Semiconductor light emitting element with improved structure of groove therein

A semiconductor light emitting element in which light leakage from the vicinity of an active layer end thereof is significantly reduced, and an interval at which the element is disposed is sufficiently narrow, so that there can be realized an optimal distance-measuring accuracy when used for a light source of a camera's automatic focusing mechanism. The semiconductor light emitting element includes a double heterojunction structure such that a GaAlAs current restriction layer formed with a conductive region is formed on a GaAs semiconductor substrate and a light emitting region of the light emitting element diode is provided therein by forming a p-n junction surfaces, the semiconductor light emitting element being characterized in that a plurality of the light emitting diodes are electrically isolated from each other by a plurality of grooves formed substantially vertical to the p-n junction and an end face of the light emitting region cut through by the groove is disposed inside a vertical line drawn from an end face of the surface of the light emitting element.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a semiconductor light emitting element 
such as a monolithic type LED (light emitting diode) which is equipped 
with a light emitting region formed on a GaAs substrate where an p-n 
junction surface is made of material such as GaAlAs. The present invention 
more particularly relates to the semiconductor light emitting element 
suitable for use as an infrared light source for an automatic focusing 
mechanism assembled in a camera and where light leakage from an end of the 
light emitting region is minimized, an interval between the light emitting 
elements is relatively narrow, and a reliable distance-measuring 
capability is achieved. 
2. Description of the Prior Art 
With reference to FIG. 1, there is shown a cross sectional view of the 
conventional semiconductor light emitting element. In the same figure, the 
semiconductor light emitting element is a monolithic type GaAlAs As 
infrared LED and is equipped with three-point light emitting elements. 
With still reference to FIG. 1, the conventional semiconductor light 
emitting element presents the following structure, wherein conductive 
regions 108 are formed on a p type GaAs substrate 106. The element 
includes a double heterojunction (DH) structure such that a GaAlAs As 
current restriction layer formed with the conductive region 108 is formed 
on the substrate 106. The double heterojunction type GaAlAs As layer 
includes an n-type Ga.sub.l-x Al.sub.x As current restriction layer 105, a 
p-type Ga.sub.l-w Al.sub.w As cladding layer 104, a p-type Ga.sub.l-z 
Al.sub.z As active layer 103, and an n-type Ga.sub.l-y Al.sub.y As 
cladding layer 102 which are formed in sequence. Then, an ohmic electrode 
101 is formed on the cladding layer 102 and is opened so that the light 
can be emitted externally from the conductive region 108. Thereafter, the 
light emitting elements adjacent to each other are electrically isolated 
by performing a halfway dicing on a region between adjacent light emitting 
elements so as to cut through a p-n Junction. As a result thereof, 
respective light emitting elements are independently operative. Here, the 
halfway dicing means a dicing which does not perform a full-cut dicing. 
When the semiconductor light emitting element thus constructed above is, 
for example, adopted for a light source of infrared rays for a camera's 
automatic focusing mechanism, the infrared rays emitted therefrom are 
passed through a collimator lens into a parallel beam toward a subject. 
Thus, the light reflected from the subject is sensed by a light receiving 
element, and a distance to the subject is measured in accordance with a 
trigonometrical survey method. 
In the above-mentioned conventional example, there is used the halfway 
dicing technique as an electrically isolating means. Therefore, when a 
light emitting element is, for example, rendered conductive, a light h' 
guided by the p-type Ga.sub.l-z Al.sub.z As active layer 103 is irradiated 
externally from dicing grooves, together with a light h from the 
conductive region 108 (see FIG. 1). Then, consulting a near field pattern 
which indicates a light density of light emitted from the semiconductor 
light emitting element, the light h' irradiated from the p-type Ga.sub.l-z 
Al.sub.z As active layer 103 shows a significant level of density against 
the light h emitted from the surface of the conductive region 108. It is 
to be noted here that the light h' is an unwanted light which may be a 
major cause for inaccurate distance measuring. 
For example, when used as the light source for the automatic focusing 
mechanism, the light h' irradiated from the grooves, that is, the light h' 
which is leaked laterally from the p-type Ga.sub.l-z Al.sub.z As active 
layer 103, may be detected by the light receiving element so as to 
indicate an improper distance between the camera and the subject, so that 
there is caused an out-of-focus problem or the like. In order to alleviate 
such a problem with reference to FIG. 1, there is provided a sufficient 
interval d between the conductive regions 108 and the end faces of active 
layer 103 at the groove sidewalls, so that the unwanted light can be 
damped and the lateral unwanted light can be suppressed. 
