Semiconductor light-emitting element and method for manufacturing therefor

A semiconductor light-emitting element has a crystal layer formed from aluminum of a high mol ratio of 60% or greater on the light producing surface. In the semiconductor light-emitting element, a conductive crystal with aluminum of a mol ratio of 50% or less, or a conductive crystal containing no aluminum is formed on the high aluminum crystal layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a semiconductor light-emitting element 
using an InGaAlP system mixed crystal with a high brightness as a Light 
Emitting Layer in a LED, and a method for fabricating this semiconductor 
light-emitting element, and, in particular, to a semiconductor 
light-emitting element with superior resistance to humidity and with a 
long life expectancy providing high output performance, and a method for 
fabricating this semiconductor light-emitting element. 
2. Description of the Prior Art 
In recent years an Light Emitting Diode (LED) has been developed with a 
light-emitting layer of an InGaAlP mixed crystal system, as a high 
brilliant LED. The use of a Ga.sub.1-x Al.sub.x As current spreading 
layer, as a current diffusion layer, with a high ratio of mixed Al 
crystals (hereinafter X.sub.Al) on the light producing surface is a 
structural feature of this LED. (Hereinafter there will be cases where, 
for brevity, when the ratio of included Al is high, the term "high Al" 
will be used, and when this ratio is low, the term "low Al" will be used.) 
FIG.1 is a general sectional view of an orange colored light-emitting 
InGaAlP LED formed using conventional technology. 
For example, with epitaxial growth of a yellow light-emitting InGaAlP LED 
used as an example, as illustrated in FIG. 1, an n-type In.sub.0.5 
(Ga.sub.0.3 Al.sub.0.7).sub.0.5 P-clad layer 2 with a film thickness of 
1.0 .mu.m fabricated by a metal organic chemical vapor deposition method 
(MOCVD method) is formed on an n-type GaAs substrate 1, and then, an 
n-type In.sub.0.5 (Ga.sub.0.72 Al.sub.0.28).sub.0.5 P active layer 3 with 
a film thickness of 0.5 .mu.m, a P-type In.sub.0.5 (Ga.sub.0.3 
Al.sub.0.7).sub.0.5 P-clad layer 4 with a film thickness of 1.0 .mu.m, and 
a P-type Ga.sub.0.2 Al.sub.0.8 As current spreading layer 5 with a film 
thickness of 10 .mu.m are successively formed, respectively. Subsequently, 
an electrode 7 is formed on the P-type Ga.sub.0.2 Al.sub.0.8 As current 
diffusing layer 5 and an electrode 8 is formed on the other side of the 
n-type GaAs substrate 1. Finally, an element is detached by means of a 
dicing process to obtain an LED pellet. 
In this manner, a high Al mixed crystal ratio X.sub.Al of 0.8 is obtained 
for a pellet light producing surface of the GaAlAs layer 5. 
However, this type of GaAlAs layer 5 with a high Al mixed crystal ratio has 
a tendency to oxidize very easily, and for this reason the light-emitting 
characteristics deteriorate. This causes an extreme reduction in the life 
expectancy of the element, and the same drawback is also found in an 
element sealed in plastic. 
As a countermeasure, conventionally, a method for forming a natural 
oxidation film has been carried out using a chemical surface treatment as 
another chemical process (for example, wet etching using a mixed reagent 
of NH.sub.4 OH and H.sub.2 O.sub.2), but the natural oxidation film 
obtained by this method is highly irregular, and the close adherence 
characteristics are weak because the oxidized film is formed forcibly. 
Because this film lacks mechanical strength, variations are produced in 
the life expectency. 
In addition, because of the character of this chemical process, problems 
arise inasmuch as it is not possible to carry out the process for forming 
the above-mentioned layers 1, 2, 3.4, and 5 continuously, and, for this 
reason, the manufacturing takes considerable time. 
Also, because of the character of a protective film of SiO.sub.2 or 
SiN.sub.x, usually formed by manufacturing using a silicon element, it is 
not possible to carry out the process For forming the above-mentioned 
layers 1, 2, 3, 4, and 5 successively, therefore there is the problem that 
the cost of manufacturing is increased. 
