JP2839539B2 - Semiconductor light emitting device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial application field) The present invention relates to a semiconductor light emitting device which is a light source for optical communication and optical information processing.

(Prior Art) As a light source for recent optical communication and optical information processing, a semiconductor laser and an LED play an extremely important role. These semiconductor lasers and light emitting devices such as LEDs are required to be able to operate at a low current, have high efficiency and high output, and in particular, to have stable characteristics such as single transverse mode oscillation. There is also a strong demand for high reliability, a simple manufacturing process, and high yield.

In general, a semiconductor laser device is largely divided into two types, one having a gain waveguide mechanism and the other having a refractive index waveguide mechanism, depending on the form of the waveguide. While the refractive index waveguide has a refractive index difference in the direction perpendicular to the active layer, the gain waveguide limits the region where the injection current flows in the direction parallel to the active layer, and the laser gain in this direction is limited. It has a spatial difference. The change in the refractive index in the direction parallel to the active layer is stepwise in the case of the refractive index waveguide, and is inclined in the case of the gain waveguide. A typical example having an index waveguide is a BH (Buried Hetero Stru
cture), PBH (Planar Buried Hetero Structure), DC
−PBH (Double Channel Planar Buried Hetero Structu
e) Typical examples having a structure and a gain waveguide are an electrode stripe laser and a planar stripe laser.

Incidentally, one of the factors that greatly affects the characteristics of the light emitting element is
One is a crystal growth method. Taking into account the influence of the active layer and its side surface on the crystallinity, the crystal growth method can be divided into the following two methods. One is a method of performing buried growth after performing DH growth and forming an energized region including an active layer, and is used for a BH, PBH, DC-PBH structure or the like. The other is a method of forming a groove on the surface after forming a semiconductor multilayer structure, and growing an active layer through a cladding layer on the groove, by a VIPS (V-grooved lnnerstripe on P type Substr).
ate), PBC (P-substrate Buried Crescent) structure and the like. In the former, the side surface of the active layer is exposed to the air and a high-temperature hydrogen atmosphere before the burying growth. In the latter case, since the side surface of the groove is difficult to grow, stress occurs at an end portion where the thickness of the active layer is thinner than the center. For this reason, both have a problem in the crystallinity of the active layer and the side surface thereof, which causes the life of the element, leak current and the like.

Now, it is possible to manufacture the device on a flat buffer layer without having the side surfaces of the active layer exposed to the atmosphere and the high-temperature hydrogen atmosphere by combining the two waveguide mechanisms of the gain waveguide mechanism and the refractive index waveguide mechanism. The semiconductor laser has a long lifetime and can prevent leakage current flowing through the side of the active layer.
A ridge-type semiconductor laser has been proposed.

As shown in FIG. 4, the ridge type laser device has
On a substrate 21, a cladding layer 22, an active layer 23, a cladding layer 24,
After forming a stripe-shaped ridge on the cladding layer 24 above the active layer 23, the contact layer 30 is covered with an insulating film 25 except for the top of the ridge, and an electrode 26 is formed. That is, the waveguide mechanism restricts the region where the current flows to only the vicinity of the active layer 23 below the ridge,
The difference in the refractive index is given by the change in the thickness.

The ridge-type waveguide has both advantages of a refractive index guiding mechanism and a gain guiding mechanism at the same time, and has a stable transverse mode and an active layer portion satisfying a single transverse mode. Has a wide allowable range, and the width is easily designed and controlled. Further, a smooth synchrotron radiation far field pattern can be obtained. Therefore, the problems of narrowing the allowable range of the active layer width and leaving the active layer in a high-temperature hydrogen atmosphere at the interface of the active layer for a long time, which are unavoidable in a normal laser device having a BH structure, are solved.

(Problem to be Solved by the Invention) The ridge-type light emitting device having the above advantages also has the following disadvantages.

