JPH09214045A - Semiconductor laser and its fabrication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent resistivity of an Fe doped InP buried layer from being lowered, and prevent impurity concentration of a p type InP layer by burying a mesa stripe including an active layer, and providing an Fe diffusion prevention layer between an Fe doped InP buried layer and the mesa stripe. SOLUTION: In this semiconductor laser, an Fe doped InP buried layer 7 is provided such that a mesa stripe including an active layer 3 is buried, and an FE diffusion prevention layer 6 is provided between the Fe doped InP buried layer 7 and the mesa stripe. The Fe diffision prevention layer 6 is an n type InP layer. Herein, after the mesa stripe including the active layer 3 is formed, the Fe diffusion prevention layer 6 is formed on an exposed surface of the mesa stripe, and then the Fe doped InP buried layer 7 is formed. The Fe diffusion prevention layer 6 is a semiconductor layer having vacant lattice points of 5.0×10<-3> cm 3 or more. Growing temperature of the Fe doped InP layer is higher than that of the Fe doped InP buried layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser and a manufacturing method thereof, and more particularly to a semiconductor laser having a Fe-doped high resistance buried layer used for optical communication and the like and a manufacturing method thereof.

[0002]

2. Description of the Related Art A conventional 1 μm band SI-BH (high resistance layer-buried heterojunction) type semiconductor laser, that is, a high resistance current confined buried structure semiconductor laser is made of InP and InGaAsP based materials on an InP substrate. After depositing the heterojunction structure described above, mesa etching was performed in a stripe shape, and the side portions of the mesa stripe were filled with a Fe-doped InP burying layer.

This conventional high resistance current confined buried structure semiconductor laser will be described with reference to FIG. See FIG. 6A. First, on the n-type InP substrate 11, n which also serves as a clad layer is formed.
Type InP buffer layer 12, InGaAsP active layer 13,
p-type InP clad layer 14 and p-type InGaAsP
After growing the contact layer 15, a SiO ₂ film is deposited on the entire surface and patterned to form a stripe-shaped SiO ₂ mask (not shown).

Then, using this SiO ₂ mask, p
Type InGaAsP contact layer 15 to n type InP substrate 11 are mesa-etched into stripes, and then high-resistance Fe-doped InP buried layer 1 is formed on the side of the mesa stripe.
9 is grown to form a current confinement structure, then a p-side electrode and an n-side electrode (both not shown) are formed, and then the device is divided to complete a high resistance current confinement buried structure semiconductor laser.

In such a high-resistance semiconductor laser having a current confinement buried structure, ideally, injected carriers do not flow in the high-resistance Fe-doped InP buried layer 19 but only in the active layer. Therefore, the current confinement efficiency is excellent, high-efficiency laser oscillation is possible with low threshold current, and high parasitic capacitance can be expected for high-speed modulation operation, making it a very important structure as a semiconductor laser for optical communication. Has become.

[0006]

However, such a high-resistance semiconductor laser having a current confinement buried structure is actually a Fe laser.
Due to thermal history in the regrowth process of the doped InP buried layer 19 and the electrode formation process, Fe diffusion occurs, and the Fe-doped InP buried layer 19 near the mesa stripe has a low resistance. There is a problem that leakage current flows.

See FIG. 6B. In the Fe-doped InP burying layer 19, Fe existing at the group III lattice point, that is, Fe ^-- _s (s: substitu)
is a hole (that is, h ⁺ ) existing in the vicinity.
Interstitial ions by coupling with interstitial ions, namely Fe ⁺ _i
(I: interstitial), and as a result, a vacancy point (that is, V ⁻ ) is generated. Fe ^- _s + h ⁺ ⇔ Fe ⁺ _i + V ^- Formula A

