JPH10215031A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a reflecting surface having high reflectance by forming an aluminum nitride intermediate layer on a substrate, whose cleavage is difficult, forming a light emitting element constituting layer on the intermediate layer, selectively etching the lower part of a layer constituting a resonator and cleaving the substrate. SOLUTION: On the substrate, whose cleavage is difficult, such as a saphire substrate 8 or the like, an intermediate layer 9 comprising aluminum nitride or the like is formed. On the intermediate layer 9, a clad layer, wherein an N-type GaN 10 is made to be the base, an active layer and the like, and a light emitting part comprising the clad layer and furthermore an N-type GaN and the like are deposited. Thereafter, the lower part of the intermediate layer 9 constituting a resonator is selectively etched, and the intermediate layer 9 is removed. One part of the part, which becomes the resonator, is floated in the physical cantilever shape, and a cleavage surface 15 is formed. Thus, the reflecting surface having the high reflectance can be formed, and the threshold- value current can be lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser diode, and more particularly to a semiconductor laser diode having a cleavage surface.

[0002]

2. Description of the Related Art In recent years, semiconductor light emitting devices have been developed and applied to various fields. Conventionally, the development of semiconductor light emitting devices has been preceded by the development of red and yellow semiconductor light emitting devices, and the development of blue semiconductor light emitting devices has been delayed.
Semiconductor light emitting devices are LED and LD (laser diode)
Divided into Considering the application field as an LED, in order to produce a full-color image, three primary colors of light, red, yellow and blue, are required, and development of a blue semiconductor LED has been awaited. In addition, there is a particularly high expectation in the application field as a signal of a traffic signal. This has already been adopted on a trial basis, and a traffic light using a light-emitting LED does not show a color that is not lit, so that there is little misunderstanding. It also has the advantages of low power consumption, high reliability and long life. Next, in the field of application as an LD (laser diode), using a blue laser as compared to a red laser allows a high-density data to be stored since the wavelength is short, and thus a long-time moving image can be recorded on a compact disc. Development of a practical blue semiconductor light emitting device has been awaited from such various application fields.

In recent years, the development of blue semiconductor LEDs has progressed dramatically, and some products having high reliability and high brightness characteristics comparable to those of red and yellow semiconductor LEDs have become commercially available. Have been. However, while blue semiconductor laser diodes have been reported at the prototype stage, they have still been compared with red and yellow semiconductor laser diodes in terms of continuous oscillation time, threshold current, and reliability. There is room for improvement.

Generally, in a semiconductor laser diode,
As shown in FIG. 1, stimulated emission light is utilized by recombination of electrons in an active region (light emitting region) between PN junctions. Stimulated emission occurs one after another inside the active layer, and the light is repeatedly reflected on both end faces (reflection surface 2) while being amplified, leading to oscillation.

In a semiconductor laser, the reflection surface 2 can be easily formed. Since the refractive index of the crystal layer constituting the active layer is much larger than that of air, the crystal layer has a sufficiently large reflectance to air. This reflecting surface 2 is obtained by simply breaking, ie cleaving, along the crystal plane of the crystal. As shown in FIG. 2, the reflection surface 2 is obtained by cleaving the waveguide made of the active layer in the direction of arrow B. When relatively soft GaAs or the like is used as the substrate of the semiconductor laser, it can be easily cleaved. That is, a cut is made on the back side of the substrate using a scriber, and then the substrate is split together with the substrate. Alternatively, a blade may be applied to the edge of the substrate and split along with the substrate along the crystal plane. By splitting, the cleavage surface of the waveguide becomes the reflection surface. Thus, a laser resonator and a semiconductor laser are formed.

However, in the case of a blue semiconductor laser, there are cases where the conventional method cannot be used. A blue semiconductor laser generally uses sapphire as a substrate. It is well known that a GaN intermediate layer is deposited on a sapphire substrate, and a GaN-based light-emitting portion composed of a cladding layer, an active layer, and the like is formed thereon. The reason why GaN is used for the intermediate layer is that a flat and high-quality film can be formed. A GaN-based multilayer crystal is grown on the intermediate layer. The problem is that when creating a cleaved surface after forming the active layer,
The sapphire substrate is too hard to break easily.

[0007] Even if you forcibly crack,
GaN and GaN forming the active layer are crystallographically integrated, and it is difficult to cleave a desired active region. In other words, there is no guarantee that a laser oscillation resonator can always be obtained. Therefore, an etching method is used as a method for generating a reflection surface. In this method, both surfaces of the active layer are partially removed by a reactive ion etching method, and an end face formed at this time is used as a reflection surface. However, a problem with this method is that the reflecting surface is not a perfect mirror. This surface has fine irregularities. If irregularities are formed on the reflection surface, irregular reflection occurs when light generated in the active layer is reflected on the reflection surface, and the efficiency is reduced. As a result, the threshold current for laser oscillation increases.

