JPS6260283A - Buried type semiconductor laser - Google Patents

Abstract

PURPOSE:To realize secure current constriction effect and facilitate stable basic horizontal mode oscillation and high output operation and improve yield by a method wherein a P<+> type GaAs layer is employed as a top layer and a P-N junction is formed. CONSTITUTION:A P<+> type GaAs layer 22 is employed as a top layer. A diffusion process of a P-type impurity is eliminated by doping the top layer 22 with a P-type impurity such as Zn or Ge with concentration of about 10<19>cm<-3>. As an N-type electrode is formed on an N<+> type GaAs layer (corresponding to the P<+> type GaAs layer 22) and, further, an N-type Al0.2Ga0.8As layer and a P-type Al0.4Ga0.6As buried layer (corresponding to a P-type Al0.2Ga0.8As layer 21 and an N-type Al0.4Ga0.6As buried layer 10) form a P-N junction, the diffusion potential is higher than that of the P-N junction in a mesa-stripe part so that a leakage current to the outside of the mesa part can be avoided completely. Moreover, the N<+> type GaAs layer can be formed to have sufficient thickness so that introduction of crystal defects caused by ohmic alloy of the N-type electrode also can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a stripe-embedded semiconductor laser with current confinement.

[Conventional technology and its problems]

The structure of a buried semiconductor laser is such that an active region with a high refractive index is surrounded by a material with a low refractive index.
In the case of the active layer, A1. A: It has a strong optical waveguide effect because it is surrounded by layers. As a result, complete refractive index waveguiding is achieved not only in the vertical direction but also in the horizontal direction with respect to the pn junction surface, making it possible to realize stable fundamental transverse mode oscillation and low astigmatism. This semiconductor laser can achieve current confinement relatively easily due to its structure, making it possible to realize a semiconductor laser with a low oscillation threshold and high efficiency.4 In order to achieve complete current confinement in such a buried structure, it is necessary to It is necessary to make the junction planes of the pn forward bias junction of the buried layer and the np reverse bias junction of the buried layer coincide with each other. However, in the embedded growth process,
-ffl, the buried layer acting as a current blocking layer is often formed on the side surface of the mesa, resulting in a two-sided structure, resulting in incomplete current confinement.

In order to improve this drawback of buried growth, it has been proposed to provide a constriction in the E portion of the pn junction of the mesa stripe and to control the reverse bias junction of the buried layer using this constriction. This is an attempt to realize a low-threshold, high-efficiency embedded semiconductor laser with good reproducibility.

For example, the structure shown in Figure 2 has been reported as a structure of a mesa stripe type semiconductor laser having this constricted part ([31st Japan Society of Applied Physics Conference Proceedings J (
1984), lecture number 30a-M-9). In this figure, 1 is n-type GaA.

Substrate, 2 is n-type person 1 o4G, n, 6As cladding layer, 3 is n-type person f20.35GaQ, 65 people. Optical waveguide layer 4 is ^Po.

+ +Gao, g9As active layer, 5 is p-type person 105
G*Q, li people.

Intermediate layer, 6 is p-type 10-4Ga0.6As cladding layer, 7 is p-type Af! o-++; Gao-5sAs electrode layer,
8 is the waist, 9 is p type person (! 0.4G + 10-6
^8 Embedded layer, 10 is n-type person f! 0.4G80.6
^8 is a buried layer, 11 is a p-type impurity diffusion layer, 12 is an n-type electrode, 13 is an n-type electrode, and 1.1 is an S+0□ film, respectively. In this 'lfi structure, an optical waveguide layer 3 is provided adjacent to the active layer 4, and most of the light is transmitted to this optical waveguide layer 3.
Since the light propagates through the mesa portion, the effective refractive index of the mesa portion becomes relatively small, and the difference in refractive index between the mesa portion and the buried portion can be reduced. As a result, stable fundamental transverse mode oscillation can be obtained even for mesa widths of 2 μm or more, and features include a low oscillation threshold, high efficiency, low astigmatism, and high output.

Furthermore, in this structure, as shown in FIG.
S in the figure, even if the O2 film 14 is removed, a low oscillation threshold and high efficiency can be achieved without impairing the current confinement effect, and the manufacturing process is simple. Since it can be formed over the entire surface, the heat dissipation characteristics are improved and laser oscillation can be performed satisfactorily even at high temperatures, and the stress on the SIO□ film 14 can also be eliminated.

However, in this structure, the p-type impurity diffusion layer 11 is
Saint (20-4Ga0.6^3 buried layer 10 and p-type A
It is necessary to perform precise depth control so that ρo, 4Gao, 6A are formed within the cladding layer 6, and there is a difficulty in manufacturing reproducibility.

