JP2616185B2 - Semiconductor laser - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an AlGaInP visible light semiconductor laser having an oscillation wavelength of 0.6 μm.

[Conventional technology]

At present, AlGaInP-based visible light semiconductor lasers having an oscillation wavelength in the 0.6 μm band are being actively developed in order to increase the density of optical disks. AlGaIn reported so far
Most of the P visible light semiconductor lasers are related to semiconductor lasers formed on an N-type substrate. The main laser structure is that an N-type AlGaInP cladding layer, a GaInP active layer, and a P-type AlGaInP cladding layer are formed in this order on a flat N-type substrate, and then the P-type AlGaInP cladding layer is formed into a mesa stripe. This is a structure in which processing is performed and the other parts are embedded with an N-type block layer. The following are examples of presentations on these laser structures. For example, “High-power operation of a transverse-mode st” described in Electronics Letters, Vol. 23, No. 18, pp. 938-939, August 27, 1987.
abilised AlGaInP visible light semiconductor lase
r ", or" High power operatio "described in 1987 19th Solid-state Device and Material Conference Proceedings, pp.115-118.
n of InGaP / InAlP transverse mode stabilized lase
r diodes ". These laser structures are
By embedding a mesa-like stripe with a block layer, it is possible to perform current confinement and form a refractive index step to control transverse mode at the same time by embedding a mesa stripe in a block layer.

[Problems to be solved by the invention]

However, Al formed on these conventional N-type substrates
In the case of a GaInP semiconductor laser, there are upper and lower problems. That is, in the AlGaInP semiconductor laser formed on the N-type substrate, the current injection portion of the mesa stripe is formed by the P-type Al
It is formed of GaInP crystal. On the other hand, it is known that it is difficult to reduce the resistance of the P-type AlGaInP crystal, and it is known that the specific resistance thereof is about one digit higher than that of the N-type AlGaInP crystal. P-type (Al _0.6 Ga _0.4) ) _0.5 I
The specific resistance of n _0.5 P (Zn-doped) is 0.7 to 1.3 Ωcm, whereas the specific resistance of N-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P (Si-doped) is 0.05 to 0.08 Ωcm. The type crystal has higher resistance by about one digit. Therefore, in particular, in a conventional AlGaInP semiconductor laser using a P-type AlGaInP crystal for a current injection portion of a narrow stripe having a width of 3 to 7 μm and a height of about 1 μm, the element resistance is extremely high, and high output and large current operation are required. The saturation of the light output due to heat generation becomes a problem.

[Means for solving the problem]

The configuration of the semiconductor laser of the present invention is as follows.
A part of the second cladding layer having at least a double heterostructure including a first cladding layer of AlGaInP or AlInP, an active layer of GaInP or AlGaInP, and a second cladding layer of AlGaInP or AlInP in this order; A semiconductor laser in which a partially thick mesa-stripe-shaped current injection region is formed, wherein the side surface of the mesa stripe and both sides of the mesa stripe are formed of P-type GaAs or P-type AlGaAs.
Current blocking layer of N-type GaInP or N-type AlG
aInP second current blocking layer, P-type GaAs or P-type
The third current blocking layer made of AlGaAs is covered in this order.

[Action]

1 and 2 show the structure of an AlGaInP semiconductor laser on a P-type substrate of the present invention, and FIG. 3 shows the structure of an AlGaInP visible light semiconductor laser formed on a conventional N-type substrate. Also,
FIG. 4 is an energy band diagram of a portion other than the mesa stripe of the semiconductor laser of the present invention (in the case where the current block layer has a three-layer structure). FIG. FIG. 3 shows an energy band diagram in the case of a current block layer. The semiconductor laser shown in FIG. 2 has an etching stopper layer 122 interposed between the N-type AlGaInP cladding layers 120 and 125 so that the semiconductor laser shown in FIG. Since this is essentially the same as the semiconductor laser of FIG. 1, it will not be described below.

Hereinafter, the operation of the present invention will be described with reference to the structural diagrams of FIGS. 1 and 3 and the energy band diagrams of FIGS. 4 and 5. First, the structure of FIG. 1 will be described. The semiconductor laser shown in FIG. 1 uses three metalorganic thermal decomposition chemical vapor deposition methods (hereinafter referred to as MO).
Abbreviation as VPE method. ) And a mesa processing process. First, in the first crystal growth,
On a P-type GaAs substrate 210, a P-type AlGaInP cladding layer 110, Ga
A double heterostructure including the InP active layer 100 and the N-type AlGaInP cladding layer 120 in this order is formed. Next, in order to form a current injection region, a part of the N-type AlGaInP cladding layer 120 is processed into a mesa shape, and the second crystal growth is used to form three current blocking layers 180, 190, 200 on the mesa side surface and on both sides of the mesa. Embed. Then, in the third crystal growth, N-type Ga
An As-kipping layer 160 is formed. This mesa structure works as a light confinement structure at the same time as the current confinement, and has a function of transverse mode control. Usually, the width of the mesa bottom is about 3 to 7 μm.

