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Metal-Semiconductor-Metal Photodetector for Dual Wavelength Operation

IP.com Disclosure Number: IPCOM000102441D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 112K

Publishing Venue

IBM

Related People

Bassous, E: AUTHOR [+4]

Abstract

Metal-Semiconductor-Metal (MSM) photodetectors can offer certain advantages over more conventional p-i-n type detectors. Their principle of operation is as follows. Alternate metal-semiconductor contacts form blocking Schottky barriers, and a voltage bias is applied between them. Carriers generated by light in the semiconductor region are swept by the field to these contacts. Interdigitated geometries maximize the collection efficiency and minimize transit time effects. Despite large area sizes capacitance is relatively small due to the edge-on geometry. Fabrication is also very simple due to the single level nature of the device. GaAs MSM detectors are compatible with MESFET preamplifiers and have been used in front-end receiver approaches for 0.8 mm [1].

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This is the abbreviated version, containing approximately 51% of the total text.

Metal-Semiconductor-Metal Photodetector for Dual Wavelength Operation

       Metal-Semiconductor-Metal (MSM) photodetectors can offer
certain advantages over more conventional p-i-n type detectors.
Their principle of operation is as follows. Alternate
metal-semiconductor contacts form blocking Schottky barriers, and a
voltage bias is applied between them. Carriers generated by light in
the semiconductor region are swept by the field to these contacts.
Interdigitated geometries maximize the collection efficiency and
minimize transit time effects. Despite large area sizes capacitance
is relatively small due to the edge-on geometry. Fabrication is also
very simple due to the single level nature of the device. GaAs MSM
detectors are compatible with MESFET preamplifiers and have been used
in front-end receiver approaches for 0.8 mm [1]. In GaAs MSM
detectors grown as a strained layer on GaAs have also been fabricated
for long wavelength detection (1.3 mm) and integration with the same
GaAs-based MESFET technology [2]. Here, the use of germanium as a
semiconductor material for MSM photodetectors is proposed.  The
absorption depth from 0.8 mm to 1.3 mm is less than 1 micron (from
about 3000 Ao to 10000 Ao, respectively, at room temperature) and is
therefore compatible with MSM interdigitated geometries (the finger
spacing should be of the order of the absorption depth for maximum
collection efficiency - this ensures that the drift region matches
the electron/hole pair creation region). Germanium may also be grown
on silicon so that the rest of the receiver circuitry can be made in
silicon - a potential advantage due to the maturity of this
technology. The lattice mismatch between germanium and silicon is
large at 4%, and special growth techniques would have to be applied
to ensure minimum defects at the MSM device (and therefore minimum
leakage current). This can be done by first ensuring a sufficiently
thick buffer layer of germanium below the surface and also by
utilizing strained superlattice buffer layers that tend to bend over
threading dislocations [3].

      Fig. 1 shows a schematic of a germanium MSM. In this case gold
contacts, 500 nm thick, which form a barrier height of approximately
0.6 eV, are used. Other metals may also be used. The metal
interdigitated contacts are...