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Browse Prior Art Database

Photodiode Compatible With Bipolar Technology Using Variable Bandgap Intrinsic Layer

IP.com Disclosure Number: IPCOM000120415D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Cressler, JD: AUTHOR [+3]

Abstract

This article describes a novel PIN photodiode that uses a variable bandgap intrinsic layer and can be easily incorporated into a bipolar process technology.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Photodiode Compatible With Bipolar Technology Using Variable Bandgap
Intrinsic Layer

      This article describes a novel PIN photodiode that uses a
variable bandgap intrinsic layer and can be easily incorporated into
a bipolar process technology.

      For future computer system applications, optical coupling of
sub- systems can offer potentially higher data transmission rates
than conventional electrical connections. While silicon PIN
photodiodes can offer very high bandwidth detectors of optical
signals, these structures are not compatible with conventional
silicon digital technologies. Thus, if PIN detectors were used, a
separate chip would be required to detect incoming optical signals,
adding a substantial delay penalty.

      Silicon PIN photodiodes operate in the following manner: large
reverse bias is applied to the diode so that the intrinsic layer is
completely depleted.  The incoming optical signal generates electron-
hole pairs which are accelerated in the applied field to the
saturation velocity (107cm/sec).  For optimal speed vs quantum
efficiency (number of pairs generated per photon), the intrinsic
layer thickness must be on the order of 1/a, where a is the
absorption coefficient of silicon (about 800 cm-1 at .8 um wavelength
at 300oK).  This requires an intrinsic thickness of greater than 10
um, and is, therefore, incompatible with digital technologies.

      It is well known that because of its smaller bandgap, germanium
has a much higher absorption coefficient than silicon (about 35000
cm-1 at 300oK).  Thus, an optimum photodiode design would only
require about .30 um of intrinsic layer.  With either Molecular Beam
Epitaxy or any other low-temperature epit...