JP2002198609A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the characteristics and reliability of a device by making clear the relationship between the thickness and reliability of a compound existing between the first and second layers in the semiconductor laser device having a layer made of a group IV element as the first layer, and a group IV nitrogen compound as the second layer. SOLUTION: Thickness d2 of a composition inclination layer SixN1-x existing between a first layer Si made of IV group and a second layer Six0N1-x0 made of the IV group nitrogen compound should preferably satisfy the relationship, namely 0.2d1<=d2<=9d1 when the film thickness of the first layer is set to d1, and the composition ration of x is set to 0.1×0<=x<=0.9×0, thus improving the maximum light output and reliability. Further, 0.3d1<=d2<=5d1 should be set preferably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device having a layer made of a group IV element and a layer made of a group IV nitrogen compound as a reflectance control layer on a cavity facet. It is.

[0002]

2. Description of the Related Art A factor that suppresses the maximum optical output of a semiconductor laser device is deterioration due to a reactive current near the cavity facet during high-power operation. Specifically, a current that does not contribute to light emission is generated on the semiconductor surface at the cavity facet, and the non-light-emitting coupling current generates heat at the cavity facet, and the heat causes deterioration of the facet, resulting in a decrease in the maximum optical output of the semiconductor laser. I do. Another problem is that when a protective film or a reflectance control layer is formed on the end face of the resonator, oxygen is taken into the semiconductor surface, which degrades the characteristics of the reflectance control layer and reduces the maximum light output. There is also.

In order to solve the above problem, US Pat. No. 4,566,638 discloses that a light emitting end face has a metal layer of 10 nm or less, for example, Al, Si, Ta, V, Sb, Mb.
It is described that n, Cr or Ti is provided to passivate a semiconductor layer near an end face, and an oxide reflectance control layer such as Al ₂ O ₃ is provided on the metal layer. Although the semiconductor surface is passivated by the out-diffusion of oxygen from the semiconductor layer to these metal layers, there is a problem that the metal layer is oxidized by the oxygen and the characteristics and reliability of the semiconductor laser device are reduced. Therefore, JP-A-11-121877 describes that after a surface of a semiconductor layer is oxidized and removed, a passivation layer such as Si is provided. Also, JP-A-3-101183
Also in the case of the above, after removing the oxide layer on the semiconductor surface at the end face of the resonator, a passivation layer of Si, Ge or Sb is provided, and a protective layer of Si ₃ N _{4 having} good thermal conductivity is provided thereon. It has been disclosed. However, a reflectance control layer formed by forming a group IV nitrogen compound on a layer of a group IV elemental element is formed of a SiO.sub.2 which is generally used as an end face protective film of a compound semiconductor laser.
₂ Unlike Al ₂ O ₃ , there is a large difference in the coefficient of linear expansion from a semiconductor. Therefore, it is vulnerable to sudden temperature changes in the storage environment,
There is a problem that peeling occurs. On the other hand, nitrogen compounds are produced by various film forming methods such as vapor deposition, sputtering, and CVD. However, in a composition in which the reaction with nitrogen is insufficient, optical absorption occurs and the output of the semiconductor laser element is reduced. There is a problem.

[0004]

Heretofore, a reflectivity control layer formed by laminating a passivation layer made of a group IV element and a group IV nitrogen compound layer in this order from the semiconductor layer side has been formed on the cavity end face. In such semiconductor laser devices, it is desired to obtain a semiconductor laser device having high output and high reliability.

In view of the above circumstances, the present invention requires at least IV
It is an object of the present invention to provide a semiconductor laser device having a high output and a high reliability in a semiconductor laser device having a reflectance control layer provided with a first layer made of a group IV element and a second layer made of a group IV nitrogen compound Things.

