JPS6064489A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To contrive to stabilize the longitudinal modes of laser beam and to accurately control the film thickness of a clad layer by a method wherein the longitudinal modes of an active layer are locked in the longitudinal modes of a photo waveguide layer formed on the active layer and the photo waveguide layer is set at Y'<0.45. CONSTITUTION:A clad layer 4 is formed on an active layer 3. The clad layer 4 consists of an n type AlZ'Gs1-Z'As layer 41, an n type AlZ''Ga1-Z''As layer 42 and an n type AlY'Ga1-Y'As photo waveguide layer (Y'<Z', Y'<Z'', Y<Y', Y'<0.45Z''>0.45) 43, and the layer 43 is formed between the layer 41 and the layer 42. The photo waveguide layer 43 is set at an interval that the layer 43 generates no laser oscillation by the operating current. By this constitution, the longitudinal modes of the active layer 3 can be locked in the longitudinal modes of the photo waveguide layer 43. Accordingly, stabilization of the longitudinal modes of laser beams can be contrived and the film thickness of the clad layer 4 can be accurately controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for forming 1)(
or n)-AlxGa, -xAs layer (referred to as the first cladding layer) and non-doped or p (or n)-Al
yGaI-yA! The present invention relates to a stripe-shaped semiconductor laser formed by forming layers (active layer), 11 (main) layers, -zAs layers (second cladding layer), and a method for manufacturing the same.

FIG. 1 is a structural sectional view of a conventional semiconductor laser as seen from the light emitting surface direction 1r11. In Figure 11, the code 1 is (or n)-GaAs substrate, 2 is 1) (and 1 is 1).
1) - to 1xGa1-xAs layer (first crano layer and -
), :(is non-doped or 1) or n-l\1y
ciaI-Vi\s )m (i8 sex layer y
<x, y<z), 41 soil, 11 (also lyo 1)) - Al
zGal-zAs layer (tj, 2-kura-nod layer and (1)
, 5 is 11 + (also 1 Sat p”) - GaAsJM, 61
Soil 1'i layer, 71st soil AuJM, and 81st soil AuGcJ layer. In such a single semiconductor laser, during continuous wave operation, the spectrum oscillates in a single mode, but when high-speed modulation is performed, the return light of the laser beam changes without a throat. If the IR does not oscillate as a laser in single mode, there is a force C. Semiconductor lasers such as distributed L11 type, distributed reflection type, and double cavity type have been developed to solve this problem. However, all of these conventional types have complicated structures. Therefore, it is unsuitable for mass production and has the drawbacks of high manufacturing costs.Furthermore, in this semiconductor laser, in order to effectively confine light in the portion 9 of the active layer 3, a second cladding layer 4 is used. is etched to a predetermined thickness except for the stripe region 10. However, in order to obtain a semiconductor laser with uniform characteristics, it is necessary to precisely control the thickness of the grown film of each layer. , second cladding layer 4
It is also necessary to precisely control the etching of
Controlling this etching is extremely difficult, and therefore requires very expensive etching means such as ion milling.

The object of the present invention is to have a simple structure suitable for mass production, to reduce manufacturing costs, to improve the stability of the longitudinal mode, and to enable such etching to be performed precisely and easily at a low cost. shall be.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. This embodiment will be explained by applying it to a refractive index guided plastic semiconductor laser. Figure 2 is a cross-sectional view of this embodiment (1v?), and parts corresponding to Figure 1 and J =
I. In Fig. 2, the symbol 1 is 1) (or o) -
GuΔS substrate, 2 is 1) (Matoko is 11) - 8l x
(i a 1-xAsJVI (referred to as first cladding layer), 3 is non-doped or I) or 11-81yGa
+-y, AsJ- (active layer y < x,
y < z), 4 is the second cladding layer. This second cladding layer 4 has the same conductivity type as the second cladding layer 4 and has the same conductivity type as 11 (or p)-Alz'Ga+-z'AsJt4! 41 and 11 (or p)-Alz"Ga+-z"AsJ142
11 (or p)-AIy'Ga, -y'As between
Layer 43 (where 1 < Zl, yl < zII, y <y'
, y′<0.45, Z゛〉(1,45). 2n(Matkoha1+)-j\IS”(IQ+-3
”/\5 The layer 43 is an optical waveguide M, and this optical waveguide layer 43
(Activation 111j) 1 and 3 are set to such a distance that they optically interact with each other and that the optical waveguide Jf/J43 does not cause laser oscillation due to the operating current. Therefore, according to this embodiment, there are two 10 resonators 3,43. Since both 3 and 43 have the same distance, they are the same resonator Et l-, but the refractive index nl and n
2 will be different. Here, the longitudinal mode of the 7Avry-Perot reflective semiconductor laser will be explained. What is a longitudinal mode? A laser oscillator with a resonator length that is much longer than the wavelength can resonate waves of many different wavelengths, and this mode is called a longitudinal mode, also called an axial mode. Therefore, in the longitudinal mode, there are waves of many wavelengths, but spectrally a single mode is one of these waves.
Only one wave is in the selected mode. It is known that if the difference between each wavelength (longitudinal mode spacing) is 8λ, this longitudinal mode spacing can be expressed by the following equation.

Δλ=λ2Δm/2nL[1-(in/n)(dn/dλ
)1 Here, Ill is the order, ■ is the refractive index, and λ is the wavelength.

Since the longitudinal mode interval is reduced in this way, the active 7I3
Since the and optical waveguide layer 43 have different refractive indexes, their longitudinal mode intervals are different, but since they are optically coupled to each other, they resonate only at the same wavelength. 2, when the active layer 3 tries to jump to another adjacent longitudinal mode due to M, the longitudinal mode cannot resonate with the optical waveguide layer 43, so the longitudinal mode of the active layer 3 is transferred to the optical waveguide layer l[3 It will be locked to that. , -Thus, in the semicircular body laser of this embodiment, the longitudinal mode can be stabilized.

