Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
1999-12-28
2001-11-06
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S432000, C257S443000, C257S446000, C257S343000
Reexamination Certificate
active
06313484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-receiving device including a built-in circuit for processing a photoelectrically converted signal (hereinafter, referred to as a “circuit-integrated light-receiving device”). More particularly, the present invention relates to a circuit-integrated light-receiving device having a capability of improving the response speed of a photodiode which generates the photoelectrically converted signal based on incident light.
2. Description of the Related Art
In recent years, an optical disk apparatus is required to process a large amount of data such as video data at a high speed. For example, an optical disk apparatus for use with a DVD (a DVD-ROM apparatus) has been rapidly improved in terms of the data read speed (e.g., from a normal-speed drive to a double-speed drive). In the future, an optical disk apparatus with an even faster data read speed (e.g., a 12×-speeddrive) will be demanded. A DVD-ROM apparatus typically uses an optical pick-up chip for reading out signals. The optical pick-up chip includes, on the same chip, a light-receiving device and a signal processing circuit for processing a photoelectrically converted signal from the light-receiving device. In order to further increase the operating speed of a DVD-ROM apparatus, there is a demand to increase the operating speed of the light-receiving device which is included in such an optical pick-up (more generically a “circuit-integrated light-receiving device”).
Conventionally, a light-receiving device included in an optical pick-up employs a PN junction between an N-type epitaxial (semiconductor crystal growth) layer and a P-type substrate, or a PN junction between an N-type epitaxial layer and a P-type diffusion layer. However, when the former type of PN junction between an N-type epitaxial layer and a P-type substrate is used, a photo carrier generated in the substrate moves by diffusion, thereby reducing the response speed. On the other hand, when the latter PN junction between an N-type epitaxial layer and a P-type diffusion layer is used, the junction capacitance increases according to the impurity concentration in the N-type epitaxial layer, thereby also reducing the response speed. Moreover, when the latter PN junction is used in a DVD apparatus, a major portion of the laser light having a wavelength of 650 nm which is used by the DVD apparatus as reproduction light goes into the substrate, thereby reducing the operational sensitivity.
As described above, the conventional circuit-integrated light-receiving device is likely to have poor operational characteristics as compared with a pin photodiode which does not include a built-in circuit.
In order to solve these problems, a number of structures have been proposed in the art.
FIG. 26
illustrates a structure which is disclosed in Japanese Laid-Open Publication No. 61-154063. In this structure, a P-type epitaxial layer
142
is provided on the surface of a P
+
-substrate
141
. The P-type epitaxial layer
142
includes a P-type high-impurity concentration layer (auto-doped layer)
142
a
and a P-type low-impurity concentration layer
142
b
. The P-type high-impurity concentration layer
142
a
is provided by an upward diffusion (auto-doping) of an impurity from the substrate
141
which occurs during the growth of the P-type epitaxial layer
142
.
An N-type epitaxial layer
143
is provided on the P-type epitaxial layer
142
. A P
+
-separation diffusion layer
144
having a high impurity concentration extends from the upper surface of the N-type epitaxial layer
143
to the underlying P-type epitaxial layer
142
. The separation diffusion layer
144
divides the N-type epitaxial layer
143
into a number of regions and separates the regions from one another.
Some of the separated regions of the N-type epitaxial layer
143
each form a light-receiving device section
180
. In particular, the light-receiving device section
180
includes a PN junction formed between one of the separated regions of the N-type epitaxial layer
143
and the underlying P-type epitaxial layer
142
. Each of the other ones of the separated regions of the N-type epitaxial layer
143
which is adjacent to the light-receiving device section
180
forms a signal processing circuit section (NPN transistor)
190
. In the illustrated example, the signal processing circuit section (NPN transistor)
190
includes a buried region
165
for reducing the collector resistance, a base region
147
and an emitter region
148
. The light-receiving device section
180
and the signal processing circuit section
190
are electrically separated from each other by the separation diffusion layer
144
.
An oxide layer
149
is provided on the upper surface of each of these structures. An electrical line layer
150
a
is connected to the contact region
145
of the light-receiving device section (photodiode)
180
via a contact hole provided in the oxide layer
149
. An electrical line layer
150
b
and an electrical line layer
150
c
are connected to the signal processing circuit section (NPN transistor)
190
similarly via a contact hole. The electrical line layer
150
b
is also connected to the separation diffusion layer
144
.
As described above, the structure illustrated in
FIG. 26
includes the substrate
141
having a high impurity concentration and the P-type epitaxial layer
142
which has a lower impurity concentration. Thus, the depletion layer on the side of the P-type semiconductor which forms the photodiode (a region denoted by a one-dot chain line) is substantially extended into the P-type epitaxial layer
142
, thereby reducing the junction capacitance of the photodiode
180
. Due to the extension of the depletion layer, a photo carrier generated in a deep location can sufficiently contribute to the photoelectric current.
Moreover, a P-type high-impurity concentration layer (auto-doped layer)
142
a
included in this structure has a concentration gradient which gradually decreases in the upward direction from the substrate
141
. A potential gradient is produced by the concentration gradient, which in turn generates an internal electric field, whereby it is possible to move at a high speed a photo carrier that is generated in a deep location (lower portion) of the P-type epitaxial layer
142
.
Next,
FIG. 27
illustrates a structure which is disclosed in Japanese Laid-Open Publication No. 4-271172. In the structure, a non-doped first epitaxial layer
224
is provided on a P-type substrate
223
, and a P-type well region
226
is formed in a portion of the non-doped first epitaxial layer
224
corresponding to the location where a signal processing circuit section (NPN transistor)
290
is provided. An N-type second epitaxial layer
225
is provided on the first epitaxial layer
224
. An N
+
-diffusion region
230
is provided in the light-receiving device section (photodiode)
280
in the vicinity of the surface of the N-type second epitaxial layer
225
. Regions
235
,
236
and
237
of the NPN transistor are provided in the signal processing circuit section
290
in the vicinity of the surface of the N-type second epitaxial layer
225
. An N
+
-diffusion region
234
is provided below the regions
235
,
236
and
237
. The signal processing circuit section
290
and the photodiode section
280
are electrically separated from each other by a separation diffusion region
227
including two regions
228
and
229
.
An oxide layer
231
is provided on the surface of each of the structures. Electrical line layers
232
and
233
are connected to the light-receiving device section (photodiode)
280
via a contact hole provided in the oxide layer
231
. An electrical line layer
238
is connected to the signal processing circuit section (NPN transistor)
290
similarly via a contact hole.
The structure illustrated in
FIG. 27
employs the substrate
223
having a specific resistance of about 40 &OHgr;cm to about 60 &OHgr; so as to control the auto-doping process from the substra
Fukunaga Naoki
Kasamatsu Toshimitsu
Kubo Masaru
Ohkubo Isamu
Oka Mutsumi
Abraham Fetsum
Andujor Leonardo
Sharp Kabushiki Kaisha
LandOfFree
Circuit-integrated light-receiving device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit-integrated light-receiving device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit-integrated light-receiving device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2580246