JP2895915B2 - Manufacturing method of semiconductor laser - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor laser made of an AlGaInP-based compound semiconductor that emits visible light.

(B) Conventional technology AlGaInP has a wavelength in the 0.6 μm band and is used as a material for visible light semiconductor lasers.

FIG. 6 shows, for example, Japanese Journal Applied Physic
s, Vol. 28, No. 9 (1989), pp. 1615-1621, showing a conventional AlGaInP-based semiconductor laser.

In the figure, (11) is a substrate made of n-type GaAs, (12)
Is a buffer layer made of n-type GaAs, and (13) is an n-type AlGaInP
An n-type cladding layer consisting of
(15) is a p-type cladding layer made of p-type AlGaInP, and (16) is a block layer made of n-type GaAs. These layers are sequentially epitaxially grown on one main surface of the substrate (11) using a well-known MOCVD method. Further, in the block layer (16), a striped groove (16 ') having a depth reaching the p-type cladding layer (15) is formed by etching.

(18) is a cap layer made of p-type GaAs epitaxially grown on the exposed p-type cladding layer (15) and the block layer (16), and (19) is a p-side electrode formed on the cap layer (18). , (20) are n-side electrodes formed on the other main surface of the substrate (11).

As the n-type impurity in such an AlGaInP-based semiconductor laser, Se or Si is usually used.

(C) Problems to be Solved by the Invention However, if Se is used as an impurity of the n-type cladding layer, the Se remaining in the growth furnace when the next active layer is formed.
Is re-evaporated and taken into the active layer to generate carriers in the active layer, so-called a memory effect appears. Seventh
The figure shows such a memory effect. The carrier concentration distribution in the thickness direction when an undoped GaInP layer (corresponding to an active layer) is laminated on an AlGaInP layer (corresponding to an n-type cladding layer) to which Se is added is shown. Is shown.

Thus, when Se is taken into the active layer, the semiconductor laser becomes longer wavelength because such Se forms a donor level,
Further, the crystallinity of the active layer itself is degraded, which causes a problem that the reliability of the semiconductor laser is lowered.

When Si is used as an impurity of the n-type cladding layer, the impurity added to the AlGaInP layer in FIG.
As shown in FIG. 9, the memory effect does not appear, but as shown by the solid line in FIG. 9, when the carrier concentration is increased, the photoluminescence (n) of the n-type cladding layer is increased to, for example, 6 × 10 ¹⁷ cm ⁻³ or more. The emission intensity of PL) decreases (the broken line in the figure indicates the case where Se is used as an impurity, and in this case, a high emission intensity can be maintained up to a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ ). This is because the crystallinity of the n-type cladding layer deteriorated due to excessive addition of Si. Such deterioration of the crystallinity of the n-type cladding layer causes deterioration of the crystallinity of the active layer formed thereon, which in turn causes an increase in the oscillation threshold value of the semiconductor laser and a reduction in the service life. .

Accordingly, an object of the present invention is to form an n-type clad layer having a sufficient carrier concentration without causing deterioration of the n-type clad layer and the active layer.

(D) Means for Solving the Problems The present invention is a method of manufacturing a semiconductor laser comprising an AlGaInP-based compound semiconductor in which an n-type cladding layer, an active layer, and a p-type cladding layer are laminated on a substrate in this order. In order to solve the above problem, the first step of forming the n-type cladding layer by epitaxially growing by supplying a Se source gas as a source gas of an n-type impurity, and stopping the supply of the Se source gas, And a second step of epitaxially growing by supplying a Si raw material gas.

(E) Function According to the present invention, the formation of the n-type cladding layer is performed by stopping the supply of the SE raw material gas and the first step of supplying the Se raw material gas as the raw material gas of the n-type impurity and performing epitaxial growth. Alternatively, a second step of epitaxially growing by supplying a Si source gas is performed, and an active layer is laminated thereon, thereby adding Si in the vicinity of the junction interface between the n-type cladding layer and the active layer. The amount may be an amount obtained by subtracting the carrier concentration caused by the memory effect of Se added before from the desired carrier concentration, and can be made smaller than the addition amount required when adding Si alone. .