In addition, as shown in the figure, p-type people 20-15GllO-
85^3 No growth is formed on the surface of the 3 electrode layer 7, selectively forming n saints! . , 4Gm0.6^, as the buried layer 10 is grown, there is generally a step that is several μm higher on the surface of the buried layer 10 than on the surface of the electrode layer 7, and when mounting the laser chip on a heat sink by fusion, in this case n Since it is mounted with the mold electrode side facing down, this difference in level tends to impair the adhesion between the laser chip and the heat sink and cause poor contact with the heat sink. For this reason, the yield rate for device assembly is low, and it is also disadvantageous in terms of heat dissipation, making high-output operation difficult.

On the other hand, the figure shows the structure of a semiconductor laser using an n-type G8^8 substrate, but in this structure, even if a p-type G, A, substrate is used, the p-type, n-type By simply inverting each of them, the pn junction plane of the mesa stripe portion and the np reverse bias junction plane formed by the buried layer coincide, resulting in a current confinement structure. However, since it is generally technically difficult to form an n-type impurity diffusion, it is difficult to form an n-type electrode and a p-type electrode.
a0.6As buried layer (n type G, A, in substrate 1, n type layer (corresponding to 20,4G-0,6^3 buried layer 10) makes ohmic contact with p type layer (20
-4G+11], 6^8 buried layer and p-type person β0-35
Leakage through the constriction where the GaO-6'i^8 optical waveguide layer (corresponding to the n-type Aβ0-95GaO-65^8 optical waveguide layer 3 in the n-type 68 substrate 1) is electrically short-circuited. Since current flows, there is a drawback that the oscillation threshold current becomes larger than the threshold current.

Another problem when forming an n-type electrode on the upper part of the mesa stripe is that when using an abrasive material such as -6=AuGeNI, which becomes the n-type electrode, a part of the ohmic alloy layer becomes spike-shaped. Since it penetrates to a depth of several micrometers or more, it reaches the active region of mesas 1 to 2, introducing crystal defects and causing problems in the reliability of the laser device.

[Object of the Invention] The object of the present invention is to eliminate these conventional drawbacks, to have a reliable current confinement effect, to enable stable fundamental transverse mode oscillation and high output operation, and to achieve high manufacturing yield and reliability. The objective is to provide an excellent buried semiconductor laser.

rStructure of the Invention] The structure of the embedded semiconductor laser of the present invention includes a semiconductor substrate of a first conductivity type, a first semiconductor layer of at least a first conductivity type, and a refractive index higher than that of the first semiconductor layer. a second semiconductor layer of a first conductivity type; an active layer having a higher refractive index than the second semiconductor layer; a third semiconductor layer of a second conductivity type having a lower refractive index than the first semiconductor layer; a strip-shaped multilayer structure formed by sequentially laminating a fourth semiconductor layer of a second conductivity type having the same refractive index as the first semiconductor layer; a fifth semiconductor layer of a second conductivity type having the same or lower refractive index; the active layer; and a third semiconductor layer; a sixth semiconductor layer of a first conductivity type provided on a side surface of the fourth semiconductor layer and having a refractive index lower than that of the active layer; A seventh layer of the second conductivity type having a lower refractive index than the layer
It is characterized by comprising a semiconductor layer.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of one embodiment of the present invention. First, the manufacturing process of this embodiment will be explained.

First, in the first liquid phase epitaxial growth step, n
Type G, A, n saints on board 1 in sequence! . , 4Ga11.
6 people, 2 people in the 7th class, n-type people 120.9. GaQ, 6
1; person.

Optical waveguide layer 3. ^1 o, + lGa0-89 people, active layer 4. p saint f Q, 5GaO95Aa intermediate layer 5. p-type ^f! 0.4GaO-6^3 cladding layer 6. p-type A
J? A 0.05GaO15^8 electrode layer 20 is sequentially formed. The thickness of each of these layers is 1°0 μm, 0.5 μm, and
They are 0.05 μm, 0.3 μm, 1.5 μm, and 0.5 μm. Here, the difference from the multilayer structure constituting a conventional semiconductor laser is that p Saint ('XG, -XA, electric i
The AFil composition (X) of the layer 20 is made relatively small,
In this embodiment, it is created under the condition of 0.05≦X≦0.1.

Thereafter, using H2O2+H3PO4+3CH30)1 etchant, mesa etching is performed in stripes until reaching the n-type G, As substrate 1, thereby forming a mesa portion having an active region. Then, when etched for 1 minute at room temperature using HF solution, p-type A# 0.5Gal], 5 people,
Only the intermediate layer 5 is selectively etched to a depth of 0.3 μm from the mesa side surface. Furthermore, H20□+)I3PO
Do not expose using 4+3CH30H etchant^1o
-r+Gs0.89^8 When the active layer 4 is lightly etched for 10 to 20 seconds at room temperature, a constriction 8 with a depth of 0.3 μm is formed on the side surface of the mesa as shown in the figure.

Next, by a second liquid phase epitaxial growth process, p Saint I! 0-4G-66^8
Buried layer9. n-type^R014GaO-6Aa buried layer 1
Forming 0 sequentially 2 At this time, n saint! 0.4 Gar1.
6As buried layer] 0 is p saint ρ0.05GaO195
^3 It does not grow on the electrode layer 20, but grows selectively on the mesa sides. This is because the growth rate on the mesa sides is usually faster than on the mesa top, and a small amount of A is grown on the electrode layer 20. ! This is due to the fact that a very thin oxide layer is formed due to the presence of carbon dioxide, making it difficult for crystal nuclei to form.

Subsequently, a p-type β0-2Ga0.8As layer 21 and a p+-type G8^8 layer 22 are grown over the entire surface of the crystal. On this occasion,
By increasing the degree of supersaturation of the growth solution used to grow p-type f2 n-2G-o, sA, layer 21, p-type f2 n-2G-o, sA. ,. It can be uniformly grown on the 5GaO-95As electrode layer 20. This means that the ^ρ composition (X
) in the range of 0.05≦X≦0.1 using various supersaturation solutions, it was confirmed that uniform growth can be achieved at a supersaturation degree of about 7° C. or higher. Here p type”
o, 2 Ga o8A s layer 21 is 0.5 μr
The n, p+ type G, A, layer 22 had a layer thickness of 5)t,m. After that, the n-type electrode 12. n-type electrode] 3 is formed to form the buried semiconductor laser of this embodiment.

",Effect of the invention〕 As described above, according to the present invention, p"G, A.

Layer 22 is the top layer, and this layer has a p-type impurity concentration of about 10
"By doping C11-3 with Zn, G, etc., there is no need for a p-type impurity diffusion process as in conventional semiconductor lasers, and good ohmic properties are obtained with the n-type electrode 22, making it easier to manufacture. The upper process becomes easier.

In addition, since the crystal surface is flat over almost the entire surface, there is good adhesion between the laser chip and the heat sink, which is advantageous in terms of heat dissipation, and it is easy to achieve high yields in device assembly and high output operation.

Furthermore, even when using p-type G, A, substrates, it is p-type.

By simply inverting each n-type, the problem can be solved as follows. In other words, the n-type electrode is an n+ type GaA three layer (
In this example, the n-type Aβ0.20@D-8Aa layer and the p-type A! 1.
4Gao, 6Aa buried layer (in this example, p Saint β0
゜2GaO-8As layer 21. n-type Aβ0-400-4O
^8 Since a pn junction is formed with the pn junction (corresponding to the buried layer 10), the diffusion potential is higher than that of the pn junction in the mesa stripe part, and leakage current to the outside of the mesa can be completely prevented. Low oscillation threshold, high efficiency, and high output operation can be easily achieved.

It is also possible to make the 3 layers of n+03 people sufficiently thick,
The introduction of crystal defects due to the ohmic alloy of the n-type electrode can also be prevented, and a highly reliable laser element can be formed.

[Brief explanation of drawings]

FIG. 1 is an i-speed sectional view of an embodiment of the present invention, FIG.
FIG. 3 shows structural cross-sectional views of conventional buried semiconductor lasers. 1 =-n-type G, A, substrate, 2-n-type A 1 o, 4G
ao, 6As crat layer, 3 = -n type A f:! Q
-3'3Ga0.66 person, optical waveguide layer, 4- AI!
o, t lGm0.89 person m active layer, 5-p saint (!
n, qGall, 5As intermediate layer, 6-r) type A l
0.4GalliAs cladding layer, 7 ・P type person j?
Q, +11G110.8! I^6 electrode layer, 8-<fin part, 9-n Saint (2Q-4GaO-6Aa buried layer, 1
1...p-type impurity diffusion layer, 12...n-type electrode, 13
...n type electrode, 14-5I02 film, 20-p type A 1
o-o5G-o-7, electrode layer, 21-p type A 20
-2G-0,8A single layer, 22...p4 type G, A, layer. 1 bacteria

Claims (1)

[Claims] On a semiconductor substrate of a first conductivity type, at least a first semiconductor layer of a first conductivity type, a second semiconductor layer of a first conductivity type having a higher refractive index than the first semiconductor layer, and a second semiconductor layer of the first conductivity type. an active layer having a refractive index higher than that of the first semiconductor layer; a third semiconductor layer of a second conductivity type having a lower refractive index than the first semiconductor layer;
a striped multilayer structure formed by sequentially laminating a fourth semiconductor layer of a second conductivity type having the same refractive index as the semiconductor layer; a fifth semiconductor layer of a second conductivity type having a refractive index; a sixth semiconductor layer of a first conductivity type provided on a side surface of the third and fourth semiconductor layers and the active layer and having a refractive index smaller than that of the active layer; A semiconductor layer; and a seventh semiconductor layer of a second conductivity type provided on the crystal surfaces of the sixth semiconductor layer and the fourth semiconductor layer and having a refractive index lower than that of the active layer. Embedded semiconductor laser.