If the Al mixed crystal ratio X.sub.Al for the Ga.sub.1-x Al.sub.x As 
current diffusing layer 5 is reduced to 0.5 or less during the formation 
of the layer, the life expectancy of the element is improved, but, 
conversely, there is a large absorption ratio for the light-emitting wave 
lengths from red to green, therefore this is not practical. 
As outlined above, with a conventional semiconductor light-emitting element 
and tile method for fabricating this element, a GaAlAs layer with a high 
Al mixed crystal ratio which is used as a current diffusing layer is very 
easily oxidized, therefore the light-emitting characteristics deteriorate, 
causing an extreme reduction in the life expectancy of the element. 
In order to solve this problem, the natural oxidation film obtained by this 
method is highly irregular, even when a method to form a natural oxidation 
film using a chemical process is utilized, and this film lacks mechanical 
strength. There is therefore the drawback that variations are produced in 
the life expectancy. In addition, this chemical surface process requires 
another process in addition to the formation of each layer of the 
semiconductor light-emitting element. There is therefore the problem that 
excessive time is required for fabricating. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is, with due consideration 
to the drawbacks of such conventional semiconductor light emitting 
devices, to provide a semiconductor light-emitting element using an 
InGaAlP system mixed crystal as a light emitting layer with superior 
resistance to humidity and high output characteristics, and to provide a 
highly efficient method for fabricating this semiconductor light-emitting 
element. 
A semiconductor light-emitting element in a preferred embodiment according 
to the present invention comprises: 
a crystal layer formed from aluminum of a high mol ratio of 60% or greater 
on the light producing surface, 
wherein a conductive crystal with aluminum of a mol ratio of 50% or less, 
or a conductive crystal containing no aluminum is formed on the high 
aluminum crystal layer. 
In the semiconductor light-emitting element above In.sub.0.5 (Ga.sub.l-x 
Al.sub.x).sub.0.5 P (where 0.ltoreq.x.ltoreq.1) is used as the crystal 
layer with aluminum of a mol ratio of 50% or less. 
In the semiconductor light-emitting element above, In.sub.0.5 (Ga.sub.1-x 
Al.sub.x).sub.0.5 P (where 0.ltoreq.x.ltoreq.1) is used as the crystal 
layer with aluminum of a tool ratio of 50% or less; and 
the film thickness of the crystal layer with aluminum of a mol ratio of 50% 
or less is 0.01 .mu.m or greater 
In the semiconductor light-emitting element above, In.sub.0.5 (Ga.sub.1-x 
Al.sub.x).sub.0.5 P (where 0.ltoreq.x.ltoreq.1) is used as the crystal 
layer with aluminum of a tool ratio of 50% or less; and 
in the case where the forbidden band width of the crystal layer with 
aluminum of a mol ratio of 50% or less is smaller than the forbidden band 
width of the light-emitting layer, the film thickness of the crystal layer 
In.sub.0.5 (Ga.sub.1-x Al.sub.x).sub.0.5 P with aluminum of a mol ratio of 
50% or less is within the range of 0.01.mu.m to 2.mu.m. 
In the semiconductor light-emitting element above, Ga.sub.1-x Al.sub.x As 
(where 0.ltoreq.x.ltoreq.0.5) is used as the crystal layer with aluminum 
of a mol ratio of 50% or less. 
In the semiconductor light-emitting element above, 
Ga.sub.1-x Al.sub.x As (where 0.ltoreq.x.ltoreq.0.5) is used as the crystal 
layer with aluminum of a mol ratio of 50% or less; and the film thickness 
of the crystal layer with aluminum of a mol ratio of 50% or less is 0.01 
.mu.m or greater. 
