JP2005260277A - Semiconductor light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve element characteristics and reduce cost by optimizing a structure of a clad layer and dopant. <P>SOLUTION: A semiconductor light-emitting device has a first clad layer, comprising a first conductive type of AlGaAsP or AlGaAs; a second clad layer which is located next to the first clad layer comprising a first conductive type of AlGaInP or AlInP and has a thickness of up to 0.5 μm; an active layer which is located next to the second clad layer comprising a first or a second conductive type of AlGaInP or GaInP and having a thickness of smaller than 0.1 μm; a third clad layer which is located next to the active layer comprising a second conductivity-type AlGaInP or AlInP and a thickness of up to 0.5 μm; a fourth clad layer which is located next to the third clad layer comprising a second conductivity-type AlGaAsP or AlGaAs; and a current blocking layer for narrowing the current to the active layer, wherein the dopant of a layer comprising AlGaAs (P) among the P-type clad layers is C, and the dopant of a layer comprising AlGaIn (P) is Be or Mg. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an AlGaInP and / or AlGaIn semiconductor material, and a semiconductor light emitting device using the AlGaAsP and / or AlGaAs semiconductor material.

An example of a conventional semiconductor laser diode (LD) using an AlGaInP-based semiconductor material is a structure as schematically shown in FIG.
That is, in FIG. 2, 201 is an n-type GaAs substrate, and 202 is a clad layer made of n-type AlGaInP formed on the substrate 201. Reference numeral 203 denotes an active layer made of AlGaInP. Reference numeral 204 denotes a clad layer made of p-type AlGaInP. That is, the mixed crystal ratio is set so that the energy gap of the AlGaInP active layer 203 is smaller than the energy gap of the AlGaInP cladding layers 202 and 204, and a double heterostructure is formed. Reference numeral 206 denotes a contact layer.

  Reference numeral 205 denotes a current blocking layer made of GaAs. The current blocking layer 205 is provided for the purpose of so-called current confinement in order to obtain a current density necessary for laser oscillation. 205 is formed by selectively etching the layer 204 to form a ridge and then selectively growing it using an amorphous film such as SiNx.

  AlGaInP or AlInP (hereinafter collectively referred to as AlGaInP-based compound) has drawbacks such as higher resistivity and higher thermal resistance than AlGaAsP or AlGaAs (hereinafter also referred to as AlGaAsP-based compound). This raises problems such as increasing the operating voltage of the element and increasing heat generation, which is a major issue in improving the characteristics and reliability of the element. In particular, the above problem becomes more serious when current confinement is performed or the light emission density is increased as in a semiconductor laser.

  In addition, zinc (Zn) is generally used as a dopant for the cladding layer of the p-type AlGaInP compound. However, since the activation rate of Zn is low, it is necessary to perform high concentration doping in order to reduce the resistivity. There is. However, in this case, Zn that has not been activated may diffuse at a high rate in the AlGaInP-based compound crystal during growth, and the pn junction position may be greatly shifted to the n side from the light emitting layer. In this case, an abnormality is caused in the current-voltage characteristic, or the threshold current of the laser is increased. Such Zn diffusion from the p-type AlGaInP-based compound layer becomes conspicuous as the layer thickness of the p-type AlGaInP-based compound layer increases. In addition, when the thickness of the light emitting layer is relatively thin like a laser, an abnormality in current-voltage characteristics due to Zn diffusion tends to occur. Si having a small diffusion coefficient is effective for the n-type AlGaInP-based compound layer.

  In general, when a double heterostructure is used, in order to sufficiently confine carriers and light in the active layer, a film thickness of about 1 to 2 μm is required for the cladding layer. When an AlGaInP-based compound is grown by metal organic vapor phase epitaxy, it is necessary to increase the supply molar ratio (V / III) between the organic metal serving as the group III material and PH3 serving as the group V material. For this reason, there are problems that the growth rate cannot be increased so much that the growth raw material cost is considerably higher than that of an AlGaAs compound or the like. In particular, in large-scale equipment for mass production capable of simultaneous growth of a large number of sheets, it becomes increasingly serious in terms of detoxification.

