JPH0786695A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser device which is capable of reducing a threshold, and minimizing temperature dependence of device characteristics by using a GaInAs strained quantum well structure which is easy to control a wavelength. CONSTITUTION:This invention relates to a semiconductor laser device which clamps an active layer 13 which is designed under strained quantum wall structure which laminates a GaInAsP barrier layer 13a and a GaInAs wall layer 13b with an InP clad layer 11 and a p type InP clad layer 15 and further inserts GaInAsP optical guide layers 12 and 14 between each of the clad layers 11 and 15. The active layer 13 is formed based on metal organic vapor deposition. Moreover, impurities, such as Si are added to the active layer 13 and the optical guide layer 14 where the concentration of Si is set to: 1X10<16>cm<-3> to 5X10<17>cm<-3>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device used for optical communication and information processing, and more particularly to a semiconductor laser device having an active layer having a quantum well structure.

[0002]

2. Description of the Related Art In recent years, semiconductor lasers using various compound semiconductor materials have been developed as a light source for information processing, optical communication, etc., and higher performance is desired. In particular, there are strong demands for low threshold characteristics, characteristics with small output fluctuations with respect to temperature, and high reliability, and research and development have been actively conducted.

In order to realize a semiconductor laser that oscillates at a low threshold value, a quantum well structure is introduced into an active layer, and recently, a well layer having a quantum well structure has a lattice constant different from that of a cladding layer. Introduction of strained quantum well structures has been carried out. In the case of introducing strain into the active layer in the case of a 1.5 μm band laser, the effect of lowering the threshold value is often realized by making the lattice constant larger than that of the substrate. In this case, the well layer of the quantum well structure has a GaI composition closer to that of InAs than in the case of lattice matching.
An nAs layer is used.

When the strained quantum well structure is introduced, the threshold current density is lowered, so that the amount of carriers in the quantum well, which increases the temperature dependence of the laser characteristics, is reduced, and the fluctuation of the characteristics due to temperature is reduced. Can be expected to do. However, although the threshold current actually decreases, it has become clear that the dependence on temperature is not necessarily small.

On the other hand, the width of the 1.3 μm band laser or the well layer of the quantum well structure is widened to make GaIn having a relatively high P composition.
It is known that the temperature characteristics can be easily improved when a laser in the 1.5 μm band is manufactured by using AsP in the well layer. However, in such a structure, since GaInAsP containing two kinds of group V elements having high vapor pressure is used for the well layer, it is difficult to control the composition and the oscillation wavelength.

These problems will be described in detail below.
In the case of introducing strain into the active layer in the case of a low threshold 1.5 μm band semiconductor laser, a GaInAs layer having a composition closer to InAs is used as a well layer than in the case of lattice matching with the substrate. In many cases. At this time, although the threshold current density decreases, the temperature dependence of the laser characteristics is less likely to decrease. It is considered that this is because Zn used in the clad layer or the substrate diffuses, and Zn accumulates in the GaInAs layer having a small Zn diffusion coefficient, and at the same time, a deep level is formed. Particularly, this problem is significant in the effect of accumulating Zn because the thickness of the well layer is thin in the quantum well structure, and the effect is remarkable.

On the other hand, the diffusion coefficient of the p-type impurity is small in the region to which the n-type impurity is added. In particular, if an n-type impurity is added at a concentration higher than the p-type impurity concentration, p
The diffusion coefficient of the type impurities becomes small. The diffusion of Zn in InP is a two-stage diffusion type, and the concentration of the low-concentration diffusion front drops sharply when the concentration is about 10 ¹⁵ cm ⁻³ or less. Therefore, if the concentration of the n-type impurity in the quantum well structure exceeds this value and exceeds a certain level, the diffusion of Zn can be suppressed, and GaIn
Accumulation of Zn in the As layer and generation of deep level can be reduced.