In the semiconductor light-emitting element above, 
Ga.sub.1-x Al.sub.x As (where 0.ltoreq.x.ltoreq.0.5) is used as the crystal 
layer with aluminum of a mol ratio of 50% or less; and 
in the case where the forbidden band width of the crystal layer with 
aluminum of a mol ratio of 50% or less is smaller than the forbidden band 
width of the light-emitting layer, the film thickness of the crystal layer 
Ga.sub.1-x Al.sub.x As (where 0.ltoreq.x.ltoreq.0.5) with aluminum of a 
mol ratio of 50% or less is within the range of 0.01 .mu.m to 2 .mu.m. 
A process for manufacturing a semiconductor light-emitting element of 
another preferred embodiment according to the present invention comprises; 
a step for forming a crystal layer formed from aluminum of a high mol ratio 
of 60% or greater on the light producing surface; and 
a step for forming a conductive crystal with aluminum of a mol ratio of 50% 
or less, or a conductive crystal including no aluminum, on the high 
aluminum crystal layer, subsequent to the foregoing step, 
wherein each of the above-mentioned crystal layers is formed using a gass 
phase growth method. 
In the process for manufacturing a semiconductor light-emitting element 
above, 
a metal organic chemical vapor deposition (MOCVD) method or a molecular 
beam epitaxial growth (MBE) method is used as the gass phase growth 
method. 
In the semiconductor light-emitting element above, the crystal layer formed 
from aluminum of a high mol ratio of 60% or greater is formed on a GaAs 
substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Other features of this invention will become apparent in the course of the 
following description of exemplary embodiments which are given for 
illustration of the invention and are not intended to be limiting thereof. 
Before describing preferred embodiments of the present invention we will 
explain the features and general concept of the semiconductor 
light-emitting element according to the present in the present invention. 
In the semiconductor light-emitting element of the present invention, and 
in the method for manufacturing this semiconductor light-emitting element 
as illustrated in FIG. 2, a group III to V crystal layer with aluminum of 
a mol ratio of 50% or less or containing no aluminum, for example, a 
protective film layer 16 of In.sub.0.5 (Ga.sub.1-x Al.sub.x).sub.0.5 P 
(where 0.ltoreq.x.ltoreq.1), Ga.sub.1-y Al.sub.y As (where 
0.ltoreq.y.ltoreq.0.5), InP, GaP, or GaAs or the like, is formed on a 
GaAlAs current diffusing layer 15 which is a light producing surface. This 
protective film 16 has the Function of a humidity resistant protective 
film. 
In addition, using a metal organic chemical vapor deposition (MOCVD) method 
or a molecular beam epitaxial growth (MBE) method which are processes for 
forming InGaAlP system mixed crystal layers 12, 13, 14, and 15, the mixed 
crystal layers 12, 13, 14, and 15 are formed successively, and the 
protective film 16 is formed as a thin-film with good efficiency. 
Accordingly, the close adhesion characteristics of the GaAlAs current 
diffusing layer 15 and the group III to V crystal layer (protective film) 
16 with aluminum of a mol ratio of 50% or less, or containing no aluminum, 
are strong. 
In addition, although the protective film 16 with aluminum of a mol ratio 
of 50% or less, or containing no aluminum is a thin film there are few 
defects, and a semiconductor light-emitting element can be provided which 
is mechanically strong so that the protective film does not peel away from 
the shock of the dicing process when forming the pellets, or from the 
shock of the wire bonding process in the manufacturing process. Because 
the protective film is conductive it is possible to form an ohmic 
electrode without the necessity of forming an opening in the protective 
film when it is required to form an ohmic electrode such as an SiO.sub.2, 
SiN.sub.x protective film or a group III to V crystal protective film with 
low carrier density and high resistance, or when it is required to provide 
a wire bonding section. 
Accordingly, by forming the protective film it is possible to avoid a 
complicated pellet forming operation, and it is possible to prevent the 
intrusion of 0H-ions which have a bad influence on high Al crystals 
because of the ohmic electrode-protective layer boundary. 
Furthermore, an oxidized film, which becomes a light absorbing layer on the 
light producing surface, is formed with extreme difficulty so that it is 
possible to provide a semiconductor light-emitting element with improved 
humidity resistance. 
