JP2000068596A - Optical semiconductor transmitter/receiver element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide photosensitivity and threshold current equal to or better than a discrete element without depending on temperature, while the number of optical part items is decreased. SOLUTION: Related to an optical semiconductor transmitter/receiver element 100, a mesa-striped laminated part and an Fe-InP 70, formed on both sides of it, are formed on an n-InP substrate 50, and an AnZnNi electrode 31 and an AnGeNi electrode 32 are provided on the upper and lower surfaces of the element, respectively. The laminated part comprises an MQW active layer 10, an Inp etch-stop layer 40, a bulk light-receiving layer 20, and a p-Inp 60 (corresponding to a clad layer 22). For the structure, an equation λLD+0.4 (nm/ deg.C)×ΔT<=λDET<=lLD+0.6 (nm/ deg.C)×ΔT is established, where active layer band gap wavelength is λLD, light-receiving layer band gap wavelength is λDET, and the ambient temperature change width is ΔT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor transmitting / receiving element which can be applied to optical communication and functions as a light emitting and receiving element.

[0002]

2. Description of the Related Art In recent years, with the strong demand for large-capacity information transmission for realizing multimedia, optical communication technology has been making remarkable progress. In the FTTH plan, a transmission network using an optical fiber is being constructed up to a general home at the end of the communication network.

[0003] In the current optical communication, optical semiconductor elements such as light emitting elements and light receiving elements are used, and optical fibers are widely used as a transmission medium. As one of the methods, the transmission and reception operation is temporally switched using the same wavelength “T
im Compression Multiplex
ing (TCM) transmission method "has been proposed.

In this transmission system, a light emitting element and a light receiving element are separately provided, and a branch circuit such as a half mirror or a 3 db coupler is arranged between the light emitting element and the optical fiber, so that light from the light emitting element can be obtained. Optical bidirectional transmission is realized by guiding the light to the end of the optical fiber and the light from the end of the optical fiber to the light receiving element. However, such bidirectional optical transmission requires insertion of a branch circuit. Therefore, the branch loss of the branch circuit and the loss of the branch circuit itself affect the optical bidirectional transmission.

In order to reduce such effects, the light emitting element and the light receiving element are required to have high light output and high light receiving sensitivity. However, the yield at the time of manufacturing an element having such performance is low, and the lifetime is low. In addition to a factor of reduction, a light emitting element, a light receiving element, and a branch circuit are necessarily required, so that the number of optical components is large and the manufacturing cost of the optical module is high.

Therefore, in order to perform optical bidirectional transmission while reducing the number of optical components without inserting a branch circuit, it has been proposed to integrate a light emitting element and a light receiving element, which is a semiconductor used as a light emitting element. Laser (hereinafter “LD” as appropriate)
Can be realized by having a certain level of light-receiving sensitivity of the active layer, and can be realized by disposing only LDs having exactly the same structure at both ends of the transmission medium.

However, in the configuration in which the LDs are arranged facing each other as described above, when the environmental temperature changes, a serious problem such as deterioration of light receiving sensitivity occurs. The reason is as follows. It is known that the band gap wavelength of a semiconductor material changes with temperature,
Since laser oscillation occurs near the bandgap wavelength λ _LD where a large gain occurs at the time of current injection, the oscillation wavelength λ _LD (both wavelengths have the same notation because they are near the bandgap wavelength) is also shown in FIG. 7A. Therefore, the receiving side is required to have a constant light receiving sensitivity within the fluctuation range of the oscillation wavelength.

On the other hand, it is known that a semiconductor material absorbs only light on the shorter wavelength side than the band gap wavelength (λ _DET ). When the value decreases, the wavelength range in which light can be received moves to the shorter wavelength side as shown in FIG. This means that, when the same LDs are arranged facing each other, as shown in FIG. 8, the transmitting side is higher than room temperature, that is,
When the temperature becomes higher than the receiving side and the oscillation wavelength changes to the longer wavelength side, it means that the light receiving sensitivity is greatly reduced on the receiving side.This problem is caused by the fact that the transmitting side becomes hotter or the receiving side becomes colder Become serious.

