JP3338778B2 - Nitride compound semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride-based compound semiconductor (In _x Al _Y Ga _{1 -XYN} , X ≧ 0, Y ≧ 0, X + Y
≦ 1) Related to laser element.

[0002]

2. Description of the Related Art FIG. 14 is a sectional view showing the structure of a conventional nitride-based compound semiconductor laser device. Sapphire C-plane substrate 101
A GaN low-temperature buffer layer 102 (thickness 30 nm), an n-type contact layer 103 made of Si-doped n-type GaN (thickness 3 μm), and a crack prevention layer made of Si-doped n-type In _0.05 Ga _0.95 N (thickness 0.1 μm) ) And Si-doped n-type Al _0.07
N-type cladding layer 1 consisting of Ga _0.93 N layer (0.4 μm thickness)
04, n-type optical confinement layer 105 composed of a Si-doped n-type GaN layer (0.1 μm thick), undoped In _0.2 Ga _0.8 N
Well layer (2.5 nm thick) and undoped In _0.05 Ga _0.95
7-period multiple quantum well active layer 106 composed of an N barrier layer (5 nm thick), p-type optical confinement layer 107 composed of Mg-doped p-type GaN (0.1 μm thick), Mg-doped p-type Al _0.07 Ga
_0.93 N (0.4 μm thick) p-type cladding layer 108, M
p-type contact layer 109 made of g-doped p-type GaN (thickness 0.2 μm), insulating layer 110, p-electrode 111 made of Ni (first layer) and Au (second layer), Ti (first layer), and Al This is a laser structure formed of an n-electrode 112 made of (second layer), and this structure allows room-temperature pulse oscillation (threshold current density
Jth = 4.6KA / cm ² ) and internal loss is 54cm
^-1 (Applied Physics Letters (APP
LIED PHYSISCS LETTERS), Vol. 69, p. 1568, 19
1996).

In general, the internal loss can be reduced by reducing the number of wells. The present inventors prototyped the following nitride-based compound semiconductor laser having a layer configuration similar to that of FIG. 14 as a comparative example. GaN low-temperature buffer layer 102 (thickness 30 nm) and n-type contact layer 10 made of Si-doped n-type GaN (thickness 2 μm) on a sapphire C-plane substrate 101
3, Si-doped n-type Al _0.08 Ga _0.92 N (0.4 μm thickness)
N-type clad layer 104 composed of
N-type optical confinement layer 105 (thickness: 0.1 μm), undoped In _0.2 Ga _0.8 N well layer (thickness: 3 nm), and undoped In _0.05 Ga _0.95 N barrier layer (thickness: 6 nm) having four cycles. Quantum well active layer 106, Mg-doped p-type GaN
(Thickness 0.1 μm), a p-type optical confinement layer 107 made of Mg-doped p-type Al _0.08 Ga _0.92 N (0.4 μm thick), a p-type cladding layer 108 made of Mg-doped p-type GaN (0.2 μm thick)
m), a p-electrode 111 made of Ni (first layer) and Au (second layer), an insulating layer 110, Ti
This is a laser structure formed of an n-electrode 112 made of (first layer) and Al (second layer). The internal loss of the laser structure was measured to be 45 cm ⁻¹ , which was slightly larger than when the number of wells was seven. Although the internal loss was reduced, it still had a large value.

In these conventional nitride-based compound semiconductor laser devices, the barrier layer is made of In _x Ga ₁ -xN (0.02 ≦ X ≦
0.05 and a thickness of 5 to 6 nm), and GaN (0.1 μm in thickness) is used for the optical confinement layer.

[0005]

As described above, the conventional nitride-based compound semiconductor laser device is
It has a large internal loss as compared with an As-based or AlGaInP-based laser diode. The internal loss of the conventional semiconductor laser diode is mainly caused by the free electron absorption and the valence band absorption of the well layer, so that the value of the internal loss is not so large. Also, the internal loss can be reduced by reducing the number of wells in the multiple quantum well (by reducing light confinement in the well layer), and the internal loss in the quantum well structure can be reduced to 5 cm ^-1 or less.

On the other hand, in the nitride-based compound semiconductor laser device, as described above, even if the number of quantum wells is reduced, the internal loss is not significantly improved.

