JP2002176228A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small loss Gaussian high-grade beam in a semiconductor laser device having an AlGaN clad layer. SOLUTION: On a GaN substrate 15', eight layers are grown. The layers includes an n-GaN buffer layer 21, an n-In0.1Ga0.9N buffer layer 22, an n-Al0.1 Ga0.9N cladding layer 23 with a thickness of 0.45 μm (Si dope), an n-GaN optical guide layer 24 (the Si dope, and thickness of 0.1 μm), an undoped active layer 25, a p-GaN optical guide layer 26 (Mg dope, and thickness of 0.3 μm), a p-Al0.1 Ga0.9N cladding layer 27 (MG dope), and a p-GaN cap layer 28 (Mg dope, and 0.25 μm). Even if the thickness of the clad layer is set to 0.45 μm, a small-loss laser beam having a propagation loss of 1 cm-1 or less can be obtained by setting the thickness of an optical guide region (the total thickness of the optical guide and active layers) to 0.4 μm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device made of an AlInGaN-based semiconductor.

[0002]

2. Description of the Related Art AlInGaN-based LEDs and semiconductor lasers have attracted attention as light sources in the short wavelength region of 600 nm or less. As an LED using this material system, Jpn. J. Appl. Phys. Vol. 34, No. 7A, pp. L797-
799, high-brightness LED in blue and green wavelength range
Has extremely excellent characteristics, and is currently widely used as a light source for traffic lights and outdoor display devices. On the other hand, as a semiconductor laser, 390-4
Practical use is being promoted in a wavelength range of 10 nm. Since a much smaller light spot can be obtained than the shortest wavelength 630 nm semiconductor laser currently in practical use, application to high-density optical disk memories is most expected. In addition, a short wavelength light source of 450 nm or less is regarded as important as a light source of a digital image forming apparatus in a field such as printing using a photosensitive material having high sensitivity in a short wavelength region. In order to use a semiconductor laser device as these light sources, optically high quality Gaussian beam single mode oscillation is required.

[0003]

However, in a semiconductor laser device using an AlInGaN-based material, there is a large problem in realizing optically high-quality single mode oscillation of a Gaussian beam. That is, in order to realize sufficient optical confinement in the optical waveguide structure in the stacking direction, AlGaN
The thickness of the cladding layer, including the
It is desirable that the thickness be 1 μm or more as in a system or InGaAsP laser. However, since AlGaN has a large strain therein, it has a defect that when it grows thickly, it cracks and the crystal breaks. For example, IEEE J. Se published in 1999
lected Topics In Quantum.Electron.Vol.5, No.3, p.765, when the thickness of the AlGaN cladding layer is increased to about 0.6μm or more, the crystal cracks and the optical confinement becomes insufficient. It is described that loss and deformation occur in the beam radiation pattern.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a semiconductor laser having a cladding layer including an AlGaN layer having a thickness of 0.5 μm or less that is less likely to crack and prevents light from leaking out from an optical guide region to achieve a uniform light density. It is an object of the present invention to provide a highly reliable semiconductor laser device having a high-quality beam having a Gaussian distribution.

[0005]

According to the semiconductor laser device of the present invention, at least one layer of AlG is formed above and below the light guide region so as to sandwich the light guide region including the active layer.
In a semiconductor laser device having a cladding layer made of a semiconductor containing aN, the thickness of each cladding layer is set to tc (n
m), and when the thickness of the light guide region is tg (nm), tc and tg are −0.25 tg + 500 ≦ tc ≦ 5
00 and 400 ≦ tg (however, when tg> 1600, 100 ≦ tc ≦ 500).

The thickness tg (nm) of the light guide region is tg ≦ tg
It is desirably 2000.

When the composition of AlGaN in each cladding layer is Al _x Ga ₁ -xN, the composition ratio x of Al is preferably x ≧ 0.1.

[0008]

According to the semiconductor laser device of the present invention, at least one clad layer made of a semiconductor containing AlGaN is provided above and below the light guide region so as to sandwich the light guide region including the active layer. When the thickness of each cladding layer is tc (nm) and the thickness of the light guide region is tg (nm), tc
By setting tg and tg within the above ranges, seepage of laser light from the light guide region to the cladding layer can be reduced, so that the propagation loss can be reduced to approximately 1 cm ^-1 or less. Therefore, Gaussian high-quality laser light having a uniform light density can be obtained.

Further, since the exudation of laser light is small,
The drive current can be reduced. Further, even if the chip length is increased, the differential efficiency does not decrease, so that high output can be achieved.

