JPH10209571A - Semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the overflow problem of electrons which are overflown to a clad layer from an active layer of a semiconductor light emitting element. SOLUTION: AlGaInNP mixed crystal is used for the semiconductor laser active layer 13 having a 650nm band (visible light) and a 1300nm band (infrared rays). The ratio of N is set at 3% or smaller for the 650nm band and 5 to 10% for the 1300nm band laser. When the ratio of N is changed, the discontinuous energy quantity ΔEc of a conduction band becomes larger, and the overflow of electron to p-clad layers 12 and 14 from the active layer can be suppressed by the enlarged electronic barrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly to an improvement in a visible light semiconductor light emitting device oscillating in a 600 nm band and an infrared semiconductor light emitting device oscillating in a 1300 nm band.

[0002]

2. Description of the Related Art Visible light semiconductor lasers oscillating in the 600 nm band have been developed as light sources for large-capacity optical disks and light sources for measurement. In this field, the emergence of a laser that oscillates at a shorter wavelength is desired in order to reduce the size of the focused spot and improve the visibility. A visible light laser in the 600 nm band is generally manufactured using a GaInP-based material as an active layer on a GaAs substrate, and is used by introducing tensile strain into GaInP of the active layer or by adding Al to the active layer.
A laser device that oscillates at a shorter wavelength has been obtained by using it as an nP active layer and further forming these materials into a quantum well structure.

[0003] In general, in AlGaInP-based visible light semiconductor lasers, an overflow of electrons from the active layer to the p-type cladding layer (hereinafter, also simply referred to as an overflow of electrons) poses a problem. That is, in AlGaInP generally used as a cladding layer in this system, the band gap increases as the Al composition increases, but (Al _0.7 Ga _0.
3 ) If the Al composition is increased beyond a certain limit such that _0.5 In _0.5 P is the boundary between the direct transition and the indirect transition, electrons cannot be confined in the active layer and the electrons overflow to the p-cladding layer. That is. For this reason, there is a limit to increasing the composition of Al.

As the oscillation wavelength becomes shorter and the band gap of the active layer becomes larger, the electron overflow problem cannot be ignored. It is known that the equivalent barrier height for electrons also depends on the dopant concentration of the p-cladding layer, and the more the dopant, the greater the barrier equivalently. For this reason, attempts have been made to increase the doping concentration of the p-cladding layer.

Regarding the problem of electron overflow, apart from the above-mentioned attempt, a very thin multilayer film is inserted between the active layer and the p-cladding layer, and the interference effect of electrons in this multilayer film is used. Equivalently trying to increase the barrier height,
It has also been proposed to use so-called multiple quantum barriers (MQBs).

Turning now to an infrared semiconductor laser that oscillates in the 1300 nm band, lasers in this wavelength band are generally used in optical subscriber systems, and there is a particular demand for the development of low-cost modules. ing. Therefore, there has been an attempt to omit the costly temperature control function from the light emitting module.
However, when the temperature control function is omitted, it is known that a problem of electron overflow similar to that of a visible light laser in the 600 nm band occurs as a cause of deterioration of laser characteristics in a high temperature environment. To solve this problem, recently,
For example, `` Japanese Journal of Applied Physics '', Vol.
35, pp. 1273-1275 (1996).
A 1.3 μm band infrared laser using GaInNAs lattice-matched on an s substrate as an active layer has been proposed.

[0007]

With a visible laser in the 600 nm band, it is very difficult for AlGaInP to dope a p-type dopant at a high concentration, and at most 1 × 10 ¹⁸ c
m ^-3 . Therefore, there is still a limit to increasing the barrier height equivalently by increasing the doping concentration of the p-cladding layer. Although the multi-quantum barrier is expected to produce a very large effect in theory, it is currently difficult to obtain an ultra-thin multilayer structure as designed. No effect has been obtained. That is, the overflow problem of electrons existing in the AlGaInP-based laser structure has not been sufficiently solved in the range of the related art.