[0008]

SUMMARY OF THE INVENTION As a blue semiconductor laser, GaN is used as an intermediate layer on a sapphire substrate,
There is known a method of forming a GaN-based light-emitting portion composed of a cladding layer, an active layer, and the like thereon. An etching method is used as a method for generating a reflection surface which is a laser resonance surface. In this method, both surfaces of the active layer are partially removed by a reactive ion etching method, and an end surface formed at this time is used as a reflection surface. However, the problem with this method is that the reflection surface does not become a perfect mirror surface and fine irregularities are formed on the surface. If the reflection surface has irregularities, light generated in the active layer is reflected on the reflection surface. Irregular reflection occurs on the surface, and the efficiency is reduced. As a result, the threshold current for laser oscillation increases. This generates extra heat and leads to a decrease in reliability. Therefore, in this specification, in order to solve these problems, a reflection surface (resonance surface) having a high reflectance for semiconductor laser oscillation is used.
And a method for reliably forming a reflecting surface with less scattering by cleavage.

[0009]

An intermediate layer made of AlN (aluminum nitride) or the like is formed on a substrate such as sapphire, which is difficult to cleave. On the intermediate layer, a light emitting element constituting layer composed of an active layer serving as a resonator is formed. Thereafter, a portion under the layer constituting the resonator is removed by selective etching. Thereby, a part of the resonator physically floats from the sapphire substrate. The raised resonator is cleaved by an ultrasonic method or a conventional method such as applying a blade to form a reflection surface having a high reflection rate.

[0010]

【Example】

Embodiment 1: When growing a single crystal film on a substrate, it is common to use a single crystal substrate having a lattice constant substantially equal to the lattice constant (distance between atoms constituting the crystal) of the single crystal film to be grown. . This is because the crystal arrangement of the single crystal substrate has a strong influence on the atomic arrangement of a film grown thereon. If a substrate having the same lattice constant as the film is selected, the film grown on the substrate is likely to be single crystal. However, in the case of GaN, there is no substrate having a lattice substantially equal to the lattice constant of GaN. For this reason, it is common to use single crystal sapphire (Al ₂ O ₃ ) having a lattice constant different by 15.4% for the substrate. On the surface of the sapphire substrate, a nitride single-layer crystal film or a multilayer crystal film required for blue laser oscillation cannot be formed as it is. Therefore, an intermediate layer is formed between the sapphire substrate and the nitride crystal film.

As shown in FIG. 3, this intermediate layer is deposited with AlN. The AlN layer has a thickness of 50 nm to 200 nm,
It is formed at a relatively low temperature of about 500 ° C. by MOCVD (organic metal CVD). As the intermediate layer, a flat film can be easily formed, and a nitride single crystal film thereon can be easily formed.
Also, considering the ease of selective etching and the like, AlN is preferable. Further, as shown in FIG. 3, n-type Ga
A light emitting portion composed of a cladding layer based on N and GaN, an active layer and the like, and a cladding layer, and further a p-type GaN and the like are deposited. This makes up the basic part of a laser diode. Next, as shown in FIG. 4, both sides are etched to expose n-type GaN on the negative electrode side. Incidentally, p-type GaN is on the positive electrode side.

FIG. 5 shows the basic parts of a laser diode formed according to the present invention on a wafer. The portion not forming the laser diode is removed by reactive ion etching up to the sapphire substrate. The active layer and the cladding layer made of a nitride polycrystalline film serving as a waveguide are left longer than the n-type GaN part. The hatched portion indicates the intermediate layer made of AlN. By selective etching, the AlN intermediate layer under the portion that becomes the waveguide, which has been left longer, is removed. FIG. 6 shows the wafer after this portion of the AlN intermediate layer has been removed. Thus, a part of the waveguide, that is, the part that becomes the resonator can be physically floated in a cantilever shape. Here, as shown in FIG. 7, a cleavage surface 15 is formed by applying a blade to the resonator portion in the direction C or applying ultrasonic vibration. Thus, the waveguide can be easily cleaved without touching the hard sapphire substrate, and a reflection surface having a desired reflectance can be formed. As shown in FIG. 8, these waveguides are separated by dicing in the horizontal and vertical directions. Thereafter, the separated waveguide is placed in a package and wired to the n-type GaN electrode and the p-type GaN electrode, whereby a blue semiconductor laser is formed.

Embodiment 2 In Embodiment 1, dicing was performed to separate each chip after cleavage was performed to form a resonator. As one application example of the present invention, after dicing in the horizontal direction, To perform selective etching. Thereby, a part of the etching process can be omitted. This will be described. The description up to the point of etching up to the n-type GaN portion is the same as that of the first embodiment, and will not be repeated.
However, there is no need for a process of cutting down to the sapphire substrate by reactive ion etching. FIG. 9 shows a wafer on which a waveguide is formed, which is diced in the horizontal direction indicated by D. By dicing, reactive ions
The AlN layer as the intermediate layer is exposed to the outside without etching. Incidentally, the diced surface has many irregularities and cannot be used as a reflector. By selectively etching this AlN layer, the waveguide portion and the N-type GaN portion are physically lifted from the sapphire surface in a cantilevered beam shape. FIG. 10 shows this state. The cross-hatched portion indicated by 14 indicates a portion that has been etched to form a cavity. After this, FIG.
As shown in FIG. 1, cleavage is performed along the E direction to form a reflection surface. Then, as shown in FIG.
The wiring in the n-type GaN electrode and the p-type GaN electrode in the package is the same. According to the above method, the process of performing reactive ion etching to the sapphire substrate to perform selective etching and exposing the AlN layer can be omitted.

[0014]

As described above, according to the present invention, when a semiconductor laser is formed on a substrate that is very hard and difficult to process, such as a sapphire substrate, a blue laser semiconductor having a cleavage surface can be formed more easily than the conventional method. Can be provided. Further, as compared with a conventional method of forming a reflection surface by an etching method, a reflection surface having a higher reflectance can be realized, and a threshold current for oscillation can be reduced. Thereby, a highly reliable and long-life semiconductor laser can be provided. Obviously, it is applicable to a wide range of applications, not just the examples disclosed herein.

[Brief description of the drawings]

FIG. 1 is a diagram showing light emission due to recombination in a semiconductor laser.

FIG. 2 is a diagram showing formation of a reflecting surface by cleavage.

FIG. 3 shows the deposition of a nitride layer.

FIG. 4 is a diagram showing exposure of n-type GaN by etching.

FIG. 5 is an isometric view of a laser chip on a wafer.

FIG. 6 is an isometric view of a laser chip on a wafer.

FIG. 7 is an isometric view of a laser chip on a wafer.

FIG. 8 is an isometric view of a diced laser chip.

FIG. 9 is an isometric view of a laser chip on a wafer.

FIG. 10 is an isometric view of a laser chip on a wafer.

FIG. 11 is an isometric view of a laser chip on a wafer.

FIG. 12 is an isometric view of a diced laser chip.

[Explanation of symbols]

 1: Reflecting surface 1 2: Reflecting surface 2 3: P-type semiconductor 4: N-type semiconductor 5: Positive electrode 6: Negative electrode 7: Active region (light-emitting region) 8: Sapphire substrate 9: AlN intermediate layer 10: n-type GaN 11: clad layer 12: active layer 13: p-type GaN 14: selectively etched AlN layer 15: cleaved surface

Claims (8)

[Claims] In a semiconductor device having a selectively etchable intermediate layer and a cleavable single-layer film crystal or a multi-layer film crystal formed on a substrate which is difficult to cleave, said single-layer film crystal or a multi-layer film crystal By selectively etching the intermediate layer located below the single-layer film crystal or the multi-layer film crystal, the single-layer film crystal or the multi-layer film crystal is floated in a beam shape and the resonance is formed by cleaving the single-layer film crystal or the multi-layer film crystal. Semiconductor laser device having a cavity. 2. The semiconductor laser device according to claim 1, wherein said cleavable single-layer film crystal or multi-layer film crystal is a nitride semiconductor crystal. 3. The semiconductor laser device according to claim 1, wherein said selectively etchable intermediate layer is AlN. 4. The semiconductor laser device according to claim 1, wherein said substrate difficult to cleave is sapphire. 5. A semiconductor device having a selectively etchable intermediate layer and a cleavable single-layer film crystal or a multi-layer film crystal formed on a substrate which is difficult to cleave. By selectively etching the intermediate layer located below the single-layer film crystal or the multi-layer film crystal, the single-layer film crystal or the multi-layer film crystal is floated in a beam shape, and the single-layer film crystal or the multi-layer film crystal is cleaved. A method for forming a resonator. 6. The method for forming a resonator of a semiconductor laser device according to claim 5, wherein said cleavable single-layer film crystal or multi-layer film crystal is a nitride semiconductor crystal. 7. The method according to claim 5, wherein the selectively etchable intermediate layer is AlN. 8. The method according to claim 5, wherein the substrate that is difficult to cleave is sapphire.