JP2000106471A - Surface emitting laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface-emitting laser equipped with a photodetector that is used for monitoring its output and easily formed. SOLUTION: A light emitting region 110 is formed of a part of a layered structure composed of an N-type DBR reflecting mirror 13, a P-type DBR reflecting mirror 15, and an active layer 14 sandwiched in between them. The light emitting region 110 is surrounded by a high-resistivity region 18. A monitoring photodiode 120 of the same layered structure with the light emitting region 110 is formed around the high-resistivity region 18. An ohmic electrode 19 is formed to serve as an upper electrode of the light emitting region 110, an ohmic electrode 19 is provided to serve as an upper electrode of the monitoring photodiode 120, and an ohmic electrode 23 is formed to serve as a common lower electrode of the light emitting region 110 and the monitoring photodiode 120.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting laser which emits light in a direction perpendicular to the surface of a substrate, and more particularly, to a method for easily producing a photodetector for monitoring the output of the laser. .

[0002]

2. Description of the Related Art Surface-emitting lasers having a wavelength of 0.85 μm have been actively developed in recent years for application to parallel interconnections and the like. When applied to a system having a high light intensity, the intensity of the light emitted from the laser must be kept constant. Therefore, a photodiode for monitoring the light intensity is required.

Conventionally, in order to monitor the output of a laser,
It is common to split a part of the laser beam with a translucent mirror and put it into a monitor photodiode, but this has the disadvantage of increasing the assembly cost.

FIG. 4 is a view showing another conventional technique, in which an n-type GaAs layer 2 is laminated on an n-type GaAs substrate 1, and a non-doped GaAs light absorbing layer 3 and a p-type GaAs layer 3 are further formed thereon. N-type GaAs layers 4
aAs layer 2, GaAs light absorbing layer 3, and p-type GaAs layer 4
This constitutes a pin-type photodiode.

Then, a surface emitting laser is continuously formed on the p-type GaAs layer 4. Specifically, p-type GaAs
On the s layer 4, a p-type distributed feedback mirror (DBR (Distrib
utedBragg Reflector) 5, an active layer 6, and an n-type DBR reflector 7 are stacked in this order, and an n-type DBR
AuGeNi ohmic electrodes 8 and 9 are provided on the upper surface of the reflecting mirror 7 and the lower surface of the n-type GaAs substrate 1, respectively. On the upper surface of the p-type GaAs layer 4, AuGeN
An i ohmic electrode 10 is provided. And p-type D
By making the reflectivity of the n-type DBR reflector 7 smaller than the reflectivity of the BR reflector 5, the laser output is mainly emitted from the upper n-type DBR mirror 7 side. Is also emitted from the lower p-type DBR reflecting mirror 5 side, and the laser light emitted from the p-type DBR reflecting mirror 5 side is absorbed by the GaAs light absorbing layer 3 and becomes ohmic electrodes 9 and 10. Photocurrent flows between them. Therefore, the laser output can be monitored by detecting the photocurrent.

[0006]

With the structure as shown in FIG. 4, it is possible to form a monitor photodiode integrally with a surface emitting laser, but the photodiode is formed on the same substrate. And the light emitting region of the surface emitting laser must be continuously grown, so that the thickness of the epitaxial layer becomes about 10 μm, the load on crystal growth is large, the yield is reduced, and the element structure is complicated. Therefore, an increase in manufacturing cost cannot be avoided after all.

The present invention has been made in view of the problems to be solved by the conventional technology, and provides a surface emitting laser which can easily produce a photodetector for monitoring the output of the laser. It is intended to be.

[0008]

In order to achieve the above object, the invention according to claim 1 provides a light emitting region having a layer structure in which an active layer is sandwiched between p-type and n-type distributed feedback mirrors. In the surface emitting laser having, the light emitting region is surrounded by a high resistance region, around the high resistance region, having a monitoring photodiode of the same layer structure as the light emitting region,
The skirt of the light intensity distribution in the light emitting region reaches the light absorbing portion of the monitor photodiode.