[0006]

A semiconductor laser device according to the present invention has a resonator made of a compound semiconductor layer. At least one of two resonator end faces facing the resonator has a resonator from the compound semiconductor layer side. In a semiconductor laser device provided with a reflectance control layer composed of a plurality of layers, one of which is made of a group IV element A ¹ and the second layer is made of a nitrogen compound of a group IV element A ² , the first layer is made A ¹ , The thickness of the _first layer d ₁ ,
The second layer is A ² _x0 N _1-x0 (0 <x0 <1), and the composition gradient layer existing between the first layer and the second layer is A _x N _1-x
(Where, A is at least one of A ¹ and A ²⁾ and,
When the thickness of the composition gradient layer is d ₂ , the d ₂ is 0.2 d ₁ ≦ d ₂ when the composition ratio of the composition gradient layer is 0.1x0 ≦ x ≦ 0.9x0.
It is characterized in that which is represented by the relationship ≦ 9d _1.

Also, d ₂ is 0.3 d ₁ ≦ d _{2 with} respect to d ₁ .
It is more preferred that ≦ 5d ₁ .

The group IV element A ¹ constituting the first layer is C,
Desirably, it is at least one of Si and Ge.

The group IV element A ² constituting the second layer is C,
Desirably, it is at least one of Si and Ge.

It is desirable that the thickness d ₁ of the first layer is 0 <d ₁ ≦ 5 (nm).

An oxide layer may be formed after the third layer of the reflectance control layer.

Preferably, the oxide is one or more oxides of Si, Al, Ti, Ta and Hf.

[0013]

According to the semiconductor laser device of the present invention, the second layer of the resonator first layer consisting of a group IV element compound semiconductor side to at least one end face (thickness d ₁₎ and group IV nitrogen compound Wherein the thickness d ₂ of the composition gradient layer present between the first layer and the second layer is 0.2 d ₁ ≦
When d ₂ ≦ 9d ₁ , the maximum light output of the laser can be improved, and the reliability over time can be improved.

Also, d ₂ is 0.3 d ₁ ≦ d ₂ ≦ 5 with respect to d ₁ .
The value of d ₁ is more preferable because the maximum light output of the semiconductor laser device can be further improved.

Further, as in the present invention, the effect of the composition gradient layer between the first layer made of the group IV element and the second layer made of the group IV nitrogen compound on the characteristics and reliability of the semiconductor laser device is described. There is no example that has been clarified from its crystal state, and thus, it is possible to optimize the reflectance control layer of the semiconductor laser device, and to provide a high-quality semiconductor laser device. .

Since the first layer of the reflectivity control layer is made of a group IV element, the group IV element has a function of gettering oxygen atoms. It is possible to prevent the characteristics and reliability of the laser device from being reduced due to diffusion of oxygen.

When the first layer is made of one or more of C, Si and Ge, oxygen can be well gettered.

Group IV element A ² constituting the second layer is C,
By using one or more of Si and Ge, good thermal conductivity can be obtained, and heat generated at the end face can be radiated well.

By setting the thickness d ₁ of the first layer to 0 <d ₁ ≦ 5 (nm), light absorption by this layer is suppressed as much as possible, and the action of gettering oxygen on the end face of the semiconductor laser element is sufficiently achieved. Can be demonstrated.

Therefore, according to the present invention, a reflectance control layer having a group IV element layer as the first layer and a group IV nitrogen compound layer as the second layer can be used in an environment where k is within the above range. It is desirable to form a group IV nitrogen compound on the first layer made of a group IV element.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The semiconductor laser device according to the first embodiment of the present invention will be described. The perspective view is shown in FIG.
FIG. 1 shows the shape of a single semiconductor laser element before being mounted on a heat sink, and is obtained by cleaving the bar-shaped sample shown in FIG.

As shown in FIG. 1, by metal organic chemical vapor deposition, n-Ga _1-z1 on the n-GaAs substrate 1 Al _z1 As
Lower cladding layer (0.55 ≦ z1 ≦ 0.7) 2, i-In _0.49 G
a _{0.5 1} P lower optical waveguide layer (thickness db = 110nm) 3, In
_{x3 Ga 1-x3 As 1-} y3 P y3 quantum well active layer (thickness da = 8
nm) 4, i-In _0.49 Ga _0.51 P upper optical waveguide layer (thickness db = 110 nm) 5, p-Ga _1-z1 Al _z1 As upper first
Cladding layer (thickness dc = 100 nm) 6, p-In _0.49 G
a _0.51 P etching stopper layer 7, p-Ga _1-z1 Al _z1 As
An upper second cladding layer 8 and a p-GaAs contact layer 9 are sequentially stacked, and an insulating film (not shown) is formed thereon.