With reference to FIG. 6, there is shown a relationship between the 
distance d and the relative light density (h' ) at the end of LED element 
relative to that of conductive region (h). For example, in order to 
suppress the relative density to 3% or therebelow, the interval d needs to 
be more than 80 .mu.m. However, there is a limit in reducing the distance 
d between the light emitting elements and there lies a great difficulty in 
achieving a semiconductor light emitting element where the interval d is 
minimal and a distance measuring performance is optimal at the same time. 
The halfway dicing accounts for the cause for light leakage. In other 
words, with reference to FIG. 5 which is an enlarged view of a portion 
circled by doted lines in FIG. 1, a shape realized by the dicing is an 
acute-angled surface. That is, an opening interval d1 in the surface of 
the light emitting element is greater than an interval d2 of the light 
emitting region in the vicinity of the p-type Ga.sub.l-z Al.sub.x As 
active layer 103. For instance, when depth of the halfway dicing is 60 
.mu.m, opening interval d1 would be 35 .mu.m and the interval d2 be 32 
.mu.m. Thereby, a portion of light irradiated from the end of the light 
emitting active layer 103 is detected at an upper portion of the 
semiconductor light emitting element. 
As mentioned above, since there is commonly used the halfway dicing and the 
shape of element isolating portion is of the acute angled type in the 
conventional semiconductor light emitting element, the light is leaked in 
the lateral directions from the isolating portion. In order to alleviate 
such the problem, there is provided an increased interval between the 
light emitting elements, so that the light is damped and the laterally 
leaked light is suppressed. However, the conventional technique set a 
limit in further dense integration therefor. Moreover, when, for example, 
used for the light source for the camera's automatic focusing mechanism, 
there lies great difficulty in realizing a semiconductor light emitting 
element in which the interval therebetween is minimal and a 
distance-measuring accuracy is maximal. 
SUMMARY OF THE INVENTION 
In view of the foregoing problems, the object of the present invention is 
to provide a semiconductor light emitting element in which the light 
leakage from the vicinity of the active layer end is significantly 
reduced, and the interval at which the element is disposed is sufficiently 
reduced, so that there can be realized an optimal distance-measuring 
accuracy when used, for example, for the light source of the camera's 
automatic focusing mechanism. Therefore, there is provided a semiconductor 
light emitting element comprising a double heterojunction structure such 
that a GaAlAs As current restriction layer formed with a conductive region 
is formed on a GaAs semiconductor substrate and a light emitting region of 
light emitting diode is provided therein by forming an p-n junction 
surfaces, the semiconductor light emitting element being characterized in 
that a plurality of the light emitting diodes are electrically isolated by 
a plurality of grooves formed substantially vertical to the p-n junction 
surfaces and an end face of the light emitting region cut through by the 
groove is disposed inside a vertical line drawn from an end face of the 
surface of the light emitting element. 
Other features and advantages of the present invention will become apparent 
from the following description taken in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Features of the present 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. 
Embodiments of the present invention will now be described with reference 
to the drawings. 
With reference to FIG. 2, there is shown a cross section of a basic 
semiconductor light emitting element according to the present invention. 
The semiconductor light emitting element is a double hetero structure (DH) 
monolithic type GaAlAs As LED (light emitting diode) and is equipped with 
three emitting element points. 
FIG. 3A through 3D show cross sectional views of process sequence for 
producing the semiconductor light emitting element shown in FIG. 2. 
In the same figures, first of all, with reference to FIG. 3A, there is 
formed an n type GaAs current restriction layer 5 having a plurality of 
conductive regions 8 at an arbitrary interval Y1, Y2, on a p type Ga As 
substrate 6. Then, an impurity concentration of the current restriction 
layer 5 is 5.times.10.sup.17 cm.sup.-3, and a thickness therefor is 5 
.mu.m. 