The present inventors have found that this is because the nitride-based compound semiconductor In _x Al _Y Ga _{1 -XYN} (X ≧ 0, Y ≧ 0, X
+ Y ≦ 1). FIG.
GaN crystal, In _0.05 Ga _0.95 N crystal, Al _0.15 G
a shows the absorption spectrum of the _0.85 N crystal. Focusing on the absorption spectrum of the GaN crystal in FIG.
It can be seen that absorption is present even on the lower energy side than the band gap of N (approximately 362 nm in converted wavelength). For example, when the emission wavelength of a laser diode is 420 nm, a GaN crystal has an absorption of about 40 cm ⁻¹ and In
_0.05 Ga _0.95 N crystal, the Al _0.15 Ga _0.85 N crystal, respectively 70cm ^-1, absorption of 14cm ^-1 is present. It was found that the internal loss in the conventional laser diode can be explained by the light confinement ratio of each layer obtained from the absorption spectrum and the structure of the laser diode.
From these facts, the present inventors have found that there is absorption on the low energy side of the nitride-based compound semiconductor, and this absorption on the low energy side exists in each layer. It has been found that the absorption in the barrier layer in the active layer having the above and the absorption in the light confinement layer having a large ratio of light confinement are large, which causes the internal loss to increase.

When the internal loss is large, the differential quantum efficiency (increase in the number of output photons / increase in the number of injected electrons above the oscillation threshold) decreases as characteristics of the laser diode,
There are adverse effects such as an increase in threshold current density.
These can be factors that hinder the realization of a high-power laser.

Accordingly, an object of the present invention is to provide a nitride-based compound semiconductor laser device having a small internal loss by changing the material, structure, and film thickness of a barrier layer of a multiple quantum well active layer and an optical confinement layer. It is to realize a high-performance laser element.

[0012]

Means for Solving the Problems The present invention is generally formed on the substrate type _{In X Al Y Ga 1-XY} N (X ≧ 0, Y ≧
0, X + Y ≦ 1), a conductive semiconductor clad layer comprising:
General formula In _X Al _Y Ga _{1 -XY} N (X ≧ 0, Y ≧ 0, X +
Y ≦ 1) and a general formula In _X
A quantum well active layer formed of two or more semiconductor layers of one or more well layers and barrier layers composed of Al _Y Ga _{1 -XYN} (X ≧ 0, Y ≧ 0, X + Y ≦ 1); I
n _X Al _Y Ga _{1 -XY} N (X ≧ 0, Y ≧ 0, X + Y ≦ 1)
A semiconductor optical confinement layer of general formula In _x Al _Y Ga
_1-XYN (X ≧ 0, Y ≧ 0, X + Y ≦ 1) and a conductive semiconductor cladding layer formed in the above order, wherein the band gap of the light confinement layer is a well layer And larger than the barrier layer and smaller than the cladding layer, and the thickness of the light confinement layer is 0.05 μm.
The present invention relates to a semiconductor laser device characterized by the following.

In general, the threshold current density of a semiconductor laser is defined by the current density when the gain and the loss are balanced from the laser oscillation conditions. The loss is the sum of the internal loss and the mirror loss, of which the mirror loss can be reduced by applying a highly reflective coating.
Therefore, if the internal loss is reduced according to the present invention, a nitride semiconductor laser device having a low threshold current density can be obtained.
As shown in the following examples, in the semiconductor laser device of the present invention, light confinement is slightly reduced as compared with the conventional structure. Therefore, the gain for the oscillation mode tends to decrease, but the magnitude of the threshold current density is determined by the ratio between the internal loss and the optical confinement coefficient, and has a trade-off relationship. As shown in the following examples, according to the present invention, the ratio between the internal loss and the optical confinement is improved as compared with the related art, so that the threshold current density is also improved.

The differential quantum efficiency of a laser diode is proportional to mirror loss / (internal loss + mirror loss). Therefore, the differential quantum efficiency increases as the internal loss decreases. For example, in the case of the semiconductor laser device of the first embodiment, in which the cavity length is 800 μm and the reflectance is 80%, and the high reflection coat is 80%,
The differential quantum efficiency is doubled compared to the conventional structure. As described above, the reduction of the internal loss can increase the efficiency at the same time as the reduction of the threshold current density, and can be said to be an important technique for developing a high-power laser.