[0010]

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 along its manufacturing process. FIG. 1 is a cross-sectional view of the semiconductor laser device during the manufacturing process of the substrate, and FIG. 2 is a cross-sectional view of the semiconductor laser device. In addition, as a growth material for the MOCVD method of each semiconductor layer described below,
Trimethyl gallium (TMG), trimethyl indium (TMI), trimethyl aluminum (TMA) and ammonia are used, silane gas is used as an n-type dopant gas, and cyclopentadienyl magnesium (Cp ₂ Mg) is used as a p-type dopant.

As shown in FIG. 1A, a sapphire substrate
11 on GaN by metal organic chemical vapor deposition (MOCVD)
The layer 12 is formed with a thickness of about 2.5 μm. in addition,
An SiO ₂ film 13 having a thickness of 0.1 μm is formed by a P-CVD apparatus, and stripes having a width of 8 μm are formed by photolithographic etching.
m at intervals of m

(Equation 1) The GaN film 14 having a thickness of 15 μm is grown on the SiO ₂ mask pattern. Further, a 200 μm GaN layer 15 is formed by HVPE.

GaN by the HVPE method is composed of GaCl produced by the reaction of Ga with HCl gas, NHCl and NHCl.
₃ and HCl, and the flow rate of H ₂ as a carrier gas, respectively.
2 l / min, 10 ml / min, 3 l / min, growth temperature 10
Grow at 00 ° C.

Next, as shown in FIG.
Is polished from the back surface of the sapphire substrate 11 to a part of the GaN layer 15 (a region having a thickness t) until the thickness of the GaN layer 15 ′ becomes 150 μm.

Next, as shown in FIG.
Atmospheric pressure MOCVD method on GaN substrate 15 '
N-GaN buffer layer 21 (Si-doped, 5 μm thick)
n-In _0.1Ga_0.9N buffer layer 22 (Si-doped, thickness 0.1
μm), n-Al_0.1Ga_0.9N clad layer 23 (Si-doped,
0.45 μm thick), n-GaN optical guide layer 24 (Si-doped, thick
0.1 μm), undoped active layer 25, p-GaN optical guide
Layer 26 (Mg doped, 0.3 μm thick), p-Al_0.1Ga_0.9N
Lad layer 27 (Mg-doped, 0.45 μm thick), p-GaN cap
A top layer 28 (Mg doped, 0.25 μm) is grown. Active layer 25
Is undoped In_{0. 1}Ga_0.9N quantum well layer (thickness 3n
m), undoped Al_0.04Ga_0.96N barrier layer (thickness 0.01
μm), undoped In_0.1Ga_0.9N quantum well layer (thickness
3 nm), p-Al_0.1Ga_0.9N barrier layer (Mg doped, thickness
MQW (Multi Quantum) with a 4-layer structure of 0.01 μm)
Well) structure. Note that the n-GaN optical guide layer 24,
Active layer 25 and p-GaN optical guide layer 26
A light guide region is formed.

Next, chlorine ions are applied by photolithography and etching to the middle of the p-Al _0.1 Ga _0.9 N cladding layer 27 and to a distance of 0.1 μm from the p-GaN optical guide layer 26 on both sides of the stripe region. The used RIBE (react
ive ion beam etching), width 2.2μ
An about m ridge stripe is formed.

Next, after an SiN film 29 is formed on the entire surface by plasma CVD, unnecessary portions on the ridge are removed by photolithography and etching. After that, the p-type impurity is activated by heat treatment in a nitrogen gas atmosphere. Thereafter, the epilayer other than the portion including the light emitting region is removed by etching until the n-GaN buffer layer 21 is exposed by RIBE using chlorine ions. Thereafter, Ti / Al / Ti / Au is used as the n-electrode 20,
Ni / Au is vacuum deposited as the p-electrode 30 and annealed in nitrogen to form an ohmic electrode. A cavity end face is formed by cleavage.

The oscillation wavelength of the semiconductor laser device according to the present embodiment is 400 nm. In this semiconductor laser device, the thickness of the Al _0.1 Ga _0.9 N cladding layer is 0.45 μm.
Despite the small size, the far-field image in the direction perpendicular to the junction has been confirmed to be monotonic and monomodal. That is, high-quality single mode oscillation having a Gaussian distribution with a uniform light density can be realized.

The semiconductor laser device according to this embodiment has a G
Each element is formed by laminating each layer on the aN substrate.
Instead of a GaN substrate, an insulating sapphire substrate may be used.

