Method for fabricating a laser diode

The present invention relates to a method for fabricating a semiconductor laser diode in optical communication system, having the steps for forming current blocking layers on the resulting structure of the mesa structure and then forming an opening through the current blocking layer on the mesa structure.

FIELD OF THE INVENTION 
This invention relates to a method for fabricating a laser diode, and more 
particularly to a method for fabricating a planar buried heterostructure 
laser diode("PBH-LD") having improved current blocking layers to decrease 
leakage current during operation. 
BACKGROUND OF THE INVENTION 
Generally, in a semiconductor laser diode, in order to achieve reliable 
device characteristics, for example current confinement, refractive index 
guide, etc., a mesa structure is useful in consideration of the size of 
the active layer and the device profile. 
The conventional method for fabricating the mesa structured laser diode is 
described hereinafter with reference to the FIG. 1 to FIG. 4, which 
illustrate the process flow of the conventional method. 
First, referring to FIG. 1, an n-InP clad layer 2, an active layer 3 and a 
p-inP clad layer 4 is successively formed on an n-InP substrate 1. 
Next, referring to FIG. 2, an oxide pattern 5 is formed on the p-InP clad 
layer 4. 
Next, referring to FIG. 3, in order to form the mesa structure, the layers 
2, 3 and 4 under the oxide pattern 5 is etched with the oxide pattern 5 
being used as an etch mask until a portion of the n-InP clad layer 2 is 
exposed. In this etching process, an under cut is formed under the edge of 
the oxide pattern 5. 
Next, referring to FIG. 4, a p-InP current blocking layer 6 and an n-InP 
current blocking layer 7 are selectively formed on the side portion of the 
mesa structure by metal organic chemical vapor deposition ("MOCVD") or 
liquid phase epitaxy("LPE"). Then, after removing the oxide pattern 5, a 
p-contact layer 8 is formed on the resulting structure and a metal contact 
layer 9 is formed on the p contact layer 8. 
However, the above mentioned conventional method for fabricating the mesa 
structured laser diode has the following problems: 
Now, referring to FIG. 3B and FIG. 4B, in case the p-InP current blocking 
layer 6 on the side portion of the mesa structure is formed broader than 
that of the above mentioned normal case by various reasons, for example 
the process variation, there will be a leakage current path 10 through the 
current blocking layer 6. FIG. 3B is a simplified cross sectional view 
which illustrates the unwanted broader formation of the current blocking 
layer 6 due to the process variations of the conventional method. 
Referring to FIG. 3B, after the step for forming the oxide characteristics 
and reliability without the effect of the process variations, by forming 
current blocking layers on the resulting structure of the mesa structure 
and then forming an opening, through which currents are injected, in the 
current blocking layer. 
In accordance with the present invention, there is disclosed a method for 
fabricating a laser diode including the steps for: successively forming a 
first clad layer, an active layer, a second clad layer and an etch stop 
layer on a semiconductor substrate; forming an oxide pattern on the etch 
stop layer; forming a mesa structure by etching a predetermined portion of 
the layers under the oxide layer from the etch stop layer to a portion of 
the first clad layer using the oxide pattern as an etch mask; removing the 
oxide pattern; forming a first and a second current blocking layer on the 
resulting structure; forming an opening to expose the etch stop layer by 
etching the current blocking layers with a predetermined photo resist 
pattern; removing the etch stop layer; forming a first contact layer on 
the resulting structure; and forming a second contact layer on the first 
contact layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A detailed description of an embodiment according to the present invention 
will be given below with reference to FIGS. 5 to 10. 
First, referring to FIG. 5, a first clad layer, for example an n-InP clad 
layer 2, an active layer 3, a second clad layer, for example a p-InP clad 
layer 4, and an etch stop layer 11 are successively formed on a 
semiconductor substrate, for example an n-InP substrate 1. 
Next, referring to FIG. 6, an oxide pattern 5 is formed on the etch stop 
layer 11, and a mesa structure is formed by etching a predetermined 
portion of the layers under the oxide pattern from the etch stop layer 11 
to a portion of the n-InP clad layer 2 using the oxide pattern 5 as an 
etch mask. 
Next, referring to FIG. 7, after removing the oxide pattern 5, a first and 
a second current blocking layer, for example a p-InP layer 12 and an n inP 
layer 13 are formed on the resulting structure. 
Next, referring to FIG. 8, after forming a predetermined photo resist 
pattern 16 on the resulting structure to expose the top of the mesa 
structure, an opening 14 is formed to expose the etch stop layer 11 by 
applying an anisotropic etching to the current blocking layers 12 and 13. 
Next, referring to FIG. 9, after removing the photo resist pattern 16, the 
exposed etch stop layer 11 is removed and the current injecting opening 15 
is formed. 
Finally, referring to FIG. 10, a first contact layer, for example a 
p-contact layer 17 is formed on the resulting structure, and a second 
contact layer 18 is formed on the p-contact layer 17. 
As described above, according to the present invention, the current 
blocking layers 12 and 13 are formed to have improved profile without the 
effect of the process variations, for example the profile of etched mesa 
structure, the width of the under cut and the thickness of the current 
blocking layer. Also, a more controllable current injecting opening can be 
achieved by the anisotropic etching. These advantages result in the 
decrease of the leakage currents in the current blocking layers, whereby 
the device characteristics, the reliability and the reproducibility of 
process are improved. 
Although the preferred embodiment of the present invention has been 
disclosed for illustrative purposes, those skilled in the art will 
appreciate that various modifications, additions and substitutions are 
possible, without departing from the scope and the spirit of the present 
invention as disclosed in the accompanying claims.