In order to keep the contact resistance of the electrodes small, it is necessary to make the width of the contact layer sufficiently large. However, as shown in FIG.
Due to structural restrictions, the width of the active layer is inevitably widened, resulting in a problem that the threshold current is high and the unification of the transverse mode cannot be controlled.

The equivalent refractive index greatly changes depending on the distance between the active layer and the flat portion 27 of the ridge and the top 28 of the ridge, so that precise control of those distances is required. There is a big problem in such points.

It is difficult to apply the insulating film and the electrode material to the step side surface in the ridge structure.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light emitting device which solves the above-mentioned problems, can reduce a threshold current and an electrode contact resistance, has a simple process, and has high reproducibility and high reliability.

[Constitution of the Invention] (Means for Solving the Problems) In the present invention, a portion of the semiconductor layer immediately above the active layer other than the current-carrying region is hollow, and the outside thereof is formed by a semiconductor layer having a current blocking function. Things. Further, the hollow region is formed by etching a semiconductor layer having a current element function.

(Operation) In the present invention, the region adjacent to the current-carrying region of the semiconductor layer immediately above the active layer is hollow, and the outside thereof is formed of a semiconductor layer having a current blocking function, so that the threshold current is reduced. And the width of the active layer can be reduced to be sufficient to obtain a stable single transverse mode. Furthermore, reliability is improved because the side surface of the active layer is not left in a hydrogen atmosphere at a high temperature for a long time. Further, unlike the conventional ridge type structure, there is no need to deposit or deposit on the step side surface, and the electrode process can be easily performed by the planar technology.

(Example) Hereinafter, an example in which the present invention is applied to an InGaAsP-based laser device will be described with reference to the drawings.

FIG. 1 is a sectional view of a light emitting device having a ridge type structure according to an embodiment of the present invention. The light emitting element of this embodiment has n
-N-InP buffer layer 2 and InGaAsP active layer on InP substrate 1
3, after the p-InP cladding layer 4 is laminated, a p-InP cladding layer 5 serving as a current passing region, a hollow region 6 outside the p-InP cladding layer 5, and further outside the p-InGaAsP layer 7, an n-InGaAsP layer 8, n A current blocking layer comprising an InP layer 9 is provided. And p ⁺ -InGaAsP
P-side electrode 11 through contact layer 10 of n-InP
An n-side electrode 12 is formed on the back surface of the substrate 1.

In this light emitting device, a current guide region is limited to the p-InP clad layer 5 to realize a gain waveguide mechanism, and a hollow region 6 is provided to realize a refractive index waveguide mechanism.

Next, a method for manufacturing the light emitting device of the above embodiment will be described with reference to FIG.

First, an n-InP buffer layer 2, a non-doped InGaAsP active layer 3, a p-InP cladding layer 4, a p-InGaAs
P7, n-InGaAsP8, and n-InP layer 9 (about 0.5 μm in thickness) are sequentially epitaxially grown (FIG. 2A).

Next, an etching mask made of, for example, an SiO ₂ film is formed by a photoresist process, and n-InP 9 is
Etch until it reaches nGaAsP8. Furthermore, H ₂ S
O ₄ with -H ₂ O ₂ -H ₂ O etchant, p-InGaAsP7, n-InG
The aAsP 8 is etched to reach the p-InP cladding layer 4 to form a stripe-shaped groove 15 having a predetermined shape. The width of the groove 15 was about 1.5 μm. This portion later becomes a current conduction region, and is invertedly formed in the ridge portion (second portion).
Figure (b).

On the groove 15 and n-InP9 thus formed,
A p-InP cladding layer 5 is grown, and p ⁺ -InG
An asP contact layer 10 is grown to cover the entire surface (FIG. 2 (c)).

