JPS60239083A - Optical bistable semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain an optical bistable laser having uniform characteristics by forming a current injection interrupting layer on an active layer region just under a groove and coating sections except the groove with a layer consisting of another material composition having a conduction type reverse to that of the groove. CONSTITUTION:An N-InP buffer 11, an InGaAsP active layer 12 and a P-InP 13 are superposed on N-InP 10, and grooves 22, 23 having wide width 24 and narrow width 25 and reaching to the layer 11 are formed on both sides of a mesa stripe 20. When P and N type InP current block layers 14, 15 are superposed, the layers 14, 15 do not grow on the mesa 20 in the wide groove sections 24, the grooves are filled with the layer 14 in the narrow groove section 25, the upper section of the mesa is flattened, and the layer 15 is not disconnected. P-InGaAs 16, P-InP 17 and P-InGaAsP 18 are formed, and a P side electrode is attached. An etching groove 21 is shaped on the narrow groove section 25 in the direction of a resonator axis 30, the current block layer 15 is exposed, and the P side electrode is divided into two 26, 27. When the electrodes 26, 27 are biassed positively and an electrode 28 negatively, injection currents aproximately flow through the active layer, a resistance value between the electrodes 26, 27 is increased, and injection currents to the electrodes 26, 27 are not affected mutually, thus obtaining a laser conducting uniform optical stable operation.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to an optical bistable semiconductor laser exhibiting bistable operation, which is one of the most important components as an optical functional element used for optical exchange and optical information processing. Regarding.

(Prior art and its problems) Among optical functional devices, optical bistable semiconductor lasers have a wide range of applications such as optical logic, optical switches, optical storage, optical signal waveforms, and shaping amplification. It is expected to be used as a device, and basic studies are underway. Regarding the development of optical bistable semiconductor lasers, Mr. Lascha (G, J.

Solid state electronics (5OLID 5TATE ELECTRO-N) by LASHER)
1. The first paper was published in vol. 7, page 707 of C8) magazine in 1964, and in later years Mr. Low (K, Y, LAU) et al.・Physics Letters (APPLIED
PHYSIC8LETTER8) magazine 1982 No.40
This is reported in the paper on page 369 of Vol. 3 in the form of a heterostructure with embedded tandem electrodes. In this semiconductor laser, the electrode near the active layer is divided into two parts by a groove: an optical amplification region where the gain exceeds the loss in the active layer, and an optical amplification region where the gain exceeds the loss because no current is injected. It is divided into two distinct saturable absorption regions. Is the groove in this case simply to electrically isolate the two regions? Also, current is injected into the active layer directly under the trench by the diffusion current from the optical amplification region. Therefore, in this semiconductor laser, if the two divided electrodes are made common, the optical output-current characteristics (
(hereinafter referred to as L-I characteristic), and optical bistable operation does not occur. To achieve optical bistable operation, it is necessary to reduce the current injected into the saturable absorption region to about -100 μA (
In this case, the current injected into the optical amplification region is approximately +30mA)
. However, a paper by Dr. Low et al. reported that a change in the current injected into the saturable absorption region by just a few μA can significantly change the hysteresis shape in the L-I characteristic and the current width that indicates optical bistable operation. has been done. Therefore, for optical functional devices that require stable operation, it is important to improve the controllability of this injection current. As a countermeasure to this problem, an optical bistable semiconductor laser (
There is a patent application No. 58-142922). This is a semiconductor laser having a structure in which a semiconductor layer that blocks current injection is laminated on a part of an active layer, and a groove is formed directly above the semiconductor layer. By employing this semiconductor layer, a saturable absorption region is formed in the active layer portion directly under the groove, and the current injected into the two halves of the electrode is approximately several tens of mA. In this case, even if the injection current fluctuated by several hundred μA due to external factors or other factors, the change in the L-■ characteristic of optical bistable operation could be almost ignored. However, if the grooves are not etched close to the active layer,
For example, when the groove width is 30 μm, the resistance between the two divided electrodes is only about 61Ω, and therefore, due to the potential difference between the two divided electrodes, a part of the injected current flows on the order of milliamperes during that time, and the static characteristics are Even if the characteristics were stable, there was a problem that the independence of the injection current itself could not be maintained, such as the dynamic characteristics becoming somewhat unstable. In the trench etching method, the thickness of the semiconductor layer after crystal growth may vary depending on the location, and a method of determining the trench depth simply by the etching time is not very desirable, and there are some problems in terms of reliability. Ta. Therefore, Ken et al. proposed forming a semiconductor layer above the active layer to stop the etching as a method of determining the etching depth of the groove, and filed a patent application under the name ``Bistable Semiconductor Laser.'' 58-1677
98). In the case of this invention, the resistance between the divided electrodes can be increased to IKO, and the characteristics can also be made more uniform compared to the conventional method.