In the case of an infrared laser in the 1300 nm band,
Since the lattice matching is achieved by adding N to GaInAs which is not originally lattice matched to the GaAs substrate,
Determining the lattice matching condition and band gap for As,
There is a problem that the composition is uniquely determined and the degree of freedom in designing the active layer is low.

In view of the above, it is an object of the present invention to solve the problem of electrons overflowing from the active layer to the p-type cladding layer in each of the 600 nm band and 1300 nm band semiconductor light emitting devices.

[0010]

In order to achieve the above object, a semiconductor light emitting device according to the present invention has an active layer made of AlGaInN.
It is characterized by containing a P mixed crystal.

Here, the oscillation wavelength is in the 600 nm band (600 nm).
When the present invention is applied to a semiconductor light emitting device having a wavelength of about 680 nm (about 680 nm), the ratio of N in the AlGaInNP mixed crystal is preferably 3% or less. The oscillation wavelength is 1300n
In a case where the present invention is applied to a light-emitting element in the m band (1280 to 1340 nm), it is preferable that the ratio of N be 5% to 10% or less.

Hereinafter, the principle of the present invention will be described in more detail with reference to the drawings. _{First, (Al z Ga 1 -z)} x In 1-x N v P
_In a mixed crystal system represented by _1-v , lattice matching with GaAs is satisfied, and the condition that the band gap wavelength is 650 nm (band gap wavelength of GaInP) is satisfied (x, z,
The set v) was calculated. FIG. 1 is a graph showing the relationship between the N composition v and the composition x (broken line) of Al + Ga and the composition z (solid line) of Al satisfying the above conditions. As shown in the figure, when the Al composition z is increased, it is necessary to increase the N composition v from the condition that the band gap is constant. is there. AlGa with respect to the Al composition z at this time
FIG. 2 is a plot of the band position of the InNP mixed crystal. The solid line in the figure indicates the band position of the conduction band, and the broken line indicates the band position of the valence band.

Referring to FIG. 2, it can be seen that by adding a small amount of N to AlGaInP, the relative position of the band can be changed almost linearly while satisfying the lattice matching condition and the constant band gap condition. That is, in consideration of the band positions (1.65 eV and -0.25 eV) of the conduction band and the valence band of (Al _0.7 Ga _0.3 ) InP illustrated in the figure, the discontinuous energy of the conduction band is obtained in the conventional GaInP active layer. Unlike the case where the amount ΔEc is about 250 meV and the discontinuous energy amount ΔEv of the valence band is about 150 meV, which is constant, the use of the AlGaInNP active layer according to the present invention makes it possible to obtain a semiconductor laser having an oscillation wavelength of 600 nm. The discontinuous energy of the band ΔEc is 250
It can be arbitrarily changed from meV to 550 meV. In other words, the height of the p-cladding barrier for electrons is dramatically increased, and the problem of overflow of electrons can be suppressed.

Here, if too much N is added, the band gap becomes too small, and is not particularly suitable for an active layer of a visible light semiconductor laser. Therefore, in the light emitting device in the 650 nm band, the amount of N added to AlGaInP is as shown in FIG.
As can be understood from FIG.

On the other hand, in the case of a laser in the 1300 nm band, the degree of freedom in designing the active layer can be increased by using AlGaInNP obtained by adding N to AlGaInP as the active layer. _{(Al z Ga 1-z)} x In 1-x N v in P _1-v and mixed crystal represented, lattice-matched to GaAs, and satisfies the bandgap wavelength is 1310 nm (x,
The set of z, v) was calculated. FIG. 3 shows N composition v and Al + Ga composition x (broken line) and Al satisfying the above conditions.
4 is a graph showing a relationship with a composition z (solid line).

When the Al composition z is increased, it is necessary to increase the N composition v from the condition that the band gap is constant.
Increases, it is necessary to reduce the composition x of Al + Ga from the lattice matching condition. AlGaIn with respect to the Al composition z at this time
FIG. 4 is a plot of the band positions of NP mixed crystals. The solid line in the figure indicates the band position of the conduction band, and the broken line indicates the band position of the valence band. Referring to FIG.
By adding a small amount of N to InP, 1300 nm
It is understood that the relative position of the band can be changed substantially linearly while satisfying the lattice matching condition and the constant band gap condition in the semiconductor laser in the band.

