JPH06196804A - Surface emitting type semiconductor laser element - Google Patents

Abstract

PURPOSE:To provide a surface emitting type semiconductor laser element with a semiconductor multilayer-film reflecting mirror film having low resistance and enabling high reflectivity. CONSTITUTION:A double hetero-structure section consisting of an n-type Ga0.6Al0.4As first clad layer, a p-type GaAs active layer formed onto said first clad layer and a p-type Ga0.6Al0.4As second clad layer 5 formed onto said active layer is provided, and a second semiconductor multilayer-film reflecting mirror 7, in which p-type AlAs first semiconductor layers 7a and a p-type Ga0.85Al0.15As second semiconductor layer 7b are laminated alternately through i-type Ga0.85 Al0.15As second semiconductor layer 7c, is formed onto the double hetero-structure section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting semiconductor laser device.

[0002]

2. Description of the Related Art In recent years, semiconductor laser devices have been used as light sources in optical electronics such as optical information devices and optical communication devices, and have been actively researched and developed. Recently, with the demand for integration of electronic devices, etc., a surface-emitting type semiconductor laser device has been developed in which a semiconductor layer is epitaxially grown on a substrate and laser light is extracted from a direction perpendicular to the substrate surface. Such a semiconductor laser device is described, for example, in "Surface emitting laser" (published September 25, 1990) published by Ohmsha.

Such a surface-emitting semiconductor laser device has reflecting mirrors above and below the active layer in order to form an optical resonator. As this reflecting mirror, for example, the energy corresponding to the oscillation wavelength (here, the energy corresponding to the oscillation wavelength is the energy obtained by converting the oscillation wavelength into energy) is larger than the bandgap energy (the bandgap of large energy). ) Is used to form a semiconductor multilayer film reflecting mirror, and
The second semiconductor layer having a smaller bandgap energy than the semiconductor layer and the first semiconductor layer, that is, the first semiconductor layer having a refractive index difference.
The semiconductor layers and the second semiconductor layers are alternately stacked.

FIG. 4 is a sectional view of a conventional AlGaAs surface emitting semiconductor laser device.

Reference numeral 21 is an n-type GaAs substrate.
An n-type semiconductor multilayer film reflecting mirror (n-type G
a _0.85 Al _0.15 As second semiconductor layer / n-type AlAs first semiconductor layer 30 pair) 22, n-type Ga _0.6 Al _0.4 As clad layer 23, p-type GaAs active layer 24, p-type Ga _0.6 A
A heterojunction portion 26 made of _0.4 As cladding layer 25 is formed. On this heterojunction 26, a p-type semiconductor multilayer film reflecting mirror (25 pairs of p-type Ga _0.85 Al _0.15 As second semiconductor layer / p-type AlAs first semiconductor layer) 27, p-type Ga _0.85 Al _0.15 As contact layer 28 are arranged in this order.

The p-type semiconductor multilayer film reflecting mirror 27 is provided with an H ⁺ ion implantation current block portion 29 into which H ⁺ ions (hydrogen ions) are implanted except for the central portion and the upper side thereof. A p-type ohmic electrode 30 is formed on the upper surface of the p-type contact layer 28 except for a central portion serving as a light extraction port, and an n-type ohmic electrode 31 is formed on the entire lower surface of the n-type GaAs substrate 21. ing.

[0007]

By the way, in order to increase the refractive index, such a semiconductor multilayer film reflecting mirror has a large refractive index difference, that is, a large difference in bandgap energy E _g. And the second semiconductor layer are selected. However, the p-type AlAs first semiconductor layer and the p-type Ga are shown in FIG.
As shown in the band energy diagram of the junction of the _0.85 Al _0.15 As second semiconductor layer, in the first semiconductor layer and the second semiconductor layer having a large difference in band gap energy E _g , the hetero barrier width W generated at the junction is Since it becomes large, there is a problem that the probability of a current (hole in the case of p-type) passing through the hetero barrier due to the tunnel effect becomes small and the resistance becomes extremely high. As a result, in particular, almost no current flows through the p-type semiconductor multilayer film reflecting mirror 27, and even when a current flows, the oscillation threshold current increases and the element characteristics deteriorate due to heat.

