JPH04115588A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To make it possible to reduce device resistance and constrict current flow favorably by forming a mesa with N type AlGaInP and forming three layer structure for a current block layer. CONSTITUTION:A first clad layer 110, an active layer 100, and an N type AlGaInP-made second clad layer are installed on a P type GaAs substrate 210 where a part of the second clad layer 120 forms a mesa stripe-shaped current injection region having a film thickness locally increased. The side of the mesa stripe and both sides of the mesa stripe are covered with a three structure current block layer comprising a first current block layer 180 made of P type GaAs or P type AlGaInP or a second current block layer 190 made of N type GaInP or N type AlGaInP and a third current block layer 200 made of P type GaAs or P type AlGaAs. This construction makes it possible to reduce device resistance, improve thermal radiation characteristic during high output operation and constrict current flow favorably.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an A II G having an oscillation wavelength of 0.6 μm.
This invention relates to an aInPIn optical semiconductor laser.

[Conventional technology]

Currently, in order to increase the density of optical disks, AlGaInP-based visible light semiconductor lasers having an oscillation wavelength in the 0.6 μm band are being actively developed. Most of the AuGaInP visible light semiconductor lasers that have been reported so far are reports on semiconductor lasers formed on N-type substrates.

In addition, the main laser structure is N-type on a flat N-type substrate.
Type Aj2GaInP cladding layer, GaInP active layer, P
A type AuGaInP cladding layer is formed in this order, and then
It has a structure in which a P-type AβGa I nP cladding layer is processed into mesa-like stripes, and the remaining portion is filled with an N-type block layer. Examples of presentations regarding these laser structures are shown below. For example, Electronics Letters August 27, 1987 Vol.

23Nα18 pp, 938-939
h-power operation of a tr
anverse-mode 5-tabilised
A (IG a I n P visible I
"High Semiconductor Laser", or "High
power operation of I n G
a P / I n A j2 Ptransver
se mode 5tabilized 1aser
reported in diodesl+. These laser structures have been well known since the days of Al2GaAs semiconductor lasers, and by burying mesa-shaped stripes with a blocking layer, they perform current confinement and at the same time form a refractive index step to control transverse mode. is possible.

[Problem to be solved by the invention]

However, Aρ formed on these conventional N-type substrates
In the case of Ga InP semiconductor lasers, the following problems exist. That is, AρGaIn formed on an N-type substrate
In the P semiconductor laser, the current injection portion of the mesa-like stripe is formed of P-type ApGaInP crystal. On the other hand, it is known that it is difficult to reduce the resistance of P-type Aj7GaInP crystal, and its resistivity is about one order of magnitude higher than that of N-type AρGaInP crystal. If we were to show a specific value using our data, it would be P type (AA o, eG a Q, 4) 0.5
The specific resistance of I no,s P (Zn doped) is 0
．． 7 to 1.3 Ωam, whereas N type (Aj2 o
, aG a O, 4) 0.5 I n osP (S
The specific resistance of the i-doped crystal is 0.05 to 0.08Ω, and the P-type crystal has a resistance about one order of magnitude higher. Therefore, in particular, the conventional Aj2 that uses P-type AρGaInP crystal in the current injection part of a narrow stripe with a width of 3 to 7 μm and a height of about 1 μm.
GaInP semiconductor lasers have extremely high element resistance;
Saturation of optical output due to heat generation during high-output, large-current operation becomes a problem.

[Means to solve the problem]

The structure of the semiconductor laser of the present invention is such that a first cladding layer made of Al2InP or Al2InP, an active layer made of GaInP or Al2InP, and a second cladding layer made of A, ffGaInP or Al2InP are formed on a P-type GaAs substrate.
In the semiconductor laser, the semiconductor laser has at least a double heterostructure including cladding layers in this order, and a part of the second cladding layer partially forms a thick mesa stripe-shaped current injection region, The sides of the mesa stripe and both sides of the mesa stripe are made of P-type GaAs or P-type AβG.
A first current blocking layer made of aAs, a second current blocking layer made of N-type GaInP or N-type AlGaInP,
A third current blocking layer made of P-type GaAs or P-type Aj7GaAs is coated in this order.