Next, there are formed in sequence a p type Ga0.7-Al0.3-As cladding layer 
4, a p type Ga0.97-Al0.03-As active layer 3 and an n type Ga0.7-Al0.3-As 
cladding layer 2 so as to form a GaAlAs As layer of double hereto 
structure. Then, the impurity concentration for the cladding layer 4 was 
1.times.10.sup.18 cm.sup.-3 and the thickness therefor was 5 .mu.m. The 
impurity concentration for the active layer 3 was 1.times.10.sup.17 
cm.sup.-3 and the thickness therefor was 1 .mu.m. The impurity 
concentration for the cladding layer 2 was 1.times.10.sup.18 cm.sup.-3 and 
the thickness therefor was 10 .mu.m. 
Next, with reference to FIG. 3B, there is formed an ohmic electrode 1 
having an opening portion therein so that the light emitted from the 
conductive region 8 can be emitted externally through the opening portion. 
Then, the electrode on the GaAlAs As layer adjacent to each element is 
removed using a photoresist patterning method. 
Thereafter, with reference to FIG. 3C, on a GaAlAs wafer there is formed a 
protection mask such as a SiO.sub.2 sputtering film 9 for reactive ion 
etching (RIE) so that the opening portions are etched by the reactive ion 
etching (RIE) technique. 
Thereafter, with reference to FIG. 3D, the above wafer is set in a dry 
etching vessel, and then reactive gases comprising boron trichloride 
(BCl.sub.3) and chlorine (Cl.sub.2) are introduced into the vessel so as 
to be excited to a plasma state by means of discharge or the like. As a 
result thereof, there is made an active seed such as a halogen radical and 
ion, thereafter, etching is performed by a reaction with the GaAlAs As 
material or a sputtering operation. Here, FIG. 4 shall be referred to, 
which shows an enlarged cross sectional view for an isolation portion. 
Then, argon (At) is introduced to utilize the sputtering action thereof so 
that interval D2 of the light emitting region in the vicinity of the 
active region 3 can be made equal to or greater than the interval D1 of 
the light emitting element surface by means of etching in a state of 
anisotropic etching. It shall be appreciated that there may be used gases 
among SiCl.sub.4, HCl, PCl.sub.3, CH.sub.4 plus H.sub.2, BBr.sub.3 and HBr 
for an etching purpose. 
More specifically, a gas flow rate of BCl.sub.3 was 40 SCCM, a Cl.sub.2 gas 
flow rate was 15 SCCM, an Ar gas flow rate was 30 SCCM, and a pressure in 
the vessel was 0.05 Torr. Moreover, a etching rate then was approximately 
2 .mu.m/minute. In order to ensure to that electrically isolation is 
secured after the RIE was carried out, a shape of the element was such 
that a depth of the etching was 25 .mu.m, interval D1 between the adjacent 
element surfaces was 30 .mu.m, and interval D2 of the active layer 3 which 
is the p type Ga0.97-Al0.3-As layer was 32 .mu.m. 
Thereby, even if the light leaked from the p type Ga0.97-Al0.3-As active 
layer 3 is guided toward the upper surface of the element, such leaked 
light is reflected by the GaAlAs As crystal so as to maximally suppress 
the light from being emitted externally. 
FIG. 6 shows correlation of a relative intensity between interval D between 
the conductive region 8 and the end of the light emitting element (as 
shown in FIG. 2), and the end of the conductive region. In the same 
figure, it is known that interval D can be as short as a half of that in 
the conventional halfway dicing technique, against the same intensity. 
In order to avoid an erroneous measurement due to light leakage from the 
end of the light emitting element if used for the automatic focusing 
mechanism, there is necessity in that the relative density shall be below 
3%. In this case, there is needed approximately 80 .mu.m for the interval 
d in the conventional practice. In contrast thereto, there is needed 
approximately 40 .mu.m in the present invention, thus reducing such an 
interval by half. 
Though not shown in FIG. 6, a substantially same effect is observed by the 
present invention when the distance D1 is approximately equal to the 
interval D2 which is an interval of the light emitting region in the 
vicinity of the active layer 3. 
Though aforementioned of the DH monolithic type GaAlAs As LED, it shall be 
appreciated that a single heterostructure (SH) GaAlAs LED may serve a same 
purpose in this present invention. 
Moreover, stoichiometric ratios x, y, z, w of Al in DH are preferred to 
satisfy the following relation in the n type Ga.sub.l-y Al.sub.y As 
cladding layer 2, the p type Ga.sub.l-z Al.sub.z As active layer 3, the p 
type Ga.sub.l-w Al.sub.w As cladding layer 4, and the n type Ga.sub.l-x 
Al.sub.x As current restriction layer 5. 
