JP2002057410A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser in which a high quality beam is obtained and the element resistance is reduced. SOLUTION: An n-Ga1-z3Alz3N/GaN multiple quantum well step inclination layer 20 is provided between an n-GaN layer 19 and an n-Ga1-z1Alz1N/GaN superlattice clad layer 21; an n-Ga1-z4Alz4N/GaN multiple quantum well step inclination layer 22 is provided between the n-Ga1-z1Alz1N/GaN superlattice clad layer 21 and an n-Ga1-z2Alz2N optical waveguide layer 23; a p-Ga1-z4Alz4N/ GaN multiple quantum well step inclination layer 27 is provided between a p-Ga1-z2Alz2N optical wavegudie layer 26 and a p-Ga1-z1Alz1N/GaN superlattice clad layer 28; and a p-Ga1-z3Alz3N/GaN multiple quantum well step inclination layer 29 is provided between the p-Ga1-z1Alz1N/GaN superlattice clad layer 28 and a p-GaN contact layer 30. Each multiple quantum well step inclination layer 20, 22, 27, 29 substantially has an energy gap between the energy gaps of two layers which sandwich each multiple quantum well step inclination layer 20, 22, 27, 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device, and more particularly, to a semiconductor laser device having a plurality of semiconductor layers including an active layer laminated on a GaN layer.

[0002]

2. Description of the Related Art A 400 nm band short-wavelength semiconductor laser having a minute spot used in fields such as high density optical disk memory and printing using a photosensitive material oscillates in a fundamental transverse mode with a highly reliable Gaussian beam. Is expected.

[0003] Jpn. J. Appl. Phys. Lett., Vol. 37 (1
998) In pp.L1020 ”, after GaN is formed on a sapphire substrate, GaN is formed by selective growth using SiO ₂ as a mask.
A thick film is formed, the GaN thick film is peeled off to form a GaN substrate, and an n-GaN buffer layer, an n-InGaN crack preventing layer, an n-AlGaN / GaN modulation-doped superlattice cladding layer, an n-GaN
Optical waveguide layer, n-InGaN / InGaN multiple quantum well active layer, p-AlGaN
A 410 nm band short wavelength semiconductor laser comprising a carrier block layer, a p-GaN optical waveguide layer, a p-AlGaN / GaN modulation-doped superlattice cladding layer, and a p-GaN contact layer has been reported. However, here, a ridge structure of about 2 μm is formed to form a refractive index waveguide structure, but it is very difficult to control the etching depth when forming the ridge structure. In this semiconductor laser, only a transverse fundamental mode oscillation of about 30 mW is obtained. Further, although the element resistance is reduced by the modulation-doped superlattice cladding layer, since it is not sufficient, the reliability is deteriorated due to the generation of Joule heat during driving.

[0004]

That is, in the above-described structure, the element resistance is not sufficiently reduced, and particularly in a single mode semiconductor laser having a small contact area with a contact layer, the effect of heat generation is a serious problem in practical use. Becomes

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a semiconductor laser device capable of suppressing the influence of heat generation by reducing element resistance and outputting a highly reliable and high quality beam up to a high output. It is intended to do so.

[0006]

A semiconductor laser device according to the present invention comprises at least a lower cladding layer on a GaN layer.
A lower optical waveguide layer, an active layer, an upper optical waveguide layer, an upper cladding layer, and a GaN contact layer are laminated in this order,
An InGaAlN-based semiconductor laser device having a current injection window with a predetermined stripe width above an active layer,
the G layer disposed between the aN layer and the lower cladding layer;
a first AlGaN / GaN quantum well graded layer having an energy gap greater than the aN layer and smaller than the lower cladding layer, and / or the GaN contact layer disposed between the upper cladding layer and the GaN contact layer A second AlGaN / GaN quantum well gradient layer having a larger energy gap than the upper cladding layer is provided.

Here, the energy gap means a substantial energy gap, and the energy gap in the quantum well gradient layer means a substantial energy gap obtained in consideration of a tunnel effect. The same applies hereinafter.

That is, the semiconductor laser device of the present invention
Provided between the GaN layer and the lower cladding layer and / or between the contact layer and the upper cladding layer is an AlGaN / GaN quantum well gradient layer having an energy gap intermediate between the upper and lower layers. Thus, the energy gap difference between adjacent layers is reduced.

Note that the inclined quantum well layer is composed of at least one quantum well layer and a pair of barrier layers sandwiching the quantum well layer. Here, a single quantum well layer having an energy gap such that the energy gaps of the upper and lower layers are connected stepwise. It may be a quantum well gradient layer or a multiple quantum well gradient layer. In the case of a multiple quantum well gradient layer, the energy gap of each layer may be continuously connected to the energy gaps of the upper and lower layers.