However, if only the depth of the groove is formed with good reproducibility, the area directly under the groove becomes a saturable absorption region, and the diffusion current will cause the injection current to flow into the active layer directly under the groove. There has been a desire for an optically bistable semiconductor laser with a structure that can uniformly realize optically bistable operation due to rounding.

(Objective of the Invention) An object of the present invention is to provide an optically bistable semiconductor laser having uniform characteristics by further improving the yield of optically bistable operation.

5- (Structure of the Invention) The present invention provides a semiconductor laser in which an electrode is divided into a plurality of parts in the direction of the core loss axis by a groove.
The second semiconductor layer is characterized by having a semiconductor layer having a conductivity type different from that of the first semiconductor layer and a material composition different from that of the first semiconductor layer.

(Detailed Description of Configuration) The present invention solves the problems of the prior art by adopting the above-described configuration. First, a first semiconductor layer is crystal-grown so that current injection is blocked so that a saturable absorption region is formed in a part of the active layer, and then a second semiconductor layer having a different material composition is formed on top of the first semiconductor layer. When a groove is formed by, for example, chemical etching after crystal growth, the first semiconductor layer and the second semiconductor layer have different material compositions, so the groove can be formed by utilizing the difference in etching speed due to the difference in etchant. The depth of the first semiconductor layer is limited from the electrode to a point where the first semiconductor layer remains. The resistance between two or more electrodes divided in the resonator axis direction in this manner can be made greater than IKΩ. The resistance of a normal semiconductor laser itself is 5~
Since it is about 7Ω, the current between the divided electrodes is several tens of μ.
Can be kept below A.

independence can be maintained. In addition, regarding the L-I characteristic, since the region directly below the groove becomes a saturable absorption region, optical bistable operation with uniform characteristics can be realized. As described above, the yield of optical bistable operation can be further improved and an optically bistable semiconductor laser having uniform characteristics can be realized.

(Example) Plane sectional view showing the shape of the active layer in the case where no
Figure (a) is a sectional view taken along line AA' in Figure 1, (blFiB-
B' sectional view and FIG. 3 each show a perspective view of this embodiment.

The side surface of the two grooves opposite to the mesa stripe is partially narrowed so that the groove dividing the electrode into two has a desired depth. A Brehner-Strife-type buried heterostructure semiconductor laser is a semiconductor laser in which a mesa stripe including an active layer is buried with P- and N-type semiconductor layers, and this is a patent-pending invention by Mr. Kitamura et al. I am familiar with Gansho 56-166666J.

This embodiment is fabricated as follows. First, by liquid phase or vapor phase growth, n-InP is deposited on the n-InP substrate 1o.
-InP layer 77 layer 11, non-doped InQaAsP
The active layer is a DH layered with P-InP cladding layer]3.
A wafer having the shape shown in FIG. 1 is fabricated by coating a substrate with photoresist and performing conventional photolithography and etching. Next, this wafer is grown using a liquid phase growth method.
P-InP first current blocking layer 14, n-InP second current blocking layer 15, P-InGaAsP etching layer 16, P-InP buried layer 17, P-In
GaAsP cap layers 18 are sequentially formed. As shown in FIG. 1, a mesa stripe 20 including an active layer 12
The two second and third grooves 22 and 23 for forming the grooves are straight on the mesa stripe 20 side, and have a partially wide part 24 and a narrow part 25 on the side away from the mesa stripe 20. ing. In the second crystal growth, in the wide portions 24 of the second and third grooves 22 and 23 forming the mesa stripe 20, as shown in FIG. ] 5 does not grow on the mesa stripe 20. On the other hand, in the narrow portions 25 of the second and third grooves 22.23, the second and third grooves 22.23 are filled with the first current blocking layer ]4, so that the second current block The shape near the mesa stripe immediately before the formation of layer 15 becomes a thousand voices.