Next, FIG. 3A is a sectional view of a layer structure optically similar to that of the semiconductor laser device according to the above embodiment, and the thickness (Tclad) of the Al _0.1 Ga _0.9 N cladding layer is shown in FIG. ) As a parameter, the propagation loss due to the light absorption of the p-electrode metal is calculated as the thickness tg (n
FIG. 3B shows the result calculated as a function of m). Although FIG. 3A shows a configuration in which a sapphire substrate is present, light absorption due to this is negligibly small.

As shown in FIG. 3B, if the thickness of the light guide region (the total thickness of the InGaN SQW and the GaN layers above and below it) is 400 nm or more, the thickness of the AlGaN cladding layer is 0.5
It can be seen that there is a range where the propagation loss can be reduced to 1 cm ^-1 or less even in the case of less than μm. Since the propagation loss of the semiconductor laser device currently in practical use is about 1 cm ^-1 or less, the propagation loss of the present invention is also about 1 cm ^-1.
A preferred range of the thickness of the cladding layer and the light guide region is defined as ^-1 or less.

Next, FIG. 4 shows contour loss of the propagation loss as a function of the thickness of the cladding layer and the thickness of the light guide region.
As shown in FIG. 4, assuming that the thickness of the cladding layer is tc (nm) and the thickness of the light guide region is tg (nm),
0.25tg + 500 ≦ tc ≦ 500 and 400 ≦ tg
(However, when tg> 1600, 100 ≦ tc ≦ 50
It can be seen that in the region satisfying the relationship 0), the propagation loss is 1 cm ^-1 or less. In this region, the cladding layer has a thickness of 500 nm or less where cracks are unlikely to occur, but because of its thinness, there is a problem that the laser light seeps from the light guide region into the cladding layer. However, by setting the thickness of the cladding layer and the thickness of the light guiding region to the above ranges, it is possible to suppress the leaching of the laser light from the light guiding region to the cladding layer, and furthermore, due to the laser light leaking out of the cladding layer. By reducing the light absorption of the electrode part, the propagation loss can be reduced to approximately 1 cm ^-1 or less. Thus, Gaussian laser light with a uniform light density can be obtained. Further, since there is little exudation of laser light, it is possible to reduce the drive current.
Further, even if the chip length is increased, the differential efficiency does not decrease, so that high output can be achieved. There is also an advantage that the resistance can be reduced by increasing the chip length. Although FIG. 4 shows the thickness of the light guide region only up to 1000 nm, the propagation loss linearly decreases even if the thickness is 1000 nm or more. However, if it is larger than 2000 nm, the light confinement coefficient of the quantum well layer in the active layer decreases, the threshold current increases, and the temperature characteristics also deteriorate. Therefore, the thickness of the light guide region is set to 2000 nm or less. Is preferred. Further, the thickness of the cladding layer is preferably 100 nm or more, because if the thickness is too small, the propagation loss increases. Therefore, when the thickness of the light guide region is larger than 1600 nm, the thickness of the cladding layer is 100 nm or more and 50 nm or more.
It is preferably in the range of 0 nm or less.

Next, a semiconductor laser device according to a second embodiment of the present invention will be described. FIG. 5 is a cross-sectional view of the semiconductor laser device, which is perpendicular to the laser light emission direction. The semiconductor laser device according to the present embodiment is different from the semiconductor laser device according to the first embodiment in that an n-type electrode is formed on the back surface of the SiC substrate using a SiC substrate. The thickness is the same as that of the semiconductor laser device according to the first embodiment.

As shown in FIG. 5, on an n-SiC substrate 31, an n-GaN buffer layer 32, an n-In _0.1 Ga _0.9 N buffer layer 33, an n-Al _0.1 Ga _0.9 N cladding layer 34, an n-
GaN light guide layer 35, MQW active layer 36, p-GaN light guide layer 37, p-Al _0.1 Ga _0.9 N clad layer 38, p-G
An aN cap layer 39 is laminated, and a region other than the ridge stripe is removed to a part of the p-Al _0.1 Ga _0.9 N cladding layer 38 to form a ridge stripe. SiO ₂ film 4 on it
0 is formed on the entire surface on the stripe, the SiO ₂ film 40 on the ridge stripe is removed, and a p-electrode 41 is formed. An n-electrode 42 is formed on the back surface of the SiC substrate.

Also in the semiconductor laser device according to the present embodiment, a high-quality beam having a Gaussian light density can be obtained as in the above-described embodiment.

