# Presentation: 145741

## Objective:  Photonic crystal based integrated optic & THz devices based on patterned, epitaxial LiNbO3 thin films.

-   Solutions:  Eliminate OH as source of autocatalytic cycle (*e.g*., Me3ClSi).
- 	        Introduce decomposition intermediate as precursor.
-  Obstacle: LiNbO3 highly inert  photolithographic patterning impractical.
-    Solution:  Amorphous LiNbO3
- 	–  Can be lithographically patterned, doped & etched.
- 	 – Indistinguishable from the LiNbO3 substrate after
-                    solid state regrowth.

- Thomas F. Kuech & Leon McCaughan
- University of Wisconsin – Madison
- DMR-0505775

**Objective:  Photonic crystal based integrated optic & THz devices based on **_***patterned, epitaxial LiNbO***__***3***__*** thin films***_**.**

**Notes:**
Ferroelectrics are but one class of materials capable of performing direct wavelength transformations of electromagnetic radiation via nonlinear  processes [e.g, optical  THz; wavelength switching for WDM (wavelength division multiplexed) fiber optic systems] as well as very high speed optical modulation and quantum-noise limited amplification via parametric processes. 

The combined attributes of low loss waveguiding, large 2nd order non-resonant nonlinearity (i.e., wide bandwidth), a wide window of transparency (0.4 – 5 um), and ease of velocity (phase) matching the product and pump(s) via periodic poling, make LiNbO3 and its sister ferroelectrics superior to both group IV and III-V semiconductors.  And unlike their polymer counterparts, the performance parameters (low loss and large nonlinear efficacy in one device) of ferroelectric oxide devices  such as LiNbO3 have been commercially corroborated.  

 One capability of these oxides still eludes us: the ability to grow optically-thick (several microns) films with well defined stoichiometries. CVD growth rates for  these ferroelectric films are notoriously low.  Earlier, we identified H20-driven  autocatalytic processes that convert deposition products to hydroxides instead of oxides – lowering the growth rate.  Based on these results, we are developing new chemistry to eliminate this pathway and raise the growth rate.
 Patterning is impractical:  etch rates (wet or dry) of ferroelectrics such as LiNbO3 are extremely low.  However, we have found that an amorphous version of  LiNbO3 will rapidly etch in even weak HF solutions.  Equally significant, the pattern can be converted to its crystalline form with a solid state regrowth (annealing at ~ 900 C for 1 h).  Preliminary results (via an EO modulator and Maker fringe analysis) have confirmed that the annealing restores the 2nd order nonlinear optical properties.

Preliminary results:
1. Introduction of  Me3SiCl  as  a  Reactive Carrier Gas  Doubles growth rate.
      Experiment:     Me3SiCl + Nb(OEt)5   Nb(OEt)xCly +  Me3Si-OEt
      Conclusions:     
         OEt groups on Nb (containing elements of H2O) replaced by Cl
         Me3SiCl short-circuits detrimental auto-catalytic cycle 

2. Intermediate as a precursor:  Nb(OEt)xCly decomposes by a simpler mechanism at a lower temp than Nb(OEt)5 or NbCl5:  cooperative ligand decomposition mechanism.

3. Amorphous LiNbO3: 
-LN can be more rapidly grown (>2 um/h) & patterned using standard photolithography. 
-LiNbO3 etches rapidly in dilute HF (~7 mm/min. in 4% HF)
      -LiNbO3 grown on LiNbO3 crystallizes on annealing at 1000oC for 1h. 
      Crystalline LiNbO3 substrate serves as an etch stop.

## Results: 
Growth rate doubles with Me3SiCl  as  a  Reactive Carrier Gas.
Intermediate Nb(OEt)xCly as a precursor. 
Amorphous LiNbO3 (or Ti:LiNbO3) film easily patterned by standard photolithography and wet etching.

- Growth rate doubles with Me3SiCl  as  a  Reactive Carrier Gas.
- Intermediate Nb(OEt)xCly as a precursor.
- Amorphous LiNbO3 (or Ti:LiNbO3) film easily patterned by standard photolithography and wet etching.

- Ridge Waveguides

- FIB: IR photonic crystal (*a*~2 m)

- RIE: THz photonic
- crystal (*a*~ 7 m)

_*Payoff:*_*  Enable a new class of truly compact, ultra-fast electro-optic and all-optical devices and circuits.*

***  ******Outreach efforts focus on the inclusion of undergraduate women in the program research***

**Objective:  Photonic crystal based integrated optic & THz devices based on **_***patterned, epitaxial LiNbO***__***3***__*** thin films***_**.**

- Thomas F. Kuech & Leon McCaughan
- University of Wisconsin – Madison
- DMR-0505775