JPH07176826A - Gallium nitride compound semiconductor laser element - Google Patents

Abstract

PURPOSE:To form a P-type GaN layer and a P-type GaAlN layer, which are brought into a low resistance state evenly within their surfaces, by a method wherein the width of the waveguide of a gallium nitride compound semiconductor laser element is specified and an annealing is performed. CONSTITUTION:A GaN buffer layer 2 is formed on a sapphire substrate 1. An N-type GaN contact layer 3, an N-type GaAlN clad layer 4 and an N-type InGaN active layer 5 are each doped with Si and are formed on the layer 2. Moreover, a P-type GaAlN clad layer 6 and a P-type GaN contact layer 7 are each doped with Mg and are formed. Then, a mask is formed on the uppermost P-type Mg-doped GaN layer 7 and an etching is performed until the layer 3 is exposed to form a waveguide of a stripe width formed in a width of 50mum. After the etching, the mask is peeled from the layer 7 and an annealing is performed, whereby hydrogen gas in a semiconductor layer doped with a P-type dopant is discharged from the side surfaces of the semiconductor layer and an Mg-doped GaN layer 7 and a GaAlN layer 6, which are brought into a low resistance state evenly within their surfaces, can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride-based compound semiconductor laser device having a pn junction.

[0002]

2. Description of the Related Art Semiconductor lasers currently in practical use are
There are only those that emit in the red region of the visible light region, semiconductor lasers that emit in the blue ultraviolet region have not yet been obtained,
Early realization is desired. Among them, Ga _1-xy In _x A
since it has a band gap in the visible region in a direct transition-type gallium nitride compound semiconductor is represented by _{l y N (0 ≦ x ≦} 1,0 ≦ y ≦ 1), as a promising material for blue semiconductor laser Is expected.

Conventionally, a gallium nitride-based compound semiconductor doped with a p-type dopant has only to be a high resistance i-type,
It was impossible to obtain a laser device because the p-type could not be formed. However, recently, p-type conversion has become possible (Japanese Patent Laid-Open Nos. 2-257679 and 3-2183).
25, JP-A-5-183189, etc.), p-
There is a possibility of realizing an n-junction type semiconductor laser device.

Annealing described in JP-A-5-183189 is a useful method for obtaining a p-type gallium nitride compound semiconductor. However, a laser device using a gallium nitride-based compound semiconductor has not yet been realized, although the p-type conversion was realized by this method.

[0005]

DISCLOSURE OF THE INVENTION As described above,
Although a laser device using a gallium nitride-based compound semiconductor has not been realized, if a laser device of this short wavelength can be realized, it will be very useful for information processing, a writing light source and the like. Therefore, it is an object of the present invention to realize a short wavelength laser device using a gallium nitride compound semiconductor.

[0006]

In order to solve the above problems, the inventors of the present invention use the annealing technique disclosed in Japanese Patent Laid-Open No. 5-183189 to reduce the width of the waveguide to form a semiconductor layer. We have made it possible to realize a semiconductor laser device by uniformly reducing the resistance.

That is, in the gallium nitride-based compound semiconductor laser device of the present invention, an n-clad layer made of at least an n-type gallium nitride-based compound semiconductor is formed as a waveguide on the surface of the n-type GaN layer, and an n-type or p-type gallium nitride. A double-heterostructure laser device in which an active layer made of a compound semiconductor and a p-clad layer made of a p-type gallium nitride compound semiconductor are sequentially laminated in a stripe shape, and the stripe width of the waveguide is 50 μm or less. It is characterized by being.

FIG. 1 is a cross-sectional view showing a gallium nitride-based compound semiconductor laser device of the present invention, in which a buffer layer 2 made of GaN and an n-type GaN contact layer 3 doped with Si are formed on a sapphire substrate 1. . On the Si-doped n-type GaN contact layer 3, as a waveguide,
Si-doped n-type GaAlN cladding layer 4, Si-doped n-type InGaN active layer 5, Mg-doped p-type GaAlN cladding layer 6, Mg-doped p-type G
It has a double hetero structure in which the aN contact layer 7 is formed, and as the electrodes, a p-layer ohmic electrode 8 is formed on the p-type GaN contact layer 7 and an n-layer ohmic electrode 9 is formed on the n-type GaN contact layer 3. It is made up of

FIG. 2 is a sectional view of the laser device shown in FIG. 1 viewed from the electrode side. As described above, in the laser device of the present invention, the waveguide has a stripe shape and the width thereof is narrowed.

To form the above-mentioned waveguide, after stacking n-type and p-type gallium nitride-based compound semiconductor layers, etching is performed so as to obtain the shape shown in FIG. Dry etching is used as the etching method. For dry etching, for example, ion milling, ECR etching,
There are reactive ion etching (RIE), ion beam assisted etching and the like. At this time, the width d of the waveguide stripe is 50 μm or less, and more preferably 20 to 5 μm.

The semiconductor thus obtained in a desired shape is annealed to make the gallium nitride-based compound semiconductor layer doped with a p-type dopant p-type.
The detailed conditions of the annealing at this time are described in the above-mentioned Japanese Patent Laid-Open No. 5-183189.