Therefore, it has been considered to provide a light-receiving layer having a composition having a wavelength longer than the band gap wavelength of the active layer in order to obtain a constant light-receiving sensitivity regardless of the temperature. For example, the light-receiving layer designed independently of the temperature change of the band gap wavelength of the active layer as described above enables light reception in a wide wavelength range.

[0010]

However, although this method can improve the light receiving characteristics, since the light receiving layer has a large light absorption at the oscillation wavelength, the threshold current for performing the light output operation is reduced. It has been reported that transmission characteristics such as a large increase and kink (discontinuous optical output characteristics) near a threshold due to supersaturation absorption cause large deterioration in transmission characteristics. For such reports, see, for example, "R. Ben-Mi
chael et al., IEEE Photonics Technology Letters, vol.
7, no. 2, pp. 1424-1426, 1955. "

Therefore, in view of the above-mentioned matters, it has been desired to design the light receiving layer so as to satisfy the characteristics of both transmission and reception. The present invention has been made to solve such a conventional problem, and an object of the present invention is to reduce the number of optical components and to make the light-receiving sensitivity and threshold current independent of the temperature of the individual element without depending on the temperature. It is an object of the present invention to provide a means for realizing an optical transmitting / receiving element which is not inferior to that of the optical transmitting / receiving element.

[0012]

According to a first aspect of the present invention, there is provided an element for performing an optical signal transmitting / receiving operation, wherein a band gap wavelength λ is formed on a semiconductor substrate.
An active layer having an _LD , a light receiving layer having a band gap wavelength λ _DET, and an electrode capable of simultaneously injecting a current into the active layer and the light receiving layer and taking out a light receiving current,
If the temperature variation range of the surrounding environment and [Delta] T, between the lambda _LD and the lambda _{DET, "λ LD +0.4 (nm / ℃)} × ΔT ≦ λ DET ≦ λ LD +0.6 (nm / ℃) × ΔT ”(1) An optical semiconductor transmission / reception element is configured to satisfy the following relationship.

[0013] The invention according to claim 2, in claim 1, further, the thickness d _DET of the light receiving layer, the length L _DET, optical confinement coefficient gamma _DET which depends on the d _DET,
Absorption coefficient alpha _DET in the bandgap wavelength lambda _DET, the length L of the active layer, and, during the conversion factor G of the gain and the injection current in the active layer, "1-exp (-Γ _DET × α _DET × L _DET) ≧ 0.8 "(2), and," as _{exp (Γ DET × α DET ×} L DET /(G×L))≦1.5'(3) the relationship is established It is characterized by comprising.

The principle for achieving the above objects of the present invention will be described. FIG. 2 schematically shows a cross section in the longitudinal direction of the optical semiconductor transmission / reception element. The optical semiconductor transmission / reception element is provided with an active layer 10 for generating transmission light by laser oscillation, and receiving light provided on the active layer 10. A light-receiving layer 20 for photoelectrically converting an optical signal, an upper cladding layer 22 and a lower cladding layer 24 provided on the upper and lower sides thereof, and an electrode 31 provided on the outer surface thereof for performing current injection and current detection; 32.

First, the condition of the wavelength required for light reception will be analyzed. As described above, when the environmental temperature changes, the band gap wavelength of the semiconductor material changes, and this change is about 0.5%.
(Nm / ° C.).

The fluctuation of the oscillation wavelength of the Fabry-Perot LD, the longest wavelength that can be absorbed by the light-receiving layer, and the so-called absorption edge wavelength with temperature depend on the change of the bandgap wavelength, and each is about 0.5 (nm / nm). ° C).

For this reason, if the temperature fluctuation is ΔT, the oscillation wavelength has a fluctuation width Δλ represented by the following equation (4), and it is necessary that the receiving side can receive all the light in this fluctuation range.

