JPH0546115B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to semiconductor lasers, particularly graded index wave separation-confirmation heterostructures.
Waveguide Separate−Confinement
Heterostructure (GRIN-SCH) structure semiconductor laser (Appl.phys.Lett., vol 40, No. 3, P. 217,
1982))).

(Prior art and its problems) A conventional GRIN-SCH structure semiconductor laser has a refractive index between the active layer and the cladding layer, and moreover, the refractive index decreases with a power law distribution as it approaches the active layer and the cladding layer. A graded guide layer is provided between the active layer and the cladding layer, and this plays the role of a light guide layer. Therefore, even if the active layer is made into an ultra-thin film with a thickness of 200 A or less, it is possible to suppress light seepage from the active layer, and this type of semiconductor laser oscillates with an ultra-low threshold current of several hundred A/ ^cm2 . do. However, the crystallinity of the graded guide layer in contact with the active layer was still insufficient, and the luminous efficiency was low, especially when evaluated by photoluminescence and other evaluation methods. For this reason, the threshold current density of this type of semiconductor laser has not yet been sufficiently low and needs to be improved.

(Object of the Invention) An object of the present invention is to provide a good semiconductor laser that oscillates at a lower threshold current density than the current CRIN-SCH structure semiconductor laser.

(Structure of the Invention) The semiconductor laser of the present invention has a multilayer structure including at least an active layer and two graded guide layers sandwiching the active layer above and below, and these graded guide layers form potential wells and potential barriers. It has a superlattice structure in which layers are alternately stacked, and the height of the potential barrier increases as it moves away from the active layer.

(Example) Next, the present invention will be described in detail with reference to the drawings.
A cross-sectional view of one embodiment of the present invention is shown in FIG. In the figure, 1 is an n-GaAs substrate, 2 is a buffer layer (n
-GaAs), 3 is an n- _type cladding layer (n-Al
Ga _1-X3 As, 0.3≦X ₃ <1), 4 is the first graded guide layer (consisting of superlattice structure, thickness 300~
5000A), 5 is the active layer (Al _X5 Ga _1-X5 As, X ₅ < X ₃ ,
6 is the second graded guide layer (consisting of superlattice structure, thickness 300-5000A), 7 is the P-type cladding layer (P-Al _X7 Ga _1-X7 As, 0.3≦X ₇ <
1, x ₇ > x ₅ ), 8 is the cap layer (P ⁺ GaAs), 9 is
SiO ₂ film, 10 is a P-type electrode, 11 is an n-type electrode, 1
This is the 2-stripe part. In this embodiment, a so-called SiO ₂ stripe type current confinement structure in which the SiO ₂ film 9 is used as an insulating film and electrodes are formed only in the stripe portion 12 is adopted.

FIG. 2 shows an energy band diagram of the main parts of this embodiment. The first graded guide layer 4 is a potential well layer 20 (n-type or non-doped).
Al _X20 Ga _{1-X20 As} , typically
It has a superlattice structure in which Al _X21 Ga _1-X21 As (X ₂₀ <X ₂₁ ≦1, X ₂₁ changes graded in the film thickness direction) are stacked alternately. Potential barrier layer 21
Since the thickness of the superlattice is set to be less than the electron de Broglie wavelength (<40A), the quantization level of this superlattice forms a mini-band, and electrons can easily tunnel through the potential barrier. Furthermore, the Al composition ratio X ₂₁ of the potential barrier layer 21 is the same as that of the active layer 5.
It changes to become smaller as it approaches . As an example, assume that the thicknesses of the potential well layer 20 and the potential barrier layer 21 are 10A and 10A, respectively.
When the magnitude of X ₂₁ is changed from 1 to 0.4, the equivalent Al composition ratio of the first graded guide layer 4 changes from 0.5 to 0.2. As described above, in the semiconductor laser of this embodiment, by changing the Al composition ratio _X21 of the potential barrier layer 21 to a graded value, a graded guide layer is equivalently formed. Similarly, the second graded guide layer 6 also has a potential well layer 22 (P
_{type or nondope Al _ _ _}
1, _X23 has a periodic structure (graded changes in the film thickness direction).

