JPS6058696A - Bi-stable semiconductor laser - Google Patents

Abstract

PURPOSE:To improve the yield of the titled device by etching of the electrode close to the active layer to the location before the etched layer by a method wherein semiconductor etching stop layers of the same conductivity type and different material compositions are laminated on the clad layer immediately on the active layer. CONSTITUTION:The p-InP clad layer 11, InGaAsP active layer 12, and p-InP clad layer 13 are laminated on an n-InP substrate 10, and the first and second grooves 14 and 15 are formed by normal photolithography. Next, the first current block layer 16 of p-InP and the second current block layer 17 of n-InP are successively formed. At this time, layers 16 and 17 are not grown on a mesa stripe 18, the grooves 14 and 15 being completely filled after growth of the layer 17, and the periphery on the stripe 18 being then formed into a flat recess. Then, the p-InGaAsP etching stop layer 19 is formed, and the yield of the title device is improved by etching to the location before the layer 19, the third groove 30 that splits the P type electrode 22 close to the active layer 12 into two or more in the direction of the resonator axis.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a 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.

Among optical functional devices, bistable devices have a wide range of applications such as optical logic, optical switches, optical storage, optical amplification, and optical signal waveform shaping, and are expected to be devices that take advantage of the essential characteristics of light. Basic studies are underway in various places.

The operation of bistable devices has been confirmed using various materials such as electro-optic crystals and liquid crystals, but devices using semiconductor materials are attracting particular attention as they can best take advantage of their high speed and integration potential. ing.

Regarding this, see, for example, Mr. Ransher (G, J.

LASHER) by SOLID-8TATE-ELECTRONI
The possibility of bistable operation in semiconductor lasers was theoretically estimated in a paper published in 1964, Vol. Shear Bride Fixtures Letters (APPLIED PHY) by Mr. (K, Y, LAU) etc.
SIC8LETTER8) magazine, 1982, Volume 40, 36
The paper on page 9 reports a tandem buried heterostructure bistable semiconductor laser. In this semiconductor laser, the electrode on the side closer to the active layer is divided into two parts by a groove); the optical amplification region where the gain in the active layer is higher than the loss; and the optical amplification region where the gain is higher than the loss due to no current injection. It is divided into a saturated absorption region. The groove merely separates the optical amplification region from the saturable absorption region. In this semiconductor laser, 2
If the separated electrodes are made common, the current-optical output characteristics of a normal semiconductor laser will be exhibited, and therefore no bistable characteristics will occur. In order to obtain bistable characteristics, it is necessary to reduce the injection current to the saturable absorption region to about -100 pA (in this case, the injection current to the optical amplification region is about 3QtnA). This is considered to be because the saturable absorption region behaves like a photodiode. However, if the current injected into the saturable absorption region changes by a number/JA, the current -
The shape of hysteresis in the optical output characteristics and the current width that indicates bistable operation will change significantly. Therefore, in order to utilize this bistable operation in optical functional devices, it is necessary to extremely improve the controllability of the injection current. As a countermeasure for this, the inventors of the present application presented their work at the General National Conference of the Institute of Electronics and Communication Engineers in 1981, and published it in Volume 4, Volume 937 of the Proceedings of the Conference. Tandem electrode structure described on page 23
C-PBH) semiconductor laser. In this bistable semiconductor laser, the groove not only separates the electrodes, but also serves as a current non-injection region where injection current is prevented from flowing directly under the bay. However, even if the two divided electrodes are made common, bistable operation is observed in the current-light output characteristics due to the presence of the groove.

Also, by combining the injection currents to the separated electrodes, the stain current
The shape of the hysteresis in the optical output characteristics, the shape of the hysteresis in the current-optical output characteristics indicating bistable operation, and the current width indicating bistable operation can be controlled to desired magnitudes, and the controllability of the injection current is also 0. A fluctuation range of about 5 mA is sufficient. However, the yield of bistable semiconductor lasers having such characteristics is not necessarily good, and recent experimental results have revealed that the cause of this is the etching depth when forming the grooves. If the etching is insufficient, there is almost no difference from the characteristics of Low et al. shown in the conventional example, and if the etching becomes excessive and reaches the active layer, laser oscillation will no longer occur. Therefore, in order to increase the yield, it was necessary to stop the formation of grooves by etching at a certain appropriate depth.

An object of the present invention is to improve the yield of bistable operation and provide a bistable semiconductor laser having uniform characteristics.

