JPH11112078A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To substantially dissolve a laser beam absorption at an end face of a laser resonator, and suppress the deterioration of the end face, by suppressing the concentration of introduced impurities so that the current density at operation of a semiconductor laser in a window structure region where the width of a forbidden band is enlarged may be specified times as high as the current density in the active layer excepting the window region. SOLUTION: After stacking of a ZnO film 11 and an SiO2 film 112, the ZnO film 111 is processed to leave only within a groove 110, in the region to serve as a laser stripe. The zinc diffusion from the ZnO film 111 is performed by heating such a wafer to 500-600 deg.C in hydrogen atmosphere. In the region where the ZnO film 111 is left, a zinc-diffused region 118 about 1×10<19> cm<3> in zinc concentration is made. The concentration of p-type carriers in this region becomes about 5×10<18> cm<3> , thus obtaining favorable window structure. Since atoms between lattices in high concentration exist at the diffused interface region of the zinc-diffused region, the density of the current flowing in the window region is about several tens/cm<2> , and it is several figures less (1/50) than the current density outside the window region, thus the deterioration of the end face can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device, and more particularly to a device structure suitable for an AlGaInP-based high-power semiconductor laser device and a method of manufacturing the same.

[0002]

2. Description of the Related Art AlGaInP-based high-power semiconductor lasers are used as light sources for optical disks, digital video disks, and the like, and require high power and high reliability. To achieve this, for example, Arimoto and other IEs
EEJ. QuantumElectron. , Vo
129, pp1874-1879, (1993). In this document, as shown in FIG. 14, in an AlGaInP / GaInP-based semiconductor laser, zinc diffusion is performed near the end face of a laser resonator to obtain GaInP.
A mixed window region of the natural superlattice was provided. The mixed crystal of the natural superlattice increases the forbidden band width of the active layer, so that absorption of laser light by the active layer at the end face, which caused the end face breakdown phenomenon, disappears. Thereby, the end face breakdown phenomenon is prevented, and a semiconductor laser having a maximum light output of 204 mW is realized.

[0003]

In the prior art, when a semiconductor laser is operated by injecting a current, a current blocking layer is selectively grown on the window region after the window region is formed in order to prevent leakage of current at the cavity end face. Had to be provided. In order to produce the current block layer, a p-type cladding layer is partially processed into a ridge shape using a stripe-shaped mask produced by photolithography just above the laser waveguide, and then the portion other than the upper portion of the window region is formed. It was necessary to process again using photolithography so that the mask was left only in the portion directly above the waveguide, and to selectively grow the current blocking layer. Among them, the steps of processing the mask again by using the photolithographic method were many as compared with the steps of manufacturing a normal ridge structure. Further, when the current block layer is formed, only the region immediately above the window region becomes a region more convex than the other region. Thereafter, in order to enhance the adhesion of the electrode, crystal growth of the contact layer is performed by several microns, so that it is necessary to planarize the crystal. there were.

[0004]

Means for Solving the Problems To solve the above problems, a manufacturing method was devised in which the electric resistance in the window region was higher than that of other portions of the waveguide when the window region was formed, and a current blocking layer was formed on the window region. By eliminating the necessity, the process can be simplified. As a method for forming such a window region, a method is employed in which, after crystal growth of a semiconductor laser structure is performed, solid layer diffusion is performed in hydrogen or nitrogen using zinc oxide as a diffusion source.

[0005] Zinc becomes a p-type carrier in the group III-V compound semiconductor, and has a concentration of 5 × 10 ¹⁷ c
When m ⁻³ to 1 × 10 ¹⁹ cm ⁻³ , the carrier density is about 5 × 10 ¹⁷ cm ⁻³ to 5 × 10 ¹⁸ cm ⁻³ . Even if the concentration of zinc in the crystal is the same as above, the activation rate of the carrier is low. For example, in the case of 5 × 10 ¹⁶ cm ⁻³ , the zinc atoms which are not activated due to interstitials become defects and the electric resistance of the crystal becomes low. Is rather high. At this time, zinc atoms form impurity levels in the semiconductor crystal and, for example, reduce the forbidden band width in the active layer, so that there is a problem that light corresponding to the emission wavelength of the active layer is absorbed.

