The ability to fabricate high resolution nanostructures is fundamental to next generation research at CQD. Electron beam lithography allows users to precisely define the placement and dimensions of nanoscale features on a variety of different substrate materials.

After performing pattern definition in resist, the pattern can be transferred using additive methods such as metal deposition and lift off or subtractive methods such as dry or wet etching.

At CQD, electron beam lithography research is driven by the need for advanced optoelectronic devices such as low threshold laser structures, high efficiency photodetectors, and multicolor optical detectors.

Nanopillars

Accurate size control and placement after pattern transfer into Type-II InAs/GaSb superlattices.

Using electron beam lithography and reactive ion etching techniques, low dimensional nanopillar structures have been formed in GaSb, InAs/GaSb, GaInAs and GaInP, GaN, InGaN and AlGaN basedmaterials. Etched pillar diameters of 20 nm have been achieved with aspect ratios over 10:1.

Left, GaSb nanopillar with 20 nm diameter. Right, Metal etch mask after liftoff with diameters < 40 nm.

GaInAs/InP nanopillars exhibited a strong photoluminescence peak wavelength blue-shift compared to the as-grown quantum well material, confirming the expected quantum size effect confinement in such nanostructures.

GaInAs/InP nanopillars photoconductors shown covered with a metal top contact.

In addition, top and bottom metal contacts have been successfully realized using a polyimide planarization and etchback procedure. I-V and noise measurements have been performed. Optical measurements indicate photoconductive response in selected nanopillar arrays. Device peak wavelength response occurs at about 8 μm with peak device responsivity of 420 mA/W. Peak detectivity of 3x10⁸ cm·Hz^½/W has been achieved at -1V bias and 30K.

Gratings

Linear and circular grating structures are also routinely fabr icated in our laboratory using continuous path control writing which avoids stitching errors.

Circular grating with 130 nm linewidth and a period of 250 nm at a beam energy of 5 keV and dry etch depth of 230 nm defined in GaAs. These grating structures find applications in VCSEL.

Depending on the material system, a variety of grating periods can be achieved. These grating structures find applications in DFB (Distributed Feedback) lasers and VCSELs (Vertical Cavity Surface Emitting Laser).

Linear grating with a period of 270 nm, linewidth of 85 nm and etch depth of 100 nm is defined into AlGaN/GaN material system.

Micro-Ring Resonators

In optical transmission systems, filters are essential components that combine/separate wavelength carrying different information and can be used to increase the channel information capacity of optical fibers. This de-/multiplexing capability of closely spaced channels is a key requirement for wavelength division multiplexing (WDM) and dense WDM (DWDM) in optical telecommunication and especially All Optical Networks (AON).

There is a large interest in the 1.3 μm and 1.55 μm wavelength windows for this purpose, and several types of filters have been designed and fabricated for those windows, including micro-ring resonator (MRR).

SEM imaging of fabricated micro ring resonators.

These micro-ring resonators are ideal candidates for very large scale integrated (VLSI) photonic circuits, as they provide a wide range of optical signal processing functions while being ultra compact. Their typical size ranges from a few μm to 200 μm, resulting in a 105 devices/cm² density.

In particular, micro-ring resonators using GaInAsP/InP based materials have the highest potential for telecommunication applications because their bandgap range covers the 1.3 μm and 1.55 μm spectral windows.

The Center for Quantum Devices has demonstrated microring resonators in this material system through the use of electron beam lithography and dry etching.

Optical micrograph of a resonator structure containing racetrack resonators (top) that are coupled with waveguides by two small ring resonators as illustrated in the magnified view of the red rectangle (bottom).

Last Updated 01/31/2007