JPH06204599A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To use InGaAs and InGaAlAs as a quantum well active layer, and to provide a semiconductor laser having low threshold currents, stable temperature characteristics, high reliability and high performance. CONSTITUTION:When an N-GaAs buffer layer 2, an N-Al0.6Ga0.4As clad layer 3, an undoped superlattice optical guide layer 4, an undoped In0.2Ga0.8As quantum well layer 5, an undoped superlattice optical guide layer 6, a P-Al0.6Ga0.4As clad layer 7 and a P-GaAs cap 8 are formed continuously onto an N-GaAs substrate 1 by using an MBE method, GaAs three molecule layers and Al0.6Ga0.4 As two molecule layers are laminated alternately at fifty periods in the superlattice optical guide layers 4, 6, and a growth temperature is changed during the formation of the superlattice optical guide layer 4.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a semiconductor laser, and more particularly to about 7
The present invention relates to a semiconductor laser having an oscillation wavelength in the range of 70 nm to 1100 nm and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, optical communication technology and optical information processing technology have come to play a central role in various fields. For example, digital optical communication using an optical fiber dramatically increases the data communication density. In addition, optical discs and laser printers have significantly expanded the application range of optical information processing. The development of such optical communication technology and optical information processing technology largely depends on the progress of the semiconductor laser (laser diode) which is a light source. Utilizing the excellent features of small size and high efficiency, compact disks, video disks, optical communication Widely used as a light source for nets. As is well known, a semiconductor laser uses a PN junction,
By injecting a large number of carriers into the active layer, an excited state is realized and laser oscillation is performed. And recent advances in semiconductor technology, especially molecular beam epitaxy (MB
E) method and metal-organic vapor phase epitaxy (MOCVD) method have made it possible to control an ultra-thin epitaxial growth layer to an atomic order of about 10 Å or less. Along with that, 20
A semiconductor laser having an active region of a quantum well of about 0 Å or less has been realized, and high efficiency and low driving current have been advanced (reference: WTTsang, in Semiconductors and Semimetals vo
l.24, "pp.397 edited by R.Dingle, Academic Press, San
Diego (1987)).

Recently, a semiconductor laser using a strained quantum well having a lattice constant different from that of the surrounding semiconductor has been attracting attention. This is because the MBE method or MOCVD method is capable of stacking crystals without causing lattice defects as long as they are within the critical film thickness.
It can be said that the device takes advantage of the law. In particular, a strained quantum well laser using InGaAs having an oscillation wavelength of 980 nm as a quantum well active layer is regarded as an important light source for pumping an optical fiber amplifier. Conventionally, in this type of semiconductor laser, GaAs not containing Al has been often used as a barrier layer. This is because InGaAs contains In having a high vapor pressure, so it is necessary to grow the quantum well layer at a relatively low temperature, and by sandwiching the quantum well with GaAs, which can obtain good crystallinity at a low temperature,
This is because a high quality heterostructure can be manufactured.

On the other hand, it has been reported that when AlGaAs containing Al is used for the barrier layer, the luminous efficiency is significantly lowered (reference: B. Pezeshki, SM Lord, and
JSHarris, Jr., in Proceedings of International Sym
posium on Gallium Arsenideand Related Compounds, Se
attle, 1991; Inst.Phys.Conf.Ser.No.120 (IOP, London) p.
437.).

That is, InGaAs or InGaAlA is formed by the MBE method using AlGaAs as a cladding layer.
When manufacturing a semiconductor laser having an In-containing quantum well as an active layer such as s, the optimum growth temperature is different for each, so that the cladding layer is at a high temperature of 700 ° C. or higher and the quantum well layer is at a low temperature of 550 ° C. or lower. Need to grow. As a method of achieving the optimum growth temperature at this time, the temperature can be changed by suspending the crystal growth, but since the non-radiative recombination centers are present at a high density at the interface where the growth is interrupted, It is not usually adopted because it impairs the efficiency and reliability of. Thus, when a mixed crystal containing In is used as the quantum well active layer, it is necessary to grow the AlGaAs barrier layer at a low temperature or change the temperature during the growth of the AlGaAs barrier layer. Therefore, it was not possible to manufacture a high-quality heterostructure that satisfies the laser characteristics.

