JPH047594B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-quantum well semiconductor laser.

[Conventional technology]

The active layer of a conventional multi-quantum well semiconductor laser has a thickness of less than the thickness at which the quantum size effect appears.
A semiconductor layer (quantum well layer) and a second semiconductor layer (barrier layer) having a wider forbidden band width than the quantum well layer are laminated alternately, and the forbidden band width of the quantum well layer and the barrier layer is within the layer. It was uniform. A paper describing such a conventional example is, for example, Applied Physics Letters, No. 26.
Vol. 1975, p. 463.

[Problem that the invention seeks to solve]

In the conventional multi-quantum well semiconductor laser described above, in order to uniformly distribute the carrier to each quantum well layer and achieve a low threshold current, it is possible to make the barrier layer thinner, but if the barrier layer is thinned too much, the active layer The disadvantage is that the shape of the wave function within the quantum well becomes gentle, so to speak, the "coupling" between the quantum wells increases, and the threshold current increases, making it difficult to lower the threshold current.

An object of the present invention is to provide a multi-quantum well semiconductor laser with reduced threshold current.

[Means for solving problems]

In the multi-quantum well semiconductor laser of the present invention, a first semiconductor layer having a thickness equal to or less than the thickness at which a quantum size effect appears and a second semiconductor layer having a wider forbidden band width than the first semiconductor are alternately laminated. In the multi-quantum well semiconductor laser having an active layer formed by the above-described structure, the second semiconductor layer has a structure in which the forbidden band width changes in the thickness direction.

[Effect]

Since the multi-quantum well semiconductor laser of the present invention has an active layer in which the barrier layer has a forbidden band width that changes in the thickness direction, for example, the width of the potential barrier for electrons in each potential well is , among several discrete energy levels, which are smaller for the excited state than for the ground state. As a result, the probability that electrons in an excited state within each potential well will move into other potential wells increases. Therefore, while the injected electrons are in an excited state, they are evenly distributed to each quantum well layer due to the tunnel effect. The same holds true for holes, so in the end, the polarization of electrons and holes becomes smaller.

Regarding the carrier in the ground state, which mainly contributes to laser oscillation, the thickness of the potential barrier is large, so the above-mentioned "coupling" between each quantum well is small.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

The first is a perspective view of an embodiment of the present invention, and the second is an enlarged view of section A in FIG.

Each active layer is undoped with a thickness of 150㎓
A quantum well layer consisting of GaAs layers 1-1, 1-2, and 1-8 and a non-doped Al _x Ga _1-x As layer 2- with a thickness of 50 mm.
It has a structure in which barrier layers 1, 2-2, . . . , 2-8 are alternately laminated. Non-doped Al _x
The value of x giving the mixed crystal ratio of the Ga _1-x As layer 2-1 is 0 on the side of the non-doped GaAs layer 1-1, and
It increases linearly to 0.3 on the GaAs layer 1-2 side. Non-doped Al _x Ga _1-x As layer 2-2,
The same applies to ..., 2-8. Furthermore, Al _x
The forbidden band width of Ga _1-x As increases as x increases.

The components other than the active layer are the same as those of a known buried heterojunction type semiconductor laser, and numeral 3 is a 1.5 μm thick cladding layer consisting of an N-type Al _0.4 Ga _0.6 As layer, and 4 is a P-type Al _0.4
1.5 μm thick cladding layer consisting of Ga _0.6 As layer, 5
is a 1.0 μm thick buffer layer made of N-type GaAs layer,
6 is a 1.0 μm thick cap layer made of a P-type GaAs layer, 7 is a block layer made of a P-type A _0.4 Ga _0.6 As layer,
8 is a block layer consisting of an N-type Al _0.4 Ga _0.6 As layer; 9
is an N-type GaAs substrate, 10 is an N-side electrode layer, and 11 is a P
This is a side electrode layer. Moreover, the resonator length is 300 μm.

In order to form the Al _x Ga _1-x As layer by changing the mixed crystal ratio, the temperature of the Al cell may be changed by, for example, molecular beam epitaxial growth. It is also possible to achieve this by using a metal organic vapor phase epitaxy method and changing the flow rates of component gases.

The multi-quantum well type semiconductor laser of this example oscillated at about half the threshold current as compared to one in which the mixed crystal ratio of the barrier layer was constant. No changes were observed in other properties such as temperature characteristics and differential quantum efficiency.

Although an example has been described in which the forbidden band width of the barrier layer increases linearly in the thickness direction, it may conversely decrease linearly. Furthermore, the manner of change does not have to be linear; it may change monotonically, or it may increase and then decrease again. After all, it is sufficient if the thickness changes in the thickness direction.

〔Effect of the invention〕

As explained above, the present invention uses a barrier layer that constitutes the active layer of a multi-quantum well structure and has a forbidden band width that changes in the thickness direction. Since the bias of the carrier can be reduced without increasing the current, there is an effect that the threshold current for laser oscillation can be reduced.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is an enlarged view of section A in FIG. 1-1 to 1-8...Quantum well layer made of GaAs layer, 2-1 to 2-8...Barrier layer made of Al _x Gaa _1-x As layer, 3...N-type Al _0.4 Ga _0.6 As layer 4...A clad layer made of a P-type Al _0.4 Ga _0.6 As layer, 5... A buffer layer made of an N-type GaAs layer, 6... A cap layer made of a P-type GaAs layer, 7
...Block layer consisting of P-type Al _0.4 Ga _0.6 As layer, 8
...Block layer consisting of N-type Al _0.4 G _a0.6 As layer, 9
...N-type GaAs substrate, 10...N-side electrode layer, 11
...P-side electrode layer.

Claims (1)

[Claims] 1. A multiple quantum well having an active layer formed by alternately stacking a first semiconductor layer having a thickness equal to or less than the thickness at which a quantum size effect appears and a second semiconductor layer having a wider forbidden band width than the first semiconductor. A multi-quantum well semiconductor laser, wherein the second semiconductor layer has a forbidden band width that changes in the thickness direction.