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Papers by Tamara Isaacs-Smith

We present results on ZrB2 Schottky contacts deposited on n-type SiC by DC magnetron sputtering a... more We present results on ZrB2 Schottky contacts deposited on n-type SiC by DC magnetron sputtering at temperatures between 20 ^oC and 800 ^oC. The Schottky barrier heights determined by current-voltage measurements, increased with the deposition temperature from 0.87 eV for contacts deposited at 20 ^oC to 1.07 eV for those deposited at 600 ^oC. The RBS spectra of these contacts revealed a substantial decrease in oxygen peak with increase in the deposition temperature and showed no reaction at the ZrB2/SiC interface. The barrier heights of the contacts annealed in nitrogen for 20 mins at 200 ^oC to 500 ^oC using a rapid thermal processor revealed only a slight increase. These results indicate improvement in the electrical properties and thermal stability of ZrB2 on n-type SiC when the contacts are deposited at elevated temperatures, making them attractive for high temperature applications.

Solid-State Electronics, 2008

Thermal oxides on the Ga-face of low defect density bulk gallium nitride (GaN) were controllably ... more Thermal oxides on the Ga-face of low defect density bulk gallium nitride (GaN) were controllably produced under varying conditions and subsequently analyzed. The thermal oxidation was performed in a dry oxygen atmosphere at different temperatures and different oxidation times. Each oxide layer was identified as the monoclinic b-Ga 2 O 3 by a h-2h X-ray diffraction (XRD) scan. Complementary Auger electron spectroscopy (AES) and high-resolution X-ray photoelectron spectroscopy (XPS) were also performed to study the chemical and electronic states of the oxide. The surfaces of the as-grown oxide and the GaN surfaces (after oxide removal) were studied using scanning electron microscopy (SEM). The roughness of both surfaces was found to increase with increasing oxidation temperature. Schottky diodes were fabricated on the GaN surfaces after oxide removal to further examine the surface quality. An excess reverse leakage current was found for Schottky diodes fabricated on GaN surfaces that were oxidized at 950°C or 1000°C, indicating possible surface decomposition at these two temperatures. The characteristics of wet and dry etching of the gallium oxide layer were also investigated. Finally, metal-oxide-semiconductor (MOS) capacitors were fabricated using thermally oxidized bulk GaN substrates. Current-voltage (I-V) measurements showed a low reverse current of 1.5 pA at À10 V. The oxide breakdown field was determined to be 0.65 MV/cm. Capacitance-voltage (C-V) measurements displayed a deep depletion feature, and the interface trap density near the conduction band was estimated to be in the low 10 11 eV À1 cm À2 range.

Journal of Electronic Materials, 1998

Results on ZrB2 Schottky contacts deposited on n-type SiC by DC magnetron sputtering at temperatu... more Results on ZrB2 Schottky contacts deposited on n-type SiC by DC magnetron sputtering at temperatures between 20 ^oC and 800 ^oC are presented. The Schottky barrier heights determined by current-voltage measurements, increased with the deposition temperature from 0.87 eV for contacts deposited at 20 ^oC to 1.07 eV for those deposited at 600 ^oC. The RBS spectra of these contacts revealed a substantial decrease in oxygen peak with increase in the deposition temperature and showed no reaction at the ZrB2/SiC interface. The barrier heights of the contacts annealed in nitrogen for 20 mins at 200 ^oC to 500 ^oC using a rapid thermal processor revealed only a slight increase. These results indicate improvement in the electrical properties and thermal stability of ZrB2 on n-type SiC when the contacts are deposited at elevated temperatures, making them attractive for high temperature applications.

Materials Science Forum, 2006

Silicon has been the semiconductor of choice for microelectronics largely because of the unique p... more Silicon has been the semiconductor of choice for microelectronics largely because of the unique properties of its native oxide (SiO2) and the Si/SiO2 interface. For high-temperature and/or high-power applications, however, one needs a semiconductor with a wider energy gap and higher thermal conductivity. Silicon carbide has the right properties and the same native oxide as Si. However, in the late 1990’s it was found that the SiC/SiO2 interface had high interface trap densities, resulting in poor electron mobilities. Annealing in hydrogen, which is key to the quality of Si/SiO2 interfaces, proved ineffective. This paper presents a synthesis of theoretical and experimental work by the authors in the last six years and parallel work in the literature. High-quality SiC/SiO2 interfaces were achieved by annealing in NO gas and monatomic H. The key elements that lead to highquality Si/SiO2 interfaces and low-quality SiC/SiO2 interfaces are identified and the role of N and H treatments is ...