However, a single quantum well (6 nm) of In _0.2 Ga _0.8 As is used as an Al _x Ga _1-x As barrier layer (x is Al.
(A mixed crystal ratio) of the sample was prepared by MBE method at 520 ° C., and the emission intensity of photoluminescence was measured at room temperature of 300 K. As a result, as shown in FIG. It was found to increase exponentially. Therefore, by using AlGaAs as the barrier layer instead of using GaAs as the barrier layer, it is possible to reduce the threshold current and improve the temperature characteristics. However, as described above, in the MBE method, about 640
There is a temperature region where AlGaAs does not grow like a mirror surface in the temperature range of up to 700 ° C (reference: T. Hayakaw
a, M.Morishima, M.Nagai, H.Horie, and K.Matsumoto, Appl
ied Physics Letters vol.59, No.19, pp.2415 (1991)).
Therefore, it was necessary to provide a thin GaAs barrier layer between the InGaAs quantum well active layer and AlGaAs and change the temperature during the growth of this layer.

A conventional procedure for forming a strained quantum well laser is shown in FIG.
Will be explained.

An n-GaAs buffer layer 42 and n-Al _0.6 G are formed on an n-GaAs substrate 41 having a (100) orientation.
a _0.4 As clad layer 43 is provided, and the Al mixed crystal ratio is gradually reduced from 0.6 to 0.05 as the clad layer 43 approaches an InGaAs quantum well 46 described later.
After forming a RIN (graded index) optical guide layer 44 and a relatively thin GaAs barrier layer 45, an InGaAs quantum well 46 is formed. Hereinafter, the GaAs barrier layer 47, the GRIN optical guide layer 48, the p-Al _0.6 Ga _0.4 As clad layer 4 so as to sandwich the InGaAs quantum well 46.
9. The p-GaAs cap layer 50 is continuously formed using the MBE method. After the crystal growth by the MBE method, a SiN _x film 51 is formed by plasma CVD, and a part of the SiN _x film is removed by photolithography and chemical etching by diluted HF to form a stripe shape with a width of 50 μm. The window 54 is formed. Finally, Mo / Au 52 and n-GaAs substrate 4 are provided on the p-GaAs cap layer 49 side.
After vacuum deposition of AuGe / Ni / Au53 on the 1 side, 460
Anneal at ℃ to form an ohmic electrode. In this way, the strained quantum well laser is formed, and the GRIN optical guide layer 4 is formed.
4 and 48 reduce carrier leakage to the cladding layer and increase light confinement in the quantum well. In addition, the quantum well 46 is formed into a relatively thin GaAs barrier layer 4
By sandwiching between 5, 47, the temperature is changed during the growth of these GaAs layers to realize the optimum crystal growth temperature, eliminate the temperature mismatch due to the composition, and prevent the deterioration of the crystallinity.

[0009]

However, since the conventional strained quantum well laser has an extra GaAs barrier layer, the thickness of the optical guide layer (the total of 44 to 48 layers) becomes large as a whole, and the thickness of the optical guide layer in the direction perpendicular to the pn junction is increased. There is a drawback that the beam spread of the laser light becomes large and the coupling efficiency with the optical system becomes small. Furthermore, when GaAs is used as a barrier layer, a heterobarrier cannot be sufficiently taken, so that a laser with InGaAs having a low In mixed crystal ratio having an energy gap close to that of GaAs or InGaAlAs having a larger energy gap as a quantum well active layer is realized. could not.

Further, when the crystal growth is carried out using the MBE method or the MOCVD method, the optimum growth temperature is limited to a narrow range depending on the kind of the mixed crystal, so that it is difficult to select the conditions.

Therefore, the present invention is based on InGaAs and InGa.
The objective is to easily provide a high-performance semiconductor laser having a low threshold current, stable temperature characteristics, and high reliability, using AlAs as a quantum well active layer.

