Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
1999-12-03
2001-08-28
Chapman, Mark (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
Reexamination Certificate
active
06281428
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photovoltaic generator and, more particularly, to a photovoltaic generator with such advantages as high photoelectric conversion efficiency, low series resistance, easy circuit layout design, and feasibility of integration with other devices on the same chip without utilizing any extra photolithographic procedure for device isolation.
BACKGROUND OF THE INVENTION
A photovoltaic generator is a widely used photoelectric device that can be used not only for detecting the optical radiation but also for generating electric power from the optical radiation.
A photovoltaic generator is mainly operated in the depletion region adjacent the pn junction. When the external optical radiation impinges on the photovoltaic generator, the device internal can be excited to generate electron-hole pairs. These electron-hole pairs then will be separated by the electric field induced by the built-in potential in the depletion region, and the photogenerated current occurs. This photogenerated current can be used to drive an external circuit.
FIG. 1A
is a sectional view of a typical conventional photovoltaic generator that comprises: a substrate
11
, an oxide layer
12
, a p-type impurity diffusion region
13
, a heavily doped n-type impurity diffusion region
14
, an oxide layer
15
, and a metal layer
16
.
In
FIG. 1A
, the oxide layer
12
isolates predetermined isolation regions on the top portion of the substrate
11
. The p-type impurity diffusion region
13
and the heavily doped n-type impurity diffusion region
14
in each of the isolation regions form a pn junction. The metal layer
16
connects the heavily doped n-type impurity diffusion region
14
to the p-type impurity diffusion region
13
of the next pn junction. Series-connected pn junctions are formed in this way as shown in the figure. The oxide layer
15
isolates the metal layer
16
to prevent the occurrence of short circuit between the p-type impurity diffusion region
13
and the heavily doped n-type impurity diffusion region
14
within the same isolation region.
FIG. 1B
is a schematic plan view of the conventional photovoltaic generator. In
FIG. 1B
, the numeral
17
represents a positive electrode and numeral
18
represents a negative electrode. Each square region represents an isolation region, i.e., the region containing a single pn junction. The negative electrode
18
can be connected to the positive electrode
17
of the next stage to obtain more pn junctions in series.
FIG. 1A
clearly shows that each isolation region, which contains a pn junction, is isolated by an oxide layer
12
. Not only does this kind of isolation have a low yield rate, but it also involves a complicated manufacturing process. In addition, it wastes much area on the surface of the silicon substrate, and thus increases the production cost.
The U.S. Pat. No. 5,633,526 discloses another photovoltaic generator that uses a silicon-on-insulator (SOI) wafer as its substrate and takes the insulating layer in the SOI wafer as the isolation. This device resolves the problems of low yield rate and high cost derived from the conventional isolation technology applied on the conventional photovoltaic generator. Nevertheless, this improved photovoltaic generator requires a complicated manufacturing procedure and does not provide a good way to increase the photoelectric conversion efficiency. Furthermore, the concentric plan structure used in this improved photovoltaic generator, as shown in
FIG. 2
, incurs a difficult circuit layout design and many electric application parameters, e.g. the maximal photogenerated current, are limited by the pn junction of the smallest area (i.e. the innermost pn junction). Therefore, the application purview of this prior art photovoltaic generator is limited.
Furthermore, a photovoltaic generator usually needs to be used together with some external circuits. In the prior art, if the photovoltaic generator and some circuit devices are to be integrated into a single chip, extra isolation procedures are needed for the isolation between the devices in addition to the respective manufacturing procedures of the photovoltaic generator and these circuit devices. Therefore, the number of manufacturing procedures increases.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a photovoltaic generator that has high photoelectric conversion efficiency and does not require a complicated manufacturing procedure.
Another object of the invention is to provide a photovoltaic generator that is easy to control and design in a plan circuit layout.
Yet another object of the invention is to provide a photovoltaic generator that can be integrated with other devices within the same chip without the need of an extra photolithographic procedure to isolate them.
The present invention provides a photovoltaic generator comprising a substrate; an insulating layer provided on the substrate; a plurality of first impurity diffusion zones formed on the insulating layer; a plurality of second impurity diffusion zones deep enough to reach the insulating layer and of an opposite polarity to that of the first impurity diffusion zones, the second impurity diffusion zones and the first impurity diffusion zones being alternately positioned on the surface of the substrate to form a plurality of substantially vertical pn junctions; a plurality of third impurity diffusion zones provided on the surface of the first impurity diffusion zones and the second impurity diffusion zones opposite to the insulating layer and of the same polarity as that of the second impurity diffusion zones, one end of each of the third impurity diffusion zones connecting to the adjacent one of the second impurity diffusion zones while the other end connecting to the adjacent one of the first impurity diffusion zones so that the third impurity diffusion zone strides over one of the plurality of vertical pn junctions; a plurality of fourth impurity diffusion zones formed on the surface of the adjacent one of the first impurity diffusion zones and the adjacent one of the second impurity diffusion zones opposite to the insulating layer and being a heavily doped impurity diffusion zones of the same polarity as that of the first impurity diffusion zones, each of the fourth impurity diffusion zones connecting to the adjacent one of the first impurity diffusion zones without contact with the adjacent one of the third impurity diffusion zones that connects to the same one of the first impurity diffusion zones and striding over at most one of the plurality of vertical pn junctions; a plurality of thin-film electrodes each connecting the adjacent one of the fourth impurity diffusion zones and the adjacent one of the second impurity diffusion zones and/or the adjacent one of the third impurity diffusion zones on the adjacent one of the second impurity diffusion zones; and a plurality of isolation zones each provided between the plurality of thin-film electrodes.
Furthermore, each of the third impurity diffusion zones that extends to the adjacent one of the first impurity diffusion zones can increase both the area of the pn junction and the photoelectric conversion efficiency.
Moreover, to increase the optical radiation absorption rate, the height of the first and second impurity diffusion zones on the substrate are increased in the vertical direction. However, due to the manufacturing consideration of the second impurity diffusion zones, heavily doped impurity diffusion zones are necessary.
In accordance with a preferred embodiment of the invention, the first impurity diffusion zones and the second impurity diffusion zones are linearly deployed in a parallel photovoltaic generator structure that is fairly easy to design for circuit layout designers.
The above-mentioned linear parallel photovoltaic generator array takes advantage of the mesa structure formed on the peripheral region for isolation. Not only is this manufacturing process easier but it also increases the production yield.
Moreover, the photovoltaic generator ar
Chiu John C. C.
Lai Steven
Chapman Mark
Opto Tech Corporation
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