Microcavity plasma photodetectors: Photosensitivity, dynamic range,and the plasma-semiconductor interface

Detailed measurements of the photosensitivity of Si microcavity plasma photodetectors in the visible and near-infrared (420-1100 nm) are reported for input optical intensities to a 100 × 100 μ m 2 inverted pyramid device varied over three orders of magnitude ( 10 − 5 - 10 − 2 W cm − 2 ) . By resolving the contribution to the overall device response from the plasma/semiconductor interaction, as opposed to bulk Si photoconductivity, the photosensitivity of the plasma photodetector operating in 500 Torr of Ne was determined to range from ( 2.2 ± 0.4 ) A ∕ W for 2 nW of input power (at λ = 780 nm ) to ( 1.3 ± 0.2 ) A ∕ W at ∼ 0.65 μ W . The spectral response profile of the hybrid plasma/semiconductor detector is similar to that of a conventional p n junction photodiode, but is blueshifted by ∼ 60 nm . Also, the peak photosensitivity ( 3.5 A ∕ W at λ ≃ 900 nm ) of a Si microplasma device having a 50 × 50 μ m 2 aperture is approximately twice that for its larger ( 100 × 100 μ m 2 ) counterpart under identical conditions. Analysis of the data suggest that bandbending at the p -Si surface is sufficiently strong for a thin n -type region to form, thereby resembling a metal-oxide-semiconductor capacitor in the inversion mode. Electrons in this thin layer tunnel through the vacuum (Si-plasma) barrier, followed by electron avalanche in the nonequilibrium plasma. These results illustrate the potential for novel optoelectronic devices when interfacing a plasma with a semiconductor and coupling the two media with a strong electric field imposed across the interface.