NSF CAREER Awardee

Ph.D., University of Pennsylvania, 1994.

NRC Post-doctoral Fellow, Naval Research Laboratory, 1994-96.

Professor Thibado's primary research interests are to study the physical properties of small structures on technologically important semiconductor surfaces. This includes atomic diffusion, spin-dependent tunneling, and optical properties. To achieve this, he has combined the state-of-the-art in device fabrication using molecular beam epitaxy (MBE) with the powerful atomic-scale characterization capability of scanning tunneling microscopy (STM).

SURFACE PHYSICS

Devices based on III-V compound semiconductors (e.g., GaAs, InP, GaN, etc.) have fueled the growth of the multibillion dollar telecommunications industry, making possible such technologies as fiber-optic communications, cellular phones, direct broadcast satellite TV, and global positioning systems. Unlike silicon-based devices, which are produced primarily by ion implantation techniques, the III-V device structures must be formed by depositing one plane of atoms after another until the entire structure is grown. Necessarily, III-V device fabrication occurs solely at a semiconductor surface. The better one can control and manipulate the motion of atoms on surfaces, the more sophisticated the devices structures one can make. In order to better understand the surface processes important to device fabrication, we combine the state-of-the-art in III-V [(Al,Ga,In)-(As,P)] structure growth using molecular beam epitaxy (MBE) with the state-of-the-art in atomic-scale surface characterization using scanning tunneling microscopy (STM).

Our current research interests can be conveniently classified into three areas. First, we are growing Mn-doped GaAs layers using MBE. These growths are being done using different substrate temperatures and Mn-doping levels. Under certain growth conditions the samples become ferromagnetic while maintaining their semiconducting properties. These samples are generally characterized using SIMS depth profiling, SQUID, and Hall Effect. Our second project is characterizing the Mn-doped GaAs layers using cross-sectional STM at low temperatures. Our third project is in the area of research called spintronics. This area of electronics uses the spin of the electron (i.e., its quantized magnetic moment) to produce novel transport properties. By replacing the normal metal STM imaging tip with a ferromagnetic metal, we can study the spin-dependent tunneling properties of the electron at the scale of an atom. In particular, we can identify which atomic-scale structures efficiently scatter the electron's spin. For this project we have built a low-temperature STM with two independently controlled tips. These tips can be brought as close together as one nanometer. This equipment forms a three-terminal STM similar to a transistor.

As devices continue to shrink, conventional characterization techniques are increasingly ineffective in identifying factors relevant to device failure. However, since the invention of the STM, individual atoms may be viewed on a wide variety of systems and surfaces. Through the unique combination of MBE device growth and STM characterization, significant progress in the development of next generation devices can be achieved.