When forming the quantum well structure of the active layer, I
In the case of nP type, high quality crystal can be grown by a vapor phase growth method, particularly a metal organic vapor phase growth method. GaIn
When As is grown, Si is the main element in the background and becomes n-type, and the impurity concentration is 10
^It is usually less than ¹⁵ cm ^-3 . When the strained quantum well structure is used, the GaInAs composition of the well layer is I.
Although it is close to nAs, Si is difficult to be taken in as impurities in the layer having such a composition, and Si in the background
The concentration will be even lower. Therefore, Zn is likely to diffuse and accumulate.

[0009]

As described above, the conventional Ga
Even if a strained quantum well structure is introduced using an InAs layer, the dependence on temperature cannot be reduced. Furthermore, if GaInAsP having a high P composition is used as the well layer of the quantum well structure, it becomes difficult to control the wavelength of the laser. There was a problem.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to make it easy to control the wavelength.
An object of the present invention is to provide a semiconductor laser device using a strained quantum well structure of aInAs, which has a low threshold value and can reduce temperature dependence of device characteristics.

[0011]

In order to solve the above problems, the present invention employs the following configurations. That is, the present invention relates to a semiconductor laser device in which an active layer having a strained quantum well structure of GaInAs is sandwiched by p-type and n-type cladding layers, the active layer being formed by a vapor phase epitaxy method, and the active layer or the active layer being active. The concentration of Si as an impurity is set to 1 × 10 ¹⁶ cm ^{−3 to} 5 × 10 ¹⁷ cm ⁻³ in at least a part of the optical guide layer provided between the layer and the p-type cladding layer. To do.

Here, the Si concentration is approximately 1 × 10 ¹⁶ cm ^-3.
The atomic concentration of ~ 5 × 10 ¹⁷ cm ^-3 means SIMS
It is a value measured by (Secondary Ion Mass Spectrometry) and includes a factor 3 error. The following are preferred embodiments of the present invention. (1) The clad layer is a layer containing InP. (2) As the well layer in the quantum well structure of the active layer, use GaInAs lattice-matched with the cladding layer or GaInAs lattice-mismatched with the substrate. The well layer may be GaInAsP having a low P composition. (3) It is necessary to use the vapor phase epitaxy method to create the quantum well structure, and in particular, the metal organic vapor phase epitaxy method is used.

[0013]

According to the present invention, S is contained in the active layer of the semiconductor laser.
By positively adding i, diffusion of p-type impurities (for example, Zn) in the active layer can be suppressed, and accumulation of p-type impurities and generation of deep level in the quantum well structure can be suppressed. Is possible.

The region to which Si is added may be the entire active layer or only the well layer having the quantum well structure, and the barrier layer having the quantum well structure alone has an effect of suppressing diffusion of p-type impurities. Further, even if Si is added to the optical guide layer provided between the active layer and the p-type cladding layer, the effect of suppressing the diffusion of the p-type impurities is obtained.

Particularly in a buried type laser, p-type impurities are easily diffused from the buried layer to the surface of the quantum well structure of the active layer in the GaInAs layer having the quantum well structure. Since this diffusion occurs along the well layer of the quantum well structure, it is difficult to suppress the diffusion of the p-type impurity by the optical guide layer or the like.
Diffusion of type impurities can be suppressed significantly. Also,
Even when the present invention is used for the active layer of the strained quantum well structure,
Since Si is intentionally added, the Si concentration in the well layer is sufficiently high, and the effect of suppressing the diffusion of p-type impurities is remarkable.

As described above, as a result of suppressing the diffusion of p-type impurities, even if the active layer is a GaInAs layer, the dependence of laser characteristics on temperature can be reduced.
If the Si concentration in the active layer is too high, the laser oscillation threshold current will increase and the life of the laser element will shorten, but if the concentration is within the range of the present invention, such a problem occurs. I didn't.