However, by optimizing the process by setting the temperature of solid-phase diffusion of zinc from zinc oxide as a raw material in the range of 500 ° C. to less than 600 ° C. and the diffusion time in the range of 20 minutes to 90 minutes. A state in which the activation rate of the carrier is high and the light is not absorbed can be created while maintaining the state where the electric resistance of the crystal is high. According to this method, for example, when 2.5 V corresponding to the driving voltage of the semiconductor laser is applied to the semiconductor laser crystal, the current density flowing in the window region becomes about several tens of amperes per square centimeter, and the current outside the window region (that is, (A region where no diffusion occurs), two orders of magnitude lower than the current density.

Based on the above findings in the process, the present inventor has studied the structure of a semiconductor laser device suitable for high-power laser light oscillation, and has realized a device performance suitable for avoiding end face deterioration. It was conceived that the magnitude relationship between the current densities flowing through the zinc diffusion region and the non-diffusion region was important.

That is, the present invention provides an active layer composed of a semiconductor layer having a periodic fluctuation and a semiconductor layer composed of semiconductor layers having different forbidden band widths and different conduction types than the active layer provided with the active layer interposed therebetween. A semiconductor laser having cladding layers of various kinds and electrodes formed on the upper and lower parts of the above-mentioned layer structure, and forming a resonator using a crystal plane provided vertically to a laminated structure comprising the above-mentioned active layer and the cladding layer as a reflecting mirror In the element, the periodic fluctuation of the active layer is smoothed by introducing an impurity in the vicinity of at least one of the reflecting mirrors so that the forbidden band width of the active layer is larger than the forbidden band width of the active layer in the other region. The impurity introduction concentration is set so that the current density of the window structure region having the increased bandgap at the time of operating the semiconductor laser is 1/50 or less of the current density in the active layer other than the window region. Te, suppresses substantially eliminated by and end face deteriorates the laser beam absorption in the laser cavity end face. The impurity to be introduced is preferably zinc. Also,
In a so-called AlGaInP-based semiconductor device in which at least one of gallium, indium, and phosphorus is contained as a constituent element in a semiconductor material forming the active layer and the cladding layer, a more remarkable effect of the present invention can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to Embodiments 1 to 3 and related drawings.

<Embodiment 1> The structure of a semiconductor laser according to a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is an overview of the device. First, a double hetero structure having a cross-sectional structure as shown in FIG. 2 is manufactured by using a metal organic chemical vapor deposition method. Reference numeral 101 denotes a GaAs substrate.
The plane orientation of the substrate 101 is the (100) plane. On this substrate, an n-type cladding layer 102 made of n-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P and having a thickness of about 1.8 μm,
Optical guide layer 10 made of n _0.5 (Ga _0.7 Al _0.3 ) _0.5 P
3, the multiple quantum well active layer 104, p-type I
1.5 μm thick consisting of n _0.5 (Ga _0.3 Al _0.7 ) _0.5 P
About a p-type cladding layer 105, a p-type In _0.5 Ga _0.5 P layer 106, and an n-type GaAs cap layer 107 were sequentially crystal-grown. The multiple quantum well active layer has three layers of In _0.51 Ga
_0.49 P (7 nm) well layer 108 and two layers of In _0.5 (G
a _0.7 Al _0.3 ) _0.5 P109 is laminated.

Here, the active layer may have either a constant composition such as a double hetero structure or a structure having energy modulation such as a multiple quantum well structure. It is necessary that the semiconductor layer be formed so as to produce a periodic composition fluctuation of In and Ga during growth, that is, a so-called natural superlattice.

