JPS6377182A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To reduce the loss of injection carrier in a semiconductor light emitting device by suppressing nonlight emitting recombination of minority carrier impregnated to a compound semiconductor layer having a large gap from a compound semiconductor side having a small energy band gap for forming a hetero junction. CONSTITUTION:Nonlight emitting recombination suppressing layers 6, 7 have predetermined thickness and predetermined impurity concentration as essential data. A compound semiconductor for forming the layers 6, 7 selects GaAs which has a value substantially equal to an energy band gap in InAlAs for forming clad layers 3, 5 and has less center of deep level. When the thickness of the layers 6, 7 is, for example, approx. 30Angstrom , no dislocation due to irregular lattice matching occurs in the state a strain is applied thereto. Thus, since the nonlight emitting recombination of minority carrier impregnated to the semiconductor layer having small energy band gap from the semiconductor layer having large energy band gap for forming a hetero junction is suppressed, the loss of injection carrier is reduced.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a semiconductor light-emitting device with a compound semiconductor layer having a specified energy band gap and thickness, thereby reducing the dark value current. Density has been halved compared to previous standards.

[Industrial application field]

The present invention relates to improvements in semiconductor light emitting devices using heterojunctions, such as semiconductor lasers.

[Conventional technology]

Semiconductor light emitting devices using the above heterojunction, such as semiconductor lasers, are positioned as key devices and extremely important components in optical communication systems.

At present, multilayer compound semiconductor layers forming the heterojunction structure required to create semiconductor lasers are grown by liquid phase epitaxial growth (LI).
(quid phase epitaxy: LPE)
However, in recent years, molecular beam epitaxial growth (molecular beam epitaxial growth) in
Due to rapid progress in the pitaxy (MBE) law, the so-called
A quantum well semiconductor laser has been realized, Ga As
/AIC;a The dark current density in an AS-based semiconductor laser has been significantly improved.

[Problem that the invention seeks to solve]

As mentioned above, Ga As / AI Ga
Although As-based quantum well semiconductor lasers have been put into practical use, low threshold currents have not yet been achieved in quantum well semiconductor lasers using long wavelength band materials, such as InGaAs/InAlAs systems. It is well known that laser light in a long wavelength band is advantageous because there is an optical transmission path with extremely low loss for propagating the laser light.

Now, the main reason why long wavelength band semiconductor lasers have not been made to have a low threshold current is the poor optical quality of the multilayer compound semiconductor layer forming the heterojunction structure.

The reason for this is that in the case of the MBE method, it is difficult to use phosphorus (P), and therefore materials that do not contain P, such as In
A GaAs/InAlAs system is used.

Figure 2 shows the experimentally produced I n Ga As /
I nAI! FIG. 2 is a front view with a main part cut away for explaining the layer structure of an As-based semiconductor laser.

In the figure, 1 is an n+ type InP substrate, 2 is an n type InGa substrate
As buffer layer, 3 is n-type 1nAj! As clad layer,
4 is a non-doped InGaAs active layer, 5 is a p-type In,
An! Each shows an As cladding layer.

Examples of main data of each layer in the illustrated example are as follows.

■ Substrate 1 Impurity concentration: 2X1018 (■-3) ■ Buffer layer 2 Thickness: 1 [μm] Impurity concentration: 2 X 10 I8 (cm-') ■ Clad layer 3 Thickness: 1.5 (μm) Impurity concentration : 5 X I Q"(cm-')■
Active layer 4 Thickness: 300 [people] ■ Clad N5 Thickness: 1.5 (μm) Impurity concentration: 5 × 1017 (am-”) However, since the InAlAs used here contains Al as a matrix constituent element, , the quality of the crystal is not good.

The inventor is Aji! In the case of GaAs, we succeeded in increasing the quality by raising the growth temperature by about 100 ('C) higher than conventional ones, but In/lj! In the case of As, there is a problem of re-evaporation of In, so the growth temperature cannot be increased excessively.

As mentioned above, if the quality of InAlAs is poor, I
The following problems occur in the nGaAs/I nAlAs system.

That is, In, 6j! Since As has a larger energy band gap than InGaAs, it must play a role in confining carriers and light.

The problem here is that the quality of InGaAs is good, so radiative recombination takes place actively in that region, but the quality of InAlAs is poor, so the minority carriers seeping out there are at deep levels. Non-radiative recombination occurs through the center of

Therefore, the presence of poor quality InAlAs overall
This causes a large loss in the injected carriers and prevents the semiconductor laser from achieving a low threshold current.

The present invention provides a semiconductor light-emitting device in which non-radiative recombination of minority carriers leaked to the compound semiconductor layer side having a large energy band gap is prevented, and the threshold current is reduced.

