JP2792177B2 - Semiconductor laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used as a light source for laser printers, bar code readers, optical disks, and the like, and more particularly to a visible light semiconductor laser having an oscillation wavelength of 670 nm or less. is there.

[Conventional technology]

Semiconductor lasers are used as light sources for optical information processing devices such as optical communication devices and optical disk devices, and semiconductor lasers having various structures have been proposed.

As examples of conventional visible light semiconductor lasers, see pp. 746, 19a-ZR-4, 19a-ZR-5, Proceedings of Autumn 1987, and 198
Proceedings of the Spring Meeting of Spring 2009, 886 pages, 1p-ZC-2, 1p-ZC-3, 1p
-ZC-4.

[Problems to be solved by the invention]

FIG. 3 shows an example of the above-described conventional semiconductor laser.
In a conventional semiconductor laser, a Ga _0.5 In _0.5 P active layer (4) serving as a light emitting region is formed on an n-GaAs substrate (1) by Al _0.5 In _0.5 P or (Al _0.4 Ga _0.6 ) having a larger forbidden band width. ) _0.5 I
n _0.5 P cladding layers (3) and (5) are provided, and a current blocking layer (7) having a conductivity opposite to that of the adjacent side of the crystal stack is provided adjacent to the crystal stack. And a semiconductor layer (contact layer) (10), and then electrodes (11) and (12).

However, in a semiconductor laser having this structure, the astigmatic difference is 10
It is as large as about μm. The astigmatic difference is related to the lateral refractive index difference, and the lateral refractive index difference is determined by the thickness of the cladding layer (5) on the ridge side of the semiconductor laser and the absorption loss of the current blocking layer (7). In addition, the cladding layer (5)
The ridge side thickness and ridge width of the
Related to I _th . Therefore, there is a problem that can not be controlled lateral refractive index difference independently of the oscillation threshold current I _th.

Further, in the structure using Si ₃ N ₄ as shown in FIG. 4, the astigmatism can be reduced, but the manufacturing process of the semiconductor laser becomes complicated, and there is a disadvantage that the yield and reliability of the device are deteriorated. .

[Means for solving the problem]

In the semiconductor laser of the present invention, the oscillation threshold current I _th is controlled by the ridge width and the thickness of the ridge side cladding layer, and the lateral refractive index difference ΔN is controlled by the current block layer.
Al _z Ga ₁ -z As (0z1) and GaAs have a structure that can be controlled by their thickness and composition ratio. That is, the active layer serving as the light emitting region is formed of Ga _0.5 In _0.5 P and (Al _0.4 Ga _0.6 ) _0.5 In _0.5
It is formed of a multiple quantum well structure (MQW) composed of P and has a larger forbidden band width (Al _y Ga _1-y ) _0.5 In _0.5 P (0.5
y1) has a double heterostructure sandwiching the active layer in the cladding layer, adjacent the cladding layer comprises a Ga _0.5 In _0.5 P layer having the same conductivity and the clad layer, the Ga _0.5 an In
Adjacent to the _0.5 P layer, a second (Al _y Ga _1-y ) _0.5 In _0.5 P (0.
5y1) A current blocking layer having a cladding layer and a Ga _0.5 In _0.5 P layer, and having Al _z Ga ₁ -z As (0z ₁ ) and GaAs having opposite conductivity to the cladding layer sequentially laminated on both sides of the ridge stripe. And a GaAs contact layer is further provided.

