Fabrication of infrared detector with monolithic microlens produced in thermal reflow process

We report fabrication of monolithic GaAs immersion lens with a sub-milimeter diameter for InAsSb infrared detectors. The microlenses were produced by thermal reflow process of cylindrical photoresist structures, followed by dry etching. The implementation of microlens leads to an increase in the optical area of the photodetector, while maintaining the electrical area dimensions. Detectors with microlenses exhibit three times higher normalized detectivity D* than flat detectors, while conserving a similar level of resistance and current sensitivity. This result proves that the processes related to lens formation do not result in degradation of the photosensitive structure.