Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2001-09-24
2003-03-04
Zarabian, Amir (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S094000, C257S095000, C257S096000, C257S097000, C257S012000, C257S013000, C257S103000, C257S184000, C257S201000
Reexamination Certificate
active
06528823
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-296823, filed Sep. 28, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light-emitting element and a method of manufacturing the same.
In recent years, proposed are various semiconductor light-emitting elements using an InGaAlP series material having light-emitting characteristics in the visible wavelength region.
FIG. 7
is a cross sectional view showing as an example the construction of an LED (light emitting diode) using a conventional InGaAlP series material and producing a visible light output. As shown in the drawing, a double hetero structure including an active layer
53
and p-type and n-type cladding layers
54
,
52
having the active layer
53
sandwiched therebetween is formed on an n-type GaAs substrate
50
. Also, an electrode
57
is formed on the p-type cladding layer
54
and an electrode
58
is formed on the lower surface of the n-type GaAs substrate
50
.
It is necessary to select most suitably the band gap of each of the layers
52
to
54
forming the double hetero structure in accordance with the design in order to obtain a desired wavelength of the emitted light and to confine carriers. Also, it is desirable for the lattice constant of each of the layers
52
to
54
to conform with the lattice constant of the substrate
50
in order to achieve a satisfactory epitaxial growth of the layers
52
to
54
. It should be noted that InGaAlP, which is a III-V compound, contains III group elements of In, Ga and Al. Therefore, it is possible to design independently the band gap and the lattice constant of InGaAlP by suitably selecting the composition ratio of these III group elements of In, Ga and Al.
It is possible to select the wavelength of the emitted light within the visible light region when the InGaAlP series double hetero structure is formed by the layers
52
to
54
. Also, it is possible to form the InGaAlP series double hetero structure by the epitaxial growth having a lattice alignment with the GaAs substrate that is the most general compound semiconductor substrate. It is possible to obtain easily the GaAs substrate
50
, and the epitaxial growth layers
52
to
54
can also be formed relatively easily. However, the GaAs substrate
50
is defective in that the transmittance of the light of the visible region is low. As a result, the light emitted from the InGaAlP series double hetero structure
53
to
54
is partly absorbed by the GaAs substrate
50
, with the result that it is unavoidable for the brightness of the LED to be lowered.
In order to avoid the decrease in the brightness, it is necessary to use a material transparent to the light of the visible region for forming the substrate. In general, GaP is known as a transparent material. However, a lattice alignment cannot be achieved between the GaP substrate and the InGaAlP series material, resulting in failure to achieve a satisfactory epitaxial growth.
In order to avoid the difficulty noted above, proposed is a wafer bonding method in which the InGaAlP epitaxial growth layer and the GaP substrate are subjected to the wafer bonding. In this method, an epitaxial layer is grown first on the GaAs substrate, followed by removing the GaAs substrate from the grown epitaxial layer and subsequently attaching a GaP substrate prepared in advance to the epitaxial growth layer. In this case, the resultant structure consisting of the epitaxial growth layer and the GaP substrate is subjected to a heat treatment while applying pressure to both the epitaxial growth layer and the GaP substrate so as to make the structure integral.
It is certainly possible for the wafer bonding method described above to improve the brightness of the LED. However, it is difficult to handle the epitaxial growth layer after removal of the GaAs substrate because the epitaxial layer is thin. Also, a special apparatus is required because a heat treatment is applied while applying pressure to the structure consisting of the GaP substrate and the epitaxial growth layer. Such being the situation, a problem remains unsolved in terms of the stability and the productivity of the wafer bonding process.
On the other hand, concerning the wafer bonding method, developed is a technology called a direction adhesion or a direct bonding in which wafers each having a clean surface are bonded to each other. For example, a direct bonding of silicon wafers is disclosed in Japanese Patent No. 1420109, filed in 1983. Also, a direct bonding of compound semiconductor wafers is disclosed in Japanese Patent No. 204637, filed in 1985.
The light emitting efficiency of the LED manufactured by applying the bonding technology noted above is about twice as high as that of the conventional LED that does not employ the bonding technology in the manufacturing process and, thus, the LED manufactured by applying the bonding technology is called a high brightness LED.
On the other hand, it has been clarified that the brightness of a high brightness LED is rendered markedly nonuniform depending on the product in the high brightness LED of the bonding type, compared with the conventional LED. The reason for this problem is as follows.
FIG. 8
is a cross sectional view showing the construction of an LED prepared by the direct bonding method described above. As shown in the figure, a so-called n-up structure consisting of a p-type cladding layer
54
, an active layer
53
, an n-type cladding layer
52
and an n-type current diffusion layer
51
, which are laminated in the order mentioned as viewed from below in the drawing, is mounted to a p-type substrate
60
with adhesive layers
61
and
55
interposed therebetween. Where Zn is used as a p-type dopant, Zn is contained in each of all the layers ranging between the active layer
53
and the substrate
60
. Particularly, in order to decrease the series resistance of the LED, it is necessary for a substrate having a high impurity concentration, e.g., an impurity concentration not lower than 1×10
18
cm
−3
, to be used as the p-type GaP substrate
60
. It should be noted that Zn contained in the p-type GaP substrate
60
and the InGaAlP epitaxial growth layers
54
,
55
, and
61
is diffused into the active layer
53
in the heat treating step after the direct bonding step. Zn diffused in the active layer
53
forms an impurity level in the active layer
53
. Since the impurity level acts as a non-light-emitting center relative to the current injected carriers, the density of the non-light-emitting centers is increased with increase in the amount of Zn diffused into the active layer
53
. It follows that the injected carriers are caused to disappear without passing through the route of light emission/recombination. As a result, the brightness of the LED chip is markedly lowered.
The situation pointed out above is described in detail in, for example, (Jpn. J. Appl. Phys Vol. 33 (1994) pp. L857 to L.859 “Effect of Substrate Micro-orientation and Zn Doping Characteristics on Performance of AlGaInP Visible Light Emitting Diode” and Solid State Electron Vol. 38, No. 2, PP. 305 to PP. 308, 1995 “AlGaInP ORANGE LIGHT EMITTING DIODES GROWN ON MISORIENTED p-GaAs SUBSTRATES”).
The amount of Zn diffused into the active layer
53
is determined by the temperature and time of the heat treatment and by the amount of Zn held in the p-type layers acting as a diffusion source. Among these factors, it is possible to control the temperature and time of the heat treatment. The holding temperature of the actual heat treatment falls within a range of between 700° C. and 770° C., and the holding time is 1 hour.
It follows that, in order to control the amount of Zn diffused into the active layer
53
, it is necessary to set constant the Zn concentration in each of the p-type GaP substrate
60
, and the epitaxial layers
54
,
55
and
61
. Particularly, the GaP substrate
60
i
Akaike Yasuhiko
Furukawa Kazuyoshi
Soward Ida M.
Zarabian Amir
LandOfFree
Semiconductor light-emitting element and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor light-emitting element and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor light-emitting element and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3035829