An embodiment of the present invention will now be explained with reference 
to the drawings. 
FIG. 2 is a general sectional view of an embodiment of a semiconductor 
light-emitting element which emits yellow light (wave length approximately 
590 nm) of the present invention. 
First, an n-type In.sub.0.5 (Ga.sub.0.3 Al.sub.0.7).sub.0.5 p-clad layer 12 
(Si dopant, carrier density 5.times.10.sup.17 cm.sup.-3) with a film 
thickness of 1.0 .mu.m fabricated by the metal organic chemical vapor 
deposition method (MOCVD method) or by the molecular beam epitaxial growth 
method (MBE method) is formed on a (100) n-type GaAs substrate 11, 
followed by an n-type In.sub.0.5 (Ga.sub.0.72 Al.sub.0.28).sub.0.5 p 
active layer 13 (undoped, carrier density 1.times.10.sup.17 cm.sup.-3 or 
less) with a film thickness of 0.5 .mu.m; a p-type In.sub.0.5 (Ga.sub.0.3 
Al.sub.0.7).sub.0.5 p-clad layer 14 (Zn dopant, carrier density 
5.times.10.sup.17 cm.sup.-3) with a film thickness of 1.0 .mu.m; then a 
p-type Ga.sub.0.2 Al.sub.0.8 As current diffusing layer 15 (Zn dopant, 
carrier density 1 to 2.times.10.sup.18 cm.sup.-3) with a film thickness of 
10 .mu.m; successively formed. 
Next following this, an In.sub.0.5 (Ga.sub.1-x Al.sub.x).sub.0.5 P (where 
0.ltoreq.x.ltoreq.1) protective film 16 (Zn dopant, carrier density 
5.times.10.sup.17 cm.sup.-3) is formed with aluminum of a mol ratio of 50% 
or less, using the MOCVD method or the MBE method, to complete the 
formation of the crystals. 
If the thickness of the In.sub.0.5 (Ga.sub.1-x Al.sub.x).sub.0.5 P (where 
0.ltoreq.x.ltoreq.1) protective film 16 is greater than 0.01 .mu.m, it 
will function as a humidity resistant protective layer, but if the film 
becomes too thick it cannot be ignored as a light absorbing layer for 
light emission, therefore, the film thickness is set at about 0.01 to 2.0 
.mu.m. 
Next, an AuZn (Zn 3 wt %, i.e., Zn is 3% by weight) surface electrode 17 
with a film thickness of 1.0 .mu.m is formed on the In.sub.0.5 (Ga.sub.1-x 
Al.sub.x).sub.0.5 P protective film 16, and an AuGe (Ge 3 wt%) surface 
electrode 8 with a film thickness of 1.0 .mu.m is formed on the n-type 
GaAs substrate 1. 
An element is then detached using the dicing process, to complete the 
process of forming a pellet of the semiconductor light-emitting element. 
With the embodiment of this type, by forming the In.sub.0.5 (Ga.sub.1-x 
Al.sub.x).sub.0.5 P protective film 16 with aluminum of a mol ratio of 50% 
or less, or containing no aluminum, on the GaAlAs current diffusing layer 
15 which becomes the light producing surface, using the metal organic 
chemical vapor deposition method which is the process for growing the 
InGaAlP system mixed crystal layers 12, 13, 14, and 15; and by 
successively forming each of the layers 12, 13, 14, and 15, these layers 
are thinly formed with good efficiency so that the GaAlAs current 
diffusing layer 15 and the In.sub.0.5 (Ga.sub.1-x Al.sub.x).sub.0.5 P 
protective film 16 have strong, close adherence. 
In addition, the In.sub.0.5 (Ga.sub.1-x Al.sub.x).sub.0.5 P protective film 
16 is thin with few defects, making it possible to provide a semiconductor 
light-emitting element which has the advantage of being mechanically 
strong. The formation of a Ga.sub.1-y Al.sub.y As (where 
0.ltoreq.y.ltoreq.0.5) protective film instead of the In.sub.0.5 
(Ga.sub.1-x Al.sub.x).sub.0.5 P protective film 16 provides the same 
effect. 
