The present invention relates generally to a method for fabricating LED, and more particularly to a method for increasing emitting efficiency via removing the light-absorbing substrate and forming a transparent conductive layer on the n-type conductive semiconductor layer.
On the grounds that the light emitting device of LED structure possesses a variety of character, the application of the modern industry and people living is in widespread use. As an analogy, LED provides a small emitting area when needing the illuminating within a small region is required. And the rate of the power consumption of LED is far lower than that of the tradition incandescent lamp. Further, seeing that band width of the spectrum of the light rays emitted by from LED is narrow than that of the traditional lighting device, LED may permit emitting the illumination light rays with certain specific frequency band. LED owns various kinds of colors such as red, yellow, green, blue green, blue, etc. LED with the dissimilar color could be employed to indicate different status.
The current LED is shown in
Providing that most of the current flow from p electrode 27 toward through the p-type conductive semiconductor layer 26 directly, then the hole-electron combination occurs within a small area on the active layer 24 only. The main purpose of the transparent conductive layer 28 is to allow the current of the p type electrode 27 would diffuse on the transparent conductive layer 28 evenly. Afterwards, the current flows downward to p-type conductive semiconductor layer 26 evenly. This could lead to more efficient use of the injected current and more even distribution of lighting area, and hence higher efficiency of LED operation.
It is difficult to form an Ohmic contact between the ITO and the p-type conductive semiconductor layer 26, as a consequence, leads to hinder the current flowing from the transparent layer toward the p-type conductive semiconductor layer 26. Accordingly, the fabricating of LED is arduous and the yield rate of the product is low.
One of the solutions is to search other transparent conductive material which has better Ohmic contact when it contacts with the p-type conductive semiconductor layer. Nevertheless, all the nowadays transparent conductive material has better Ohmic contact with the n-type conductive semiconductor layer. It's exhausting to discover the transparent conductive material having an Ohmic contact with the p-type conductive semiconductor layer.
Correspondingly, it is yearning to demand a solution of fabricating LED for increasing the emitting area of LED to address the foregoing problems.
According to the background of the invention, it's aware of plenty problems and defects of the traditional LED. The main purpose of the present invention provides a method for fabricating LED, the LED wherein includes forming a transparent conductive layer with the material of the Indium Tin Oxide (ITO) on the n-type conductive semiconductor layer and forming a proper metal Ohmic contact layer and metal substrate on the p-type conductive semiconductor layer. The light rays emitted from the n-type conductive semiconductor layer in the present invention, it is suitable with the transparent conductive material having the Ohmic contact with the n-type conductive semiconductor layer.
The other purpose of the present invention is increasing the efficiency of utilizing emitting area of LED. The increase results from the current diffusing on the transparent conductive layer and n-type conductive semiconductor layer evenly with the Ohmic contact between the transparent conductive material and n-type conductive semiconductor layer.
The further purpose of the present invention is adopting the lift-off process for removing the semiconductor substrate.
The further purpose of the present invention is that the light rays emitted toward the p-type conductive semiconductor layer turned to reflect toward the n-type conductive semiconductor layer via the metal substrate. More, the metal substrate could be a p electrode and could promote the heat dissipation for LED.
According to the foregoing purposes, the present invention provides a method for fabricating LED, the method wherein includes forming a high etching selective ration layer on the semiconductor substrate. And the light emitting structure includes an n-type conductive semiconductor layer on the high etching selective ratio layer and a p-type conductive semiconductor layer on the n-type conductive semiconductor layer. Afterwards, form a p-type Ohmic contact layer on the light emitting structure and forming a metal layer on the p-type Ohmic contact layer. Then, remove the semiconductor substrate and the high etching selective ratio layer. And form a n-type contact electrode and a transparent conductive layer as the ITO adjacent to the foregoing n-type conductive semiconductor layer.
The present invention is described with the preferred embodiments and accompanying drawings. It should be appreciated that all the embodiments are merely used for illustration. Hence, the present invention can also be applied to various embodiments other than the preferred embodiments. Besides, the present invention is not limited to any embodiment but to the appending claims and their equivalents.