EQU 0.ltoreq.x, z.ltoreq.0.4 
EQU z&lt;y, w 
For example, in the above embodiments for an infrared LED, an Al mixed 
stoichiometric ratio for the p type Ga.sub.l-z Al.sub.z As active layer 3 
was 0.03. However, the Al mixed ratio z for the active layer 3 may be 
adopted to a range of 0.3 through 0.4 where the ratio becomes a direct 
transition type from infrared to red region. 
Moreover, the light leakage also occurs in the light emitting region 
surrounding the monolithic LED element which is located in the vicinity of 
the active layer 3, thus also causing the erroneous automatic focusing 
measurement. 
Therefore, when the end face of the light emitting region is located inside 
a vertical line drawn from the the surface of the light emitting element, 
the erroneous measurement can be further securely avoided. 
With reference to FIGS. 7A through 7C and FIGS. 8A-8B, there are shown 
various shapes for the isolating grooves. 
FIG. 7A shows the isolating groove where a shape thereof caused by an RIE 
process is of a linearly shaped type. FIG. 7B shows the isolating groove 
whose base portion is etched relatively wider. FIG. 7C shows the isolating 
groove having a certain curvature therealong. 
FIG. 8A shows the light emitting element where the end of an electrode 1 is 
disposed inside the end of the cladding layer 2. FIG. 8B shows the light 
emitting element where the end of the electrode 1 is extended over the 
cladding layer 2. 
In addition to the basic best-mode shape for the isolating groove, with 
reference to FIG. 9A, the isolating groove may be disposed Just above the 
current restriction layer 5 and without penetrating the current 
restriction layer 5. Distance .beta. away from the upper surface of the 
current restriction layer 5 is preferably smaller than the thickness 
.alpha. of the active layer 3. Alternatively, with reference to FIG. 9B, a 
bottom end of the isolating groove may be located in the current 
restriction layer 5. 
In the above embodiments, the three-point light emitting element has been 
described. However, the present invention can be utilized for a light 
emitting element whose structure has two points or points equal to or 
greater than four. Furthermore, the present invention may be implemented 
for a case where the light emitting points have an arbitrary arrangement 
in two dimensions. 
Moreover, the present invention may be implemented for the light emitting 
element using InGaAlP in which red to green light emitting is possible in 
a similar manner described in the above as in GaAlAs. In this case, the 
crystal ratio is preferably such that In.sub.0.5 (Ga.sub.l-x 
Al.sub.x).sub.0.5 P where 0.ltoreq.x&lt;1. It shall be further appreciated 
that GaP and Ga As.sub.l-x P.sub.x where 0.ltoreq.x&lt;1 may serve good as 
well in the similar manner as in GaAlAs As. 
In summary, by implementing the present invention as mentioned above, the 
interval between the adjacent isolation regions which are the light 
emitting regions of the light emitting element in the neighborhood of the 
active layer are made equal to or wider than that of the opening portion 
of the surface of the light emitting element by means of the reactive ion 
etching technique. In other words, the upper end of a plurality of grooves 
which electrically separates the LED are made vertical or in the direction 
inside the vertical line of a pn junction surface of the element. 
Therefore, even if the light is irradiated upwards from the light emitting 
region of the LED end, such unwanted light is sufficiently suppressed from 
being emitted outwardly because the light is reflected by the GaAlAs As 
crystal. Thus, the present invention can realize to provide the 
semiconductor light emitting element in which the light leakage from the 
active layer end of the light emitting element is minimally suppressed. 
For example, the present invention realizes to significantly reduce the 
interval between the elements when used for the automatic focusing 
mechanism. Moreover, the present invention achieves to reduce occurrence 
frequency of the mistaken measurement to 1% from the current 5%. As a 
result, an area occupancy thereof in a semiconductor chip can be 
significantly reduced, thus minimizing a product cost thereof and 
providing a semiconductor light emitting element with a significantly 
increased distance-measuring accuracy. 
Besides those already mentioned above, many modifications and variations of 
the above embodiments may be made without departing from the novel and 
advantageous features of the present invention. Accordingly, all such 
modifications and variations are intended to be included within the scope 
of the appended claims.