In the prior art, lattice matching is performed by adding N to GaInAs, which is not originally lattice matched to the GaAs substrate, and the composition is uniquely determined if the lattice matching conditions for GaAs and the band gap are determined. . In this conventional technique, a band arrangement in which the amount of discontinuous energy ΔEc in the conduction band becomes large is merely obtained by accident. On the other hand, in the present invention, the lattice matching condition and the constant band gap condition are satisfied as described above, and in addition, the band arrangement can be arbitrarily adjusted, so that the degree of freedom in design is greatly improved. In order to obtain an oscillation wavelength in the 1310 nm band, the amount of N added to AlGaInP is preferably 6% or more and 9% or less, as can be understood from FIG.

[0018]

FIG. 5 is a cross-sectional view of an AlGaInNP-based semiconductor laser fabricated on a GaAs substrate according to an embodiment of the present invention. This semiconductor laser is obtained as follows. First, on an n-type GaAs (n-GaAs, the same applies hereinafter) substrate 10, n-GaAs is formed by MOCVD.
As buffer layer 11, n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P
Lower cladding layer 12, AlGaIn NP active layer 13, p-
(Al _0.7 Ga _0.3 ) _0.5 In _0.5 P First upper cladding layer 1
4, p-GaInP etch stop layer 15, p- (Al _0.7
Ga _{0 .3) 0.5} In _0.5 P second upper cladding layer 16, p-Ga
An InP intermediate layer 17 is sequentially grown and formed.

An insulating film (not shown) (for example, SiN) is deposited on the lamination formed above, and the second upper cladding layer 16 is formed by photolithography and chemical etching.
And the p-GaInP intermediate layer 17 is formed in a mesa structure. S
With the iN insulating film left, an n-GaAs current blocking layer 18 is formed by the second MOCVD growth to bury both sides of the mesa structure. 3rd MOC after removing the SiN insulating film
By growing the p-GaAs contact layer 19 over the entire surface by VD growth, and further forming the upper electrode 20 and the lower electrode 21, the light emitting device shown in FIG. 5 is obtained.

Although the method of manufacturing the semiconductor light emitting device of the above embodiment and the structure of the device itself are almost the same as the conventional one, the difference from the conventional one is that AlGaInNP is used as the active layer. For comparison, a structure having a structure similar to that of the above-described embodiment, in which the ratio of N in the active layer is 0% (that is, the conventional GaInP active layer) (Comparative Example 1) is 0.7%. (Example 1) and 1.6% (Comparative Example 2) were prototyped. The threshold current of the device is such that the amount of N added is 0.
% Of about 45 mA, 0.7% of about 45 mA,
It was about 60 mA at 1.6%.

When the amount of N added is 1.6% (Comparative Example 2)
It can be understood from FIG. 2 that, as can be understood from FIG. 2, the discontinuous energy amount ΔEv in the valence band is almost 0, and the confinement of holes is weakened, so that the threshold value is increased. Can be The oscillation wavelength was 652 nm in each case. Next, the temperature dependence of the threshold current was measured to determine the characteristic temperature T ₀ .

The characteristic temperature T ₀ is about 60 K and 0.7% (Example 1) when the amount of N added is 0% (Comparative Example 1).
About 120K, 1.6% (Comparative Example 2) about 150
It was K. From this, the use of the AlGaIn NP active layer to which N is added in accordance with the present invention makes it possible to obtain 600 n
In an m-band semiconductor laser, it was found that the overflow of electrons from the active layer to the p-cladding layer was suppressed, and the temperature characteristics of the laser were significantly improved.