The cause of the large internal loss of the nitride-based compound semiconductor laser is absorption existing on the lower energy side of the band gap of the nitride-based compound semiconductor. This lower energy side absorption is present in each layer of the laser element. However, in particular, the absorption in the barrier layer and the light confinement ratio in the active layer having a band gap close to the emission wavelength is large, and the absorption in the light confinement layer is large, which causes the internal loss to increase. ing. Therefore, widening the gap or reducing the thickness of the barrier layer or the light confinement layer reduces the amount of absorption and the internal loss.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail based on embodiments with reference to the drawings. Reference Example 1 A reference example will be described with reference to FIGS. FIG. 1 is a semiconductor
A structural cross-sectional view of the body laser element, FIG. 2 is a diagram showing the band structure of the semiconductor laser device.

On a sapphire C-plane substrate 1, a GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ^-3 , thickness 2 μm), Si-doped n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type GaN (silicon concentration 4
× 10 ¹⁷ cm ⁻³ , 0.1 μm thick) n-type optical confinement layer 5, In _0.2 Ga _0.8 N well layer (2.5 nm thick) and Al
_An undoped multiple quantum well active layer 6 (7 wells) composed of a _0.05 Ga _0.95 N barrier layer (thickness: 5 nm) and a Mg-doped p-type GaN (Mg concentration: 2 × 10 ¹⁷ cm ⁻³ , thickness: 0.1 μm) p-type optical confinement layer 7, Mg-doped p-type Al _0.1 G
a p-type cladding layer 8 made of a _0.9 N (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm);
A p-type contact layer 9 having a concentration of 2 × 10 ¹⁷ cm ⁻³ and a thickness of 0.2 μm) is sequentially grown to form an LD structure.
In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in this embodiment .

Next, the n-electrode 12 is dry-etched.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Reference Example 1 is different from the conventional nitride-based compound semiconductor laser device.
In the above configuration, a wide gap was formed by using Al _0.05 Ga _0.95 N as the barrier layer. As a result, FIG.
As shown in (2), at the oscillation wavelength of 423 nm, the absorption in the barrier layer was greatly reduced, and the internal loss was 25 cm ^-1 . 2 compared to the conventional semiconductor laser device described in the above document.
Internal losses as low as 9 cm ^-1 have been reduced.

Reference Example 2 A reference example will be described with reference to FIGS. FIG. 1 is a structural sectional view of a semiconductor laser device, and FIG. 3 is a diagram showing a band structure of the semiconductor laser device.

On a sapphire C-plane substrate 1, a GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ^-3 , thickness 2 μm), n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type GaN (silicon concentration 4
× 10 ¹⁷ cm ⁻³ , 0.1 μm thick) n-type optical confinement layer 5, In _0.2 Ga _0.8 N well layer (2.5 nm thick) and Al
_An undoped multiple quantum well active layer 6 (4 wells) comprising a _0.05 Ga _0.95 N barrier layer (5 nm in thickness), and a Mg-doped p-type GaN (Mg concentration: 2 × 10 ¹⁷ cm ⁻³ , thickness: 0.1 μm) p-type optical confinement layer 7, Mg-doped p-type Al _0.1 G
a p-type cladding layer 8 made of a _0.9 N (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm);
A p-type contact layer 9 having a concentration of 2 × 10 ¹⁷ cm ⁻³ and a thickness of 0.2 μm) is sequentially grown to form an LD structure.
In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in this embodiment .

Next, the n-electrode 12 is dry-etched.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Reference Example 2 is different from the nitride-based compound semiconductor laser device of the comparative example having the same number of quantum wells in that the above structure uses Al _0.05 Ga _0.95 N as a barrier layer. Wide gap was implemented. As a result, as shown in FIG.
At 23 nm, the absorption in the barrier layer was significantly reduced, and the internal loss was 24 cm ^-1 . The internal loss was reduced by as much as 21 cm ^-1 as compared with the semiconductor laser device of the comparative example.

Reference Example 3 A reference example will be described with reference to FIGS. Figure 1
A structural cross-sectional view of the body laser element, FIG 4 is a diagram showing the band structure of the semiconductor laser device.