In order to solve this problem, there is a method of increasing the carrier concentration of the semiconductor multilayer film reflecting mirror, but such a method has a problem that the reflectance is lowered because the absorption loss of light increases. In addition, even in the semiconductor multilayer film reflecting mirror film having a gradient in the composition ratio, there is a new problem that the reflectance is similarly reduced.

The present invention has been made in view of the above-mentioned various problems, and an object of the present invention is to provide a semiconductor laser device having a semiconductor multilayer film reflecting mirror film having a low resistance and a high reflectance.

[0010]

A surface emitting semiconductor laser device of the present invention comprises a first clad layer, an active layer formed on the first clad layer, and a second layer formed on the active layer. A surface provided with a double heterostructure part composed of a clad layer and a semiconductor multilayer film reflecting mirror composed of a semiconductor layer having a bandgap energy larger than the energy corresponding to the oscillation wavelength on at least one of the upper and lower sides of the double heterostructure part. In the light emitting semiconductor laser device, the semiconductor multilayer film reflecting mirror includes a first semiconductor layer of a first conductivity type and a second semiconductor layer of the same conductivity type as the first semiconductor layer and having a smaller bandgap than the first semiconductor layer. The semiconductor layer and the second semiconductor layer are alternately arranged via the non-doped third semiconductor layer having the same composition as the second semiconductor layer and having a small layer thickness.

[0011]

According to the configuration of the present invention, the semiconductor multilayer film reflecting mirror has the first semiconductor layer of the first conductivity type and the band gap which is the same conductivity type as the first semiconductor layer and which is larger than that of the first semiconductor layer. When the small second semiconductor layers are alternately formed via the non-doped third semiconductor layers having the same composition as the second semiconductor layers and the small thickness, the junction between the second semiconductor layers and the third semiconductor layers is Since the width of the hetero barrier at the hetero junction between the first semiconductor layer and the third semiconductor layer can be reduced and the non-doped third semiconductor layer has a small thickness, the high reflection of the semiconductor multilayer film reflecting mirror can be achieved. It is possible to reduce the resistance and the resistance.

[0012]

EXAMPLE A surface-emitting type semiconductor laser device according to an example of the present invention will be described below with reference to FIG. still,
2 (a) and 2 (b) are enlarged views of essential parts of the first and second semiconductor multilayer film reflecting mirrors in FIG. 1, respectively.

In the figure, 1 is a 600 μm square n-type GaAs substrate. On the surface of this substrate 1, {oscillation wavelength λ / (4
n ₁ )} Å thick n-type AlAs first semiconductor layer (31 layers in total)
2a, 2a, ... and {oscillation wavelength λ / (4n ₂ )} Åthick n-type Ga _0.85 Al _0.15 As second semiconductor layer (30 layers in total)
The first semiconductor multilayer film reflecting mirror 2 is formed by alternately stacking 2b, 2b, .... Here, n ₁ and n ₂ are the refractive indices of the first and second semiconductor layers 2a and 2b, respectively.

An n-type Ga _0.6 Al _0.4 As first cladding layer 3 having a layer thickness of 1.5 μm and a p layer having a layer thickness of 1 μm are formed on the reflecting mirror 2.
-Type GaAs active layer 4, p-type Ga _0.6 Al _{0.4 with} a layer thickness of 1 μm
The As second cladding layer 5 is laminated in this order to form the double hetero structure portion 6.

On the second clad layer 5, a p-type AlAs first semiconductor layer (carrier concentration 2 × 10 ¹⁸ cm ^-3 , total 26 layers) 7a having {oscillation wavelength λ / (4n ₃ )} Å thickness, 7a,
..., {oscillation wavelength λ / (4n ₄ ) -2 × t} Å thickness n
Type Ga _0.85 Al _0.15 As second semiconductor layer (carrier concentration 2
X10 ¹⁸ cm ^-3 , 25 layers in total) 7b, 7b, ... are alternately laminated with non-doped i-type Ga _0.85 Al _0.15 As third semiconductor layers 7c, 7c, ... Having a layer thickness tÅ. The second semiconductor multilayer film reflecting mirror 7 thus obtained is created. Here, n ₃ and n ₄ are the first and second semiconductor layers 7a and 7b, respectively.
And the layer thickness t is 30Å in this embodiment.

