JPH069274B2 - Method for manufacturing semiconductor laser - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a semiconductor laser.

(b) Conventional Technology Conventionally, semiconductor lasers have been used as electronic components for optical information processing and optical communication, and their application fields are going to be multi-functional. As one of the characteristics required for the semiconductor laser, one of the technical problems is how to reduce the threshold current, that is, the forward current of the semiconductor laser that changes from the spontaneous emission state to the laser oscillation state.

2A and 2B are cross-sectional views showing a conventional method for manufacturing a semiconductor laser. In the figure (A), 1 is an n-type G
aAs substrate, 2 is n-type AlGaAs cladding layer, 3
Is an AlGaAs active layer containing no impurities, and 5 is p-type A
1 GaAs is a clad layer, and 9 is a p-type GaAs cap layer. After each layer is grown on the substrate as described above, the current blocking region 10 is formed by implanting protons or the like as shown in FIG. In this way, between the current blocking regions (hereinafter referred to as stripes).
The current concentration in the active layer is increased.

However, because the current blocking region is insulated by implanting protons, the crystallinity of the active layer is disturbed, which adversely affects the life. Therefore, this problem can be solved by forming a current blocking region by making a part of the clad layer the opposite conductivity type. FIGS. 3A and 3B show an example thereof. 2A has the same structure as that shown in FIG. 2A, except that the stripes are to be formed as shown in FIG. 3B after each layer is grown on the substrate. The n-type current blocking region 11 is formed by diffusing impurities or implanting ions into.

(c) Problems to be Solved by the Invention However, in the conventional semiconductor laser shown in FIG. 3 (B), photoexcitation is performed in the active layer to emit laser light, so that the degree of current concentration in the active layer is high. Need to increase. For that purpose, the dimension t in the figure must be made as small as possible. On the other hand, since the p-type cladding layer 5 serves as a light waveguide, the optical loss becomes large unless it is thicker than 1.0 to 0.5 μm. In addition, the cap layer 9 prevents the solder material from affecting the active layer during soldering with the heat sink,
Further, in order to prevent the influence of the electrode metal, if it is not thick to some extent, a problem will occur in practical use. Therefore, these two layers require a thickness of 3 to several μm. However, both diffusion and ion implantation are 100Å at a depth of 3 to several μm.
It is difficult to provide a certain degree of accuracy, and thus it is difficult to form the current blocking region 11 to the immediate vicinity of the active layer.

Further, the p-type clad layer 5 and the p-type cap layer 9 are 3 to
The thickness is several μm, the stripe layer on which the current is concentrated is thick, and the resistance value is high.

For this reason, the threshold current is not reduced, and there is a problem of an increase in operating voltage and heat generation. The purpose of this invention is
It is an object of the present invention to provide a method for manufacturing a semiconductor laser which can easily reduce the above-mentioned t dimension and obtain a semiconductor laser having a low threshold current.

(d) Means for Solving the Problems A method for manufacturing a semiconductor laser according to the present invention is the same as a lower clad layer, an active layer, a lower clad layer and an upper first clad layer and a lower clad layer of reverse conduction type on a substrate. After forming a conductive upper second cladding layer and a protective layer having a higher evaporation rate in the molecular beam epitaxial growth chamber than the upper second cladding layer in this order, impurities are ion-implanted from the surface of the protective layer to the upper first cladding layer. Or diffusing to form a stripe portion having the same conductivity type as the upper first cladding layer in the upper second cladding layer, evaporating the protective layer in a molecular beam epitaxial growth chamber, and then forming the stripe on the upper second cladding layer. The step of forming a stripe portion, an upper third clad layer of the same conductivity type, and a cap layer in this order by molecular beam epitaxial growth.

(e) Action In the method for manufacturing a semiconductor laser according to the present invention, when the lower clad layer, the active layer, the upper first clad layer, the upper second clad layer and the protective layer are formed in this order on the substrate, Impurities are ion-implanted or diffused from the surface of the protective layer to the upper second cladding layer to form a stripe portion on the upper second cladding layer, and then on the upper second cladding layer, an upper portion of the same conductivity type as the stripe portion is formed. The third clad layer and the cap layer are formed in this order. As described above, since the stripe portion is formed by ion implantation or diffusion of impurities in the intermediate stage before forming the upper third clad layer and the cap layer having a predetermined thickness, a region other than the stripe portion of the upper second clad layer is formed. Serves as a current blocking layer, the dimensional accuracy of the current blocking region is improved, and the above-described semiconductor laser with a small t can be obtained. Further, since the impurity ions are implanted or diffused in a state where the protective layer is formed on the surface of the upper second cladding layer to form the stripe portion of the upper second cladding layer, the surface of the upper second cladding layer is damaged. Alternatively, it is possible to prevent fouling, and since the protective layer is evaporated in the molecular beam epitaxial growth chamber, as compared with the case where the protective layer is removed by, for example, normal wet etching or dry etching,
The flatness and crystallinity of the upper second cladding layer are improved, the transition from the removal of the protective layer to the formation of the upper third cladding layer can be performed smoothly, and a semiconductor laser having excellent characteristics can be easily manufactured. be able to.

(f) Embodiments FIGS. 1A to 1D are sectional views in each step showing a method for manufacturing a semiconductor laser according to an embodiment of the present invention.

