JPH02228087A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To improve the high output and low noise characteristic by constructing an active layer of a single quantum well layer and superlattice multiple quantum well layers provided on the upper and lower surfaces thereof and forming a ridged waveguide structure for obtaining a self-oscillating laser element. CONSTITUTION:An active layer is constructed of a single quantum well layer 5 and superlattice multiple quantum well layers 4, 6 provided on the upper and lower surfaces thereof, and composition, film thickness, and impurity concentration of respective layers 4, 5, 6 are caused by have predetermined values. A light waveguide layer, on the opposite side of a semiconductor substrate with respect to the active layer, has a mesa-stripe-like ridged part extending in the resonator length direction, and light absorption and current constriction parts are formed on the light waveguide layer with the ridge part at the both ends of the ridged part, and self-oscillation is effected. Therefore, the laser light distribution is controlled and the light absorption layer is provided at a predetermined position relative to the active layer, so that the effective refraction index difference in the lateral direction of the active layer can be caused to have a desired value. Thus, a high output characteristic required by a writing and erasing light source for an optical disk, and a low noise characteristic required by a reading light source can be obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a semiconductor laser device having high output and low noise characteristics suitable as a light source for a rewritable optical disk.

[Prior Art] Conventionally, the single quantum well layer side of a semiconductor laser is mainly used to reduce the threshold current. Furthermore, superlattice optical waveguide layers are provided above and below the single quantum well active layer in order to improve the flatness of the quantum well interface and improve crystallinity. Regarding this type of semiconductor laser, 1. For example, the 46th Japan Society of Applied Physics Academic Conference, Proceedings IP-N-8, P196.
It is stated in [Problems to be Solved by the Invention] The above-mentioned conventional technology does not take into consideration the transverse mode control of the laser beam and the longitudinal mode control based on the refractive index difference in the lateral direction of the active layer on the semiconductor laser element layer side. There was a problem that desired high output characteristics and low noise characteristics could not be obtained. An object of the present invention is to realize a semiconductor laser device that satisfies high output and low noise characteristics.

[Means to solve the problem]

In order to achieve the above objective, the active layer is formed on the layer side where superlattice multiple quantum well layers are provided above and below the single quantum well layer, and the composition, film thickness and impurity concentration of each layer are set to predetermined values. This is a fabricated laser device. Furthermore, in order to obtain a self-oscillation laser device, a ridge waveguide layer side is formed, and the effective refractive index difference in the lateral direction of the active layer is controlled to a predetermined value.

[Function 1] It will be explained below that the present invention provides low noise and high output characteristics necessary for a light source for writing and erasing an optical disk and a light source for reading. Conventionally, it is known that the threshold current of laser oscillation can be lowered by introducing the single quantum well layer side into the active layer. Additionally, Applied Fixtures Letters,
Appl, Phys, Lett. 45 (1984) p. 836, a single quantum well active layer laser device has a lower refractive index due to carrier injection than a normal double hetero active layer or multi-quantum well active layer laser device. is small. As a result, a laser device with a single quantum well active layer has high output characteristics with large king-generated light output without destabilizing the built-in effective refractive index difference in the lateral direction of the active layer to a high carrier injection level. It is suggested that this can be obtained. However, since the single quantum well active layer is thin, the laser light widely spreads to the cladding layer. Therefore, in a laser element in which a light absorption layer is provided to control the transverse mode, there is a problem in that the effective difference in refractive index in the transverse direction of the active layer becomes large. Further, there is a problem in that it is difficult to control the longitudinal mode by controlling this refractive index difference. On the other hand, self-sustained oscillation lasers, which achieve excellent low-noise characteristics with a relative noise intensity of 10-14 to IQ-''Hz even when reflected light occurs, have an effective refractive index difference in the lateral direction of the active layer of lXl0-' It occurs in a range of about 5×10−”. Therefore, in order to realize a self-oscillation laser, it is important to control the effective refractive index difference in the lateral direction of the active layer. This effective refractive index difference in the lateral direction of the active layer can be controlled by the active layer thickness and cladding layer thickness of the element. In the present invention, superlattice multiple quantum well layers are provided above and below the single quantum well layer, so the wave functions of electrons and holes as carriers are not confined within the single quantum well layer.
