Characterization of nGaAs-Au Schottky Diodes as Grating Coupled Photodetectors

Abstract

Using holography and wet chemical etching, a grating of period 450nm and depth of 15nm was fabricated on a n-type GaAs substrate having a doping of 10¹⁶ cm^-3. A 30 nm layer of Au was deposited on the substrate forming a Schottky contact. The ohmic back contact is an alloy of Ni, Au and Ge. These devices were optically and electrically characterized.

Optical characterization was done using a polarized 632.8 nm HeNe laser. Reflectivity measurements for complete angular scans with output currents were determined. It was observed that as reflectivity dropped to a minimum, at a specific incident angle, the output current peaked. This was attributed to excitation of surface plasma oscillations in the grating, allowing greater photon absorption in the depletion region. This was observed only when the incident electric field was p-polarized and normal to the orientation of the grating, thus satisfying the surface plasma resonance conditions.

Under the above conditions, it was observed that in a grating coupled photodetector a higher quantum efficiency can be achieved.