FIG. 3 is a graph showing the changes in the relative light output versus 
elapsed time for an LED lamp under conditions of high temperature and high 
humidity. The effectiveness of the semiconductor light-emitting element of 
this embodiment will be substantiated with reference to this drawing. 
FIG. 3 shows the relationship between the relative light output (%) versus 
the time during which current is applied, in the case of 60.degree. C. 
ambient temperature, 90% relative humidity, and 20 mA current flow (IF). 
In the drawing, a dotted line A shows the case of a conventional 
semiconductor light-emitting element, specifically, an InGaAlP system LED 
with no special process used; the dashed line B shows the case of applying 
an oxidation film process, using a mixed reagent of NH.sub.4 OH and 
H.sub.2 O.sub.2, to an InGaAlP system LED in a conventional semiconductor 
light-emitting element; and the alternate short and long dash line C shows 
the case of a semiconductor light-emitting element InGaAlP system LED 
formed with the In.sub.0.5 (Ga.sub.1-x Al.sub.x).sub.0.5 P protective film 
16 with a film thickness of 0.1 .mu.m; for tile embodiment shown in FIG. 
2. 
All these curves are made up of average lot values, therefore the ranges 
represented by the vertical lines show a large variation with respect to 
the time. 
In the drawing, with the curve (A), where no special process has been used, 
a large deterioration occurs as time elapses. The curve (B), where the 
oxidation process has been used, shows an improvement over the curve (A), 
although a large variation is evident. In the curve (C) for the present 
embodiment it can be seen that there is almost no deterioration after 1000 
hours, and, also, the variation is small. 
FIG. 4 is a graph showing the relationship between the Al mol ratio of a 
protective film on the pellet surface and the change in the relative light 
output values (life expectancy) for the semiconductor light-emitting 
element. The measured ambient conditions are 60.degree. C. temperature, 
90% relative humidity, and 20 mA current flow (IF), and the measurements 
were made after current had been passed through an LED lamp produced from 
the semiconductor light-emitting element of the present invention for 1000 
hours. 
The vertical axis represents the change in the relative light output 
values, and the horizontal axis represents the Al mol ratio of the pellet 
surface. 
The solid line shows the case for Ga.sub.1-y Al.sub.y As and the dotted 
line shows the case of the In.sub.0.5 (Ga.sub.1-x Al.sub.x).sub.0.5 P 
protective film. 
As can be seen from this graph, when the Al mol ratio of the protective 
film layer 16 is below 50% , the change in the relative light output 
values is maintained at 50% or greater, even after 1000 hours of electric 
current application. 
FIG. 5 is a graph showing the relationship between the film thickness of an 
In.sub.0.5 (Ga.sub.1-x Al.sub.x).sub.0.5 P protective film 16 and the 
change in the relative light output values (%) for this embodiment of a 
semiconductor light-emitting element. 
The measured ambient conditions are 60.degree. C. temperature, 90% relative 
humidity, and 20 mA current flow (IF), and the measurements were made 
after current had been passed through an LED lamp produced from the 
semiconductor light-emitting element of the present invention for 1000 
hours. 
The vertical axis represents the change in the relative light output values 
(%), and the horizontal axis represents the thickness [.mu.m] of the 
humidity resistant film. 
The graph shows that when the thickness of the protective film layer 16 is 
0.01.mu.m or greater, this film functions as a humidity resistant 
protective layer. 
As outlined above, InGaAlP and GaAlAs are used as the protective film layer 
16 in this embodiment. However, InP, GaAs, GaP, GaAlP, GaAsP can also be 
used as the protective film layer 16. 
Also, the MOCVD method and the MBE method are used as the crystal forming 
methods for the light-emitting layer and the protective film layer, but, 
in addition to these, other methods such as an MOMBE method, a hydride VPE 
method, a chloride VPE method and the like can be used. 
