JPH0654806B2 - Optical / electronic integrated circuit and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed and highly reliable optical / electronic integrated circuit used in a transmitter for optical communication and a method for manufacturing the same.

(Problems to be Solved by Prior Art and Invention) A conventional optical transmitter is a semiconductor laser (hereinafter, LD) serving as a light source.
And each of the electronic circuits that drive and modulate it are manufactured as individual parts, and then they are connected. However, in such a system, the operation is slowed due to the propagation delay and the stray capacitance associated with the wiring between the components, and the reliability is deteriorated due to the connection portion. Therefore, in order to construct a high-speed and highly reliable optical transmitter, an optical / electronic integrated circuit in which an optical element and an electronic element are integrated is required.

As such an opto-electronic integrated circuit, a field effect transistor (FE) is used as a transistor for driving an LD.
T) may be used and a heterojunction bipolar transistor (hereinafter referred to as HBT) may be used. Among them, HBT has high current driving capability and high speed operability, and therefore, Suitable for modulation.

As an attempt to construct an integrated circuit using HBT and LD,
Report by J. Katz et al. (Appl. Phys. Let
t. , 37 (2), 1980). FIG. 3 shows the above structure. This device comprises a first layer n-AlGaAs21, a second layer p-GaAs22, and a third layer n-AlGaAs23 on the n ⁺ -GaAs substrate 20 from the substrate side.
An HBT having an npn structure grown on an epitaxial film
And the Be ions from the third layer 23 to p-GaAs22.
To a portion of the n-AlGaAs in the third layer 23
It is designed so that it can be operated as an LD having an npp structure instead of the type 24. However, such a structure has the following drawbacks.

That is, p− of the second layer 22 used as the active layer of the LD
In GaAs, it is not desirable to increase the doping concentration (5 × 10 ¹⁷ cm ⁻³ ) because it is necessary to prevent the laser oscillation threshold from increasing due to light absorption by free carriers. On the other hand, this p-GaAs layer is also used as the base portion of the HBT, but in the HBT, the cutoff frequency _{c that} is a measure of the operating speed is As can be seen from (R ₆ : base resistance, C _c : collector capacitance), it is necessary to reduce the base resistance in order to speed up the device. Therefore, it is operationally advantageous to dope the base layer with a high concentration to reduce the sheet resistance of this layer. As can be seen from the above, L
In order to simultaneously improve the performance of the D and HBT elements,
It is necessary to select a composition, film thickness, and doping concentration suitable for each, and a method using only an epitaxial film having a simple npn structure, such as Kaatsu, is not sufficient.

In order to solve this problem, an epitaxial multilayer film having an nnp (or npp) structure suitable for LD and an npn structure suitable for HBT is continuously formed, and LD, LD, The HBTs may be manufactured separately, but in order to continuously form such an epitaxial multilayer film, growth with different compositions and doping conditions is repeated, which complicates the crystal growth process. Further, in such a multilayer structure, it is necessary to perform deep etching when taking out the lower electrode of the LD or HBT.
There is also a problem in that the surface step becomes large and the structure becomes unsuitable for integration.

(Means for Solving the Problems) An object of the present invention is to enable growth of an epitaxial film, which is advantageous in terms of device characteristics, for each of HBT and LD, and to overcome the complexity of crystal growth and the step difference caused thereby. SUMMARY OF THE INVENTION It is an object of the present invention to provide an element structure and a manufacturing method for avoiding the above problems and realizing an optical / electronic integrated circuit having high performance and easy integration.

To achieve the above object, the present invention provides a first conductive type first semiconductor layer on a semi-insulating substrate, and a first conductive type second semiconductor which is a narrow gap compared to the first semiconductor layer. Layer, the first layer being a wide gap compared to the second semiconductor layer
A lateral junction stripe laser having a second semiconductor layer as an active layer and first and third semiconductor layers as cladding layers is formed on a first multilayer epitaxial film in which a conductive type third semiconductor layer is sequentially stacked. A fourth semiconductor layer having a high-concentration impurity of the first conductivity type on the first multilayer epitaxial film;
The fifth semiconductor layer is formed on the second multilayer epitaxial film in which the fifth semiconductor layer of the conductivity type and the sixth semiconductor layer of the second conductivity type, which is a narrow gap compared to the fifth semiconductor layer, are sequentially stacked. A heterojunction bipolar transistor having an emitter, a first conductivity type impurity region formed in the sixth semiconductor layer as a collector, and a region sandwiched between the emitter and collector in the sixth semiconductor layer as a base. The gist of the invention is an optical / electronic integrated circuit characterized by the above.

