Design and Fabrication of Semiconductor Laser Arrays for Biosensing Applications

In addition to the arrival of aging society, the growing demands on the improvement of the quality of life have driven the booming development of the health care market. Among them, in vitro diagnostic medical devices will play a crucial role in future medical industry due to their highly innovation and convenience. In fact, how to establish a direct and rapid detection of biological samples by using micro-biosensing chip is also an important work to disease prevention, and to achieve real-time detection and treatment. Nowadays, fluorescence-based detection methodologies have extensively used in a variety of biological applications; however, the drawbacks of such work including a complex procedure and expensive analytical equipments, which are adverse to the feasibility of their mass production. In order to simplify the analysis processes, reduce costs and accurately detect the presence of specific biological molecules, semiconductor laser arrays in combination with micro-fluidic channels are proposed to serve as the biological sensor. The biological molecules with different sizes and shapes function as optical waveguides in the micro-fluidic channels can confine the laser beam and thus create a unique optical spectrum associated with the biological molecules. Because the optical signals can be enhanced by the cavity effects, the fabricated biosensors will exhibit both real-time and improved detection sensitivity. Taking the optical absorption loss and the effective index into account, GaAs-based 850-nm semiconductor lasers are preferential. With the merits of low manufacturing cost as well as excellent device characteristics, the oxide-confined vertical cavity surface emitting lasers (VCSELs) are thought as the preferential candidate in biosensing applications. Besides, the micro-fluidic channels can be formed easily by wet etching of AlxOy while keeping the optical and carrier confinements conserved. Further improvement of detection sensitivity of the biosensors can be done by filtering off the high-order transverse modes of VCSELs. With reduction the size of the oxide aperture to the point where only the fundamental mode is supported, we can succeed in fabricating a single transverse-mode VCSEL. However, the drawback of this approach is the lower light output power, and a reduced laser lifetime due to the small active volume. Besides, when light pass through the narrow oxide aperture the diffraction effect becomes severe and thus deteriorates the fiber coupling efficiency significantly. Instead of conventional VCSELs, we will design and fabricate the “one-dimensional (1D) ring-shaped laser arrays with micro-fluidic channels” in this project. Because the respective lasing element within the light emission region couples coherently into an in-phase array mode, the fabricated laser array could fulfill the requirements of high-power (＞ 10 mW), single transverse mode, and on-axis projection. Experimentally, we shall optimize the geometry of the laser array, and then using surface etching or ion implantation technique to define a selective high-loss region so that all of the array elements can be kept in-phase. On the other hand, we will also seek the optimum layer thickness of Al0.98Ga0.02As so as to satisfy the fluent transport of the biological molecule within the micro-fluidic channels, simultaneously, possessing a stable lasing-mode. Eventually, we anticipate to realization of a high-sensitivity miniaturized biosensor for the real-time detection of human blood cells and protein.

Project ID:PB9907-12645
External Project ID:NSC99-2221-E182-043