Δλ ≒ 0.5 (nm / ° C.) × ΔT (4) That is, how the light-receiving layer should be designed in consideration of the worst condition that the transmission side becomes high temperature and the reception side becomes low temperature. This will be described in detail with reference to FIG.

Here, as described above, the bandgap wavelength changes depending on the temperature. However, the bandgap wavelength is usually measured by photoluminescence at room temperature. Description will be given as a value at room temperature.

When the transmission side has the maximum value Tmax, the variation from the band gap wavelength λ _LD of the active layer is represented by Δ
λ ₊ , when the receiving side has reached the minimum temperature Tmin,
The change from the band gap wavelength λ _DET of the light-receiving layer Δλ _-
And

At this time, the oscillation wavelength λ ₁ on the transmission side is expressed by the following equation (5). λ ₁ = λ _LD + Δλ ₊ (5) On the other hand, the absorption edge wavelength λ ₂ on the receiving side is as shown in the following equation (6).

The _{λ 2 = λ DET -Δλ - (} 6) where, in order to sufficiently received by the receiving side the transmitted light that has been propagated through the optical fiber, to satisfy the condition of the following formula (7) There is a need.

Λ ₂ ≧ λ ₁ (7) Therefore, this equation (7) becomes the following equation (8). λ _DET ≧ λ _LD + Δλ ₊ + Δλ ₋ (8) The sum of the second and third terms on the right side of equation (8) is nothing less than Δλ itself, and minimizes the effect on the transmission characteristics of the light receiving layer. For this purpose, it is desirable to set the composition of the light receiving layer on the short wavelength side where absorption is as small as possible, that is, as in the following equation (9).

Λ _DET ≒ λ _LD +0.5 (nm / ° C.) × ΔT (9) On the other hand, ± 0.1 (nm / ° C.) due to manufacturing variations and the like.
Therefore, it is necessary to design such that the band gap wavelength of the light receiving layer satisfies the condition of the above-described equation (1).

That is, “λ _LD +0.4 (nm / ° C.) × ΔT
≦ λ _DET ≦ λ _LD +0.6 (nm / ° C.) × ΔT ”, the light receiving sensitivity does not depend on the temperature.

Next, the light receiving layer and the active layer (laser characteristics and light receiving characteristics) need to be designed in consideration of the following matters. First, when the light receiving characteristics are analyzed, the light absorption A in the light receiving layer is represented by the following equation (10) by the light confinement coefficient Γ _{DET indicating the} ratio of the light distribution in the light receiving layer, its length L _DET, and the absorption coefficient α _DET . Is represented by

[0027] _{A = 1-exp (-Γ DET} × α DET × L DET) (10) where, gamma _DET is dependent on the thickness of the light absorbing layer, gamma _DET =
0.3, α _DET = 5000 (cm ⁻¹ ), the light absorption increases exponentially with respect to the length of the light receiving layer, and becomes 80%
If the length is absorbed, it becomes substantially constant even when the length is changed, and saturates. Therefore, the above-mentioned equation (2), ie, “1-exp
It should satisfy _{(-Γ DET × α DET × L} DET) ≧ 0.8 (2) "following condition. If the length of the light-receiving layer is too long, there is a concern that the transmission characteristics will deteriorate. Therefore, it is desirable to select a value near the saturation of light absorption.

Next, when the oscillation characteristics are analyzed, LD oscillation occurs when the following formula (11) is satisfied between the threshold gain g _th generated by the current and the absorption in the resonator. R × exp { _act (g _th −α _i ) L− { _DET α _DET L _DET } = 1 (11) where R is the reflectance at both end faces, Γ _act is the light confinement coefficient of the active layer, α _i is the absorption coefficient of the active layer, and L is the length of the active layer.

On the other hand, since the relationship between the gain g and the current I is nonlinear, it is difficult to obtain it analytically, but the following (12)
For example, "East et al., Evaluation of temperature dependence of gain in a semiconductor laser, '96 Autumn meeting of the Japan Society of Applied Physics, 8p-KH-2"
And the like.

