Lynn Rathbun

Photoluminescence of AlxGa1−xAs grown by molecular beam epitaxy

Reduction of background oxygen containing species, higher substrate temperature, and low arsenic fluxes during growth have all been found critical to improve the luminescence of molecular beam epitaxy AlxGa1−xAs alloys. Attention to these parameters has allowed greatly improved quality films to be grown which show strong exciton recombination for the first time. The main unintentional acceptor impurity was then found to be carbon.

GaInAs‐AlInAs structures grown by molecular beam epitaxy

Growth of GaInAs and A1InAs by molecular beam epitaxy on idium phosphide substrates is reported. Unintentionally doped, closely lattice matched GaInAs layers were n‐type with μ300 up to 8800 cm2 V−1 s−1 and n as low as 1×1016 cm−3 whereas undoped A1InAs layers were typically high resistance. 2‐MeV Rutherford backscattering showed good GaInAs crystal quality although the A1InAs was somewhat disordered. Evidence for cation exchange at interfaces and surface accumulation of indium was evident from both RBS and sputter Auger profiles. In situ grown A1 films on A1InAs showed an effective barrier height∼0.8 eV from 1/C2 V s V curves, however attention to the forward I‐V characteristics indicated lower values. DLTS results indicate the GaInAs to be virtually trap‐free but that A1InAs has high deep level concentrations owing to low growth temperatures. Good photoluminescent efficiencies were demonstrated for GaInAs layers, however, poor results were obtained for A1InAs.

A critical discussion of emission mechanisms and reaction rates for the ion‐assisted etching of GaAs(100)

Emission mechanisms and reaction rates for the ion‐assisted etching of GaAs(100) have been studied in detail using energetic argon ions and chlorine gas. Ion energies of 500 and 1000 eV were used with chlorine/argon ion surface‐flux ratios of 1–120. The major molecular etchant products were found to be GaCl2 and AsCl3. Gas phase products were detected at different flight distances to investigate the nature of surface residence times. It is concluded, based on these measurements, that GaCl2 emission is best interpreted in terms of the collisional‐cascade sputtering model for the specific range of ion energies and surface‐flux ratios studied. Using a similar analysis, it is concluded that AsCl3 may be emitted by either the thermal desorption or the collisional‐cascade mechanisms, with the former favored in the range of higher surface‐flux ratios and lower ion energies. Furthermore, the thermal desorption of AsCl3 appears to follow a first‐order surface process. Comparison of our data with those of others in...

Interfacial reaction between a Ni/Ge bilayer and silicon (100)

The sequential formation and dissociation of compounds in the Ni/Ge/Si(100) system have been studied by using Rutherford backscattering spectroscopy, Auger depth profiling, x‐ray diffraction, and cross‐sectional transmission electron microscopy. Ni2Ge phase is formed first on the Si substrate at 250 °C. A layered structure of NiGe/NiSi/Si(100) is formed after thermal annealing at 350 °C. Upon annealing from 350 to 425 °C, the NiGe phase dissociates, inducing further growth of NiSi phase at the nickel germanide/Si(100) interface. The NiSi phase grows with a (time)1/2 dependence and with an activation energy of 2.1 eV. Marker experiment shows that Ni is a dominant moving species. The dissociation of NiGe lead to an extensive redistribution of Ge and Ni with a configuration of Ge66Si17Ni17/NiSi/Si(100) and this layered structure remains stable until 680 °C. Cross‐sectional transmission electron microscopy results show that there are polycrystalline Ge plus a ternary NiSiGe phase on the top layer. High‐temper...

Molecular‐beam epitaxial group III arsenide alloys: Effect of substrate temperature on composition

Ion dechanneling and sputter‐auger spectroscopy have shown the composition of molecular‐beam epitaxial ternary group III arsenide alloys to depend upon the growth temperature in a manner consistent with preferential congruent desorption of the more volatile group III element.