Since this Fe ⁺ _i diffuses with a very large diffusion coefficient, the Fe concentration near the side of the mesa stripe is reduced to form a low-concentration Fe-doped InP layer 34 having a low resistivity, and the inter-lattice gap is formed. Fe ⁺ _i diffused is p-type InP
When reaching the cladding layer 14, Zn ^- _s , which is an impurity ion in the p-type InP cladding layer 14, is knocked out from the lattice point by the reaction process of the following formula B, and as a result, the p-type In
The impurity concentration on the side portion of the P clad layer 14 decreases and the resistivity increases. Fe ⁺ _i + Zn ^- _s → Fe ^- _s + Zn ⁺ _i Formula B

As described above, in the vicinity of the mesa stripe, the resistivity of the Fe-doped InP buried layer 19 decreases and the resistivity of the side surface of the p-type InP clad layer 14 increases, so that the injected current is injected into the active layer side. Since it flows from the portion to the n-type InP buffer layer 12 through the low-concentration Fe-doped InP layer 34 having a low resistivity, this current becomes a leak current, and there is a problem that the current injection efficiency is significantly reduced.

Also in the case of a high resistance current confined buried structure semiconductor laser using a p-type InP substrate, Fe-doped In
The diffusion of Fe and the accompanying ejection of Zn occur between the P buried layer and the p-type InP buffer layer, which lowers the resistivity of the Fe-doped InP buried layer and the carrier concentration of the p-type InP buffer layer. However, there is a problem in that a current leak path is generated.

Therefore, the present invention is directed to Fe-doped InP.
It is intended to prevent the resistivity of the buried layer from being lowered and the impurity concentration of the p-type InP layer from being lowered.

[0012]

FIG. 1 is an explanatory view of the principle configuration of the present invention, and means for solving the problems in the present invention will be described with reference to FIG. See FIG. 1. (1) In the present invention, in the semiconductor laser, the Fe-doped InP buried layer 7 is provided so as to fill the mesa stripe including the active layer 3, and the Fe-doped InP buried layer 7 and the mesa stripe are arranged between the Fe-doped InP buried layer 7 and the mesa stripe. The Fe diffusion prevention layer 6 is provided.

By thus providing the Fe diffusion prevention layer 6, the diffusion of Fe from the Fe-doped InP buried layer 7 is suppressed, so that the resistivity of the Fe-doped InP buried layer 7 is not reduced, Moreover, since Fe does not diffuse, the impurity concentration of the p-type InP layer forming the p-type cladding layer or the p-type buffer layer does not decrease, the current leakage path is not formed, and the current injection efficiency improves.

(2) Further, the present invention is characterized in that in the above (1), the Fe diffusion prevention layer 6 is an n-type InP layer.

In this n-type InP layer, since the hole concentration is very low, Fe ⁺ _i formed by thermal history is formed.
Is diffused in the vicinity of the interface between the n-type InP layer and the Fe-doped InP buried layer 7, the leftward reaction of the above formula A, that is, the reaction represented by Fe ⁺ _i + V ⁻ → Fe ⁻ _s + h ⁺ As a result, the Fe-doped InP burying layer 7 is retained in the group III lattice point and is no longer diffused from the Fe-doped InP burying layer 7 to the Fe diffusion preventing layer 6. Of large Fe ⁺ _i is p
Since the p-type InP layer is not reached, the impurity concentration of the p-type InP layer does not decrease.

(3) In the method of manufacturing a semiconductor laser according to the present invention, after forming a mesa stripe including the active layer 3, an Fe diffusion preventing layer 6 is formed on the exposed surface of the mesa stripe, and then Fe is formed. It is characterized in that the doped InP buried layer 7 is formed.

As described above, by forming the Fe diffusion preventing layer 6 before forming the Fe-doped InP buried layer 7, the diffusion of Fe is caused by the heat history when the Fe-doped InP buried layer 7 is formed. Even if it occurs, it does not reach the p-type InP layer, and the current leak path is not formed.

(4) Further, the present invention is characterized in that in the above (3), the Fe diffusion prevention layer 6 is a semiconductor layer containing vacancies of 5.0 × 10 ¹⁴ cm ⁻³ or more. .