On the other hand, a conventional semiconductor laser on an N-type
Shown in the figure. The laser fabrication process and structure are shown in FIG.
It is almost the same as a mold substrate semiconductor laser. The difference between FIG. 3 and FIG. 1 is that in FIG. 3, the substrate 400 is N-type GaAs, whereas in FIG. 1 the substrate 210 is P-type GaAs. Accordingly, in FIG. 3, the mesa cladding layer 330 forming the current injection region is formed of P-type AlGaInP.

As described above in the section of the problem, it is difficult to reduce the resistance of the P-type AlGaInP crystal, and it has been found that the specific resistance thereof is higher by about one digit than that of the N-type AlGaInP crystal.
P-type (Al _0.6 G
a _0.4 ) _0.5 In _0.5 P (Zn doped) has a specific resistance of 0.7 to 1.3Ω
m, whereas N-type (Al _0.5 Ga _0.4 ) _0.5 In _0.5 P (Si
The specific resistance of the dope is 0.05 to 0.08 Ωcm, and the P-type crystal has a higher resistance by about one digit. Therefore, in particular, the width is 3 to 7 μm.
m, P is applied to the current injection portion of a narrow stripe of about 1 μm in height.
In the conventional semiconductor laser shown in FIG. 3 using the type AlGaInP crystal, the element resistance is extremely high, and there is a problem of saturation of the optical output due to heat generation at high output and large current operation.

However, in the semiconductor laser of FIG. 1 of the present invention, since the mesa is formed of N-type AlGaInP having a low resistance of about one digit, it is possible to greatly reduce the element resistance and significantly improve the heat dissipation characteristics. The structure is very suitable for high output.

Another feature of the semiconductor laser of the present invention shown in FIG. 1 is that a potential barrier caused by absorption of oscillation light in the current blocking layer is prevented by forming the current blocking layer into a three-layer structure. Can be Hereinafter, the mechanism will be described in detail with reference to FIGS. FIG. 4 is an energy band diagram at both sides of the mesa stripe of the semiconductor laser of FIG. 1 of the present invention, and FIG. 5 is a conventional example in which the current block layer is made of a single P-type GaAs or AlGaAs (FIG. 3
FIG. As shown in FIG. 5, the current block layer has a single-layer structure and is of P-type GaAs or P-type AlGaAs.
In the case of, the following is known from the study of the conventional AlGaAs laser (reference: S. Yamamoto et al. APL 40).
(5), 1 March 1982, PP.372-374). That is, the light generated in the active layer seeps into the P-type GaAs layer which is the current blocking layer. On the other hand, since the forbidden body width of the P-type GaAs layer is lower than that of the light generated in the GaInP active layer, the P-type GaAs layer absorbs the oscillating light and forms an electron-hole pair in the current blocking layer. However, the diffusion length of electrons and holes in GaAs is ~ 3 μm each,
0.60.6 μm, so that only the electrons in which the internal diffusion length of the generated electron-hole pairs is much larger than the current block layer thickness,
The holes are diffused to both sides of the current blocking layer, and only the holes accumulate (FIG. 5A). Therefore, the potential of the current blocking layer decreases, and finally the effect of the current blocking is lost, and the current confinement structure does not function (FIG. 5 (b)). The thickness of the current block layer is usually about 1 μm. Therefore, the current blocking layer is generally made of N-type GaAs.

However, when the substrate is P-type and the mesa stripe is above the active layer as in the semiconductor laser of the present invention, the current blocking layer must be P-type. Therefore, as shown in FIG. 4, three current blocking layers were used as a structure for preventing the potential of the current blocking layer from lowering due to light absorption. In FIGS. 1 and 4, the current block layers are a first current block layer 180 made of P-type GaAs or P-type AlGaAs, a second current block layer 190 made of N-type GaInP or N-type AIGaInP, and a P-type GaAs. Alternatively, the third current blocking layer 200 made of P-type AlGaAs has a three-layer structure. As shown in FIG. 4 (a), light generated in the active layer is absorbed by the first P-type GaAs current blocking layer, electrons are diffused, and only holes are formed as in FIG. Accumulate in the first current blocking layer. As a result, the potential barrier of the first current blocking layer decreases. However,
As shown in FIG. 4 (b), the holes accumulated in the first current blocking layer have a valence band potential barrier between the first current blocking layer and the second current blocking layer. Cannot flow into the third current blocking layer. For this reason, the third current blocking layer functions normally and functions well as a current blocking layer. Therefore, in the semiconductor laser of the present invention, the potential barrier does not decrease due to the light absorption of the current blocking layer, and a good current confinement structure can always be obtained. In FIG. 4, it is assumed that the third current blocking layer is sufficiently separated from the active layer and hardly absorbs oscillation light.