[0012]

In order to solve the above-mentioned problems, the present invention has an active layer composed of at least one quantum well layer, and the quantum well layer comprises at least In, Ga, and A.
In the semiconductor laser made of a semiconductor containing s, at least one of the barrier layers adjacent to the quantum well layer is a superlattice layer in which GaAs and AlGaAs or AlAs are alternately laminated. The growth temperature is changed during the growth of at least one of the superlattice layers at the time of manufacturing.

[0013]

In the present invention, at least In, Ga, A
In a semiconductor laser having a quantum well active layer containing s as an active layer, a superlattice layer in which GaAs and AlGaAs or AlAs are alternately stacked is used as a barrier layer sandwiching a single or multiple quantum well active layers, and equivalently high quality is obtained. The same high efficiency and high reliability as the quantum well semiconductor laser having the AlGaAs barrier layer can be obtained. Further, by adopting a method of changing the growth temperature during the growth of the superlattice barrier layer, the growth temperature is relatively low without compromising the crystallinity of the barrier layer, which is suitable for a quantum well containing In, Ga, As. It can be manufactured at an optimum temperature with a suitable AlGaAs cladding layer.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows InGaAs / which is a first embodiment of the present invention.
The cross section of an AlGaAs quantum well laser is shown typically.

On the n-GaAs substrate 1 (Si = 2 × 10 ¹⁸ cm ^-3 ) having the (100) orientation, the n-GaAs buffer layer 2 (Si = 1 × 10 ¹⁸ cm ^-3 , 0.5 μm), n −
Al _0.6 Ga _0.4 As clad layer 3 (Si = 1 × 10 ¹⁸
cm ⁻³ , 1.5 μm), non-doped superlattice optical guide layer 4, non-doped In _0.2 Ga _0.8 As quantum well layer 5
(0.006 μm), non-doped superlattice optical guide layer 6,
p-Al _0.6 Ga _0.4 As clad layer 7 (Be = 1 × 1)
0 ¹⁸ cm ⁻³ , 1.5 μm), p-GaAs cap 8
(Be = 1 × 10 ¹⁹ cm ⁻³ , 0.5 μm) is continuously formed using the MBE method. Here, the non-doped superlattice optical guide layers 4 and 6 are composed of GaAs trimolecular layer Al _0.6 Ga.
_{It is} formed by alternately stacking 50 cycles of _0.4 As2 molecular layers. At this time, the average Al mixed crystal ratio is 0.24. The growth temperature is n-Al _0.6 Ga _0.4 As clad layer 3.
After growth at 720 ° C., an undoped In _0.2 stabilizes the undoped growth initiation of the superlattice optical guide layer 4 at the same time as 520 ° C. during the growth of the non-doped superlattice optical guide layer 4 lowers the temperature
The Ga _0.8 As quantum well layer 5 is grown at 520 ° C. Next, at the same time when the growth of the non-doped superlattice light guide layer 6 is started, the temperature is raised to 720 during the growth of the non-doped superlattice light guide layer 6.
Stabilize to 0 ° C and subsequent growth at 720 ° C.
In this way, even if the growth temperature is changed in the superlattice containing GaAs, perfect mirror growth is possible, and crystal growth by the MBE method is possible without deteriorating the device characteristics. Here, the undoped In _0.2 Ga _0.8 As quantum well layer does not cause significant deterioration in characteristics even if the growth temperature changes by about ± 20 ° C., but the crystallinity of the Al _0.6 Ga _0.4 As clad layers 3 and 7 is sensitive to the growth temperature. It is necessary to stabilize the temperature within ± 5 ° C. After MBE growth, a SiN _x film 9 (3000 Å) is formed by plasma CVD, a part of the SiN x film is removed by photolithography and chemical etching using diluted HF, and a striped window 12 having a width of 50 μm is formed. To form. Finally, Mo / Au10 on the p-GaAs cap layer side and AuG on the n-GaAs substrate side.
After e / Ni / Au11 is vacuum-deposited, it is annealed at 460 ° C. for 5 minutes to form an ohmic electrode.