... Key words: 6H-SiC, AiN, capacitance-voltage (CV), high-electric field breakdown, low-pressure... more ... Key words: 6H-SiC, AiN, capacitance-voltage (CV), high-electric field breakdown, low-pressure metalorganic chemical vapor deposi-tion (MOCVD ... A1N growth was initiated at the desired growth temperature with the introduction of ammo-nia (NH 3) and trimethylaluminum (TMA ...

IEEE Transactions on Applied Superconductivity

Journal of Applied Physics

2005 International Semiconductor Device Research Symposium, 2000

In this paper, the problem of high interface traps at the SiO2/SiC interface is introduced and th... more In this paper, the problem of high interface traps at the SiO2/SiC interface is introduced and their possible cause and physical nature are discussed. Different state-of-the-art approaches to chemically modify the interface for 'passivating' such electrically active traps is reviewed. In particular, the significant improvement of the interface by nitridation via nitric oxide post-oxidation annealing is highlighted. Correlations between electrical

physica status solidi (a), 2015

Journal of Materials Science Letters, 1996

1998 Fourth International High Temperature Electronics Conference. HITEC (Cat. No.98EX145), 1998

Postoxidation annealing in nitric oxide ͑NO͒ results in a significant reduction of electronic sta... more Postoxidation annealing in nitric oxide ͑NO͒ results in a significant reduction of electronic states at SiO 2 / 4H-SiC interfaces. Measurements of electron trapping dynamics at interface states in both thermally oxidized and NO annealed SiO 2 / 4H-SiC interfaces were performed using constant-capacitance deep level transient spectroscopy ͑CCDLTS͒ and double-CCDLTS. We show that the interface state density in as-oxidized samples consists of overlapping distributions of electron traps that have distinctly different capture cross sections. The dominant trap distributions, centered at E c − 0.24 eV with ϳ 7 ϫ 10 −19 cm 2 , and at E c − 0.46 eV with ϳ 4 ϫ 10 −17 cm 2 are passivated by NO annealing. The remaining interface states all have capture cross sections in the range 10 −19 −10 −21 cm 2 .

AIP Conference Proceedings, 1996

Defects can be easily generated by high electric fields such as those encountered at the Schottky... more Defects can be easily generated by high electric fields such as those encountered at the Schottky barrier or p-n junctions under bias. Operation of devices at high temperatures further promote the formation of defects. The study of the nature and behavior of such defects would help in defining the operational limits of SiC junction-based devices. This paper reports on the

AIP Conference Proceedings, 1995

We report specific contact resistances measured at elevated temperatures for Ni ohmic contacts to... more We report specific contact resistances measured at elevated temperatures for Ni ohmic contacts to 6H-SiC. The specific contact resistances were measured with the linear transmission line method at both room temperature and at 773 K and yielded values <5×10−6 Ω-cm2 at both temperatures. The trend shows a decreasing contact resistance at higher temperatures. The annealed metal film is a nickel

Al-Ti alloys are widely used as ohmic contacts to p-type SiC. This work will summarize many of th... more Al-Ti alloys are widely used as ohmic contacts to p-type SiC. This work will summarize many of the recent findings where Al-Ti contacts have been used. The composition 70 wt.% Al provides low resistance contacts with excellent electrical uniformity on p-type SiC. Specific contact resistances as low as 5x10 -6 ohm-cm 2 have been reported for contacts fabricated to heavily doped p-type layers grown using liquid phase epitaxy (LPE). Scanning electron microscopy and atomic force microscopy have been used to investigate the surface morphology and edge definition of annealed Al-Ti contacts to epitaxial layers grown by CVD. The morphology of the buried metal/semiconductor interface was examined by etching away the contact metallization and imaging the freshly exposed SiC surface. Patterned contacts exhibited good edge definition, a root-mean-square surface roughness of 11 nm, and a root-mean-square interfacial roughness of 12 nm. The deepest observed penetration of the metallization into the SiC was 65 nm, and the lateral length scale of the morphological features at the buried metal/semiconductor interface was sufficiently small compared to the active area of the contact to allow good contact-to-contact reproducibility. In addition to summarizing recent results, this work will present new data concerning the high temperature specific contact resistance of the 70/30 contact.