In the semiconductor laser device, a third AlGaN disposed between the lower cladding layer and the lower optical waveguide layer and having an energy gap smaller than the lower cladding layer and larger than the lower optical waveguide layer.
/ GaN quantum well gradient layer and / or a fourth AlGaN disposed between the upper optical waveguide layer and the upper cladding layer and having an energy gap smaller than the upper cladding layer and larger than the upper optical waveguide layer. It is desirable to have a / GaN quantum well gradient layer.

Here, as in the above, each of the quantum well gradient layers may be a single quantum well gradient layer or a multiple quantum well gradient layer. In the case of a multiple quantum well gradient layer, the energy gap may change stepwise or may change continuously depending on each layer.

[0012] Of the barrier layers and quantum well layers constituting each of the quantum well gradient layers, only the barrier layers may be doped with impurities, or both the barrier layers and the quantum well layers may be doped with impurities. It may be doped.

The stripe width is 1 μm or more and 2.5 μm
It is desirable that the equivalent refractive index step be 0.002 or more and 0.01 or less, or that the stripe width be greater than 2.5 μm and the equivalent refractive index step be 0.002 or more and 0.015 or less.

[0014]

According to the semiconductor laser device of the present invention, the first AlGaN disposed between the GaN layer and the lower cladding layer and having an energy gap larger than the GaN layer and smaller than the lower cladding layer. / GaN quantum well gradient layer and / or the GaN layer disposed between the upper cladding layer and the GaN contact layer.
Second AlGaN / GaN having an energy gap larger than the contact layer and smaller than the upper cladding layer
With the provision of the quantum well gradient layer, the barrier height caused by the band offset generated between the two layers sandwiching the quantum well gradient layer can be reduced, the element resistance can be reduced as a whole, and the characteristic deterioration due to heat generation can be achieved. Can be suppressed. Therefore, device characteristics and reliability are improved,
A high quality beam can be obtained.

In the semiconductor laser device, a third AlGaN disposed between the lower cladding layer and the lower optical waveguide layer and having an energy gap smaller than the lower cladding layer and larger than the lower optical waveguide layer.
/ GaN quantum well gradient layer and / or a fourth AlGaN disposed between the upper optical waveguide layer and the upper cladding layer and having an energy gap smaller than the upper cladding layer and larger than the upper optical waveguide layer. By providing the / GaN quantum well gradient layer, similarly to the above, the change in the barrier height caused by the band offset can be reduced, and the device resistance can be further reduced, so that the characteristics and reliability are improved, and a high-quality beam is improved. Can be obtained.

The stripe width is 1 μm or more.
When it is 5 μm or less and the equivalent refractive index step is 0.002 or more and 0.01 or less, high-quality fundamental transverse mode oscillation can be obtained.

When the stripe width is larger than 2.5 μm and the equivalent refractive index step is 0.002 or more and 0.015 or less, multimode oscillation is obtained, but a stable oscillation mode with little noise can be obtained.

[0018]

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

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention.

Trimethyl gallium (TM)
G) Organometallic vapor phase using trimethyl indium (TMI), trimethyl aluminum (TMA) and ammonia as raw materials, silane gas as n-type dopant gas, and cyclopentadienyl magnesium (Cp2Mg) as p-type dopant By the growth method, as shown in FIG.
01) A GaN buffer layer 12 is formed on a plane sapphire substrate 11 at a temperature of 500 ° C. with a thickness of about 20 nm. Then, set the temperature
The GaN layer 13 is grown to about 2 μm at 1050 ° C. Then Si
After forming an O ₂ film (not shown) and applying a resist (not shown), the substrate is

(Equation 1) In the direction, the stripe region where the 5 μm SiO film was removed
A line-and-space pattern is formed with a period of about intervals. Using the resist and the SiO ₂ film as a mask, a part of the GaN buffer layer 12 and the GaN layer 13 is removed to the upper surface of the sapphire substrate 11 by dry etching using a chlorine-based gas. At this time, the sapphire substrate 11 may be etched. After removing the resist and the SiO ₂ film, a GaN layer 16 is selectively grown on the GaN layer 13 and the exposed sapphire substrate 11 by about 10 μm. At this time, the GaN layer 16 grows in the lateral direction with the exposed portion of the sapphire substrate 11 as a growth nucleus, and the surface is finally flattened. Next, an SiO ₂ film 17 is formed on the GaN layer 16,
By the usual lithography, the SiO ₂ film 17 is removed in a stripe shape, leaving a region having a width of about 7 μm covering a portion where the GaN layer 13 is present. Subsequently, the SiO ₂ film 17 and the exposed Ga
A GaN layer 18 is further grown on the N layer 16. GaN layer 18 is a GaN layer
The 16 exposed portions are grown laterally with the growth nucleus as a nucleus, and the surface is finally flattened.

