JPH0567836A - Algainp semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a stable and reliable AlGaInP visible-region laser having an index-guided structure and a current confinement structure that are formed in a single growth step. CONSTITUTION:A p-type laminated AlGaInP structure is formed on a substrate 100 having a stripe groove 110. The laminated structure includes a p-type clad layer 101, an active layer 102, an n-type clad layer 103, and an n-type contact layer 105. Between the clad layer 103 and the contact layer 105 is formed a p-type intermediate layer 104 having a narrower forbidden band than the clad layer 103. The intermediate layer 104 is thinner above the groove sides and thicker above the groove bottom than the de Broglie wavelength of the carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AlGaInP-based visible light semiconductor laser device.

[0002]

2. Description of the Related Art In recent years, semiconductor laser devices have been widely used in fields such as light sources of information recording / reproducing devices, optical communication and optical measurement control. In particular, it is lattice-matched to a GaAs substrate (Al _y Ga _1-y ) _x In _1-x P ( _x ~ 0.5, 0≤y≤1)
Semiconductor laser devices that use mixed crystals have received attention because they can obtain visible light in the 600 nm band. Such a short-wavelength visible light can be used for a light source of an information recording / reproducing device such as an optical disc or a video disc, and the light spot can be narrowed down. is there.

Hitherto, various structures of AlGaInP semiconductor laser devices have been proposed. For example, FIG. 4 shows an example of a conventional AlGaInP-based semiconductor laser device (see Ishikawa et al., Japan Society for the Promotion of Science, Optoelectronic Interconversion 125th Committee 121st Workshop Material (1987), pages 35-40). The semiconductor laser device shown in this figure is an SBR (Selectively Buri
ed Ridge Waveguide) structure, which is called metalorganic vapor phase epitaxy (M
It is manufactured as follows by three crystal growth steps using the OCVD method).

First, as the first crystal growth step, n-
The n-AlGaInP first cladding layer 401, the GaInP active layer 402, the p-AlGaInP second cladding layer 403, and the p-GaAs cap layer 404 are sequentially grown on the GaAs substrate 400 by using the low pressure MOCVD method. Then, using a suitable etching technique, a mesa stripe reaching the second cladding layer 403 is formed. Subsequently, in the second crystal growth step, the n-GaAs current confinement layer 405 is selectively grown on the portion excluding the upper portion of the mesa. Further, as the third crystal growth step, the p-GaAs contact layer 406 is grown on the entire surface including the upper portion of the mesa. Finally, the p-side electrode 407 is formed on the front surface of the contact layer 406, and the n-side electrode 408 is formed on the rear surface of the substrate 400 to obtain a semiconductor laser device as shown in FIG. In this structure, the current confinement layer 405 limits the current injection region to the active layer 402 by the pnp structure and also functions as a light absorption layer, so that an optical waveguide is formed.

FIG. 5 shows another conventional AlGaInP semiconductor laser device (Itaya et al., IEICE Technical Report OQE89-44 (1989), pp. 49-54). The semiconductor laser device shown in this figure is HBB (Hetero Barrier Blocking).
It is called a structure and is manufactured as follows by two crystal growth steps using the MOCVD method.

First, as the first crystal growth step, n-
An n-AlGaInP first cladding layer 501, a GaInP active layer 502, a p-AlGaInP second cladding layer 503, and a p-GaInP intermediate layer 504 are sequentially grown on the GaAs substrate 500 by using the low pressure MOCVD method. Then, a stripe-shaped mesa reaching the second cladding layer 503 is formed by using an appropriate etching technique. Then, as a second crystal growth step, the p-GaAs contact layer 505 is grown on the entire surface including the mesa region. The intermediate layer 504 is the second clad layer 503 and the contact layer 505.
With a forbidden band width between. Finally, the contact layer 50
A p-side electrode 507 is formed on the front surface of 5, and n is formed on the back surface of the substrate 500.
By forming the side electrode 508, a semiconductor laser device as shown in FIG. 5 is obtained.

The optical waveguide mechanism in this structure is based on the above SB
Similar to the R structure, light absorption by the contact layer 505 is used. On the other hand, as the current confinement mechanism, the second clad layer is used.
The discontinuity of the band structure on the valence band side between 503 and the contact layer 505 is used. That is, at the heterojunction interface between the second cladding layer 503 and the contact layer 505, a large spike appears due to the discontinuity of the band structure on the valence band side. This spike acts as a barrier to holes, causing a large voltage drop at this interface. On the other hand, in the stripe region where the intermediate layer 504 is interposed,
Since the above spikes are divided into the interface between the second cladding layer 503 and the intermediate layer 504 and the interface between the intermediate layer 504 and the contact layer 505, it is possible to reduce an effective barrier against holes. Therefore, it is possible to form a large difference in voltage drop between the stripe region and other portions. That is, when a voltage is applied between both electrodes of the device, a current can be injected only into the stripe region, so that a current constriction mechanism is formed. However, in order to divide the height of the spike into the above two interfaces, the layer thickness of the intermediate layer 504 must be sufficiently thick. This layer thickness depends on the carrier concentration of the intermediate layer 504, but it is essential that the layer thickness is thicker than the de Broglie wavelength of carriers (holes).