(Effects of the Invention) It has been experimentally confirmed that these AlGaAs/GaAs superlattices have better crystallinity, especially luminous efficiency, etc., than conventional AlGaAs liquid crystals in which Al and Ga are randomly mixed. Therefore, since the semiconductor laser of the present invention uses such a superlattice structure with excellent luminous efficiency for the graded guide layer, it is more efficient than a semiconductor laser having a graded guide layer using conventional AlGaAs liquid crystal. It has become possible to oscillate with a low threshold.

Next, the manufacturing method will be briefly described. First, a buffer layer 2, an n-type cladding layer 3, a first graded guide layer 4, an active layer 5, a second graded guide layer 6, a p-type cladding layer 7, and a cap layer are formed on an n-GaAs substrate 1. 8 is sequentially crystal-grown. During this crystal growth, a superlattice structure of the first graded guide layer 4 and the second graded guide layer 6 is formed. Crystal growth methods include MBE method, MO-CVD method,
Any method such as the HT-VPE method may be used.
Next, a SiO ₂ film 9 is formed, and the SiO ₂ film on the striped portions 12 is removed using a photoetching method or the like.
Next, a P-type electrode 10 and an n-type electrode 11 are formed.
Finally, the pellet is cut into pellets using a cleavage process, fused to a heat sink, and lead wires attached to complete the pellet.

In this embodiment, GaAs is used as the semiconductor with the smaller forbidden band width in the superlattice of the graded guide layer, but the semiconductor is not limited to this, and AlGaAs may also be used. In this example, the thicknesses of the superlattice potential well layer and potential barrier layer of the graded guide layer were constant in the film thickness direction, but the thickness is not limited to this, and it is also possible to change these thicknesses in the film thickness direction. good. In this example, the graded guide layer is uniformly doped with n-type or p-type in the thickness direction.
Although nondoped is used, the present invention is not limited to this, and a selectively doped superlattice in which only a portion of the superlattice is doped may also be used. Further, in this example, the SiO ₂ stripe structure was used as the current confinement structure, but it is clear that the present invention can be applied to any structure such as a planar stripe structure, a bridge waveguide structure embedded structure, etc. It is. In this embodiment, an n-type substrate is used, but on the contrary, a p-type substrate may be used to create a structure in which the conductivity types are all reversed.

In addition, in this example, the entire graded guide layer had a superlattice structure, but the superlattice structure was used only in the vicinity of the active layer, which is effective in achieving a low threshold, and the part far from the active layer was made of AlGaAs liquid crystal. A graded guide layer may also be used. Further, in this embodiment, the active layer has a single-phase structure, but the active layer is not limited to this, and may have a multilayer structure such as a multiple quantum well structure.
In addition, although AlGaAs/GaAs-based material was used in this example, the material is not limited to this, and may include InGaAlAs/InP-based material,
It is clear that the present invention can be applied to other materials such as GaAlSb/GaSb-based and InGaAsP/InP-based materials.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the present invention. FIG. 2 is an energy band diagram of the main parts of an embodiment of the present invention. In the figure, 1 is an n-GaAs substrate, 2 is a buffer layer, 3 is an n-type cladding layer, 4 is a first graded guide layer, 5 is an active layer, 6 is a second graded guide layer, and 7 is a P layer. type clad layer, 8 is the cap layer,
9 is a SiO ₂ film, 10 is a P-type electrode, 11 is an n-type electrode,
12 is a stripe portion, 20 is a potential well layer, 21 is a potential barrier layer, 22 is a potential well layer, and 23 is a potential barrier layer.

Claims (1)

[Claims] 1 A multilayer structure comprising at least an active layer and graded guide layers sandwiching the active layer above and below, and these graded guide layers form a superlattice structure in which potential wells and potential barriers are stacked alternately. 1. A semiconductor laser comprising: a semiconductor laser, wherein the height of the potential barrier increases as the distance from the active layer increases.