Thus, the Fe diffusion preventing layer 6 is 5.0
× 10¹⁴cm^-3Above vacancies (V ^-) Containing semiconductor layer
Fe formed by thermal history by using⁺ _i
Reaches the Fe diffusion preventive layer 6, the left-handed counteraction of the above formula A is
O, that is, Fe⁺ _i+ V^-→ Fe^- _s+ H⁺ By the reaction represented by
Since it forms an anti-layer, leakage current can be prevented.
You.

(5) Further, the present invention is characterized in that in the above (4), the semiconductor layer containing vacancies of 5.0 × 10 ¹⁴ cm ⁻³ or more is an Fe-doped InP layer.

The effect of preventing Fe from being diffused by the semiconductor layer containing vacancies is effectively achieved by using the Fe-doped InP layer.

(6) Further, in the present invention, in the above (5), the growth temperature for growing the Fe-doped InP layer is
It is characterized in that the temperature is higher than the growth temperature when growing the Fe-doped InP buried layer.

Since the vacancy concentration of this Fe-doped InP layer depends on the growth temperature, that is, the number of lattice defects increases at a growth temperature higher than the optimum growth temperature, the vacancy is controlled by controlling the growth temperature. The point density can be set to an appropriate value.

(7) Further, the present invention is characterized in that in the above (3), the Fe diffusion prevention layer is an n-type InP layer.

As described above, by using the n-type InP layer, Fe-doped InP can be used without special temperature control.
It is possible to prevent the diffusion of Fe ⁺ _i generated by the thermal history in the buried layer 7.

(8) Further, in the invention (7), the electron concentration of the n-type InP layer is made higher than the hole concentration of the p-type InP layer forming a part of the mesa stripe. And

Thus, the electron concentration of the n-type InP layer is changed to p
N is made higher than the hole concentration of the InP layer.
The n-type InP layer serves as a barrier against holes, and even if holes are injected from the p-type InP layer, they can be effectively canceled by the electrons.
Fe ⁺ _i diffused near the interface with the nP buried layer 7
It can be incorporated into Group I lattice points.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The SI-BH type semiconductor laser of the first embodiment of the present invention will be described with reference to FIG. See FIG. 2A. First, using the MOVPE method (metal organic chemical vapor deposition method),
On the n-type InP substrate 11, the impurity concentration also serving as the cladding layer is 7 × 10 ¹⁷ cm ⁻³ , the Si-doped n-type InP buffer layer 12 is 0.8 μm thick, and the thickness is 0.3 μm.
An undoped InGaAsP active layer 13 having a 1.3 μm wavelength composition, an impurity concentration of 7 × 10 ¹⁷ cm ⁻³ , and a thickness of 1.5.
μm Zn-doped p-type InP cladding layer 14 and an impurity concentration of 1 × 10 ¹⁹ cm ⁻³ and a thickness of 0.3 μm,
An undoped InGaAsP contact layer 15 having a 1.3 μm wavelength composition is sequentially grown.

Next, referring to FIG. 2B, a SiO ₂ film is deposited on the entire surface and patterned to form a stripe-shaped SiO ₂ mask 16, and then the SiO ₂ mask 16 is used to p-type I.
nGaAsP contact layer 15 to n-type InP substrate 11
Are mesa-etched to form a mesa stripe 17.

Next, referring to FIG. 2 (c), again using the MOVPE method,
For example, at the growth temperature of 660 ° C., the hole concentration is 5 ×
A Fe-doped InP layer 18 of 10 ¹⁶ cm ⁻³ and a thickness of 0.05 to 1.0 μm, preferably 0.2 μm is grown.

In this case, since lattice defects are likely to occur at a growth temperature higher than the optimum growth temperature, the vacancy concentration depends on the growth temperature, and the vacancy concentration in the Fe-doped InP layer 18 is 5. In the case of 0 × 10 ¹⁴ cm ⁻³ or more and 660 ° C., it becomes 1.0 × 10 ¹⁵ cm ⁻³ .