In the figure (A), 1 is 250 μm in length, 250 μm in width,
200 μm thick n-type Ga, As substrate, 2 is 1.5
μm n-type Al _0.6 Ga _0.4 As lower clad layer 3 has a thickness of 800 Å and contains no impurities Al _0.15 G
a _0.85 As active layer, 4 0.2 μm thick p-type Al
_0.6 Ga _0.4 As upper first cladding layer, 5 is 0.4 μm thick n-type Al _0.6 Ga _0.4 As upper second cladding layer, and 6 contains 400 Å thick impurities Each represents a protective layer of no GaAs. These layers are sequentially grown on the substrate 1 by the molecular beam epitaxial method.

Next, the wafer grown as shown in FIG. 6B is taken out, and a resist having a thickness of 1.5 μm is attached by photolithography to a region except a region having a width of 4 μm where a stripe portion is to be formed. After that, the Mg ions are accelerated at a voltage of 12
Implantation is performed under the conditions of 0 Kev and a dose amount of 1 × 10 ¹⁴ cm ⁻² . At this time, the driving depth is 0.6 μm. With such shallow ion implantation or diffusion, the depth can be controlled with an accuracy of about 100Å. Therefore, the gap t between the current blocking region 5b and the active layer 3 is determined by the thickness of the upper first cladding layer 4, so that its size can be reduced according to the accuracy of the ion implantation or diffusion depth.

Next, after removing the resist 7 by organic cleaning, it is placed in a molecular beam epitaxial growth chamber. As for wafer
Approximately 3 at a temperature of 750-760 ° C while applying the molecular beam of
Hold for 0 minutes. The evaporation rate of GaAs, which is the protective layer, is 0.7 to 1.0 μm / h, while Al _0.6
The evaporation rate of the upper second cladding layer, which is Ga _0.4 As, is 0.05 μm / h or less. Therefore, the protective layer is selectively evaporated as shown in FIG. 1 (C). At this time, the Mg ions implanted in the step shown in FIG. 1 (B) are activated by the annealing effect and are striped 5a.
Region becomes p-type. Note that the growth chamber of the molecular beam epitaxial apparatus is in an ultrahigh vacuum state, and Al of the cladding layer is not oxidized, and the upper third cladding layer can be directly grown on this cladding layer as described below.

As shown in FIG. 1 (D), the p-type Al _0.6 Ga _0.4 As upper third layer on the upper second cladding layer is further formed.
The cladding layer 8 is grown by molecular beam epitaxy until the thickness becomes 0.9 μm, and the cap layer 9 of p-type GaAs is further grown by molecular beam epitaxy until the thickness becomes 2 μm.

As described above, the gap t between the active layer and the current blocking region 5b
Is manufactured, and a semiconductor laser in which an upper clad layer having a predetermined thickness is formed is manufactured.

In this embodiment, since the current blocking region 5b is made of AlGaAs having the same composition as that of the cladding layer, the light spreading from the active layer is not absorbed in this blocking region, so that the width of the stripe is narrowed and t By reducing the thickness, the threshold current and the like can be easily improved.

(g) Effect of the Invention As described above, according to the present invention, since the thickness of the stripe can be formed with high dimensional accuracy, the gap t between the active layer and the current blocking layer can be reduced. Moreover, since the thickness of the stripe portion can be reduced and the thickness of the upper clad layer can be formed to a predetermined size, the current can be concentrated only in the stripe and the threshold current can be reduced. Furthermore, according to the present invention, the impurity ions are implanted or diffused in the state where the protective layer is formed on the surface of the upper second cladding layer to form the stripe portion in the upper second cladding layer. The surface of the second clad layer can be prevented from being damaged or soiled, and the protective layer is evaporated in the molecular beam epitaxial growth chamber, so that the flatness and crystallinity of the upper second clad layer can be kept high. Since the transition from the removal of the layer to the formation of the upper third cladding layer can be performed smoothly, a semiconductor laser having excellent characteristics can be easily manufactured.

[Brief description of drawings]

1 (A) to 1 (D) are cross-sectional views showing respective steps of a method for manufacturing a semiconductor laser which is an embodiment of the present invention, FIGS. 2 (A), (B) and 3 (A), ( FIG. 3B is a sectional view showing a method for manufacturing a conventional semiconductor laser. 1 ... Substrate, 2 ... Lower cladding layer, 3 ... Active layer, 4 ... Upper first cladding layer, 5 ... Upper second cladding layer, 5a ... Stripe, 5b ... Current blocking region, 8 ... ... upper third cladding layer, 9 ... cap layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kaoru Kusunoki 21 Saito Mizozakicho, Ukyo-ku, Kyoto City, Kyoto Prefecture Rome Co., Ltd. Incorporated (72) Inventor, Yuji Ishida, 21 Mizozaki-cho, Saiin, Ukyo-ku, Kyoto City, Rome (56) References JP-A-57-198684 (JP, A) JP-A-57-112090 (JP) , A) JP-A-56-90586 (JP, A) JP-A-61-150392 (JP, A)

Claims (1)

[Claims] 1. An evaporation in a lower clad layer, an active layer, an upper first clad layer of a reverse conductivity type to the lower clad layer, an upper second clad layer of the same conductivity type as a lower clad layer, and a molecular beam epitaxial growth chamber on a substrate. After forming a protective layer having a speed higher than that of the upper second cladding layer in this order, impurities are ion-implanted or diffused from the surface of the protective layer to the upper first cladding layer to form an upper first cladding layer in the upper second cladding layer. A step of forming a stripe portion of the same conductivity type,
Evaporating the protective layer in a molecular beam epitaxial growth chamber,
Then, a method of manufacturing a semiconductor laser comprising the steps of forming the stripe portion, an upper third clad layer of the same conductivity type and a cap layer on the upper second clad layer in this order by molecular beam epitaxial growth.