(F) Embodiment First, the principle of the present invention will be described with reference to FIG.

FIG. 4 shows that a second AlGaInP layer is grown on a first AlGaInP layer grown by supplying a Se source gas as an n-type impurity, by switching the source gas of the impurity to a Si source gas. 4 shows a carrier concentration distribution in a layer thickness direction when an undoped GaInP layer is grown. In the figure, the portion A indicates carriers generated by Se, and the portion B indicates carriers generated by Si.

Here, the first and second AlGaInP layers in FIG.
The undoped GaInP layer corresponds to the active layer, corresponding to the n-type cladding layer of the lGaInP-based semiconductor laser.

As shown in the drawing, in the present invention, by utilizing the memory effect of Se described above, the carrier concentration of the second AlGaInP layer is formed by adding the carrier generated by the memory effect to the carrier by Si added during the growth. I do. As a result, the amount of Si added during the growth of the second AlGaInP layer is smaller than that obtained by adding only Si, and the memory effect of Se in the undoped GaInP layer is suppressed.
The interface between the nP layer and the GaInP layer becomes steep.

In addition, when the second AlGaInP layer is grown, a substantially constant carrier concentration is obtained over the first and second AlGaInP layers by appropriately increasing the supply amount of the Si source gas, as shown in FIG. be able to.

Next, an example of an AlGaInP-based semiconductor laser manufactured by applying the method of the present invention is shown in FIG.

In the figure, (1) is an n-type G having a (100) plane as a main surface.
Substrate made of aAs, (2) is one main surface (1a) of substrate (1)
This is a buffer layer made of n-type GaAs having a thickness of 0.3 μm laminated thereon. (3) is a type cladding layer made of n-type AlGaInP having a thickness of 0.8 μm, and a first layer (3a) formed on the buffer layer (2) by supplying only a Se source gas as an n-type impurity source gas. ) And a second layer (3a) formed by supplying only a Si source gas.

(4) is a thickness laminated on the n-type cladding layer (3).
An active layer made of undoped GaInP having a thickness of 0.08 μm, and (5) is a 0.8 μm-thick p-type AlGaI laminated on the active layer (4).
p-type cladding layer made of nP, (6) laminated on p-type cladding layer (5), contact layer composed of p-type GaInP having a thickness of 0.05 μm, (7) laminated on contact layer (6) This is a block layer made of n-type GaAs having a thickness of 0.4 μm. In the block layer (7), a stripe-shaped groove (7 ') having a width of 5 μm reaching the contact layer (6) is formed by etching.

(8) is a cap layer made of p-type GaAs having a thickness of 1.5 μm laminated on the block layer (7) and the exposed contact layer (6), and (9) is formed on the cap layer (8). A p-side electrode made of an alloy of Au and Cr, and (10) is an n-side electrode made of an alloy of Au, Sn, and Cr formed on the other main surface (1b) of the substrate (1).

Next, a method for manufacturing the device of this embodiment will be described with reference to FIG.

FIG. 2 (a) shows a first step, in which a buffer layer is formed on one main surface (1a) of the substrate (1) by using a reduced pressure MOCVD method at a growth temperature of 700 ° C. and a growth pressure of 70 torr. 2), an n-type cladding layer (3), an active layer (4), a p-type cladding layer (5), a contact layer (6), and a block layer (7) are successively grown.

Here, a method of growing the n-type cladding layer (3) will be specifically described with reference to FIG. FIG. 3 shows the supply profile of the carrier gas when growing the n-type cladding layer (3).

As shown in FIG. 3, first, a source gas of an n-type impurity is used.
A Se source gas, for example, H ₂ Se, is supplied for about 10 minutes at a molar ratio of about 1 × 10 ⁻⁶ (H ₂ Se / V group gas) to the group V gas (that is, the P source gas), and the first layer (3a ) Is grown to a thickness of about 0.3 μm. V / III ratio at this time (V to III group gas total
Molar ratio of group gas) is 550.

