Ph.D. Oral Examination --Xiaojun Yu (Tuesday,October 25, 2005, 9:15AM)
xjyu at stanford.edu
Mon Oct 24 00:22:45 PDT 2005
Department of Materials Science and Engineering
University PhD Dissertation Defense
MBE growth of III-V materials with orientation-patterned artificial structure for nonlinear optics
Advisor: Prof. James S. Harris, Jr
Tuesday, October 25, 2005
9:15AM (refreshments served at 9AM)
Center for Integrated Systems Extension (CISX) Auditorium
There are numerous applications of nonlinear optical frequency conversion in the infrared, ranging from generation of coherent radiation for spectroscopy and military applications, to wavelength conversion in communication systems. Semiconductors such as AlxGa1-xAs and GaP have excellent properties for nonlinear frequency conversion, in particular large nonlinear coefficients and transparency throughout the mid-infrared. However, due to the absence of birefringence, quasi-phasematching (QPM) has to be used for the phasematching, requiring a modulation of the sign of the nonlinear coefficient along the material. In this work we have developed an all-epitaxial process to fabricate orientation-patterned AlxGa1-xAs and orientation-patterned GaP structures, used for both bulk-like and waveguide devices. Various nonlinear optical interactions have been demonstrated which show that orientation-patterned AlxGa1-xAs is a promising candidate for infrared applications.
Our orientation-patterned GaAs template is fabricated in three steps. First, we use the polar-on-nonpolar growth of GaAs/Ge/GaAs heterostructure to control the lattice inversion. The orientation pattern is then defined by a combination of photolithography and a series of selective chemical etching steps. Template and waveguide growth is completed in the MBE regrowth. Critical regrowth issues are elimination of antiphase defects within each single domain of the template while still maintaining the induced antiphase domains at the pattern boundaries. Appropriate growth conditions were developed which met this challenges and produced vertical propagation of domain boundaries under all MBE conditions tested. Low corrugation template has been achieved by optimizing the growth conditions of GaAs on Ge. QPM periods demonstrated are short enough to phasematch any interaction in the transparency range of AlxGa1-xAs.
Using this technique, low loss AlxGa1-xAs QPM waveguide devices were fabricated and second harmonic generation was demonstrated from a pump laser at 1.55 μm. A waveguide loss, ~4.5 dB/cm at 1.55 μm, was measured, which is close to that of the unpatterned waveguides. A record-high conversion efficiency, 43 %W-1, was demonstrated. These achievements provide solid basis for the fabrication of highly efficient nonlinear optical devices based on the GaAs material system.
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