Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1999-11-29
2002-04-09
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C257S013000, C257S079000, C313S500000, C313S506000, C313S512000
Reexamination Certificate
active
06369506
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light emitting apparatus incorporating a semiconductor light emitting device using a nitride semiconductor (e.g., gallium nitride compound semiconductor In
x
Al
y
Ga
1−x−y
N, where 0≦x, 0≦y, and x+y≦1) and a method for mounting the light emitting device. In particular, the present invention relates to a light emitting apparatus incorporating a nitride semiconductor light emitting device including a substrate which transmits light therethrough and a method for mounting the light emitting device.
2. Description of the Related Art
Typically, a nitride semiconductor light emitting device is produced by depositing a semiconductor multilayer which includes a number of nitride semiconductor layers on an insulative substrate. The semiconductor multilayer is then partially etched into a step like shape. Then a p-type electrode and an n-type electrode are formed on the semiconductor multilayer. The n-type electrode is formed on a lower step of the partially etched semiconductor multilayer. Thus, the height of the n-type electrode differs from that of the p-type electrode. Typically, the n-type electrode is formed at a height which is about 1 &mgr;m lower than that of the p-type electrode. One way to emit the light from the nitride semiconductor light emitting device is to include a light transmissive substrate. Conventional mounting methods for electrically connecting such p-type and n-type electrodes formed at different heights to respective electrodes of respective lead frames will be described below.
For example, Japanese Laid-open Patent Publication No. 9-181394 discloses a method in which a nitride semiconductor light emitting device provided with a height difference is mounted on a heat sink that is also provided with a height difference so as to conform with the height difference between the p-type electrode and the n-type, electrode of the light emitting device.
FIG. 8
is a schematic diagram illustrating the mounting method. Referring to
FIG. 8
, a p-type electrode
71
and an n-type electrode
72
are formed on one side of a nitride semiconductor light emitting device
70
. A height difference section
700
is provided in a heat sink
73
so as to match with the height difference between the p-type electrode
71
and the n-type electrode
72
. The n-type and p-type electrodes
72
and
71
are connected to lead electrodes
75
and
74
, respectively, with a conductive material
77
.
Japanese Laid-open Patent Publication No. 6-177434 discloses another conventional method for mounting a nitride semiconductor light emitting device, in which the height of an n-type electrode is adjusted to match with that of a p-type electrode.
FIG. 9
is a schematic diagram illustrating the mounting method. A thick n-type electrode
80
and a thin p-type electrode
81
are formed on a nitride semiconductor light emitting device
79
so that the surface heights thereof match with each other. The n-type and p-type electrodes
80
and
81
are surrounded by an insulative protective film
82
, and connected to lead electrodes
85
and
86
via conductive adhesive layers
83
and
84
, respectively.
The first conventional method shown in
FIG. 8
has the following problems. In this method, the nitride semiconductor light emitting device
70
needs to be mounted on the heat sink
73
while the p-type electrode
71
and the n-type electrode
72
of the light emitting device
70
are simultaneously placed on (and thus connected to) the lead electrodes
74
and
75
of the heat sink
73
, respectively. Therefore, the method requires a very high die bonding accuracy. This causes difficulties during the manufacture of the light emitting device.
The second conventional method shown in
FIG. 9
has the following problems. When this method is used with an ordinary light emitting diode or laser, the n-type electrode
80
needs to be as thick as about 1 &mgr;m. Such a thick electrode complicates the production process. In stead of making the n-type electrode
80
thicker than the p-type electrode
81
, the conductive adhesive layer
83
may be made thicker than the conductive adhesive layer
84
to similarly compensate for the height difference. In such a case, during a die-bonding process for the nitride semiconductor light emitting device, the conductive adhesive material may extend beyond the periphery of the electrode
80
or
81
, which may short-circuit the electrodes
80
and
81
with each other. Thus, the production yield may be reduced considerably.
In either one of the conventional methods described above, since the semiconductor layer side is fixed to the heat sink with an adhesive (such as a silver paste and a solder), the semiconductor layer tends to be distorted thereby shortening the lifetime of the nitride semiconductor light emitting device.
Another problem with a conventional light emitting device is that the emission efficiency is decreased because the emitting light is absorbed and scattered by the electrodes formed on the semiconductor layer.
As described above, it has been difficult to provide a method for mounting a nitride semiconductor light emitting device, which improves the emission efficiency and hence the lifetime thereof.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a light emitting apparatus including: a light emitting device for emitting light; and a first lead frame and a second lead frame on which the light emitting device is mounted. In this apparatus, the light emitting device includes: a substrate which is light transmissive, the substrate defining an output surface; a semiconductor layer formed on the substrate which includes a light emitting layer made of a nitride semiconductor; a first electrode provided lower than a plane running parallel through the light emitting layer with respect to the substrate; and a second electrode provided higher than the plane running parallel through the light emitting layer with respect to the substrate; the first lead frame includes a first lead pad section to which the first electrode is connected; the second lead frame includes a second lead pad section to which the second electrode is connected, at least one of the first and second lead frames includes a die pad section on which the substrate is mounted; and the die pad section does not substantially cover the first output surface.
In one embodiment of the present invention, the light emitting device includes a reflective layer which reflects the light generated in the light emitting layer toward the substrate.
In another embodiment of the present invention, the reflective layer is formed between the light emitting layer and the second electrode.
In still another embodiment of the present invention, the reflective layer is formed to surround the light emitting device.
In still another embodiment of the present invention, the semiconductor layer includes at least a pair of cladding layers, the light emitting layer being made of a gallium nitride type compound semiconductor and being formed between the cladding layers; the reflective layer is a multilayer film including at least two different types of layers which are alternately deposited on one another; and the at least two different types of layers include a first layer made of a nitride semiconductor and having a refractive index of n, and a thickness of &lgr;/(4·n
1
) (where &lgr; denotes an emission wavelength of the light emitting device), and a second layer made of a nitride semiconductor with a refractive index of n
2
and having a thickness of &lgr;/4·n
2
.
In still another embodiment of the present invention, the semiconductor layer includes at least a pair of cladding layers, the light emitting layer being made of a gallium nitride type compound semiconductor and being formed between the cladding layers; the second electrode has a property of transmitting light with a specific wavelength: and the reflective layer is an insulative multilayer film which is formed
Berck Ken A
Nixon & Vanderhye P.C.
Patel Vip
Sharp Kabushiki Kaisha
LandOfFree
Light emitting apparatus and method for mounting light... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light emitting apparatus and method for mounting light..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light emitting apparatus and method for mounting light... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2872663