G = G × lnA (I / I ₀ ) + B (12) Here, G, A, I ₀ and B are constants. Now, the threshold gain o'clock L _DET = 0 in the above equation g _th0, when the threshold current and I _th0, threshold gain at the threshold current I _th g _th is expressed by the following equation (1
It looks like 3).

G _th = G × ln (I _th / I _th0 ) + g _th0 (13) Here, G is a converted value and a value experimentally obtained for each element. Therefore, the threshold current is given by the equation (1)
1) From the equation (13), the following equation (14) is obtained.

I _th = I _th0 × exp ( _ΓDET × α _DET × L _DET / (G × L)) (14) According to the equation (14), when L _DET increases, I _th becomes exponential. Therefore, it is necessary to achieve both transmission and reception characteristics by keeping the light-receiving layer length to a minimum necessary for light reception. If the increase in threshold current can be suppressed to 1.5 times or less, there is no practical problem. "Ex
_{p (Γ DET × α DET ×} L DET /(G×L))≦1.5
(3) "should be satisfied. Therefore, equation (1)
In addition, if the conditions of the equations (2) and (3) are taken into consideration, the light receiving sensitivity does not depend on the temperature, and the optical semiconductor transmitting / receiving element whose light receiving sensitivity and threshold current are comparable to those of the individual elements can be realized. .

In a device to be actually manufactured, it is possible to satisfy the conditions of the above expressions (1), (2) and (3). Assuming that an optical semiconductor transmitting / receiving element having a structure in which a light receiving layer is laminated on an active layer is manufactured, the band gap wavelength λ _LD of the active layer is set to 1.30 (μ).
m). The bandgap wavelength λ _DET of the light receiving layer is
In the equation (1), “λ _DET = λ _LD +0.5 (nm / ° C.) × Δ
T, ΔT = 100 (° C.) ”to obtain 1.35.
(Μm). At this time, the absorption coefficient α _DET of the light-receiving layer is 5000 cm ⁻¹ , and the thickness and width of the light-receiving layer are each 0.1 mm.
15 (μm) and 1.5 (μm). As a result, the light confinement coefficient Γ _DET of the light-receiving layer was 0.3, and the length of the active layer was 300 μm.

FIG. 4 shows the dependence of the threshold current (right vertical axis, arbitrary unit (arbitrary.unit)) and light receiving sensitivity (left vertical axis, arbitrary unit (au)) on the light receiving layer length. The threshold current (open circle) increases exponentially as the length of the light-receiving layer is increased, and agrees well with the above approximate expression (dotted line). At this time, the converted value G is 200 (cm ^-1 ). . In FIG. 5, the region where the conditions of the above equations (2) and (3) are satisfied where the light absorption is substantially saturated in the light reception and the threshold current is about to increase rapidly in the light emission is the light receiving layer length. L _DET is around 15 μm.

Therefore, it is possible to design the optical semiconductor transmitting / receiving element while satisfying the conditions of the equations (1), (2) and (3).

[0036]

Embodiments of the present invention will be described below with reference to the drawings. First, a method for manufacturing an optical semiconductor transmitting / receiving element according to an embodiment of the present invention will be described with reference to FIGS.

First, as shown in FIG.
On a (μm) n-InP substrate 50 (corresponding to the lower cladding layer 22), a G (band gap wavelength) of 1.3 (μm)
aInAsP-MQW active layer 10, n-InP etch stop layer 40, band gap wavelength 1.35 (μm)
The GaInAsP bulk light-receiving layer 20 having a layer thickness of 0.15 (μm) designed to have a light confinement coefficient of 0.3 in this order is sequentially formed in this order by metalorganic vapor phase epitaxial growth (MO).
(VPE) method.

Next, the entire surface of the bulk light receiving layer 20 is made of SiO.
_{The second} film 62 is formed by the plasma CVD method, and the SiO2 film other than the upper part of the region length (light receiving layer length) 15 (μm) to be the light receiving layer 20 is removed by photolithography and RIE (FIG. 5B )).