Next, on the GaN layer 18, an n-GaN layer 19 and a first quantum
N-Ga as a well graded layer_1-z3Al_z3N (2.5nm) / GaN (2.5nm)
Quantum well step inclined layer 20 (about 0.1 μm)
N-Ga that is a pad layer_1-z1Al_z1N (2.5nm) / GaN (2.5nm) superlattice
The cladding layer 21 and the n-Ga_1-z4Al
_z4N (2.5 nm) / GaN (2.5 nm) multiple quantum well step gradient layer 22
(About 0.1 μm), n-Ga as the lower optical waveguide layer_1-z2Al_z2N light guide
Wave layer 23, In_x2Ga_1-x2N (Si-doped) / In_x1Ga_1-x1N heavy weight
Subwell active layer (0.5> x1> x2 ≧ 0) 24, p-Ga_1-z5Al _z5N key
Carrier blocking layer 25, upper optical waveguide layer p-Ga_1-z2
Al_z2N optical waveguide layer 26, p-Ga as the fourth quantum well gradient layer
_1-z4Al_z4N (2.5nm) / GaN (2.5nm) multiple quantum well step tilt
Oblique layer 27 (approximately 0.1 μm), p-Ga_1-z1A
l_z1N (2.5 nm) / GaN (2.5 nm) superlattice cladding layer 28, second amount
P-Ga which is a sub well inclined layer_1-z3Al_z3N (2.5nm) / GaN (2.5nm)
Multi-quantum well step gradient layer 29 (about 0.2 μm) and p-G
The aN contact layer 30 is grown. Subsequently, SiO_TwoMembrane and cash register
Forming a strike (not shown) and performing normal lithography
This stripe is left with a stripe area of 1 to 2.5 μm wide.
Resist and SiO outside the IP area_TwoRemove the film. RIE (anti
Selective etching with reactive ion etching equipment)
Etching to the middle of the mold superlattice cladding layer 28, and
Forming an edge part. The p-type super lattice by this etching
The remaining thickness of the lad layer 28 can achieve the fundamental transverse mode oscillation.
Thickness.

Next, the resist and the SiO ₂ film used as a mask at the time of forming the ridge portion are removed, and then an SiO ₂ film and a resist (not shown) are formed on the lamination surface. The SiO ₂ and the resist in the outer region are removed while leaving a range of 20 μm in the width direction from the stripe region, and etching is performed by RIE until the n-GaN layer 19 is exposed. After that, the resist and SiO ₂ are all removed.

Next, an insulating film 32 is formed, and a striped Ti / Au n-electrode 36 and a p-GaN contact layer 30 are formed on the exposed surface of the n-GaN layer 19 by using a usual lithography technique. A stripe-shaped p-electrode 34 made of Ni / Au is formed on the surface. Thereafter, the substrate 11 is polished and the sample is cleaved to form a resonator surface, which is coated with a high reflectance coating and a non-reflection coating, and then chipped to produce a semiconductor laser device.

The composition of GaAlN is such that 1>z1> z2 ≧ 0,
z5> z2, z4> z2.

Further, by controlling the thickness of the p-type superlattice cladding layer 28 as the upper cladding layer, the equivalent refractive index of light propagating in the vertical direction at the bottom of the ridge is set to nA, and the light is propagated in the vertical direction of the ridge. Assuming that the equivalent refractive index of the light to be emitted is nB, the equivalent refractive index step represented by nB−nA is 0.01> nB−
It can be controlled in the range of nA> 0.002.

FIG. 2 shows the n-GaN layer 19 and the n-type superlattice cladding layer 2.
Ga _1-z3 Al _z3 N / GaN multiple quantum well which is the first or second quantum well gradient layer provided between the 1 and / or p-type superlattice cladding layer 28 and the p-GaN contact layer 30 Specific examples of the step gradient layers 20 and 29 will be described. FIG. 2A shows an example of a Ga _1-z3 Al _z3 N / GaN multiple quantum well step gradient layer in which the energy gap changes stepwise, and FIG. 2B shows a Ga in which the energy gap changes continuously. _1-z3 Al _z3 N / Ga
9 is an embodiment of an N-multi quantum well gradient layer.