According to this invention, there are two substantially parallel first... In a semiconductor laser in which a mesa stripe including an active layer formed by a second groove is embedded with at least a semiconductor layer of a conductivity type different from the semiconductor layer above the mesa stripe, a semiconductor cladding layer immediately above the active layer is provided. A semiconductor etching stop layer of the same conductivity type but different material composition is laminated on the upper layer, and a third groove that divides the electrode near the active layer into two or more in the resonator axis direction is the semiconductor etching stop layer. A bistable semiconductor laser is obtained which is characterized in that the layer is etched to the front.

In this invention, in a semiconductor laser having two or more electrodes divided in the direction of the cavity axis, it is possible to form a groove, which is important for bistable operation, or to make the width and depth of the groove to a desired size with good reproducibility. It is in. The width of the groove can be formed with an accuracy of ±1 .mu.m using the current standard 7-orthotlin graphic technology. However, with regard to the depth of the groove, the reproducibility of the depth from the active layer to the electrode is rather poor due to variations from wafer to wafer after crystal growth or from location to location even within the same wafer.

To improve this, a semiconductor etching stop layer with a material composition different from that of the surrounding semiconductor layer is provided between the active layer and the electrode, and when forming the third groove, the etching stop layer is etched to the front of the semiconductor etching stop layer. It is sufficient to completely remove the semiconductor layer. If such processing is performed, the depth from the groove to the active layer will be approximately constant, and variations in characteristics can be reduced. Since the depth from the active layer to the groove is less than 1 pm, the leakage current from the electrode to the active layer under the load, which is the non-current injection area, is significantly reduced, and the reproducibility of bistable operation is almost the same as the groove size. It is determined by Since the groove width can be easily controlled, bistable semiconductor lasers with uniform characteristics can be obtained with high yield.

The present invention will be described in detail below with reference to the drawings.

The first diagram shows a perspective view of a bistable semiconductor laser which is a first embodiment of the present invention. A planar type buried heterostructure semiconductor laser is one in which a mesa stripe including an active layer is buried with p and n type semiconductor layers. -16
I am familiar with 6666.

The first embodiment is manufactured as follows. First, by liquid phase or vapor phase growth method, on the n-InP substrate 10,
n-InP buffer layer 11, non-doped InGaAs
A photoresist is coated on the DH substrate on which the P active layer 12 and the P-InP cladding layer 13 are laminated, and the conventional 7-input graphic technique is applied.1. A wafer with *2 grooves 14 and 15 is manufactured. Next, this wafer is deposited with a first current blocking layer 16, n of p-InP using a liquid phase growth technique.
- A second current blocking layer 17 of InP is sequentially formed. In this case, since the width of the mesa stripe 18 is usually narrow, 1 to 2 μm, there is a first stripe on the mesa stripe 18. The second current blocking layer 16.17 is not grown. After the growth of the second current blocking layer 17, the first current blocking layer 17 is grown. When the second grooves 14 and 15 are completely filled, the area around the upper part of the mesa stripe 18 becomes a flat concave area approximately l'L. Next, a p-InGaAsP etching stop layer 19, which is important for controlling the depth of the third groove 18 by etching, is formed, followed by a p-InP buried layer 20, a p-In
A GaAsP key 221 layer 21 is formed. After crystal growth, AuZn is deposited on the cap layer to establish ohmic contact on the p-side.

Further, a photoresist is applied and a third groove 30 is formed by ordinary photolinographic technology and etching so as to divide the p-side electrode 22 into two in the resonator axis direction. In this case A u Z n (l-1, K I +
I.

