Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With housing or contact structure
Reexamination Certificate
1998-04-21
2001-08-21
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With housing or contact structure
C257S091000, C257S093000, C257S097000, C257S103000, C372S045013
Reexamination Certificate
active
06278136
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a semiconductor light emitting element, its manufacturing method and a light emitting device. More specifically, the invention relates to a light emitting element, its manufacturing method and a light emitting device in which the p-side electrode and the n-side electrode of a light emitting element using nitride compound semiconductors are formed on a common plane to obtain a high performance and high integration and to simplify the manufacturing and assembling process.
Semiconductor light emitting elements have advantageous features, namely, compactness, high reliability, high efficiency, and capability of emitting light in a wide wavelength range from the infrared range to the blue-violet range when appropriate materials are chosen. Making the best use of these features, they are widely used regardless of the industrial use or civil use.
Made below is a review of light emitting elements using nitride compound semiconductors among such semiconductor light emitting elements. Throughout the specification, the nitride compound semiconductors pertain to any semiconductors with all varieties of mole fractions x and y from zero to 1 in the chemical formula In
x
Al
y
Ga
1−x−y
N 0≦x≦1 , 0≦y≦1, x+y=1). For example, GaN (x=0, y=0) is also one of nitride compound semiconductors.
Nitride compound semiconductors are III-V compound semiconductors of direct transition type, whose band gaps can be varied from 1.89 to 6.2 eV by controlling their mole fractions x and y, and are remarked as hopeful materials of LED (light emitting diodes) and semiconductor lasers. Especially, if they successfully emit highly luminous light in the blue wavelength range, it is possible to double the recording capacity of various optical disks and to provide full color displays. From these expectations, blue light emitting elements using In
x
Al
y
Ga
1−x−y
N semiconductors have been used to improve initial characteristics and reliability.
Referential documents disclosing conventional blue light emitting elements using nitride compound semiconductors involve Jpn. J. Appl. Phys., 28(1989) p.L2 112, Jpn. J. Appl. Phys., 32(1993) p. L8, and Japanese Patent Laid-Open Publication 5-291621.
FIG. 8
is a schematic cross-sectional view of a conventional blue light emitting element.
Its construction is roughly explained below.
The light emitting element
100
has a multi-layered structure stacking semiconductors on a sapphire substrate
102
. More specifically, stacked on the sapphire substrate
102
are a buffer layer
104
, n-type contact layer
106
, active layer
108
, and p-type contact layer
110
in this order.
The stacked structure is partly removed by etching to form a step where the n-type contact layer
106
is partly exposed. The n-side electrode
120
is formed on the exposed surface of the n-type contact layer
106
, and the p-side electrode
130
is formed on the p-type contact layer
110
. A reason of etching the structure to the n-type contact layer
106
to form the n-side electrode lies in that the sapphire substrate
102
has an electrically insulating property.
The buffer layer
104
may be made of GaN, for example. The n-type contact layer
106
is an n-type semiconductor layer having a high carrier concentration enough to ensure ohmic contact with the n-side electrode
120
, and may be made of, for example, AlGaN doped with silicon (Si). The active layer
108
is a semiconductor layer where electric charges injected as a current into the light emitting element recombine and emit light. Usable as its material is, for example, In
x
Al
y
Ga
1−x−y
N doped with zinc (Zn). The p-type contact layer
110
is a p-type semiconductor layer having a high carrier concentration to ensure its ohmic contact with the p-side electrode, and may be made of, for example, AlGaN doped with magnesium (Mg).
When a current is injected to the light emitting element, light in the blue wavelength range is emitted in the active layer
108
having luminescent centers in zinc (Zn).
However, since the conventional blue light emitting element shown in
FIG. 8
makes the n-side electrode
120
on the surface of the n-type contact layer
106
, it needs the process of etching the structure to the depth of the n-type contact layer
106
. Moreover, the n-side electrode
120
must be made on the bottom surface of a step formed by the etching. That is, it is necessary to stack materials of the n-side electrode
120
on the bottom surface of the step and to pattern it appropriately. This process is not easy, and are apt to decrease the yield.
Another problem of the conventional element lies in that the light emitting element
100
has a step and has the n-side electrode
120
and the p-side electrode in different levels, which results in requiring positional adjustment to respective levels of the electrodes and therefore complicating the process. In the step of wire bonding to the n-side electrode
120
, a bonding tool for supplying the wire may bump against the side surface of the step (shown at S in FIG.
8
). To avoid this, the bottom surface of the step must be enlarged. It cause another problem, namely, an increase of the element size and the manufacturing cost.
Conventional light emitting elements having the n-side electrode and the p-side electrode in different levels, and not on a common plane, made so-called flip-chip mounting difficult. Another problem, therefore, is that light emitting elements could not be used to various applications relying on flip-chip mounting and that it was difficult to provide improvements of electric, optical characteristics and reduction of the packaging size.
All these problems with conventional techniques as explained above are caused by the step-containing structure of conventional gallium nitride light emitting elements.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a semiconductor light emitting element having no step and having formed the n-side electrode and p-side electrode on a common plane to simplify the wafer process and to enlarge the range of its applications, and to provide a method for manufacturing the light emitting element.
According to the invention, there is provided a semiconductor light emitting element comprising:
a multi-layered structure including at least a substrate, a nitride compound semiconductor layer of a first conduction type formed on the substrate, and a nitride compound semiconductor layer of a second conduction type formed on the first conduction type nitride compound semiconductor, and further including a first conduction type region made by selectively introducing a first conduction type dopant from a selective area of the surface of the second conduction type nitride compound semiconductor to extend from the surface of the multi-layered structure to the first conduction type nitride semiconductor layer;
a first electrode formed in contact with the surface of the first conduction type region of said multi-layered structure; and
a second electrode formed in contact with the surface of the second conduction type nitride compound semiconductor.
A specific version of the multi-layered structure includes a substrate, an n-type conduction layer made of an n-type nitride semiconductor on the substrate, an n-type cladding layer made of an n-type nitride compound semiconductor on the n-type conduction layer, an active layer made of a nitride compound semiconductor on the n-type cladding layer, a p-type cladding layer made of a p-type nitride compound semiconductor on the active layer, and a p-type contact layer made of a p-type nitride compound semiconductor on the p-type cladding layer.
Elements used as dopants of respective layers, thicknesses of respective layers and other parameters can be optimized appropriately.
When a high-resistance region is formed to surround the first conduction type region, leak current can be blocked effectively.
According to the invention, there is also provided a method for manufactur
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Jackson, Jr. Jerome
Kabushiki Kaisha Toshiba
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