Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2001-07-10
2004-09-28
Zarabian, Amir (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S293000
Reexamination Certificate
active
06798001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device, more particularly relates to a semiconductor device having a photo diode for receiving a plurality of light having different wavelengths.
2. Description of the Related Art
Light receiving elements, that is, photodiodes, are being widely used as optical sensors for converting an optical signal to an electrical signal for control use in optical sensor applications in a variety of photoelectronic conversion apparatuses and for optical pickup applications installed in CD, DVD, and other optical disk drives.
There are several kinds of the above photo diode, but basically it is comprised of a pn junction of a semiconductor.
When applying an inverse bias to a pn junction, a depletion layer spreads in a p-type semiconductor region and an n-type semiconductor region, respectively, from a pn-junction surface. Electron-hole pairs are generated by light absorbed mainly in the depletion layer. The electrons move to the n-type semiconductor region drawn by the electric field, while the holes move to the p-type semiconductor region and are detected as a current.
Particularly, by providing an I layer (p
−
-layer or n
−
-layer) containing conductive impurities at a low concentration between the p-layer and n-layer, it is possible to have the depletion layer spread by a low voltage. This is called a PIN photo diode.
FIG. 1A
is a sectional view of the above PIN photo diode.
For example, a p
−
-type semiconductor layer
11
is formed on the p
+
-type semiconductor substrate
10
, furthermore, an n-type semiconductor layer
12
is formed at a surface region of the p
−
-type semiconductor layer
11
so that the pn junction is formed.
A p
+
-type semiconductor layer
13
is formed to surround the PIN diode region. It becomes a take-out portion of a p-region and isolates the PIN diode region from other elements.
A protective insulating film
14
comprised of silicon oxide etc. is formed at an upper layer of the n-type semiconductor layer
12
and the p
+
-type semiconductor layer
13
. Contacts respectively reaching the n-type semiconductor layer
12
and the p
+
-type semiconductor layer
13
are opened, and take-out electrodes (
15
a
and
15
b
) are formed.
When applying a predetermined inverse bias to the pn-junction of the PIN photo diode shown in
FIG. 1A
, a depletion layer V spreads from the pn-junction surface to the directions of the p
−
-type semiconductor layer
11
and n-type semiconductor layer
12
as shown in FIG.
1
B.
Here, the depletion layer V spreads so that the total number of carriers becomes equal at the n-side and p-side, so spreads more to the p
−
-type semiconductor layer
11
side having a low carrier concentration.
However, a photo diode such as the above conventional PIN photo diode is normally designed to be in a structure which is optimized for light having a certain wavelength, for example, near 780 nm when used in a CD system and near 650 nm when used in a DVD system. Generally, in a photo diode of the same structure, there is a large wavelength dependence of the light receiving sensitivity, so when trying to receive a plurality of light having different wavelengths such as light of wavelengths of 780 nm and 650 nm, by an identical photo diode or by a plurality of photo diodes of the same structure present on an identical substrate, the sensitivity ends up greatly differing at the different wavelengths. Thus, for practical use, it was necessary to make the sensitivities match in a required wavelength region.
The above wavelength dependence of the light receiving sensitivity is derived from the fact that the light receiving sensitivity differs in accordance with the laser wavelengths and the structure of the photo diode since when the reflection of light at the light receiving surface is 0%, the light receiving sensitivity S=e&lgr;/hc at a quantum efficiency of 100% stands, so the light receiving sensitivity at the quantum efficiency of 100% rises as the wavelength becomes longer in proportion to the wavelength, while the length of light absorption becomes shorter as the light wavelength becomes shorter.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device having a photo diode having substantially the same sensitivity for a plurality of light of different wavelengths.
To achieve the above object, a semiconductor device of the present invention is a semiconductor device having a photo diode comprising a first conductivity type semiconductor layer and a second conductivity type semiconductor layer formed at a surface layer portion of said first conductivity type semiconductor layer, wherein the sensitivity of said photo diode to light of a first wavelength and the sensitivity to light of a second wavelength which is different from said first wavelength are made to become substantially the same by designing a region in which a depletion layer spreads from a junction surface of said first conductivity type semiconductor layer and said second conductivity type semiconductor layer when inverse biases are applied to said first conductivity type semiconductor layer and said second conductivity type semiconductor layer.
In the semiconductor device of the present invention, preferably the sensitivity of said photo diode to light of a first wavelength and the sensitivity to light of a second wavelength are made to become substantially the same by designing impurity concentrations and said inverse biases of said first conductivity type semiconductor layer and said second conductivity type semiconductor layer and by designing said region in which a depletion layer spreads.
Preferably, in the above semiconductor device of the present invention, the depletion layer is designed to spread in a region including a region 3 to 6 &mgr;m or 2 to 7 &mgr;m in the depth direction from a surface of the second conductivity type semiconductor layer.
Preferably, in the above semiconductor device of the present invention, the first conductivity type semiconductor layer is formed on a first conductivity type semiconductor substrate containing a first conductivity type impurity at a higher concentration than the first conductivity type semiconductor layer.
More preferably, the concentration of the first conductivity type impurity on the surface of the first conductivity type semiconductor substrate is at least 1×10
17
/cm
3
.
More preferably, a distance between an end face of said depletion layer on said first conductivity type semiconductor substrate side and the surface of said first conductivity type semiconductor substrate is 3 &mgr;m or less.
In the semiconductor device of the present invention, preferably said first wavelength is 780 nm and said second wavelength is 650 nm.
Furthermore, to achieve the above object, a semiconductor device of the present invention is a semiconductor device comprising a first conductivity type semiconductor substrate, a first conductivity type semiconductor layer formed on a first conductivity type semiconductor substrate and containing a first conductivity type impurity at a lower concentration than said first conductivity type semiconductor substrate, and a second conductivity type semiconductor layer formed at a surface layer portion of said first conductivity type semiconductor layer, wherein a photo diode is formed by spreading a depletion layer from a junction surface of said first conductivity type semiconductor layer and said second conductivity type semiconductor layer when inverse biases are applied to said first conductivity type semiconductor layer and said second conductivity type semiconductor layer, and the concentrations of the impurity of said first and second conductivity layers are adjusted so that the depletion layer spreading region is made wherein the sensitivity of said photo diode to light of a first wavelength and the sensitivity to light of a second wavelength which is different from said first wavelength become sub
Arai Chihiro
Fujisawa Tomotaka
Rose Kiesha
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
Zarabian Amir
LandOfFree
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