The cap layer 21 is removed with a sulfuric acid/decahydrogen peroxide based etching solution, and the button embedding layer 20 is removed with a nitric acid based etching solution. Nitric acid-based etching solution etches InP, but InGaA etches.
Since sP is not etched, p-InGaA++P
Etching stops when the etching stop layer appears on the surface, and the third groove 30 is formed. Next, AuZn is alloyed. Next, the n-InP substrate 10 is polished to 120
After making the thickness about μm, Au-Ge-Nif is vapor-deposited for the n-side ohmic contact, and alloyed to complete the °C wafer fabrication. This wafer is subjected to a normal valve opening method to form a resonator at right angles to the mesa stripe 18 so that the p-side electrode 22 is divided by the third groove 30, thereby producing an element. Half length of this element fLfc p
When the flIU electrode 22 is biased as positive and the nIII electrode 23 is biased as negative, 1. This device works as a bistable semiconductor laser with two levels that are stable with respect to current input or source input. This is due to the following reason. In this bistable semiconductor laser, the third groove 30 serves as a current non-injection region, so the portion directly below the third groove 30 is considered to be a saturable absorption region. The saturable absorption region acts as a loss having a finite magnitude when the 7-oton density or carrier density is sufficiently small, and has the property that when it becomes large enough, the loss nonlinearly becomes zero. Because this bistable semiconductor laser is a buried heterostructure, it can easily be operated at room temperature and with low operating currents. Furthermore, since the third groove 30 is a saturable absorption region, by appropriately combining the currents injected into the p-side electrode 22 divided into two and changing the size of the saturable absorption region, the width of the bistable operation can be increased. For example, the current width can be changed. In the first example, when the currents injected into the two divided p-side electrodes 22 are equal, the threshold for starting oscillation is 40 mA at room temperature, and the current width indicating bistable operation at this time is 10 mA. In addition, by combining the current injected into the p-side electrode 22, the current width indicating bistable operation is set to 1 to 30 mA.
could be varied within a range.

These characteristics have been improved so that the depth from the third groove 30 to the active layer layer 2 is approximately the same for each element, so instead of having characteristics that vary as in the past, it is possible to obtain devices with relatively uniform characteristics. Now you can. The size of the bistable semiconductor laser of this embodiment is mesa stripe width 1.5 μm, and the lengths of the two p-side electrodes 22 are each 100/'J150/'F.
n, the width of the third groove 300 is 251'm. Since the appearance of crystal growth varies greatly depending on the growth method, growth line characteristics, etc., it goes without saying that appropriate dimensions should be adopted in conjunction with these factors.

Next, FIG. 2 shows a sectional view of a bistable semiconductor laser which is a second embodiment of the present invention. In this second real gloss example,
Instead of layering the p-InGaAsP etching stop layer 9 formed in the first embodiment onto the n-InP current solo 22 layer 17, the p-InP cladding layer 9, which is the final step of forming a DH crystal, is used. This is carried out subsequent to the growth of layer 13. Therefore, the first. When forming the second trenches 14,15, the etch stop layer 19 is removed as shown in FIG. Other steps are the same as in the first embodiment. In this example as well, as in the first example, the yield of bistable operation was improved and uniform characteristics were obtained.

In the above embodiment, the p-side electrode had a full-surface electrode structure of AuZn, but in order to increase the resistance between the two pO1II electrodes 22, an oxide stripe structure or a p-side electrode was used.
InGaA++P n-In for the cap layer 21
Mesa stripe 18 by growing a GaAsP cap layer
For example, it may be converted into 92 layers by diffusing Zn only in the vicinity of the upper surface. Furthermore, in the above embodiments, InP/In
GaAsP-based semi-solid material was used, but GaAlAg
Other semiconductor materials such as /GaAs may also be used. Further, in the above embodiment, the p-side electrode is divided into two by the third groove 30, but two or more grooves corresponding to the third groove 30 are made to divide the p-side electrode into two.
By dividing the side electrode into three or more parts, bistable or even multistable (
It may also have multi-stable characteristics.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a first embodiment of the present invention, and FIG. 2 is a perspective view of a second embodiment of the present invention.
It is a figure which shows the sectional view of the Example. In the figure, 10... n-InP substrate, 11...
・p-InP cladding layer, 12-InGaAsP active layer, 13... p-InP cladding layer, 14... first groove, 15... second groove, 16... p-InP first current blocking layer, 17- n-InP second current blocking layer, 18- mesa stripe, 19- p-InP
GaAgP x 7 pulling stop layer, 20-...p-
InP buried layer, 21- p-InGaAsP key?
/p layer, 22 -p side electrode, 23...n side electrode, 30
...Only the third hail, respectively.

Claims (1)

[Claims] There are two almost parallel first lines that reach the active layer. In a semiconductor laser in which a multilayered mesa stripe including the active layer sandwiched between second grooves is buried with at least a semiconductor layer of a conductivity type different from the semiconductor layer above the mesa stripe, a semiconductor cladding layer immediately above the active layer. A semiconductor etching stop layer of the same conductivity type but different material composition is laminated on the upper layer, and a third groove that divides the electrode near the active layer into two or more in the resonator axis direction forms the semiconductor etching stop layer. A bistable semiconductor laser characterized by being etched upside down to the front.