Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2001-12-14
2004-02-10
Fourson, George (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S030000, C438S031000, C438S032000, C257SE33011
Reexamination Certificate
active
06689631
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 2000-78543 filed Dec. 19, 2000 in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light-emitting device having a resonant cavity structure for emitting light perpendicularly to the plane of an active region and a method of manufacturing the same. More particularly, the present invention relates to a semiconductor light-emitting device in which a central axis of an upper electrode window, through which resonated light is emitted, and a central axis of a current aperture of an oxidized layer are automatically aligned, and a method of manufacturing the same.
2. Description of the Related Art
Semiconductor light-emitting devices, first developed by General Electric (GE) in 1962, are designed to recombine electrons with holes by applying forward current across a PN junction in a compound semiconductor to generate light having a wavelength corresponding to band gap energy determined according to a structure of the semiconductor.
Semiconductor light-emitting devices are divided according to a process of emitting light into a light emitting diode, which emits incoherent light using spontaneous emission, and a semiconductor laser, which emits coherent light using stimulated emission.
Semiconductor lasers are divided according to the positions of their reflectors. For example, a Fabry-Perot semiconductor laser has reflectors that are positioned at opposite sides of a chip. A Vertical Cavity Surface Emitting Laser (VCSEL) having a resonant cavity structure has reflectors that are horizontally positioned within a chip.
VCSELs do not need an optical system to correct the shape of a beam because they emit a nearly circular Gaussian beam in a direction in which semiconductor material layers are stacked. In addition, since the size of VCSELs is small, a plurality of lasers can be integrated on a single semiconductor wafer. Therefore, VCSELs have a wide range of optical applications such as optical communication, electronic calculators, audio-video devices, laser printers, laser scanners and medical instruments.
FIGS. 1A through 1E
show a conventional method of manufacturing a VCSEL.
FIG. 1A
shows that a lower reflector layer
13
, an active layer
15
, a pre-oxidized layer
17
, and an upper reflector layer
19
are sequentially stacked on a substrate
10
. Here, the substrate
10
is formed of, for example, a semiconductor material having n-type impurities. The lower reflector layer
13
is doped with impurities of the same type as the substrate
10
. For example, the lower reflector layer
13
is formed by stacking 20-30 layers of n-type GaAs, in which the ratio of Ga to As is different in each layer, on top of the substrate
10
. The upper reflector layer
19
is formed of the same semiconductor material as the lower reflector layer
13
but contains the opposite type of impurities to those contained in the lower reflector layer
13
. In other words, the upper reflector layer
19
is formed of p-type GaAs. The pre-oxidized layer
17
is subjected to a horizontal oxidation process in vapor.
FIG. 1B
shows that a plurality of VCSEL posts I, II and III and spaces
21
are formed after a dry etching process and through which light will be independently radiated. Referring to
FIG. 1C
, when an oxidation atmosphere is provided after the spaces
21
are formed, the pre-oxidized layer
17
is oxidized horizontally from its outside to its inside, thereby forming horizontally oxidized high-resistance portions
18
and current apertures
17
a
which are not oxidized.
Subsequently, as shown in
FIG. 1D
, the spaces
21
are filled with polyimide fillings
23
in order to prevent the posts I, II, and III from being damaged during a lapping process. Then, the polyimide fillings
23
are planarized to be level with the surroundings. Afterwards, the resultant structure is turned over and most of the substrate
10
is removed by a lapping process.
FIG. 1E
shows that upper electrodes
25
having a window
25
a
is formed on the VCSEL posts I, II and III and the polyimide fillings
23
. Finally, a lower electrode
27
is formed on a bottom surface of a lapped substrate
10
a
, thereby completing the manufacture of a VCSEL. VCSELs having the above structure may be used as a single chip array structure or may be cut at each polyimide portion to be used separately.
According to a conventional technique shown in
FIG. 2A
, the current apertures
17
a
formed by a horizontal oxidation process after the posts were formed and the window
25
a
of the upper electrodes
25
formed by a photolithographic process are not exactly aligned. Therefore, an alignment error exists where a central axis
16
of the window
25
a
and a central axis
14
of the aperture
17
a
deviate from each other. Such an alignment error results in a loss of emitted light and hinders formation of an exact Gaussian beam, thereby degrading the electro-optical characteristics of a VCSEL.
To take into account of an alignment error,
FIG. 2B
shows a VCSEL designed by way of “electrode pulling.” Here, the upper electrodes
25
are formed beyond the region of the current apertures
17
a
between the high-resistance portions
18
. However, a current path
30
is lengthened and the overall device resistance is increased. Alternatively,
FIG. 2C
shows a VCSEL design according to “electrode pushing.” In this case, the upper electrodes
25
are formed to extend over the current apertures
17
a
between the high-resistance portions
18
. Because an upper electrode window size
34
is smaller than a current aperture size
32
, a loss of emitted light occurs.
Therefore, it is necessary to exactly align the central axis of an upper electrode window and the central axis of a current aperture.
SUMMARY OF THE INVENTION
To solve the above and other problems, it is an object of the present invention to provide a semiconductor light-emitting device with improved electro-optical characteristics by exactly aligning a central axis of an upper electrode window and a central axis of a current aperture, and a method of manufacturing the same.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention, there is provided a semiconductor light-emitting device having a post that is composed of a plurality of layers including at least one pre-oxidized layer on a substrate, and an upper electrode on the post, the semiconductor light-emitting device is manufactured according to an embodiment of the present invention by forming the post by etching, by way of self-alignment using the upper electrode, and horizontally oxidizing the pre-oxidized layer by a predetermined distance from a sidewall of the post.
According to another embodiment of the present invention, the post is formed using the upper electrodes as a guide during an etching process to align a central axes of a window defined by the upper electrodes and a central axes of a current aperture of the pre-oxidized layer.
According to an aspect of the invention, during the etching process, a sidewall of the pre-oxidized layer included in the post is exposed, and the pre-oxidized layer is horizontally oxidized by an oxidizing process to a predetermined distance from the sidewall.
According to another aspect of the invention, when a diameter of the post is about 60 &mgr;m, about 45-50 &mgr;m of the pre-oxidized layer is oxidized, a portion of the pre-oxidized layer oxidized by the oxidizing process becomes a high-resistance portion, and a portion of the pre-oxidized layer unoxidized during the oxidizing process becomes the current aperture through which current or light passes, and since the post is formed by way of self-alignment using the upper electrode, and the c
Fourson George
Pham Thanh
Samsung Electronics Co,. Ltd.
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