  Therefore, the present inventors have reduced the thickness of the Zn-doped p-type AlGaInP-based compound clad layer in a semiconductor light emitting device having an active layer made of AlGaInP or GaInP to such an extent that the element characteristics of the light emitting element are not deteriorated. The idea is to reduce Zn diffusion into the n-side cladding. However, if the thickness of the AlGaInP-based compound cladding layer above and below the active layer is reduced, the confinement of carriers and light becomes insufficient and the device characteristics deteriorate. Therefore, it has been found that the shortage can be substituted with an AlGaAsP compound having substantially the same band gap and refractive index. In addition, since n-type AlGaAsP-based compounds are less likely to cause Zn diffusion than AlGaInP-based compounds having the same carrier concentration, the n-type AlGaInP-based compound cladding has a thinner layer thickness that shifts the pn junction position due to Zn diffusion. It is effective in preventing, thinning the AlGaInP-based compound cladding layer is also effective in reducing operating voltage and thermal resistance, and from the viewpoint of mass production, growth time, raw material cost, detoxification, etc. In view of the above, it has been found that it is more effective to make the AlGaInP-based compound layer as thin as possible and to use more AlGaAsP-based compounds. Further, when an AlGaInP-based compound cladding layer is provided with an active layer interposed therebetween and an AlGaAsP-based compound cladding layer is provided outside the active layer, beryllium or magnesium is used as a dopant for the cladding layer made of a P-type AlGaInP-based compound. The present inventors have found that it is preferable to use carbon as a dopant for a clad layer made of a P-type AlGaAsP-based compound, and reached the present invention. That is, the gist of the present invention is that a first cladding layer made of AlGaAsP or AlGaAs of the first conductivity type, and a thickness of 0.5 μm or less made of AlGaInP or AlInP of the first conductivity type adjacent to the first cladding layer. A second cladding layer, an active layer made of AlGaInP or GaInP of the first or second conductivity type and having a thickness of less than 0.1 μm, adjacent to the second cladding layer, and adjacent to the active layer, A third clad layer made of two-conductivity type AlGaInP or AlInP and having a thickness of 0.5 μm or less; a fourth clad layer made of second-conductivity type AlGaAsP or AlGaAs adjacent to the third clad layer; A current blocking layer for confining a current to the layer, and a cladding layer made of P-type AlGaAsP or AlGaAs is carbon as a doping impurity And it contains, consists in the semiconductor light-emitting device, wherein a clad layer formed of P-type AlGaInP or AlGaIn is contained beryllium and / or magnesium as a doping impurity.

Hereinafter, the present invention will be described in more detail.
The semiconductor light emitting device of the present invention includes a first cladding layer made of a first conductivity type AlGaAsP compound, and a thickness of 0.5 μm or less made of a first conductivity type AlGaInP compound adjacent to the first cladding layer. Adjacent to the second cladding layer, an active layer made of AlGaInP or GaInP of the first or second conductivity type and having a thickness of less than 0.1 μm, adjacent to the active layer, A third cladding layer made of a second conductivity type AlGaInP-based compound having a thickness of 0.5 μm or less and a fourth cladding layer made of a second conductivity type AlGaAsP-based compound are provided adjacent to the third cladding layer. And a current blocking layer for confining a current to the active layer.
Note that the content ratio of the constituent elements in each layer of the semiconductor light emitting device of the present invention may be determined in consideration of lattice matching between the substrate and each layer.
A description will be given below with reference to the element of FIG. 1, which is an example of an embodiment in which the light emitting device of the present invention is realized as a laser diode.

FIG. 1 is an example of a semiconductor device of the present invention, and is an explanatory view of the device manufactured in the example. When manufacturing the apparatus of the present invention, it is usually constructed on a single crystal substrate. The substrate 101 is not particularly limited, but a GaAs substrate is usually used. It is preferable to use a buffer layer 102 of about 2 μm or less on the substrate in order not to bring defects of the substrate into the epitaxial growth layer. Then, the first, second clad layer, active layer, third and fourth clad layers of the present invention are laminated in this order on the buffer layer, and the current to the active layer is confined to reduce the current density in the active layer. A current blocking layer is provided for improvement. The first cladding layer 103 is an AlGaAsP-based compound of the first conductivity type, and the thickness is usually preferably 0.3 to 3 μm. A more preferable thickness of the first cladding layer is 0.5 μm or more as a lower limit and 1.5 μm as an upper limit. The carrier concentration is preferably in the range of 1 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ , particularly preferably 2 × 10 ¹⁷ cm ⁻³ as the lower limit and 2 × 10 ¹⁸ cm ⁻³ as the upper limit. Range.