Next, Zn is diffused into a part of the wafer by the process shown in FIG. First, an n-type GaAs cap layer 107 is formed by forming a groove 11 having a width of 30 to 50 μm and a length of 50 to 200 μm perpendicular to the direction in which a laser stripe is formed.
Remove to zero shape. Next, the ZnO film 11 is formed by sputtering.
After depositing the SiO ₂ film 112 and the SiO ₂ film 112, the ZnO film 111 is processed by photolithography so that the ZnO film 111 remains only in the groove 110 in a region to be a laser stripe. Further, the n-type GaAs cap layer 107 other than the region where ZnO is left is removed. The zinc was diffused from the ZnO film 111 by heating such a wafer from 500 degrees Celsius to 600 degrees Celsius in a hydrogen atmosphere. The diffusion time was chosen so that zinc did not reach the n-type GaAs substrate.

In the region where the ZnO film 111 remains, zinc is directly diffused from the ZnO film 111 and the zinc concentration is about 1 × 10 ¹⁹
A cm- ³ zinc diffusion region 118 is formed. The p-type carrier concentration in this region was about 5 × 10 ¹⁸ cm ⁻³ , and a good window structure was obtained.

After the ZnO film 111 and the n-type GaAs cap layer 107 are removed, Ga is removed by metal organic chemical vapor deposition.
The As layer 113 is regrown, and the Si layer is
Deposit an O ₂ film. SiO ₂ using photolithographic technology
The film is processed into a stripe having a width of about 5 μm. This SiO
_{Using the two} stripes as a mask, the middle of the p-type cladding layer 105 was processed into a ridge shape, and the n-type GaAs current block layer 114 was selectively grown using the SiO ₂ stripe as a mask.

After removing the GaAs regrown layer 113,
n-type GaAs current blocking layer 114 and p-type In _0.5
On the Ga _0.5 P layer 106, a p-side electrode 116 made of an Au—Zn alloy is provided via a contact layer 115 made of p-type GaAs. Then, the GaAs substrate 10
The n-side electrode 117 made of Au.Ge alloy is
Is provided. A wafer having such a structure is about 6 in length.
The laser chip was cleaved at 00 μm. The cleavage position was controlled so that the cleavage position was in the region where the stripes of the ZnO film 111 were provided. FIGS. 4 and 5 show the cross-sectional structure of the window portion and the portion other than the window of the semiconductor laser formed by the above steps. In the figure, a region 11 in which zinc is diffused
8 is indicated by oblique lines.

At this time, since a high concentration of interstitial atoms is present in the diffusion interface region of the zinc diffusion region, as shown in FIG. 6, for example, a driving voltage of 2.5 V corresponding to the driving voltage of the semiconductor laser was applied to the semiconductor laser crystal. In this case, the current density flowing in the window region was several tens of amperes per square centimeter, which was several orders of magnitude lower than the current density flowing outside the window region.

The semiconductor laser of this embodiment has a wavelength of 680 nm.
m, the threshold current is about 5% lower than the conventional device by about 10%.
It oscillates continuously at room temperature at 0mA and the maximum light output is about 300mW
Thus, continuous operation for 5000 hours or more at an optical output of 100 mW was possible.

Embodiment 2 FIGS. 7 to 10 show the structure of a semiconductor laser according to a second embodiment of the present invention. First, a double hetero structure as shown in FIG. 7 is formed by metal organic chemical vapor deposition. Reference numeral 201 denotes a GaAs substrate.
The s-substrate 201 is moved from the (100) plane in the [011] direction by 7
It has a plane orientation inclined at an angle. On this substrate, n-type In
_0.5 (Ga _0.3 Al _0.7 ) _0.5 P n-type cladding layer 102 having a thickness of about 1.8 μm and multiple quantum well active layer 20
2, p-type In _0.5 (Ga _0.3 Al _0.7) having a thickness of about 1.5μm consisting _0.5 P p-type cladding layer 105, p-type In _0.5
Ga _0.5 P layer 106 and n-type GaAs cap layer 1
07 was grown sequentially.

The active layer 202 is made of In _0.55 Ga having a thickness of 5 nm.
_0.45 P layer 203 and 5 nm thick In _0.45 (Ga _0.5 Al
_0.5 ) _{0.55 It} has a multiple quantum well structure in which P layers 204 are stacked four periods.