When GaInAsP is used instead of GaInAs for the well layer of the strained quantum well structure of the active layer, the p-type impurity concentration is small and the diffusion coefficient is small as a characteristic of the material. Hard to accumulate. In addition, the background impurity concentration during crystal growth is less likely to decrease, so that there is an effect of suppressing diffusion of p-type impurities.
The same effect as nAs can be realized to a small extent, and the temperature characteristic of the laser can be improved. In particular,
In the case of GaInAsP having a low P composition, the material properties are Ga
Since it is close to InAs, its effect is remarkable.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the device structure of a semiconductor laser according to the first embodiment of the present invention. n-type InP substrate 1
0, an n-type cladding layer 11, an optical guide layer 12, an active layer 13, an optical guide layer 14 and a p-type cladding layer 15 are grown and formed in this order.

The n-type cladding layer 11 has a carrier concentration of 10
^{It is 18} cm ⁻³ Si-added n-type InP. Light guide layer 1
2 is Si-added n-type Ga with a carrier concentration of 10 ¹⁷ cm ^-3
InAsP (thickness 0.1 μm, band gap 1.3 μm
m). The active layer 13 has a carrier concentration of 5 × 10 ¹⁶ c
m ^-3 Si-added GaInAsP barrier layer 13a (thickness 1
0 nm, band gap 1.3 μm, 7 layers), and carrier concentration 5 × 10 ¹⁶ cm ⁻³ Si-added Ga _0.35 In
It has a strained quantum well structure in which _0.65 As well layers 13b (thickness 3 nm, 8 layers) are alternately repeated. The optical guide layer 14 is a Si-added G having a carrier concentration of 10 ¹⁶ cm ^-3.
aInAsP (thickness 0.1 μm, band gap 1.3
μm). The p-type clad layer 15 is formed of Zn-added p-type InP (having a carrier concentration of 10 ¹⁸ cm ⁻³ ) (thickness: 0.5).
μm).

A layer above the n-type InP clad layer 11 has a mesa structure having a width of about 1.5 μm, and both sides of the mesa structure have a carrier concentration of 10 ¹⁸ cm ^{−3 and} a Zn-added p-type InP layer 1 is formed.
6 and a carrier concentration of 10 ¹⁸ cm ⁻³ , Si-added n-type In
It is filled with the P current blocking layer 17. Furthermore, on the upper part thereof, Zn-added p-type In having a carrier concentration of 10 ¹⁸ cm ⁻³
The P layer 18 and the Zn-added p-type Ga _0.47 In _0.53 As contact layer 19 having a carrier concentration of 5 × 10 ¹⁸ cm ⁻³
(Thickness 0.5 μm) is formed.

Then, an Au-Zn / Au electrode (p-side electrode) 21 is formed on the GaInAs contact layer 19 by vapor deposition, and Au-Ge / Ni is formed on the lower surface of the n-type InP substrate 10.
The / Au electrode (n-side electrode) 22 is formed by vapor deposition.

The semiconductor laser of this embodiment has a cavity length of 20.
The thickness was 0 μm, and a high-reflection coating having a reflectance of 70% on one end face and a reflectance of 90% on the other end face was applied by a multilayer film of Si and SiO ₂ .

The oscillation wavelength of the semiconductor laser of this embodiment is 1.
At 56 μm, the threshold current was 3 mA, and the temperature variation of the slope efficiency η was η (75 ° C.) / Η (25 ° C.) to 0.7, which was a large value for a laser device having such a low threshold current. . In an element having a similar structure in which Si was not added to the active layer, η (75 ° C.) / Η (25 ° C.) to 0.6
Became.