[0008]

[Problems to be Solved by the Invention] First, the SBR shown in FIG.
In the structure, three crystal growth steps are indispensable, and further, in the second crystal growth step, it is necessary to use a selective growth technique so that the current confinement layer 405 does not grow on the upper part of the mesa. In order to perform selective growth, it is necessary to control the substrate temperature and adjust the composition ratio of the source gas. Therefore, the crystal growth process becomes complicated, resulting in a decrease in yield and an increase in manufacturing cost.

Further, in the HBB structure shown in FIG. 5, the crystal growth process is performed only twice, but since the re-growth interface is included in the current injection path, the device characteristics are deteriorated due to the deterioration of the crystallinity in this portion, And reliability is reduced.

Further, in any structure, AlGaIn
Since it is necessary to form a stripe-shaped mesa in a laminated structure composed of two or more layers such as a P layer, a GaInP layer, and a GaAs layer, the application of etching technology is essential. In such an etching process, it is difficult to control the residual thickness of the second cladding layer, which is important for stabilizing the transverse mode, and variations occur within the wafer, which lowers the yield.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a structure capable of forming a refractive index guiding structure and a current constriction structure in a single crystal growth step. AlGaInP has stable device characteristics and high reliability without concern about deterioration of crystallinity at the interface.
The present invention is to provide a visible light semiconductor laser device.

[0012]

A semiconductor laser device according to the present invention comprises a first conductivity type first clad made of an AlGaInP mixed crystal on a GaAs substrate of the first conductivity type having recesses or protrusions in stripes. An AlGaInP-based semiconductor laser device having a laminated structure including a layer, an active layer, a second conductivity type second cladding layer, and a second conductivity type GaAs contact layer,
If the first conductivity type is p-type, p-GaAs substrate and p-AlGaInP first
A p-AlGaInP intermediate layer having a bandgap smaller than that of the first clad layer is provided between the clad layer and the p-AlGaInP second clad layer and p-GaAs contact layer when the first conductivity type is n-type. P-AlGaInP with a smaller forbidden band than the second cladding layer between
An intermediate layer is provided, and its layer thickness is thinner than the de Broglie wavelength of the carrier above the step slope of the recess or protrusion,
In other parts, it is thicker than the de Broglie wavelength of the carrier, and thereby the above-mentioned object is achieved.

One or more stripe-shaped grooves having a triangular cross-section may be provided on both sides of the stripe-shaped concave or convex portion of the substrate. When a substrate having such a stripe-shaped groove is used, an insulating film for limiting a current path is unnecessary, so that the manufacturing process is further simplified.

The AlGaInP mixed crystal system used in the present invention is (Al _y Ga _1-y ) _x In _1-x P ( _x ~
0.5, 0 ≦ y ≦ 1) means a mixed crystal, and the mixed crystal ratio x and y is
It is selected appropriately. For example, if x = 0.5 and y = 0, Ga _0.5 I
n _0.5 P represents a mixed crystal.

In general, when a group III-V compound semiconductor is grown by the molecular beam epitaxial growth method (MBE method),
The growth rate is limited by the supply amount of the group III raw material (molecular beam). When the substrate is placed so as to be tilted with respect to the group III molecular beam, the growth area for a given molecular beam intensity increases, so the growth rate becomes smaller than when the substrate is placed perpendicular to the molecular beam. Therefore, when the substrate is provided with a concave portion or a convex portion and has a step, above the flat portion (for example, the groove bottom portion or the terrace flat portion) and the slope portion (for example, the groove side surface portion or the terrace side surface portion). Above, the growth layer thickness is different.

By utilizing such a phenomenon, in the AlGaInP semiconductor laser device of the present invention, the first conductivity type is p
Type, p-AlGaInP having a band gap smaller than that of the first clad layer between the p-GaAs substrate and the p-AlGaInP first clad layer
If the first conductivity type is n-type, a p-AlGaInP intermediate layer having a band gap smaller than that of the second clad layer is formed between the p-AlGaInP second clad layer and the p-GaAs contact layer. The layer can be grown so that the layer thickness is thinner than the de Broglie wavelength of the carrier above the step slope of the concave or convex portion, and thicker than the de Broglie wavelength of the carrier in other portions.