Next, this SiO_TwoUsing the film 62 as a mask
The n-InP etch stop layer 40 and the bulk light receiving layer 2
Bulk receiving by wet etching selective to 0
The optical layer 20 is directly above the n-InP etch stop layer 40
Removed (FIG. 5 (c)) and the SiO _TwoWhen the film 62 is removed,
A p-InP cladding layer 22 is formed on the entire surface by MOVPE.
(FIG. 5D).

Next, an SiO ₂ film 64 is formed on the entire surface by plasma C.
The SiO ₂ film 64 is formed by a VD method, and the SiO ₂ film 64 other than the upper part of the region to be a mesa stripe having a width of 1.5 (μm) and a length of 300 (μm) is removed by photolithography and RIE (FIG. 5E). )).

Next, using the SiO ₂ film 64 as a mask, the cladding layer 22 and the bulk light receiving layer 2 are formed by RIE.
The MQW active layer 10 and a part of the n-InP substrate 50 are removed (FIG. 5F).

[0042] Then, as shown in FIG. 6 (a), SiO ₂
Using the film 64 as a selective growth mask, Fe-InP 70 which is Fe-doped InP other than the mesa stripe is MOV
Formed by the PE method, the SiO ₂ film 64 is removed, and n-In
An AuGeNi electrode 32 is formed on the lower surface of the P substrate 50 by a resistance heating evaporation method, and an Au
By forming the uZnNi electrode 31 by the resistance heating evaporation method (FIG. 6B), an optical semiconductor transmitting / receiving element having a length of 300 (μm) can be manufactured.

FIG. 1 schematically shows an external view in which a part of the optical semiconductor transmitting / receiving element 100 manufactured in this way is cut away. This optical semiconductor transmitting / receiving element 100 has n-I
On a nP substrate 50, a mesa-stripe laminated portion and Fe-InP 70 formed on both sides thereof are formed, and further, AuZnNi electrodes 3 are formed on the upper and lower surfaces of the element, respectively.
1. An AuGeNi electrode 32 is provided.

Further, the laminated portion includes the MQW active layer 10,
It comprises an InP etch stop layer 40, a bulk light receiving layer 20, and a p-InP 60 (corresponding to the cladding layer 22). Then, light is oscillated from the MQW active layer 10 by the current injected from the AuZnNi electrode 31 and the AuGeNi electrode 32, and the light received by the bulk light receiving layer 20 is photoelectrically converted to the AuZnNi electrode 31, the AuGeNi.
It is extracted as an electric signal from the electrode 32.

In this structure, λ _DET is 1.35
(Μm), λ _LD is 1.3 (μm), and ΔT is 100
(° C.), so that the above-described expression (1) is satisfied. Further, the light confinement coefficient Γ _DET is 0.3, the L _DET is 15 (μm), and the measurement results show that the absorption coefficient α _DET is 5000
Because became (cm ^-1), "1-exp (-Γ _DET × α
_DET × L _DET ) = 1−exp (−0.3 × 5000 (c
m- ¹ ) .times.15 (.mu.m)) = 0.895 ", thereby satisfying the condition of the above expression (2).

Further, G was determined to be 200 (cm)
^-1 ) and L is 300 (μm), and is expressed as “exp ( _ΓDET × α)
_DET × L _DET /(G×L))=exp(0.3×500
0 (cm ⁻¹ ) × 15 (μm) / (200 (cm ⁻¹ ) × 3
00 (μm)) = 1.45 ”, which also satisfies the condition of the above expression (3).

Therefore, since the conditions of the expressions (2) and (3) are satisfied in addition to the expression (1), the optical semiconductor transmission / reception element 100 does not depend on the temperature but has the light reception sensitivity and the threshold. The current is comparable to that of the individual elements.

The above-mentioned optical semiconductor transmitting / receiving element 100
It was confirmed that excellent characteristics of light transmission / reception with a threshold current at room temperature of 12 (mA) and a light receiving sensitivity of 0.35 (A / W) were obtained.