Furthermore, the present invention provides a first conductive type first semiconductor layer on a semi-insulating substrate, a first conductive type second semiconductor layer and a second semiconductor layer which are narrow gaps compared to the first semiconductor layer. In comparison with the above, a third semiconductor layer of the first conductivity type, which is a wide gap, is sequentially laminated to form a first multilayer epitaxial film, and the second semiconductor layer is activated in the first multilayer epitaxial film. Layer, a lateral junction stripe laser using the first and third semiconductor layers as cladding layers, and a fourth semiconductor layer having a high-concentration impurity of the first conductivity type on the first multilayer epitaxial film; The fifth semiconductor layer of one conductivity type and the sixth semiconductor layer of the second conductivity type, which is a narrow gap compared to the fifth semiconductor layer, are sequentially stacked to form a second multilayer epitaxial film. Of the first conductivity by ion implantation or vapor phase diffusion method in the semiconductor layer of Heterojunction bipolar based on the fifth semiconductor layer selectively formed as an emitter, the first conductivity type impurity region as a collector, and the area between the emitter and collector in the sixth semiconductor layer as a base. The gist of the invention is a method of manufacturing an optical / electronic integrated circuit characterized by forming a transistor.

Therefore, the features of the present invention are as follows.

First, in order to realize a film thickness, composition, and impurity concentration suitable for HBT and LD, a multilayer film of nnnn ⁺ np is sequentially grown from the substrate side as an epitaxial structure corresponding to each element structure. The growth method at this time is MO
Any method such as VPE, MBE, LPE may be used. In the structure of the multilayer film, most of the layers are n-type and only the uppermost layer serving as the base region of the HBT is p-type for the purpose of facilitating the control of doping. The HBT collector region is formed by inverting a part of the uppermost p layer into n-type by ion implantation or vapor phase diffusion after the growth of the multilayer film. Since the function of the collector is mainly to pull out the carrier injected into the base layer, it is sufficient for device operation if it has a good reverse breakdown voltage characteristic. Therefore, a pn junction formed by ion implantation or the like is used. But it doesn't matter.

On the other hand, for LD, since it is necessary to form a pn junction in the n-type multilayer epitaxial film, a p ⁺ region is formed in a part of the lower nnnn ⁺ layer by ion implantation or vapor phase diffusion method, and the p
^A pn junction is formed by rediffusion of the ⁺ layer. This is a structure generally called a TJS laser. By using this TJS structure, the electrode in the p-type region may be taken from the uppermost part of this region, and therefore it is not necessary to take the electrode out from the lower portion of the multilayer film by deep etching, so that a relatively flat surface structure is obtained. It becomes feasible.

Next, embodiments of the present invention will be described with reference to the accompanying drawings.

Needless to say, the embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the present invention.

FIG. 1 shows an embodiment of the present invention, the constitution of which is as follows. In the figure, reference numeral 1 is a semi-insulating substrate made of GaAs. On this semi-insulating substrate, the n-Al _x Ga _1-x As of the first semiconductor layer 2 of the first conductivity type and the first semiconductor layer 2 are formed. In comparison, n− of the second semiconductor layer 3 of the first conductivity type which is a narrow gap
GaAs (or Al _y Ga _1-y As) (x> y), second semiconductor layer 3
N-Al _x Ga _1-x As of the _first semiconductor layer 4 of the first conductivity type, which is a wide gear gap, is sequentially stacked to form the semiconductor layer 2,
A first multilayer epitaxial film is formed by 3 and 4, and a lateral junction stripe laser having the semiconductor layer 3 as an active layer and the semiconductor layers 2 and 4 as a cladding layer is formed on the multilayer epitaxial film. Then, a fourth semiconductor layer 5 having a high-concentration impurity of the first conductivity type is formed on the first multilayer epitaxial film.
n ⁺ −GaAs, and then n ⁻ of the fifth semiconductor layer 6 of the first conductivity type
Al _z Ga _1-z As is formed, and then p-Ga of the second conductivity type sixth semiconductor layer 7 which is a narrow gap compared to the semiconductor layer 6 is formed.
As is formed, and then an n-type region 8 is formed in a part of the semiconductor layer 7 by an ion implantation method or a vapor phase diffusion method to form an n-type region 8. The semiconductor layer 6 is an emitter, the semiconductor layer 7 is a base, and the semiconductor layer 8 is a base. Is used as a collector to configure the HBT. E, B, C
Indicate the emitter, base, and collector electrodes, respectively.