Therefore, the second current blocking layer 15 has a mesa stripe 2
It covers the entire area without being interrupted at the top of 0. Similarly, the etching layer 16 is also completely covered. After crystal growth, a cap layer of 18g Au Z is used to make an ohmic contact on the P side.
Deposit n9-. Furthermore, a photoresist// is applied and the AuZn, cap layer 18, buried layer 17, and etching layer 16 directly above the wide narrow portions 25 of the second and third grooves 22 and 23 are sequentially removed by normal photolithography and etching. The first groove 21 is formed so that the P-side electrode is divided into two in the direction of the resonator axis 3o. For AuZn etching, use a mixture of KI+I2 and InGaAsP.
For etching the single layer 18 and etching layer 16, use a mixture of H2SO4 and H2O2, and for etching the buried layer 17 of nP, use HeI and H2O2.
20 dilutions were used. H2SO4+H20z-? H.C.
1+H20 alloys most of the other materials with Zn. Then n-
After polishing the InP substrate 1o to a thickness within the range of 100 to 150 μm, A is used for the n-side ohmic contact.
LAGeNi ft is deposited and alloyed to complete wafer fabrication. A resonator surface is formed on this wafer at right angles to the mesa stripe 20 so that the first and second P-side electrodes 26 and 27 are divided by the first groove 21 by a normal cleavage method.
A device is manufactured. When the first and second I' side electrodes 26 and 27 of this element are biased positively and the n side electrode 28 is biased negatively,
This element can exhibit stable bistable operation in terms of L-I characteristics and optical input/output characteristics. The first P-side electrode 26 and the second P-side electrode 27 are electrically bridged by the P-InP cladding layer 13, but since they are adjacent to the active layer, most of the injected current flows through the active layer. flows to Therefore, the first groove 21
When the width of the electrode was 25 μm, the resistance between the electrodes on the P side could exceed IKQ. Because of this degree of resistance, the first
The currents injected into the second P-side electrodes 26 and 27 were able to realize uniform optical bistable operation with a high yield in the range of 20 to 40 mA without affecting each other. The size of the optical bistable semiconductor laser in this example is 20 mesa stripes.
The width of the wide groove portion 24 is 7 μm, the width of the narrow portion 25 is 3 μm, the length of the narrow groove portion 25 is 20 μm1, the length of the first P-side electrode 26 is 100 μm,
The length of the second P-side electrode 27 is 150 μm. Since the appearance of crystal growth varies greatly depending on the growth method, growth conditions, etc., it goes without saying that appropriate dimensions should be adopted in conjunction with these factors. Furthermore, the ratio of the lengths of the first P-side electrode 26 and the second P-side electrode 27 in the direction of the camera axis 30 is not limited. the second of
As a method for forming the current blocking layer 15 over the entire area including the upper part of the mesa stripe 20, the second and third current blocking layers 15 are formed.
Grooves 22 and 23 are straight on the mesa stripe 20 side. The side away from the mesa stripe 20 has a wide part 24 and a narrow part 25, but the side away from the mesa stripe 20 has a straight line, and the side away from the mesa stripe has a wide part 24 and a narrow part 25. You can do it like this. In this case as well, if the first groove 2 corresponds to the narrow portion 25, the same crystal growth as in the above embodiment is possible, and there is no difference in characteristics. In the example, the P-side electrode had a full-surface electrode structure of AuZn, but it could also have an oxide stripe structure, or an n-I electrode instead of the P-InGaAsP cap.
For example, the nGaAsP cap layer may be converted into a P layer by diffusing Zn only in the vicinity of the upper surface of the mesa stripe 20.

Although InP/InGaAsP-based semiconductor materials were used in the above embodiments, other semiconductor materials such as GaA I As /GaA, s-based, etc. may also be used.

Furthermore, although the embodiment employs a buried stripe structure, other stripe structures may be used.

[Brief explanation of drawings]

FIG. 1 is a plan sectional view of an embodiment of the present invention, and FIG.
) and (b) are partial sectional views of FIG. 1, and FIG. 3 is a perspective view of an embodiment of the present invention. In the figure, 10... n-InP substrate, 11...
n-InP buffer layer, 12...InGaAs
P active layer, 13...P-InP cladding layer, 1
4... P-InP first current blocking layer, 1
5... Second current blocking layer of n-In, P,
16...P-InGaAsP-[-etching layer, 17----- P-I n P buried layer,]
8...P-InGaA, sP cap layer, 20
...Mesa stripe, 21...First groove, 22...13-2 groove, 23...Third groove, 24... ...
Wide part, 25... Narrow part, 26.
...First P side electrode, 27... Second P side electrode
Side electrode, 28...n side electrode, 30...
The respective camera axes are shown. 14-

Claims (1)

[Claims] A semiconductor laser in which a groove divides a stain pole into a plurality of parts in the cavity axis direction, including a first semiconductor layer above an active layer that blocks current injection into a region of the active layer immediately below the groove, Furthermore, a second semiconductor layer having a conductivity type different from that of the first semiconductor layer and having a different material composition is provided above the first semiconductor layer excluding at least the groove portion. Bistable semiconductor laser.