JPH01257385A - semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To expand the applicable temperature range by a method wherein the composition of an active layer is varied a little in the direction of lamination and the width of an EL spectrum is enlarged. CONSTITUTION:An active layer 7 is composed of, for instance, a first nondoped InGaAsP active layer 7a and a second nondoped InGaAsP active layer 7b. The band gap wavelengths of the first and second active layers 7a and 7b at 25 deg.C are 1.290mum and 1.310mum respectively and there is a difference of 200Angstrom between each other. The thicknesses of the respective layers 7a and 7b are both 0.075mum and the total thickness is the same as the conventional constitution. By constituting the active layer 7 as described above, the EL spectrum of the active layer 7 is obtained by the superposition of the respective EL spectra of the layers 7a and 7b and the width of the resultant EL spectrum is widened so as to have the wider peak. Even if the EL spectrum is shifted largily toward the longer wavelength side in the high temperature side, it hardly comes out of the peak part, so that the applicable temperature range for a single mode can be widened corresponding to the widened width of the spectrum.

Description

[Detailed Description of the Invention] [Summary] A semiconductor light emitting device having a distributed feedback function and having a laminated structure of an active layer, a light guide layer, a diffraction grating, and a cladding layer sandwiching these and having a wider bandgap than these, The purpose is to expand the usable temperature range in a single mode without doping the active layer with impurities. It is configured so that the width of the image is expanded.

[Industrial application field]

The present invention relates to a semiconductor light emitting device having a stacked structure of an active layer, a light guide layer, a diffraction grating, and a cladding layer sandwiching these and having a wider bandgap than these, and having a distributed feedback function.

The above semiconductor device is called a distributed feedback (DFB) laser, and has excellent monochromaticity (single mode) in that it oscillates at a single wavelength to emit laser light, and has good temperature characteristics. It plays an important role in being used as an optical signal source for long-distance optical communications. It is desired to expand the temperature range that can be used in a single mode.

[Conventional technology]

Figure 3 (The main part side sectional view of al is InP/InG
A crystal part of a conventional example using an aAs P yarn long wavelength DFB laser is schematically shown.

In the figure, 1 is an n-InP cladding layer, 2 is a diffraction grating formed on the surface of the cladding layer 10, with a pitch of about 2000 and a height of 200 to 400, and 3 is a diffraction grating 2.
With an n-InGaAsP light guide layer grown on
Bandgap wavelength 1.2μm, thickness approximately 0.2μI, 4 is undoped InGaA grown on the optical guide layer 3
The sP active layer has a bandgap wavelength of 1.3 μm and a thickness of about 0.15 μm. 5 is a p-TnP cladding layer grown on the active layer 4.
The thickness is about 1.5 μm, and 6 is p −1nGaAs grown on the cladding layer 5.
The P contact layer has a bandgap wavelength of 1.3 μm and a thickness of approximately 0.2 μm.

Although not shown, these are for transverse mode control.
It forms a narrow stripe structure with a width of 1 to 2 μm (the width side is the front and back of the page), and both sides are buried and grown to a size of 3 μm.
6.00μm square.

As shown in the diagram showing the bandgap in FIG. terrorism) structure.

The DFB laser has electrodes on the top and bottom surfaces of this crystal chip, and an Al103. S
It is equipped with a non-reflective coating film such as i3 N4.

In this DFB laser, when current is passed in the forward direction, electrons and holes recombine in active N4, and the bandgap wavelength of the active layer 4 peaks, as shown in the emission spectrum diagram of FIG. It emits EL light with a spectrum widely spread on both sides, and at the same time, the light of a specific wavelength is fed back by the diffraction grating 2, and when the current increases, laser oscillation occurs near the fed back wavelength (= 1.3 μm) emits laser light.

When the temperature is increased from state A (solid line) in Figure 4, the EL spectrum (EL
light spectrum) and oscillation wavelength shift to longer wavelengths.

The temperature coefficient of the movement of the EL spectrum at that time is the active layer 4
approximately 4 people/℃ depending on the narrowing of the bandgap of
This is equal to the temperature coefficient of change in the oscillation wavelength of a Fabry-Perot (FP) laser (ordinary semiconductor laser) which does not have the diffraction grating 2 and thus does not cause the above-mentioned feedback of light. On the other hand, the temperature coefficient of the above-mentioned oscillation wavelength change of the DFB laser is mainly determined by the pitch of the diffraction grating 2 and the refractive index of the crystal, so the temperature dependence is extremely small (about 0.8 people/℃). .

Therefore, the oscillation wavelength of the DFB laser is extremely stable against temperature changes compared to the FP laser.

[Problem to be solved by the invention]

By the way, the above-mentioned situation regarding the DFB laser means that the oscillation position and the peak position of the EL spectrum in FIG. Therefore, sufficient gain cannot be obtained for the feedback light caused by the oscillation, and oscillation in a good FB mode becomes impossible.

The temperature range in which this good FB oscillation is possible is mainly due to E
It is determined by the width of the L spectrum, and the wider the width, the wider this temperature range. On the other hand, the width of the EL spectrum is mainly determined by the composition and carrier concentration of the active layer.

Under these circumstances, in the conventional example having the active layer 4 described above, the half width of the EL spectrum is discolored by about 400 degrees, so the width of the temperature range that can be used in a single mode is 40 degrees.
The temperature is 0 to 50°C.

However, for practical purposes, a wider range of about 70 to 90°C is desired.