On a sapphire C-plane substrate 1, a GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ^-3 , thickness 2 μm), a Si-doped layer n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type Al _0.05 Ga _0.95 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³⁾ , A 0.1 μm thick n-type optical confinement layer 5 and an In _0.2 Ga _0.8 N well layer (thickness 2.
5 nm) and an undoped multiple quantum well active layer 6 (7 wells) composed of an In _0.05 Ga _0.85 N barrier layer (5 nm thick), Mg
Doped p-type Al _0.05 Ga _0.95 N (Mg concentration 2 × 10 ¹⁷ c
m ⁻³ , thickness 0.1 μm), p-type optical confinement layer 7, M
g-doped p-type Al _0.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ c
m ⁻³ , 0.4 μm thick) p-type cladding layer 8, Mg
Doped p-type GaN (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness of 0.
An LD structure is formed by sequentially growing a p-type contact layer 9 of 2 μm). In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in the present reference example .

Next, the n-electrode 12 is dry-etched.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Reference Example 3 has the same structure as that of the conventional nitride-based compound semiconductor laser device described in the above-mentioned document, but has
A wide gap was formed using l _0.05 Ga _0.95 N.
As a result, as shown in FIG.
At m, the absorption in the light confinement layer was significantly reduced, and the internal loss was 21 cm ^-1 . The internal loss was reduced by as much as 33 cm ^-1 as compared with the conventional semiconductor laser device described in the above document.

Reference Example 4 A reference example will be described with reference to FIGS. Figure 1
A structural cross-sectional view of the body laser element, FIG 5 is a diagram showing the band structure of the semiconductor laser device.

On a sapphire C-plane substrate 1, a GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ^-3 , thickness 2 μm), a Si-doped layer n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type Al _0.05 Ga _0.95 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³⁾ , A 0.1 μm thick n-type optical confinement layer 5 and an In _0.2 Ga _0.8 N well layer (thickness 2.
Undoped multiple quantum well active layer 6 (4 wells) consisting of 5 nm) and an In _0.05 Ga _0.85 N barrier layer (5 nm thick), Mg
Doped p-type Al _0.05 Ga _0.95 N (Mg concentration 2 × 10 ¹⁷ c
m ⁻³ , thickness 0.1 μm), p-type optical confinement layer 7, M
g-doped p-type Al _0.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ c
m ⁻³ , 0.4 μm thick) p-type cladding layer 8, Mg
Doped p-type GaN (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness of 0.
An LD structure is formed by sequentially growing a p-type contact layer 9 of 2 μm). In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in the present reference example .

Next, the n-electrode 12 is dry-etched.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Reference Example 4 has the same structure as the nitride-based compound semiconductor laser device of the comparative example but has an Al _0.05 G
a Wide gap was formed using _0.95N . Thus, as shown in FIG. 15, at the oscillation wavelength of 423 nm,
Absorption in the optical confinement layer is greatly reduced, and the internal loss is
cm ⁻¹ . The internal loss was reduced by as much as 25 cm ^-1 as compared with the semiconductor laser device of the comparative example.

Reference Example 5 A reference example will be described with reference to FIGS. Figure 1
A structural cross-sectional view of the body laser element, FIG. 6 is a diagram showing the band structure of the semiconductor laser device.

On a sapphire C-plane substrate 1, a GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ^-3 , thickness 2 μm), Si-doped n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type GaN (silicon concentration 4
× 10 ¹⁷ cm ⁻³ , 0.1 μm thick) n-type optical confinement layer 5, In _0.2 Ga _0.8 N well layer (2.5 nm thick) and In
Undoped multiple quantum well active layer 6 (7 wells) consisting of _0.05 Ga _0.85 N barrier layer (thickness 3 nm), Mg-doped p-type Ga
P-type optical confinement layer 7 made of N (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.1 μm), Mg-doped p-type Al _0.1 Ga _0.9
P-type cladding layer 8 made of N (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm), p-type cladding layer made of Mg-doped p-type GaN (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.2 μm) The contact layer 9 is sequentially grown to form an LD structure. In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in this embodiment .

Next, the n-electrode 12 is dry-etched.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

In the nitride-based compound semiconductor laser device of Reference Example 5, the barrier layer thickness was set to 3 nm and the thickness was reduced in comparison with the conventional nitride-based compound semiconductor laser device described in the above-mentioned document. Thereby, the absorption in the barrier layer was reduced, and the internal loss was 24 cm ⁻¹ . The internal loss was reduced by as much as 30 cm ^-1 as compared with the conventional semiconductor laser device described in the above document.