In order to achieve the above object, the invention according to claim 2 has a light emitting region having a layer structure in which an active layer is sandwiched between p-type and n-type distributed feedback mirrors, In a surface emitting laser having a gain waveguide structure in which the refractive index of a region in contact with and surrounding the active layer of the light emitting region is the same as the refractive index of the active layer, the light emitting region is surrounded by a high resistance region, A monitor photodiode having the same layer structure as the light emitting region is provided around the region, and an upper electrode of the monitor photodiode and an upper electrode of the light emitting region are insulated from each other by the high resistance region, and the monitor photo diode is provided. The lower electrode of the diode and the lower electrode of the light emitting region are common, and the diameter of the active layer of the light emitting region is φ, the effective refractive index of the active layer of the light emitting region is n ₁ , and the high resistance region is Is the width of d The yield coefficient α, the oscillation wavelength of the laser λ
Where d <(φ ^1/2 λ ^1/4 ) / (πn ₁ α) ^1/4 -φ / 2.

In order to achieve the above object, the invention according to claim 3 has a light emitting region having a layer structure in which an active layer is sandwiched between p-type and n-type distributed feedback mirrors, In a surface emitting laser having a refractive index waveguide structure in which the refractive index of a region in contact with and surrounding the active layer of the light emitting region is smaller than the refractive index of the active layer, the light emitting region is surrounded by a high resistance region, A monitor photodiode having the same layer structure as that of the light emitting region, and an upper electrode of the monitor photodiode and an upper electrode of the light emitting region are insulated from each other by the high resistance region. And the lower electrode of the light emitting region is common, and the diameter of the active layer of the light emitting region is φ, the effective refractive index of the active layer of the light emitting region is n ₁ , and the activity of the light emitting region is Touching layers N ₂ the refractive index of the region surrounding it, the width of the high resistance region d, the absorption coefficient of light alpha, when the oscillation wavelength of the laser was set to ^{λ, d <{(4π 2} / λ 2) (1 / n ₂ ² −1 / n ₁ ² ) −23.1 / (n
₁ ² φ ² )｝ ^1/2 −φ / 2.

Here, according to the present invention, a monitor photodiode is provided around a light emitting area of the surface emitting laser,
Both are electrically separated by a high resistance region,
The monitoring photodiode has the same layer structure as the light emitting region. On the other hand, by surrounding the active layer with a material having a small refractive index, the light distribution of the laser is confined in the active layer, and the light intensity distribution has a transverse mode. But,
The tail of the light intensity distribution in the transverse mode also extends around the active layer, and the length of the spread depends on the relationship between the refractive index of the active layer and the refractive index around the active layer. Therefore, the positional relationship between the two is selected so that the bottom of the light intensity distribution of the lateral mode of the surface emitting laser reaches the light absorption part of the photodiode. For example, by sufficiently reducing the distance between the two, the laser oscillation A photocurrent proportional to the light flows through the monitor photodiode.

More specifically, an electrode is provided so as to surround the emitting portion of the surface emitting laser, and a reverse bias is applied to the electrode so that the electrode functions as a monitoring photodiode. Then, a reverse bias is applied between the active layer and the monitor photodiode, the non-doped active layer is depleted, and a pair of electron holes is generated by the lateral mode skirt extending to this point, and a photocurrent flows. Since the magnitude of the photocurrent is substantially proportional to the intensity of the laser oscillation light, the intensity of the oscillation light can be monitored.

According to the structure of the present invention, the surface emitting laser and the monitoring photodiode are integrated on the same substrate, and a new crystal is formed only for forming the monitoring photodiode. No layer structure is required.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are views showing a configuration of a surface emitting laser 100 according to an embodiment of the present invention. FIG. 1 is a plan view, and FIG. 2 is an enlarged front sectional view.

That is, on the n-type GaAs substrate 11, n-type Ga
A buffer layer 12 made of an As layer is laminated, and an n-type DBR reflector 13 is further laminated thereon. n-type D
The BR reflector 13 is made of Si-doped n-type Al _0.9 Ga _0.1 A.
s layer (thickness 69 nm) and Si-doped n-type Al _0.15 Ga
37 pairs of _0.85 As layers (thickness: 62 nm) are alternately stacked. The optical length of each layer is １ ／ of the laser oscillation wavelength λ.

An active layer 14 is provided on the n-type DBR reflector 13.
Are laminated. The active layer 14 is made of non-doped Al
_{It is} composed of a non-doped GaAs (8 nm thick) quantum well layer sandwiched between _0.5 Ga _0.5 As (88 nm thick) spacer layers.

Then, a p-type DBR reflecting mirror 15 is laminated on the active layer 14, whereby the active layer 14
A layer structure sandwiched between the BR reflector 13 and the p-type DBR reflector 15 is formed.

The p-type DBR reflecting mirror 15 is a C-doped p-type A
1 _0.9 Ga _0.1 As layer (thickness 69 nm) and C-doped p-type Al _0.15 Ga _0.85 As layer (thickness 62 nm)
Three pairs are stacked.

An arbitrary position on the surface of the p-type DBR reflecting mirror 15 is an emission surface 16 for emitting a laser beam. A circular ohmic electrode 17 made of AuZnNi surrounds the emission surface 16. Is provided.

On the other hand, the emission surface 16 and the ohmic electrode 17
P-type DBR reflector 15, active layer 14, and n-type DB
A cylindrical high resistance region 18 is formed so as to surround a part of the R reflecting mirror 13. The high-resistance region 18 is for electrically separating a light emitting region 110 formed inside the light emitting region 110 from a monitor photodiode to be described later formed outside the light emitting region 110. In this region, protons are injected into appropriate places of the p-type DBR reflector 15, the active layer 14, and the n-type DBR reflector 13 to narrow the injection current into the high-resistance region.

The diameter φ of the light emitting region 110 is 10 μm.
m, and the width d of the high resistance region 18 is 2.5 μm. A C-shaped ohmic electrode 19 made of AuZnNi is provided on the surface of the p-type DBR reflecting mirror 15 along the outer periphery of the high-resistance region 18. Therefore, between the ohmic electrode 17 and the ohmic electrode 19, the high resistance region 18
Insulated by Further, the p-type DBR reflecting mirror 15 under the ohmic electrode 19, the active layer 14, and the n-type D
A high resistance region 20 in which polyimide is buried in a cylindrical shape is formed so as to surround a part of the BR reflecting mirror 13, and a layer of a portion sandwiched between the high resistance region 20 and the high resistance region 18 is formed. Monitor photodiode 1 depending on the structure
20 are configured.

Then, on the surface of the p-type DBR reflecting mirror 15,
Substantially rectangular SiO ₂ films 21A and 2A are provided at two positions: a position facing the opening of the C-shaped ohmic electrode 19 and a position just opposite to the position with the emission surface 16 therebetween.
1B is provided. However, one SiO ₂ film 21
In A, a convex portion 21a that passes through the opening of the C-shaped ohmic electrode 19 and reaches the vicinity of the ohmic electrode 17 is formed.
Are formed.

On these SiO ₂ films 21A and 21B, bonding pads 22A and 22 made of a metal film are provided.
B, and one of the bonding pads 22A
Are electrically connected to the ohmic electrode 17 through the upper surface of the projection 21a, and the other bonding pad 22B is electrically connected to the ohmic electrode 19.

Further, on the lower surface of the n-type GaAs substrate 11, an ohmic electrode 23 made of AuGeNi is provided. Here, the ohmic electrode 17 corresponds to the light emitting region 1.
The upper electrode 10 and the ohmic electrode 19 are the upper electrodes of the monitoring photodiode 120, while the ohmic electrode 23 is the lower electrode common to both the light emitting region 110 and the monitoring photodiode 120.

When the surface emitting laser 100 is used, the ohmic electrode 17 serving as the upper electrode of the light emitting region 110 is replaced with the ohmic electrode 23 serving as the common lower electrode.
To the active layer 14 by applying a forward bias voltage that is positive with respect to
Is injected into the carrier to cause laser oscillation. At this time, since the high resistance region 18 is formed around the active layer 14, the current is confined, the refractive index is uniform in the horizontal direction, and the transverse mode of laser oscillation is formed by gain waveguide. That is,
Light is amplified by the gain in the region where the current is injected, but the light is attenuated by absorption around the region.