Table 1 gives an example of calculated values for the light transmittance 
(P/P.sub.0) of a Ga.sub.1-y Al.sub.y As protective film (in the cases 
where y=0 and y=0.5) for a light-emission wave length [.lambda.p] of the 
semiconductor light-emitting element where thickness [.mu.m] and 
absorption coefficient [60] are used as parameters. 
Table 2 gives an example of calculated values for the light transmittance 
(P/P.sub.0) of an In.sub.0.5 (Ga.sub.1-x Al.sub.X).sub.0.5 P protective 
film (in the cases where x=0 and x=0.5) for a light-emission wave length 
[.lambda.p] of the semiconductor light-emitting element where thickness 
[.mu.m] and absorption coefficient [.alpha.] are used as parameters. 
In order to maintain the light transmittance at about 0.8(about 80% ), the 
thickness of the protective film differs in accordance with the value of 
the Al mixed crystal ratio X.sub.Al. 
In the 560 nm band this thickness is in the range of 0.02 to less than 0.05 
.mu.m. Also, in the 650 nm band, this thickness differs greatly in 
accordance with the value of the Al mixed crystal ratio X.sub.Al, and when 
X.sub.Al is close to 0.7, at a thickness of 10 .mu.m or more, almost none 
of the emitted light is absorbed but is nearly all is transmitted. 
However, when it is necessary to have a protective film of greater 
thickness, the cost of forming the pellet is increased. The optimum value 
is about 2.mu.m or less. 
As explained above, by means of tills embodiment it is possible to provide 
an LED with superior humidity resistance by forming a group III to V 
crystal with aluminum of a mol ratio of 50% or less, or containing no 
aluminum. Further, this embodiment was explained using an In.sub.0.5 
(Ga.sub.1-x Al.sub.x).sub.0.5 P (where 0x.ltoreq.1) protective film 16 as 
the humidity-resistant protective film 16, but it is also possible to 
provide an LED with the same characteristics using group III to V crystals 
such as a Ga.sub.l-y Al.sub.y As (where 0.ltoreq.y.ltoreq.0.5) crystal, or 
another GaAs crystal containing no Al, or InP, or the like. 
In addition, the above-mentioned embodiment was explained with respect to a 
semiconductor light-emitting element with yellow emissions. However, the 
same effect can be obtained for an orange In.sub.0.5 (Ga.sub.0.57 
Al.sub.0.13).sub.0.5 p, or a green In.sub.0.5 (Ga.sub.0.6 
Al.sub.0.4).sub.0.5 P obtained by changing the Al component ratio of the 
active layer. 
Also, with respect to the pellet structure, pellets provided with a 
light-reflecting layer formed by means of laminated layers of group III to 
V crystals between n-type clad layers, and n-type GaAs substrates; pellets 
using a current narrow blocking structure, or pellets combining both 
structures, give the same characteristics. 
Furthermore, the GaAs substrate has the same characteristics as a material 
with a surface direction offset from a surface with a surface direction 
[100], or a material using a surface with a surface direction or miller 
indices (111), and a surface direction(110). 
The same effect is also obtained with a semiconductor light-emitting 
element formed in which each layer of the conductive type is the opposite 
of the conducting type in the case of the above-mentioned embodiment, that 
is, using the P-type rather than the n-type substrate as a GaAs substrate. 
By means of the present invention as outlined above, a protective film 
layer from a group III to V crystal layer with aluminum of a mol ratio of 
50% or less, or containing no aluminum, for example, In.sub.0.5 
(Ga.sub.1-x Al.sub.x).sub.0.5 P, Ga.sub.1-y Al.sub.y As (where 
0.ltoreq.y.ltoreq.0.5), InP, or GaAs or the like, is formed on a crystal 
layer (GaAlAs current diffusing layer) containing Al, which is a light 
producing surface, with successive formation of an InGaAlP system mixed 
crystal layer using, for example, the metal organic chemical vapor 
deposition method which is a process for forming InGaAlP system mixed 
crystal layers, so that a thin-film formation is possible with good 
efficiency. 