[Effect]

Figures 1 and 2 show A, ffGaIn on the P-type substrate of the present invention.
A structural diagram of a P semiconductor laser is shown in FIG. 3, and a structural diagram of a conventional AρGaInP visible light semiconductor laser formed on an N-type substrate is shown in FIG. In addition, FIG. 4 shows the energy band diagram of the semiconductor laser of the present invention in a part other than the mesa stripe (when the current blocking layer has a three-layer structure), and FIG. An energy band diagram is shown in the case where the layer is a current blocking layer. The semiconductor laser shown in FIG. 2 has an etching stopper layer 122 between the N-type A4GaInP cladding layers 120 and 125 in order to provide etching selectivity during mesa formation compared to the semiconductor laser shown in FIG.
Since it is essentially the same as the semiconductor laser shown in FIG. 1, the following explanation will be omitted.

Below, the structural diagrams of FIGS. 1 and 3 and FIG. 4 are shown.

The operation of the present invention will be explained using the energy band diagram shown in FIG. First, the structure shown in FIG. 1 will be explained. The semiconductor laser shown in FIG. 1 is formed by crystal growth using metal organic pyrolysis vapor phase epitaxy (hereinafter abbreviated as MOVPE method) three times and a mesa processing process. First, in the first crystal growth, P-type AJ2 is grown on a P-type GaAs substrate 210.
GaInP cladding layer 110. GaInP active layer 100
．． A double heterostructure including N-type Aj7GaInP cladding layers 120 in this order is formed. Next, in order to form a current injection region, an N-type Aj2GaInP cladding layer 12 is formed.
0 is processed into a meza shape, and by second crystal growth, a three-layer current blocking layer 18 is formed on the mesa side surface and both sides of the mesa.
Embed with 0,190,200. Then, in the third crystal growth, an N-type GaAs cap layer 16 is formed on the upper part of the mesa part.
form 0.

This mesa structure functions as a light confinement structure as well as current confinement, and has the function of transverse mode control.

Usually, the width of the mesa bottom is about 3 to 7 μm.

On the other hand, a conventional N-type semiconductor laser on a substrate is shown in FIG. The laser manufacturing process and structure are almost the same as the P-type substrate semiconductor laser shown in FIG. Figure 3 and Figure 1
The difference between the figures is that in FIG. 3, the substrate 400 is of N type Ga A
In contrast, in FIG. 1, the substrate 210 is P-type G.
It is a point that a A s.

Therefore, in FIG. 3, the mesa-shaped cladding layer 330 forming the current injection region is formed of P-type A4GaInP.

As mentioned in the previous topic section, P-type AρGaInP
It is difficult to reduce the resistance of crystals, and their specific resistance is lower than that of N-type AuGa
It is known that the value is about one order of magnitude higher than that of InP crystal. If we were to show concrete numbers using our data, it would be P type (
A RO, 6G a O, 4) o, s I no,
5 The specific resistance of P (Zn doped) is 0.7 to 1.3 Ωc
m, whereas N type (Aj2 osG a 04)
The specific resistance of 0.5 Ino, sP (Si doped) is 0.05 to 0108 Ωcm, and the P type crystal is 1
It has an order of magnitude higher resistance. Therefore, in particular, P-type Ajl is applied to the current injection part with a narrow stripe of 3 to 7 μm in width and about 1 μm in height.
In the conventional semiconductor laser shown in FIG. 3 using a GaInP crystal, the element resistance is extremely high, and saturation of optical output due to heat generation during high-output, large-current operation becomes a problem.

However, in the semiconductor laser of the present invention shown in FIG.
Because it is formed of N-type AβGaInP, which has an order of magnitude lower resistance,
It is possible to significantly reduce element resistance and significantly improve heat dissipation characteristics, making it an extremely suitable structure for increasing output power.