Thereafter, an etching mask made of, for example, an SiO ₂ film is formed by a photoresist process, and H ₂ SO ₄ —H ₂ O ₂ —H ₂ O and HC
Etch successively using l etchant until it reaches n-InP9, and strip small holes on both sides of groove 15
Form 13. Furthermore, H ₂ SO ₄ −H ₂ O ₂
In etchant -H ₂ O, 1 part of p-InGaAsP7, n-InGaAsP8, to form a hollow, such as to be adjacent to the ridge portion of the p-InP cladding layer 5.

Next, electrodes 11 and 12 are formed by applying a conductive metal layer to the back surface of the n-InP substrate 1 and the surface of the p ⁺ -InGaAsP contact layer 10. At this time, since the etchant injection port 13 is narrow and the hollow region is wide, the electrode does not adhere to the side surface of the hollow region, and a short circuit of current does not occur (FIG. 2 (d)).

The light-emitting element having the ridge-type structure of the present invention can sufficiently narrow the width of the active layer, which is a light-emitting region, has a low threshold current, and can obtain a stable single transverse mode even at a high output. Yes, good reliability. Further, since the entire electrode structure can be formed by the current blocking layer, the process is easy, and the yield of the device is extremely high.

FIG. 3 shows current-light output characteristics of the semiconductor laser having the ridge type structure of the present embodiment. Curve A is for the present embodiment, and curve B is for a conventional semiconductor laser having a ridge-type structure. Compared with the current-light output characteristics of a conventional semiconductor laser having a ridge-type structure, the device according to the present embodiment has a low threshold current of 15 mA, and the quantum efficiency is greatly improved.

The life of the conventional light-emitting element having the BH structure is about 3 × 10 ⁵ hours as a result of the accelerated deterioration test, whereas the life of the light-emitting element having the ridge type structure of the present invention is 2 × 10 ⁶ hours. It was confirmed that the performance was greatly improved.

The light emitting device of the present invention is not only an InP-based semiconductor,
The present invention can be implemented using other semiconductors. Further, the crystal growth and etching methods used in the manufacturing method,
It can also be carried out by vapor phase growth and dry etching.

In addition, the present invention can be applied not only to a semiconductor laser but also to a current narrowing of a surface emitting LED as a columnar current injection region.

[Effect of the Invention] The light emitting device of the present invention operates with low current and high efficiency. Particularly when applied to a laser element, stable single transverse mode oscillation can be obtained. Further, the reliability is extremely high, the manufacturing process is easy, and a light-emitting element can be manufactured with a high yield.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a light emitting device having a ridge type structure according to one embodiment of the present invention, FIG. 2 is a view showing a manufacturing process of FIG. 1, and FIG. FIG. 4 is a cross-sectional view of a light emitting device having a conventional ridge type structure. 1 n-InP substrate 2 n-InP buffer layer 3 non-doped InGaAsP active layer 4 p-InP cladding layer 5 p-InP cladding layer 6 hollow region 7 p-InGaAsP Current blocking layer 8 n-InGaAsP current blocking layer 9 n-InP current blocking layer 10 p ⁺ -InGaAsP contact layer 11 p-side electrode layer 12 n-side electrode layer 13 hole

Claims (2)

(57) [Claims] An active layer formed on a semiconductor substrate, a first cladding layer formed on the active layer, and a second cladding layer formed on the first cladding layer and having a ridge portion. A semiconductor light emitting device comprising: a cladding layer; a hollow region having a predetermined shape adjacent to a ridge portion of the second cladding layer; and a layer having a current blocking function outside the hollow region. A semiconductor light emitting device characterized by the above-mentioned. 2. A step of sequentially growing a crystal on an active layer and a first cladding layer on a semiconductor substrate; a step of laminating a layer having a current blocking function on the first cladding layer; Forming a groove by partially removing the layer having the first clad layer so as not to remove the first clad layer until reaching the first clad layer; and forming a groove in the groove and the layer having the current blocking function. Forming a second cladding layer thereon, and selectively etching a portion of the layer having a current blocking function adjacent to a side surface of the groove to make the portion hollow. A method for manufacturing a semiconductor light emitting device, characterized by: