JPH10326934A - Semiconductor light emitting device and method of manufacturing the same - Google Patents

Abstract

In a semiconductor light emitting device such as a ridge waveguide type stripe laser, a complicated and fine photolithography technique is not required, the element manufacturing process is simplified, and the element manufacturing yield is greatly increased. Improve. SOLUTION: A first conductivity type first cladding layer, an active layer, a second conductivity type first cladding layer, and a ridge type second conductivity type second cladding layer formed in a stripe region into which current is injected are formed on a substrate. And a second conductive type contact layer, and a protective film covering both sides of the stripe region, wherein the protective film is not formed on a side surface of the ridge. A first cladding layer, an active layer,
After growing the first cladding layer of the second conductivity type, the second cladding layer of the second conductivity type of the ridge type and the second conductivity type contact are formed on the stripe region on the second cladding layer of the second conductivity type by using a protective film. A method for manufacturing a semiconductor light emitting device, comprising: selectively growing a layer; and forming electrodes on the side and top surfaces of the ridge without forming a protective film on the side surface of the ridge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor light emitting device and a method of manufacturing the same, and more particularly, to a semiconductor light emitting device having a ridge-type stripe structure suitable as a semiconductor laser and a method of manufacturing the same.

[0002]

2. Description of the Related Art FIG. 2 is a cross-sectional view of a conventional semiconductor laser manufacturing method and its structure. In this figure, 201
Is a substrate, 202 is a first conductivity type cladding layer, 203 is an active layer, 204 is a second conductivity type cladding layer, 205 is a second conductivity type contact layer, 206 is a protective film made of an insulator, 20
7 is an epitaxial side electrode, and 208 is a substrate side electrode. A method of manufacturing a conventional ridge waveguide type semiconductor laser having a stripe structure will be described below. First, a double hetero (DH) structure in which the active layer 203 is vertically sandwiched between cladding layers is manufactured (FIG. 2A). The ridge portion 209 is formed by etching using a stripe-shaped etching mask, and the non-ridge portion 210 at this time is etched halfway of the second conductivity type cladding layer 204 above the active layer 203 (FIG. 2). (B)) Then, by covering the side surfaces of the ridge and the surface of the non-ridge with a protective film 206, current does not flow except from the top of the ridge, and an electrode 207 including the upper portion of the ridge is formed thereon. The electrode 208 is also formed on the substrate side. With such a structure,
The current is injected into the active layer 203 after being injected through the ridge of the cladding layer. Therefore, current concentrates in a region below the ridge portion of the active layer 203, and light having a wavelength corresponding to the band gap of the active layer 203 is generated. At this time, since the band gap of the active layer is usually smaller than that of the upper and lower cladding layers, and the refractive index of the active layer is larger than that of the upper and lower cladding layers, carriers and light can be effectively confined in the active layer. In addition, the threshold current for laser oscillation can be reduced. On the other hand, the non-ridge portion 210 has a protective film 2 having a smaller refractive index than the semiconductor portion.
06, the effective refractive index of the active layer 203 below the non-ridge portion 210 is smaller than that of the ridge portion. As a result, the generated light is confined in the active layer 203 below the ridge portion 210.

Since such a conventional ridge waveguide type semiconductor laser having a stripe structure is intended to make the electrode 207 contact only with the contact layer on the top of the ridge portion,
The surface on the epitaxial side is covered with a protective film 206, and thereafter, by patterning by photolithography,
A stripe-shaped window is opened in the resist, the insulator layer 206 is removed by etching only on the upper part of the ridge portion 209, and the contact layer 205 is exposed to manufacture. In some cases, a protective film such as SiN _x may be formed on the sidewall of the ridge.

[0004]

However, usually,
When manufacturing a single transverse mode laser, the width of the ridge top is at most several microns at most, and it is usually difficult to use process simplification techniques such as self-alignment in this manufacturing method. Very high precision alignment technology is required. Such complicated and fine photolithography technology complicates the manufacturing process of the device,
The production yield of the device is also reduced. Furthermore, S
When the iN _x film is formed on the side wall of the ridge, a depletion layer (about 0.1 μm) is formed on the surface of the side surface of the ridge, so that the effective current channel width is reduced and the passage resistance is increased. Will happen.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, in a known ridge-type semiconductor light emitting device, both sides of a stripe region are covered with a protective film and both sides of the ridge are covered with protective films. By adopting a structure in which a protective film is not formed, a complicated and fine photolithography technique is not required, so that it is found that the device manufacturing process can be simplified and the device manufacturing yield can be greatly improved. The present inventors have found that a semiconductor light emitting device having a structure can be easily manufactured by selective growth using a protective film, and arrived at the present invention.

That is, the gist of the present invention is that a first-conductivity-type first cladding layer, an active layer, a second-conductivity-type first cladding layer, and a ridge-type first cladding layer formed in a stripe region into which a current is injected are formed on a substrate. A semiconductor light-emitting device comprising: a second conductive type second clad layer, a second conductive type contact layer, and a protective film covering both sides of the stripe region, wherein the protective film is not formed on a side surface of the ridge. In addition, after growing a first conductive type first clad layer, an active layer, and a second conductive type first clad layer on a substrate, using a protective film in a stripe region on the second conductive type second clad layer. A ridge-type second conductive type second cladding layer and a second conductive type contact layer are selectively grown, and electrodes are formed on the side surfaces and the upper surface of the ridge without forming a protective film on the side surfaces of the ridge. Of semiconductor light emitting devices It resides in the way.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The method of growing a crystal used for fabricating the structure of the present invention is not particularly limited. For example, a metal organic chemical vapor deposition (MOCVD) and a molecular growth method may be used to grow a crystal having a double hetero (DH) structure and a selective growth of a ridge. Known growth methods such as linear epitaxy (MBE), hydride or halide vapor phase epitaxy (VPE), and liquid phase epitaxy (LPE) may be used.

The conductivity and material of the substrate are not particularly limited as long as a crystal having a double hetero structure can be grown thereon. It is preferable to use a semiconductor crystal substrate of GaAs, InP, Si, ZnSe or the like suitable for growing a crystal thin film thereon, particularly a semiconductor crystal substrate having a zinc blende structure, in which case the crystal growth surface of the substrate is (100)
A plane or a plane crystallographically equivalent thereto is preferred. In addition,
In this specification, the (100) plane does not necessarily have to be strictly a (100) just plane.
This includes up to a case having an off angle of about 5 °.

The cladding layer, the active layer and the contact layer are not limited, but may be any of AlGaAs, AlGaInP,
GaInAsP, AlGaInN, BeMgZnSS
e, a DH structure may be formed using a general III-V or II-VI group semiconductor such as CdZnSeTe. A material having a lower refractive index than the active layer is selected for the cladding layer. When the first conductive type first clad layer, the second conductive type second clad layer, and the second conductive type second clad layer are Al-containing III-V compound semiconductor layers, more preferably AlGaAs layers, the refractive index is high. This is preferable because the light emission can be lowered to sufficiently confine light, and the band gap can be increased to sufficiently confine carriers. As the contact layer, a material having a band gap smaller than that of the cladding layer is usually selected. The contact layer has a low resistance for obtaining ohmic contact with the metal electrode and has an appropriate carrier density, that is, 1 × 10 4.
^{18 to} 5 × 10 ¹⁹ , more preferably 5 × 10 ¹⁸ to 2 × 10
Preferably, it has a carrier concentration of about ¹⁹ . A layer having a higher carrier concentration may be used as the contact layer even with the same material as the second cladding layer of the second conductivity type, or a portion having a higher carrier concentration may be provided on a part of the surface of the second cladding layer of the second conductivity type. Then, a portion having a high carrier concentration may be used as a contact layer. The active layer is not limited to a single layer, but includes a single quantum well structure (SQW) including a quantum well layer and optical guide layers sandwiching the quantum well layer from above and below, and a plurality of quantum well layers. It also includes a multi-quantum well structure (MQW) composed of a barrier layer sandwiched between them and an optical guide layer stacked above the uppermost quantum well layer and below the lowermost quantum well layer.

The protective film is not particularly limited as long as it is a material having an insulating property. Preferably, a dielectric such as SiN _x , SiO ₂ , Al ₂ O ₃ suitable for selective growth of the ridge portion is used. Further, in order to stabilize the transverse mode of laser oscillation and reduce the threshold current, the effective refractive index in the active layer below the ridge portion for light emitted from the active layer is set to be lower than that in the non-ridge portion. It is effective to make the refractive index higher than the effective refractive index in the active layer, and it is preferable to use a protective film in which the refractive index of the protective film is smaller than the refractive index of the cladding layer in the ridge portion. However, in practice, if the refractive index difference is too large, the effective refractive index step in the lateral direction in the active layer is likely to be large, so that the first cladding layer below the ridge must be thickened. On the other hand, if the difference in the refractive index is too small, it is necessary to increase the thickness of the protective film to some extent because light easily leaks to the outside of the protective film. Considering these facts, the difference in the refractive index between the protective film and the cladding layer, particularly the second cladding layer of the second conductivity type, is 0.1.
1 to 2.5 is preferable, and 0.2 to 2.0 is more preferable.
It is. Even more preferably, it is 0.7 to 1.8. There is no particular problem with the thickness of the protective film as long as it has sufficient insulation properties and does not leak light outside the protective film. The thickness of the protective film is 10 to 50
0 nm is preferable, more preferably 50 to 300 nm, and most preferably 100 to 200 nm.

In the method for manufacturing a semiconductor light emitting device according to the present invention, after a double hetero structure is first formed on a substrate, a ridge-type second conductive type second clad layer and a second conductive type contact layer are formed using a protective film. And selectively forming electrodes on the side and top surfaces of the ridge without forming a protective film on the side surfaces of the ridge. The specific growth conditions and the like of each layer vary depending on the composition of the layer, the growth method, and the like.
When a III-V compound semiconductor layer is grown by using the MOCVD method, a double hetero structure has a growth temperature of about 700 ° C.
The V / III ratio is about 25 to 45, and the ridge portion has a growth temperature of 630.
It is preferable to carry out at a temperature of about 700 ° C. and a V / III ratio of about 45 to 55. In particular, the ridge portion selectively grown using the protective film is made of Al.
In the case of a III-V group compound semiconductor containing Al such as GaAs (preferably having an Al mixed crystal ratio of 0.3 or more), introduction of a small amount of HCl gas during growth prevents deposition of poly on the mask. And very preferred. In that case, HCl
If the introduction amount of the gas is too large, the growth of the AlGaAs layer does not occur, and the semiconductor layer is etched instead (etching mode). However, the optimal introduction amount of HCl is the supply amount of the group III source material containing Al such as trimethylaluminum. It depends greatly on the number. Specifically, the ratio of the number of moles of HCl supplied and the number of moles of Group III raw material containing Al (HCl / III) is:
0.01 or more and 50 or less, more preferably 0.05 or more and 1
0 or less, and most preferably 0.1 or more and 5 or less.

In addition to the structure of the present invention, a ridge-shaped clad is formed by regrowth with an oxidation suppressing layer provided on the epitaxial surface side of the DH structure so as to increase the passage resistance at the regrowth interface. It is possible to easily prevent generation of a high-resistance layer. The oxidation suppressing layer is a layer that does not absorb light from the active layer (selection of material or thickness).
The material is not particularly limited as long as the material is hardly oxidized or easily oxidized even if oxidized. In order not to absorb light, a semiconductor layer having a band gap larger than that of the active layer material is selected. However, even a material having a small band gap has a thickness of 50 nm or less, more preferably 30 nm.
m or less, and most preferably 10 nm or less, can be used because light absorption can be substantially ignored. Further, as a material that is hardly oxidized or easy to clean even if oxidized, specifically, a III-V compound semiconductor layer having an Al mixed crystal ratio of 0.3 or less, more specifically, AlGaAs
s layer.

Further, the cladding layer of the regrown portion is grown so as to cover the upper surface of the protective film made of an insulator, thereby improving the controllability of the distribution of light seeping into the vicinity of the protective film and the ridge, and improving the regrowth. The contact layer of the part is grown so as to cover the upper surface of the protective film, and the oxidation of the side surface of the cladding layer is suppressed, the contact area with the electrode on the epitaxial surface side is increased, and the contact resistance with the electrode is reduced. You can also. The growth of the cladding layer and the contact layer of these regrowth portions so as to cover the upper portion of the insulating film may be performed independently, or both may be combined. Furthermore, when the ridge is formed by regrowth, in order to improve the controllability of the composition, carrier concentration and growth rate of the ridge, a ridge dummy layer having a larger area than the ridge to which the current is injected is not used. It is also possible to provide them outside the stripe region.
At this time, a thyristor structure or the like, which is insulated from an oxide film or the like, is formed in the ridge dummy layer in order to prevent the passage of current. As described above, the present invention is applicable to various ridge stripe type waveguide semiconductor light emitting devices.

The preferred embodiments of the present invention include the following:
A semiconductor light emitting device wherein the first conductive type clad layer, the second conductive type second clad layer, and the second conductive type second clad layer are layers containing Al; 2) a ridge dummy outside the stripe region; Semiconductor light-emitting device having a layer; 3) the refractive index difference between the protective layer and the second cladding layer of the second conductivity type is 0.1 to
2.5 and the like.

In a most preferred embodiment to which the present invention is applied, a protection film made of an insulator is used, and an oxidation suppressing layer is provided on the epitaxial surface side of the DH structure. The contact layer is regrown so as to cover the upper part of the protective film made of an insulator, and at this time, a non-current injection ridge dummy layer having a larger area than the ridge portion is provided, and a side surface of the ridge is provided. No. 1 has no protective film made of an insulator, and has electrodes formed on the top and side surfaces of the ridge.
The laser chip cut out from the above-mentioned wafer with electrodes by cleavage is usually sealed together with a heat sink and a light output monitoring photodiode in a CAN package in a nitrogen atmosphere and assembled. Recently, in order to reduce the size and cost, a laser chip is sometimes assembled as an integrated optical pick integrated with an optical component.

[0016]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.
However, the present invention is not limited to the following
It is not limited by the example. (Embodiment) This embodiment is shown in FIG. First,
N-type with 350μm thickness and (100) surface first
GaAs substrate (n = 1 × 10¹⁸cm^-3) On 101
1.5 μm thick Si-doped Al by OCVD_xGa
_1-xAs (x = 0.55: n = 1 × 10¹⁸cm^-3) N-type
1 clad layer 102, 0.06 μm thick non-doped A
l_yGa_1-yAs (y = 0.14) active layer 103, thickness of 0.1
25 μm Zn-doped Al_zGa_1-zAs (z = 0.5
5: p = 1 × 10¹⁸cm^-3) P-type first cladding layer 10
4. 10 nm thick Zn-doped Al_uGa_1-uAs (u =
0.2: p = 1 × 10¹⁸cm^-3) Oxidation prevention layer 105
The next layer was formed to form a double heterostructure
(FIG. 1 (a)). Next, the surface of the double
Marginal SiN _x Protective film 106 (refractive index: 1.9＠780n)
m) is deposited to a thickness of 200 nm,
Riko SiN_x The width of the protective film 106 in the [01-1] B direction
A large number of 2.2 μm stripe windows 107 are opened. one
In general III-V and II-VI compound semiconductors, (10
(11-1) exists between the (0) plane and the (01-1) plane.
[01-] so that the surface is the surface where the group V or group VI element appears.
1] Define the B direction. At this time, on both sides of the stripe area
SiN to leave_xThe width D of the protective film is 10 μm on both sides.
And the repetition width of the ridge portion was set every 250 μm.
(D / L = 0.04). This striped window 107
Then, by selective growth using MOCVD, a thickness of 1.2
μm Zn-doped Al_wGa_1-wAs (w = 0.57: p
= 1 × 10¹⁸cm^-3) P-type second cladding layer 108 (refractive
Rate: 3.25＠780 nm) and a 0.2 μm thick Zn layer
GaAsp type contact layer (p = 1 × 10¹⁸cm^-3)
A ridge made of No. 109 was formed (FIG. 1B). this
Sometimes, Zn-doped Al_wGa_1-wAs (w = 0.57) p
The mold second cladding layer 108 mainly has a (311) A plane
Presenting a ridge shape as a set, Zn-doped GaAs core
The contact layer 109 is made of Zn-doped Al_wGa_1-wAs (w
= 0.57) Ridge-shaped p-type second cladding layer 1
08 grown almost isotropically and covered the entire ridge.

In the above-mentioned MOCVD method, trimethylgallium (TMG) and trimethylaluminum (TMA) were used as the group III raw material, arsine was used as the group V raw material, and hydrogen was used as the carrier gas. Dimethyl zinc was used as the p-type dopant, and disilane was used as the n-type dopant.
During the growth of the ridge, HCl gas was introduced so that the molar ratio of HCl / III group was 0.12, especially the molar ratio of HCl / TMA was 0.22. Thereafter, the p-type electrode 11
0 is deposited on the epitaxial surface side,
After the thickness was reduced to μm, an n-type electrode 111 was deposited on the substrate side to form an alloy (FIG. 1C). Chips were cut out from the wafer thus manufactured by cleavage to form a laser resonator structure. At this time, the resonator length was 250 μm. After assembling by junction up, current-light output and current-voltage characteristics were measured at 25 ° C. by continuous energization (CW). As shown in FIG. 4, the characteristics of the laser chip manufactured in this manner show very good current-voltage characteristics and current-output characteristics, and the threshold voltage is 1.7 V, which corresponds to the band gap of the active layer. It was confirmed that no high resistance layer was present. Table 1 shows the standard specifications when a laser that performs a low-output self-pulsation operation and is used as a light source for reading a compact disk or the like is manufactured. In the laser of this embodiment, when the distribution in the batch and between the batches were measured, the threshold current was 2 on average.
It was found that the characteristics were very good and uniform, for example, 6 mA and the slope efficiency was 0.56 mW / mA on average, and the element yield was almost 100%.

[0018]

TABLE 1 threshold current I _th I _th ≦ 30mA threshold voltage V _th V _th ≦ 2.0V operating current I _op I _op ≦ 37mA operating voltage V _op V _op ≦ 2.3V slope efficiency SE 0 0.4 ≦ SE ≦ 0.7 Vertical beam spread angle θ _v 30 ° ≦ θ _v ≦ 40 ° Horizontal beam spread angle θ _h 8 ° ≦ θ _h ≦ 14 ° Wavelength λ 780 nm ≦ λ ≦ 810 nm Coherency γ γ ≦ 0.95 ＠ 25 ° C, 3mW (excluding I _th and V _th )

(Comparative Example) This comparative example is shown in FIG. After the formation of the contact layer 309, before the p-type electrode 310 is deposited on the epitaxial surface side, the surface on the epitaxial side is covered with a protective film 306, and thereafter, a stripe-shaped window is opened in the resist by patterning by photolithography. A semiconductor laser chip was manufactured in exactly the same manner as in the above example, except that only the upper part of the protective film 305 was removed by etching and the contact layer 308 was exposed. As for the characteristics of the laser chip manufactured in this way, when the distribution in the batch and between the batches were measured, the characteristics such as the threshold current and the slope efficiency varied greatly, and the element yield was only about 50%.
As a result of observing the cross-sectional shape and the like, since the electrode 7 is intended to be brought into contact only with the contact layer on the top of the ridge, a complicated and fine photolithography technique is required. It was found that the yield was also lowered.