It seeps out significantly on both sides of the single quantum well layer. As a result, the spread of laser light distribution in the active layer is smaller than in the case of a conventional single quantum well active layer. The width of the single quantum well layer can take a relatively large value within the range where the quantum size effect occurs, and is preferably in the range of 10 to 30 nm. In this manner, by controlling the laser beam distribution and providing the light absorption layer at a predetermined position from the active layer, it is possible to realize the effective refractive index difference in the lateral direction of the five active layers to a desired value. By controlling the refractive index difference, self-oscillation laser devices can be fabricated, and since the refractive index decrease due to carrier injection is small in a single quantum well layer, the built-in refractive index difference is not lost even at high injection levels and is stable. High output characteristics with large king-generated light output can be obtained in the fundamental transverse mode. [Embodiment 1 Embodiment 1] Embodiment 1 of the present invention will be described with reference to FIG. First, an n-type GaAs (001) substrate 1 (thickness 100 μm
), an n-type GaAs buffer layer 2 (thickness 0.5 μm)
, n-type ARxGal-xAs clad M3 (thickness 1.0
~1.5 μm, x=0.45-0.55), undoped or n-type or p-type multi-quantum well 1! F4 (Quantum barrier layer is AnyGa, -yAs layer, width 2-5 nm, y = 0.20
~ 0.45, and the quantum well layer is an Alzoa, -zAs layer, width 3 ~ 10 nm, and z = o ~ 0.20.
~6 times, or by forming each Al
, Ga, -As superlattice barrier layer width 0.5-1 nm, A
By repeatedly forming a QzGal-zAs superlattice well layer with a width of 0.5 to 2 nm 10 to 15 times, the energy band layer side of the conduction band and valence band in the active layer as shown in FIG. 2 is formed. ), undoped single quantum well layer 5
(A Q z'Gag-z' As layer, 10-30n
m, z' = O ~ 0.15), undoped, n-type or P-type multiple quantum well layer 6 (quantum barrier layer is AlyGa□-y
As layer, width 2-5 nm, y=0.20-0.45,
The quantum well layer is an AlzGal-zAS layer, Itlii3~
These are repeatedly formed 3 to 6 times with lOnm and z=O to 0o20. or AlyGai-yAs superlattice barrier layer, flQiio, 5~L nm, AlzGa
An x-zAs superlattice well layer with a width of 0.5 to 2 n ITI is repeatedly formed 10 to 15 times. ), p-type A Q x
Ga knee x As cladding layer 7 (thickness 1.0 to 1.6
μm, X=0.45-0.55), p-GaAs/if
(thickness 0.2 to 0.3 μm) using secondary beam epitaxy (MBE) using metal organic chemical vapor deposition (MOCVD)
Epitaxial growth is performed by the method. Next, a Sio2 film is formed and a stripe mask pattern is produced by photolithography. Using this striped Sin film as a mask, M8 and layer 7 are etched using a phosphoric acid solution to form a ridge-shaped optical waveguide. Thereafter, an n-GaAs current blocking layer 9 (thickness: 0.7 to 1.0 μm) is selectively grown while leaving the SiO□ film. Next, after removing the Sin film mask by etching with a hydrofluoric acid aqueous solution, the p-GaAs cap layer 10 (thickness 1.0
~2.0 μm) is buried and grown. Thereafter, a p-type layer side electrode 11 and an N-type layer side electrode 12 are formed, and then cleaved and scribed to cut out into an element shape. In this example, in order to laser oscillate in the fundamental transverse mode and with a low threshold current, the stripe @S at the bottom of the ridge must be 4
~6 μm was appropriate. Furthermore, the thickness d of the cladding layer after fabricating the ridge waveguide is 0.3 to 0.6.
A laser device that self-oscillates when the diameter is μm was obtained. This device oscillated with a threshold current of 10 to 20 mA, and self-oscillated with an output power of 2 to 30 mW. The King generation optical output was 50 to 60 mW6.Furthermore, n-type or p-type impurities were added to the multiple quantum well layer in the active layer.
By doping 10" to I x 10"am-", it was possible to oscillate the laser with a threshold current of 10 to 20 mA, and to control the self-oscillation frequency by the dopant polarity and doping concentration. By applying an asymmetrical coating to the end face of the resonator, self-oscillation is achieved with an optical output of 2 to 50 mW.
