Research interest: increased functionality in Si-based materials and devices. There are three projects currently being pursued:  

RF Cross-talk Isolation: Portable electronics, especially the IC’s for cellular telephone handsets, is the fastest growing sector of the entire microelectronics industry. The rapid expansion of the market is fueled by the reduction in cost, which in turn is made possible by the increasing scale of integration. The key components of today’s cellular telephone handset consist of digital and RF analog circuits, and they are on separate chips. Further integration of the digital and RF analog circuits is hampered by the cross-talk issue, for which there is no viable solution at the current time.  
 Our effort concentrates on the reduction of the cross-talk using porous Si. We make use of the high resistivity characteristics of porous Si for isolation. The porous Si formation process converts the material with resisitivity as low as 0.005 W-cm in the bulk form to as high as 1 MW-cm in the porous form. Our objectives are to understand the various properties such as the mechanical strength, the impedance of the porous Si structure, the details of vapor phase deposition process involving porous structures, and to develop this into a Si VLSI compatible process module. 

Self-assembled Quantum Dot Arrays by epitaxy: Along with the continued shrinking of device dimensions in Si VLSI, the task of exploring and understanding new device structures that are based on quantum mechanical effects has become more urgent. These are devices with their critical dimensions smaller than the quantum mechanical wavelength of electrons. One such group of devices is based on semiconductor islands of several hundred angstroms in size that are formed during hetero-epitaxial growths, also known as self-organized quantum dots. One of the major challenges in fabricating self-organized quantum dots is the uniformity in the size and the spatial distribution. Under current practice, semiconductor islands form at random. Consequently, they are randomly distributed with a size distribution that is wider than desirable for various device applications.  
 The objective of our research is to fabricate three-dimensional semiconductor quantum dot arrays with uniform spatial and size distribution. It is well known that for multi-layer self-organized island structures, the islands in the upper layer sense the strain field of the underlying islands. As a result, islands in subsequent layers naturally line up with the islands underneath. The task of fabricating a three-dimensional regular array is thus reduced to that of a two-dimensional regular array. Our approach is to pattern the substrate using three different, non-lithographic, methods. The first method utilizes the periodic strain field of a buried misfit dislocation network. The second method relies on the periodic strain field of a compliant substrate. The third method uses what is known as “nature lithography”. The epitaxy growth is done with molecular beam epitaxy. 
  

Si Optical Bench: Si optical bench refers to the class of photonic devices consists of SiO₂ waveguides fabricated on Si substrates. These devices are used in switches and as transceivers in the optical communication network. Our research efforts focus on two aspects of the technological challenges: developing a more efficient method of fabricating thick (>15 mm) SiO₂ cladding layers, and reducing the stress in the SiO₂ waveguides which causes birefringence.  

 
Selected Publications: 

1. “An Approach For Fabricating High Performance Inductors On Low Resistivity Substate”, Y.H. Xie, M.R. Frei, A.J. Becker, C.A. King, D. Kossives, L.T. Gomez, and S.K. Theiss, IEEE Journ. Solid State Circuits, 33, 1433 (1998);
2. “ Experimental Evidence for a two-dimensional quantized Hall insulator”,  M. Hilke, D.Shahar, S.H.Song, D.C.Tsui, Y.H.Xie, and Don Monroe, Nature, 395, 675 (1998).
3. “Relaxed Template for Fabricating Regularly Distributed Quantum Dot Arrays”, Y.H.Xie, S.B.Samavedam, M. Bulsara, T.A.Langdo, and E.A.Fitzgerald, Appl. Phys. Lett., 71, 3567 (1997);
4. "Semiconductor Surface Roughness:  Dependence on Sign and Magnitude of Bulk Strain", Y.H. Xie, G.H. Gilmer, C. Roland, P.J. Silverman, S.K. Buratto, J.Y. Cheng, E.A. Fitzgerald, A.R. Kortan, S. Schuppler, M.A. Marcus, P.H. Citrin,   Phys. Rev. Lett., 73, 3006 (1994);
5. "Very High Mobility Two-Dimensional Hole Gas in Si/GexSi1-x/Ge Structures Grown by Molecular Beam Epitaxy," Y.-H. Xie, D.P. Monroe, E.A. Fitzgerald, P.J. Silverman, F.A. Thiel, G.P. Watson, Appl. Phys. Lett., 63(16), 2263 (1993);
6. "Fabrication of High Mobility Two-Dimensional Electron and Hole Gases," Y.-H. Xie, E.A. Fitzgerald, D.P. Monroe, P.J. Silverman, G.P.Watson,   J. Appl. Phys., 73(12), 8364 (1993);
7. "Extremely High Electron Mobility in Si/Gex Si1-x Structures Grown by Molecular Beam Epitaxy", Y.J. Mii, Y.-H. Xie, E. A. Fitzgerald, D. Monroe, F. A. Thiel, B. E. Weir, and L. C. Feldman, Appl. Phys. Lett., 59, 1611 (1991).
8. "Absorption and Luminescence Studies of Free-standing Porous Silicon Films," Y.H. Xie, M.S. Hybertsen, W.L. Wilson, S.A. Ipri, G.E. Carver, W.L. Brown, E. Dons, B.E. Weir, A.R. Kortan, G.P. Watson, and A.J. Liddle, Phys. Rev. B,  49(8), 5386 (1994);
9. "Light Emission From Silicon", S.S. Iyer, Y.-H. Xie,  Science, 260, 40 (1993).

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