JPH01189188A - semiconductor laser device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device, and more particularly to a structure of a semiconductor laser device that improves the luminous efficiency of laser light.

[Prior Art] In recent years, semiconductor laser elements have been used as light sources in information equipment, communication equipment using optical fiber cables, and the like, and the demand for them has further expanded. These semiconductor laser devices are desired to have high efficiency characteristics such as high light emitting output and low threshold current.

In order to meet such demands, there is, for example, a buried type semiconductor laser element having a structure in which both sides of a laser light emitting region are buried with buried layers.

The structure of this buried semiconductor laser device will be explained using FIG. 3. This semiconductor laser device has a p-type InP cladding layer 2 on a p-type InP substrate 1, ! nGaAs P active layer 3
, n-type 1n-P Clarado layer 4, and n-type! nGaAs
After laminating the P contact layer 5, it is formed into an inverted mesa shape. In the regions on both sides of this inverted mesa structure, p-type In
P first buried layer 6, n type! The nP second buried layer 7 and the p-type 1nP third buried layer 8 form a current blocking buried layer. Furthermore, an insulating film 9 is formed on the third buried layer 8. Furthermore, electrodes 10 are formed so as to sandwich these laminated structures from above and below.

The buried layer formed in this semiconductor laser device functions to block current. Therefore, the current applied by the electrode 10 flows through the region having an inverted mesa structure and the InGa
Concentrates on the AsP active layer 3 region. A semiconductor laser device having a so-called current confinement structure constituted by the buried layer 6.7.8 has the advantage of having a low threshold current and oscillating in a stable transverse mode.

In addition to such structural improvements, it is known that the carrier concentration of the p-type cladding layer contributes to improving the emission efficiency of laser light. For example, Figure 4 shows the relationship between the carrier concentration of the p-type cladding layer and the oscillation threshold current density (Jth) in a semiconductor laser device having a p-type InP cladding layer doped with Zn (zinc). There is. As can be seen from this figure, when the carrier concentration of the p-type cladding layer exceeds 1 x 1018 cm-'', the lasing threshold current density increases rapidly, that is, the luminous efficiency deteriorates. The lower the carrier concentration of the mold cladding layer, the better the luminous efficiency of the semiconductor laser device.

[Problems to be Solved by the Invention] However, the structure of the p-type cladding layer 2 has the following restrictions. That is, (1) When the carrier concentration of the p-type cladding layer becomes low,
The electrical resistance of this cladding layer increases.

(2) It is necessary to increase the thickness of the p-type cladding layer to some extent. One of the reasons for this is to prevent the influence of the thermally degraded layer generated near the interface between the substrate 1 and the cladding layer 2 epitaxially grown on the substrate 1 from adversely affecting upper layers such as the active layer 3. The second reason is that the region of the laser light that is emitted in the active layer 3 region and spreads around it due to the seepage effect of the light is kept within the region of the cladding layer 2.4.

Therefore, in order to improve the luminous efficiency of a semiconductor laser device, if the carrier concentration of the p-type cladding layer 2 of the conventional semiconductor laser device shown in FIG. It increases depending on the carrier concentration and layer thickness, making it difficult for current to flow to the active layer 3. As a result, there is a problem in that the luminous efficiency of the semiconductor laser device is not improved. To explain this more specifically, for example, in the semiconductor laser device shown in FIG.
In the case of IO'' cm-3, the electrical resistance of this cladding layer 2 is about 6Ω.
．． The conduction start voltage of 3.4 is about 0.52V lower than the conduction start voltage of the buried region 6.7.8 for current interruption. Therefore, a voltage is applied to the electrode 10, and in the low voltage range, current flows intensively to the mesa structure region including the active layer 3, but as the applied voltage increases, the electrical resistance of the cladding layer 2 directly below the active layer 3 increases. When the voltage drop increases and reaches around 0.52V, the leakage current flowing through the buried region 7.8 increases rapidly. The current value corresponding to the voltage drop at this time is about 86 mA, which is an extremely insufficient value for operating the semiconductor laser device. In this way the third
In the buried semiconductor laser device shown in the figure, p
When the carrier concentration of the mold cladding layer is set low, there is a problem in that leakage current occurs in the buried region provided for current interruption, causing the opposite effect of reducing the emission efficiency of laser light.

Accordingly, an object of the present invention is to provide a semiconductor laser device with high luminous efficiency that can emit high-output laser light with a low threshold current.

