JP2678153B2 - Method for manufacturing semiconductor laser device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser device, and more particularly to a semiconductor laser having a buried hetero structure. 2. Description of the Related Art A semiconductor laser having a buried heterostructure in which a laser oscillation active layer is surrounded by a heterojunction interface enables a low oscillation threshold current value, a stabilized oscillation lateral mode, and high temperature operation. It has excellent characteristics such as that and is expected to be used as a laser light source. In particular, in a semiconductor laser using a P-type substrate as a substrate for epitaxial growth, the pn junction forming the current narrowing path has a large withstand voltage, so that a high voltage can be applied to perform a large output operation. is there. However, FIG.
, A P-type InP buffer layer 2, a non-doped InGaPAs active layer 3, and an n-type In are formed on the P-type InP substrate 1.
After the P clad layer 4 is sequentially grown, both sides of the growth layer are etched deeper than the active layer 3 along the stripe, and the n-type InP current blocking layer 5 and the P-type current narrowing layer 6 are regrown in this portion. In the conventional semiconductor laser device structure in which the buried growth is performed, the cladding layer 4 and the current blocking layer 5 are formed.
Since it is necessary to prevent conduction between the current blocking layer 5 and the current blocking layer 5, it is necessary to regulate the height of the current blocking layer 5 to be equal to or lower than the height of the active layer 3. Therefore, it is important to accurately control the etching depth and the growth thickness of the current blocking layer 5, but it cannot be said that the current liquid phase epitaxial growth technology and wet etching method have sufficient controllability, and the yield is reduced. Has the drawback of causing In view of the above problems, the present invention grows a multi-layer crystal structure having a laser oscillation active layer limited by a heterojunction and then etches it into a mesa shape. , as an embedded structure of the etching unit, p cover the entire mesa stripe sides ^- p containing buffer layer ^-
Provided is a method of manufacturing a semiconductor laser device, which is formed by stacking -np structures, can prevent generation of a leak current from a mesa stripe portion, and does not require a high degree of controllability in etching processing and crystal growth. The purpose is to According to the method of manufacturing a semiconductor laser device of the present invention, a first conductivity type buffer is provided on a first conductivity type substrate.
Layer, the active layer, and the second conductivity type cladding layer are laminated in this order.
And at least the second conductivity type cladding layer and the
The active layer is removed by etching to remove the first conductivity type semiconductor.
At least the active layer and the second conductivity type clad layer are exposed.
Forming a mesa stripe structure consisting of
In the area excluding the upper surface of the sustain stripe structure,
The side surface of the substrate structure and the exposed first conductivity type semiconductor,
A first conductivity type resistance layer having a low carrier concentration so as to completely cover it.
And the upper surface of the mesa stripe structure.
A current of the second conductivity type on the resistance layer of the first conductivity type in a region.
A block layer and a first conductivity type current confinement layer are formed in this order.
And the upper surface of the mesa stripe structure and the first conductive layer.
A second conductivity type buried layer so as to cover the conductivity type current confinement layer.
And a forming step . Embodiments of the present invention will be described in detail below with reference to FIGS. 1 (A) and 1 (B). P type (1
00) P-type InP buffer layer 2 (thickness 3 μm), non-doped InGaPAs, active layer 3 (emission wavelength L 3 μm, thickness 0.2 μm), n-type InP clad layer 4 (thickness 0.5 μm) on InP substrate 1. Are sequentially grown by a liquid phase epitaxial method. Next, a photoresist stripe (not shown) having a width of about 3 μm is formed in the <011> direction by the photolinography technique, and then the multilayer crystal structure is etched from the surface to the middle of the buffer layer 2 with a Br-methanol solution. Form a mesa-shaped stripe. This is shown in FIG. At this time, the mesa size is the stripe width w
= 2 to 4 μm and height h = 2 μm, it becomes possible to suppress the growth on the upper surface of the mesa at the time of embedded growth in a later process (Mito et al .: Technical Report OQE80-116 of the Institute of Electronics and Communication Engineers). ). Buried growth is carried out along the mesa stripes with the P ^-- InP buffer layer 7 (thickness of 0.
5 μm), n-InP current blocking layer 5, P-InP current narrowing layer 6 (thickness at flat portion 0.5 μm), n-InP
The buried layer 8 (thickness at the flat portion is 3 μm) is sequentially formed by the liquid phase epitaxial method. This step is shown in FIG.
Next, n-side and P-side electrodes (not shown) are formed on the front surface of the InP buried layer 8 and the back surface of the InP substrate 1, and <110>.
The surface is cleaved to form a laser resonator. In the semiconductor laser device having the above structure, the InGaPAs layer serving as the laser oscillation active layer 3 is the InP layers of the buffer layer 2 and the cladding layer 4 in the thickness direction, and the InP layer of the buffer layer 7 in the left and right surface directions. They are joined to each other to form an active region limited to a stripe shape by a heterojunction.
