JPH04199587A - Optical semiconductor device - Google Patents

Abstract

PURPOSE:To prevent the penetration of impurities into an active layer by a method wherein the impurity contained at the highest concentration in the fourth semiconductor layer is the IV group element, and the impurity contained at the highest concentration in the semiconductor layer opposite to the second semiconductor layer with respect to the fourth semiconductor layer the II group element. CONSTITUTION:To suppress the diffusion of the II group element which is a p-type impurity source of high diffusion coefficient, a region doped with the IV group element which is an n-type impurity source is formed between an active layer 13 and a p-type region 17 to serve as an impurity diffusion suppressing layer 14. At this time, the highest concentration of the IV group element in the diffusion suppressing layer 14 is made higher than that of the II group element in the p-type region 17. That is, it is utilized that when p-type, n-type, and hetero-type impurities are present at the same time, interaction between the impurities reduces diffusion of impurities to make an impurity of high diffusion coefficient have a diffusion profile as sharp as an impurity of small diffusion coefficient. This can suppress the diffusion of the p-type impurity into the active layer 13.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a semiconductor laser and a semiconductor diode.

Or related to optical semiconductor devices such as absorption type light modulation devices,
In particular, it relates to an optical semiconductor element having a double heterojunction in which a light emitting region is surrounded by a semiconductor layer having a wider forbidden band width than the light emitting region.

(Prior art) In optical semiconductor devices such as semiconductor lasers, semiconductor diodes, or absorption type optical modulators having a double heterojunction, both sides of an active layer are formed with semiconductor layers of different conductivity types. . However, due to the thermal history of crystal growth or the process that occurs after crystal growth, interdiffusion of p-type and n-type impurities occurs, causing the p-n junction to become far away from the heterojunction interface (hereinafter referred to as a remote junction). ) There was a problem that the current confinement efficiency decreased. As a means to overcome this problem, the impurity concentration of the P-type region and the n-type region can be lowered near the active layer, or an undoped spacer layer can be formed between the active layer and the P-type region or the n-type region. Attempts have been made to control the impurity and carrier concentration profiles by intercalation.

However, since this method uses the diffusion profile of impurities, it is difficult to control the carrier concentration in a low concentration region, and the reproducibility is also low. Therefore, attempts have been made to intentionally add impurities into the active layer. However, when the amount of impurities added to the active layer is small, there is a problem in that the carrier concentration in the active layer changes due to diffusion of impurities from outside the heterojunction. On the other hand, if impurities are added at a high concentration into the active region, the diffusion of impurities from the outside of the heterojunction can be suppressed, but the crystallinity of the active layer will deteriorate, the luminous efficiency will decrease, and the characteristics as an optical semiconductor device will be affected. There was a problem that it deteriorated.

(Problems to be Solved by the Invention) As described above, in the conventional double heterojunction type optical semiconductor device, the heterojunction position and the pn junction position are far apart. Alternatively, the carrier concentration in the active layer cannot be controlled. Alternatively, because the carrier concentration in the active layer is too high, there is a problem that the characteristics as an optical semiconductor device deteriorate. The present invention has been made in consideration of the above circumstances, and its purpose is to prevent impurities from penetrating into the active layer by suppressing the diffusion of impurities, and to further reduce the impurity concentration in the active layer. The goal is to control with high precision. Since an arbitrary carrier concentration profile can be formed in the active layer while suppressing a decrease in luminous efficiency due to the addition of high-concentration impurities, a high-performance optical semiconductor device can be provided.

[Structure of the invention]

(Means for Solving the Problems) The gist of the present invention is to provide a thin film-like region doped with impurities with a small diffusion coefficient around an active layer in an optical semiconductor element, and to diffuse impurities with a large diffusion coefficient. By adding an impurity having a large diffusion coefficient and an electrically different type of impurity to act as a suppression layer, a diffusion suppression layer that is more efficient than a conventional undoped spacer layer can be formed.

In particular, in the optical semiconductor device of the present invention formed of a ■-■ group compound semiconductor, in order to suppress the diffusion of the group ■ element, which is a p-type impurity source with a large diffusion coefficient, A region doped with group elements is formed between the active layer and the p-type region to serve as an impurity diffusion suppressing layer. At this time, the maximum concentration of the group Ⅰ element in the diffusion suppressing layer needs to be higher than the concentration of the group Ⅰ element in the p-type region. In particular, in the optical semiconductor device of the present invention formed on an InP substrate, when Si is used as the group Ⅰ element, the diffusion coefficient is small, so the steep p-
An n-junction is obtained. At this time, in order to suppress the diffusion of Si itself, the Si concentration needs to be 2 x 10''rx-'' or less.

