JPH02224385A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser low in oscillation threshold by a method wherein the semiconductor laser is provided with a double hetero-structure in which an n-clad layer is formed of InGaAsP mixed crystal and a p-clad layer is formed of InGaAlAs mixed crystal, where both the clad layers are larger than an active layer in forbidden bandwidth. CONSTITUTION:An active layer 13 is formed of InGaAlAs mixed crystal, and a semiconductor laser is provided with a double hetero-structure in which an n-clad layer 12 is formed of InGaAsP mixed crystal and a p-clad layer 14 is formed of InGaAlAs mixed crystal, where the width of forbidden energy band of the active layer 13 is smaller than those of the clad layers 12 and 14. By this setup, a semiconductor laser, which is provided with a double hetero-structure excellent in trapping of carriers of electron and hole without the reduction in carrier injection efficiency and low in threshold, can be obtained.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to the structure of a semiconductor laser.

(Prior Art) A double heterostructure is widely used as a structure of a semiconductor laser that oscillates with a low threshold current. In this structure, efficient carrier confinement is achieved by sandwiching the active layer between cladding layers made of a semiconductor with a wider forbidden band width than the semiconductor in the active layer (Hiroo Yonezu, "Optical Communication Engineering", Chapter 2, Kogaku Tosho, Tokyo) 1984).

(Problems to be Solved by the Invention) In order to efficiently confine carriers in a double heterostructure, energy discontinuities ΔEc and , energy discontinuity ΔE at the conduction band edge between the semiconductor #-1 and the semiconductor 3 forming the P-clad layer must both be large. In conventional double heterostructures, the same semiconductor is used for the n-cladding layer and the p-cladding layer, so the difference in forbidden band width may be biased towards only one of ΔE0 and ΔE4. ΔE in the InGaAsP/InP double heterostructure used in semiconductor lasers. :ΔE,=4:6, the energy discontinuity at the edge of the valence band is large, and there is a possibility that electron overflow from the active layer to the p-cladding layer occurs.

Furthermore, if the difference in the forbidden band is increased in order to improve carrier confinement, a high votive spike will be generated on the side into which carriers are injected, resulting in a decrease in carrier injection efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser with a low threshold, which has a double heterostructure that provides high carrier confinement efficiency for electrons and holes, and at the same time does not reduce carrier injection efficiency.

(Means for Solving the Problems) The semiconductor laser of the present invention uses an InGaA IAs mixed crystal or an InGaAs P mixed crystal as an active layer, and an InGaAsP mixed crystal having a larger forbidden band width than the semiconductor of the active layer. It is characterized by having a double heterostructure in which the p-cladding layer is an InGaAlAs mixed crystal having a larger forbidden band width than the semiconductor of the active layer.

(Function) FIG. 2 is a diagram showing a potential diagram in the semiconductor laser of the present invention. FIG. 2(a) is a band diagram at thermal equilibrium, and FIG. 2(b) is a band diagram at forward bias.

At the time of forward bias, the heterobarrier for electrons between the active layer and the ρ-cladding layer is approximately (Eo E-t)
be equivalent to. Also, the heterobarrier for holes between the active layer and the n-cladding layer is approximately equal to (Ev, , E, 2). In the present invention, (E, 3E, , ), (E, l-E, 2)
Since both become large, carrier confinement is performed efficiently.

On the other hand, the size of the spike felt by the electrons injected at the heterojunction between the n-cladding layer and the active layer is (E-2E-+
), and the size of the spike felt by holes injected at the heterojunction between the P-cladding layer and the active layer is (E-3-
E-s>. In the present invention, (E, 2-Ea,), (E
, , -E, and 3) are both small, so the carrier injection efficiency is not reduced by the heterojunction.

(Example) FIG. 1 is a sectional view of an embodiment of the present invention.

In manufacturing this embodiment, an n-type InP substrate 11
n-cladding layer 1 made of InP doped with S: on top
2. I no76G O,24A S o, s lattice-bonded to InP with an undoped band gap of 0.94 eV
Active layer 13 consisting of sP 0.45, Zn doped I
Jno, 52Gao, +sA 1G lattice matched to nP
, 3 As, the ρ-cladding layer 14 is sequentially laminated to form a double heterostructure. Next, after mesa etching, p-type layers no, szG ao, +aA I
n-type layer 15 made of o, s A S, block layer 16 made of n-type InP, and n-type layer 17 made of n-type InP.
, n-type I no, 6 Gao, 2 A 50.46P
A contact layer 18 made of O and S4 is sequentially laminated to form a buried structure, and an n1tll electrode 19 and a P-side electrode 20 are respectively formed.

In the double heterostructure in this example, activity 1
The values of the conduction band discontinuity and the valence band discontinuity between the conduction band 13 and the n-cladding layer 12 are 164 meV and 246 meV, respectively, and both electrons and holes are efficiently confined. Further, the values of the conduction band discontinuity and the valence band discontinuity between the active layer 13 and the p-cladding layer 14 are 280 meV and 16 meV, respectively, and the confinement of electrons is sufficiently large and the electrons are injected. Since the potential spike for holes is small, high injection efficiency can be obtained.

In addition, in the present invention, the composition of the materials may be any combination as long as laser oscillation is possible, and the structure of the laser is not limited to the embedded type. It may be.

(Effects of the Invention) As described above, the semiconductor laser of the present invention has a double heterostructure with high carrier confinement efficiency and at the same time a small drop in injection efficiency. Therefore, the semiconductor laser of the present invention has a low oscillation threshold.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of an embodiment of the present invention. In the figure, 11 is the substrate, 12 is the n-cladding layer, 13 is the active layer, 14 is the p-cladding layer, 15 is the p-type layer, 16 is the block layer, 17 is the n-type layer, 18 is the contact layer, and 19 is the n-type layer. The side electrode 20 is a p-side electrode. FIG. 2 is a diagram showing a potential diagram of the semiconductor laser of the present invention, in which (a) is a band diagram at thermal equilibrium, and (b) is a band diagram at forward bias.

Claims (1)

[Claims] An InGaAlAs mixed crystal or an InGaAsP mixed crystal is used as an active layer, an InGaAsP mixed crystal having a bandgap larger than that of the semiconductor in the active layer is used as an n-cladding layer, and an InGaAlAs mixed crystal has a bandgap larger than the semiconductor in the active layer. A semiconductor laser characterized by having a double heterostructure in which the crystal is a p-cladding layer.