Then, the width is reduced to 30 by ordinary lithography.
Peripheral area continuous with a stripe of about 250 μm
Insulation film with a width of about 10 μm (parallel to
Is removed, and this insulating film (not shown) is used as a mask.
And p-In by wet etching_0.49Ga_0.51
The upper part of the P etching stopper layer 7 is removed, and the ridge strike is removed.
Form a ripe. Sulfuric acid and peroxide as etchant
Use a hydrogen water-based solution. Use this etchant
Automatically etches p-In_0.49Ga _0.51
Stop at the top of the P etching stop layer 7
You.

Insulating film used as mask (not shown)
Is removed, an insulating film 11 is formed on the entire surface, and a part of the insulating film 11 on the ridge stripe is removed along the ridge stripe by ordinary lithography to form a current injection window. A p-side electrode 12 is formed on the entire surface, and Au plating 13 is applied on the p-side electrode 12 by 5 μm or more. Thereafter, polishing is performed until the thickness of the substrate becomes 100 to 150 μm to form the n-side electrode 14.

With respect to the wavelength band in which the semiconductor laser device according to the present embodiment oscillates, In _x3 Ga _1-x3 As _{1-y3 Py 3}
By controlling the composition of the active layer consisting of (0 ≦ x3 ≦ 0.5, 0 ≦ y3 ≦ 0.5), the range of 750 <λ <1100 (nm) is possible.

As a method of growing each semiconductor layer, a molecular beam epitaxial growth method using a solid or gas as a raw material may be used.

In the above structure, each semiconductor layer is formed on an n-type substrate, but a p-type substrate may be used. In this case, the conductivity of each of the semiconductor layers may be inverted.

Next, the reflectance control layers 15 and 16 are formed on the cavity facets of the semiconductor laser device manufactured as described above. Here, when forming a layer made of a group IV element as the first layer of the reflectance control layer and forming a layer made of the group IV nitrogen compound as the second layer, the composition gradient between the first layer and the second layer Devices having different layer thicknesses are manufactured, the crystal state of the reflectance gradient layer is analyzed, and the thickness of the composition gradient layer and the characteristics and reliability of the semiconductor laser device are evaluated.

In the structure of the semiconductor laser device, the stripe width is 50 μm, the oscillation wavelength is 809 nm, the suffixes of the semiconductor layers are z1 = 0.64, x3 = 0.12, y3 = 0.24,
Resonator length 0.9 in air in the direction where (100) plane is exposed
Then, the sample is cleaved to a length of 10 mm to 20 mm to form a bar-shaped sample 21 as shown in FIG.
The bar-shaped sample is set in a coating jig in the atmosphere, and the jig is set in an ECR sputtering apparatus to perform vacuum evacuation. Ultimate vacuum 1 × 10 ^-4 P
a, Ar is introduced into the sputtering apparatus,
After setting the argon gas pressure in the range of 0.8 × 10 ^{-1 to} 1.1 × 10 ^-1 Pa, a Si (purity of 99.999% or more) target was used to form a first layer on the light emitting surface 22 using a Si (purity of 99.999% or more) target. A film (having a thickness of d ₁ ) of about 1 nm is formed. Next, the introduction of N ₂ was started, and the nitrogen flow rate was increased with time until the flow rate ratio reached N ₂ / Ar = 25%, and the Si _x0 N ₁ -x0 was changed to λ at 809 nm.
/ 2, a reflectance of 3% is obtained.
A 2% front end face (light emitting face) reflection control layer is formed. N ₂
The / Ar ratio adjusts the amount of change with time so as to obtain a predetermined composition gradient layer thickness (d ₂ ). Various samples having different amounts of change in N ₂ / Ar with respect to this time, that is, samples having different composition gradient layers (thickness is d ₂ ) are prepared. For comparison, a sample in which a film without a Si layer (d ₁ = 0) was formed is also prepared.