FIG. 6 shows a semiconductor laser according to a second embodiment of the present invention, which is an AlGaInN fabricated on a GaAs substrate.
It is sectional drawing of a P type semiconductor laser. The semiconductor laser shown in the figure is manufactured in the same manner as the semiconductor laser shown in FIG.
_{The present} embodiment is different from the previous embodiment in that _0.5 In _0.5 P is used for the cladding layers 32, 34, and 36, and AlGaIn NP to which N is added about 6% is used for the active layer 33.

Semiconductor laser of this embodiment (Example 2)
Was actually fabricated and its oscillation wavelength was measured.
310 nm. Next, the temperature dependence of the threshold current was measured to determine the characteristic temperature T ₀ . The measured characteristic temperature T ₀ was about 180K. For comparison, oscillation wavelength 1
InP commonly used in 310 nm lasers
The characteristic temperature of GaInAsP-based semiconductor laser on the substrate (Comparative Example 3) was measured and the characteristic temperature T ₀ was 80K. From this, Al added with N according to the present invention is
By using the GaInNP active layer, it was confirmed that in a 1300 nm band semiconductor laser, the overflow of electrons from the active layer to the p-cladding layer was suppressed, and the temperature characteristics of the laser were significantly improved.

In each of the above embodiments, the active layer has a bulk structure. However, even if a so-called quantum well structure is employed and AlGaInNP is used as the quantum well layer, the effect of the present invention is similarly obtained. can get.

Although the present invention has been described based on the preferred embodiments, the semiconductor light-emitting device of the present invention is not limited to the configuration of the above-described embodiments, but rather the configuration of the above-described embodiments. Various modifications and changes of the semiconductor light emitting device are also included in the scope of the present invention.

[0027]

As described above, according to the semiconductor light emitting device of the present invention, since the active layer has a structure including AlGaInNP mixed crystal, the composition of N is controlled to thereby control the discontinuous energy of the conduction band. ΔEc can be increased, the overflow of electrons from the active layer to the p-cladding layer can be suppressed, and there is an effect that a light emitting element having good temperature characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is lattice matched to GaAs, and the band gap is GaIn.
9 is a graph showing the relationship between the proportion of N added to AlGaInP and the Al + Ga composition x and the Al composition z when the condition that the band gap is equal to P is satisfied.

FIG. 2 is a graph showing the relationship between the ratio of N added to AlGaInP and the band position of a mixed crystal thereof under the same conditions as in FIG.

FIG. 3 shows lattice matching with GaAs, and a band gap of 131.
AlGaInP when the condition of being equal to 0 nm is satisfied
And the Al + Ga composition x and the Al composition z
The graph which shows the relationship with.

4 is a graph showing the relationship between the ratio of N added to AlGaInP and the band position of the mixed crystal under the same conditions as in FIG.

FIG. 5 is a cross-sectional view of an AlGaInNP-based 600 nm band laser fabricated on a GaAs substrate according to the first embodiment of the present invention.

FIG. 6 is a cross-sectional view of an AlGaInNP-based 1300 nm band laser fabricated on a GaAs substrate according to a second embodiment of the present invention.

[Explanation of symbols]

10, 30 n-GaAs substrate 11, 31 n-GaAs buffer layer 12 n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P lower cladding layer 13, 33 AlGaInNP active layer 14 p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P First upper cladding layer 15, 35 p-GaInP etch stop layer 16 p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second upper cladding layer 17, 37 p-GaInP intermediate layer 17 18, 38 n-GaAs current blocking layer 18 19, 39 p-GaAs contact layer 20, 40 upper electrode 21, 41 lower electrode 21 32 n-Al _0.5 In _0.5 P lower cladding layer 34 n-Al _0.5 In _0.5 P upper first upper cladding layer 36 n-Al _0.5 In _0.5 P upper second upper cladding layer

Claims (3)

[Claims] 2. A semiconductor light emitting device according to claim 1, wherein the active layer contains an AlGaInNP mixed crystal. 2. An oscillation wavelength of 600 to 680 nm,
The light emitting device according to claim 1, wherein the ratio of N is 3% or less. 3. The light emitting device according to claim 1, wherein the oscillation wavelength is 1280 to 1340 nm and the ratio of N is 5% or more and 10% or less.