By doping the active layer 4 with impurities, it is possible to widen the width of the EL spectrum and expand the usable temperature range, but this also increases light absorption loss in the active layer 4, for example. This results in an increase in threshold current and a decrease in luminous efficiency, which is not a good idea from the viewpoint of the characteristics of the DFB laser.

Therefore, the present invention provides an active layer, a light guide layer, a diffraction grating, and
A cladding layer sandwiching these and having a wider bandgap has a laminated structure, and can be used in a single mode without doping the active layer with impurities in a semiconductor light emitting device (DFB laser) that has a distributed feedback function. The purpose is to expand the temperature range.

[Means to solve the problem]

The above object is achieved by the semiconductor light emitting device of the present invention, in which the active layer has a composition slightly different in the direction of the lamination, thereby widening the width of the EL spectrum.

[For production]

When the composition of the active layer is varied as described above, a width is provided in the band gap size of the active layer, and the width of the EL spectrum is expanded according to the width compared to the case of a single composition.

As described above, the temperature range in which good FB oscillation can be achieved is mainly determined by the width of the EL spectrum, and the wider the EL spectrum, the wider this temperature range becomes.

This expands the temperature range that can be used in single mode without doping the active layer with impurities.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a side cross-sectional view of the main part of the example (al and a diagram showing the band gap (bl), and FIG. 2 is an emission spectrum diagram of the example, and the same reference numerals indicate the same objects throughout the figures.

Figure 1 (al is the same as Figure 3 (a) showing the conventional example,
A crystal part of an example of an InP/InGaAsP yarn long wavelength DFB laser is schematically shown.

In this figure, this crystal is obtained by changing the undoped InGaAs P active layer 4 of the crystal shown in FIG. 3(a) to an undoped InGaAs P active layer 7 having a 2N configuration.

An undoped InGaAs P first active layer 7a and an undoped InGaAs P second active layer 7 constituting the active layer 7
b has a bandgap wavelength of 1 at 25°C, respectively.
．． The thicknesses are 290 μm and 1.310 μm, with a difference of 200 μm between each other, and the respective thicknesses are 0.075 μm, and the combined thickness is <0.15 μm, which is the same as the active layer 4.

In addition, the diffraction grating 2 has an oscillation wavelength of 1 at 25°C,
The pitch was precisely adjusted to 305 μm.

In this DFB laser, by configuring the active layer as shown in 7, the EL spectrum becomes a superposition of the EL spectra of the first active layer 7a and the second active layer 7b, as shown in FIG. In addition, the width is wider at the top than in the case of Fig. 4, and the half width is approximately 1.5 compared to the conventional example.
The number of people will increase to 600.

However, as shown in Figure 2, due to the adjustment of the diffraction grating, the oscillation wavelength is on the long wavelength side (right side) at the top of the EL spectrum at the low temperature side A (solid line), and on the long wavelength side (right side) at the high temperature side. At a certain point B (dashed line), even if the EL spectrum moves significantly toward longer wavelengths, it becomes difficult to deviate from the top, and as the width of the EL spectrum expands, the temperature range that can be used in a single mode becomes wider. Become.

According to the inventor's confirmation, in the conventional example, the threshold current It
h #15 mA, oscillation efficiency η = 0.27 mW/mA, usable temperature range 5 to 55°C, whereas in the example, 1th # 17 mA, η #0.27 mW/mA,
The usable temperature range is 5 to 90° C., and the usable temperature range of the embodiment is greatly expanded in the form of a rod with no difference in properties compared to the conventional example.

In the above embodiment, the active layer 7 has a two-layer structure, but as is clear from the above description, the active layer 7 has a three-layer structure within the range of slightly different compositions to widen the width of the EL spectrum. The above layer may be multi-layered, or the composition may be changed continuously in the lamination direction.

Furthermore, although the above embodiments take an InP/InGaAsP long wavelength DFB laser as an example, the present invention is not limited to the InP/InGaAsP system based on its principle.

〔Effect of the invention〕

As explained above, according to the configuration of the present invention, the active layer, the optical guide layer, the diffraction grating, and the cladding layer sandwiching these and having a wider bandgap form a laminated structure, and the semiconductor light emitting device has a distributed feedback function. (DFB laser), the temperature range that can be used in a single mode can be expanded without doping the active layer with impurities, which satisfies the needs of the semiconductor light emitting device and makes its use more convenient. effective.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view of the main part of the example and a diagram showing the band gap, Fig. 2 is an emission spectrum diagram of the example, and Fig. 3 is a side sectional view of the main part of the conventional example and a diagram showing the band gap. Figure 4 is an emission spectrum diagram of the conventional example. In the figure, ■ is an n-type cladding layer, 2 is a diffraction grating, 3 is an n-type optical guide layer, 4.7 is an undoped active layer, 5 is a p-type cladding layer, 6 is a p-type contact layer, 7a is an undoped layer of 7 7b is the undoped second active layer of 7; A is the emission spectrum on the low temperature side; B is the emission spectrum on the high temperature side. C(1')
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Claims (1)

[Claims] In a semiconductor light emitting device having a stacked structure of an active layer, a light guide layer, a diffraction grating, and a cladding layer sandwiching these and having a wider band gap than these, and having a distributed feedback function,
A semiconductor light emitting device characterized in that the active layer has a composition slightly different in the direction of the lamination, thereby widening the width of the EL spectrum.