JPS6057692A - Distributed bragg-reflector type semiconductor laser - Google Patents

Abstract

PURPOSE:To make the length of the titled element longer to the same extent as that of an ordinary semiconductor laser and to upgrade reproducibility of the element characteristics and yield of the element structure by a method wherein a rotating lattice is formed on the flat surface of the semiconductor of the element, and at the same time, a control electrode is formed at the upper part of the rotating lattice for a reflection type. CONSTITUTION:A rotating lattice 2, a P type optical guide layer 3 and an N type optical guide layer 4 are successively laminated, all in a thickness of 0.2mum, on an N type InP substrate 1, and moreover, a P type InP layer 5 is laminated in a thickness of 0.1mum and a semiconductor hetero-structure wafer is constituted. An etching is selectively performed on the wafer using an SiO2 film 16 as a mask, and a buffer layer 7, an active layer 8 and a clad layer 9 are formed. Moreover, etching grooves 10 and 12 and a mesa-type stripe 11, which are located in parallel to the crystal direction of the substrate 1, are formed and they are buried-grown in a liquid-phase growing process. A rotating lattice is formed on the flat wafer of the distributed Bragg-reflector semiconductor laser BH-DBR-LD in the hetero structure having a wavelength control function and a control electrode 19 is formed at the upper part of the rotating lattice for a reflection type. By such a constitution, reproducibility of the characteristics of the semiconductor laser and yield of the element structure can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a semiconductor laser in which a light guide layer having a diffraction grating is directly coupled to an embedded active layer, and in particular has a wavelength control region, has no axial mode skipping, and is stable over a wide temperature range. This invention relates to a buried heterostructure distributed Bragg reflection type semiconductor laser exhibiting single-axis mode oscillation. C at high speed modulation
Distributed feedback semiconductor lasers (DFH-LD) and distributed Bragg reflection semiconductor lasers (DBR-LD), both of which have a diffraction grating, are used as semiconductor light sources that exhibit stable single-axis mode oscillation and are therefore capable of long-distance, large-capacity transmission. It's a development party. All of these semiconductor lasers have a diffraction grating with an appropriate pitch, and results have been obtained in which they oscillate at a short wavelength even when high-speed modulation is performed at several hundred megabits/second. By the way, 1) In a 13-LD, the DBR reflectance with respect to wavelength is given by a curve that is greatest at the Bragg wavelength, and there are several resonance points on this curve where the phases of the active region and the DBR region match. . Among these resonance points, at the point where the DB reflectance is maximum, the threshold gain becomes the maximum I, and that wavelength becomes the oscillation principal axis mode.

With respect to the main axis mode, the point with the second smallest threshold gain provides the sub-axis mode.

When the temperature changes, the isolateral refractive index in the active region and the DBRB region changes, and the resonance point moves on this curve. Therefore, when the suspension changes, at a certain temperature, the resonance point where the threshold gain is minimum shifts to the next resonance point. 'That is, the oscillation main axis mode and the sub-axis mode take over, causing a jump in the oscillation axis mode. It is not possible to bring out the special characteristics of such a mode within the operating precision range. In order to avoid such a phenomenon, it is important to introduce a wavelength control mechanism that does not cause mode skipping in the operating temperature range near room temperature. As an example, in the spring of 1980, Tomori et al. developed a directly coupled distributed Bragg reflection semiconductor laser (BJB-DBRLD) having a wavelength control function, as reported at the 945 National Conference of the Institute of Electronics and Communication Engineers. This semiconductor laser has a DBRB region and a wavelength control region on both sides of an active layer. In the wavelength control region, by injecting a control current into the output side optical guide layer, the difference in gain between the pla mode and the submode is kept constant, and stable single-axis mode oscillation can be obtained at all times.

Mr. Tomori et al. used the above-mentioned wavelength control BJJ3-DBRLD,
By injecting a control current of 18 mA, a wavelength shift of 1.4 A to the shorter wavelength side was observed. The wavelength of the striped structure developed by Tomori et al.
In LD, stripe width is 20 μm and active region length is 350 μm.
, wavelength control region 200 μm, D, BJl, region length 2
00 to 500 μnl, active region □t (distance between dik and wavelength control region electrode is 100 μm).

However, in the above-mentioned semiconductor laser, the diffraction grating is formed in the BP-region ζ after all the crystal growth steps have been completed, and laser interference exposure is performed on the portions with a difference of about 5 μln. There is.

Therefore, when applying this structure to a buried laser, the stripes of the DBR circumferential optical guide layer with a width of about 2 μm are covered with an InP buried semiconductor layer, and a 7-photoresist is applied to the uneven parts. Then, laser interference exposure is performed.

4) Apply photoresist to the area where the buried InP layer is higher than the optical guide layer.
Since the photoresist becomes thick, it is difficult to fabricate a diffraction grating properly. It would be better to selectively etch the buried InP layer little by little and perform laser interference exposure while the etching becomes as quiet as the light guide layer.
The etching is not easy to control, and the manufacturing yield is low.