(Function) In the present invention, when impurities of different conductivity types, such as p-type and n-type, exist at the same time, the interaction between the impurities reduces the diffusion of the impurities, so that the impurity with a large diffusion coefficient changes from the impurity with a small diffusion coefficient. The diffusion of impurities into the active layer of an optical semiconductor element is suppressed by utilizing the fact that it has a diffusion profile as steep as that of impurities. ■-p in group V compound semiconductors
When a Group Ⅰ element is used as a −-type impurity, diffusion is intense and it is difficult to control the carrier concentration profile. At this time, if a group III element is used as an n-type impurity and an n-type thin film is provided as an impurity diffusion suppressing layer at the boundary between the active layer and the p-type region, the p-type impurity can be diffused into the active layer. can be suppressed. At this time, the n-type impurity concentration in the diffusion suppressing layer needs to exceed the p-type impurity concentration. When a diffusion suppressing layer doped with n-type impurities at a high concentration is provided in this manner, the diffusion profile of the impurity is determined by the diffusion profile of the n-type impurity. Moreover, when Si is used as the n-type impurity, the Si diffusion coefficient is extremely small.
Diffusion of impurities can be effectively ignored. By suppressing the diffusion of p-type impurities in this way, it becomes possible to ignore the intrusion of impurities into the active layer from the outside.
It becomes possible to freely control the amount of impurities added even at low concentrations in the active layer, allowing freedom in carrier concentration design.

Therefore, it becomes possible to realize an optical semiconductor device with excellent device characteristics. If the diffusion suppressing layer is formed outside the active layer region, in a strict sense, the positions of the heterojunction interface and the pn junction interface will be shifted, resulting in a moat junction. However, in the optical semiconductor device of the present invention, the relationship between the positional deviation between the heterojunction interface and the pn junction interface can be arbitrarily controlled 8 with an accuracy of 50 Å or less. The misalignment between the Peter junction surface and the p-n junction interface is 10
If it is less than 00 Å, the remote junction will not be a problem in practice.

In order to increase the luminous efficiency of an optical semiconductor element, it is necessary to increase the potential barrier of the p-n junction, and the higher the concentration of both the p-type impurity and the n-type impurity, the better. When InP is used in the p-type region of a (1-2) group compound semiconductor, when the p-type impurity concentration exceeds 1.2 to 1.5XIO''(!1-'), the diffusion coefficient of the impurity increases rapidly. For this reason, it is desirable that the Si concentration in the diffusion suppressing layer is 1.5 x 10''Ql-' or more.On the other hand, according to the research of the inventors, InP and GayIn, which is approximately lattice-matched to InP, -
It has been found that in xAsyPl -y (0≦X≦1.0≦y≦1), when the Si concentration exceeds 2 x 101 scsi-'', the morphology of the crystal deteriorates rapidly. Focusing on this, for an optical semiconductor element formed on an InP substrate, the Si concentration in the diffusion suppressing layer is set to 1.5 x 10''-3 to 2 x 101''1''3. In this case, it is possible to prevent impurities from entering the remote junction and the active layer while maintaining good crystallinity in the diffusion suppressing layer, allowing freedom in designing the carrier concentration in the active layer and achieving excellent device characteristics. It becomes possible to realize optical semiconductor devices.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a sectional view showing a schematic structure of a semiconductor laser device according to a first embodiment of the present invention. In the figure, 11 is a (001) substrate of Sn-doped n-type InP (n = 2 An n-type InP cladding layer 12 (n=2XIO"am-3) is formed, and further on the cladding layer 12, a layer of 1.55. The thickness of the composition that allows the band to emit light is 0.1. A GaInAsP active layer 13 was formed. Zn was uniformly added to this active layer 13 in an amount of I x 1017 dll-'. A GaInAsP diffusion suppressing layer 14 having a thickness of 0.1- and a composition capable of emitting light in the 1.1-band is formed thereon, also serving as a light guide layer. A diffraction grating is formed on the diffusion suppressing layer 14. The diffusion suppressing layer 14 contains 6 to 20 x 10 Si.
The active layer 13, the diffusion suppressing layer 14, and the cladding layer 12 form a mesa stripe with a width of 1 to 1.5p. On both sides of the mesa, there is a Fe-doped high-resistance InP buried layer 15 and a Si-doped current blocking layer 16.
(n = 6 x 10"am-"). The top of the mesa and the top of the buried layer have a thickness of 2.
0. Zn-added P-type InP cladding layer 17 (p =
5 XIO” (!1-3), Zn-added GaIn
An AsP contact layer 18 is formed. Au/AuGe is used as the n-type power supply 19 on the lower surface of the substrate 11, and Au-AuGe is used as the p-type electrode 110 on the contact layer 18.
Zn is provided.