A second cladding layer 104 made of an AlGaInP-based compound of the first conductivity type and having a thickness of 0.5 μm or less is laminated on the first cladding layer. The more preferable lower limit of the thickness of this layer is 0.01 μm or more, and the upper limit is 0.3 μm. The carrier concentration is preferably in the range of 1 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ , particularly preferably 2 × 10 ¹⁷ cm ⁻³ as the lower limit and 2 × 10 ¹⁸ cm ⁻³ as the upper limit. Range.

  An active layer 105 made of AlGaInP or GaInP of the first or second conductivity type and having a thickness of less than 0.1 μm is laminated on the second cladding layer. As the active layer, an active layer having a quantum well structure may be used. The carrier concentration of the active layer is not particularly limited. Rather, it is not doped in particular and is in an undoped state (in this case, it is slightly in the first or second conductivity type). More preferable from the viewpoint of stabilization.

On the active layer, a third cladding layer 106 made of an AlGaInP compound of the second conductivity type and having a thickness of 0.5 μm or less is laminated. The carrier concentration is preferably in the range of 1 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ , particularly preferably 2 × 10 ¹⁷ cm ⁻³ as the lower limit and 2 × 10 ¹⁸ cm ⁻³ as the upper limit. Range.

Furthermore, a fourth cladding layer 107 made of an AlGaAsP-based compound of the second conductivity type is laminated on the third cladding layer. The thickness is preferably in the range of 0.3 to 3 μm, and the more preferable range is 0.5 μm as the lower limit and 1.5 μm as the upper limit. The carrier concentration is preferably in the range of 1 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ , particularly preferably in the range of 2 × 10 ¹⁷ cm ⁻³ as the lower limit and 2 × 10 ¹⁸ cm ⁻³ as the upper limit. It is.

  The current blocking layer 108 used in the present invention is a layer provided for reasons such as increasing the current density in the active layer without changing the current flowing through the element. The position of the current blocking layer is not particularly limited, but it is easy to obtain a flat active layer or a high-quality epitaxial growth layer. Therefore, it is on the opposite side of the substrate from the active layer that vapor deposition such as MOCVD is performed. Preferred in some cases.

  In addition, it is best to make it exist on the side surface of the active layer from the viewpoint of current confinement. However, since the active layer is easily damaged, a structure in which the current blocking layer extends just before the third cladding layer or a part of the third cladding layer is preferable. The conductivity type of the current blocking layer is preferably a high resistance undoped layer or a conductivity type opposite to that of the adjacent cladding layer. Further, if the thickness is too thin, current blocking may be hindered. Therefore, the thickness is preferably 0.1 μm or more, more preferably 0.5 μm or more. What is necessary is just to select from the range of about 1-3 micrometers. In order to improve the characteristics of the laser element, the current blocking layer is made of AlGaAsP or AlGaAs, and the refractive index of the current blocking layer is smaller than the refractive index of the ridge structure portion serving as a current path. preferable.

  The types of dopants such as the cladding layer described above include carbon as a doping impurity when the p-type layer is an AlGaAsP-based compound layer, and beryllium and doping impurities when the p-type layer is an AlGaInP-based compound. Use magnesium. Silicon is preferable as the n-type doping impurity.

As other layers, the cap layer 109, the contact layer 110, the protective layer 112, and the like may be formed according to a conventional method.
EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to an Example, unless the summary is exceeded.

  According to the present invention, by optimizing the structure of the cladding layer sandwiching the active layer made of AlGaInP or GaInP and the dopant of the P-type cladding layer, the characteristics and reliability of the light emitting device can be improved, and the raw material cost can be improved. Can also be reduced.

Hereinafter, embodiments of the present invention will be described in detail. In this example, a MOVPE method having excellent film thickness, composition controllability, and mass productivity was used as the crystal growth method. The source gases used were trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMI), phosphine (PH ₃ ), arsine (AsH ₃ ), and hydrogen (H ₂ ) Gas was used.

An epitaxial wafer used for manufacturing the laser diode of the present invention as shown in FIG. 1 was manufactured according to the procedure described below. First, an n-type GaAs buffer layer 102 (thickness 0.5 μm), an n-type Al _0.7 Ga _0.3 As first cladding layer 103 (thickness 1.0 μm), and an n-type (Al _0.7 Ga) are formed on an n-type GaAs (100) substrate 101. _0.3 ) _0.5 In _0.5 P second cladding layer 104 (thickness 0.2 μm), Ga _0.5 In _0.5 P active layer 105 (thickness 0.06 μm),
p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P third cladding layer 106 (thickness 0.2 μm), p-type Al _0.7 Ga _0.3 As fourth cladding layer 107 (thickness 1.0 μm), p-type GaAs cap layer 109 ( A thickness of 0.2 μm) was sequentially grown (FIG. 3).