Embodiment 1 Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of one embodiment of the present invention. First, the first crystal growth was performed by MO-VPE method at a growth temperature of 630 ° C. and a growth pressure of 75
Under the condition of rr, a Si-doped GaAs buffer layer (2) was deposited on a GaAs substrate (1) at a carrier concentration of 1 × 10 ¹⁸ cm ^-3 at 0.5 μm
Doped n- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer (3), carrier concentration 5 × 10 ¹⁷ cm ^-3 1 μm, undoped
Ga _0.5 In _0.5 P, three well layers of 40Å and undoped (Al
_0.4 Ga _0.6 ) _0.5 In _0.5 P, consisting of two barrier layers 40 mm thick
MQW active layer (4), Zn-doped p- (Al _0.6 Ga _0.6 ) _0.5 In
_0.5 P first cladding layer (5) Carrier concentration 6 × 10 ¹⁷ cm ^-3 ,
0.25 μm, Zn-doped p-Ga _0.5 In _0.5 P etching stopper layer (6), carrier concentration 1 × 10 ¹⁸ cm ^-3 at 40 °, Zn-doped p- (Al _0.6 Ga _0.6 ) _0.5 In _0.5 P second cladding layer (8) A 0.7 μm carrier density of 6 × 10 ¹⁷ cm ⁻³ , a Zn-doped p-Ga _0.5 In _0.5 P heterobuffer layer (9) and a 0.2 μm thickness of 1 × 10 ¹⁸ cm ⁻³ of carrier density are sequentially stacked.

Next, an SiO ₂ film serving as an etching mask for forming the ridge stripe (13) and a mask for selective growth is formed to a thickness of 2000 °, and a resist is applied.
An SiO ₂ stripe is formed in the direction, and subsequently, etching is performed up to the etching stopper layer (6) using a hydrogen bromide-based etchant and a sulfuric acid-based etchant. Ridge width W
Is 5 μm. Then, the second crystal growth is performed by MO-VPE method using Si-doped A
l _0.5 Ga _0.5 As current blocking layer (71), carrier concentration 1 × 1
0 ¹⁸ cm ^-3 is a 0.3 μm thick, Si-doped GaAs current blocking layer (7
2) Selectively grow a carrier concentration of 3 × 10 ¹⁸ cm ^-3 with a thickness of 0.4 μm.

Next, after removing SiO ₂ , MO-VP
By the E method, a Zn-doped GaAs contact layer (10) and a carrier concentration of 2 × 10 ¹⁹ cm ⁻³ are grown to 3 μm. Subsequently, the electrodes (11) and (12) are formed to complete the semiconductor laser of the present invention.

Since the semiconductor laser according to the present invention is an MQW active layer, the oscillation threshold current I _th = 35 mA, the oscillation wavelength is 650 nm, and the astigmatic difference is 5 μm.

Second Embodiment Next, a second embodiment will be described. The layer structure of the semiconductor laser is as shown in FIG. 2, and is the same as that of the first embodiment shown in FIG. The difference is in the direction of the ridge stripe (13), here the ridge stripe (13) in the [0] direction.
Is the point that forms In this embodiment, since the current path is narrow, carriers can be injected efficiently. As a result, the oscillation threshold current I _th can be reduced by several mA as compared with the first embodiment. The astigmatic difference was about 5 μm as in Example 1.

Further, the semiconductor laser of the present invention can be manufactured not only by the MO-VPE method but also by the MBE method, the MO-MBE method, the gas and the MBE method.

〔The invention's effect〕

In the present invention, the injected current is injected into the MQW active layer (4) through the p-first cladding layer (8) from the striped window between the current blocking layers (71) and (72). . The carriers injected into the active layer (4) diffuse in the lateral direction of the active layer (4) to form a gain distribution and start laser oscillation. At this time, since the carrier density of the active layer (4) is as high as 1 to 2 × 10 ¹⁸ cm ⁻³ , the carrier diffusion length in the active layer (4) is shortened, and the gain distribution mainly depends on the ridge stripe (13). Is formed in the portion of the active layer (4), and the shape becomes steep. As a result, only the portion below the ridge stripe (13) has a high gain, and the outside becomes a loss region.