Next, a reflectance control layer having a high reflectance is formed on the end face opposite to the light exit face. In the same manner as the light emitting surface, 1 nm of Si is formed as the first layer, the composition gradient layer is formed in the same manner as the front surface, and _{Six x} N _{1 -x 0} as the second layer is formed corresponding to λ / 4. / 4 oxide layered structure (for example, TiO ₂ (S
TiO ₂ / TiO ₂ ) ⁴ ; From the cleavage surface, TiO ₂ , Si
O ₂ , TiO ₂ , SiO ₂ , TiO ₂ , SiO ₂ , TiO ₂ ,
SiO ₂ and TiO ₂ are laminated in this order) to obtain a reflectance of 95% or more.

Next, the bar-shaped sample having the reflectance control layers formed on the front and rear surfaces thereof was formed into a sample having a width of 500 to 60%.
The device was cleaved at 0 μm to produce a single element. The heat sink performs Ni plating (5 μm) on Cu, and Ni
(5) 0 to 150 nm), Pt (50 to 200 nm) and In (3.5 to 5.5 μm) are deposited in this order in a region (at least four times) larger than the bonding area of the semiconductor laser device. This heat sink
The semiconductor laser element is formed by heating in a temperature range of 80 to 220 ° C. to melt In, and bonding the p-side of the element to a heat sink.

Next, the Si film thickness d ₁ corresponding to the first layer of the reflectance control layer formed on the end face of the semiconductor laser device,
A method of _calculating the ratio of the composition gradient layer existing between _{Six x} N _{1 -x 0 as} the second layer and the film thickness d ₂ will be described. The semiconductor laser device used as an example is a semiconductor laser device formed on a GaAs substrate, and the end face of the semiconductor laser device is made of 5n of Si as a first layer.
m, a layer provided with 140 nm of Si _x0 N _1-x0 as the second layer.

First, an XPS (X-ray pho
toelectron spectrometory (X-ray photoelectron analysis)
In accordance with the measurement conditions shown in FIG.
Measure h profile. Binding energy range of each element
Calculate area using Shirley type background
By doing so, each element concentration ratio is calculated. Its typical
FIG. 4 shows the measurement results. Second layer Si_x0N_1-x0Is a graph
In the figure, only a region of about 14 nm is displayed. Where S
i2p. ls1, Si2p. ls3 is Si-N, Si-Si
Corresponds to the element concentration of Si atoms related to the bonding of This measurement
The etching conditions used during the deposition were Si, Si_x0N_1-x0
Etching rates are 1.56 nm / min and 1.26 nm, respectively.
/ Min. Si2p. Etch with the maximum signal strength of ls3
Increase from 0.1 times to 0.1 times with aging time
The time to be reduced is t1, Si2p. The signal intensity of ls1 is the largest in the film
T2 is the time from 0.9 to 0.1 times the value
You. In addition, the average escape depth dx of the XPS information is the measurement condition.
Is 5 nm. From the above, d ₁= (T1-dx / e2) x e1,
d2 = e2 × t2, k = d_Two/ D₁Is established and k is determined.
can do. In the measurement result of FIG. 4, t1 = 6.
Since 1min and t2 = 2.6min, k = 32.76 / 33.2 = 0.98
Becomes

Here, d ₁ is smaller than the designed film thickness of 5 nm because N is diffused into the Si layer when the second layer Si _x0 N _{1-x 0} is formed on Si, This is because the -N bonding state is created.

[0036] Based on the method of obtaining the above k, described above, the thickness d ₂ of the graded composition layer element mounted on the heat sink seeks k each also different samples. Next, 50 samples of each composition having a different thickness of the composition gradient layer were prepared for each level, and a heat cycle test (-20 ° C to 80 ° C heat cycle test,
After performing 4H / cycle for 50 cycles), the laser end face after the test was observed with a 200 × optical microscope, and the presence or absence of occurrence of peeling of the coat film was inspected. FIG. 5 shows that the ratio k and the survival rate of the device (for devices having different composition gradient layer thicknesses d ₂₎
(The number of peelings observed with respect to 50 levels). As shown in FIG. 5, it can be seen that when k is 0.2 or more, environmental preservation is realized. When k <0.2, peeling occurs because the adhesion between the layer made of the group IV element and the layer made of the group IV nitrogen compound deteriorates.