The wafer thus manufactured was cleaved to have a cavity length of 500 μm, and Al ₂ having a reflectance of 10% was formed on the front end face.
After coating the O ₃ film and the rear end surface of Al ₂ O ₃ having a reflectance of 95% and amorphous Si by two cycles alternately by electron beam vapor deposition, the chip is cut into a chip with a width of 500 μm and In solder is used. Mount it on a copper heat sink. When the characteristics of the strained quantum well laser manufactured in this way are measured, the threshold current is 55 m at 25 ° C.
It oscillates at A, and a light output of 1 W or more can be obtained from the front end face. The oscillation wavelength at this time is about 980 nm. Further, this strained quantum well laser has excellent temperature characteristics, and the characteristic temperature T ₀ when the threshold current is expressed by Aexp (T / T ₀ ) [A is a constant, T is temperature] is the same as that of the conventional GaAs.
Compared to about 120 degrees when using as a light guide layer,
It improved to 0 degrees or more. This is because leakage of carriers, mainly electrons, from the quantum well to the barrier layer (optical guide layer) could be reduced.

FIG. 2 shows InGa which is a second embodiment of the present invention.
1 schematically shows a cross section of an AlAs / AlGaAs strained multiple quantum well laser.

An n-GaAs buffer layer 22 (Si = 1 × 10 ¹⁸ cm ^-3 , 0.5 μm) on an n-GaAs substrate 21 (Si = 2 × 10 ¹⁸ cm ^-3 ) having a (100) orientation,
n-Al _0.7 Ga _0.3 As clad layer 23 (Si = 1 ×
10 ¹⁸ cm ⁻³ , 1.4 μm), non-doped superlattice optical guide layer 24, non-doped In _0.1 (Ga _0.85 Al _0.15 ).
_0.9 As strained multiple quantum well active layer 25, non-doped superlattice optical guide layer 26, p-Al _0.7 Ga _0.3 As clad layer 27 (Be = 1 × 10 ¹⁸ cm ⁻³ , 1.4 μm), p-G
aAs cap 28 (Be = 1 × 10 ¹⁹ cm ⁻³ , 0.7
μm) are continuously formed using the MBE method. here,
The undoped superlattice optical guide layers 24 and 26 are made of GaAs.
Two molecular layers of Al _0.7 Ga _{0.3 As} 2 molecular layers are alternately laminated for 61 cycles, and the average Al mixed crystal ratio is 0.35. The strained multiple quantum well active layer 25 includes three In _0.1 (Ga)
_0.85 Al _0.15 ) _0.9 As Strained quantum well (0.006 μm)
Are separated by superlattice barrier layers in which GaAs bilayers Al _0.7 Ga _{0.3 As} bilayers are alternately laminated for 8 periods (Al _0.7 Ga _0.3 As is 9 layers at the volume end). Also in this embodiment, as in the first embodiment, the growth temperature is such that the AlGaAs cladding layers 23 and 27 are grown at 720 ° C., and the temperature is changed during the growth of the non-doped superlattice optical guide layers 24 and 26 to obtain strained multiple quantum wells. The active layer 25 was grown at 520 ° C. After MBE growth, a 50 μm wide SiN _x stripe laser 32 similar to that of the first embodiment is produced.

The wafer thus produced was cleaved to have a cavity length of 500 μm, and Al ₂ having a reflectance of 10% was formed on the front end face.
After coating the O ₃ film and the rear end surface of Al ₂ O ₃ having a reflectance of 95% and amorphous Si by two cycles alternately by electron beam vapor deposition, the chip is cut into a chip with a width of 500 μm and In solder is used. Mount it on a copper heat sink. When the characteristics of the strained quantum laser manufactured as described above are measured, it is possible to oscillate at a threshold current of 75 mA at 25 ° C. and obtain an optical output of 1 W or more from the front end face. The oscillation wavelength at this time is about 830 nm. Since a strained quantum well containing In is used, A having the same oscillation wavelength
It is possible to obtain a lower threshold current and higher reliability than the laser of the 1GaAs unstrained quantum well.

