R. P. Tompkins

GaN Photonic Crystal-Based, Enhanced Fluorescence Biomolecule Detection System

The need for small form factor, portable biosensing platforms is prevalent across a wide range of medical, environmental, and defense applications. This paper presents the design of a novel, integrated optofluidic photonic crystal biosensor architecture that shows potential for meeting the single molecule detection requirements of these application areas. GaN is being targeted as the photonic crystal slab material due to its transparency in the visible spectral range and also the potential for creating high aspect ratio photonic crystal lattices via polarity inverted MBE growth. Results of optical modeling efforts indicating 10-15x resonant enhancement of fluorescent emission and polarity inversion GaN growth techniques will be discussed.

Optofluidic photonic crystals for biomolecular fluorescence enhancement : a bottom-up approach for fabricating GaN-based biosensors

The application of photonic crystals in biosensor applications has lead to the development of highly sensitive and selective sensor elements. The research efforts undertaken by this group have led to the development of a photonic crystal transducer that acts as a waveguide, nanofluidic flow channel, and resonant defect cavity. This sensor architecture shows promise for greatly enhancing the emission of naturally fluorescent or fluorescently-labeled biomolecules. Due to its transparency in the visible regime, GaN is a viable candidate for this photonic crystal biosensor application. This paper provides an overview of the sensor architecture as well as a discussion of one particular bottom-up approach to its fabrication. Molecular Beam Epitaxy (MBE) growth of heavily Mg doped GaN can result in inversion of the surface polarity from Ga-polar to N-polar GaN. This bottom-up approach includes patterning and etching of the Mg inversion layer, followed by re-growth of the opposite polarity to produce periodically poled GaN. Subsequent wet etching of N-polar regions then produces a GaN based photonic crystal structure. This process shows promise for achieving high aspect ratio, highly anisotropic nanostructures.

Design and Characterization of Optofluidic Photonic Crystal Structures for the Detection of Fluorescent-Labeled Biomolecules

Nanoscale photonic crystal (PhC) materials enable the application of optical bandgap engineering in optofluidic systems, further enhancing their utility and range of function [1]. A photonic bandgap can be formed in a photonic crystal material by periodically varying the refractive index in 1, 2, or 3 dimensions, creating a nanoscale lattice structure that is analogous to the atomic structure found in homogenous crystalline materials. The design and fabrication of this engineered lattice, as well as the controlled introduction of lattice defects [2], allows the unique properties of 2-dimensional PhC structures to be exploited in a variety of optical biosensor designs [3],[4].

Polarity Inverted GaN for Photonic Crystal Biosensor Applications

Periodic poling of GaN (alteration of the crystallographic direction along the c-axis) has potential for applications in photonics, sensing, and non-linear optics. One approach to periodic poling of GaN, involves Molecular Beam Epitaxy (MBE) growth of heavily Mg doped GaN which results in inversion of the surface polarity from Ga-polar to N-polar GaN. Fabrication and dry etching of the inversion layer followed by re-growth, and a subsequent highly anisotropic wet etch of re-grown N-polar regions can result in periodically poled GaN with features on either the micro or nanoscale. This paper outlines the design of GaN based photonic crystal biosensors based on periodic poling. Initial results of growth, fabrication, and theoretical modeling will be discussed.