The semiconductor layer 9 is a p region, and a pn junction is formed with the semiconductor layer 10 to form a laser. P and N represent electrodes, respectively. Reference numeral 11 indicates an insulating isolation region.

Next, adding a further explanation, the semi-insulating GaAs substrate 1
2 immediately above is n-Al _x Ga _1-x As (0 <x <1), which is the cladding layer of the LD. 3 is a portion serving active layer n-GaAs or n-Al of LD _y Ga _1-y As (where
x> y). The appropriate impurity (Si) concentration is 5 × 10 ¹⁷
/ Cm ³ . Reference numeral 4 is n-Al _x Ga _1-x As, which serves as the cladding layer of the LD. Since the Al composition is x> y, the refractive index of the semiconductor layer 3 is larger than that of the semiconductor layers 2 and 4, and the optical confinement effect works to reduce the threshold value of the laser. Reference numeral 5 is n ⁺ -GaAs provided as a contact layer, which is used as the n-type electrode of the LD and is also connected to the emitter electrode of the HBT. 6 is n-Al _z Ga _1-z As (0 <z <1), HBT
It becomes the emitter part of. Reference numeral 7 denotes p-GaAs, which is a base layer of HBT. A suitable impurity (Be) concentration is 5 × 10 ¹⁸ / cm ³ . Further, a part of the semiconductor layer 7 is made into an n-type region 8 by an ion implantation method or a vapor phase diffusion method and used as a collector of the HBT.

Next, the manufacturing order will be described.

(B) n-Al _x of the first semiconductor layer 2 on the semi-insulating GaAs substrate 1
Ga _1-x As is formed, and then n-GaAs or n- of the second semiconductor layer 3 which is a narrow gap compared to the first semiconductor layer is formed.
Al _y Ga _1-y As (where x> y) is formed, and then n of the third semiconductor layer 4, which is a wider gap than the semiconductor layer 3, is formed.
-Al _x Ga _1-x As is formed to form a first multilayer epitaxial film, and the semiconductor layer 3 is the active layer and the semiconductor layers 2 and 4 are the cladding layers in the first multilayer epitaxial film. To form a lateral junction stripe laser.

(B) Then, n ⁺ -GaAs of the fourth semiconductor layer 5 having a high concentration of impurities is formed on the first multilayer epitaxial film, and then n-Al _z Ga _{1-z of} the fifth semiconductor layer 6 is formed. A sixth semiconductor layer 7 that is formed of As and is a narrow gap compared to the semiconductor layer 6.
Second p-GaAs is formed to form a second multilayer epitaxial film, and then n-type impurities such as Si and S are ion-implanted or vapor-phase diffused into a part of the semiconductor layer 7 to form a collector portion of the HBT. To form. Next, the remaining semiconductor layers 6 and 7 are removed by etching, leaving the collector and base portions of the HBT, and the contact layer 5 is exposed to form an emitter electrode.

(C) In the LD, after removing the semiconductor layers 6 and 7 by etching, p-type impurities such as Zn and Be are ion-implanted or vapor-phase diffused from the contact layer 5 to the semi-insulating substrate 1 to form a p ⁺ region, Then, the p-type impurities are rediffused by heat treatment to form a pn junction. The electrode is the n ⁺ region of the contact layer 5
It is formed in the p ⁺ region 9. The isolation between the LD and the HBT is performed by implanting ions such as B and H between both the elements to isolate the insulating isolation region 11.
Form and secure. When the pn junction is energized, the current flows through the pn junction inside the semiconductor layers 2, 3 and 4.
However, in this case, in the pn junction formed in the semiconductor layer 3 and the pn junctions formed in 2 and 4, the built-in barrier to the carrier is lower in the semiconductor layer 3, so that the current flows mainly in the semiconductor layer 3.
Flowing through the pn junction, and this portion becomes a light emitting region.

The tilted band structure as described above can be realized by changing the ratio of the material used as the raw material during the crystal growth. For example, when the tilted band structure of AlGaAs is produced by the metalorganic vapor phase epitaxy method, the flow rates of hydrogen gas containing trimethylgallium (TMG) and arsine (AsH ₃ ) gas are kept constant, This is a method of continuously changing the flow rate of hydrogen gas containing trimethylaluminum (TMA).