Next, in order to form a ridge, a SiNx film 111 was formed on the portion where the ridge was formed. Subsequently, the fourth cladding layer 107 and the cap layer 109 were etched, and the etching was stopped on the surface of the third cladding layer 106. As a result, a ridge as shown in FIG. 4 was formed.
At this time, phosphoric acid-hydrogen peroxide system, tartaric acid-hydrogen peroxide system, or the like is used for etching the GaAs cap layer and the AlGaAs cladding layer. In these etchings, since the etching rate of AlGaInP is much slower than that of AlGaAs, the thickness of the portion outside the ridge can be determined with good controllability.

The wafer on which the ridge is formed is set in an MOCVD apparatus, and as shown in FIG. 5, the side surface of the ridge portion including the cap layer 109 and the etched layer using the n-type Al _0.8 Ga _0.2 As layer 108 as a current blocking layer, as shown in FIG. Growing 0.8 μm on 107 by MOCVD.
Further, an n-type GaAs layer 112 was grown as a protective layer on the current blocking layer 108 by 0.2 μm. At this time, a small amount of HCl gas was introduced into the growth space during the growth in order to suppress the deposition of polycrystals on the SiNx film of the Al _0.8 Ga _0.2 As layer.

After removing the SiNx film 111 as shown in FIG. 1, the p-type GaAs contact layer 110 was grown by 2 μm, and the production of the epitaxial wafer of the present invention was completed.
An electrode was deposited on the obtained epitaxial wafer, then diced, and cleaved to form a Fabry-Perot surface to produce a laser diode. The threshold current was as very low as 20 mA, and the in-plane uniformity was very good at about ± 5% for a 2-inch wafer. Furthermore, by using AlGaAs for the ridge as compared with the conventional AlGaInP ridge, the element resistance can be reduced to about half.

The crystal growth conditions in the above examples are as follows: growth temperature 650-750 ° C., pressure 10 ² hPa, V / III ratio 25-50 (AlGaAs) and 500-750 (AlGaInP, GaInP), growth rate 1-5 μm / hr (AlGaAs ) And 0.5-2 μm / hr (AlGaInP, GaInP).
In the above embodiment, an n-type substrate is used on the substrate side. However, an epitaxial wafer may be manufactured by inverting the conductivity type of each layer of the above structure using a p-type substrate. Further, the crystal growth method is not limited to the MOVPE method, and the present invention is also very effective in a vapor phase growth method such as an MBE method or a CBE method.

  In semiconductor lasers, the active layer is relatively thin (usually 0.1 μm or less), so if an impurity with a large diffusion coefficient such as zinc or selenium is used as the dopant, the dopant in the cladding layer passes through the active layer. As a result, it diffuses to the opposite layer, which easily deteriorates the laser characteristics and greatly deteriorates the reproducibility. As a method for suppressing Zn diffusion, an attempt was made to increase the carrier concentration of the n-side cladding, but the device characteristics were deteriorated due to deterioration of crystal quality such as poor surface morphology and increase of non-luminescent center. Therefore, by reducing the thickness of the AlGaInP cladding layer as much as possible as in the present invention, the total impurity diffusion amount can be reduced, and unnecessary doving for preventing diffusion is unnecessary. Therefore, the carrier concentration of the n-type cladding layer can be suppressed to 1 × 10 18 cm −3 or less, and the crystal quality and device characteristics can be improved.

  If the active layer is an ultra-thin film such as a quantum well structure, it is more and more necessary to suppress the diffusion of impurities as described above. Therefore, in the present invention, carbon is used as the doping impurity of the p-type AlGaAsP-based compound cladding layer, beryllium or magnesium is used as the doping impurity of the p-type AlGaInP-based compound cladding layer, and the n-type AlGaAsP-based compound cladding layer and the n-type AlGaInP-based compound cladding layer. By using silicon as each doping impurity, impurity diffusion can be further reduced, and the yield and reproducibility of device fabrication can be greatly improved.

  In addition, the AlGaAsP-based compound has advantages such as lower resistivity and lower thermal resistance than the AlGaInP-based compound. By using an AlGaAsP-based compound as the ridge portion formed for current confinement. As compared with the conventional element structure, the operating voltage and heat generation of the element can be reduced. As a result, the characteristics and reliability of the element could be improved.

