The structural, optical, and electronic properties of an insulating material prepared by the thermal oxidation of AlN thin films on Si have been studied by a number of different experimental techniques. The thermal oxidation at 1100°C of reactively sputtered AlN films on Si wafers was found to result in the formation of an oxide with a relative Al to O concentration near Al 2 O 3 with small amounts of incorporated N. The structure of the AlO:N oxide could be varied between amorphous and polycrystalline, depending on the preparation conditions, and the oxide surface was found to be approximately three time smoother than the as-sputtered AlN films. Metal-oxidesilicon capacitors had an oxide charge density of about 10 11 cm Ϫ2 , capacitance-voltage characteristics similar to pure SiO 2 , and a dielectric constant of 12.4. Infrared measurements yielded a refractive index of 3.9. These results indicate that thermally oxidized AlN films show promise as insulating structures for many integrated circuit applications, particularly for the case of III-V and group III-nitride based semiconductors.

In this letter, we report on heterostructure bipolar transistors ͑HBTs͒ based on silicon carbide ͑SiC͒ and a silicon carbide:germanium ͑SiC:Ge͒ alloy. The SiC:Ge base alloy was formed by the ion implantation of Ge into p-type 4H-SiC and subsequent annealing. HBT mesa structures were fabricated using a reactive ion etching process. The incorporation of Ge was found to increase the gain and the Early voltage of the devices. A common-emitter current gain ͑␤͒ of greater than 3 was measured for the SiC:Ge HBTs. Homojunction SiC transistors were fabricated as a reference using the same process ͑except no Ge in the base region͒ and exhibited a ␤ of 2.2. The transistors exhibited high breakdown voltages ͑Ͼ50 V without passivation͒, that typify SiC-based devices. These results indicate that SiC:Ge is a promising material for use in SiC-based heterostructure devices.

The structural, electronic, and optical properties of single crystalline n-type 4H-SiC implanted with Ge atoms have been investigated through x-ray diffraction ͑XRD͒, Rutherford backscattering spectroscopy ͑RBS͒, Raman spectroscopy, and sheet resistivity measurements. Ge atoms are implanted under the conditions of a 300 keV ion beam energy with a dose of 2ϫ10 16 cm Ϫ2. X-ray diffraction of the Ge-implanted sample showed broadening of the Bragg peaks. A shoulder on the ͑0004͒ reflection indicated an increase in the lattice constant corresponding to substitutional Ge and implantation induced lattice damage, which was repaired through thermal annealing at 1000°C. The diffraction pattern after annealing indicated improved crystal structure and a peak shift to a lower reflection angle of 35.2°. The composition of Ge detected through XRD was reasonably consistent with RBS measurements that indicated 1.2% Ge in a 1600-Å-thick layer near the SiC surface. Raman spectroscopy also showed fundamental differences in the spectra obtained for the Ge-implanted SiC ͑SiC:Ge͒ compared to a pure sample of SiC. Sheet resistivity measurements indicate a higher conductivity in the Ge implant by a factor of 1.94 compared to unimplanted SiC. These results have demonstrated the possibility of substitutional implantation of Ge atoms into the crystalline lattice of 4H-SiC substrates. The change in composition and properties may have numerous electronic device applications including high power, high temperature, optoelectronic, as well as high frequency device structures.

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