Subsequently, using the MOVPE method, 55
At a growth temperature of 0 to 640 ° C, for example 600 ° C,
Hole concentration is 5 × 10¹⁶cm^-3Fe-doped InP buried layer
19 is grown to form a high resistance current confinement structure. What
Vacancy points in the Fe-doped InP buried layer 19
The concentration is 1.0 × 10 ¹⁴cm^-3It is as follows.

Next, although not shown, the SiO ₂ mask 16 is removed, a p-side electrode and an n-side electrode are formed, and the elements are divided to complete the SI-BH type semiconductor laser.

[0034] In the SI-BH type semiconductor laser of the first embodiment, the thermal history in the process of forming the formation process and the electrode of the Fe-doped InP burying layer 19, the Fe-doped InP burying layer 19, Fe ^- Fe ⁺ _i having a large diffusion coefficient is generated by the reaction process of _s + h ⁺ → Fe ⁺ _i + V ⁻ and diffuses to the mesa stripe 17 side, but vacancy, that is, Fe with a high V ⁻ concentration is generated. In the doped InP layer 18, Fe ⁺ _i is taken into the group III lattice point by the reverse reaction process of Fe ⁺ _i + V ⁻ → Fe ⁻ _s + h ⁺ , and the Fe-doped InP layer 18 becomes a high resistance layer having a large resistivity. Since the above Fe ⁺ _i diffusion is prevented, F
The impurity concentration of the e-doped InP buried layer 19 does not decrease.

Fe ⁺ _i is the Fe-doped InP layer 18
To the Z-axis of the p-type InP cladding layer 14.
Since n ions are not knocked out, the Zn concentration on the side portion of the p-type InP clad layer 14 is not reduced, and therefore the resistivity is not increased, so that the injected carriers almost pass through the active layer. Become.

As described above, in the first embodiment,
Since the injected carriers effectively contribute to laser oscillation, it is possible to perform laser oscillation with low threshold current and high efficiency.

Next, an SI-BH type semiconductor laser according to the second embodiment of the present invention will be described with reference to FIG. See FIG. 3. In the second embodiment, the Fe-doped InP layer 18 as the Fe diffusion prevention layer in the first embodiment is used.
Is replaced with the n-type InP layer 20, and the other structure is the same as that of the first embodiment.

That is, in the second embodiment,
After forming the mesa stripe, again using the MOVPE method so that the electron concentration becomes higher than the hole concentration of the p-type InP clad layer 14, preferably with an impurity concentration of 2 × 10 ¹⁸ cm ⁻³ and a thickness of The Si-doped n-type InP layer 20 has a thickness of 0.05 to 0.5 μm, preferably 0.1 μm.

The SI-BH type semiconductor laser of the second embodiment.
Also in the laser, the formation of the Fe-doped InP buried layer 19
And the thermal history of the electrode formation process
Fe with a large diffusion coefficient in the buried InP buried layer 19⁺
_iOccurs and diffuses toward the mesa stripe 17 side
However, in the n-type InP layer 20 having a very low hole concentration, Fe⁺ _i+ V^-→ Fe^- _s+ H⁺ By the reverse reaction process of Fe⁺ _iIncorporated into the group III lattice points
Rare and more Fe⁺ _iTo prevent the diffusion of Fe,
The impurity concentration of the doped InP buried layer 19 may decrease.
Absent.

In this case, holes are p-type InP clad layer 1
The electron concentration of the n-type InP layer 20 is
Since the hole concentration is higher than that of the p-type InP clad layer 14,
The injected holes can be effectively canceled by the electrons, and Fe ⁺ _i diffused in the n-type InP layer 20 can be taken into the group III lattice points.

Further, since Fe ⁺ _i stays in the n-type InP clad layer 20, Zn ions in the p-type InP clad layer 14 are not knocked out, so that the Zn concentration on the side of the p-type InP clad layer 14 is also increased. Since it does not decrease and therefore the resistivity does not increase, the injected carriers almost pass through the active layer.