In the above embodiment, AlGa was used as the wide gear semiconductor.
As, the combination of GaAs as the narrow gap semiconductor has been described, but in addition, the first, third, and fifth semiconductor layers are made of InP,
The second and fourth semiconductor layers are InGaAs or InGaAsP, the sixth
The semiconductor layer of may be InP, InGaAs, or InGaAsP. In this case, InP can also be used as the semi-insulating substrate. Further, by performing re-diffusion from the p ⁺ region 9 to form the re-diffusion region 9 ', the laser oscillation characteristics can be improved.

Further, as a base of HBT, instead of p-GaAs, as a tilted band gap base, and as a sixth semiconductor layer, p-Al.
with _{z 'Ga 1-z' As} , continuously contain altered the value of z ',
When the Al composition z ′ = 0 at the connection portion with the collector, the Al composition at the connection portion of the fifth semiconductor layer 6n-Al _z Ga ₁ -z As is equal to the Al composition of the fifth semiconductor layer. It can also be The band structure in this case is as shown in FIG. 2 (b). Therefore, the electrons injected into the base region are
It is accelerated by the internal electric field and travels at a higher drift velocity than in the case where electrons are diffused in the conventional base region (see FIG. 2a). This effect is based on the base running time τ
Compared with the case of diffusion, (K: Bolsoman constant, T: absolute temperature, q: electron charge amount), so the bandgap difference ΔEg at both ends of the base
If it is set to 0.2 eV, the running time will be reduced to about 1/4. As a result, the current gain β can be increased and the recombination of electrons and holes can be reduced, so that the characteristics of the HBT can be improved.

In the above description, p-type may be n-type and n-type may be p-type.

(Effects of the Invention) As described above, according to the present invention, the LD and the HBT are integrated on the same substrate without impairing the characteristics of both, and as a result, a high-speed and highly reliable optical / electronic integrated circuit is provided. Can be manufactured. Such an optical / electronic integrated circuit has an advantage that it can be used as an optical transmitter suitable for increasing the capacity of optical communication.

Furthermore, in the present invention, since the active layer concentration of the lateral junction stripe laser and the base concentration of the heterojunction bipolar transistor can be set separately, the threshold current of the laser is low (about 10 mA) and the lateral junction stripe is reduced. A laser and a heterojunction bipolar transistor having a high cutoff frequency (1 GHz or more) can be formed on the same substrate.

Further, since the lateral injection type junction stripe laser is used, it is not necessary to form a deep etching groove for taking out the electrode from the lower side of the laser as in the conventional example, and the surface step can be reduced.

Further, since the emitter / base junction layer has a structure that is not damaged by ion implantation, the implantation effect can be efficiently performed.

In addition, since the transistor has the inclined band gap base structure, the current amplification factor can be increased.

[Brief description of drawings]

FIG. 1 shows the configuration of the optoelectronic integrated circuit of the present invention.
FIG. 3 is an explanatory view of a band gear, and FIG. 3 shows a conventional example. 1 ...... the semi-insulating substrate GaAs 2 ...... first semiconductor layer _{n-Al x Ga 1-x} As 3 ...... second semiconductor layer n-GaAs or _{Al y Ga 1-y As (} x>
y) 4 ...... third semiconductor layer _{n-Al x Ga 1-x} As 5 ...... fourth semiconductor layer n ⁺ -GaAs 6 ...... fifth semiconductor layer _{n-Al z Ga 1-z} As 7 ... … Sixth semiconductor layer p-GaAs 8 …… p region 9 …… p region 10 …… n region 11 …… insulation isolation region

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsuro Koumae 3-1, Morinosato Wakamiya, Atsugi City, Kanagawa Pref. Atsugi Telecommunications Research Laboratories, Nippon Telegraph and Telephone Corporation (56) Reference JP-A-62-147793 (JP, A) JP 62-165387 (JP, A) Appl. Phys. Lett. Vol. 45, No. 3 (1984-8-1) P. 191-193 Appl. Phys. Lett. Vol. 37, No. 2 (1980-7-15) P. 211-213

Claims (12)