Moreover, it was possible to obtain an element with a king-generated light output of 80 to 90 mW. By controlling the thickness of the entire active layer and the thickness of the cladding layer to predetermined values, 5 (active layer thickness: 0.0
4-0.08 μm, cladding layer thickness: 0.3-0.6
μm), self-sustained oscillation in the optical output range of 2 to 10 mW, and a device with a king generation optical output of 110" and 120 mW. This has made it possible to realize an element that is necessary as a light source for writing and erasing optical discs and a light source for reading. Low noise and high output characteristics could be satisfied in one device. Example 2 Example 2 of the present invention will be explained using FIG. 3. FIG. 3 shows the energy band layer of the conduction band in the active layer. In the multiple quantum well layers 4 and 6 provided above and below the single quantum well layer in the active layer, the quantum well layer A
A laser device was fabricated in which the Al set iz of Q zGa, -zAsll was larger than the Al composition 2' of the single quantum well N5, A n z'Ga□-z' As layer (z>z'). Here, the quantum level formed in the multiple quantum well layer is at the same level as or higher than the quantum level formed in the single quantum well layer. The layer sides of multi-quantum well layers 4 and 6 were designed. According to this example, the threshold current could be further reduced and laser oscillation was possible at 5 to 10 mA. Other characteristics similar to those of Example 1 are obtained. Embodiment 3 A third embodiment of the present invention will be explained using FIG. 4. FIG. 4 schematically shows the energy band layer side of the conduction band in the active layer. In the multiple quantum wells N4 and 6 provided above and below the single quantum well layer in the active layer,
The widths and Al compositions of the lzGa and -zAs layers 4' and 6' are made gradually thicker from the single quantum well N5 to the cladding layers 3 and 7, respectively. In addition, a laser element having a layer side whose size is changed to increase in size was fabricated. The layer sides of the multiple quantum well layers 4 and 6 are arranged so that the quantum level formed in the multiple quantum well layer is at the same level as or higher than the quantum level formed in the single quantum well layer. Designed. This example also had the same effect as Example 2. Embodiment 4 Embodiment 4 of the present invention will be explained using FIG. 5. FIG. 5 shows a schematic view of the energy band layer side of the conduction band in the active layer, showing quantum barrier layers AU in multiple quantum wells M4 and M6 provided above and below the single quantum well layer in the active layer.
A laser device was fabricated as a graded layer in which the Al composition y of the yGa-As layer was gradually changed from the single quantum well layer to the cladding layer. here,
The quantum levels formed in the quantum well layer of the multiple quantum well layer are graded energy levels that gradually become higher levels from the single quantum well layer toward the cladding layer. This example also had the same effects as Examples 2 and 3. [Effects of the Invention] According to the present invention, it is possible to control the effective refractive index difference in the lateral direction of the active layer on the single quantum well layer side, which was difficult to achieve with conventional techniques. This has the effect that mode control becomes easy and desired laser characteristics can be obtained. On the ridge waveguide layer side of the present invention, the cladding layer film thickness after ridge formation is 0.3 to 0.6 μm, and
The thickness of the entire active layer is in the range of 0.05 to 0.08 μm,
A laser element was obtained which self-oscillated in an optical output range of 2 to 30 mW and had a kink-generating optical output of 50 to 60 mW. A device with a threshold current of 5 to 10 mA was obtained. moreover,
By applying an asymmetrical coating, the light output is 2 to 50
Self-sustained oscillation in the mW range, King generation light output 80-90
By controlling the effective refractive index difference in the lateral direction of the active layer, we were able to obtain a device with a power output of 2 to 1 mW.
Self-sustained pulsation in the range of 0 mW and king generation optical output 110
A device with a power of ~120 mW was obtained. Therefore, it was possible to satisfy the high output characteristics required for an optical disk write/erase light source and the low noise characteristics required for a read light source. Although the present invention has been explained using AlGaAs-based materials,
ADGaInP/GaAs system, InGaAsP/InP
It goes without saying that the same thing can be done for systems as well.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a semiconductor laser according to Examples 1 to 4 of the present invention, and FIGS. 2 to 5 are schematic views of the energy band layer side of the active layer in Examples 1 to 4, respectively. . 1-=n-GaAs substrate, 2-n-GaAs buffer layer, 3-n-A Q xGa, -xAs cladding layer. 4... Undoped or n-type or p-type impurity-doped multiple quantum well layer, 5... Undoped single quantum well layer, 6...