Furthermore, since the DB control region wavelength control region is formed in addition to the active region, the device becomes too large, and it is difficult to mount it on a heat sink. That is, there is a particular problem in the production of the diffraction grating, and if the diffraction grating can be formed on a uniform surface, the production yield will also improve. Furthermore, since the element becomes too large, it is more preferable to make the length approximately 500 μm.

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, an object of the present invention is to provide a buried heterostructure distributed Bragg reflection semiconductor laser in which a wavelength control mechanism is formed, and the reproducibility of characteristics and the yield of device manufacturing are significantly improved. be.

The structure of the distributed Bragg reflection type semiconductor laser according to the present invention includes at least an active layer on a semiconductor substrate and an energy gear larger than the active layer, and a period of n.
λ/2 (where n is an integer and λ is the oscillation wavelength in the active layer)
In the distributed Bragg reflection type half-A-body laser, the active layer J? The optical power layer 41 is coupled in a direction parallel to the laser resonance axis, and an 'lj control' pole is formed on the top of the optical guide layer.

Hereinafter, the present invention will be explained in more detail using drawings showing examples.

FIG. 1 shows a buried heterostructure distributed Bragg reflection semiconductor laser (Bl-I-DBI(,-L4)) according to the present invention.
) is a perspective view showing the manufacturing process of one embodiment. To obtain such an H-DBR-LD, first, as shown in FIG. 1(a), a diffraction grating 2 is formed on an n-InP substrate 1.
and P −1 corresponding to the emission wavelength of 1.2 μm on top of it.
No? llGao, 22Aso0g po, 52 light guide layer 3. n -■nn-78 G-4, A shame, 4°-P. ,, the thickness of each of the two optical guide layers 4 is 0.2 μm,
P-InP layers 5 are sequentially stacked to a thickness of 1 μm. The diffraction grating 2 was formed on the n-InP substrate 1 having the (10D) plane orientation in the 11>crystal orientation. Etching was carried out using a photolithography technique and an HBr-based mixed etching solution.

To prevent the disappearance of the diffraction grating 2 due to retention during liquid phase growth, meltback, etc., Ri-b, 7BGa1.22AS4
0.1) (1,52 The optical guide layer 3 was grown at a low temperature of around 600°C. In particular, it was grown using a super cooling solution with a supersaturation level of around 10"C to prevent meltback. As shown in FIG. 1(b), the semiconductor heterostructure wafer thus fabricated was selectively etched down to the top surface of the n-InP substrate using the SIO2 film 6 as a mask. A second liquid phase growth is performed while leaving the 5in2 film 6, and the n-InP buffer layer 7 is grown to a thickness of 0.2 μm2 with non-doped Ir1o, F2'ao, ta "6I, 6 with an emission wavelength of 1.3 μm.
1" o,n active layer 8 with thickness O, 1 μm, p-fn
A P cladding layer 9 is laminated to a thickness of about 1 μm. SiO□ film 6
was formed parallel to the <01.1> direction, and the surface of the p-InP cladding IA9 was grown at almost the same height as the p-InPIi5. At this time, the growth r' crystallinity should be around 17-i650℃, which is the normal growth temperature, and n-
During the growth of the InP%y layer 7, the diffraction grating 2 melts back or disappears thermally, and the active layer 8! (This will be grown on the flattened semiconductor 1 film.Subsequently, 5i02 film 6
After removing <01.1> as shown in Figure 1(C)
Two etched grooves parallel to the direction 10.12. and forming mesa stripes 11 sandwiched between them,
Filling growth is performed in the third liquid phase growth step.

Each of the etched grooves 10 and 12 had a depth of 3 .mu.Tn and a width of 10 .mu.m, and the mesa stripe 11 had a width of 1.5 .mu.m in the part of the first ancient layer 8. 9 p-1n in embedded growth
P' Ichiryu t block f @ 13. All of the n-InP current blocking layers 14 except for the upper surface of the mesa stripe 11 are further covered with a p-InP buried layer 151 with an emission wavelength of 1.
1) 'Ino, equivalent to 2μm? 8 Ga6.22 A
SQ, 48 Po, 62'm, and D layers 16 are laminated over the entire song. Finally, after forming an AuZn electrode on the entire surface of the element, a separation groove 17 for electrical insulation is etched and formed, and the active region electrode 4if 18. Control electrode 1
9. Further, an n-type ohmic electrode 20 is formed on the entire surface of the substrate. The isolation trench 17 only needs to have good electrical insulation, and must not reach the depth of the active layer 8 . The desired BE (-DB) produced as described above
T, D (active region length 200 μm η, DB control region length 200 μm), oscillation threshold current 40+nA at room temperature y, differential quantum efficiency 20%, 5
Stable single-axis mode oscillation was obtained with good reproducibility even during continuous operation at 00 Mb/s.