〔Example〕

Hereinafter, the AlGaInP semiconductor laser on a P-type substrate of the present invention will be described using specific numerical examples. Here, the structure of FIG. 2 will be described as a more optimized structure. The substrate used was a Zn-doped P-type GaAs substrate 210 of 1 × 10 ¹⁹ cm ⁻³ . On the substrate, the MOVPE method at 70 Torr
Buffer layer 140 made of P-type GaAs having a thickness of μm, P-type GaInP layer 130 having a thickness of 0.02 μm, P-type AlGaInP cladding layer 11 having a thickness of 1.1 μm.
0, 0.04 μm thick undoped GaInP active layer 100, 0.25 μm thick N-type AlGaInP cladding layer 120, 0.005 μm thick N-type GaInP
An etching stopper layer 122, a 0.9 μm thick N-type AlGaInP cladding layer 125, a 0.01 μm thick N-type GaInP layer 150, and a 0.5 μm thick N-type GaAs cap layer 160 are sequentially crystal-grown in this order to form a basic double hetero structure. A wafer was formed. Next, in order to form a laser structure, N-type AlGaInP125 was processed into a mesa shape. For mesa processing, use GaAlP instead of AlGaInP.
A selective etchant having a sufficiently high etching rate was used. Then, in the second MOVPE crystal growth,
0.3μm thick P-type GaAs on the mesa side and both mesa frames
s first current blocking layer 180, 0.3 μm thick N-type GaI
nP second current blocking layer 190, 0.3 μm thick P-type Ga
A third current blocking layer 200 made of As was crystal-grown sequentially. For this crystal growth, a selective growth method was used. And
Finally, the third MOVPE crystal growth is used
A semiconductor laser of the present invention was fabricated by growing a cap layer 170 of type GaAs and attaching electrodes to both sides of the device.

In the above description, Zn was used for all P-type impurities, and Si was used for all N-type impurities. The P-type AlGaInP cladding layer has a carrier concentration of 3 × 10 ¹⁷ cm ⁻³ and a specific resistance of 0.8.
Ωm, the carrier concentration of the N-type AlGaInP cladding layer was 1.5 × 10 ¹⁷ cm ⁻³ , and the specific resistance was 0.08 Ωm.

The following characteristics were obtained as the characteristics of the semiconductor laser having the structure shown in FIG. 2 manufactured by the above method. The oscillation threshold current was 50 mA for an element having a current injection width of 5 μm and a resonator length of 400 μm. The device resistance of the semiconductor laser shown in FIG. 3 was 14Ω, whereas the device resistance of the semiconductor laser shown in FIG. 2 could be greatly reduced to 8Ω. The light output characteristics of the conventional semiconductor laser of FIG. 3 prototyped with the same size have a maximum light output of 30 mW, while the semiconductor laser of FIG. 2 causes thermal saturation up to 40 mW. And good high output characteristics were obtained. Also, good current confinement was obtained up to 40 mW light output. The semiconductor laser whose optical output characteristics were measured was 6% in the front surface and 6% in the rear surface in both the structures shown in FIGS.
After applying a 95% asymmetric coating, the measurement was performed by fusing on a diamond heat sink.

〔The invention's effect〕

As described above, according to the semiconductor laser of the present invention,
The device resistance of the AlGaInP visible light semiconductor laser can be significantly reduced, the heat dissipation characteristics during high-power operation can be significantly improved, and good current confinement can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are structural views (perspective views) of an AlGaInP semiconductor laser on a P-type substrate of the present invention, and FIG.
FIG. 4 is a structural diagram (perspective view) of a GaInP semiconductor laser, FIG. 4 is an energy band diagram of a portion other than the mesa stripe of the semiconductor laser of the present invention, and FIG. 5 is an energy band diagram of a single-layer current block structure. 100 ... active layer, 110, 120, 125 ... clad layer, 122 ...
Etching stopper layer, 130: P-type GaInP layer, 140: buffer layer, 150: N-type GaInP layer, 160: cap layer, 1
70 ... cap layer, 180 ... first current blocking layer, 190
... A second current blocking layer, 200 a third current blocking layer, 210 a substrate, 330 a cladding layer, 400 a substrate.

Claims (1)

(57) [Claims] 1. A double heterostructure including a first clad layer made of AlGaInP or AlInP, an active layer made of GaInP or AlGaInP, and a second clad layer made of AlGaInP or AlInP in this order on a P-type GaAs substrate. In the semiconductor laser in which a part of the second cladding layer partially forms a thick mesa stripe current injection region, a side surface of the mesa stripe and both sides of the mesa stripe are P Current blocking layer made of p-type GaAs or p-type AlGaAs, second current blocking layer made of n-type GaInP or n-type AlGaInP, and third current blocking layer made of p-type GaAs or p-type AlGaAs A semiconductor laser characterized in that: