JPS60102787A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To contrive to reduce the wattless current and to convert the current into current of a lower threshold value by a method wherein the width of an optical guide layer is made larger than that of an active layer, current blocking layers are provided and the positions of interfaces to the active layer are respectively controlled. CONSTITUTION:Each mesa stripe of a first clad layer 2, an optical guide layer 3, an active layer 4, a second clad layer 5 and a cap layer 6 is laminatedly provided on a substrate 1 in the abovementioned order. The width of the optical guide layer 3 is formed wider than that of the active layer 4, and the side parts of the mesa stripes are buried with a multilayer film, which includes at least one layer of current blocking layers 7 of a reverse conductive type to that of the substrate 1 and has a larger forbidden band width than that of the active layer 4 and has a smaller refractive index than that of the layer 4. In this semiconductor laser constituted in such a way, at least one interface of either of the interface of the current blocking layer 7 and that of the current blocking layer 7 buried in the next place has been connected with the cap layer 6 at the sides of the mesa stripes. As a result, the sides of the active layer 4 are buried with the current blocking layers 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a high-output buried hetero type semiconductor laser device.

[Background of the invention]

Many proposals have been made to try to increase the output of semiconductor laser devices. Typical examples include providing a so-called optical guide layer in contact with the active layer and making the output end face of the laser beam transparent, but it cannot be said that a sufficiently high output has been achieved yet.

[Purpose of the invention]

An object of the present invention is to provide a high output and low threshold semiconductor laser device.

Another object of the present invention is to provide a semiconductor laser device with high output and stabilized transverse mode.

[Summary of the invention]

A first layer is formed on a predetermined semiconductor substrate. Second. 3rd and 4th
The first and fourth semiconductor layers have a refractive index smaller than that of the second and third semiconductor layers, and the refractive index of the third semiconductor layer is smaller than that of the second and third semiconductor layers. is set to be equal to the refractive index of the second semiconductor layer. At least the first and fourth semiconductor layers are provided to have opposite conductivity types. At the same time, the forbidden band widths of the second and fourth semiconductor layers are set to be at least wider than that of the third semiconductor layer. Thus, carriers are confined to the third semiconductor layer, while photons are confined to the second and third semiconductor layers. The second semiconductor layer is commonly called a light guide layer, the third semiconductor layer is called an active layer, and the first and fourth semiconductor layers are called cladding layers. In a specific semiconductor laser device, between the substrate and the optical confinement region,
Although a semiconductor layer may be further provided above the optical confinement region, the present invention can be applied in this case as well, and the essence of the present invention is not affected.

In the present invention, the width of the second semiconductor layer in the cross section perpendicular to the traveling direction of the laser beam and in the direction parallel to the pn junction surface is wider than that of the third semiconductor layer, and at least The semiconductor layer No. 4 is formed into a mesa stripe shape, and the entire side wall of the mesa stripe semiconductor layer in a direction perpendicular to the traveling direction of the laser beam is buried with the fifth semiconductor layer. The refractive index of the fifth semiconductor layer is made smaller than the refractive index of at least the second and third semiconductor layers. In this case, it is preferable for manufacturing reasons that the buried layer reach the semiconductor substrate. Further, the fifth semiconductor layer may be composed of multiple layers.

Since the width of the light guide layer is larger than that of the active layer, higher output can be achieved than by providing the light guide layer.

The present invention further provides a current blocking layer (buried layer) and controls the position of this interface with respect to the active layer to reduce reactive current and lower the threshold current value.

Further, in a cross-sectional structure taken in a plane parallel to the traveling direction of the laser beam, it is more preferable that the active layer does not reach the output end face, while the light guide layer reaches the output end face. Since the active layer is covered with the buried layer, light is mainly emitted outside the light guide layer, making it more suitable for high output and advantageous for extending life.

Note that the stacking order of the light confinement region formed by stacking the first to fourth semiconductor layers may be reversed to the above-described order with respect to the substrate.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 2 and 3. Note that FIG. 1 is a sectional view showing a comparative example.

Example 1 FIG. 2 is a cross-sectional view when the present invention is applied to a GaAtAs-based semiconductor laser. (a) shows a case where there is one current blocking layer, and (b) shows a case where there are two current blocking layers. It is.

First, pn-GaAs was grown by liquid phase epitaxial growth.
nGao, 6s At, 34AS cladding layer 2 (0.8~211 m), nGao, t on substrate 1
Alo, sAS optical guide layer 3 (0.4-3 μm), undoped oao, ssA to, 14 A S active layer 4 (
0.04-0.4μm), p-Gap, 5Am, 5A8
Cladding layer 5 (0.8-2 μm), 1) Gao, s
Ato, 2 A s cap layer s (0,5~1 tt
m) are grown sequentially. At this time, the refractive index of the n and p cladding layers is smaller than the refractive index of the active layer and the light guide layer, and the refractive index of the light guide layer is V smaller than the refractive index of the active layer.
Also make it smaller. Furthermore, the composition of AtAs in each layer may be appropriately selected in addition to the present embodiment within a range that satisfies the above relationship in magnitude of refractive index. In this example, in order to avoid epitaxial growth on the mesa stripe during buried growth and to make ohmic contact as easy as possible, the cap layer was a Ga00IIAM and 2AS layer.

Next, after a photo-etching process, mesa-etching is performed to form mesa stripes in a direction in which the p-section has a trapezoidal shape. Furthermore, the p-Gao, At, 5A8 cladding layer 5 is selectively etched to narrow the width.

Next, the active layer 4 exposed by the selective etching is removed by etching.

Next, on the sides of the mesa stripe, at least one current blocking layer of a conductivity type opposite to that of the substrate (ll''j:p type in this example) is formed, which has a large forbidden band width and a small refractive index compared to the active layer. In the case of Fig. 2(a), first pG
ao, 5A4+, 5A s current proc layer 7, and ``Gao, s A4+, s Ass layer.

12) When current tff is applied to layer 7 and nGaQ, ri A
! The interface between the A and B Ass layers is made to contact the cap layer 6 at the side of the mesa stripe. 1, current blocking layer 7
It is necessary to make the carrier concentration of the up-cladding layer 5 smaller than that of the up-cladding layer 5. In this example, the carrier concentration of the p-cladding layer 5 is 6X1017m-3, and the carrier concentration of the current blocking layer 7 is lXl0''. crn-”. In the case of FIG. 2(b), first, p-Gao, 5A
tn, s A S Buried with current blocking layer 7 and further n G
ao, s layer, sAS layer 8, pGao, s Ato, 6
As current blocking layer 9, n Gao, s Ala, s
The As layer 10 is buried in this order.

When the current blocking layer 9 and n Gao, a Ato,
The interface of the BAs layer 10 is brought into contact with the cap layer 6 at the side of the mesa stripe, and the side of the active layer 4 is buried with the current blocking layer 9. Also in this embodiment, the carrier concentrations of the p-cladding layer 5 and the current blocking layer 9 are each 6.
X 10” cm-”, I X 1017Crn-”
And so.

Current blocking layer 7 and n-oao in FIG. 2(a)
, 5A, 5A The interface between the 5 layers 8 and the current blocking layer 9 in FIG. 2(b) and the n-Gao, 5A, SA
Ideally, it is desirable that the interface of the s-layer 10 be at the same position as the active layer 4 or very close to it.
In the (iedHeterostructure) type laser, it is very difficult to control the position of the interface to be close to the active layer 4. On the other hand, it is easy to control the interface so that it is in contact with the cap layer 6 as in this embodiment. Further, as the buried layer, only the current blocking layer that buries the sides of the active layer may be a GaAtA3 layer having a larger forbidden band width and a lower refractive index than the active layer.

Next, selective diffusion 11 of Zn is applied to the mesa stripe area (
However, in this embodiment, the current blocking layer is provided in areas other than the mesa stripe area, so the entire surface may be diffused). 12.
13 are n and p electrodes.

In FIG. 2(b), the case where the current blocking layer is two layers is shown, but the current blocking layer is made of two or more layers of n-Gao,
The s Ato and s A s layers may be buried alternately. However, the sides of the active layer 4 are always filled with at least one current blocking layer. Providing a large number of current blocking layers in this manner increases the effect of blocking current flow to areas other than the mesa stripe region.

p-G ao, s A tCl, s A s layer is n G
ao, 5Ato, s layer Since the specific resistance is higher than that of the s layer, the side part of the active layer 4 is I) Gao, 5At as in this example.
o, s layer buried with s layer (current blocking layer 7 or 9), and buried with current blocking layer and then n Gao
, s ALo, B A By creating a structure in which at least one interface of the s layer is in contact with the cap layer 6 at the side of the mesa stripe, the area flowing outside the substantial stripe region (corresponding to the width of the active layer) in FIG. The reactive current as shown by the arrow can be reduced.