The radius of the mode based on the gain guiding is as follows: the diameter of the active layer 14 in the light emitting region 110 is φ;
When the effective refractive index of the active layer 14 is n ₁ , the light absorption coefficient is α, and the laser oscillation wavelength is λ, φ ^1/2 λ ^1/4 / (πn ₁ α) ^1/4 Becomes

Therefore, the width d of the high resistance region 18 which is the distance between the light emitting region 110 and the monitor photodiode 120 is set to be d <(φ ^1/2 λ ^1/4 ) / (πn ₁ α) ^{1 / If 4} −φ / 2, the skirt of the transverse mode reaches the light absorbing portion of the monitoring photodiode 120.

On the other hand, a reverse bias voltage which is negative with respect to the ohmic electrode 23 which is a common lower electrode is applied to the ohmic electrode 19 which is the upper electrode of the monitoring photodiode 120. Then, the active layer 14 in the monitoring photodiode 120 is depleted.
The active layer 14 of the monitoring photodiode 120 has a structure in which a GaAs quantum well layer having a large refractive index is sandwiched between spacer layers having a small refractive index. The electron-hole pairs absorbed by the layer and generated by the absorption are swept by the reverse bias electric field and contribute to the photocurrent.

Here, the oscillation wavelength λ is 0.85 μm, which is the oscillation wavelength of a GaAs surface emitting laser, and the refractive index n ₁ is AlG.
Assuming that the absorption coefficient α of the aAs spacer layer is 3.3 and the absorption coefficient α is 20 cm ⁻¹ , which is a typical value between the periphery of the spacer layer and the DBR layer, when φ = 10 μm, d <3 μm. Therefore,
By setting the width d to 3 μm or less, the surface emitting laser 1
The intensity of the oscillating light in the light emitting region 110 of 00 can be monitored by the output voltage of the monitoring photodiode 120. In this case, when the width d is larger than 3 μm, the monitoring photodiode 120 detects spontaneous emission light from the active layer 14 in the light emitting region 110. The spontaneous emission increases with the injection current below the laser oscillation threshold, but is constant above the threshold, so that the intensity of the laser oscillation cannot be monitored.

As described above, according to the present embodiment, the light emitting region 110 of the surface emitting laser 100 and the monitoring photodiode 120 can be formed on the common n-type GaAs substrate 11 with the same layer structure. Therefore, the monitoring photodiode 120 as a photodetector for monitoring the intensity of the laser beam can be easily formed in the surface emitting laser 100, and the manufacturing cost can be reduced.

In the above embodiment, the case where the present invention is applied to the surface emitting laser 100 having the gain waveguide structure has been described. However, in the present invention, the area around the active layer in the light emitting region is defined as the active layer. The present invention is also applicable to a surface emitting laser having a refractive index waveguide structure surrounded by materials having different refractive indexes. For example, in FIG. 2, the case where the refractive index of the high resistance region 18 is different from the refractive index of the active layer 14 of the light emitting region 110 is that another semiconductor is buried and grown in the portion where the high resistance region 18 is formed. This can be achieved by:

The radius of the transverse mode in the case of the refractive index waveguide structure is given by: ｛(4π ² / λ ² ) (1 / n ₂ ² −1) where n ₂ is the refractive index around the active layer in the light emitting region. ^{_{/ n 1 2) -23.1 / (}} n 1 2 φ 2)}
^1/2 (for example, "DGDeppe.THOh and DLHuffake
r, IEEE Photonics Technology Letters, Vol.9, p136.199
See 7. ). Accordingly, the width ^{d, d <{(4π 2} / λ 2) (1 / n 2 2 -1 / n 1 2) -23.1 / (n
_By setting ₁ ² φ ² )｝ ^1/2 −φ / 2, light in the oscillation mode can be detected, and in this case, the same effect as in the above embodiment can be obtained. FIG. 3 shows the refractive index difference Δn (=
n ₁ −n ₂ ) and the width d, the diameter φ = 3, 5, 1,
This is shown for each of 0 μm.

[0033]

As described above, according to the surface emitting laser according to the present invention, the light emitting region is surrounded by the high resistance region, and the monitor photo having the same layer structure as the light emitting region is surrounded around the high resistance region. The light emitting region of the surface emitting laser and the monitor photodiode are shared by a common substrate because the light emitting region has a diode and the bottom of the light intensity distribution in the light emitting region reaches the light absorbing portion of the monitor photodiode. The same layer structure can be formed on the upper surface, and the monitoring photodiode for monitoring the intensity of the laser beam can be easily built in the surface emitting laser, thereby reducing the manufacturing cost. is there.