After the growth of the first layer (3a), supply of Se source gas is stopped, and Si
Start supplying source gas. At this time, Si source gas, for example,
SiH ₄ is present in a molar ratio of 0 to 8
The second layer (3b) is grown to a thickness of about 0.5 μm by supplying the solution for 20 minutes while increasing the pressure to × 10 ⁻⁴ (SiH ₄ / III group gas).

By the above method, the first layer (3a) and the second layer (3b)
Has a carrier concentration of 5 to 8 × 10
^It is kept at around ¹⁷ cm ^-3 .

FIG. 2 (b) shows the second step, wherein H ₂ SO ₄ : H ₂ O: H ₂ O ₂ =
Using a 3: 1: 1 etchant, a 5 μm-wide striped groove (7 ′) reaching the contact layer (6) is formed in the block layer (7) by etching.

FIG. 2 (c) shows a third step, in which a block layer (7) is formed.
A cap layer (8) is epitaxially grown on the top and the exposed contact layer (6).

Finally, by forming a p-side electrode (9) on the cap layer (8) and an n-side electrode (10) on the other main surface (1b) of the substrate (1), respectively, the book shown in FIG. An example device is manufactured.

An aging test was performed on the device of this embodiment by a constant output operation at an ambient temperature of 60 ° C. and 3 mW. The result is shown by a solid line in FIG. For comparison, the AlGaIn shown in FIG.
The aging test results of the P-type semiconductor laser using only Si as the impurity of the n-type cladding layer (13) are shown by broken lines, and the aging test results of the n-type cladding layer (13) using only Se as the impurity are shown. It is also shown in FIG. 5 by a dashed line.

From the figure, it can be seen that in the device of the present embodiment, there is no change in the drive current for 4000 hours, so that the device deterioration is small and the reliability is high. This is the memory effect of Se, and
This is because crystallinity of the active layer was improved by suppressing excessive addition of Si.

(G) Effect of the Invention According to the method of the present invention, the formation of the n-type cladding layer includes the first step of supplying an Se source gas as an n-type impurity source gas to perform epitaxial growth, and the supply of the Se source gas. The second step of epitaxially growing by supplying a Si source gas instead of stopping, thereby improving the crystallinity of the active layer laminated thereon and providing a highly reliable semiconductor laser with little deterioration. Obtainable.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the apparatus of the present invention, FIG. 2 is a cross-sectional view of each step for explaining a method of manufacturing the apparatus of this embodiment, and FIG. 3 is an n-type cladding layer of the apparatus of this embodiment. N at the time of growth
FIG. 4 is a growth program diagram showing the profile of the supply amount of the impurity impurity source gas, FIG. 4 is a carrier concentration distribution diagram for explaining the principle of the apparatus of the present invention, and FIG. 5 shows the aging test results of the apparatus of the present embodiment and the comparative example. FIG. 6 is a sectional view showing a conventional device, FIG. 7 is a carrier concentration distribution diagram showing a memory effect when Se is used as an n-type impurity of an n-type cladding layer of the conventional device, and FIG. FIG. 9 is a characteristic diagram showing a carrier concentration distribution when Si is used as an n-type impurity of the n-type cladding layer of the device. FIG. 9 shows a carrier concentration distribution when Se or Si is used as an impurity of the n-type cladding layer of the conventional device. FIG. 4 is a characteristic diagram showing the photoluminescence intensity of the n-type cladding layer with respect to FIG.

Claims (1)

(57) [Claims] 1. A method of manufacturing a semiconductor laser comprising an AlGaInP-based compound semiconductor in which an n-type cladding layer, an active layer, and a p-type cladding layer are laminated on a substrate in this order. Se as a source gas for type impurities
A first step of supplying a source gas and epitaxially growing; and a second step of stopping the supply of the Se source gas and supplying a Si source gas instead to supply the source gas to perform epitaxial growth.
A method of manufacturing a semiconductor laser.