When the p-AlGaInP intermediate layer having the above-mentioned layer thickness is used, a hetero interface (when the first conductivity type is p-type) between the p-GaAs substrate and the p-AlGaInP first cladding layer, Or, the discontinuity of the band structure on the valence band side at the hetero interface (when the first conductivity type is n-type) between the p-AlGaInP second cladding layer and the p-GaAs contact layer is Above
Since the p-AlGaInP intermediate layer is thick enough, the barrier against carriers (holes) is effectively reduced, while the p-AlGaInP intermediate layer is thin above the step slope,
A large barrier for carriers (holes) remains. In other words, p-GaAs substrate (when the first conductivity type is p-type) or p-GaA
When current is injected from the s contact layer (when the first conductivity type is n-type), current can be injected only into the step flat portion,
A current constriction mechanism is formed.

As described above, the first portion having the concave portion or the convex portion
A laminated structure including a first conductivity type first clad layer, an active layer, a second conductivity type second clad layer, and a second conductivity type GaAs contact layer made of an AlGaInP mixed crystal system on a conductivity type GaAs substrate. A current confinement structure can be formed in a single crystal growth step for forming a step, and an optical waveguide structure utilizing the difference in the refractive index of the active layer above the step flat part and the step slope part is provided. You can

[0019]

In the AlGaInP-based semiconductor laser device of the present invention, when the first conductivity type is p-type, the band gap is smaller than that of the first clad layer between the p-GaAs substrate and the p-AlGaInP first clad layer.
When the p-AlGaInP intermediate layer is provided and the first conductivity type is n-type, the p-AlGaInP having a band gap smaller than that of the second cladding layer is formed between the p-AlGaInP second cladding layer and the p-GaAs contact layer. An intermediate layer is provided. Moreover, the layer thickness is thinner than the de Broglie wavelength of the carrier above the step slope of the concave or convex portion, and thicker than the de Broglie wavelength of the carrier in other portions. Therefore, p-Al is above the step slope.
GaInP intermediate layer between p-GaAs substrate and p-AlGaInP first cladding layer (when the first conductivity type is p-type), or p-AlGaI
The relaxation of the valence band barrier due to the band discontinuity between the nP second cladding layer and the p-GaAs contact layer (when the first conductivity type is n type) does not occur, and current injection is blocked by the heterobarrier effect. .. As a result, the current flows only in the flat part of the step,
A current constriction structure is realized. Also, the layer thickness of the active layer is thick above the flat portion of the step and thin above the slope portion of the step, similarly to the intermediate layer. Therefore, the thick active layer portion above the flat portion of the step functions as an optical waveguide.

[0020]

EXAMPLES Examples of the present invention will be described below.

(Embodiment 1) FIG. 1 shows a schematic sectional structure of an AlGaInP based semiconductor laser device of the present embodiment. This semiconductor laser device was manufactured as follows.

First, the Si-doped n-GaAs substrate 100 (impurity concentration 2 × 10 ¹⁸ cm ⁻³ ) is formed by using the photolithography method and the wet etching technique, and the stripe-shaped groove 110 to be a concave portion is formed.
(Width 4 μm, depth 1 μm). Then, this substrate 10
On top of 0, Si-doped n- using the MBE method (substrate temperature 510 ℃)
(Al _0.7 Ga _0.3 ) _0.5 In _0.5 P First cladding layer 101 (impurity concentration
1x10 ¹⁸ cm ^-3 ), non-doped Ga _0.5 In _0.5 P active layer 102, Be-doped p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 103 (impurity concentration 1x10 ¹⁸ cm ^-3 ), Be-doped p- Ga _0.5 In _0.5 P Intermediate layer 104
(Impurity concentration 2 × 10 ¹⁸ cm ⁻³ ) and Be-doped p-GaAs contact layer 105 (impurity concentration 2 × 10 ¹⁸ cm ⁻³ ) were grown in sequence.

By this crystal growth process, the layer thickness of the intermediate layer 104 is 10 nm above the groove side surface portion and 2 above the groove bottom portion.
It became 2 nm. The layer thickness of the active layer 102 was 32 nm above the side surface of the groove and 70 nm above the bottom of the groove. Thus, above the bottom of the groove, the layer thickness of the intermediate layer 104 is thicker than the de Broglie wavelength of carriers, so that it does not function as a barrier to carrier injection, whereas above the side surface of the groove, the intermediate layer 104 is not formed. Since it is thinner than the de Broglie wavelength of carriers, it becomes a barrier to carrier injection and functions as a current confinement structure. On the other hand, due to the difference in layer thickness of the active layer 102 above the groove side surface portion and above the groove bottom portion, a refractive index waveguide structure is formed.

After that, a Si ₃ N ₄ film 106, which serves as an insulating film for limiting the current path, was formed on the contact layer 105 except above the stripe-shaped groove 110 by the plasma CVD method. Finally, the p-side electrode is formed on the surface of the contact layer 105 located above the stripe-shaped groove 110 and the surface of the Si ₃ N ₄ film 106.
By forming 107 and forming an n-side electrode 108 on the back surface of the substrate 100, a semiconductor laser device as shown in FIG. 1 was obtained.

The thus-obtained semiconductor laser device of this example continuously oscillated at a threshold current of 47 mA and an oscillation wavelength of 663 nm, and showed good device characteristics.

(Embodiment 2) FIG. 2 shows a schematic sectional structure of an AlGaInP based semiconductor laser device of this embodiment. This semiconductor laser device was manufactured as follows.

First, a stripe terrace serving as a convex portion is formed on a Si-doped n-GaAs substrate 200 (impurity concentration 2 × 10 ¹⁸ cm ⁻³ ) by using a photolithography method and a wet etching technique.
210 (width 3 μm, height 1.5 μm) was provided in the forward mesa direction. Then, on this substrate 200, Si-doped n- (A
l _0.8 Ga _0.2 ) _0.5 In _0.5 P First cladding layer 201 (impurity concentration 1x
10 ¹⁸ cm ^-3 ), undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P Active layer 2
02, Be-doped p- (Al _0.8 Ga _0.2 ) _0.5 In _0.5 P Second cladding layer 2
03 (impurity concentration 8x10 ¹⁷ cm ^-3 ), Be-doped p-Ga _0.5 In _0.5 P
Intermediate layer 204 (impurity concentration 5x10 ¹⁸ cm ^-3 ), and Be-doped p
-A GaAs contact layer 205 (impurity concentration 2x10 ¹⁸ cm ^-3 ) was grown successively.

By this crystal growth process, the layer thickness of the intermediate layer 204 was 10 nm above the terrace side surface portion and 22 nm above the terrace flat portion. The layer thickness of the active layer 202 is
It was 32 nm above the terrace side surface and 70 nm above the terrace flat portion. Thus, above the flat terrace portion, the layer thickness of the intermediate layer 204 is thicker than the de Broglie wavelength of carriers, so that it does not function as a barrier to carrier injection. Since the layer thickness of 204 is thinner than the de Broglie wavelength of carriers, it becomes a barrier to carrier injection and functions as a current confinement structure. On the other hand, due to the layer thickness difference of the active layer 202 above the terrace side surface portion and above the terrace flat portion, a refractive index waveguide structure is formed.

After that, a Si ₃ N ₄ film 206 serving as an insulating film for limiting a current path was formed on the contact layer 205 except above the striped terraces 210 by the plasma CVD method. Finally, the surface of the contact layer 205 located above the striped terraces 210 and the surface of the Si ₃ N ₄ film 206 have p
By forming the side electrode 207 and forming the n-side electrode 208 on the back surface of the substrate 200, a semiconductor laser device as shown in FIG. 2 was obtained.

The semiconductor laser device of this example obtained in this way continuously oscillated at a threshold current of 56 mA and an oscillation wavelength of 647 nm, and showed good device characteristics.

(Embodiment 3) FIG. 3 shows a schematic sectional structure of an AlGaInP based semiconductor laser device of this embodiment. This semiconductor laser device has a structure obtained by one crystal growth step without using an insulating film that limits a current path, and was manufactured as follows.

First, a stripe-shaped groove 310 to be a concave portion is formed on a Si-doped n-GaAs substrate 300 (impurity concentration 2 × 10 ¹⁸ cm ⁻³ ) by using a photolithography method and a wet etching technique.
(Width 4 μm, depth 1.5 μm), and a grating region 311 having stripe-shaped grooves (depth 1.5 μm) having a triangular cross-section on both sides thereof. Then, on this substrate 300,
Si-doped n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P using MBE method
Cladding layer 301 (impurity concentration 1x10 ¹⁸ cm ^-3 ), Be-doped pG
a _0.5 In _0.5 P active layer 302 (dopant concentration 2x10 ¹⁷ cm ^-3), Be-doped _{p- (Al 0.7 Ga 0. 3)} 0.5 In 0.5 P second cladding layer 303 (dopant concentration 1x10 ¹⁸ cm ^-3), Be Doped p-Ga _0.5 In _0.5 P Intermediate layer 304
(Impurity concentration 5 × 10 ¹⁸ cm ⁻³ ) and Be-doped p-GaAs contact layer 305 (impurity concentration 2 × 10 ¹⁸ cm ⁻³ ) were sequentially grown.