Next, a semiconductor laser device according to a third embodiment of the present invention will be described. FIG. 6 is a cross-sectional view of the semiconductor laser device, which is perpendicular to the laser light emission direction.
The semiconductor laser device according to the present embodiment is different from the semiconductor laser device according to the first embodiment in that the semiconductor laser device has an internal current confinement structure, and the composition and thickness of each layer are different from those of the semiconductor laser device according to the first embodiment. It is the same as the element.

As shown in FIG. 6, an n-GaN buffer layer 51 is provided on the GaN substrate 15 'used in the first embodiment.
n-In _0.1 Ga _0.9 N buffer layer 52, n-Al _0.1 Ga
_0.9 N clad layer 53, n-GaN optical guide layer 54, MQW
Active layer 55, p-GaN optical guide layer 56, p-Al _0.1 Ga
_{A 0.9} N clad layer 57 and a p-GaN layer 58 are stacked. Next, an SiO ₂ film and a resist are formed on the surface, and both sides of the current injection portion are etched using a chlorine-based gas. Next, the Al _0.1 Ga _0.9 N current confinement layer 59 is regrown, the p-GaN cap layer 60 is laminated thereon, and the p electrode 61 and the n electrode 62 are formed.

In the semiconductor laser device according to this embodiment, a high-quality beam having a Gaussian light density can be obtained as in the above-described embodiment. In addition, since the internal current confinement structure is employed, the contact area with the p-electrode can be increased, the contact resistance can be reduced, and characteristics such as threshold current can be improved.

The present invention is not limited to the semiconductor laser device of the above embodiment, but may have other refractive index waveguide structures and current confinement structures.

The calculation results shown in FIGS. 3 and 4 or in the above three embodiments, the cladding layer is made of Al _0.1
Although the case where Ga _0.9 N and the light guide layer are GaN has been described, an Al composition of the cladding layer of 0.1 or more is used to obtain the effect of carrier confinement. In order to improve the above, the above conditions are sufficient, and good light confinement can be achieved by thin A
It can be realized using an lGaN cladding.

It is also possible to use a superlattice structure containing AlGaN or the like as the cladding layer. For example, A
A superlattice structure of lGaN and GaN may be used.

Further, another layer may be formed between the light guide region and the cladding layer, and the effect of the present invention is the same.

By using the present invention, a semiconductor laser device with low loss can be realized, so that a short-wavelength semiconductor laser with high output and low power consumption can be realized and reliability can be improved. In addition, since the optical waveguide is sufficiently performed and the radiation mode of the unnecessary laser light to the substrate is reduced, a good single-peak beam radiation pattern can be obtained, and the optical characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of a GaN substrate.

FIG. 2 is a sectional view showing the semiconductor laser device according to the first embodiment of the present invention;

FIG. 3 is a cross-sectional view of a layer structure optically similar to the semiconductor laser device according to the first embodiment of the present invention and a calculation result of propagation loss.

FIG. 4 is a diagram showing the relationship between the thickness of the cladding layer and the thickness of the light guide region in the propagation loss.

FIG. 5 is a sectional view showing a semiconductor laser device according to a second embodiment of the present invention;

FIG. 6 is a sectional view showing a semiconductor laser device according to a third embodiment of the present invention;

[Explanation of symbols]

11 sapphire substrate 12 GaN layer 13 SiO ₂ film 14 GaN film 15 GaN layer by HVPE 15 ′ GaN substrate 21 n-GaN buffer layer 22 n-In _0.1 Ga _0.9 N buffer layer 23 n-Al _0.1 Ga _0.9 N cladding layer 24 n -GaN optical guide layer 25 Undoped active layer 26 p-GaN optical guide layer 27 p-Al _0.1 Ga _0.9 N clad layer 28 p-GaN cap layer 29 SiN film 30 p electrode 20 n electrode

Claims (3)

[Claims] 1. A light guide region including an active layer is sandwiched between at least one of upper and lower sides in the stacking direction of the light guide region.
In a semiconductor laser device provided with a cladding layer made of a semiconductor containing AlGaN as a layer, when the thickness of each cladding layer is tc (nm) and the thickness of the light guide region is tg (nm), tc And t
g is -0.25tg + 500≤tc≤500 and 400≤t
g (However, when tg> 1600, 100 ≦ tc ≦ 50
0) A semiconductor laser device characterized by the following. 2. The thickness tg (nm) of the light guide region
2. The semiconductor laser device according to claim 1, wherein tg ≦ 2000. 3. The semiconductor laser according to claim 1, wherein the composition ratio of Al is x ≧ 0.1, where the composition of AlGaN in each of the cladding layers is Al _x Ga ₁ -xN. element.