doped Al 0.25 Ga 0.75 N layer was approximately half as large as GaN layers. The impurity and electrical characteristics of the delta doped layers are further discussed.

III-Nitride Epitaxial Material on Large-Diameter Semi-Insulating SiC Substrates for High Power RF Transistors

Metalorganic chemical vapor deposition was employed to deposit high quality, highly uniform III-Nitride transistor structures on 100 mm diameter semi-insulating 4H-SiC substrates. Electron mobility was over 2000 cm/Vs at room temperature. Sheet resistivity uniformity was as low as 0.75%. Typical standard deviations were about 1% in most properties including sheet resistivity, carrier concentration, mobility, and AlGaN composition. Additionally, wafers maintained their flat shape after deposition of these structures. Wafer bow and warp were typically less than 20 μm for optimized structures and <5 μm for the best wafers.