[Means for Solving the Problems] The present invention provides a semiconductor laser element formed by laminating an active layer between n-type cladding layers,
The n-type cladding layer is composed of a plurality of layers having different carrier concentrations, and among the plurality of layers, a first layer formed adjacent to the active layer has a lower carrier concentration than the other layers. It is characterized by being formed.

Further, in the semiconductor laser device of the present invention, the active layer is made of InGa.
The n-type cladding layer is made of either AsP or InGaAs, and the n-type cladding layer is made of InP or InGaAsP.
The n-type cladding layer is InP.
Alternatively, one made of either InGaAsP is preferable. Furthermore, in this semiconductor laser device, the carrier concentration of the first layer of the n-type cladding layer is 1×1018 c.
When it is less than m-3, the effects described below become more pronounced.

In addition, the structure of the semiconductor laser device is such that the active layer is laminated between the n-type cladding layers and the active layer is deposited on the substrate in an inverted mesa shape, and both sides of the active layer are buried with buried layers. It is also possible to have an element structure that does.

[Function] In the semiconductor laser device of the present invention, the n-type cladding layer is formed of a plurality of layers having mutually different carrier concentrations, and among them, the carrier concentration of the first layer in contact with the active layer is set to be low. This serves to reduce the threshold current of the semiconductor laser element and improve the emission efficiency of laser light. Further, a plurality of n-type cladding layers are formed on the side opposite to the active layer, sandwiching the first layer. These plural layers form the entire p-type rad layer to a predetermined thickness. The predetermined thickness is the thickness necessary to contain within the cladding layer the area where the laser light emitted by the active layer leaks out to the cladding layer side due to the light seepage effect, or the thickness required to cover the area between the semiconductor substrate and the cladding layer. The thickness is sufficient to suppress the influence of a thermally degraded layer generated at the interface with the n-type cladding layer epitaxially grown on the cladding layer. Furthermore, the carrier concentration of these multiple layers is set higher than that of the first layer. Therefore, the electrical resistance of these plural layers having a predetermined thickness is reduced, and the electrical resistance of the entire p-type rad layer including the first layer can also be reduced.

Further, the present invention is also provided when the active layer is I nGaAsP or I n
Made of GaAs, with an n-type cladding layer of InP or In
When applied to a ■-v group compound semiconductor laser device made of GaAsP and whose n-type cladding layer is made of either InP or InGaAsP, the above effect becomes more pronounced. Furthermore, in this semiconductor laser element, n
When the carrier concentration of the first layer in contact with the active layer of the type cladding layer is set to 1.times.10.sup.18 cm.sup.-' or less, the effect of lowering the threshold current for emitting laser light is significant.

Furthermore, when the present invention is applied to a buried semiconductor laser element, the current confinement effect exerted by the buried layer can be sufficiently maintained, and leakage current in the buried layer can be suppressed.

[Example] Hereinafter, one embodiment of the present invention will be described in detail using the drawings.

First, as a first embodiment of the present invention, a buried type ■-
A V group compound semiconductor laser device will be explained. FIG. 1 shows a cross-sectional structural diagram of a semiconductor laser device according to the first embodiment. First, a carrier concentration of 2×10” cm was formed on a p-type 1nP substrate 1 using a liquid phase epitaxial method.
-” or more p-type 1nP second cladding layer 11 (layer thickness 2 μm
), and a low concentration p-type InP first cladding layer 12 (layer thickness 0.5μ) with a carrier concentration of 5×10” cm−’ or less
form m). Furthermore, there is an InGaAsP active layer 3 on top of the n-type 1nP active layer 3 with a carrier concentration of lXl0'8cm-'.
A cladding layer 4 and an n-type InGaAsP contact layer 5 for forming a layer having low contact resistance with an electrode are sequentially formed using a liquid phase epitaxial method. Further, a layer with a width of 8 μm is formed on the contact layer 5 by photolithography.
A silicon nitride film of m is formed, and using this as a mask, a portion from the contact layer 5 to the lower part of the p-type InP second cladding layer is mesa-etched using a bromine-methanol etching solution to form a striped active layer having an inverted mesa-shaped cross section. Form. After that, a buried layer consisting of a P-type InP first buried layer 6, an n-type InP second buried layer 7, and a p-type 1nP third buried layer 8 is sequentially refilled in the part removed by this mesa etch process using a liquid phase epitaxial method. Form.

After this epitaxial growth, an insulating film 9 is deposited, an opening is provided at the contact portion with the contact layer 5, and finally electrodes 10 are formed from both sides to complete the manufacturing process.