In FIG. 2, the vertical axis represents the Al composition (z3) and the energy gap (Eg), and the horizontal axis represents the distance from a layer having a low energy gap among the layers sandwiching the inclined quantum well layer. Note that the broken line in the graph indicates a substantial energy gap obtained in consideration of the quantum effect.
The _{Ga1 -z3Alz3N} / GaN multiple quantum well gradient layer is composed of a _{Ga1 -z3Alz3N} barrier layer and a GaN quantum well layer, and both layers are alternately arranged. If the case of increasing the energy gap increases the Al composition z3 of the barrier layer Ga _1-z3 Al _z3 N increases energy gap, conversely, the energy gap decreases when decreasing the Al composition z3 of the barrier layer. The energy gap may be changed stepwise as shown in FIG. 2A, or may be changed continuously as shown in FIG. For example, as the first quantum well gradient layer disposed between the n-GaN layer 19 and the n-type superlattice cladding layer 21, the n-GaN layer 19 having a small energy gap and the n-type superlattice having a large energy gap are used. The substantial energy gap may be increased stepwise or continuously toward the cladding layer 21 so that the energy gaps of the upper and lower layers are connected.

In the above description, the first (or the first (or p-type) superlattice cladding layer 21 provided between the n-GaN layer 19 and the n-type superlattice cladding layer 21 (or the p-GaN contact layer 30 and the p-type superlattice cladding layer 28) is provided. The second quantum well gradient layer has been described, but the third and fourth quantum well gradient layers provided between the optical waveguide layer and the cladding layer are described.
Barrier layer Ga _1-z4 Al _z4 N
The energy gap can be changed by changing the Al composition z4 of the optical waveguide layer so that a substantial energy gap is connected between the upper and lower optical waveguide layers and the cladding layer.

It is desirable that the composition of the gradient layer has its energy gap substantially coincident with each energy gap at the interface with the adjacent cladding layer or optical waveguide layer.

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

In this embodiment, an n-type substrate is used. However, a p-type substrate may be used. In this case, the conductivity of each layer may be reversed (p-type and n-type are interchanged).

In the above structure, only the barrier layer of the gradient layer is doped, but the quantum well layer may be doped.

In this embodiment, the description has been given of the refractive index guided laser having the ridge structure. However, the present invention is directed to the laser having the current confinement structure and the refractive index guided laser having the embedded ridge structure. It can also be applied to molds.

The wavelength λ at which the semiconductor laser device oscillates can be controlled within the range of 360 <λ <550 (nm) depending on the composition of the active layer.

In the above embodiment, a sapphire substrate is used as a base substrate, but a SiC substrate, ZnO, LiGaO ₂ ,
LiAlO ₂ , GaAs, GaP, Ge or Si may be used.

The layer structure according to the present invention may be formed by growing a conductive GaN layer on a sapphire substrate and then removing the sapphire substrate and growing the conductive GaN layer on a GaN substrate.

In this embodiment, a semiconductor laser that oscillates in a fundamental transverse mode has been described. However, a wide stripe semiconductor laser device having a stripe width of 2.5 μm or more may be formed. A low-noise element can be obtained even in the mode, and such a wide-stripe semiconductor laser is suitable as a wavelength conversion element or an excitation light source for a fiber laser.

In the present embodiment, since the multiple quantum well step gradient layer in which the band gap changes continuously is provided, the barrier height caused by the band offset can be reduced, so that the device resistance can be reduced. Can be. Therefore, heat generation of the element can be reduced, reliability can be improved, and a Gaussian high-quality beam can be obtained.

Next, for each of the semiconductor laser devices with and without the quantum well gradient layer, the voltage-
FIG. 3 shows a graph of the current characteristics.

The semiconductor laser device used for the evaluation shown in FIG. 3 has the same composition as that of the semiconductor laser device of the above embodiment except that the composition is z1 = 0.16, x2 = 0.02, x1 = 0.14, z5 = 0.15, z2 = 0.
And then, the electrode size and 5μmx500μm, Ga _{1-z 3} between the graph (a) and between superlattice cladding layer 28 of a dashed line superlattice cladding layer 21 and the n-GaN layer 19 and the p-GaN contact layer 30 The device has Al _z3 N / GaN quantum well step gradient layers 20 and 29. (b) The broken line indicates the superlattice cladding layer 21 and the n-
Ga _{1 -z 3} Al _{z 3} N / GaN multiple quantum well step gradient layers 20 and 29 are provided between the GaN layer 19 and between the superlattice cladding layer 28 and the p-GaN contact layer 30. Ga _1-z4 Al _z4 N / GaN multiple quantum well step gradient layers 22, 27 between the lattice cladding layer 21 and between the optical waveguide layer 26 and the superlattice cladding layer 28.
It is an element provided with. The Ga _1-z3 Al _z3 N / GaN multiple quantum well step gradient layers 20 and 29 have a configuration in which the energy gap changes in three steps of z3 = 0.12, 0.08 and 0.04, and each composition has a barrier of 10 layers. And a quantum well layer. Further, the solid line (c) in the figure indicates which of the quantum well step gradient layers 20 and 2 in the semiconductor laser device described above.
2, 27 and 29 are not provided.

