Photodiode Compatible With Bipolar Technology Using Variable Bandgap Intrinsic Layer
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Cressler, JD: AUTHOR [+3]
This article describes a novel PIN photodiode that uses a variable bandgap intrinsic layer and can be easily incorporated into a bipolar process technology.
Photodiode Compatible With Bipolar Technology Using
describes a novel PIN photodiode that uses a
variable bandgap intrinsic layer and can be easily incorporated into
a bipolar process technology.
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.
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...