As described above, by using the short period superlattice of GaAs and AlGaAs as the barrier layer, the conventional In
750 not covered by AlGaAs laser
It is possible to improve the characteristics of the semiconductor laser in the wavelength range of ˜880 nm. Further, a semiconductor laser in the wavelength range of about 880 to 940 nm, which has not been covered in the past, can be realized without deterioration of characteristics.

The above embodiment shows a semiconductor laser having a superlattice barrier layer having the same structure in one device.
It is possible to change the composition or period of each superlattice barrier layer, change the period or composition within one superlattice barrier layer, or configure a superlattice barrier layer with multiple superlattice layers having different periods or compositions. It is possible.

Further, in the above embodiments, only the element having the simplest electrode stripe structure has been described in detail, but it goes without saying that the invention can be applied to semiconductor lasers having various stripe structures including various refractive index guiding structures.

Furthermore, it is not necessary to use the MBE method as a manufacturing method, and MBE using a gas raw material instead of the metal material is used.
Method and also when using the MOCVD method, AlG is generally used.
Since the optimum manufacturing temperature greatly differs between compound semiconductors containing aAs and In, it is possible to realize a high-quality semiconductor laser by making it possible to change the temperature between these layers without stopping the growth.

[0024]

As described above, according to the semiconductor laser of the present invention, InGaAlAs or InGa is used.
When the As-strained quantum well is used as the active layer, the energy of the hetero barrier of the quantum well can be made higher than in the conventional case, and an element having low current and high efficiency and excellent temperature characteristics can be realized. The InGaAlAs strained quantum well is AlGaAs.
It is possible to improve characteristics such as a lower threshold than that of the non-strained quantum well and also improve reliability. Further, by using the manufacturing method of the present invention, the clad layer and the active layer can be manufactured under the optimum conditions, respectively, so that it is possible to manufacture a highly reliable element with good reproducibility without impairing the crystallinity. . In particular, when the MBE method or a similar manufacturing method is used, the strained quantum well of InGaAs or InGaAlAs having AlGaAs as a barrier layer, which has been extremely difficult to manufacture due to the existence of a temperature region where AlGaAs causes non-mirror-like growth, is activated. It is possible to easily obtain a high-performance semiconductor laser having a layer with a low threshold current, stable temperature characteristics, and high reliability.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a strained quantum well laser according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of a second embodiment of the strained quantum well laser according to the present invention.

FIG. 3 is an explanatory diagram showing the dependence of photoluminescence emission intensity at 300 K of an In _0.2 Ga _0.8 As / Al _x Ga _1-x As single strain quantum well structure on the Al mixed crystal ratio x.

FIG. 4 is a schematic sectional view of a conventional strained quantum well laser.

[Explanation of symbols]

1 n-GaAs substrate 2 n-GaAs buffer layer 3 n-AlGaAs clad layer 4 undoped superlattice light guide layer 5 non-doped InGaAs quantum well layer 6 non-doped superlattice light guide layer 7 p-AlGaAs clad layer 8 p-GaAs cap layer 9 SiN _x film 10 p-electrode 11 n-electrode

Claims (2)

[Claims] 1. The active layer comprises at least one quantum well layer, and the quantum well layer comprises at least In, Ga, A.
In a semiconductor laser made of a semiconductor containing s, at least one of the barrier layers adjacent to the quantum well layer is G
A semiconductor laser comprising a superlattice layer in which aAs and AlGaAs or AlAs are alternately laminated. 2. The active layer comprises at least one quantum well layer, and the quantum well layer comprises at least In, Ga, A.
In the method of manufacturing a semiconductor laser made of a semiconductor containing s, at least one of the barrier layers adjacent to the quantum well layer is G
A method of manufacturing a semiconductor laser, comprising a superlattice layer in which aAs and AlGaAs or AlAs are alternately laminated, and changing a growth temperature during growth of at least one of the superlattice layers.