[Means for solving problems]

In the semiconductor light emitting device according to the present invention, a compound semiconductor layer with a large energy band gap (for example, n-type 1nAIAs cladding layer 3, p-type InA
lAs cladding layer 5) and a compound semiconductor layer with a small energy band gap (for example, non-doped 1nGaA
s active layer 4), the energy band gap is approximately the same as that of the compound semiconductor layer with the large energy band gap, and the thickness is the compound semiconductor layer with the small energy band gap. Compound semiconductor N (e.g., n-type GaAs non-radiative recombination suppressing layer 6, n-type GaAs non-radiative recombination suppressing layer 6, n-type GaAs non-radiative recombination suppressing layer 6, layer 7).

[Effect]

By taking the above measures, non-radiative recombination of minority carriers leaking from the compound semiconductor layer side with a small energy band gap to the compound semiconductor layer side with a large energy band gap constituting the heterojunction is suppressed. So,
The loss of injected carriers is reduced and the dark current density is halved compared to the conventional standard value.

〔Example〕

FIG. 1 shows a cutaway front view of essential parts of one embodiment of the present invention, and FIG.
Symbols used in the drawings indicate the same parts or have the same meaning.

In the figure, 6 is an n-type GaAs non-radiative recombination suppressing layer;
1 and 2 respectively indicate n-type GaAs non-radiative recombination inhibiting layers.

Examples of main data of each of the non-radiative recombination suppression layers 6 and 7 are as follows.

■ Non-radiative recombination suppression layer 6 Thickness = 30 [people] Impurity concentration: 5 X I Q” (cm-') ■
Non-radiative recombination suppressing layer 7 Thickness: 30 [person] Impurity concentration: 5×1017C value 1] In this example, the craft layers 3 and 5 are used as compound semiconductors constituting the non-radiative recombination suppressing layers 6 and 7. We selected GaAs, which has approximately the same energy band gap as InAlAs constituting the material and has fewer centers such as deep levels. Note that if GaAs is used as the non-radiative recombination suppressing layers 6 and 7, G is used in the cladding layer.
Although it may be possible to use aAs, this is impossible because it cannot achieve lattice matching with the InP substrate 1.As in the example, the thickness of the GaAs non-radiative recombination suppressing layers 6 and 7 is 30 mm. If it is about the size of a human being, it is in a state where so-called strain is applied, and dislocations due to lattice mismatch do not occur.

The main conditions for growing this GaAs non-radiative recombination suppression layer 6 or 7 are: Growth temperature: 550 ("C) Growth rate: 1 [μm/hour] Substrate rotation speed: 10 [rotation 7 minutes]" Ta.

〔Effect of the invention〕

The semiconductor light emitting device according to the present invention has a structure in which a compound semiconductor layer having a specified energy band gap and thickness is inserted at the hetero interface.

By adopting such a configuration, non-radiative recombination of minority carriers leaking from the compound semiconductor layer side with a large energy band gap to the compound semiconductor layer side with a small energy band gap constituting the heterojunction can be suppressed. Therefore, the loss of injected carriers is reduced, and the dark value current density is halved compared to the conventional standard value.

[Brief explanation of the drawing]

FIG. 1 is a cutaway front view of essential parts of an embodiment of the present invention, and FIG. 2 is a cutaway front view of essential parts of a conventional example. In the figure, l is an n+ type InP substrate and 2 is an n type InGa substrate.
As buffer layer 3 is n-type 1nA/! As clad layer,
4 is a non-doped InGaAs active layer, 5 is a p-type InGaAs active layer, and 5 is a p-type InGaAs active layer.
A#As cladding layer, 6 an n-type GaAs non-radiative recombination suppressing layer, and 7 an n-type GaAs non-radiative recombination suppressing layer, respectively. Patent Applicant: Fujitsu Co., Ltd. Representative Patent Attorney: Akira Aitani Representative Patent Attorney: Hiroshi Watanabe - Cutaway Front View of Main Parts of Embodiment Figure 1 Cutaway Front View of Main Parts of Conventional Example Figure 2

Claims (1)

[Claims] A compound semiconductor layer with a large energy band gap and a compound semiconductor layer with a small energy band gap are interposed to form a heterojunction, and the energy band gap is the same as that of the energy band gap. band·
It is approximately the same as that in a compound semiconductor layer with a large gap, and the thickness is the mean free path of minority carriers leaking from the compound semiconductor layer with a small energy band gap to the compound semiconductor layer with a large energy band gap. 1. A semiconductor light-emitting device comprising a compound semiconductor layer of about 100% or less.