In order to reduce the element capacitance, this element has a mesa structure in which the entire element above the n-type Inp cladding layer 12 has a mesa width of 8 to 10 degrees.

The threshold current of the semiconductor laser device of this example is approximately 10++
It was +A. The threshold current was much lower than about 30 mA when Si was not added to the GaInAsP diffusion suppressing layer 14. This is because diffusion of Zn from the p-InP cladding layer 17 to the active layer 13 could be prevented.

In addition, the Zn concentration of the p-InP cladding layer 17 is I
The threshold current was lower than the threshold current of about 20 A when no impurity was added to the diffusion suppressing layer 14 at 0"cm-". This is because Si is added to the diffusion suppressing layer 14, so p
- The Zn concentration of the InP cladding layer 17 is 5 x 10"
This is because the semiconductor laser device according to the embodiment of the present invention has a cutoff frequency of about 15 GHz under the condition of an output of 10 mW. The cutoff frequency of a semiconductor laser device in which impurities were not added to the active layer 13 was approximately 10 GHz under the condition of an output of 10 W. Furthermore, the yield was extremely low. By adding type impurities, the lifetime of carriers can be shortened and the cut-off frequency can be improved.Also, the active layer 13
The yield was improved because the impurity concentration inside was controlled.

FIG. 2 is a sectional view showing a schematic structure of a semiconductor laser device according to another embodiment of the present invention. In the figure, 21 is Sn-doped n-type InP (n = 2 x 10"am-'
) (001) substrate, and a diffraction grating including a λ/4 shift is formed on this InP substrate 21. A GaInAsP light guide layer 22 is formed on the diffraction grating, and on top of it is an MQ layer in which a 60-thick GaIn^3 quantum well and a 60-thick GaInAsP barrier are laminated in 5 layers and 4 layers, respectively.
A W active layer 23 is formed. In the Ga1nAsP barrier there are 5 X 10"cs-2~I X 1017>-
” of Zn was added. On the MQW active layer 23, Ga was added.
InAsP upper light guide layer 24,300-700 layers are stacked. Furthermore, on top of that, the Si concentration is 6 x 1
An n-type InP diffusion suppressing layer 25 having a thickness of 0" cm and a thickness of 300 cm is formed. On top of that, Zn concentration 1.5~5
A p-type InP cladding layer 26 of X1011114 is laminated. InP substrate 21, GaInAsP optical guide layer 22, MQW active layer 23. GaInAsP upper light guide layer 24, n-type InP diffusion suppression layer 25, p-type I
After the nP cladding layer 26 is etched into a mesa shape,
p-type InP buried layer 27, n-type InP current blocking layer 2
8. It is buried by a p-type InP buried layer 29. Furthermore, in the mesa part and the upper part of the buried layer, p-type InP
Cladding layer 210, P-type GaInAs contact layer 2
11 is formed on the upper surface of the s InP substrate 21, n
Au/AuGe is deposited as a - type electrode 212, and a P- type electrode 213 is deposited on the contact layer 211.
Au/AuZn is deposited. Note that this device has a mesa structure with a mesa width of 8 to 10 − for the entire device above the InP substrate 21 to reduce device capacitance, and the laser length is 1.2 g.
An anti-reflection film was laminated on the separated rear end face.

In the semiconductor laser device of this example, the width of the oscillation spectrum was 120 kHz at an output of 5 IIW. This was a significant improvement compared to 220 kHz when the diffusion suppressing layer 25 was not included. This is because the impurity concentration in the GaInAsP barrier of the MQW active layer 23 is controlled to be low and uniform, so that the distribution of carriers in the MQW active layer 23 is controlled to be uniform.