The thickness of the barrier layer needs to be 5 nm or less, preferably 1 nm to 5 nm, more preferably 3 nm to 5 nm.

Reference Example 6 A reference example will be described with reference to FIGS. FIG. 1 is a structural sectional view of a semiconductor laser device, and FIG. 7 is a diagram showing a band structure of the semiconductor laser device.

A GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ^-3 , thickness 2 μm) on a sapphire C-plane substrate 1, n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type GaN (silicon concentration 4
× 10 ¹⁷ cm ⁻³ , 0.1 μm thick) n-type optical confinement layer 5, In _0.2 Ga _0.8 N well layer (2.5 nm thick) and In
_An undoped multiple quantum well active layer 6 (4 wells) consisting of a _0.05 Ga _0.85 N barrier layer (thickness: 3 nm) and a Mg-doped p-type GaN (Mg concentration: 2 × 10 ¹⁷ cm ⁻³ , thickness: 0.1 μm) p-type optical confinement layer 7, Mg-doped p-type Al _0.1 G
a p-type cladding layer 8 made of a _0.9 N (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm);
A p-type contact layer 9 having a concentration of 2 × 10 ¹⁷ cm ⁻³ and a thickness of 0.2 μm) is sequentially grown to form an LD structure.
In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in this embodiment .

Next, the n-electrode 12 is formed by dry etching.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Reference Example 6 was thinner than the nitride-based compound semiconductor laser device of Comparative Example, except that the thickness of the barrier layer was set to 3 nm in the above configuration. This reduces absorption in the barrier layer,
The internal loss was 28 cm ^-1 . The internal loss was reduced by as much as 17 cm ^-1 as compared with the semiconductor laser device of the comparative example.

(Embodiment 1 ) An embodiment will be described with reference to FIGS. FIG. 1 is a structural sectional view of a semiconductor laser device of the present invention, and FIG. 8 is a diagram showing a band structure of the semiconductor laser device.

A GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ^-3 , thickness 2 μm) on a sapphire C-plane substrate 1, n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type GaN (silicon concentration 4
× 10 ¹⁷ cm ⁻³ , 0.03 μm thick) n-type optical confinement layer 5, In _0.2 Ga _0.8 N well layer (2.5 nm thick) and In
_An undoped multiple quantum well active layer 6 (7 wells) composed of a _0.05 Ga _0.95 N barrier layer (5 nm thick) and a Mg-doped p-type GaN (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.03 μm) p-type optical confinement layer 7, Mg-doped p-type Al _0.1 G
a p-type cladding layer 8 made of a _0.9 N (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm);
A p-type contact layer 9 having a concentration of 2 × 10 ¹⁷ cm ⁻³ and a thickness of 0.2 μm) is sequentially grown to form an LD structure.
In this embodiment, the substrate is a sapphire substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Further, in the present invention, doping of the light confinement layer is not essential, but in the present embodiment, doping is preferable.

Next, the n-electrode 12 is dry-etched.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Example 1 has a light confinement layer having a thickness of 0.0
The thickness was set to 3 μm, and the thickness was reduced. Thereby, the absorption in the light confinement layer was reduced, and the internal loss was 19 cm ^-1 .
The internal loss was reduced by as much as 35 cm ^-1 as compared with the semiconductor laser device described in the above document.

In the present invention , the thickness of the optical confinement layer needs to be 0.05 μm or less, preferably 0.01 to 0.05 μm, but also depends on the number of wells in the multiple quantum well active layer. Therefore, when the number of wells is 1 to 4, the thickness is more preferably 0.025 to 0.05 μm, and the number of wells is 5
0.01 to 0.05 μm is more preferable when the number of wells is 10 to 10, and 0.01 to 0.03 when the number of wells exceeds 10.
μm is more preferred.

(Embodiment 2 ) An embodiment will be described with reference to FIGS. FIG. 1 is a structural sectional view of a semiconductor laser device of the present invention, and FIG. 9 is a diagram showing a band structure of the semiconductor laser device.

A GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 2 μm) on a sapphire C-plane substrate 1, n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type GaN (silicon concentration 4
× 10 ¹⁷ cm ⁻³ , 0.03 μm thick) n-type optical confinement layer 5, In _0.2 Ga _0.8 N well layer (2.5 nm thick) and In
_An undoped multiple quantum well active layer 6 (4 wells) consisting of a _0.05 Ga _0.95 N barrier layer (thickness: 5 nm) and a Mg-doped p-type GaN (Mg concentration: 2 × 10 ¹⁷ cm ⁻³ , thickness: 0.03 μm) p-type optical confinement layer 7, Mg-doped p-type Al _0.1 G
a p-type cladding layer 8 made of a _0.9 N (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm);
A p-type contact layer 9 having a concentration of 2 × 10 ¹⁷ cm ⁻³ and a thickness of 0.2 μm) is sequentially grown to form an LD structure.
In this embodiment, the substrate is a sapphire substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Further, in the present invention, doping of the light confinement layer is not essential, but in the present embodiment, doping is preferable.

Next, the n-electrode 12 is dry-etched.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Example 2 has a light confinement layer having a thickness of 0.03 in the above-described configuration as compared with the nitride-based compound semiconductor laser device of Comparative Example.
The film thickness was reduced to μm. Thereby, the absorption in the light confinement layer was reduced, and the internal loss was 15 cm ⁻¹ .
The internal loss was reduced by as much as 30 cm ^-1 as compared with the semiconductor laser device of the comparative example.

Reference Example 7 A reference example will be described with reference to FIGS. Figure 1 is semi-conductive
A structural cross-sectional view of the body laser element, FIG. 10 is a diagram showing the band structure of the semiconductor laser device.

On a sapphire C-plane substrate 1, a GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 2 μm), a Si-doped layer n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type GaN (silicon concentration 4
FIG. 1 shows an n-type optical confinement layer 5 and an In _0.2 Ga _0.8 N well layer (thickness: 2.5 nm) each having a thickness of × 10 ¹⁷ cm ⁻³ and a thickness of 0.1 μm).
GaN / Al _0.1 G showing an energy band of 0
undoped multiple quantum well active layer 6 (7 wells) composed of a _0.9 N superlattice barrier layer (thickness 5 nm, layer thickness ratio 1: 1), Mg
Doped p-type GaN (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness of 0.
P-type optical confinement layer 7 of 1 μm), Mg-doped p-type Al _0.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness of _0.1 μm).
4 μm), p-type cladding layer 8, Mg-doped p-type G
An LD structure is formed by sequentially growing a p-type contact layer 9 made of aN (Mg concentration: 2 × 10 ¹⁷ cm ⁻³ , thickness: 0.2 μm). In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in this embodiment .

Next, the n-electrode 12 is formed by dry etching.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Reference Example 7 is different from the conventional nitride-based compound semiconductor laser device described in the above-mentioned document in that it has a GaN barrier layer in the above configuration.
A wide gap was formed using a / Al _0.1 Ga _0.9 N superlattice. As a result, as shown in FIG. 15, at the oscillation wavelength of 423 nm, the absorption in the barrier layer was significantly reduced, and the internal loss was 25 cm ⁻¹ . The internal loss was reduced by as much as 29 cm ^-1 as compared with the conventional semiconductor laser device described in the above document.

Reference Example 8 A reference example will be described with reference to FIGS. FIG. 1 is a structural sectional view of a semiconductor laser device, and FIG. 11 is a diagram showing a band structure of the semiconductor laser device.

A GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 2 μm) on a sapphire C-plane substrate 1, An n-type clad layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm), Si-doped n-type GaN and Si-doped Al _0.1 as shown in the energy band of FIG. Superlattice with Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ^-3 , thickness 0.1 μm)
m, an n-type optical confinement layer 5 having a film thickness ratio of 1: 1), In _0.2
Ga _0.8 N well layer (2.5 nm thick) and In _0.05 Ga _0.85 N
An undoped multiple quantum well active layer 6 (7 wells) composed of a barrier layer (5 nm thick), Mg-doped p-type GaN and Mg-doped Al _0.1 G as shown in the energy band of FIG.
a superlattice with _0.9 N (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness
P-type optical confinement layer 7 of 0.1 μm, film thickness ratio 1: 1), M
g-doped p-type Al _0.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ c
m ⁻³ , 0.4 μm thick) p-type cladding layer 8, Mg
Doped p-type GaN (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness of 0.
An LD structure is formed by sequentially growing a p-type contact layer 9 of 2 μm). In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in the present reference example .