By the element shown in this example? Then, D B 1:(
When a positive polarity is applied to the control head, a reverse bias is formed at the pn junction in the light guide layer, and the depletion layer spreads to both sides. 2~3×10
A depletion layer is formed by applying a positive O solution pressure to a moderately doped optical guide layer, and the carrier concentration there becomes almost zero, resulting in a relatively large change in refractive index due to the plasma oscillation effect. can get. That is, DBR
By changing the voltage applied to the control region, the refractive index of the light guide station changes, making it possible to match the resonance wavelength and Bragg wavelength, resulting in stable single-axis mode oscillation without mode skipping over a wider temperature range. can be obtained. In fact, it was observed that by applying a voltage of 5V, the oscillation wavelength shifted by 3A to the long wavelength -1i(tj).In addition, the control voltage was not applied +10. °C to 40°C and 40°O
It exhibits leather-axis mode oscillation in the range from 40° to 65°C.
There was a 1111 jump in the axis mode near C. If you stand on this IL and apply 1 tonne pressure to about 7V for 1 hour, it will be 1. From this, it became possible to change the refractive index of the D IJ R region, and thus to align the resonance wavelength and the Bragg wavelength. Wide up to? There was (!) the same single-axis mode imitation behavior over the crystallinity range.

The flow Il of the oscillation wavelength at that time (change L/4 is /, I
It was A/deg.

In an illustrative example of the present invention, Hll' shaved area, 1 with 1 table
In the 3J DBR-LD, the diffraction grating 2 is formed on the flat l+ u++ n-fn PJ plate 1 by θ3.
C, the reproducibility of characteristics and the yield of device manufacturing have been greatly improved.

At the same time, by introducing a wavelength control mechanism into the DBR region, the length of the element has been reduced from the conventional length of nearly 1 mm to 400-5 mm.
00 μm, making it sufficiently easy to handle the device when mounting it on a heat sink, etc.

In addition, in the actual example of the present invention, the DBR control area is set to P-
A method was adopted in which the refractive index was changed by using the N-P-N structure and the expansion of the depletion layer due to voltage application.As with the conventional example, this method uses the effect of changing the refractive index due to carrier injection as a P-N structure. You may use the . In that case, the refractive index decreases due to current (carrier) injection, so the oscillation wavelength shifts to a shorter wavelength. Further, in the embodiment, the transverse mode control structure has a shape in which a mesa stripe is sandwiched between two etched grooves, but the present invention is not limited to this, and includes any buried structure. Furthermore, the semiconductor materials used are InP for the substrate and InG for the substrate.
Although we have shown a material with a wavelength of 1 μm that uses aAsP as the active layer and optical guide layer, it is not limited to this, and GaA
Materials such as JAs/GaAs and InGaAsP/GaAS are acceptable.

The feature of the present invention is that B I-f-1) has a wavelength control function.
In the BR-LD, a diffraction grating was formed on a flat semiconductor surface of 1 m, and a control electrode was formed above the DBR diffraction grating. As a result, the length of the element can be made comparable to that of a normal LD, and the reproducibility of characteristics and the yield of the element structure are greatly improved.

[Brief explanation of the drawing]

FIG. 1 (aHbHc) is an embodiment of the present invention B)
It is a perspective view showing the manufacturing process of I-DBR-LD. In the figure, 1 is an n-InP substrate, 2 is a diffraction grating, 3 is a p-Ina substrate,
7a Gao, 22-kso, 43 PO, 52 light guide layer, 4 is n-In676Ga6, 22Aso. -P
Q, 52 optical chi) one layer, 5 tti p-InP layer,
6uSiO, film, 7 is n-InP buffer layer, 8 is In
o-72Ga0828Aso, , Po., 9 active layer 1
, 9 is a p-InP cladding layer, 10.1.2 is an etched groove, 11 is a mesa stripe, 13 is a p-InP current-current bluff 2 layer 4 is an n-InP current-current bluff 2 layer 5 is a p-InP current-current bluff 2 layer
-InP buried layer, 16 is I) -Ino, 7a Ga
0.22 kso, aP6. ．． 2@pole layer, 17 is a separation groove, 18 is an active region electrode, 19 is a control electrode, and 20 is an n-type ohmic electrode. Buried I' by Patent Attorney Uchihara E

Claims (1)

[Claims] At least the active layer and the active layer 1 have a large energy gap, and one surface is subjected to a periodic force Sn/IA (however, n
is an integer and λ is the oscillation wavelength in the active layer).
a light guide layer formed, the active layer and the light guide layer being optically coupled in the direction of a laser resonance axis;
and has a laminated structure in which one active layer in the striped active region is embedded in a semiconductor layer having a larger energy gap than the active layer, and further, a control electrode is formed on the optical guide layer. Distributed Bragg reflection type semiconductor laser with standby function.