TUNNELING MICROSCOPY

Scanning Tunneling Microscope-based Nanolithography

I. Adesida,* S. Bishop,* P. Bohn,* K. Y. Cheng,* K. Hess,* J. W. Lyding,* J. R. Tucker*
U.S. Office of Naval Research URI, N00014-92-J-1519

Scanning tunneling microscopy (STM) is being developed as a nanofabrication tool to extend electronic device fabrication into the sub-0.1 µ regime. This University Research Initiative (URI) is combining STM nanolithography with electron beam lithography, molecular beam epitaxy, dry processing, and silicon and III-V device fabrication to pursue this goal. To date, linewidths of 1 nm have been achieved on silicon surfaces using a unique ultrahigh vacuum (UHV) STM system constructed at the Beckman Institute. This capability is now being applied to fabricate devices that are controlled by quantum size effects.

Cryogenic Ultrahigh Vacuum Scanning Tunneling Microscopy

J. W. Lyding,* E. T. Foley, A. Kam
U.S. Office of Naval Research, N00014-91-J-1675

An ultrahigh vacuum (UHV) scanning tunneling microscope (STM) has been constructed that is capable of operation from above room temperature down to 1.5 K. This instrument is coupled to an existing room temperature UHV-STM to enable sample and tip transfer under UHV conditions and to make use of the existing preparation facilities. This system is being used to perform atomic resolution imaging and spectroscopy experiments on adsorbed atoms, molecules, and biomolecules, as well as on semiconductor heterostructures.

Scanning Tunneling Microscopy

J. W. Lyding*
NSF Center for Compound Semiconductor Microelectronics

The scanning tunneling microscope (STM) has been developed to image the heterointerfaces of ultrahigh vacuum (UHV) cleaved III-V compound semiconductor structures that are grown for electronic and optoelectronic device applications. Atomic resolution images of various III-V systems have provided direct views of interface roughness, alloy distribution, two-dimensional electron gas (2DEG) formation, and the penetration of the electron wavefunction into barrier layers. This information is being used as input to the crystal growth and device fabrication processes in collaboration with industrial colleagues.

Scanning Tunneling Microscopy of Semiconductor Devices

J. W. Lyding,* J. R. Tucker,* T.-C. Shen
Joint Services Electronics Program, N00014-90-J-1270
(Conducted in the Coordinated Science Laboratory)

We have developed an ultrahigh vacuum, temperature-variable scanning tunneling microscope (STM) system for use in exploring semiconductor device operation on the nanometer scale. This capability will be used to analyze interface properties of AlGaAs heterolayers cleaved in vacuum in terms of topography and electronic spectroscopy. One of the most exciting uses of STM will be to directly probe electronic energy levels of quantized heterolayer systems, in which carriers are confined in one or more dimensions to regions smaller than their DeBroglie wavelength. Success in this area is expected to provide information crucial to the design of future devices.