From the graph of FIG. 3, it is found that the semiconductor laser device (a) according to the present invention provided with at least one quantum well gradient layer (quantum well step gradient layer in the above example),
In (b), the rise of the voltage-current characteristic is earlier than in the conventional device (c), and the same current value can be obtained at a lower voltage than the conventional device. Further, the element (b) provided at four locations shows better characteristics than the element (a) provided at only two locations of the quantum well gradient layer. These are considered to be the result of the reduction of the resistance of the device due to the provision of the quantum well gradient layer.

As described above, the semiconductor laser device of the present invention
Since the heat generation can be suppressed by reducing the element resistance as compared with the conventional element, high reliability can be obtained.

Since the semiconductor laser device according to the present invention has a low device resistance and a high-quality Gaussian beam, it can be used as a light source in the fields of high-speed information / image processing and communication, measurement, medical care, and printing. Applicable.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a composition and an energy gap of a quantum well gradient layer in a semiconductor laser device according to an embodiment of the present invention.

FIG. 3 is a graph showing voltage-current characteristics of a semiconductor laser device with and without a quantum well gradient layer.

[Explanation of symbols]

11 Sapphire substrate 12 GaN buffer layer 13 GaN layer 16 GaN layer 17 SiO ₂ film 18 GaN layer 19 n-GaN layer 20 n-Ga _1-z3 Al _z3 N / GaN multiple quantum well step gradient layer 21 n-Ga _1-z1 Al _z1 N / GaN superlattice cladding layer 22 n-Ga _1-z4 Al _z4 N / GaN multiple quantum well step gradient layer 23 n-Ga _1-z2 Al _z2 N optical waveguide layer 24 In _x2 Ga _1-x2 N (Si (Doped) / In _x1 Ga _1-x1 N multiple quantum well active layer 25 p-Ga _1-z5 Al _z5 N carrier blocking layer 26 p-Ga _1-z2 Al _z2 N optical waveguide layer 27 p-Ga _1-z4 Al _z4 N / GaN multiple quantum well step gradient layer 28 p-Ga _1-z1 Al _z1 N / GaN superlattice cladding layer 29 p-Ga _1-z3 Al _z3 N / GaN multiple quantum well step gradient layer 30 p-GaN contact layer 32 Insulating film 34 P electrode 36 N electrode

Claims (5)

[Claims] 1. At least a lower clad layer, a lower optical waveguide layer, an active layer, an upper optical waveguide layer, an upper clad layer, and a GaN contact layer are laminated on a GaN layer in this order. An InGaAlN-based semiconductor laser device having a current injection window having a predetermined stripe width, wherein the semiconductor laser device is provided between the GaN layer and the lower cladding layer.
A first AlGaN / GaN having an energy gap larger than the GaN layer and smaller than the lower cladding layer
The Ga well gradient layer and / or the Ga layer disposed between the upper cladding layer and the GaN contact layer;
A second AlGaN / Ga having an energy gap larger than the N contact layer and smaller than the upper cladding layer;
A semiconductor laser device comprising an N quantum well gradient layer. 2. A third AlGaN / GaN quantum well gradient layer having an energy gap smaller than the lower cladding layer and larger than the lower optical waveguide layer, disposed between the lower cladding layer and the lower optical waveguide layer. And / or a fourth AlG disposed between the upper optical waveguide layer and the upper cladding layer and having an energy gap smaller than the upper cladding layer and larger than the upper optical waveguide layer.
2. The semiconductor laser device according to claim 1, further comprising an aN / GaN quantum well gradient layer. 3. A method according to claim 1, wherein only the barrier layer or both the barrier layer and the quantum well layer among the barrier layers and the quantum well layers constituting the respective quantum well gradient layers are doped with impurities. 3. The semiconductor laser device according to claim 1, wherein 4. The stripe width is 1 μm or more and 2.5 μm.
4. The semiconductor laser device according to claim 1, wherein an equivalent refractive index step is 0.002 or more and 0.01 or less. 5. 5. The semiconductor laser device according to claim 1, wherein said stripe width is larger than 2.5 μm and an equivalent refractive index step is 0.002 or more and 0.015 or less.