Furthermore, the surface orientation can be changed from (100) for the suppression of the band gap reduction by ordering of the atomic arrangement peculiar to the AlGaInP compound, that is, the suppression of the longer emission wavelength, or the improvement and stabilization of the surface morphology. [011] It is effective to use a GaAs substrate of the first conductivity type inclined by 5 to 25 degrees in the direction.
Further, reduction of the Al composition of the light emitting layer is important in terms of improving the reliability and life of the device, but this can be easily achieved by using a GaAsP substrate. In this case, an AlGaAsP clad may be used for lattice matching.

  Furthermore, according to the present invention, the growth time and raw material cost can be reduced and the burden on the apparatus such as detoxification can be greatly reduced, and stable production by a large-scale mass production apparatus capable of simultaneously growing a large number of sheets becomes possible.

FIG. 1 is an explanatory view showing an example of a light emitting device of the present invention. FIG. 2 is an explanatory view showing an example of a conventional light emitting device. FIG. 3 is a view for explaining a method for manufacturing a light emitting device of the present invention. FIG. 4 is a view for explaining a method for manufacturing a light emitting device of the present invention. FIG. 5 is a view for explaining a method for manufacturing a light emitting device of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Substrate 102 Buffer layer 103 First clad layer 104 Second clad layer 105 Active layer 106 Third clad layer 107 Fourth clad layer 108 Current blocking layer 109 Cap layer 110 Contact layer 111 SiNx film 112 Protective layer

Claims (8)

A first cladding layer made of AlGaAsP of the first conductivity type or AlGaAs; a second cladding layer made of AlGaInP or AlInP of the first conductivity type and having a thickness of 0.5 μm or less adjacent to the first cladding layer; An active layer made of AlGaInP or GaInP of the first or second conductivity type adjacent to the second cladding layer and having a thickness of less than 0.1 μm, and an AlGaInP or AlInP of the second conductivity type adjacent to the active layer. A third clad layer having a thickness of 0.5 μm or less, a fourth clad layer made of AlGaAsP or AlGaAs of the second conductivity type adjacent to the third clad layer, and for confining current to the active layer And a clad layer made of P-type AlGaAsP or AlGaAs contains carbon as a doping impurity, and P-type AlGaAs The semiconductor light emitting device aInP or consisting AlGaIn cladding layer is characterized by containing beryllium and / or magnesium as a doping impurity. 2. The semiconductor light emitting device according to claim 1, wherein the n-type cladding layer contains silicon as a doping impurity. 3. The semiconductor light emitting device according to claim 1, wherein the first cladding layer and / or the fourth cladding layer has a ridge structure, and current blocking layers are provided on the left and right sides of the ridge structure. 4. The semiconductor light emitting device according to claim 3, wherein the current blocking layer is in contact with the ridge side wall and the AlGaInP or AlInP cladding layer. A first cladding layer made of AlGaAsP of the first conductivity type or AlGaAs; a second cladding layer made of AlGaInP or AlInP of the first conductivity type and having a thickness of 0.5 μm or less adjacent to the first cladding layer; Adjacent to the second cladding layer, an active layer made of AlGaInP or GaInP of the first or second conductivity type and having a thickness of less than 0.1 μm, and adjacent to the active layer, from AlGaInP or AlInP of the second conductivity type A third cladding layer having a thickness of 0.5 μm or less, a fourth cladding layer having a ridge structure made of AlGaAsP of the second conductivity type or AlGaAs, adjacent to the third cladding layer, and AlGaAsP on the left and right of the ridge structure. Or a current blocking layer made of AlGaAs for confining the current to the active layer, and P-type AlGaAsP or AlGaAs The cladding layer contains carbon as a doping impurity, the cladding layer made of P-type AlGaInP or AlInP contains beryllium and / or magnesium as a doping impurity, and the refractive index of the current blocking layer has a ridge structure A semiconductor light emitting device characterized by being smaller than the refractive index of the portion. 6. The semiconductor light emitting device according to claim 5, wherein the n-type cladding layer contains silicon as a doping impurity. 7. The semiconductor light emitting device according to claim 5, wherein the current blocking layer is in contact with the ridge side wall and the AlGaInP or AlInP clad layer. The semiconductor light emitting device according to claim 1, wherein the n-type cladding layer has a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or less.

Images