Even if a leak current tries to flow through the n-type InP layer 20, since the n-type InP layer 20 is a very thin layer of about 0.1 μm, the series resistance becomes high, and the n-type InP layer becomes high. The leakage current through layer 20 is negligible.

Next, the SI-BH type semiconductor laser of the third embodiment of the present invention will be explained with reference to FIG. See FIG. 4. In the third embodiment, all the conductivity types in the first embodiment are inverted. The configurations and manufacturing conditions of the Fe-doped InP layer 26 and the Fe-doped InP buried layer 27 are exactly the same as those in the first embodiment.

In this case, the p-type I also serving as the cladding layer
In nP buffer layer 22, the Zn ions in the p-type InP buffer layer 22 is sputtered by the Fe ⁺ _i which has been diffused, the reaction process of the above formula B, _{^{ie, Fe + i + Zn - s}} → Fe - s + Zn + i Z in the p-type InP buffer layer 22 by the reaction process of
There is a possibility that the n concentration is reduced and a current leak path is formed.

However, as described in the first embodiment, Fe ⁺ _i generated by the thermal history is taken into the group III lattice point in the Fe-doped InP layer 26 having a large vacancy density, and more than that. Since no diffusion occurs, no current leak path is formed.

In the third embodiment, Fe
Although the Fe-doped InP layer 26 is used as the diffusion prevention layer, an n-type InP layer may be used as in the second embodiment, and the action of the n-type InP layer in that case and the accompanying The effect is similar to that of the second embodiment.

Next, referring to FIG. 5, a fourth embodiment of the present invention will be described.
SI-PBH (high resistance layer-planar buried hetero)
A junction type semiconductor laser will be described. See FIG. 5. First, using the MOVPE method (metal organic chemical vapor deposition method),
On the n-type InP substrate 11, the impurity concentration also serving as the cladding layer
Degree 7 × 10¹⁷cm^-3And 0.8 μm thick Si
N-type InP buffer layer 12 having a thickness of 0.3 μm,
Undoped InGaAsP active layer with 1.3 μm wavelength composition
13 and the impurity concentration is 7 × 10¹⁷cm ^-3And the thickness is
1.5 μm Zn-doped p-type InP clad layer 14
Grow next.

Next, a SiO ₂ film is deposited on the entire surface and patterned to form a stripe-shaped SiO ₂ mask (not shown). Then, using this SiO ₂ mask, the p-type InP cladding layers 14 to n are formed. The type InP substrate 11 is mesa-etched to form a mesa stripe.

Then, again using the MOVPE method, the impurity concentration is preferably 2 × 10 ¹⁸ cm ⁻³ and the thickness is adjusted so that the electron concentration becomes higher than the hole concentration of the p-type InP cladding layer 14. 0.05-0.5 μm, preferably 0.1 μm
Of Si-doped n-type InP layer 20 of
At a growth temperature of 0 to 640 ° C, preferably 600 ° C,
The Fe-doped InP buried layer 19 having a hole concentration of 5 × 10 ¹⁶ cm ⁻³ is grown, and then the electron concentration is grown later.
It is preferably 4.0 × 10 ¹⁸ cm ⁻³ and has a thickness of 0.05 so as to be higher than the hole concentration of the InP clad layer 32.
Si-doped n-type InP having a thickness of μm or more, preferably 0.4 μm
Grow layer 31.

Then, SiO_TwoAfter removing the mask,
Using the MOVPE method, the impurity concentration is 1.0 × on the entire surface.
10¹⁸cm^-3And the thickness on the mesa stripe is 1.
0 μm Zn-doped p-type InP clad layer 32, and
Impurity concentration is 1 × 10¹⁹cm ^-3And the thickness is 0.3 μm
And an undoped InGaAsP film with a 1.3 μm wavelength composition
After sequentially growing the contact layer 33, the p-side electrode and n
Forming side electrodes (both not shown) and dividing into elements
Thus, the SI-PBH type semiconductor laser is completed.

