JPS59119884A - Semiconductor light-emitting device - Google Patents

Abstract

PURPOSE:To prevent the generation of a crystal defect in an active layer by dividing an upper clad layer into two, extremely thinning the thickness of a lower layer being directly in contact with the active layer and removing a region, which does not correspond to a stripe region of an upper layer. CONSTITUTION:A lower clad layer 12, the active layer 13, the upper clad layer first layer 14' in approximately 0.3mum thickness and a layer 14'' as the upper clad layer second layer in approximately 2mum thickness are formed on the surface of a substrate 11, an upper confining layer 14 is left, and the layer 14'' is removed. A current limiting layer 15 is buried and formed at a growth temperature of approximately 550 deg.C. The upper clad first layer 14' functions as a protective layer during the growth period to directly protect the active layer 13 from a thermal atmosphere, and a thermal deterioration is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a semiconductor light emitting device. In particular, the present invention relates to improvements in buried semiconductor lasers which have the advantage of having a large lateral carrier confinement effect and a small threshold current.

(2) Background of the Technology In a semiconductor laser, it is desirable that the threshold current be small and the lateral mode be unified and stable. For this purpose, it is absolutely necessary that the active layer has no crystal defects, and in addition, it is necessary to provide an extremely thin active layer in the vertical direction (direction along the current path) with a lower refractive index and a different dielectric type. The structure is sandwiched between two cladding layers to limit the recombination region and confine the light, while in the lateral direction the current path is limited to a limited region along the optical axis to limit the recombination region. A buried heterostructure semiconductor laser is known as a structure that satisfies this requirement.

(3) Prior Art and Problems An example of the conceptual layer structure of a buried double heterostructure semiconductor laser in the prior art is shown in FIG. The figure is a side view viewed from the end face in the optical axis direction, that is, from the direction in which light is emitted. In the figure, 1 is a semiconductor substrate, 1 and 2 are buffer layers and lower cladding layers, 3 is an active layer, 4 is an upper cladding layer, and 5 is a buried layer.

In a semiconductor laser with such a buried structure, both the recombination region and the light are limited in the vertical direction, and the recombination region is effectively limited in the horizontal direction, resulting in (a) reduction of threshold current. (b) It has a great effect on stabilizing the lateral mode, but because it is a buried type, the end face of the active layer is exposed to a hot atmosphere during the etching process and the subsequent (crystal growth process). It has the drawback that it is prone to deterioration and crystal defects, which causes leakage current and increases the threshold current.

(4) Purpose of the Invention The purpose of the present invention is to eliminate this drawback, and in a semiconductor light emitting device having a buried heterostructure, leakage current etc. can flow without generating crystal defects in the active layer. The object of the present invention is to provide a stable six-semiconductor light-emitting device with a low threshold current, a single lateral mode, and a stable semiconductor light-emitting device.

(5) Structure of the Invention The above object is to provide a semiconductor light emitting device which has an upper cladding layer and a lower cladding layer with an active layer in between, and in which a current path is restricted to a stripe region formed along the optical axis. , the upper cladding layer comprises a lower layer consisting of a thin semiconductor layer extending over the active layer and having a larger band gap than the active layer; and a lower layer comprising a thin semiconductor layer extending over the lower layer and having a larger band gap than the active layer. The lower layer consists of an upper layer made of a semiconductor that can be selectively etched, and this is achieved by having a reverse pn junction between the lower layer and a region of the upper layer that does not correspond to the stripe region.

In order to prevent crystal defects from occurring in the active layer of a semiconductor laser with a buried structure, it is sufficient to prevent the active layer from coming into contact with a thermal atmosphere during the manufacturing process. As a means for this purpose, a method of forming the buried layer so that it does not reach the active layer is conceivable, but in this structure, the buried layer loses its original meaning.