Next, the maximum light output of the device mounted on the heat sink was measured. FIG. 6 shows the relationship between the maximum light output and the ratio k. The maximum light output is standardized and shown for an element having no Si layer (d ₁ = 0).

As shown in FIG. 6, in the range of 0.2 ≦ k ≦ 9, the maximum light output is improved with respect to the device having no Si layer (d ₁ = 0). This tendency is remarkable in the region of.

Next, a semiconductor laser device according to a second embodiment of the present invention will be described.

N-GaAs is formed by metal organic chemical vapor deposition.
N-In _0.49 (Ga _{1 -z 1} Al _z1 ) _0.51 P lower cladding layer (0 ≦ z1 ≦ 0.5), i-In _x2 Ga _1-x2 As on the substrate
_1-y2 P _y2 lower optical waveguide layer (x2 = 0.49y2 ± 0.01,0.1 ≦ y2 ≦
0.9, the thickness _{db = 75~400nm), In x3 Ga} 1-x3 As 1-y3
_Py3 quantum well active layer (0 ≦ x3 ≦ 0.4, 0 ≦ y3 ≦ 0.6), i−
_{In x2 Ga 1-x2 As 1} -y2 P y2 upper optical waveguide layer (x2 = 0.49y2
± 0.01, 0.1 ≦ y2 ≦ 0.9, thickness db = 75-400nm), p-
In _0.49 (Ga _1-z1 Al _z1 ) _0.51 P upper cladding layer, p
Growing a GaAs contact layer; Subsequently, an insulating film is formed.

Thereafter, the width 3 is obtained by ordinary lithography.
The insulating film of the stripe having a width of about 10 μm, which is parallel to the peripheral portion of the stripe having a thickness of about 5 μm, is removed, and the insulating film is used as a mask to perform wet etching.
The ridge stripe is formed by removing the upper part of the i-In _x2 Ga _1-x2 As _{1-y2 Py 2} upper optical waveguide layer.

After removing the insulating film used as a mask, a new insulating film is formed on the upper surface, a part of the insulating film on the ridge stripe is removed along the ridge stripe by ordinary lithography, and current injection is performed. Form a window. A p-electrode is formed over the entire surface, and a gold plating layer is formed on the p-electrode at a thickness of 5 μm or more. Thereafter, the substrate is polished to form an n-side electrode on the back surface.

Regarding the wavelength band in which the semiconductor laser device oscillates, In _x3 Ga _{1 -x3} As _{1 -y3 Py 3} (0 ≦ x3 ≦ 0.5,
0 ≦ y3 ≦ 0.5), 750 <λ <
Control up to the range of 1100 (nm) is possible.

In the configuration of the semiconductor laser device according to the second embodiment, the oscillation wavelength is set to 980 to 1100 n.
m, the suffix of the semiconductor layer is z1 = 0.64, x2 = 0.3, y2 =
0.4, x3 = 0.05 to 0.3, y3 = 0, and (10
0) A predetermined resonator length is set at 0.
A single mode laser processed to a range of 75 to 2.5 mm, preferably 0.75 to 1.5 mm is cleaved in a bar shape. Next, this sample is placed in an ECR sputtering apparatus,
After setting the sputtering gas pressure with argon in the range of 0.8 × 10 ^{-1 to} 1.1 × 10 ^-1 Pa, C (purity: 99.999)
% Or more) Using a target, a C film is formed as a first layer on the light emitting surface. Next, N ₂ was introduced starting, N ₂ flow rate ratio
/ Ar = 25%, the flow rate of nitrogen is increased with time, and as a second layer, C ₃ N ₄ is formed at 809 nm to a film thickness corresponding to λ / 2, whereby the front end face (light (Emission surface) Reflectivity was formed. On the rear surface, a C film is formed, and after increasing the nitrogen flow rate with time until N ₂ / Ar = 25%, a C ₃ N ₄ film is formed corresponding to λ / 4.
A film made of iO ₂ (SiO ₂ / TiO ₂ ) ⁴ is formed to form a reflective film having a reflectivity of 95%.