The object of the present invention is to form a transparent conductive layer on the n-type conductive semiconductor layer. The interface between the transparent conductive layer and the n-type conductive semiconductor layer forms a better Ohmic contact. And the illumination of LED would emit from the n-type conductive semiconductor layer. Accordingly, removing the semiconductor substrate is essential and it's preferred to adopt the lift-off process for removing the semiconductor substrate. Additionally, a metal substrate would be formed on the p-type conductive semiconductor layer. The metal substrate includes a p electrode and a function of enhancing heat dissipation for LED.
Consequently, the present invention provides a method for fabricating LED. The method comprises forming a high etching selective ratio layer on a semiconductor substrate layer. Afterwards, a light emitting structure is formed on the high etching selective ratio layer. Aforementioned light emitting structure includes an n-type conductive semiconductor layer on the high etching selective ratio layer and a p-type conductive semiconductor layer on the n-type conductive semiconductor layer. Additionally, a p-type Ohmic contact layer is stacked on the light emitting structure. And after that a thick metal layer is then formed on the p-type Ohmic contact layer. Moreover, the next step is to remove the semiconductor substrate and high etching selective ratio layer. Thereafter, n-type contact electrodes and a transparent conductive layer are formed is adjacent to the n-type conductive semiconductor layer, wherein the transparent conductive layer includes Indium Tin Oxide (ITO).
The foregoing semiconductor substrate is a III-V compound semiconductor substrate. Preferably, GaAs could be used to act as the substrate. The aforementioned high etching selective ratio layer includes AlAs or AlGaAs. The steps for forming p-type Ohmic contact layer include forming a p-type metal contact layer on the p-type semiconductor layer. Furthermore, the semiconductor substrate should be removed via the high etching selective ratio layer by Hydrofluoric Acid. Cutting the semiconductor substrate to expose the high etching selective ratio layer would help to improve the lift-off process yield. However, the cutting step is optional. Thus, the high etching selective ratio layer could be lifted of by Hydrofluoric Acid solution, directly. The user may select one of the processes depends on the efficiency of the removing the substrate.
The embodiment of the present invention could refer to the flowchart in the
The steps for fabricating LED are shown in
Refers to the
Since the material of the AlAs possesses a high etch selectivity raito, AlAs is the better candidate to act as the material of the high etching selective ratio layer 112. The method for forming AlAs could be CVD (Chemical Vapor Deposition) like MOCVD (Metal Organic CVD), or PECVD (Plasma Enhanced CVD), or MBE (Molecular Beam Epitaxy). The thickness of the high etching selective ration layer 112 is about 20-20,000 angstroms.
According to the illustration in
Afterwards, a p-type metal Ohmic contact layer 130 is formed on the light emitting structure 120 as the illustration in
According to the
Accordingly, the semiconductor substrate 110 is separated as the illustration of the
Accordingly, as the illustration of the
According to the
Since the transparent conductive material nowadays has the Ohmic contact with the n-type conductive semiconductor layer. In the present invention, the transparent conductive material such as the ITO or the IZO is formed on the n-type conductive semiconductor layer for ameliorating a variety of problems of LED and ameliorating the efficiency of LED. Because the illumination emitted from the n-type conductive semiconductor layer, it is suitable with the transparent conductive material has the Ohmic contact with the n-type conductive semiconductor layer. Owing to the Ohmic contact between the transparent conductive material and n-type conductive semiconductor layer, the current will diffuse in the transparent conductive material and n-type conductive semiconductor layer. Thus, the active emitting area of LED will increase. Additionally, a proper metal Ohmic contact layer and the metal substrate are formed on the p-type conductive semiconductor layer. The light emitted toward the p-type conductive semiconductor layer will be reflected toward the n-type conductive semiconductor layer via the metal substrate. Further, the metal substrate could be a p electrode and could promote the heat dissipation for LED. Furthermore, adopt the lift-off process for removing the semiconductor substrate could lift off between two different kinds of material of the layer.
As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, and the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure. While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
---|---|---|---|
094120604 | Jun 2005 | TW | national |