Here, conditions for forming the p-type box 1 cladding layer 12 and the p-type box 2 cladding layer 11 will be explained.

P-type box 1 cladding layer 12 with low carrier concentration
It is desirable to form the layer as thin as possible in order to reduce the electrical resistance. However, if it is formed too thin, when the temperature is raised to around 600°C in the crystal growth process of the first to third buried layers 6.7.8, the carrier concentration will be set from the p-type box 2 cladding layer 11, which has a high carrier concentration. Zn added for this purpose is diffused, which may increase the carrier concentration in the p-type box 1 cladding layer 12. Therefore, in order to suppress the influence from the high concentration layer, a thickness of at least about 0.3 μm is required. In addition, the layer thickness of the p-type box 2 cladding layer 11, which is set to have a high carrier concentration, is at least about 1.5 to 2 μm, considering that it includes the region where laser light seeps out from the active layer and generates an electric field. It is preferable that moreover,
As shown in FIG. 1, when an element is formed on a p-type InP substrate 1, the p-type box 2 cladding layer 11 is formed on the p-type InP substrate 1.
Since it is formed by epitaxial growth in contact with the upper layer, in order to prevent the effects of defects occurring at the interface with the substrate 1 and defects in the substrate 1 from reaching upper layers such as the p-type box 1 cladding layer 12 and the active layer 3. It is better to form it slightly thicker, about 2 to 3 μm.

In the semiconductor laser device constructed in this manner, the electrical resistance of the portion immediately below the active layer is suppressed to a low level of about 1.8 to 2 Ω. Under these conditions, the buried layer 6.7.8 is kept until the operating current of the semiconductor laser element reaches 250 mA.
The semiconductor laser device of the present invention can operate very efficiently as long as no current leakage occurs and the operating current range is about 50 to 100 mA, which is commonly used. For example, when compared with a conventional semiconductor laser device shown in Figure 3, which differs only in the structure of the p-type cladding layer, the threshold armor current value of the conventional semiconductor laser device is 129 mA on average and 46 mA with a standard deviation. On the other hand, the threshold armor type current value of the semiconductor laser device of this example is 36 mA on average and 13 mA with standard deviation.
The average value was reduced to about one-third compared to the conventional one. In addition, when comparing and estimating the temperature rise of the element when driven with the same operating current, for example, when the operating current is set to the oscillation threshold armor current value Jth + 30 mA, in the conventional semiconductor laser probe, the series resistance region directly below the active layer While the consumed power alone corresponds to a temperature rise of 15° C. or more, the temperature rise of the semiconductor laser device of this embodiment can be suppressed to 1° C. or less. Furthermore, the light emission output of the laser light at this operating current is about 2 mW or less even under the best conditions in the conventional semiconductor laser element due to the reduction in light emission efficiency due to the aforementioned heat generation, whereas the semiconductor laser of this embodiment The element is capable of outputting approximately 3.5 to 4 mW.

Next, a second embodiment of the present invention will be described using FIG. 2.

The second embodiment differs from the first embodiment in that the structure of the p-type cladding layer is a three-layer structure having mutually different carrier concentrations. That is, the carrier concentration is 2X10" cm-
A carrier concentration of 2X10'' cm- is formed between the p-type box 2 cladding layer 13 with a high concentration of 2X10''cm-'' or more and the p-type Box1 cladding layer 15 with a low concentration of 5x10''cm-2 or less.
A p-type 1nP third cladding layer 14 with a low concentration of about 3.3 μm is formed thinly to a layer thickness of about 0.2 to 0.3 μm. In such a structure, the diffusion of the additive Zn that occurs when the temperature is increased during the crystal growth process of the buried layer 6.7.8 is caused by the diffusion from the second cladding layer 13, which is a layer with a high carrier concentration, to the third cladding layer, which has a low concentration.
This is performed on the cladding layer 14. Therefore, the third cladding layer 14 becomes a layer with high carrier concentration and its electrical resistance value decreases. At the same time, the second cladding layer 13 with high concentration
The Zn diffused from the Zn is accumulated in the third cladding layer 14, and the intrusion into the low concentration first cladding layer 15 is suppressed to a minimum. That is, this third cladding layer 14 serves as a stop layer for Zn diffusion. Note that this third cladding layer 14 may be further formed of a plurality of layers having different carrier concentrations.