In particular, according to the second or third aspect of the present invention, the bottom of the light intensity distribution in the light emitting region surely reaches the light absorbing portion of the monitor photodiode. .

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of an embodiment of the present invention.

FIG. 2 is an enlarged front sectional view.

FIG. 3 is a diagram showing a relationship between a refractive index difference Δn and a width d.

FIG. 4 is a front sectional view showing a conventional configuration.

[Explanation of symbols]

Reference Signs List 11 n-type GaAs substrate 12 buffer layer 13 n-type DBR reflector (distributed feedback mirror) 14 active layer 15 p-type DBR reflector (distributed feedback reflector) 16 emission surface 17 ohmic electrode (upper electrode of light emitting region) Reference Signs List 18 high-resistance region 19 ohmic electrode (upper electrode of monitor photodiode) 20 high-resistance region 21A SiO ₂ film 21B SiO ₂ film 21a convex portion 22A bonding pad 22B bonding pad 23 ohmic electrode (lower electrode of light-emitting region, monitor photo Lower electrode of diode) 100 surface emitting laser 110 light emitting region 120 monitor photodiode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kota Tateno 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Within Japan Telegraph and Telephone Corporation (72) Inventor Osamu Tadanaga 3-19, Nishi-Shinjuku, Shinjuku-ku, Tokyo 2 Nippon Telegraph and Telephone Corporation F-term (reference) 5F073 AB13 AB17 CA04

Claims (3)

[Claims] 1. A surface emitting laser having a light emitting region having a layer structure in which an active layer is sandwiched between p-type and n-type distributed feedback mirrors, wherein the light emitting region is surrounded by a high resistance region, and the high resistance A monitor photodiode having the same layer structure as the light emitting region is provided around the region, and the bottom of the light intensity distribution of the light emitting region reaches the light absorbing portion of the monitor photodiode. A surface emitting laser characterized by the above. 2. A light-emitting region having a layer structure in which an active layer is sandwiched between p-type and n-type distributed feedback mirrors, and a refractive index of a region in contact with and surrounding the active layer of the light-emitting region is In a surface emitting laser having a gain waveguide structure having the same refractive index as that of the active layer, the light emitting region is surrounded by a high resistance region, and a monitor photo having the same layer structure as the light emitting region is provided around the high resistance region. A diode having an upper electrode of the monitor photodiode and an upper electrode of the light emitting region which are insulated from each other by the high-resistance region; and a lower electrode of the monitor photodiode and a lower electrode of the light emitting region are common. The diameter of the active layer in the light emitting region is φ, the effective refractive index of the active layer in the light emitting region is n ₁ , the width of the high resistance region is d, the light absorption coefficient is α, and the laser oscillation wavelength Is λ, d <( A surface emitting laser satisfying φ ^1/2 λ ^1/4 ) / (πn ₁ α) ^1/4 -φ / 2. 3. A light emitting region having a layer structure in which an active layer is sandwiched between p-type and n-type distributed feedback mirrors, and a refractive index of a region in contact with and surrounding the active layer of the light emitting region is In a surface emitting laser having a refractive index waveguide structure smaller than the refractive index of the active layer, the light emitting region is surrounded by a high resistance region, and a monitoring photodiode having the same layer structure as the light emitting region around the high resistance region. The upper electrode of the monitor photodiode and the upper electrode of the light emitting region are insulated by the high resistance region, and the lower electrode of the monitor photodiode and the lower electrode of the light emitting region are common, The diameter of the active layer of the light emitting region is φ, the effective refractive index of the active layer of the light emitting region is n ₁ , the refractive index of the region in contact with and surrounding the active layer of the light emitting region is n ₂ , The width of the high resistance region is d The absorption coefficient of the light alpha, when the oscillation wavelength of the laser was set to ^{λ, d <{(4π 2} / λ 2) (1 / n 2 2 -1 / n 1 2) -23.1 / (n
₁ ² φ ² )｝ ^1/2 −φ / 2.