The second semiconductor multilayer film reflecting mirror 7 has H ⁺ ions (hydrogen) whose conductivity type is n-type in the range of 0.5 μm thickness from the second cladding layer 5 except for the diameter range of 10 μm in the central portion. (Ion) injection current block portion 8 is formed. A layer thickness of 0.5 μm is formed on the second semiconductor multilayer film reflecting mirror 7.
The m-type p-type Ga _0.85 As _0.15 As contact layer 9 is formed. A p-type ohmic electrode 10 made of Au-Cr is formed on the contact layer 9 except for a central portion having a diameter of 10 μm, and an n-type Au-Cr-Sn layer is formed on the lower surface of the n-type GaAs substrate 1. Ohmic electrode 1
1 is formed.

In such a semiconductor laser device, a first semiconductor multilayer film reflecting mirror 2, a first cladding layer 3, an active layer 4, a second cladding layer 5 and a second semiconductor multilayer film reflecting mirror 7 are provided on an n-type GaAs substrate 1. , The contact layer 9 is continuously grown by the MBE method (molecular beam epitaxial growth method) or the MOCVD method (metalorganic chemical vapor deposition method), and then H ⁺ ions are applied from the contact layer 9 side through the mask to the second semiconductor multilayer. It is formed by implanting into a predetermined range of the film reflecting mirror 7 and changing the range to n-type conductivity to form an H ⁺ ion implantation current block section 8.

In such a semiconductor laser device, the second semiconductor multilayer film reflecting mirror 7 has the first semiconductor layer 7a, the same conductivity type as that of the first semiconductor layer 7a, and a band gap larger than that of the first semiconductor layer 7a. The second semiconductor layer 7b having a small energy is alternately formed via the non-doped third semiconductor layer 7c having the same composition ratio as the second semiconductor layer 7b, that is, the same bandgap energy and a small film thickness. There is.

In this structure, as described above, the band gap energy difference is large, that is, the refractive index difference is large.
Since the second semiconductor layers 7a and 7b can be selected, the second semiconductor multilayer film reflecting mirror 7 has a high reflectance of 98% or more, which is equivalent to the conventional one.

In the Ga _{1 -x} Al _x As system, the Al composition ratio x
Is larger, the band gap energy E _g is larger. Therefore, as described above, the larger A is used as the first semiconductor layer 7a.
The Ga _1-x Al x As with l composition ratio x, corresponding to Ga _1-x Al x As small Al composition ratio as the second semiconductor layer 7b, the oscillation wavelength such that each does not absorb light of the oscillation wavelength It is possible to increase the refractive index by selecting such that the difference in the Al composition ratio is large within a range in which the band gap energy is larger than the energy.

Further, since the resistance value of the second semiconductor multilayer film reflecting mirror 7 is as small as 2-3Ω, heat generation in the reflecting mirror 7 can be suppressed, and deterioration of the semiconductor laser element can be suppressed and laser light oscillation can be suppressed. The threshold current could be reduced.

Thus, the resistance of the second semiconductor multilayer film reflecting mirror 7 is
The reason why the resistance value can be reduced is shown in FIG.
This will be described with reference to the band energy diagram of the reflecting mirror 7. Figure
Medium, E _cIs the energy level at the edge of the conduction band, E_VIs the valence band
Edge energy level, E_FIndicates the Fermi level.