Further, no pulsation is observed during transmission modulation, and a good eye pattern is obtained.
No floor was observed in the bit error rate (BER) measurement at 56 (Mbps), and the minimum reception sensitivity Pmin = -2
It was confirmed that 9.8 (dBm) (when BER = 10 ⁻¹⁰ ) could be obtained.

Further, when the wavelength of the transmission light is set to be 40 (nm) longer than the band gap wavelength of the MQW active layer 10 so as to correspond to the temperature fluctuation on the transmission side (this is 80%).
(Corresponding to a temperature fluctuation of (° C.)), the power penalty of the BER was only 0.55 (dB), and it was also confirmed that the power penalty could be reduced to a practically acceptable range.

According to the embodiment of the present invention described above, the 1.3 (μm) band optical semiconductor transmitting / receiving element using the GaInAsP system has been described. The same effect can be obtained as an optical semiconductor transmitting / receiving element of AlGaAsP type and GaIn.
It goes without saying that a similar effect can be obtained even with an As-based semiconductor element. Further, an optical functional element for performing spot size conversion may be provided at the front end of the optical semiconductor transmitting / receiving element to improve the coupling efficiency with the optical fiber.

[0052]

As described above, according to the present invention,
It is possible to realize an optical transmitter / receiver whose light receiving sensitivity does not depend on temperature and whose light receiving sensitivity and threshold current are not inferior to those of individual elements, thereby reducing the number of optical components constituting optical bidirectional transmission. The effect that it becomes possible also to obtain is obtained.

[Brief description of the drawings]

FIG. 1 is an external view of an optical semiconductor transmitting / receiving element according to an embodiment of the present invention.

FIG. 2 is a schematic explanatory view of a cross section in a longitudinal direction of an optical semiconductor transmitting / receiving element.

FIG. 3 is an explanatory diagram for explaining a method of designing a light-receiving layer in consideration of a worst condition.

FIG. 4 is an explanatory diagram showing a dependency of a threshold current and a light receiving sensitivity on a light receiving layer length.

FIG. 5 is an explanatory diagram of a method for manufacturing an optical semiconductor transmitting / receiving element according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram of a method for manufacturing an optical semiconductor transmitting / receiving element according to an embodiment of the present invention.

FIG. 7 is an explanatory diagram of a conventional technique.

FIG. 8 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

Reference Signs List 10 MQW active layer (active layer) 20 bulk light receiving layer (light receiving layer) 22 clad layer (upper clad layer) 24 lower clad layer 31 AuZnNi electrode (electrode) 32 AuGeNi electrode (electrode) 40 n-InP etch stop layer 50 n -InP substrate 62 SiO ₂ film 64 SiO ₂ film 70 Fe-InP 100 Optical semiconductor transmitting / receiving element

Claims (2)

[Claims] 1. An element for transmitting and receiving an optical signal, comprising: an active layer having a band gap wavelength λ _LD on a semiconductor substrate; a light receiving layer having a band gap wavelength λ _DET ; provided and the possible simultaneously injecting a current into the light-receiving current possible extraction electrode layers, and the temperature variation range of the surrounding environment and [Delta] T, between the lambda _DET and the lambda _LD, "lambda _LD +0.4 ( nm / ° C) × ΔT ≦ λ _DET ≦ λ _LD +
0.6 (nm / ° C.) × ΔT ”. 2. The method of claim 1, further, the thickness d _DET of the light receiving layer, the length L _DET, optical confinement coefficient gamma _DET which depends on the d _DET, the absorption coefficient alpha _DET in the bandgap wavelength lambda _DET , the length L of the active layer, and, during the conversion factor G of the gain and the injection current in the active layer, _{"1-exp (-Γ DET × α} DET × L DET) ≧ 0.8 "
And “exp (Γ _DET × α _DET × L _DET / (G × L))
An optical semiconductor transmitting / receiving element configured to satisfy a relation of ≦ 1.5 ”.