Further, as a third embodiment, referring to FIG. 2, a p-type In
Further, between the P substrate 1 and the high concentration p-type InP second cladding layer 13, a layer having a higher carrier concentration, for example, 1×10
A third cladding layer of cm-' may be formed. In this case, as described in the second embodiment, it is effective to set the first p-type cladding layer to be slightly thicker, taking into consideration the diffusion effect of Zn. In this embodiment, the distance between the InP substrate and the active layer can be increased. Further, the effect of reducing dislocations can be expected due to the pinning effect of the third cladding layer. Therefore, crystal defects in the InP substrate are not transmitted to the active layer side, improving the crystallinity of the active layer and improving the reliability of the device.

In the above example, the InGaAsP/InP system ■-
Although the explanation has been made using a group V compound semiconductor, the invention is not limited to this, and for example, InGaAs P/Ga
It may be As-based or may be made of other semiconductor materials.

Further, although the above embodiment is explained using an embedded semiconductor laser device, even if the semiconductor laser device has a Brehner type or other structure, the same effect of improving the emission efficiency of laser light as in this embodiment can be obtained. be able to.

Further, the carrier concentration doped into the p-type cladding layer is not limited to the value shown in the above embodiment, but may be appropriately set to an optimal value to obtain the desired effect. Alternatively, the structure is not limited to a three-layer stacked structure, but may be formed with a multilayer stacked structure.

Further, in the above embodiments, a semiconductor laser device constructed using a p-type semiconductor substrate has been described, but the present invention can also be applied to a semiconductor laser device constructed using an n-type semiconductor substrate.

[Effects of the Invention] As described above, in the semiconductor laser device of the present invention, the p-type cladding layer is formed of a plurality of layers having different carrier concentrations,
Since the carrier concentration of each laser beam is set to improve the emission efficiency of the laser beam, the operating current is reduced to about one-third and the power consumption is reduced to about one-thirtieth compared to conventional semiconductor laser elements. It was done. Furthermore, the embedded semiconductor laser device according to the present invention suppresses the occurrence of leakage current and can output high-power laser light. In addition, the semiconductor laser device of the present invention reduces heat generation and can be used at low temperatures and with low power, so it is possible to reduce the burden on the circuit for driving the semiconductor laser device. The heat dissipation structure has been simplified, making it possible to create a compact and highly reliable laser. Furthermore, when this semiconductor laser device is used in the field of optical fiber communication, the improvement in light emission output allows for larger tolerances in the optical system for introducing laser light into the optical fiber, making it easier to manufacture and reducing the manufacturing cost. This makes it possible to reduce the

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional structural diagram of a semiconductor laser device according to a first embodiment of the present invention. FIG. 2 is a cross-sectional structural diagram of a semiconductor laser device according to a second embodiment of the present invention. Further, FIG. 3 is a cross-sectional structural diagram of a conventional semiconductor laser device. FIG. 4 is a correlation diagram showing the relationship between the concentration of Zn doped into the p-type cladding layer and the threshold armor flow density of the semiconductor laser device in a semiconductor laser device having a p-type cladding layer made of InP. be. In the figure, 4 is an n-type 1nP cladding layer, and 6 is a p-type 1nP cladding layer.
P first buried layer, 7 is n-type InP second buried layer, 8
11 is a p-type InP third buried layer, and 11 is a high-concentration p-type InP layer.
The second cladding layer 12 indicates a low concentration p-type 1nP first cladding layer. Note that in each figure, the same reference numerals indicate the same or equivalent parts. Figure 4

Claims (4)

[Claims] (1) In a semiconductor laser device formed by laminating an active layer between a p-type cladding layer and an n-type cladding layer, the p-type cladding layer is composed of a plurality of layers having mutually different carrier concentrations, and the plurality of A semiconductor laser device, wherein a first layer formed adjacent to the active layer among the layers has a lower carrier concentration than other layers of the plurality of layers. (2) The active layer is InGaAsP or InGaA
s, and the p-type cladding layer is In
2. The semiconductor laser device according to claim 1, wherein the n-type cladding layer is made of either P or InGaAsP, and the n-type cladding layer is made of either InP or InGaAsP. (3) The semiconductor laser device according to claim 2, wherein the first layer of the p-type cladding layer has a carrier concentration of 1×10^1^8 cm^-^3 or less. (4) A structure in which the active layer is laminated between the p-type cladding layer and the n-type cladding layer is deposited on a substrate in a mesa shape, and both sides of the active layer are buried with buried layers. 2. The semiconductor laser device according to any one of 2.