This semiconductor laser device was capable of oscillation up to 140° C., which was superior to 120° C. in the case without the diffusion suppressing layer 25. This is because the p-n junction position is between the MQW active layer 23 and the p-type region and coincides with the boundary between the p-type InP cladding layer 26, so the overflow of electrons from the MQW active layer 23 is suppressed. It's for a reason.

Note that the present invention is not limited to the embodiments described above.For example, in the embodiments described above, Si is used as the group element.
was added, but the group Ⅰ element may be Sn, Ge, p-
Although Zn was used as the type impurity, Cd or Mg may also be used. In addition, in the first embodiment, the light guide layer 14
Although Si is added to the p-type 1nP cladding layer 17, group II elements may also be added to several hundred angstroms of the active layer side of the p-type 1nP cladding layer 17 to form a diffusion suppressing layer. In addition, in the above-mentioned embodiments, GaInAs(P)/InP system was used as an example, but Ga(
AQ) InP/GaAs system, 1InAs/GaInA
Application to s/InP system and 1GaAs/GaAs system is also possible.

Particularly when applied to an AQGaAslGaAS system including a quantum well structure, it is possible to prevent disturbance of the quantum well structure due to impurity diffusion. In the above-described embodiments, a semiconductor laser device was described, but it is also possible to apply the present invention to a light emitting diode, an absorption type light changing device, etc. In addition, various modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to prevent mismatch between the pn junction position and the heterojunction position due to diffusion of impurities, or to prevent impurities from penetrating into the active layer. Therefore, the impurity concentration in the active layer, as well as the carrier concentration and potential distribution, can be freely designed, and an optical semiconductor device with good characteristics can be realized. In particular, when used in a semiconductor laser device, the improvement of high-speed modulation characteristics leads to high purity of the single oscillation spectrum, and its usefulness is enormous.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a schematic structure of a semiconductor laser device according to a first embodiment of the present invention, and FIG. 2 is a sectional view showing a schematic structure of a semiconductor laser device according to a second embodiment of the present invention. be. 1l-n-type InP substrate, 12...n-type InP cladding layer, 13=-GaInAsP active layer, 14--GaInAsP diffusion suppression layer, 15...high resistance InP buried layer, 16...current Blocking layer, 17...p-type InP cladding layer, 18... GaInAs contact layer. 19...n-type electrode 110...P-type electrode 2l-n-type InP substrate, 22-GaInA5P light guide layer. 23...MQW active layer, 24...GaInAsP upper light guide layer, 25...
n-type InP diffusion suppression layer, 26...p-type InP cladding layer, 27...p-type InP buried layer, 28...n-type InP current blocking layer. 29...P-type InP buried layer. 210...p-type InP cladding layer, 211, -p-
type GaInAs contact layer, 212...n-type electrode, 213...p-type electrode. Agent Patent Attorney Noriyuki ChikaFigure 1Figure 2

Claims (1)

[Scope of Claims] (1) A semiconductor layer of a first conductivity type on a III-V compound semiconductor substrate, and a second semiconductor layer having a narrower forbidden band width than the first semiconductor layer.
and a third semiconductor layer of a second conductivity type having a wider forbidden band width than the second semiconductor layer, and a semiconductor layer of the first semiconductor layer and the second semiconductor layer. An optical semiconductor device in which a fourth semiconductor layer of a second conductivity type is inserted between the second semiconductor layer or a fourth semiconductor layer of the first conductivity type between the second semiconductor layer and the third semiconductor layer. In the fourth semiconductor layer, the impurity contained in the highest concentration is a group IV element, and the impurity contained in the highest concentration in the semiconductor layer on the opposite side of the fourth semiconductor layer from the second semiconductor layer is An optical semiconductor device characterized in that impurities contained in the element are Group II elements. (2) The concentration of the group IV element contained in the fourth semiconductor layer is higher than that of the group IV element contained in the semiconductor layer on the opposite side of the second semiconductor layer with respect to the fourth semiconductor layer.
2. The optical semiconductor device according to claim 1, wherein the concentration is higher than the group I element concentration. (3) The semiconductor substrate is InP, the group IV element contained in the fourth semiconductor layer is Si, and the concentration of Si is 1.
5x10^1^8cm^-^3~2x10^1^9cm
3. The optical semiconductor device according to claim 2, wherein the optical semiconductor element is ^-^3.