[0020]

According to the present invention, in a semiconductor light emitting device such as a ridge waveguide stripe laser, a ridge is formed by selective growth in a stripe region into which current is injected, using a protective film made of an insulator. By adopting a structure in which a protective film made of an insulator is not formed on the side surface of the ridge, complicated and fine photolithography technology is not required, thereby simplifying the device manufacturing process and greatly improving the device manufacturing yield. be able to.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a semiconductor light emitting device and a method for manufacturing the same according to the present invention.

FIG. 2 is a cross-sectional view illustrating a conventional semiconductor light emitting device in which a ridge portion is formed by etching and a method for manufacturing the same.

FIG. 3 is a cross-sectional view illustrating a semiconductor light emitting device described in a comparative example, in which the entire ridge except the upper portion is covered with a protective film, and a method for manufacturing the same.

FIG. 4 is a graph showing current-voltage characteristics and current-output characteristics of the semiconductor laser described in the example. In the graph,
The horizontal axis represents current, the right vertical axis represents voltage, and the left vertical axis represents output.

[Explanation of symbols]

101: n-type GaAs substrate 102: n-type first cladding layer 103: active layer 104: p-type first cladding layer 105: antioxidant layer 1
06: protective film 107: stripe region 108: p-type second cladding layer 109: p-type contact layer 110: epitaxial side electrode 111: substrate side electrode 201: substrate 202: first conductivity type cladding layer 203: active layer 204: first layer 2-conductivity-type cladding layer 205: second-conductivity-type contact layer 206: protective film 207: epitaxial-side electrode 208: substrate-side electrode
209: Ridge part 210: Non-ridge part 211: Resist for etching
301: Substrate 302: N-type cladding layer 303: Active layer 304: P-type first cladding layer 305: Antioxidant layer 3
06: protective film 307: stripe region 308: p-type second cladding layer 309: contact layer 310: epitaxial side electrode 311: substrate side electrode

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideki Goto 1000 Higashi-kuana-cho, Ushiku-shi, Ibaraki Mitsubishi Tsukuba Works

Claims (7)

[Claims] 1. A first conductivity type first cladding layer, an active layer, a second conductivity type first cladding layer, and a ridge type second conductivity type second cladding formed in a stripe region into which current is injected. A semiconductor light emitting device comprising: a contact layer, a second conductivity type contact layer, and a protective film covering both sides of the stripe region, wherein no protective film is formed on a side surface of the ridge. 2. The semiconductor light emitting device according to claim 1, wherein electrodes are formed on side and top surfaces of said ridge. 3. The semiconductor light emitting device according to claim 1, wherein the ridge-type second conductive type second cladding layer and the second conductive type contact layer are selectively grown. 4. The first conductive type first clad layer, the second conductive type second clad layer, and the second conductive type second clad layer are made of Al.
The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is a layer containing: 5. The semiconductor light emitting device according to claim 1, further comprising a ridge dummy layer outside the stripe region. 6. The semiconductor light emitting device according to claim 1, wherein a difference in refractive index between the protective film and the second conductive type second cladding layer is 0.1 to 2.5. 7. After growing a first conductive type first clad layer, an active layer, and a second conductive type first clad layer on a substrate, forming the second conductive type first clad layer.
A ridge type second conductive type second clad layer and a second conductive type contact layer are selectively grown in a stripe region on the conductive type second clad layer using a protective film, and further, a protective film is formed on a side surface of the ridge. Forming an electrode on the side and upper surfaces of the ridge without performing the method.