Patent Application
20120325300
This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 100121674 filed in Taiwan, R.O.C. on Jun. 21, 2011, the entire contents of which are hereby incorporated by reference.
The present invention relates to an inverted metamorphic (IMM) solar cell semiconductor structure and a laser lift-off (LLO) method for the same, and more particularly, to semiconductor structure that lifts off a substrate layer from a plurality of bandgap layers by using extrinsic laser.
In the prior art, a gallium nitride (GaN) light-emitting diode (LED) adopts sapphire as a substrate material due to limitations of epitaxy. However, a sapphire substrate has a rather unsatisfactory heat conductivity, which severely depreciates light-emitting efficiency of the LED. Therefore, the sapphire substrate is removed and is replaced by a substrate made of other materials having a better heat conductivity.
There are three conventional methods for removing the sapphire substrate. The first method is removing the sapphire by abrasion, the second is by etching, and the third is by laser. Among the three methods, removing the sapphire substrate by laser is the most effective.
However, the three methods above are only applicable to an LED comprising GaN and a sapphire substrate. For an IMM solar cell that is becoming increasingly prevalent, there is a need for a material that matches a sacrifice layer and suitable for a gallium arsenide (GaAs) substrate for overcoming issues associated with the conventional manufacturing of a solar cell.
It is an object of the present invention to provide an inverted metamorphic (IMM) solar cell semiconductor structure for use of a laser lift-off (LLO) process using external laser.
It is another object of the present invention to provide an IMM solar cell semiconductor structure for providing a high-efficiency IMM solar cell.
It is yet another object of the present invention to provide a laser lift-off method for an IMM solar cell semiconductor structure, so as to lift-off a substrate layer from the IMM solar cell semiconductor structure.
To achieve the above objects, an IMM solar cell semiconductor structure is provided according an aspect of the present invention. The IMM solar cell semiconductor structure, for use of an LLO process using external laser, comprises a substrate layer, a sacrifice layer, a plurality of bandgap layers and a handle layer. The sacrifice layer, formed on the substrate layer, is made of a material containing a III-V compound. The bandgap layers, formed on the sacrifice layer, are for producing movements of electronic holes according to an absorbed extrinsic light wavelength. The handle layer is formed on the bandgap layers.
A laser lift-off method for an IMM solar cell semiconductor structure is further provided according to another aspect of the present invention. The method comprises: a) forming a sacrifice layer on a substrate layer, the sacrifice layer being a made of a material containing a III-V compound and having a bandgap smaller than a bandgap of the substrate layer; b) forming a plurality of bandgap layers on the sacrifice layer, and forming a handle layer on the bandgap layers; and c) rendering an external laser entering the sacrifice layer from the substrate layer, penetrating the substrate layer and being absorbed by the sacrifice layer, such that the bandgap layers are lifted off by the sacrifice layer.
Compared with the prior art, the IMM solar cell semiconductor structure and the LLO method disclosed by the present invention, by flexibly adjusting a lattice constant and an energy bandgap of the sacrifice layer made of a material containing a III-V compound, are capable of matching the substrate layer also containing the same III-V compound, and removing the substrate layer from the IMM solar cell by using external laser, thereby increasing efficiency of the solar cell.
a and 1b are schematic diagrams of an IMM solar cell semiconductor structure according to an embodiment of the present invention;
The present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings.
a and 1b show schematic diagrams of an IMM solar cell semiconductor structure according to an embodiment of the present invention. In
The IMM solar cell semiconductor structure 2 comprises a substrate layer 4, a sacrifice layer 6, bandgap layers 8 and a handle layer 10. The substrate layer 4 provides a base layer required for developing epitaxy for the solar cell semiconductor, and may be made of a material containing a III-V compound, e.g., GaAs.
The sacrifice layer 6 is formed on the substrate layer 4, and is made of a material containing a III-V compound. Thus, the sacrifice layer 6 is at least one compound containing indium, gallium, arsenic and/or nitrogen. For example, the sacrifice layer 4 is made of nitrogen indium gallium arsenide (InGaAsN).
A ratio of the nitrogen in the sacrifice layer is 10% to 20% of the compound making up the material of the sacrifice layer 6; a thickness of epitaxy of the sacrifice layer 6 may be smaller than a thickness of the substrate layer.
In order to lift-off the substrate layer 4 from the bandgap layers 8 by the sacrifice layer 6, a wavelength λ1 corresponding to a bandgap ev1 of the sacrifice layer 6 is greater than a wavelength λ0 of the laser 1, and the wavelength of the laser 1 is greater than a wavelength corresponding to a bandgap ev2 of the substrate layer 4, as shown in
The bandgap and the wavelength are configured in a way that the wavelength and energy of the laser 1 enter from the substrate layer 4 to fall on the sacrifice layer 6 to be directly absorbed by the sacrifice layer 6 (i.e., the laser 1 is not absorbed by the substrate layer 4), such that the sacrifice layer 6 comprising a III-V compound decomposes into vapor and liquid. The vapor becomes a gas and dissipates, whereas the liquid remains between the sacrifice layer 6 and the substrate layer 4. More specifically, the laser 1 heats the sacrifice layer 6 to break a link between the substrate layer 4 and the sacrifice layer 6, as shown in
The bandgap layers 8, formed on the sacrifice layer 6, are for producing movements of electronic holes according to an absorbed extrinsic light wavelength (e.g., a sunlight light source). The bandgap layers 8 may be consisted of materials having different bandgaps (or electron volts, e.g., indium gallium phosphide (InGaP) and GaAs.
The handle layer 10 is formed on the bandgap layers 8. In practice, after lifting off the substrate layer 4 using the laser 1, the IMM solar cell semiconductor structure 2 is inverted such that the handle layer 10 originally located at the uppermost side becomes the lowermost side, and thus an inverted epitaxial structure is adopted as an illustrative example. In another embodiment, the IMM solar cell semiconductor structure 2 may be a non-inverted epitaxial structure.
In Step S2, a plurality of bandgap layers are formed on the sacrifice layer, and a handle layer is then formed on the bandgap layers.
In Step S3, external laser enters via the substrate layer to fall on the sacrifice layer. The laser penetrates the substrate layer and is absorbed by the sacrifice layer such that that the bandgap layers are lifted off by the sacrifice layer. A wavelength corresponding to the bandgap of the sacrifice layer is greater than a wavelength of the laser, and the wavelength of the laser is greater than the bandgap of the substrate layer.
The LLO method for an IMM solar cell semiconductor structure may further comprise Step S5 for integrating a new substrate layer on the bandgap layers to form a chip-form IMM solar cell having the semiconductor structure.
With description of the above embodiments, it is illustrated that the IMM solar cell semiconductor structure and the LLO method for the same, by flexibly adjusting a lattice constant and an energy bandgap of the sacrifice layer made of a material containing a III-V compound, are capable of matching the substrate layer also containing the same III-V compound, and removing the substrate layer from the IMM solar cell by using external laser, thereby increasing efficiency of the solar cell.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is illustrative and needs not to be limited to the above embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 100121674 | Jun 2011 | TW | national |