In the semiconductor laser having the structure shown in FIG. 1, the active layer is 3 to 5μ
The threshold current was about 70 to 100 mA (9) degrees. However, according to this embodiment, the threshold current can be reduced to about 40 to 50 mA at the active layer width, and 5 A of SAS to the current blocking layer 7 or 9 and the n-()a buried next. The same level of threshold current reduction effect as when the interface between the layers was located at the same position as the active layer 4 or very close thereto was obtained.

Example 2 FIG. 3 shows the above semiconductor laser manufacturing in Example 1,
This figure shows a cross-sectional structure in the laser optical axis direction of an element whose end face is made transparent to laser light.

The light guide layer 3 exists up to the laser beam reflecting end face, and the active layer 4
The end face is located inside the reflective end face. In Example 1, after forming a mesa stripe in a direction in which the cross-sectional shape becomes a trapezoid by mesa etching, a pGaQ, 8 Ato4A8 cap layer 6, I) near the end face is formed.
-Gao, s Ato, 5A S Only the cladding layer 5 and active layer 4 are removed by etching. after that,
The outside of the mesa stripe was filled in by the filling growth method shown in Example 1. At this time, (10) As shown in FIG.
ao, 5Ato, B A s layer 7).

In this example, the threshold current was reduced to the same level as in Example 1, and a visible semiconductor laser device with a maximum optical output IW was obtained. In addition, because the current flowing near the laser beam reflecting end face can be reduced, damage to the end face due to heat is also reduced and reliability is improved.

〔Effect of the invention〕

According to the present invention, reactive current can be reduced by controlling the position of the current blocking layer, and threshold current can be reduced. Therefore, reliability is improved, especially in high-power operation. The threshold current has an oscillation wavelength of 780 nm,
An output of 40 to 50 mA was obtained in a device with an active layer width of 3 to 5 μm.

In addition to the above characteristics, the maximum light output I
A W element was obtained, and by reducing the current flowing near the end face, damage to the end face due to heat was reduced and reliability was improved.

(11) In the semiconductor laser device having the structure shown in FIG. 1, there is a reactive current that does not contribute to laser oscillation, as indicated by an arrow in the figure. These reactive currents have a considerably large proportion compared to the current flowing through the substantial stripe region (corresponding to the width of the active layer). Therefore, this structure has the disadvantage that the threshold current is large.

In addition, in FIG. M1, the same parts as in FIG. 2 are designated by the same reference numerals.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a semiconductor laser device showing a comparative example to the present invention, FIG. 2 is a sectional view of a semiconductor laser device according to the present invention, and FIG. 3 is a semiconductor laser device of FIG. FIG. 1-n-GaAS substrate, 2 = n Gao, ss A
7! (+, 3JAs cladding layer, 3”・n Ga
+1.7 At43.3As optical guide layer, 4... Undoped Gao, HA414 A 8 active layer, 5...
pG ao, s A Lo, s A s cladding layer, 6
,・I) -Ga0,8Am,2AS cap layer, 7
...-1) -GaQ, 5 Ato, 5AS electric (12
) flow block layer, 8...n-Gao, s Ato,
s A 8 layers, 9... pGao, s Alo4 A
s current blocking layer, 10.n-Ga0. II Alo
, 5As layer, 1l-Zn diffusion layer, 12-n (13) Fig. 1 Fig. 3 Continued from Fig. 1 page ■ Inventor Michiharu Nakamura Kokubunji ■ Minoru Keo Research Institute Uchikubo 1-28 Hitachi, Ltd. Middle 439-

Claims (1)

[Claims] 1. The mesa stripes of the first cladding layer, the optical guide layer, the active layer, the second cladding layer, and the middle layer are stacked in the above order on the substrate, and the width of the optical guide layer is The width of the active layer is wide, and the sides of the mesa stripes include at least one current blocking layer of the conductivity type opposite to that of the substrate. In the embedded semiconductor laser device, at least one interface between the current blocking layer and the next buried layer is in contact with the cap layer on the side of the mesa stripe, and the side of the active layer is buried in the current blocking layer. A semiconductor laser device characterized in that: 2. In the semiconductor laser device according to claim 1, the optical guide layer exists up to the reflective end face of the laser resonator, the active layer end face is located inside the reflective end face, and the vicinity of the reflective end face is located in the semiconductor layer. A semiconductor laser device characterized by being fully embedded.