Next, in this embodiment, each layer is formed by molecular beam epitaxial growth or the like. The optical waveguide N43 of the second cladding layer is set as y'<(+,・15.Here, Ah,
FIG. 3 shows the etching rate 4ij of Ga1-zAs. FIG. 3 is a diagram showing the value of l on the JjQ axis and the etching rate on the vertical axis when etching υ]\1zGa+-7As with hot hydrochloric acid. As is clear from Fig. 3, when z<0.45, ＼1zGa, -z
As is not Lychched, and when z>0.45, ×
A I 7. with an etching rate proportional to the value of . Ga
, -y, A s I soil etched, - and 1
This will happen.

Therefore, by covering the stripe region 10 with a mask of Si, N4, etc.
Selectively remove the S layer 5 or remove the S layer 5 or
+81-7゜゛After removing part of the SA8 layer,
Further etching with hot hydrochloric acid results in AIZ”C:a+
-z"As layer 42 is removed. Therefore, the film thickness of the second cladding layer 4 is 41, 43, except for the stripe region 10.
Each film thickness is precisely controlled.

As described above, according to the present invention, the second cladding layer is of the same conductivity type as the @2 cladding layer and is 11 (or p) -A Iz'
Ga1-z'As layer and n (or 1))-A lz"
11 (or p)-Al between the Ga1-z” As layer
y'C;a+-y'As layer (however, yl x Z11y x Z'', y<y', y'<0.45, Z''>0.45
, y<x, y<z', y(,, l l ), and the distance between the AIy'Ga+-y'As1 (referred to as a leading wave layer) and the active layer is optically set to each other. In addition to interacting with each other, the optical waveguide layer is set at a spacing that does not cause laser oscillation due to the operating current, so even if the active layer tries to jump to another longitudinal mode due to return light, etc., the longitudinal mode cannot resonate with the leading wave layer. The longitudinal mode of the active layer is locked to that of the leading wave layer, and the longitudinal mode can be stabilized.

Further, the leading wave layer of the second cladding layer has y'<0. 45, Si3N was added to the stripe area using hot hydrochloric acid.
, etc., first n+ (or ρ”
) - (A) After selectively removing the 3rd layer or removing up to a part of the AIZ"C+11-7."A3 layer, further etching with hot hydrochloric acid results in A17."C
+al-2"As layer is removed, and therefore the thickness of the second cladding layer is accurately controlled to each predetermined thickness except for the stripe region.

[Brief explanation of the drawing]

FIG. 1 is a structural cross-sectional view of a conventional example, FIG. 2 is a structural cross-sectional view of an embodiment of the present invention, and FIG. 3 is a structural cross-sectional view of a conventional example.
FIG. 3 is a diagram showing etching rate characteristics of z AS. ], , p (or n ) −(ia AS substrate,
2. ,,++(or 11)-l\1xGa,-xAs
layer (referred to as first cladding layer), 3.0. Non-doped or 1) or a+4As layer in n-Aly (referred to as active layer, y<z), 4. . , 11 (or p)-1\1zGa=zAs layer (referred to as second cladding layer), 508. n” (or ll+) C
;+IAS layer, 6,,,"riJl,7.,,Au layer,
800. AuGeJt'), 41. ,,n(or 1+
)-A I7. '(ia, -2' ASJ(11,4
2, ,, n (or p) Alz” to al-z”As
layer, 436. , n (or p)-toly'Gu, -y'
As layer (optical waveguide layer) Applicant ROHM Co., Ltd. Agent Patent attorney Kazuhide Okada

Claims (2)

[Claims] (1) P (or n) on p (or n)-GaAs substrate
)-AlxGal-xAs layer (referred to as first cladding layer)
and undoped or p or n-AlyGa+-yA
s layer (referred to as active layer) and n (or p)-AlzGa
In a striped semiconductor laser in which a +-zAs layer (referred to as a second cladding layer) is formed, the second cladding layer is of the same conductivity type as the second cladding layer and is of n (or p)-
Alz'Ga+-z'As7ii1 and n (or p)-
n (or p)- between Alz"Ga, -z"As layer
AIy'GaI-y'As layer (where l < zll
, I<zII, y<y', y'<0.45, z''>0.
45, y<x, y<z', y<2"), and the distance between the Aly'Ga1-y"As layer (referred to as a leading wave layer) and the active layer is optically set to each other. A semiconductor laser in which the leading wave layer interacts with each other and is set at intervals such that the leading wave layer does not cause laser oscillation due to operating current. (2) A D (or n)-GaAs substrate, a + (or n)-AlxGa, xAs layer (referred to as the first cladding layer), and a non-doped (or I) or n-A 1yGa
1-yAs layer (referred to as active layer) and 11 (or p)-
In the method of manufacturing a stripe-shaped semiconductor laser by forming an AlzGa+-zAs layer (referred to as a second cladding layer), the second cladding layer is formed of n (or p) -A
Iz'Ga+-z' AsIvi and n (or p)-
11 (or p)- between the Alz"Ga and z"As layers
Aly'Ga+-y'As layer (where yl < ,,
ll, l < Zll, y <y',y'< o, 45,
z">0.45, y<x, y<z', y<Zl 1
), the distance between the Aly'Ga1-y'As layer (referred to as an optical waveguide layer) and the active layer is controlled so that they optically interact with each other, and the waveguide layer causes laser oscillation by an operating current. A method of manufacturing semiconductor lasers by setting intervals that do not cause