c -axis lithium niobate thin film growth on silicon using solid-source metalorganic chemical vapor deposition
- PDF / 243,094 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 76 Downloads / 224 Views
MATERIALS RESEARCH
Welcome
Comments
Help
c-axis lithium niobate thin film growth on silicon using solid-source metalorganic chemical vapor deposition S. Y. Leea) and R. S. Feigelson Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (Received 12 May 1998; accepted 22 February 1999)
Textured c-axis oriented LiNbO3 films have been grown for waveguiding applications on silicon substrates by the solid-source metalorganic chemical vapor deposition (MOCVD) method using tetramethylheptanedionate sources. Thermally grown SiO2 layers were used as cladding layers to provide optical confinement in the LiNbO3 films. The texture direction could be varied from the [006] to the [012] direction by either increasing the growth temperature and/or decreasing the growth rate. Under optimal growth conditions, 100% [006] texturing could be achieved without the aid of an electric field or by using a SiNx buffer layer. The crystallinity and surface rms roughness of c-axis oriented films were found to be strongly dependent on the growth rate. Rocking curve full-width half-maximum (FWHM) values of (006) peaks could be decreased to less than 2± by increasing the growth rate. The surface roughness also decreased with growth rate, and rms values as low as 1.5 nm were achieved. On the other hand, too high a growth rate leads to increased roughness due to gas phase nucleation. The optical losses were closely correlated with surface roughness, and the best films had optical losses near 4.5 dBycm at a wavelength of 632.8 nm.
I. INTRODUCTION
Lithium niobate (LiNbO3 ) has excellent ferroelectric and piezoelectric properties and large electro-optic and nonlinear optical coefficients.1 Currently many optical components, such as modulators and switches (which are essential for integrated optical devices), have been fabricated either from titanium (Ti) in-diffused or proton exchanged bulk LiNbO3 (LN) waveguide structures. Ti in-diffusion has a problem in that it enhances optical damage in the near infrared region, thus limiting the maximum transmitted power, while proton exchange waveguides can guide the extraordinary wave only through the waveguide layer.2 Consequently, there has been a strong interest in LN thin films which can be formed epitaxially on inexpensive foreign substrates. Films have several advantages over bulk devices including (i) a higher power density through tight beam confinement resulting from a large optical index difference between film and substrate, (ii) the possibility of monolithic integration with widely used microelectronic or optoelectronic components, and (iii) resistance to optical damage.3 This results in much higher secondharmonic-generation (SHG) efficiencies (2 orders of magnitude) and electro-optic devices which can operate at much faster speeds than bulk structures.4 The preparation of high quality LN waveguiding layers on Si substrates has been of particular interest for a)
Address all correspondence to this author. e-mail: [email protected]
2662
http://journals.c
Data Loading...