Next, the n-electrode 12 is dry-etched.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Reference Example 8 has a G confinement layer as an optical confinement layer in the above-described configuration, as compared with the conventional nitride-based compound semiconductor laser device described in the above document.
A wide gap was formed using an aN / Al _0.1 Ga _0.9 N superlattice. As a result, as shown in FIG. 15, at the oscillation wavelength of 423 nm, the absorption in the light confinement layer was significantly reduced, and the internal loss was 21 cm ⁻¹ . The internal loss was reduced by as much as 33 cm ^-1 as compared with the conventional semiconductor laser device described in the above document.

Reference Example 9 A reference example will be described with reference to FIGS. Figure 1 is semi-conductive
A structural cross-sectional view of the body laser element, FIG. 12 is a diagram showing the band structure of the semiconductor laser device.

A GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 2 μm) on a sapphire C-plane substrate 1, n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm); Si-doped n-type GaN (silicon concentration 4
× 10 ¹⁷ cm ⁻³ , 0.1 μm thick) n-type optical confinement layer 5, In _0.2 Ga _0.8 N well layer (2.5 nm thick) and In
Undoped multiple quantum well active layer 6 (7 wells) consisting of _0.02 Al _0.06 Ga _0.92 N barrier layer (5 nm thick), Mg-doped p-type GaN (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness 0.1)
μm), p-type optical confinement layer 7, Mg-doped p-type A
l _0.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ cm ^-3 , thickness 0.4
μm), Mg-doped p-type Ga
An LD structure is formed by sequentially growing a p-type contact layer 9 made of N (Mg concentration: 2 × 10 ¹⁷ cm ⁻³ , thickness: 0.2 μm). In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in this embodiment .

Next, the n-electrode 12 is formed by dry etching.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Reference Example 9 is different from the conventional nitride-based compound semiconductor laser device described in the above-mentioned document in that it has the same structure as the barrier layer in the above structure.
_A wide gap was formed using _0.02 Al _0.06 Ga _0.92 N. As a result, as shown in FIG.
At 23 nm, the absorption in the light confinement layer is greatly reduced,
The internal loss was 29 cm ^-1 . The internal loss was reduced by as much as 25 cm ^-1 as compared with the conventional semiconductor laser device described in the above document.

Reference Example 10 A reference example will be described with reference to FIGS. Figure 1 shows a half
A structural cross-sectional view of the conductive laser element, FIG. 13 is a diagram showing the band structure of the semiconductor laser device.

On a sapphire C-plane substrate 1, a GaN buffer layer 2 (thickness 30 nm), an n-type contact layer 3 made of Si-doped n-type GaN (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 2 μm), An n-type cladding layer 4 made of n-type Al _0.1 Ga _0.9 N (silicon concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.4 μm), Si-doped n-type Al _u Ga _1-u N (however,
0 ≦ u ≦ 0.1, and the gap gradually widens toward the cladding layer side as shown in FIG. N consisting of silicon concentration of 4 × 10 ¹⁷ cm ⁻³ and thickness of 0.1 μm)
Type optical confinement layer 5, In _0.2 Ga _0.8 N well layer (thickness 2.5 n
m) and an In _0.05 Ga _0.85 N barrier layer (5 nm in thickness), an undoped multiple quantum well active layer 6 (7 wells), a Mg-doped p-type Al _u Ga _1-u N (where 0 ≦ u ≦ 0) a .1, .mg concentration 2 × 10 ¹⁷ c that gradually wide gapped toward the cladding layer side as shown in FIG. 13
m ⁻³ , thickness 0.1 μm), p-type optical confinement layer 7, M
g-doped p-type Al _0.1 Ga _0.9 N (Mg concentration 2 × 10 ¹⁷ c
m ⁻³ , 0.4 μm thick) p-type cladding layer 8, Mg
Doped p-type GaN (Mg concentration 2 × 10 ¹⁷ cm ⁻³ , thickness of 0.
An LD structure is formed by sequentially growing a p-type contact layer 9 of 2 μm). In this embodiment , a sapphire substrate is used as the substrate, but another substrate such as a GaN substrate or a SiC substrate may be used. Although doping of the light confinement layer is not essential, it is preferable to dope in the present reference example .