[0012]

In the semiconductor laser device of the present invention, when the width of the waveguide is 50 μm or less and annealing is performed as described above, hydrogen gas in the semiconductor layer doped with the p-type dopant is easily released. is there. Although p-type can be obtained only by annealing as in the conventional case, hydrogen gas is released from the side surface of the semiconductor layer. Therefore, it is easier to release hydrogen gas in the semiconductor layer when annealing is performed by narrowing the width of the waveguide. Therefore, the entire surface of the semiconductor layer doped with the p-type dopant can be made in-plane uniformly into the p-type, and a semiconductor laser device having a high light emission output can be obtained. The detailed operation of the annealing is shown in the above-mentioned Japanese Patent Laid-Open No. 5-183189.

There is another advantage in reducing the width of the waveguide. A semiconductor laser emits a current by exchanging electrons between the p-layer and the n-layer, and emits light. However, if the width of the waveguide is narrowed, electrons are concentrated and enter there, so that the current density in the semiconductor layer is large. The oscillation threshold current decreases.

[0014]

The gallium nitride-based semiconductor laser device of the present invention will be described in detail in the following examples with reference to the drawings.

[First Embodiment] First, a GaN buffer layer 2 is grown to 200 angstroms on a sapphire substrate 1 using an MOCVD apparatus. Then, S on the buffer layer 2
i-doped n-type GaN contact layer 3 having a thickness of 4 μm and S
The i-doped n-type GaAlN cladding layer 4 is 0.2 μm.
200 n-type InGaN active layer 5 doped with m and Si
Angstrom and p-type GaAl doped with Mg
N-clad layer 6 of 0.2 μm, Mg-doped p-type G
The aN contact layer 7 is sequentially grown to a film thickness of 0.5 μm.

Next, a mask having a desired shape is formed on the uppermost Mg-doped p-type GaN layer 7, and etching is performed until the n-type GaN layer 3 is exposed as shown in FIG. A waveguide having a thickness of 50 μm is obtained.

After the etching is completed, the mask is peeled off, and 60
Annealing is performed at 0 ° C. for 10 minutes to reduce the resistance of the Mg-doped GaN contact layer 7 and the Mg-doped GaAlN cladding layer 6 to obtain a pn junction.

After annealing, a p-electrode forming mask is formed, and Ni / Au is vapor-deposited on the p-layer to form a p-layer ohmic electrode 8 as shown in FIG. After vapor deposition, the mask is peeled off, a mask for forming an n electrode is subsequently formed, and Al is vapor deposited on the n layer to form an n layer ohmic electrode 9, as shown in FIG.

The wafer thus obtained was cut into chips to obtain a semiconductor laser device.

COMPARATIVE EXAMPLE A buffer layer and n-type and p-type semiconductor layers are grown on a substrate in the same manner as in the above example. After growth of the semiconductor layer, a mask is formed on the p-type GaN contact layer so that the stripe width of the waveguide becomes 60 μm, and n
Etching is performed until the type GaN contact layer is reached.
A semiconductor laser device was formed in the same manner as in the above example except for the above.

Laser oscillation is performed on the thus-formed material to obtain an oscillation threshold current density, an oscillation wavelength,
The device life was compared. Then, the oscillation threshold current density of 3 k is obtained in the conventional case where the width of the waveguide is 60 μm.
While the oscillation wavelength was 420 nm at A / cm ² and the device lifetime was about 1 hour, the semiconductor laser device obtained in this example has an oscillation wavelength of 420 nm at an oscillation threshold current density of ² kA / cm ^2. The life was remarkably improved to about 100 hours.

[0022]

As described above, by annealing the gallium nitride-based compound semiconductor laser device with the waveguide width of 50 μm or less, the hydrogen gas in the semiconductor layer doped with the p-type dopant is transferred from the side surface of the semiconductor layer. It is easy to emit, and it becomes possible to obtain a p-type GaN layer and a p-type GaAlN layer whose in-plane uniform resistance is reduced. Therefore, according to the present invention, a high-luminance gallium nitride-based compound semiconductor laser device with increased emission intensity can be realized.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a semiconductor laser device obtained in a process of an embodiment of the present invention.

FIG. 2 is a view of the semiconductor laser device obtained in the process of the embodiment of the present invention as seen from the electrode side.

[Explanation of symbols]

 1 ... Sapphire substrate 2 ... Buffer layer 3 ... Si-doped n-type GaN contact layer 4 ... Si-doped n-type GaAlN cladding layer 5 ... Si-doped n-type InGaN active layer 6 ... Mg-doped p-type GaAlN cladding layer 7 ... Mg-doped p-type GaN contact layer 8 ... p-layer ohmic electrode 9 ... n-layer ohmic electrode d ... Waveguide Stripe width

Claims (1)

[Claims] 1. An n-clad layer made of at least an n-type Gallium nitride compound semiconductor as a waveguide on the surface of an n-type GaN layer, an active layer made of an n-type or p-type gallium nitride compound semiconductor, and a p-type nitride. A gallium nitride-based compound semiconductor laser, which is a laser element having a double hetero structure in which a p-clad layer made of a gallium-based compound semiconductor is sequentially laminated in a stripe shape, and the waveguide has a stripe width of 50 μm or less. element.