Another feature of the semiconductor laser of the present invention shown in FIG. 1 is that the potential barrier is prevented from lowering due to the absorption of oscillation light by the current blocking layer by forming the current flocking layer into a three-layer structure. It will be done. The mechanism will be explained in detail below with reference to FIGS. 4 and 5. FIG. 4 shows the energy band diagram of the semiconductor laser of the present invention shown in FIG. 1 at both sides of the mesa stripe, and FIG. Figure 3) shows the energy band diagram.

If the current blocking layer has a single layer structure and is made of P-type GaAs or P-type AβGaAs as shown in FIG.
The following is known from the study of j2GaAs lasers (Reference: S, Yamamot.

et al, A, P, L, 40(5), I Marc
h 1982.

PP, 372-374). That is, light generated in the active layer leaks into the P-type GaAs layer, which is a current blocking layer.

On the other hand, since the forbidden width of the P-type GaAs layer has lower energy than the light generated in the GaInP active layer, it absorbs the oscillated light and forms electron-hole pairs in the current blocking layer. However, the diffusion length of electrons and holes in GaAs is ~3μ each.
m, ~0.6 μm, so only the electrons whose internal diffusion length of the generated electron-hole pairs is much larger than the current blocking layer thickness will diffuse to both sides of the current blocking layer, and only the holes will accumulate. (Figure 5(a)). Therefore, the potential of the current blocking layer decreases until the current blocking effect is lost and the current confinement structure ceases to function (FIG. 5(b)). Note that the thickness of the current blocking layer is usually 1μ.
It is about m. Therefore, the current blocking layer is usually N type G
Generally, it is a A s.

However, as in the semiconductor laser of the present invention, the substrate is P
type and the mesa stripe is above the active layer, the current blocking layer must be P type. Therefore, a three-layer current blocking layer as shown in FIG. 4 was used as a structure to prevent potential reduction of the current blocking layer due to light absorption. In FIGS. 1 and 4, the current blocking layer is
A first current blocking layer 180 made of P-type GaAs or P-type AnGaAs. N-type GaInP or N
Second current blocking layer 19 made of type A, ffGaInP
The third current blocking layer 2000 is made of 0° P-type GaAs or P-type AuGaAs and has a three-layer structure. Fourth
As shown in Figure (a), similar to Figure 5, the light generated in the active layer is absorbed by the first current blocking layer made of P-type GaAs, electrons are diffused, and holes are only accumulates in the first current blocking layer. As a result, the first
The potential barrier of the current blocking layer decreases. However, as shown in FIG. 4(b), the holes accumulated in the first current blocking layer are prevented from flowing through the first current blocking layer because there is a potential barrier in the valence band between the holes and the second current blocking layer. Current cannot flow from the blocking layer to the third blocking layer. Therefore, the third current blocking layer functions normally and works well as a current blocking layer.

Therefore, in the semiconductor laser of the present invention, the potential barrier does not decrease due to light absorption in the current blocking layer, and a good current confinement structure can always be obtained. Note that in FIG. 4, it is assumed that the third current blocking layer is sufficiently far away from the active layer and absorbs almost no oscillation light.

〔Example〕

The AρGaInP semiconductor laser on a P-type substrate of the present invention will be described below using specific numerical examples. here,
The structure shown in FIG. 2 will be described as a more optimized structure. The substrate is l x 10” cm-3 Zn-doped P
A type G a A, s substrate 210 was used.

By MOVPE method with reduced pressure of 70 Torr,
Buffer layer 140 made of P-type GaAs with a thickness of 0.3 μm.
0.02. P-type GaInP layer 130.1.1 with czm thickness
μm thick P-type Aj2GaInP cladding layer 110.0.
04 μm thick undoped GaInP active layer 100.0.
25 μm thick N-type Aj2GaInP cladding layer 120,
0.005 μm thick N type Ga In P engineering y Chingest collar layer 122.0.9 μm thick N type A, ffGa
InP cladding layer 125.0.01 μm thick N-type GaI
An N-type GaAs cap layer 160 having a thickness of 150 and 0.5 μm was crystal-grown in this order to form a basic double heterostructure wafer.