The active layer 13 of the semiconductor laser of this embodiment was formed by the metal organic chemical vapor deposition method. At that time, Si was added with SiH ₄ . Crystal growth temperature is 620-6
Performed at 90 ° C. Ga _0.35 In _0.65 As well layer 13
As for b, the thickness of the crystal is extremely thin, so Si in the film
Is difficult to measure. On the other hand, SiH ₄ is incorporated into InAs, and the efficiency is G at 620 ° C.
The incorporation efficiency into a _0.47 In _0.53 As was about 1.5 orders of magnitude lower, and the incorporation efficiency into Ga _0.47 In _0.53 As was about an order of magnitude lower than that into GaAs. This means that the incorporation of SiH ₄ changes exponentially with respect to the composition of Ga _x In _1-x As (0 ≦ x = 1) due to the surface reaction with the material. .

[0025] Therefore, conditions for supplying the SiH ₄ to the Ga _0.35 In _0.65 As well layer 13b is decided as an efficient captured the SiH ₄ is changing exponentially with GaInAs composition change. SiH ₄ as raw material
When Si is used, the efficiency of Si uptake has a stronger dependence on temperature as GaInAs having a higher InAs composition,
The activation energy at this time is Ga _x In _1-x As (0
It was proportional to the solid phase composition of ≦ x = 1). Therefore, taking into account the temperature dependence of the Si incorporation efficiency into InAs, the Si incorporation efficiency into Ga _0.47 In _0.53 As, and the Si incorporation efficiency relative to the material composition, Ga _0.35 I
n _0.65 As carrier concentration in the well layer 13b is 5 × 1
The supply conditions of SiH ₄ were determined so as to be 0 ¹⁶ cm ⁻³ .

Here, a desirable range of Si concentration in the active layer 13 will be described. In the semiconductor laser of the present example, when the n-type carrier concentration of the Ga _0.35 In _0.05 As well layer 13b was lower than 1 × 10 ¹⁶ cm ^-3 , the threshold current sharply increased from about 3 mA to 6 mA. on the other hand,
When the carrier concentration of the Ga _0.35 In _0.65 As well layer 13b was made higher than approximately 5 × 10 ¹⁷ cm ^-3 , the threshold value increased again.

FIG. 2 shows the carrier concentration dependence of the threshold current. The threshold current increased when the carrier concentration was lowered because the Si concentration in the Ga _0.35 In _0.65 As well layer 13b was lowered, so that the Zn concentration in the low concentration region in the first stage of the two-step diffusion of Zn and the Si concentration It is presumed that the concentrations became substantially equal to or higher, and the diffusion of Zn rapidly increased.

On the other hand, the reason why the threshold current increased when the carrier concentration was increased is considered to be as follows. In order for the laser to oscillate, the carrier concentration injected from the outside is sufficiently higher than the carrier concentration in the active layer due to the impurities in the active layer, and the population inversion of carriers must be formed. However, the impurity concentration in the well layer is about 5 × 10 ¹⁷
If it is cm ⁻³ or more, the difference from the carrier concentration injected from the outside during normal laser oscillation becomes small. Therefore, it is presumed that the concentration of injected carriers required to form the population inversion increased as the concentration of impurities in the well layer increased.

Based on these results, in the semiconductor laser of the present invention, the Si concentration in the strained quantum well layer is 1 × 1.
It was set to be between 0 ¹⁶ cm ^{-3 and} 5 × 10 ¹⁷ cm ^-3 .
As described above, according to the present embodiment, GaInA whose composition is easily controlled is formed in the well layer 13b of the active layer 13 having the strained quantum well structure.
By using s, the oscillation wavelength is extremely stable even if a strained quantum well structure whose composition is difficult to confirm is used.
It was possible to control to 6 ± 0.01 μm. In a quantum well laser having a similar structure, the well layer of the active layer has a quaternary mixed crystal G
The variation from wafer to wafer could be suppressed to about 60% as compared with the case of using aInAsP.

Moreover, Si is positively added to the active layer 13 so that the Si concentration is 1 × 10 ¹⁶ cm ^{−3 to} 5 × 10 ¹⁷ cm ^−3.
Therefore, the p-type impurity (Z
The diffusion of n) can be suppressed, and the accumulation of p-type impurities and the generation of deep levels in the strained quantum well structure can be suppressed. Therefore, the temperature dependence of the device characteristics can be reduced together with the reduction of the threshold value, and its usefulness is tremendous.

FIG. 3 is a sectional view showing the device structure of a semiconductor laser according to the second embodiment of the present invention. In the semiconductor laser of this embodiment, the carrier concentration is 4 × 10 ¹⁸ cm
^{-3 on} the Zn-doped p-type InP substrate 30, the p-type cladding layer 31, the light guide layer 32, the active layer 33, and the light guide layer 3
The 4 and n-type cladding layers 35 are grown and formed in the above order.

The p-type cladding layer 31 has a carrier concentration of 10
^It is p-type InP (thickness: 1.5 μm) with addition of ¹⁸ cm ⁻³ Zn. The optical guide layer 32 has a carrier concentration of 5 × 10 ¹⁷ cm
^-3 is GaInAsP with Si added (thickness 0.2 μm, band gap 1.13 μm). The active layer 33 is a Si-added GaInAsP barrier layer 33a (thickness: 6 nm, band gap: 1.13 μm, carrier concentration: 10 ¹⁷ cm ⁻³ ).
5 layers) and Si-added Ga having a carrier concentration of 10 ¹⁷ cm ^-3
It has a strained quantum well structure in which InAsP well layers 33b (thickness 7 nm, band gap 1.4 μm, lattice mismatch degree 0.6%, 6 layers) are alternately repeated. The light guide layer 34 is Si-added GaInAsP (bandgap 1.13 μm) with a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ . The n-type cladding layer 35 has a carrier concentration of 5 × 1.
It is n-type InP added with Si of ¹⁸ cm ^-3 .

The upper layer of the p-type InP clad layer 31 has a mesa structure with a width of about 1.5 μm, and the Zn-doped p-InP layer 3 having a carrier concentration of 10 ¹⁸ cm ^-3 is formed on both sides thereof.
6a, n-type In with Si added and carrier concentration of 10 ¹⁸ cm ^-3
A P current blocking layer 37 and a Zn-doped p-type InP layer 36b having a carrier concentration of 10 ¹⁸ cm ⁻³ are embedded. Further thereon, the carrier concentration 10 ¹⁸ cm n-type InP layer 38 of Si addition of ^-3 and the carrier concentration of 5 × 10 ¹⁸ cm ^-3, the Si added n-type thickness 0.5μm Ga _0.47 In _0.53 As
The contact layer 39 is formed.

Then, an Au-Ge / Ni / Au electrode (n-side electrode) 41 is formed by vapor deposition on the GaInAs contact layer 39, and Au-Zn is formed on the back surface of the p-type InP substrate 30.
The / Au electrode (p-side electrode) 42 is formed by vapor deposition.

The semiconductor laser of this embodiment has a cavity length of 20.
The thickness was 0 μm, and a high-reflection coating having a reflectance of 70% on one end face and a reflectance of 90% on the other end face was applied by a multilayer film of Si and SiO ₂ .

The oscillation wavelength of the semiconductor laser of this embodiment is 1.
At 3 μm, the threshold current was 2.3 mA, and the temperature variation of the slope efficiency η was η (75 ° C.) / Η (25 ° C.) ˜0.8, which was formed on the same p substrate as the laser formed on the n substrate. It showed excellent characteristics as a laser device with such a low threshold current. As an element having a similar structure in which Si is not added to the active layer, a threshold current η (75 ° C.) / Η (25 ° C.)
It became 0.7. This is because the carrier concentration in the light guide layer 32 is relatively high at 5 × 10 ¹⁷ cm ⁻³ , so that the diffusion of Zn from the substrate 30 added at a high concentration can be greatly reduced in this layer, and the active layer This is because it was possible to prevent the accumulation of Zn in the quantum well structure of No. 33. here,
When the carrier concentration in the light guide layer 32 was set to a high concentration of 5 × 10 ¹⁸ cm ⁻³ or more, the life of the device was drastically reduced.