Next, Zn is diffused into a part of the wafer by the process shown in FIG. First, the n-type GaAs cap layer 107 is removed into a groove 110 having a width of 30 to 50 μm perpendicular to the direction in which the laser stripe is formed. next,
After depositing the ZnO film 111 by the sputtering method,
Using a photolithographic technique, the ZnO film
It is processed so as to remain only in the inside 110 of the groove of the As cap layer 107. Further, the n-type GaAs cap layer 107 other than the region where the ZnO film 111 is left is removed. The zinc was diffused from the ZnO film 111 by heating such a wafer from 500 to 600 degrees Celsius in nitrogen. The diffusion time was chosen so that zinc did not reach the n-type GaAs substrate.

In the region where the ZnO film 111 remains, zinc is directly diffused from the ZnO film 111 and the zinc concentration is about 1 × 10 ¹⁹
A cm- ³ zinc diffusion region 118 is formed. In this region, crystal defects occur due to the high concentration of impurity diffusion, the p-type carrier concentration is about 10 ¹⁶ cm ^-3 , and the light emission intensity of photoexcited light emission is reduced to about 1/100. However, after removing the diffusion source, the crystal is again heated in nitrogen at 500 ° C to 60 ° C.
Heat treatment at 0 degrees increases the activation rate of the p-type carrier,
The emission intensity was recovered to about 10 times that before the heat treatment, and a good window structure was obtained. At this time, if the time of the second heat treatment was set short, the light emission intensity was recovered, but the p-type carrier concentration near the junction remained at 10 ¹⁷ cm ⁻³ or less. Therefore, the temperature and time of the second heat treatment were controlled such that the activation rate of the p-type carrier was increased and the p-type carrier concentration near the junction was 10 ¹⁷ cm ⁻³ or more.

After removing the GaAs cap layer 107,
The GaAs layer 113 is regrown by metal organic chemical vapor deposition, and a SiO ₂ film is deposited by thermochemical deposition. The SiO ₂ film is processed into a stripe having a width of about 5 μm by using a photolithographic technique. Using the SiO ₂ stripes as a mask, a part of the p-type cladding layer 105 is processed into a ridge shape, and the SiO ₂ stripes are used as a mask to form an n-type Ga.
Selective growth of the As current blocking layer 114 was performed.

After removing the GaAs regrown layer 113,
n-type GaAs current blocking layer 114 and p-type In _0.5
On the Ga _0.5 P layer 106, a p-side electrode 116 made of an Au—Zn alloy is provided via a contact layer 115 made of p-type GaAs. Then, the GaAs substrate 20
The n-side electrode 117 made of Au.Ge alloy is
Is provided. A wafer having such a structure is about 6 in length.
The laser chip was cleaved at 00 μm. The cleavage position was controlled so that the cleavage position was in the region where the stripes of the ZnO film 111 were provided. FIGS. 9 and 10 show the cross-sectional structure of the window portion and the portion other than the window of the semiconductor laser formed by the above steps.

According to this method, for example, when 2.5 V corresponding to the driving voltage of the semiconductor laser is applied to the semiconductor laser crystal, the current density flowing in the window region becomes about several tens of amperes per square centimeter, and flows outside the window region. Several orders of magnitude lower than the current density.

The semiconductor laser of this embodiment has a wavelength of 650 n.
m, the threshold current is about 5% lower than the conventional device by about 10%.
It oscillates continuously at room temperature at 0mA and the maximum light output is about 200mW
Thus, continuous operation for 5000 hours or more at an optical output of 80 mW was possible.

<Embodiment 3> The structure of a semiconductor laser according to a third embodiment of the present invention will be described with reference to FIGS. First, a double hetero structure as shown in FIG. 11 is manufactured by using a metal organic chemical vapor deposition method. Reference numeral 101 denotes a GaAs substrate, and the GaAs substrate 101 has a (100) plane orientation. On this substrate, n-type In _0.5 (Ga _0.3 Al _0.7 )
N-type cladding layer 1 made of _0.5 P and having a thickness of about 1.8 μm
02, an undoped _{In 0.5 (Ga 0.7 Al 0.3)} In 0.5 Ga 0.5 that in the optical guide layer 103 is sandwiched consisting _0.5 P
P active layer 301, p-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P
A p-type cladding layer 105 having a thickness of about 1.5 μm,
A p-type In _0.5 Ga _0.5 P layer 106 and an n-type GaAs cap layer 107 were sequentially crystal-grown.

The active layer may have a constant composition such as a double heterostructure or a structure having energy modulation such as a multiple quantum well structure. Must be formed so as to produce a periodic composition fluctuation of In and Ga during crystal growth, that is, a so-called natural superlattice. In this embodiment, In _0.5 Ga _0.5 P grown under the condition that a natural superlattice is formed.
Was used as an active layer.

Next, an SiN film having a thickness of 100 nm was deposited on a wafer having such a semiconductor laminated structure by a sputtering method. This SiN film was removed in the form of a stripe having a width of 30 μm to 50 μm orthogonal to the direction of the laser stripe, and the GaAs in the stripe portion was also removed by chemical etching. At this time, the etching of the GaAs was performed so that the side etching was about 2 μm below the SiN film. Next, the ZnO film 111 was deposited by a sputtering method. Such a wafer is heated from 500 degrees Celsius to 600 degrees Celsius.
By performing the heating, zinc was diffused from the ZnO film 111. The diffusion time was chosen so that zinc did not reach the n-type GaAs substrate.

In a region where the ZnO film 111 is directly adhered to the semiconductor layer, zinc is directly diffused from the ZnO film 111 to form a zinc diffusion region 118 having a zinc concentration of about 1 × 10 ¹⁹ cm ⁻³ . In this region, crystal defects occur due to the high concentration of impurity diffusion, the p-type carrier concentration is about 10 ¹⁶ cm ^-3 , and the light emission intensity of photoexcited light emission is reduced to about 1/100. However, if the crystal is heat-treated again at 500 to 600 degrees in nitrogen after removing the diffusion source, the activation rate of the p-type carrier increases, the emission intensity recovers to about 10 times that before the heat treatment, and a good window structure is obtained. Obtained. At this time, if the time of the second heat treatment was set short, the light emission intensity was recovered, but the p-type carrier concentration near the junction remained at 10 ¹⁷ cm ⁻³ or less. Therefore, the temperature and time of the second heat treatment were controlled such that the activation rate of the p-type carrier was increased and the p-type carrier concentration near the junction was 10 ¹⁷ cm ⁻³ or more.

The SiN film of such a wafer is removed,
Further, after removing the n-type GaAs layer 107, the p-type Ga
As regrown layer 113 was grown. Furthermore, by a thermal chemical deposition method to deposit a SiO ₂ film, processing the SiO ₂ film into stripes having a width of about 5μm using photolithographic techniques.
This SiO ₂ stripe halfway of the p-type cladding layer 105 are processed into a ridge shape as a mask, were selectively grown n-type In _0.5 Ga _0.5 P current blocking layer 302 of the SiO ₂ stripe as the mask.

After removing the p-type GaAs regrowth layer 113, the n-type In _0.5 Ga _0.5 P current blocking layer 302 and the p-type In _0.5 Ga _0.5 P layer 106 are interposed on the p-type GaAs contact layer 115. A p-side electrode 116 made of an Au—Zn alloy is provided. And GaA
On the back surface of the s substrate 101, an n-side electrode 117 made of an Au.Ge alloy is provided. A wafer having such a structure was cleaved to a length of about 600 μm to form a laser chip.
The cleavage position was controlled so that the cleavage position was in the region where the stripes of the ZnO film 111 were provided. Through the steps described above, a semiconductor laser having a sectional structure as shown in FIGS. 12 and 13 can be manufactured.

According to this method, for example, when 2.5 V corresponding to the drive voltage of the semiconductor laser is applied to the semiconductor laser crystal, the current density flowing in the window region becomes about several tens of amperes per square centimeter, and flows outside the window region. Several orders of magnitude lower than the current density.

The semiconductor laser of this embodiment has a wavelength of 680 nm.
m, the threshold current is about 5% lower than the conventional device by about 10%.
It oscillates continuously at room temperature at 0mA and the maximum light output is about 300mW
Thus, continuous operation for 5000 hours or more at an optical output of 100 mW was possible.

[0034]

According to the present invention, the leakage current at the time of current injection can be reduced without increasing the number of manufacturing steps of a semiconductor laser, and a low operating current and a long life can be realized.

[Brief description of the drawings]

FIG. 1 is a structural view of a semiconductor laser of the present invention.

FIG. 2 is a cross-sectional view of crystal growth of the semiconductor laser according to the first embodiment of the present invention.

FIG. 3 shows a window structure forming step in the first embodiment of the present invention.

FIG. 4 is a sectional structural view of a window region of the semiconductor laser according to the first embodiment of the present invention.

FIG. 5 is a sectional structural view of a region outside a window of the semiconductor laser according to the first embodiment of the present invention.

FIG. 6 shows current-voltage characteristics of a window region and a region outside a window.

FIG. 7 is a sectional view of crystal growth of a semiconductor laser according to a second embodiment of the present invention.

FIG. 8 shows a window structure forming step in the second embodiment of the present invention.

FIG. 9 is a sectional structural view of a window region of a semiconductor laser according to a second embodiment of the present invention.

FIG. 10 is a sectional structural view of a region outside a window of a semiconductor laser according to a second embodiment of the present invention.

FIG. 11 is a sectional view of crystal growth of a semiconductor laser according to a third embodiment of the present invention.

FIG. 12 is a sectional structural view of a window region of a semiconductor laser according to a third embodiment of the present invention.

FIG. 13 is a sectional structural view of a region outside a window of a semiconductor laser according to a third embodiment of the present invention.

FIG. 14 is a sectional view of a conventional semiconductor laser having a window structure.

[Explanation of symbols]

 101: GaAs substrate, 102: n-type In_0.5(Ga_0.3
Al_0.7)_0.5P cladding layer, 103 ... undoped In
_0.5(Ga_0.7Al_0.3)_0.5P light guide layer, 104 ... multiple
Quantum well active layer, 105... P-type In_0.5(Ga_0.3Al
_0.7)_0.5P cladding layer, 106 ... p-type In_0.5Ga_0.5P
Layers 107 ... n-type GaAs cap layer 108 ... In
_0.51Ga_0.49P well layer, 109 ... In_0.5(Ga_0.7A
l_0.3)_0.5P barrier layer, 110 ... n-type GaAs cap
A part where the layer is partially removed in a groove shape, 111... ZnO film, 11
2 ... SiO_TwoFilm, 113 ... GaAs regrown layer, 114 ...
n-type GaAs current block layer, 115 ... p-type GaAs core
Contact layer, 116 ... p-type electrode, 117 ... n-type electrode, 1
18 ... Zinc diffused region, 201 ... GaAs substrate, 2
02: multiple quantum well active layer, 203: In_0.55Ga_0.45
P well layer, 204 ... In _0.45(Ga_0.5Al_0.5)_0.55
P barrier layer, 301 ... In_0.5Ga_0.5P active layer, 302
... n-type In_0.5Ga_0.5P current block layer.

Claims (3)

[Claims] An active layer comprising at least a semiconductor layer having a periodic fluctuation and two types of cladding layers comprising semiconductor layers having a wider bandgap and different conductivity types than an active layer provided with the active layer interposed therebetween. Having electrodes on the uppermost layer and the lowermost layer of the layer structure, forming a resonator using a crystal plane provided perpendicular to the layer structure as a reflecting mirror, and introducing an impurity in the vicinity of at least one of the reflecting mirrors A semiconductor laser having a window structure in which the periodic fluctuation of the active layer is smoothed to make the forbidden band width of the active layer larger than the forbidden band width of the active layer in other regions. A semiconductor laser device wherein an impurity concentration is controlled so that a current density in a structure region during operation of a semiconductor laser is not more than one fifth of a current density in an active layer other than a window region. 2. The semiconductor laser device according to claim 1, wherein said impurity is zinc. 3. The semiconductor layer according to claim 1, wherein said semiconductor layer is gallium, indium,
2. The semiconductor laser device according to claim 1, comprising at least one of phosphorus as a component.