Therefore, in the present invention, the upper cladding layer is divided into two, and the lower layer that directly contacts the active layer is the first upper cladding layer.
The upper layer that is not in direct contact with the upper cladding layer is the second layer, and the upper cladding layer is the second layer.
The thickness of the layer is kept very thin (and then the areas that do not correspond to the striped areas of the second layer are removed and the first layer is applied to this area).
A current limiting layer is formed such that a reverse p-n junction is formed in contact with the top surface of the layer to confine the current path to the striped region and is very sandwiched laterally, e.g.
Recombination is made to occur only in a region of about [um], and by limiting the lateral direction of this light emitting region, unification and stabilization of the mode in the lateral direction is realized.

In this structure, the first layer of the upper cladding layer is sufficiently thin, and in regions that do not correspond to stripes, the current limiting layer extends to a region very close to the top surface of the active layer, where a pn junction exists in the opposite direction. , the ability to limit the current to the stripe region is as good as that of the prior art. In addition, this first upper cladding layer functions as a protective layer that protects the active layer from the thermal atmosphere during the confinement layer growth process, and effectively prevents thermal deterioration of the active layer, resulting in leakage current, etc. This has a very large effect in that the possibility of this occurring is much reduced compared to the conventional technology.

In the above structure, a wet etching method is suitable for the step of removing the first layer of the upper cladding layer, and in order to control this etching and reliably remove only the first layer, the first layer is removed from the second layer. It is desirable to form a dissimilar semiconductor that has etch selectivity to the etchant used to etch the layer, ie, is not etched. However, in order to fully exhibit the cladding effect, which is the original function of the first layer, it is necessary to use a semiconductor with a larger bandgap value and a lower refractive index than the active layer, similar to the second layer. is necessary.

(6) Embodiments of the Invention A semiconductor light emitting device according to an embodiment of the present invention will be described below with reference to the drawings, and the structure and unique effects of the present invention will be clarified.

As an example, indium gallium arsenide phosphide (InGaA
The manufacturing process of a buried double heterostructure striped semiconductor laser based on sP)/indium gallium phosphide (InGaP) will be described.

Refer to Figure 2. It is made of n-type gallium arsenide (nQaAs) containing about 1018 CC, n3 of n-type impurities and has a thickness of 300 mm.
78 μ+n) on the (100) plane of the substrate 11.
Using a liquid phase epitaxial growth method (hereinafter referred to as 1, LPE method) at a growth temperature of about 0°C, (a) indium gallium phosphide (nI n (b) a buffer layer/lower cladding layer 12 made of GaP) and having a thickness of about 2 [μ+n]; (b) made of undoped indium gallium arsenide phosphide (InGaAsP) and having a thickness of 0.1 to 0.2
Active layer 13 of about [μ+n], (c) n-type impurity of 2
p-type indium gallium arsenide phosphide (p In Ga As P
) and has a thickness of about 0.3 [μ+n], and (-)n type impurity is added 2×1.
It is made of p-type indium gallium phosphide (panGap) containing about 018 [CIn-3] and has a thickness of 2 (,
layer 14, which becomes the second layer of the upper cladding layer, having a thickness of about a+n]
In this laminate, P of the active layer is sequentially formed.
Since the L peak wavelength is 7.200 (X), the mixed crystal ratio of the semiconductors forming the lower cladding layer 12 and the upper cladding layer 2 is such that the PL peak wavelength is 6.500 (A), and the upper cladding layer 1 The mixed crystal ratio of the layer is such that the PL peak wavelength is 6.
The wavelength is determined to be slightly longer than 500 (A).

Refer to FIG. 3. An etching mask (not shown) made of silicon dioxide (Si02) and having a width of about 5 [μ+n] is formed using a known method in the region corresponding to the stripe on the upper surface of the above-mentioned laminate.

), the layer 14, which will become the second upper confinement layer, is mesa-etched using a wet etching method using hydrochloric acid (H(,'l) as an etchant), and the optical axis is formed in the entire region corresponding to the stripe. Leaving the upper confinement layer 14 extending along the
'' and then remove the etching mask using hydrofluoric acid (HF).

In this step, the layer 14'', which is a ternary mixed crystal, is made of hydrochloric acid (H
layer 14 which is etched by el) but is a quaternary mixed crystal;
' is not etched, allowing very precise control of the etching process.