[0045] In the semiconductor laser device according to the two embodiments, as a method of controlling the composition gradient layer from the first layer through to the second layer, although using an ECR sputtering method, a flow ratio of N ₂ and Ar As long as it can be changed with time, a magnetron sputtering device,
A vapor deposition device or a CVD device may be used.

The present invention is not limited to the semiconductor laser devices according to the above two embodiments, but can be applied to other semiconductor laser devices. The semiconductor laser device referred to here is typically I
nGaN-based (oscillation wavelength: 360-500 nm), ZnS
Se system (oscillation wavelength: 410 to 540 nm), InGaAs
1P system (oscillation wavelength: 600 to 730 nm), AlGaAs
s system (oscillation wavelength: 750-870 nm), InGaAs
P system (oscillation wavelength: 700 to 1200, 1300 to 190
0 nm), InGaAs-based (oscillation wavelength: 950 to 120)
0, 1300 to 1900 nm) and a semiconductor laser structure using an InGaSb-based (oscillation wavelength: 1.8 to 3.0 μm) material.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a bar-shaped sample of the semiconductor laser device.

FIG. 3 XPS measurement conditions

FIG. 4 is a graph showing a Depth Profile near an end surface of a semiconductor laser device having a Si film and a Si _x N _{1 -x} film formed on a light emitting end surface.

FIG. 5 is a graph showing cycle test results of semiconductor laser devices having different k.

FIG. 6 is a graph showing the relationship between k and the maximum light output.

[Explanation of symbols]

_{Reference Signs List} 1 GaAs substrate 2 n-Ga _1-z1 Al _z1 As lower cladding layer 3 i-In _0.49 Ga _0.51 P lower optical waveguide layer 4 In _x3 Ga _1-x3 As _{1-y3 Py 3} quantum well active layer 5 i-In _0.49 Ga _0.51 P upper optical waveguide layer 6 p-Ga _1-z1 Al _z1 As upper first cladding 7 p-In _0.49 Ga _0.51 P etching stopper layer 8 p-Ga _1-z1 Al _z1 As upper second cladding layer 9 p- GaAs contact layer 11 Insulating film 12 P-side electrode 13 Au plating 14 N-side electrode 15, 16 Reflectivity control layer

Claims (7)

[Claims] 1. A resonator comprising a compound semiconductor layer,
At least one of the two resonator end faces opposite the said cavity, said compound semiconductor layer the first layer group IV from side elements A ¹
Consists, the second layer consisting of nitrogen compounds of Group IV element A ^2, in the semiconductor laser device having a reflectance control layer comprising a plurality of layers, the first layer and A ^1, said further thickness d ₁ , the second layer is A ² _x0 N _1-x0 (0 <x0 <1), and the composition gradient layer existing between the first layer and the second layer is A _x N _1-x (Where A is at least one of A ¹ and A ² ), and when the thickness of the composition gradient layer is d ₂ , d ₂ is such that the composition ratio of the composition gradient layer is 0.1 × 0 ≦ x ≦ 0.9 × 0. A semiconductor laser device characterized by the following relationship: 0.2d ₁ ≦ d ₂ ≦ 9d ₁ Wherein said d ₂ is, with respect to the d _1, 0.3 d ₁ ≦
_2. The semiconductor laser device according to claim 1, wherein d ₂ ≦ 5d ₁ . 3. A group IV element A constituting said first layer
^1, the semiconductor laser device according to claim 1, wherein a is C, 1 or more Si and Ge. 4. A group IV element A constituting said second layer
^2, C, the semiconductor laser device according to claim 1, 2 or 3, wherein the at least one Si and Ge. 5. The film thickness d ₁ of the first layer is 0 <d ₁ ≦ 5 (n
m), characterized in that:
14. The semiconductor laser device according to claim 1. 6. An oxide layer is formed after the third layer of the reflectance control layer.
The semiconductor laser device according to claim 1. 7. The method according to claim 1, wherein the oxide is Si, Al, Ti, Ta.
7. The semiconductor laser device according to claim 6, wherein the semiconductor laser device is one or more oxides of Hf and Hf.