JP3752705B2 - Manufacturing method of semiconductor laser device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a semiconductor laser element suitable for an optical information terminal or an optical applied measurement light source.
[0002]
[Prior art]
Regarding optical devices that emit light in the blue wavelength region, the prior art has shown examples using, for example, GaInN / AlGaN materials. Regarding the element structure constituting the blue light emitting diode, for example, Applied Physics Letter 1994, Vol. 64 1687-1689 (Appl. Phys. Lett., 64, 1687-1689 (1994)).
[0003]
[Problems to be solved by the invention]
In the above prior art, the configuration of the light emitting active layer and the optical waveguide layer is described with respect to the blue light emitting diode using the Nitiride-based material, but the details regarding the waveguide resonance structure required for the semiconductor laser are described. Absent. Further, the contents regarding the structure for strictly controlling the transverse mode of the semiconductor laser are not described.
[0004]
The purpose of the present invention is to define the details of the waveguide resonance structure suitable for the characteristics of the material and the method of fabricating the structure utilizing the crystal growth technology, especially in the Nitride material, where it has been difficult to form waveguides and resonators. The object is to achieve laser operation in the blue-violet wavelength region at room temperature. Furthermore, the present invention provides a laser device having a waveguide structure capable of realizing a low threshold operation and a high output operation while controlling the fundamental transverse mode.
[0005]
[Means for Solving the Problems]
Means for achieving the above object will be described below.
[0006]
In the present invention, a waveguide resonance structure is fabricated by using a selective growth technique for a Nitride material that has conventionally been difficult to form a waveguide or a resonator. By defining the selective growth conditions and the insulating film mask pattern, a waveguide structure having a rectangular cross section and a resonator structure having an end face perpendicular to the substrate surface can be simultaneously produced. In the waveguide structure, a transverse mode control type buried (BH: Buried Heterostructure) structure by real refractive index guiding in which the light emitting active layer is embedded in the optical waveguide layer can be easily achieved. Further, in order to realize an element having a low threshold value operation, a DBR structure highly reflective film is formed on the end face of the resonator. An element having high output characteristics can be realized by providing an arrayed waveguide structure.
[0007]
[Action]
In order to achieve the object, the operation of the above means will be described.
[0008]
A semiconductor substrate or a ceramic substrate is used as the single crystal substrate, and the substrate surface orientation is a substrate having a Wurtzite structure having a (0001) C plane. An insulating film mask is formed on the substrate surface, and crystals are grown using a selective growth technique. At this time, the direction in which the waveguide stripe is formed is parallel to the (11-20) A plane of the substrate, or parallel to the (1-100) M plane which is perpendicular to the (11-20) A plane. Set the direction. It has been found that when a waveguide structure or a resonator structure is produced using a selective growth technique under such conditions, a waveguide side face or a resonator end face whose crystal layer is perpendicular to the substrate surface can be produced. In order to control the shape of the waveguide side surface and resonator surface as described above, it is necessary to set the nitriding treatment, growth temperature, mask width, and interval of the substrate surface within the optimum range, and these parameters are defined. It was important.
[0009]
By setting the selective growth conditions in an appropriate range, a BH stripe structure in which the fundamental transverse mode is stably guided by the actual refractive index difference can be realized by a single crystal growth. In addition, dummy patterns are provided in the vicinity of both side surfaces of the BH stripe structure in order to avoid abnormal growth or control to a rectangular shape. By providing a dummy pattern having the same insulating film mask shape at both ends of the stripe structure, the inner waveguide structure can be composed of a high-quality crystal layer. If the stripe structure on the dummy pattern is covered with an insulating film mask so as not to inject current, the fundamental transverse mode waveguide does not become unstable. As a result, a low threshold and high efficiency operation can be expected.
[0010]
Further, by forming a DBR structure highly reflective film composed of at least two types of crystal layers having different refractive indexes on the cavity end face perpendicular to the substrate surface, a remarkably low threshold operation is possible. Nitride materials have a lower refractive index than other III-V semiconductor materials, so the end-face reflectance is as low as about 20%. However, by increasing the period of the DBR structure, the end-face reflectance is 90%. The reflectivity of up to 99% was obtained. As a result, the threshold current can be reduced from 1/10 to 1/20 as compared with the element not provided with the DBR structure high reflection film.
[0011]
In addition, the stripe structure can be set in an array to achieve a high output operation. Depending on the number of stripe structures, higher output is possible. Among the arrayed stripe structures, the basic transverse mode is maintained by the phased array structure in which stripes that match the phase matching conditions of the guided transverse mode are arranged with respect to the inner optical waveguide structure excluding the dummy stripe. The maximum light output could be increased more than the number of stripes compared to a single stripe structure.
[0012]
As described above, a semiconductor laser element structure having a waveguide structure that achieves a low threshold operation and a high output operation while controlling in the fundamental transverse mode can be manufactured with respect to the Nitride material.