By this crystal growth process, the layer thickness of the intermediate layer 304 is 10 nm above the groove side surface and 2 above the groove bottom.
It became 2 nm. The layer thickness of the active layer 302 was 32 nm above the side surface of the groove and 70 nm above the bottom of the groove. Thus, above the bottom of the groove, since the layer thickness of the intermediate layer 304 is thicker than the de Broglie wavelength of carriers, it does not function as a barrier to carrier injection, whereas above the side surface of the groove, the intermediate layer 304 is not formed. Since it is thinner than the de Broglie wavelength of carriers, it becomes a barrier to carrier injection and functions as a current confinement structure. On the other hand, due to the difference in layer thickness of the active layer 302 above the groove side surface portion and above the groove bottom portion, a refractive index waveguide structure is formed. Moreover, the grating area 51
In 1, the stripe-shaped groove has a triangular cross-sectional shape, so that the layer thickness of the intermediate layer 304 is thinner than the de Broglie wavelength of the carrier as in the upper side of the groove side surface, and serves as a barrier to carrier injection. Therefore, it is not necessary to use an insulating film for limiting the current path. Finally, a p-side electrode 307 is formed on the surface of the contact layer 305, and an n-side electrode is formed on the back surface of the substrate 300.
By forming 308, a semiconductor laser device as shown in FIG. 3 was obtained.

The thus obtained semiconductor laser device of this example has a threshold current of 38 mA and an oscillation wavelength of 666 nm.
Continuous oscillating at, showing good device characteristics.

In each of the above embodiments, a semiconductor laser device having a double hetero structure has been described, but the structure near the active layer may be a structure including a quantum well structure or an optical guide layer. Further, by providing the buffer layer between the substrate and the laminated structure, the crystallinity of the semiconductor layer forming the laminated structure can be improved.

[0036]

According to the present invention, an AlGaInP-based visible light semiconductor laser device having stable device characteristics and improved reliability can be obtained. Since such a semiconductor laser device can narrow the light spot and enables high-density recording, it is very useful as a light source of an information recording / reproducing device such as an optical disc and a video disc. In addition, in the present invention, AlGaInP is formed by one crystal growth step.
Since it is possible to form the refractive index guiding structure and the current constriction structure of the visible light-based semiconductor laser device, it is possible to improve the productivity and the yield, and to supply the semiconductor laser device having excellent performance at a low price.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic structure of an AlGaInP-based semiconductor laser device which is an embodiment of the present invention.

FIG. 2 is a sectional view showing a schematic structure of an AlGaInP-based semiconductor laser device which is another embodiment of the present invention.

FIG. 3 is a sectional view showing a schematic structure of an AlGaInP-based semiconductor laser device which is still another embodiment of the present invention.

FIG. 4 is a sectional view showing a schematic structure of a conventional AlGaInP-based semiconductor laser device.

FIG. 5 is a sectional view showing a schematic structure of another conventional AlGaInP based semiconductor laser device.

[Explanation of symbols]

 100,200,300,400,500 Substrate 101,201,301,401,501 First clad layer 102,202,302,402,502 Active layer 103,203,303,403,503 Second clad layer 104,204 , 304, 504 Intermediate layer 105, 205, 305, 406, 505 Contact layer 404 Cap layer 405 Current constriction layer

Claims (1)

[Claims] 1. A first conductivity type first clad layer, an active layer, and a second conductivity type second layer made of an AlGaInP mixed crystal system on a GaAs substrate of the first conductivity type having stripe-shaped recesses or protrusions.
An AlGaInP-based semiconductor laser device having a laminated structure including a clad layer and a GaAs contact layer of the second conductivity type, wherein a p-GaAs substrate and a p-AlG are provided when the first conductivity type is the p-type.
A p-AlGaInP intermediate layer having a band gap smaller than that of the first clad layer is provided between the aInP first clad layer and the first conductivity type is n.
In the case of the p-type, a p-AlGaInP second clad layer and a p-GaAs contact layer having a smaller forbidden band width than the second clad layer are formed.
An AlGaInP-based semiconductor laser in which an AlGaInP intermediate layer is provided, and the layer thickness is thinner than the de Broglie wavelength of the carrier above the step slope of the concave or convex portion and thicker than the de Broglie wavelength of the carrier in other portions. element.