The operation and effect of the fourth embodiment are substantially the same as those of the second embodiment,
The n-type InP layer 31 serves as a diffusion barrier against holes, and the p-type InP clad layer 32 to the Fe-doped InP buried layer 19
It is possible to prevent holes from diffusing into and promoting the generation of Fe ⁺ _i .

Further, in the fourth embodiment, Fe
Although the n-type InP layer 20 is used as the diffusion prevention layer, the vacancy concentration is 5.0 × 1 as in the first embodiment.
An Fe-doped InP layer of 0 ¹⁴ cm ⁻³ or more may be used, and the action of the Fe-doped InP layer in that case and the effect accompanying it are the same as those in the first embodiment.

The impurity concentrations, layer thicknesses, or composition ratios of the buffer layer, active layer, cladding layer, and contact layer in the description of the above embodiments are merely examples, and such impurity concentrations, The layer thickness or composition ratio is not limited.

[0054]

According to the present invention, since the Fe-doped InP burying layer is provided on the side surface of the mesa stripe with the Fe diffusion preventing layer interposed, the Fe-doped InP burying layer caused by the diffusion of Fe ⁺ _i generated by the thermal history is provided. Of resistivity of the buried layer and p-type I
Since it is possible to prevent a decrease in Zn concentration in the nP layer and significantly improve the current injection efficiency, it greatly contributes to the realization of a semiconductor laser capable of high efficiency and high speed driving.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a principle configuration of the present invention.

FIG. 2 is an explanatory diagram of the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram of a conventional high resistance current confined buried structure semiconductor laser.

[Description of Reference Signs] 1 semiconductor substrate 2 buffer layer 3 active layer 4 clad layer 5 contact layer 6 Fe diffusion prevention layer 7 Fe-doped InP buried layer 11 n-type InP substrate 12 n-type InP buffer layer 13 InGaAsP active layer 14 p-type InP clad layer 15 p-type InGaAsP contact layer 16 SiO ₂ mask 17 mesa stripe 18 Fe-doped InP layer 19 Fe-doped InP buried layer 20 n-type InP layer 21 p-type InP substrate 22 p-type InP buffer layer 23 InGaAsP active layer 24 n -Type InP clad layer 25 n-type InGaAsP contact layer 26 Fe-doped InP layer 27 Fe-doped InP buried layer 31 n-type InP layer 32 p-type InP clad layer 33 p-type InGaAsP contact layer 34 Low-concentration Fe-doped InP layer

Claims (8)

[Claims] 1. An Fe-doped InP buried layer is provided so as to fill a mesa stripe including an active layer, and the Fe-containing InP buried layer is formed.
Fe between the doped InP buried layer and the mesa stripe
A semiconductor laser comprising a diffusion prevention layer. 2. The semiconductor laser according to claim 1, wherein the Fe diffusion prevention layer is an n-type InP layer. 3. A semiconductor laser, comprising: forming a mesa stripe including an active layer, forming an Fe diffusion preventing layer on the exposed surface of the mesa stripe, and then forming an Fe-doped InP buried layer. Production method. 4. The Fe diffusion prevention layer is 5.0 × 10 ¹⁴
4. The method for manufacturing a semiconductor laser according to claim 3, wherein the semiconductor layer is a semiconductor layer containing vacancies of cm ⁻³ or more. 5. The method for manufacturing a semiconductor laser according to claim 4, wherein the semiconductor layer containing vacancies of 5.0 × 10 ¹⁴ cm ⁻³ or more is a Fe-doped InP layer. 6. The semiconductor laser according to claim 5, wherein the growth temperature when growing the Fe-doped InP layer is set higher than the growth temperature when growing the Fe-doped InP buried layer. Production method. 7. The method of manufacturing a semiconductor laser according to claim 3, wherein the Fe diffusion prevention layer is an n-type InP layer. 8. The semiconductor laser according to claim 7, wherein the electron concentration of the n-type InP layer is higher than the hole concentration of the p-type InP layer forming a part of the mesa stripe. Method.