The present invention is not limited to the above embodiments. In the embodiment, Si is added to the light guide layer, the well layer having the quantum well structure, and the barrier layer. However, even if only a part of Si is added, the corresponding effect can be obtained. Further, although Zn is used as the p-type impurity in the examples, the present invention exhibits the same effect as that of Zn when Cd, Mg, Be, etc. are used as the p-type impurity.

Although the quantum well structures described in the embodiments are compression strained GaInAs or GaInAsP quantum wells, they may be strained or tensile strained quantum well structures. Further, InAsP can be applied to an active layer and the like. Further, in the embodiments, the description has been made by taking the ordinary embedded Fabry-Perot laser as an example, but the invention can be applied to a laser having a mesa structure or a ridge wave structure, a DFB laser, or a surface emitting laser. In addition, various modifications can be made without departing from the scope of the present invention.

[0039]

As described above in detail, according to the present invention, Si is positively added to the active layer of the quantum well structure so that the concentration of Si as an impurity is 1 × 10 ¹⁶ cm ^{−3 to} 5 ×. 10 ¹⁷ c
By setting m ⁻³ , it is possible to suppress diffusion of p-type impurities (for example, Zn) in the active layer, and suppress accumulation of p-type impurities and generation of deep level in the quantum well structure. Become. Therefore, it is possible to realize a semiconductor laser device having a low threshold value and a small temperature dependence of element characteristics by using a strained quantum well structure of GaInAs whose wavelength can be easily controlled.

Further, this effect can be applied to a high-power semiconductor laser, and the improvement of device characteristics can be realized. Furthermore, when a GaInAs well layer is used, the well layer is G
It is an aInAs mixed crystal, and particularly when the metal organic chemical vapor deposition method is used, the composition can be easily determined and the oscillation wavelength can be easily determined. In particular, the effect of the present invention is great in an embedded type 1.5 μm band semiconductor laser.

[Brief description of drawings]

FIG. 1 is a sectional view showing an element structure of a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the carrier concentration dependence of the threshold current in the first embodiment.

FIG. 3 is a sectional view showing a device structure of a semiconductor laser according to a second embodiment of the present invention.

[Explanation of symbols]

10 ... n-InP substrate 11 ... n-In
P-clad layer 12 ... n-GaInAsP light guide layer 13 ... Quantum well active layer 14 ... GaInAsP light guide layer 15 ... p-In
P cladding layer 16 ... p-InP layer 17 ... n-In
P current blocking layer 18 ... p-InP layer 19 ... p-Ga
InAs contact layer 21 ... Au-Zn / Au electrode (p-side electrode) 22 ... Au-Ge / Ni
/ Au electrode (n-side electrode) 30 ... p-InP substrate 31 ... p-In
P cladding layer 32 ... GaInAsP light guide layer 33 ... Quantum well active layer 34 ... GaInAsP light guide layer 35 ... n-In
P clad layer 36a, 36b ... p-InP layer 37 ... n-In
P current blocking layer 38 ... n-InP layer 39 ... n-Ga
InAs contact layer 41 ... Au-Ge / Ni / Au electrode (n-side electrode) 42 ... Au-Zn / Au
Electrode (p-side electrode)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Onomura No. 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research and Development Center

Claims (1)

[Claims] 1. A semiconductor laser device in which an active layer having a strained quantum well structure of GaInAs is sandwiched between p-type and n-type cladding layers, the active layer being formed by a vapor phase epitaxy method, and The concentration of Si as an impurity is set to 1 × 10 ¹⁶ cm ^{−3 to} 5 × 10 ¹⁷ cm ⁻³ in at least a part of the active layer or the optical guide layer provided between the active layer and the p-type cladding layer. A semiconductor laser device characterized by the following.