Instabilities in the growth of AlxGa(1−x)As/Al/AlyGa(1−y)As structures by molecular beam epitaxy

Growth of epitaxial (Al,Ga)As/Al/(AlGa)As by molecular beam epitaxy was not found successful. Thermal expansion coefficient mismatch between Al and GaAs and reduction of Al melting point by partial dissolution of incident Ga and As species and with species diffusing across the metal‐semiconductor interface, make epitaxial (AlGa)As growth on Al above ∼300 °C impossible. Below ∼200 °C GaAs tends to be polycrystalline. Even below 480 °C GaAs becomes semi‐insulating by high deep level concentrations.

Oxygen stabilization of molecular beam epitaxial Al‐GaAs Schottky barrier heights

Aluminum Schottky barrier heights (φn) to GaAs depend heavily upon the deposition conditions and the gallium arsenide surface stoichiometry. After annealing to approximately 320 °C diodes show φb approximately 0.69 eV in association with oxygen at the Al/GaAs interface. We infer that these ’’stabilized’’ barrier heights are associated with oxygen‐induced surface‐state pinning of the GaAs Fermi level. Al deposition on arsenic stabilized surfaces show variable barrier heights and no oxygen peak indicating variable Al induced states in intermediate AlGaAs layers between the Al and GaAs.

Education and Outreach of the National Nanotechnology Infrastructure Network (NNIN) 2004–2015: History and Accomplishments of Undergraduate Programs

The National Nanotechnology Infrastructure Network (NNIN) was an NSF-funded facilities program (2004–2015) which had a large and diverse education and outreach (EO international Research Experience for Undergraduates, and international Research Experience for Graduate Students. The chapter provides details on program implementation as well as assessment results.

Cornell's Nanomove: Decontamination, Safety Reviews, and Various Lessons Learned

In the fall of 2003, the Cornell NanoScale Science & Technology Facility (CNF) relocated from its 22 year-old home, Knight Lab, into Duffield Hall, a new nanotechnology research building with approximately 30 research labs totaling over 4,600 m2 (50,000 ft2) of research space and a 2,300 m2 (25,000 ft2) class 1000 cleanroom. The relocation involved moving over a three month period more than thirty major pieces of sensitive research equipment, many which used toxic or corrosive gases or liquids. In addition to the relocated equipment, the facility also installed over 20 new pieces of equipment during the initial move-in phase. To ensure the safety of the personnel moving and reinstalling the equipment, which included Cornell University personnel as well as outside contractors, a decontamination procedure and certification process was developed and implemented by CNF staff. This process is typically done by an outside specialty contractor, particularly in work situations involving outside tradesman. The decontamination protocol covered wet process equipment as well as vacuum and gas systems and included review and signoff by tool owners, lab management, the Duffield Hall construction management team, and a representative from Cornell Environmental Health and Safety (EH&S). With this process, Cornell was able to avoid the considerable expenses of an outside safety contractor. Additionally, as part of the commitment to the City of Ithaca and the local fire company during the original Environmental Impact Statement performed by the University, Duffield Hall management committed to a thorough safety and engineering review of each tool installed in Duffield Hall, both within the CNF clean room as well as within other laboratories in the building. A Pre-Operational Safety and Environmental Review (POSER) process was developed by CNF staff, Cornell EH&S, and outside consultants and applied to all tools (approximately 70) during the post construction move in period. The review process involved looking at all operational, facilities, and maintenance operations for each tool to look for and document issues related to personal exposure or injury, facilities loading, environmental releases, as well as impact to other research equipment in the building. This team-based review is done on a tool by tool basis, and is updated upon major tool or process changes. The review continues to be used for all major and minor tool installations in Duffield Hall. Cooperation between staff, facilities, construction, and safety personnel were critical in both the decontamination certification process and the POSER process. The lessons learned and the experience gained should be of value to others in the process of moving into new advanced laboratory facilities.

X-ray mask fabrication at CXrL

Availability of production-worthy x-ray masks is of great concern to the lithographic community in anticipation of insertion of x-ray lithography as the leading contender among the next generation lithographies.