[Claims] 1. A semiconductor layer of a first conductivity type on a semi-insulating substrate, a second semiconductor layer of a first conductivity type which is a narrow gap compared to the first semiconductor layer, and a second semiconductor layer. In comparison with the first layer, a third semiconductor layer of the first conductivity type, which is a wide gear gap, is sequentially laminated, and a second semiconductor layer is formed on the active layer and first and third semiconductor layers are formed on the first multilayer epitaxial film. A lateral junction stripe laser having a cladding layer is formed, and a fourth semiconductor layer having a high-concentration impurity of the first conductivity type, a fifth semiconductor layer of the first conductivity type, and a fifth semiconductor layer on the first multilayer epitaxial film are formed. The fifth semiconductor layer is formed in the emitter and the sixth semiconductor layer on the second multilayer epitaxial film in which the sixth semiconductor layer of the second conductivity type, which is a narrow gap, is sequentially stacked in comparison with the semiconductor layer of The doped first conductivity type impurity region,
An optoelectronic integrated circuit comprising a heterojunction bipolar transistor based on a region sandwiched between an emitter and a collector in a sixth semiconductor layer. 2. An optical / electronic integrated circuit according to claim 1, wherein the first conductivity type is n-type and the second conductivity type is p-type. 3. The first, third and fifth semiconductor layers are AlGaAs, the second and fourth semiconductor layers are GaAs, and the sixth semiconductor layer is GaAs or AlGaAs. The optical / electronic integrated circuit according to item 1. 4. The first, third, and fifth semiconductor layers are InP, the second and fourth semiconductor layers are InGaAs or InGaAsP, and the sixth semiconductor layers are InP, InGaAs, or InGaAsP. An optical / electronic integrated circuit according to claim 1. 5. The base region of the sixth semiconductor layer has an Al composition of 0 at the connection portion with the collector and an Al composition at the connection portion with the fifth semiconductor layer equal to the Al composition of the fifth semiconductor layer. 4. The optoelectronic integrated circuit according to claim 3, wherein the Al composition is AlGaAs whose Al composition changes sequentially so as to be equal. 6. The optoelectronic integrated circuit according to claim 1, wherein the semi-insulating substrate is GaAs or InP. 7. A first semiconductor layer of a first conductivity type on a semi-insulating substrate, a second semiconductor layer of a first conductivity type which is a narrow gap compared to the first semiconductor layer, and a second semiconductor. A third semiconductor layer of the first conductivity type, which is a wide gap compared to the layers, is sequentially stacked to form a first multilayer epitaxial film.
A lateral junction stripe laser having the second semiconductor layer as an active layer and the first and third semiconductor layers as cladding layers in the multilayer epitaxial film, and the first conductive film is formed on the first multilayer epitaxial film. Type semiconductor layer having a high-concentration impurity, a fifth semiconductor layer of a first conductivity type, and a sixth semiconductor layer of a second conductivity type, which is a narrow gap compared to the fifth semiconductor layer, are sequentially stacked. Then, a second multilayer epitaxial film is formed, and a first conductivity type impurity region is selectively formed in the sixth semiconductor layer by ion implantation or a vapor phase diffusion method to form a fifth semiconductor layer. Manufacture of an optoelectronic integrated circuit characterized in that a heterojunction bipolar transistor based on an emitter, an impurity region of the first conductivity type is a collector, and a region sandwiched between the emitter and the collector in the sixth semiconductor layer is a base. Method. 8. The method of manufacturing an optoelectronic integrated circuit according to claim 7, wherein the first conductivity type is n type and the second conductivity type is p type. 9. The first, third and fifth semiconductor layers are AlGaAs, the second and fourth semiconductor layers are GaAs, and the sixth semiconductor layer is GaAs or AlGaAs. 8. A method for manufacturing an optical / electronic integrated circuit according to item 7. 10. The first, third and fifth semiconductor layers are InP, the second and fourth semiconductor layers are InGaAs or InGaAsP, and the sixth semiconductor layer is InP or InGaAs or InGaAsP. A method for manufacturing an optical / electronic integrated circuit according to claim 7. 11. In the base region of the sixth semiconductor layer, the Al composition in the connection portion with the collector is 0, and the Al composition in the connection portion with the fifth semiconductor layer is the Al composition of the fifth semiconductor layer. 10. The method for manufacturing an optical / electronic integrated circuit according to claim 9, wherein AlGaAs is such that the Al composition changes sequentially so as to be equal. 12. The method of manufacturing an optical / electronic integrated circuit according to claim 7, wherein the semi-insulating substrate is GaAs or InP.