Since the buffer layer 7 easily grows on the side surface of the mesa stripe, the side surfaces of the cladding layer 4 and the active layer 3 are covered with the P ^-- InP layer of the buffer layer 7, and the cladding layer 4 and the current blocking layer 5 are completely cut off. This means that no leak current will occur through this path. That is, when the buffer layer 7 does not cover the entire side surfaces of the cladding layer 4 and the active layer 3 and, for example, the cladding layer 4 and the current blocking layer 5 are in direct contact with each other,
A thyristor including the buried layer 8 (n type), the current narrowing layer 6 (p type), the current blocking layer 5 (n type), and the buffer layer 2 or 7 (p type), which uses the portion as a gate, is formed.
If the drive current is increased to increase the light emission intensity, the gate current (leakage current) from the cladding layer 4 is also increased, and the thyristor is turned on, greatly reducing the supply current that can contribute to light emission. In this example, there is no such current path to the gate and turn-on of the thyristor is blocked. Further, the buffer layer 7 has a function as a resistance layer because the carrier concentration is set to be low, and prevents generation of leakage current, and at the same time, is a layer having a larger forbidden band width and a smaller refractive index than the active layer 3. Because of this, it also has the function of confining carriers and light in the active layer 3. When a driving current is injected into the device through the n-side electrode and the P-side electrode, the injected current flows only in the current path corresponding to the mesa stripe portion of the clad layer 4 and the active layer 3, and the mesa stripe portion is formed. P-n-p composed of a current constricting layer 6, a current blocking layer 5 and a buffer layer 7 around the
^-The structure blocks the current completely. Further, carriers and light are confined in the active layer 3 by the junction interface between the buffer layer 7 and the active layer 3. Each pn junction interface of the p-n-p ^- structure is focused on the shoulder portion of the cladding layer 4 in the mesa stripe portion, and extends in the left-right direction while curving from the shoulder portion of the cladding layer 4. This is because the buffer layer 7 grows laterally when it is epitaxially grown in the mesa stripe portion, and the current blocking layer and the current narrowing layer are sequentially deposited using the buffer layer 7 as a base layer. From the above,
A high-density current is supplied to the active layer 3, and as a result, the oscillation threshold current is as low as 15 to 20 mA.
It showed excellent characteristics with a characteristic temperature of 70K or higher up to around 0 ° C. Further, since the precise control of the etching depth and the growth layer thickness is not required, the device manufacturing yield is greatly improved. In the above embodiment, InGaPAs having an emission wavelength of 1.3 μm is used as the active layer, but the present invention is not limited to this, and 1.1 μm-
Either InGaPAs in the range of 1.7 μm or other compound semiconductors can be used. Although a total of four layers of InP are used for the buried growth, InGaPAs having a larger forbidden band width and a smaller refractive index than the active layer may be used. As described above in detail, according to the present invention, the second conductivity type clad layer having the mesa stripe structure is used as the second conductivity type clad layer-the second conductivity type clad layer- the first conductivity type.
Electric current confinement layer-Second conductivity type current block layer-First conductivity
The current path to the second conductivity type current block layer, which serves as the gate of the thyristor of the type resistance layer, is completely cut off, the turn-on of the thyristor due to this is blocked, the drive current range can be expanded, and the reactive current can be suppressed. It is possible to easily fabricate a semiconductor laser with a buried structure without requiring high controllability for crystal growth or etching.
It can be expected to improve the yield.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of essential parts of a buried heterojunction structure semiconductor laser according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a main part of a conventional buried heterojunction structure semiconductor laser. [Explanation of reference numerals] 1 substrate 2 buffer layer 3 active layer 4 clad layer 5 current blocking layer 6 current narrowing layer 7 buffer layer 8 buried layer

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Matsui               22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Prefecture               Sharp Corporation                (56) References JP-A-58-200584 (JP, A)                 JP 59-127893 (JP, A)

Claims (1)

(57) [Claims] First conductivity type buffer layer and active layer on first conductivity type substrate
And a step of laminating the second conductivity type cladding layer in this order, and at least the second conductivity type cladding layer and the active layer.
To remove the first conductivity type semiconductor,
Mesa consisting of at least active layer and second conductivity type cladding layer
Forming a tripe structure, and forming the mesa in a region other than the upper surface of the mesa stripe structure.
Side surface of tripe structure and the exposed first conductivity type semiconductor
And the first conductivity type of low carrier concentration so as to completely cover
The step of forming a resistance layer and the first conductive layer in a region other than the upper surface of the mesa stripe structure are performed.
The second conductive type current block layer and the first conductive layer are formed on the electric resistance layer.
A step of forming an electric current confinement layer in this order, an upper surface of the mesa stripe structure and the first conductivity type current constriction layer.
A step of forming a buried layer of the second conductivity type so as to cover the confinement layer.
Of a semiconductor laser device characterized by having
Construction method.