Al nanogrid electrode for ultraviolet detectors.

Optical properties of Al nanogrids of different pitches and gaps were investigated both theoretically and experimentally. Three-dimensional finite-difference time-domain simulation predicted that surface plasmons at the air/Al interface would enhance ultraviolet transmission through the subwavelength gaps of the nanogrid, making it an effective electrode on GaN-based photodetectors to compensate for the lack of transparent electrode and high p-type doping. The predicted transmission enhancement was verified by confocal scanning optical microscopy performed at 365 nm. The quality of the nanogrids fabricated by electron-beam lithography was verified by near-field scanning optical microscopy and scanning electron microscopy. Based on the results, the pitch and gap of the nanogrids can be optimized for the best trade-off between electrical conductivity and optical transmission at different wavelengths. Based on different cutoff wavelengths, the nanogrids can also double as a filter to render photodetectors solar-blind.

Thermal recovery processes in laser irradiated HgCdTe (PC) detectors.

An experimental method for measuring the transient and steady-state thermal characteristics of ir photoconductors is introduced. Thermal recovery processes in laser irradiated HgCdTe (PC) detectors were investigated. The characteristics of thermal recovery processes are found to be quite sensitive to the specific details of detector construction. For the most part thermal recovery in these detectors takes place on two separate time scales. Initially the signal recovers partially to an intermediate level on a time scale of several milliseconds. The rest of the recovery occurs much more slowly, i.e., on the order of hundreds of milliseconds. It was found that the magnitude of the thermally induced signal, the relative importance of the two recovery processes, and the exact shape of the thermal recovery curve vary with power density and irradiation time. A one-dimensional thermal model of the detector for both pulsed and cw laser irradiation is presented. Calculated thermal recovery curves are found to agree we l with the experimental results for irradiation times as long as 20 msec. The two recovery times are found to be due to the two thermally resistive bonding layers. The utility of this model for predicting the thermal characteristics of new improved detector designs is discussed.