This protective film has the function of a humidity resistant protective 
film, and adheres closely with strong bonding to the group III to V 
crystal layer with aluminum of a mol ratio of 50% or less, or containing 
no aluminum. Although the film of the group III to V crystal layer with 
aluminum of a mol ratio of 50% or less, or containing no aluminum is thin, 
there are few defects, and a semiconductor light-emitting element can be 
provided which is mechanically strong so that the protective film does not 
peel away from the shock of the dicing process when forming the pellets, 
or from the shock of the wire bonding process in the fabricating process. 
Because the protective film has conductive characteristics, it is possible 
to form an ohmic electrode without the necessity of forming an opening in 
the protective film, when it is required to form an ohmic electrode such 
as an SiO.sub.2, SiN.sub.x protective film or a group III to V crystal 
protective film with low carrier density and high resistance, or when it 
is required to provide a wire bonding section. 
Accordingly, by forming the protective film it is possible to avoid a 
complicated pellet forming operation, and it is possible to prevent the 
intrusion of OH.sup.- ions which have a bad influence on high Al crystals 
because of the ohmic electrode-protective layer boundary. 
Accordingly, a highly efficient manufacturing method can be provided for a 
semiconductor light-emitting element. Furthermore, an oxidized film, which 
becomes a light absorbing layer is formed with extreme difficulty on the 
light producing surface, so that it is possible to provide a semiconductor 
light-emitting element with improved humidity resistance. 
While the invention has been described with reference to the specific 
embodiments, the description is not meant to be construed in a limiting 
sense. Various modification of the disclosed embodiment, as well as other 
embodiments of the invention, will be apparent to persons skilled in the 
art upon reference to this description. It is therefore contemplated that 
the appended claims will cover any such modifications or embodiments as 
fall within the true scope of the invention. 
TABLE 1 
__________________________________________________________________________ 
P/Po 
.alpha. = 6.1 .times. 10.sup.4 cm.sup.-1 5.1 .times. 10.sup.4 4.3 .times. 
10.sup.4 3.4 .times. 10.sup.4 3.0 .times. 10.sup.4 1.9 .times. 10.sup.4 
0.05 .times. 10.sup.4 0.002 .times. 10.sup.4 
PROTECTIVE FILM LAYER 
GaAs (Eg = 1.425 cv) Ga.sub.0.5 Al.sub.0.5 Sa (Eg = 1.975 ev) 
LIGHT EMISSION WAVELENGTH (.lambda.p) 
560 nm590 nm620 nm650 nm 
560590620650 
t (.mu.m) 
(2.214 ev)(2.102)(2.000)(1.908) 
(2.214)(2.102)(2.000)(1.908) 
__________________________________________________________________________ 
0.01 0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00 10.00 
##STR1## 
##STR2## 
__________________________________________________________________________ 
P/Po = exp(-.alpha.t) 
P/Po: LIGHT TRANSMISSION VALUE 
.alpha.: ABSORPTION COEFFICIENT 
t: THICKNESS 
TABLE 1 
__________________________________________________________________________ 
P/Po 
.alpha. = 3.8 .times. 10.sup.4 2.8 .times. 10.sup.4 1.0 .times. 10.sup.4 
0.1 .times. 10.sup.4 0.0 .times. 10.sup.4 0.001 .times. 10.sup.4 0 
PROTECTIVE FILM LAYER 
In.sub.0.5 (Ga.sub.0.5 Al.sub.0.7).sub.0.5 P (Eg 
= 
In.sub.0.5 Ga.sub.0.5 P (Eg = 1.872 ev) 
2.237 ev) 
LIGHT EMISSION WAVELENGTH (.lambda.p) 
t (.mu.m) 
560 nm590 nm620 nm650 nm 
560590620650 
__________________________________________________________________________ 
0.01 .mu.m 0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00 10.00 
##STR3## 
##STR4## 
__________________________________________________________________________ 
P/Po = exp(-.alpha.t) 
P/Po: LIGHT TRANSMISSION VALUE 
.alpha.: ABSORPTION COEFFICIENT 
t: THICKNESS