BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIGS. 1A through 1C are procedural side cross-sectional views for explaining a method of manufacturing a conventional nitride semiconductor light emitting device;
FIGS. 2A and 2B are side cross-sectional views illustrating a nitride semiconductor light emitting device according to an exemplary embodiment of the invention; and
FIGS. 3A through 3F are procedural side cross-sectional views for explaining a method of manufacturing a nitride semiconductor light emitting device according to an exemplary embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
FIGS. 2A and 2B are side cross-sectional views illustrating a nitride semiconductor light emitting device according to an exemplary embodiment of the invention.
As shown in FIG. 2A, the nitride semiconductor light emitting device 20 of the present embodiment includes an electrically conductive substrate 21 for growing a nitride single crystal, a p-type nitride semiconductor layer 22 formed on the substrate, an active layer 23 formed on the p-type nitride semiconductor layer 22 and including a plurality of quantum barrier layers and a plurality of quantum well layers deposited alternately on each other, an n-type nitride semiconductor layer 24 formed on the active layer, a p-electrode 27 formed on a bottom of the nitride single crystal growth substrate 21 and an n-electrode 26 formed on a top of the n-type nitride semiconductor layer 24.
Here, the p-type nitride semiconductor layer 22 may include a p-type AlGaN layer 22b formed on the substrate 21 to have an interface contacting the active layer. Also, the p-type nitride semiconductor layer 22 may include a p-type GaN layer 22a having an interface contacting a top of the substrate 21 to reduce a contact resistance with respect to the substrate 21.
According to the present embodiment, the n-type nitride semiconductor layer 24 may be formed of n-type GaN. The n-type nitride semiconductor layer 24 may have a thickness t1 of 2 to 500 nm. Therefore, the n-type nitride semiconductor layer 24 with such a small thickness can be manufactured with less time, thereby saving manufacturing time of the nitride semiconductor light emitting device.
Additionally, a reflective metal layer 25 may be disposed between the nitride single crystal growth substrate 21 and the p-electrode 27.
FIG. 2B is a magnified side cross-sectional view illustrating the active layer 23 shown in FIG. 2A. Referring to FIG. 2B, the active layer 23 includes a plurality of quantum well layers 23b and quantum barrier layers 23a deposited alternately on each other. Among the quantum barrier layers 23a of the active layer, a quantum barrier layer having an interface contacting the p-type AlGaN layer 22b may be formed of an undoped GaN 23a layer, which prevents migration of Al atoms. Here, the undoped GaN layer 23a may have a thickness t2 of 2 to 10 nm.
FIGS. 3A through 3G illustrate a method of manufacturing a nitride semiconductor light emitting device structured as above according to an exemplary embodiment of the invention.
First, as shown in FIG. 3A, a p-type nitride semiconductor layer 32 is formed on an electrically conductive substrate 31 for growing a nitride single crystal. Typically, the substrate 31 may have a thickness t3 of hundreds of μm.
Also, as described above, the p-type nitride semiconductor layer 32 may include a p-type AlGaN layer 32b and a p-type GaN layer 32a. Here, to improve crystallinity and optical properties of a nitride semiconductor light emitting device through high-temperature growth, the p-type nitride semiconductor layer 32 may be grown at a temperature of 950° C. or higher, particularly, 1000 to 1200° C.
Then, the grown p-type nitride semiconductor layer 32 is heat-treated to activate dopant atoms. Here, the p-type nitride semiconductor layer 32 may be directly heat-treated in a reactor and thus simplified in the process over conventional heat treatment by an additional RTA equipment after all nitride layers are grown. Furthermore, the p-type nitride semiconductor layer 32 is heat-treated before an active layer 33 is grown as shown in FIG. 3B. This prevents the dopant atoms from migrating to the active layer 33, while causing less heat-induced damage to the active layer.
Thereafter, as shown in FIG. 3B, the active layer 33 is formed on the p-type nitride semiconductor layer 32. The active layer 33 may be structured as in FIG. 2B. In this structure, among quantum barrier layers 23a of the active layer 33, a quantum barrier layer having an interface contacting the p-type AlGaN layer 22b is grown as an undoped GaN layer 23a, and a plurality of quantum well layers 23b and quantum barrier layers 23a are deposited alternatively on each other on the undoped GaN layer 23a. Here, the undoped GaN layer 23a may be grown at a temperature of 950° C. or higher, thereby improving crystallinity and optical properties of the nitride semiconductor light emitting device.
Subsequently, as shown in FIG. 3C, an n-type nitride semiconductor layer 34 is formed on the active layer 33. The n-type nitride semiconductor layer 34 may have a thickness t1 of about 2 to 500 nm. The n-type nitride semiconductor layer 34 even with the thickness as small as just described ensures sufficient crsytallinity unlike a case where the n-type nitride semiconductor layer 34 is grown on the substrate. This thickness range is the one considering electrical resistance and tunneling effects. Accordingly, the n-type nitride semiconductor layer with such a small thickness can be grown in a much shorter time, e.g., about at least 1000 times shorter than a conventional n-type nitride semiconductor layer grown to a thickness of several μm.
Next, as shown in FIG. 3D, after all of the nitride layers are grown, the substrate 31 may be polished. The polishing may be carried out by a chemical or mechanical method. The polishing allows the substrate 31 to have a thickness t3 of about 50 to 100 nm. This thickness range is based on a consideration that a total thickness of the substrate 31 and the p-type nitride layer 32 may rang from 150 to 200 nm in view of reflection effects and electrical resistance effects.
As described above, the substrate with a smaller thickness may induce less electrical resistance than the conventional one with a thickness of hundreds of μm.
In addition, although not shown, the substrate may be polished, after an n-electrode 36 is formed and before a p-electrode 37 is formed as described in FIG. 3F.
Afterwards, as shown in FIG. 3F, a reflective metal layer 35 may be formed on a bottom of the nitride single crystal growth substrate 31.
Finally, as shown in FIG. 3F, the p-electrode 37 is formed on a bottom of the reflective metal layer 35 and the n-electrode 36 is formed on a top of the n-type nitride semiconductor layer 34. In a case where the formation of the reflective metal layer 35 as described in FIG. 3E is omitted, the p-electrode 37 is directly formed on the bottom of the nitride single crystal growth substrate 31.
As set forth above, according to exemplary embodiments of the invention, a p-type nitride semiconductor layer is grown before formation of an active layer. This prevents dopant atoms from migrating to the active layer, thereby allowing heat treatment to be carried out at a high temperature of 950° C. This accordingly improves crystallinity and optical properties of a nitride semiconductor light emitting device over a case where an n-type GaN substrate is employed. Moreover, a p-type nitride semiconductor layer is directly heat-treated in a reactor, thereby simplified in the heat treatment process.
Moreover, an n-type nitride semiconductor layer is grown to a small thickness of about 2 to 500 nm, thereby reducing overall manufacturing time over a conventional method.
While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.
Patent Application
20080078986