...Undoped layer is n-type or p-type impurity-doped multiple quantum well layer, 7...p-AlxGa, xAs cladding layer,
8=-p-GaAs layer, 9.=rr-GaAs current blocking layer, 10... p-GaAs cap layer, 11.
. . . n-type layer side electrode, 12 . . . n-type layer side electrode.

Claims (1)

[Claims] 1. In a semiconductor laser device in which an active layer with a small bandgap and an optical waveguide layer with a large bandgap sandwiching the active layer are formed on a semiconductor substrate, the active layer has an electron wavelength of The optical waveguide layer on the side opposite to the semiconductor substrate with respect to the active layer is a mesa extending in the cavity length direction. 1. A semiconductor laser device having a striped ridge portion, having light absorption and current confinement formed on both sides of the ridge portion on the ridge member optical waveguide layer, and self-oscillating. 2. A semiconductor laser device according to claim 1, wherein the multiple quantum well layer is formed by controlled epitaxial growth using atomic layers. 3. A semiconductor laser device according to claim 1, wherein the active layer has a thickness of 0.04 to 0.08 μm. 4. A semiconductor laser device according to claim 3, wherein the width of the single quantum well layer is in a range of 10 to 30 nm. 5. In the semiconductor laser device according to claim 4, the width of the superlattice layer in the multiple quantum well layer is 0.
A semiconductor laser element having a wavelength of 5 to 2.0 nm. 6. In the semiconductor laser device according to claim 1, the optical waveguide layer is made of an Al_xGa_1_-_xAs layer (0.45≦x≦0.55), and the quantum barrier layer in the multiple quantum well layer is made of an Al_yGa_1_ −_yAs layer (0.20≦y≦0.
45), the quantum well layer consists of an Al_zGa_1_−_zAs layer (0≦z≦0.20), and the single quantum well layer consists of an Al_z′Ga_1_−_z′As layer (0≦z′≦0.
15) A semiconductor laser device consisting of: 7. In the semiconductor laser device according to claim 6, the Al composition z of the Al_zGa_1_-_zAs quantum well layer is larger than the Al composition z' of the Al_z'Ga_1_-_z'As single quantum well layer. element. 8. In the semiconductor laser device according to claim 6, the Al of the Al_zGa_1_-_zAs quantum well layer or the Al_yGa_1_-_yAs quantum barrier layer
The semiconductor laser device is a so-called graded layer whose composition gradually increases from the single quantum well layer side to the optical waveguide layer side. 9. In the semiconductor laser device according to claim 7 or 8, each layer of the multi-quantum well layer is formed with a predetermined thickness and composition, so that a quantum standard formed in the multi-quantum well layer is formed. A semiconductor laser device in which the quantum level is at the same level or larger than the quantum level formed in the single quantum well layer. 10. The semiconductor laser device according to claim 1, 3, 4, 5, 6, 7, 8 or 9, wherein the entire multi-quantum well layer A semiconductor laser device doped with either n-type or p-type impurities, or doped with n-type and p-type impurities simultaneously. 11. In the semiconductor laser device according to claim 1, 3, 4, 5, 6, 7, 8 or 9, in the multi-quantum well layer. A semiconductor laser device in which only the quantum barrier layer is doped with either an n-type or p-type impurity, or with n-type and p-type impurities simultaneously. 12. In the semiconductor laser device according to claim 10 or 11, the doping concentration of the n-type or p-type impurity is 1×10^1^8 to 1×10^1^9c.
A semiconductor laser device in the range of m^-^3. 13.Claim 10, 11 or 12
In the semiconductor laser device described in Section 1, the n-type impurity may include Si, Se in the form of a simple substance or an inorganic or organic compound.
A semiconductor laser device characterized in that p-type impurities include Be, Mg, and Zn in the form of simple substances or inorganic and organic compounds as doping ions.