Referring to FIG. 4, a current limiting layer 15 made of n-type gallium arsenide (nQaAs) containing about 8×10''(CIn'') of n-type impurities is buried and formed using the LPE method again at a growth temperature of about 55,000. The thickness of the current limiting layer 15 is 1.5 [μ+n] in the region not corresponding to the stripe.
In the region corresponding to the stripe, that is, on the upper part of the second upper confinement layer, it hardly grows, so it is about 0.2 [μ+n]. Also, in this step, during the growth period of the current limiting layer 15, the upper cladding layer 1
fA14' functions as a protective layer, so that the active layer 13 is safely protected without being directly exposed to a thermal atmosphere, and disadvantages such as thermal deterioration are effectively prevented.

In addition, in the region not corresponding to the stripe, the interface between the current limiting layer 15 and the first upper cladding layer 14' is extremely close to each other, and since a pn junction in the opposite direction exists here, the active layer 13 is Despite the spread, the current is effective only in one stripe region, so the lateral width of the recombination region is 2 to 3 [, cg+n
), and the transverse mode is unified and stabilized.

Refer to FIG. 5 After the above steps are completed, zinc (Zn) is applied to the area corresponding to the stripes of the current limiting layer 15 using a known method.
The current limiting layer 1 is diffused to a concentration of approximately
5 is converted into a p-type conductive region (region surrounded by a broken line) 16, and a positive electrode 17 and a negative electrode 18 are formed on the upper surface and the lower surface of the substrate 11, respectively, to complete a buried structure semiconductor laser.

In this example, indium gallium arsenide phosphide (In
Although we have described a semiconductor laser having an active layer made of gallium aluminum arsenide (GaAsP), the active layer is not limited to a semiconductor layer, and similar effects can be obtained with gallium aluminum arsenide (GaAIAs), gallium arsenide (GaAs), etc. confirmed.

Furthermore, the growth method for layers 12, 13, 14', 14'' is as follows:
In addition to the LPE method described in this example, the vapor phase epitaxial growth method (VPE method), the molecular beam eviction method (MBE method)
There is no problem in using a metal-organic chemical vapor deposition method (M (JCVD method), etc. Also, the direction or shape of the mesa etch of the layer 14'' is not limited to this example. Needless to say.

(7) As described in detail, according to the present invention, in a semiconductor light emitting device having a buried heterostructure, crystal defects are prevented from occurring in the active layer (and leakage current and the like are prevented from flowing). As a result, a stable semiconductor light emitting device with a low threshold current and a single lateral mode can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the conceptual layer structure of a semiconductor laser having a buried double heterostructure in the prior art, and FIGS. FIG. 3 is a side view of the substrate after completion of each main step in the manufacturing process of the semiconductor laser of the structure. Note that FIGS. 1 to 5 are all side views seen from the end face in the optical axis direction, that is, from the direction in which light is emitted. 1.11...Substrate (nGaAs), 2.12
・・・・・・Nok・sofa layer and lower layer (nI
nGaP), 3.13... Active layer (undoped InGaAsP'), 4... Upper cladding layer (pInGaP), 14... Upper cladding layer 2nd layer (pInGap) , 14'--first upper cladding layer (pInGaAsP), 15... current limiting layer, (nGaAs), 16... p-type conductive region, 17... positive Electrode, 18... Negative electrode.

Claims (2)

[Claims] (1) In a semiconductor optical device having an upper cladding layer and a lower cladding layer with an active layer in between, and in which a current path is restricted to a stripe region formed along the optical axis, the upper cladding layer is a lower layer consisting of a thin semiconductor layer extending over the active layer and having a larger bandgap than the active layer; and a lower layer comprising a thin semiconductor layer extending over the lower layer and having a larger bandgap than the active layer; an upper layer made of a semiconductor that can be used as an active layer, and a semiconductor layer having a bandgap smaller than that of the active layer extends over the lower layer in a region of the upper layer that does not correspond to the stripe region. Device. (2) A reverse pn junction is provided between the region of the upper layer of the upper cladding layer that does not correspond to the stripe region and the lower layer of the cladding layer.
The semiconductor light emitting device according to item 1).