On the other hand, the laser beam protrudes from the active layer (4) and spreads in the vertical direction. At this time, the light that has protruded into the p-first cladding layer (5) is reflected by Al _z G on the p-first cladding layer (5).
a _1-z As current blocking layer (71), and next to the current blocking layer (71), there is a GaAs current blocking layer (72). The absorption coefficient changes and the current blocking layer (72)
Works as an absorption layer. As a result, the ridge stripe (13)
A positive refractive index difference ΔN occurs near the lower active layer, and the fundamental transverse mode oscillation is maintained. The wavefront of light in the waveguide mechanism due to absorption loss is described by CooK and Nash (J. Applied
Physics; 46p1660 (1975)), and the radius of curvature R of the wavefront is expressed as follows using the complex refractive index.

Here, _{Re (Δ eff) = Re (} eff0 - eff1) = N eff0 -N eff1 ≡ΔN Imag (Δ eff) = Imag (eff0 - eff1) = Imag (eff1) = α / 2k k = 2π / λ ridge stripe Lower _eff0 = N _eff0 (only the real part) Ridge stripe outer _eff1 = N _eff1 + i (α /
2k) The existence of such a curvature of the wavefront of light causes astigmatism. That is, the astigmatic difference can be reduced by reducing the imaginary part of the complex refractive index outside the ridge. In order to reduce the imaginary part, it is only necessary to reduce the absorption loss. By changing the Al composition and the thickness of the current blocking layer (71), the absorption loss can be reduced, and the change width can be widely recognized.

As described above, an astigmatic difference of 5 μm can be realized.

Further, since the active layer has the MQW structure, a low oscillation threshold current and an improvement in temperature characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor laser of the present invention having a ridge stripe in the [01] direction, and FIG. 2 is a sectional view of a semiconductor laser of the present invention having a ridge stripe in the [0] direction. 3 and 4 are cross-sectional views of a conventional semiconductor laser. 1 to 4, reference numerals 1... N-GaAs substrate, 2... N-GaAs buffer layer, 3.
... n- (Al _y Ga _1-y ) _0.5 In _0.5 P cladding layer ( _{0.5 y}
1), 4... MQW active layer (well layer: Ga _0.5 In _0.5 P, barrier layer: (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P), 5... P- (Al _y G
a _1-y ) _0.5 P first cladding layer, 6 p-Ga _0.5 In _0.5 P
An etching stopper _{layer, 71 ...... n-Al z Ga} 1-z As current blocking layer (0.5z1), 72 ...... n- GaAs current blocking _{layer, 8 ...... p- (Al y Ga} 1-y) 0.5 In 0.5 P second cladding layer, 9 ... p-Ga _0.5 In _0.5 P hetero buffer layer, 10 ...
p-GaAs contact layers, 11, 12,... electrodes, 13.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (1)

(57) [Claims] 1. A formed in the active layer becomes a light emitting region and the _{Ga 0.5 In 0.5 P (Al 0.4} Ga 0.6) 0.5 In 0.5 consists P multiple quantum well structure (MQW), larger than these forbidden耐幅(Al _y Ga
_1-y ) _0.5 In _0.5 P (0.5 ≦ y ≦ 1) having a double hetero structure sandwiching the active layer with a cladding layer, and adjacent to the cladding layer, having the same conductivity as the cladding layer, Ga _0.5 In _0.5 P
A second ridge stripe-shaped (Al _y G) layer having the same conductivity as the cladding layer and a ridge stripe adjacent to the Ga _0.5 In _0.5 P layer.
a _1-y ) _0.5 In _0.5 P (0.5 ≦ y ≦ 1) cladding layer and Ga _0.5 In
A current block having a _0.5 P layer and sequentially laminating Al _z Ga _{1 -z} As (0 <z ≦ 1) having opposite conductivity to the cladding layer and GaAs acting as an absorption layer on both sides of the ridge stripe. the layers were arranged, further provided GaAs contact layer, the Al _z Ga
A semiconductor characterized in that a positive refractive index difference is generated near the active layer below the ridge stripe by controlling the Al composition and thickness of the _1-z As current blocking layer, thereby reducing absorption loss outside the ridge stripe. laser.