Next, the n-electrode 12 is formed by dry etching.
After partially exposing the n-type contact layer 3 to be formed, an n-electrode 12 made of Ti / Al is formed on the exposed n-type contact layer. On the other hand, after the insulating layer 10 is formed, a p-type electrode 11 made of Ni / Au is formed on the insulating layer 10 by making contact with the p-type contact layer 9.

The nitride-based compound semiconductor laser device of Reference Example 10 is different from the conventional nitride-based compound semiconductor laser device described in the above-mentioned document in that the material from GaN to Al _0.1 Ga _0.9 N is gradually used as the optical confinement layer in the above configuration. To widen the gap. As a result, FIG.
As shown in FIG. 5, at the oscillation wavelength of 423 nm, the absorption in the light confinement layer was significantly reduced, and the internal loss was 21 cm ⁻¹ . The internal loss was reduced by as much as 33 cm ^-1 as compared with the conventional semiconductor laser device described in the above document.

[0069]

According to the present invention, there is provided a nitride-based compound semiconductor laser device having a small internal loss by changing the material, structure, and film thickness of the barrier layer and the optical confinement layer of the multiple quantum well active layer. As a result, a high-performance laser device can be realized.

[Brief description of the drawings]

FIG. 1 is a structural sectional view of a semiconductor laser device of the present invention.

FIG. 2 is a diagram showing a band structure of the semiconductor laser device of Reference Example 1.

FIG. 3 is a view showing a band structure of a semiconductor laser device of Reference Example 2;

FIG. 4 is a view showing a band structure of a semiconductor laser device of Reference Example 3;

FIG. 5 is a view showing a band structure of a semiconductor laser device of Reference Example 4;

FIG. 6 is a view showing a band structure of a semiconductor laser device of Reference Example 5;

FIG. 7 is a diagram showing a band structure of a semiconductor laser device of Reference Example 6;

FIG. 8 is a diagram showing a band structure of the semiconductor laser device of Example 1 .

FIG. 9 is a diagram showing a band structure of a semiconductor laser device of Example 2 .

FIG. 10 is a view showing a band structure of a semiconductor laser device of Reference Example 7 ;

FIG. 11 is a view showing a band structure of a semiconductor laser device of Reference Example 8 ;

FIG. 12 is a view showing a band structure of a semiconductor laser device of Reference Example 9 ;

FIG. 13 is a view showing a band structure of the semiconductor laser device of Reference Example 10 ;

FIG. 14 is a structural sectional view of a conventional semiconductor laser device.

FIG. 15 is a diagram showing an absorption spectrum of a nitride-based compound semiconductor.

[Explanation of symbols]

 1, 101 sapphire C-plane substrate 2, 102 buffer layer 3, 103 n-type contact layer 4, 104 n-type cladding layer 5, 105 n-type optical confinement layer 6, 106 undoped multiple quantum well active layer 7, 107 p-type optical confinement Layer 8, 108 p-type cladding layer 9, 109 p-type contact layer 10, 110 insulating layer 11, 111 p-electrode 12, 112 n-electrode

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-8-83954 (JP, A) Jpn. J. Appl. Phys. Vol 37 Part 2 No. 4B (1998) pp. L444-L446 Jpn. J. Appl. Phys. Vol 37 Part 2 No. 10B (1996) pp. L1315-L1317J. Appl. Phys. Vol. 81 No. 9 (1997) p. 5930−5934

Claims (1)

(57) [Claims] 1. A general formula In _x Al _Y G formed on a substrate.
a _1-XY N (X ≧ 0, Y ≧ 0, X + Y ≦ 1), and a conductive semiconductor cladding layer of the general formula In _X Al _Y Ga _1-XY
A semiconductor optical confinement layer composed of N (X ≧ 0, Y ≧ 0, X + Y ≦ 1); and a general formula In _X Al _Y Ga _1-XY N (X ≧ 0,
A quantum well active layer formed of two or more semiconductor layers of one or more well layers and barrier layers each composed of Y ≧ 0, X + Y ≦ 1, and a general formula In _X Al _Y Ga _1-XY N (X ≧
0, Y ≧ 0, X + Y ≦ 1) and a general formula In _X Al _Y Ga _1-XY N (X ≧ 0, Y ≧ 0,
X + Y ≦ 1), wherein the band gap of the light confinement layer is larger than that of the well layer and the barrier layer and smaller than that of the cladding layer. A semiconductor laser device wherein the thickness of the light confinement layer is less than 0.05 μm.