[0013]
【Example】
Example 1
An embodiment of the present invention will be described with reference to FIGS. 1 (a) and 1 (b). In FIG. 1 (a), surface nitriding treatment is first performed at a temperature of 950 to 1150 ° C. using an α-Al ₂ O ₃ substrate 1 having a (0001) C plane, and then GaN is grown at a growth temperature of 450 to 550 ° C. The buffer layer 2 and the n-type GaN optical waveguide layer 3 are crystal-grown by metal organic vapor phase epitaxy at a growth temperature of 950 to 1050 ° C. Thereafter, the insulating film mask 4 is formed by forming the insulating film and lithography, setting the mask interval W ₁ to ₁ to 2 μm and setting the mask width W ₂ to the range of 10 to 30 μm in FIG. At this time, the direction in which the insulating film mask 4 is formed in FIG. 1B is defined as a direction parallel to the (11-20) A plane of the α-Al ₂ O ₃ substrate 1. Thereafter, it is selectively grown at a temperature in the range of 950 to 1050 ° C., and an n-type GaN optical waveguide layer 5, a compression-strained multiple quantum well active layer 6 consisting of an AlGaN optical isolation and confinement layer, a GaN quantum barrier layer and a GaInN quantum well layer 6, p The type GaN optical waveguide layer 7 is sequentially provided. Next, the insulating film 8 is formed, and p-electrode and n-electrode patterns are deposited by lithography. 1 is obtained by cleaving the substrate in a direction perpendicular to the waveguide, and the element is cut out by scribing.
[0014]
According to this example, guided light can be propagated by the refractive index waveguide structure, and a BH stripe structure that stably guides the fundamental transverse mode by the actual refractive index difference can be produced. In this device, the laser operation was confirmed from the AlGaInN material formed on the sapphire substrate at room temperature. The oscillation wavelength at room temperature was in the range of 410 to 430 nm and was a blue-violet wavelength region.
[0015]
Example 2
Another embodiment of the present invention will be described with reference to FIGS. 2 (a) and 2 (b). An element is manufactured in the same manner as in Example 1, but a dummy pattern as shown in FIG. 2B is formed outside the mask pattern for manufacturing the stripe structure of Example 1, and an insulating film mask including the dummy pattern is formed. 4 is formed. In this case FIG. 2 (b), the mask distance W ₁ to waveguide structure set the mask width W ₂ and 1~2μm the range of 5 to 30 [mu] m, also 1~10μm mask interval W ₃ as dummy patterns And the mask width W ₄ is set in the range of 5 to 30 μm. Thereafter, an element is manufactured in exactly the same manner as in Example 1, and the element cross section shown in FIG.
[0016]
According to this example, the dummy pattern showed no abnormal growth on both side walls of the waveguide stripe structure, and the crystallinity of the waveguide layer could be improved. As a result, the threshold current could be further reduced from 2/3 to 1/2 compared to Example 2.
[0017]
Example 3
Another embodiment of the present invention will be described with reference to FIGS. 3 (a), 3 (b) and FIG. In this device, the device is manufactured and a dummy pattern is provided on the insulating film mask in the same manner as in Example 2. However, as shown in FIG. 3B, the insulating film mask is provided up to the vicinity of the resonator end face in the resonance direction. . With this mask pattern, the individual elements are separated from each other at the resonator end face from the beginning. At this time, the insulating film mask provided in the vicinity of the resonator end face was set in a range of 20 to 40 μm as a width W _{5 that} is half of the interval with the waveguide structure adjacent in the resonance direction. In FIG. 3B, the direction of the waveguide is defined in a direction perpendicular to the (11-20) A plane of the α-Al ₂ O ₃ substrate 1. As a result, the cavity end face perpendicular to the substrate surface can be formed simultaneously with the production of the waveguide structure by selective growth. A strain-compensated GaInN / AlGaN DBR structure high reflection film 8 is formed by subsequent selective growth of the crystal-grown layer 7. Thereafter, an element is fabricated in the same manner as in Example 2, and an element longitudinal section shown in FIG. 3A and an element transverse section shown in FIG. 4 are obtained.
[0018]
According to the present embodiment, since the resonator end face perpendicular to the substrate surface can be formed simultaneously with the waveguide structure by selective growth, it is not necessary to form the resonator surface by cleaving the substrate. By applying a DBR structure highly reflective film to the (1-100) M-plane crystal face of the Nitride material, which is the end face of the resonator, a much lower threshold operation than in Example 2 was achieved. In this device, the threshold current can be reduced from 1/5 to 1/10 as compared with the case where no DBR structure highly reflective film is provided. In this embodiment, by providing a dummy pattern in the vicinity of the resonator end face, the crystallinity and reflectivity of the resonator end face and the DBR structure high reflection film can be improved.
[0019]
Example 4
Another embodiment of the present invention will be described with reference to FIGS. 5 (a) and 5 (b). An element is fabricated in the same manner as in Example 2, but the waveguide stripe structure of Example 3 is arranged side by side to form an array. A dummy pattern is provided on both outer sides of the array stripe, and the insulating film mask 4 is formed as shown in FIG. At this time, in FIG. 5B, for example, the mask interval W ₁ is set to ₁ to 2 μm and the mask width W ₂ is set to 1 to 10 μm for the three waveguide stripe structures, and the mask is used for the dummy pattern. The interval W _{3 is set} to 1 to 10 μm, and the mask width W ₄ is set to a range of 5 to 30 μm. As shown in FIG. 5 (a), current is injected into the three inner stripe structures and covered with an insulating film mask so as not to inject current into the both-side dummy stripe structure. Thereafter, an element is fabricated in exactly the same manner as in Example 2 to obtain the element cross section shown in FIG.
[0020]
According to the present embodiment, a phased array structure in which the phases of the modes guiding each stripe structure are matched can be formed by arranging the stripe structures defined in a constant narrow period. As a result, even if a large number of stripe structures are provided, it is possible to operate in the basic horizontal mode as a whole, and a higher output operation can be achieved than in the case of the second and third embodiments having a single stripe structure. The maximum light output of this element was improved 3 to 5 times compared to Examples 2 and 3. Furthermore, higher output operation was possible by increasing the number of stripe structures.
[0021]
【The invention's effect】
According to the present invention, a waveguide resonance structure that is essential for a semiconductor laser can be manufactured using a selective growth technique for a Nitride material for which it is difficult to form a waveguide or a resonator. The waveguide structure can easily form a BH stripe structure that stably guides the basic transverse mode by the actual refractive index difference. As a result, the operation at room temperature of the laser made of the AlGaInN material formed on the sapphire substrate was confirmed. The oscillation wavelength at room temperature was in the range of 410 to 430 nm and was a blue-violet wavelength region. The threshold current could be reduced from 2/3 to 1/2 by introducing a dummy pattern on both sides of the stripe structure. Furthermore, by forming a resonator end face perpendicular to the substrate surface and then providing a DBR structure high reflection film, a markedly low threshold operation can be achieved and the threshold current can be reduced from 1/5 to 1/10. In addition, by using a phased array structure in which three waveguide stripe structures are phase-matched, the maximum light output can be increased to 3 to 5 times as compared with a single stripe structure in the basic transverse mode. Was possible.
[0022]
In the embodiment of the present invention, an AlGaInN semiconductor laser fabricated on a sapphire substrate having a hexagonal Wurtzite structure and a (0001) C plane has been described. However, other hexagonal substrates such as SiC, etc. And semiconductor lasers fabricated on GaAs, InP, InAs, GaSb, GaAsP, GaInAs, SiC, ZnSe, ZnS, etc., which are Zinc Blende structures and have a (111) surface. Needless to say, the contents of the present invention can be applied.
[0023]
[Brief description of the drawings]
1A and 1B are a longitudinal sectional view (a) and a top view (b) of an element structure showing an embodiment of the present invention.
2A and 2B are a longitudinal sectional view (a) and a top view (b) of an element structure showing another embodiment of the present invention.
FIGS. 3A and 3B are a longitudinal sectional view (a) and a top view (b) of an element structure showing another embodiment of the present invention. FIGS.
FIG. 4 is a cross-sectional view of an element structure in another embodiment of the present invention.
FIGS. 5A and 5B are a longitudinal sectional view (a) and a top view (b) of an element structure showing another embodiment of the present invention.
[Explanation of symbols]
1. (0001) C-plane sapphire single crystal substrate, 2. GaN buffer layer,
3. 3. n-type GaN optical waveguide layer; 4. Insulating film mask, n-type GaN optical waveguide layer,
6). 6. GaInN / GaN / AlGaN multiple quantum well structure active layer; p-type GaN optical waveguide layer,
8). 8. insulating film; p electrode, 10. n electrode, 11. Highly reflective film with strain compensation GaInN / AlGaN DBR structure.

Claims (1)

An optical waveguide structure is provided on the single crystal substrate,
The optical waveguide structure has an optical waveguide layer and a light emitting active layer, and the optical waveguide structure has a stripe structure having a rectangular cross-sectional shape,
The upper surface of the optical waveguide layer is a flat surface parallel to the substrate surface, the side surfaces of the optical waveguide layer are perpendicular to the substrate surface, and are smooth surfaces. The light emitting active layer is configured to be embedded in the optical waveguide layer, thereby providing an embedded stripe structure that provides a real refractive index difference in the lateral direction of the light emitting active layer and stably guides the fundamental transverse mode. A method for manufacturing a semiconductor laser device, comprising:
Forming an insulating film mask pattern having a predetermined mask width and mask interval for selective growth of the stripe structure, and a dummy pattern located in two regions corresponding to the further outside of the insulating film mask pattern;
A method of manufacturing a semiconductor laser device, wherein the optical waveguide structure is formed by crystal growth of the optical waveguide layer and the light emitting active layer in a state where the dummy pattern and the insulating film mask pattern are formed.

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