Next, to form the laser structure, N-type Al2GaIn
P125 was processed into a mesa shape. For mesa processing, GaIn
A selected etchant having a sufficiently high etching rate for AuGaInP was used.

Then, in the second crystal growth using the MOVPE method, a 0.3 μm thick P-type G
First current blocking layer made of aAs 180.0.3 μm
Second current blocking layer 1 made of thick N-type Ga I nP
A third current blocking layer 200 made of P-type GaAs with a thickness of 90.0 and 0.3 μm was successively crystal-grown. A selective growth method was used for this crystal growth. And finally, the third M
N-type GaAs is grown on the entire surface by crystal growth using the OVPE method.
A cap layer 170 was grown, and electrodes were attached to both sides of the device to fabricate a semiconductor laser of the present invention.

In the above description, Zn was used for all P-type impurities, and Si was used for all N-type impurities. In addition, P-type AβGaI
The carrier concentration of the nP cladding layer is 3 x 1017c
m-', the specific resistance is 0.8Ωσ, and the N-type AρGa I
The carrier concentration of the nP cladding layer is 1.5 x 10
"am-", and the specific resistance was 0.08 Ωcm.

As the characteristics of the semiconductor laser having the structure shown in FIG. 2 manufactured by the above method, the following characteristics were obtained. The oscillation threshold current was 50 mA for a device with a current injection width of 5 μm and a resonator length of 400 μm.

The element resistance of the semiconductor laser in Figure 3 is 14Ω.
On the other hand, the element resistance of the semiconductor laser shown in FIG. 2 was significantly reduced to 8Ω. In addition, the optical output characteristics of the semiconductor laser with the conventional structure shown in Figure 3, which was prototyped with the same size, reached thermal saturation at the maximum optical output of 30 mW, whereas the semiconductor laser with the structure shown in Figure 2 reached thermal saturation at 40 mW. Good high output characteristics were obtained without causing any problems. Also, 40
Good current confinement was obtained up to mW optical output. Regarding the semiconductor lasers whose optical output characteristics were measured above, both the structures shown in Figures 2 and 3 were coated with asymmetrical coating on 6% of the front surface and 95% of the rear surface, and then fused onto a diamond heat sink for measurement. went.

〔Effect of the invention〕

As described above, according to the semiconductor laser of the present invention, A
It is possible to significantly reduce the element resistance of the lGaInP visible light semiconductor laser, to greatly improve the heat dissipation characteristics during high-power operation, and to achieve good current confinement.

[Brief explanation of drawings]

1 and 2 are structural diagrams (perspective views) of an AρGaInP semiconductor laser on a P-type substrate according to the present invention, and FIG. 3 is a structural diagram (perspective view) of a conventional AffGaInP semiconductor laser on an N-type substrate.
, FIG. 4 is an energy band diagram of a portion other than the meza stripe of the semiconductor laser of the present invention, and FIG. 5 is an energy band diagram of a one-layer current block structure. 100... active layer, 110, 120, 125.
... Cladding layer, 122 ... Eratin stopper layer, 130 ... P-type Ga I nPl, 1
40... Buffer layer, 150... N-type GaInP layer, 160... Cap layer, 170...
... Cap layer, 180 ... First current blocking layer, 190 ... Second current blocking layer, 200 ... Third current blocking layer, 210・
... Substrate, 330 ... Cladding layer, 40
0... Board. Agent Patent Attorney Susumu Uchihara Figure 2: Eyelids Figure 3: Correctly α (b) (0,)

Claims (1)

[Claims] AlGaInP or AlIn on a P-type GaAs substrate
First cladding layer made of P, GaInP or AlGa
Active layer made of InP, AlGaInP or AlInP
A semiconductor having at least a double heterostructure including a second cladding layer in this order, wherein a part of the second cladding layer partially forms a thick mesa stripe-shaped current injection region. In the laser, a first current blocking layer made of P-type GaAs or P-type AlGaAs and an N-type G
1. A semiconductor laser comprising: a second current blocking layer made of aInP or N-type AlGaInP; and a third current blocking layer made of P-type GaAs or P-type AlGaAs.