Since the third semiconductor layer 7c is non-doped and its Fermi level E _F is higher than the Fermi level E _F of the first semiconductor layer 7a, E _{V of the} first semiconductor layer 7a is increased. And the energy difference E _p between E _F and the third semiconductor layer 7
large energy difference and the energy difference E _i of E _V and E _F of c occurs. Therefore, the width X of the heterobarrier in the heterojunction between the first and third semiconductor layers 7a and 7c is smaller than the width W of the heterobarrier in the conventional first and second semiconductor interlayer heterojunctions shown in FIG. Get smaller. As a result, the tunnel probability that the current tunnels through the hetero barrier increases, so that the resistance due to the hetero barrier in the second semiconductor multilayer film reflecting mirror 7 becomes smaller than in the conventional case. Since the second semiconductor layer 7b and the third semiconductor layer 7c have the same composition,
A homojunction is formed between these layers. Since the barrier formed by such a homojunction has a small energy width, there is almost no increase in resistance due to this barrier. Further, the thickness of the third semiconductor layer 7c can be made sufficiently small as described above, so that the increase in resistance due to being non-doped can be ignored.

Therefore, as described above, the second semiconductor multilayer film reflecting mirror 7 can reduce the resistance value without substantially reducing the reflectance of the first and second semiconductor layers 7a and 7b.

The first semiconductor multilayer film reflecting mirror 2 has the first and second semiconductor layers 2 similarly to the second semiconductor multilayer film reflecting mirror 7.
By providing a non-doped third semiconductor layer having the same composition as the second semiconductor layer 2b between a2b, it is possible to reduce the resistance of the first semiconductor multilayer film reflecting mirror 2 with almost no decrease.

In the n-type semiconductor multilayer film reflecting mirror, electrons having high mobility serve as carriers, and in the p-type semiconductor multilayer film reflecting mirror, holes having low mobility serve as carriers. A more preferable effect can be obtained by providing such an i-type layer.

[0027]

The surface-emitting type semiconductor laser device of the present invention comprises:
The semiconductor multilayer film reflecting mirror includes a first semiconductor layer of a first conductivity type, and a second semiconductor layer of the same conductivity type as the first semiconductor layer and having a bandgap energy smaller than that of the first semiconductor layer.
Since the second semiconductor layer and the third semiconductor layer are alternately arranged with the non-doped third semiconductor layer having the same bandgap energy and the small film thickness, a homojunction is formed at the junction of the second semiconductor layer and the third semiconductor layer. In addition, since the width of the hetero barrier at the junction between the first semiconductor layer and the second semiconductor layer can be reduced, and the thickness of the non-doped third semiconductor layer is small, this semiconductor multilayer film reflection mirror High reflectance and low resistance of the mirror. Therefore, the threshold current of the laser element can be reduced, and the characteristic deterioration due to heat can be suppressed.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of a main part of a semiconductor multilayer film reflecting mirror used in the above-mentioned embodiment.

FIG. 3 is a partial schematic view of an energy band structure of a second semiconductor multilayer-film reflective mirror layer according to the above-mentioned embodiment.

FIG. 4 is a cross-sectional view of a conventional surface emitting semiconductor laser device.

FIG. 5 is a partial schematic view of energy bands of the semiconductor multilayer-film reflective mirror layer of the above-mentioned embodiment.

[Explanation of symbols]

 1 n-type GaAs substrate 3 n-type GaAlAs first clad layer 4 p-type GaAs active layer 5 p-type GaAlAs second clad layer 6 double heterostructure part 7 second semiconductor multilayer film reflector 7a p-type AlAs first semiconductor layer 7b p -Type GaAlAs second semiconductor layer 7c i-type GaAlAs second semiconductor layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toru Ishikawa 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (1)

[Claims] 1. A double heterostructure part comprising a first cladding layer, an active layer formed on the first cladding layer, and a second cladding layer formed on the active layer, the double heterostructure portion comprising: In a surface emitting semiconductor laser device provided with a semiconductor multilayer film reflecting mirror made of a semiconductor layer having a bandgap energy larger than the energy corresponding to the oscillation wavelength on at least one side of the heterostructure part, the semiconductor multilayer film reflecting mirror is The first semiconductor layer of the first conductivity type and the second semiconductor layer of the same conductivity type as the first semiconductor layer and having a smaller band gap than the first semiconductor layer have the same composition as the second semiconductor layer, and A surface-emitting type semiconductor laser device, wherein the surface-emitting type semiconductor laser device is configured by alternately interposing a non-doped third semiconductor layer having a small layer thickness.