JPH0682815B2 - Optical integrated circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a structure of an optical integrated circuit in which a photodiode and a heterojunction bipolar transistor (HBT) are integrated in the same chip.

2. Description of the Related Art The optical integrated circuit of the present invention intends to integrate a photodiode and an HBT as separate elements on the same chip. However, a heterojunction phototransistor (HPT) has been used as a single element having both the functions of the photodiode and the HBT. )It has been known. As the conventional structure of HPT, for example, JC Campb
ell et al., “InP / InGaAs Heterojunction Phototransistor
s, "IEE Journal of Quantum Electronics (IEEE J.Quantum Electro
n.), vol.QE-17, P.264 (1981). In this structure, an n-type InP substrate 1 is used as an emitter, and a p-type InGaAs base 2 and an n-type InGaAs collector 3 are stacked on it to form an HPT. An Au—Sn electrode 4 is vapor-deposited on the InP substrate (emitter) 1 and collector 3, and if a bias voltage is applied between them, a photocurrent flows by incident light 5 from the substrate side.

Problems to be Solved by the Invention The HPT is a light-receiving element having an amplifying function, and it has been reported that it has a gain of 1000 times or more, but it has a drawback of slow response speed. The first reason is that the light receiving area and the area of the transistor are equal.
That is, a certain amount of light receiving area is required in order not to reduce the light receiving efficiency, and as a result, the area of the transistor also becomes large, so that the junction capacitance increases and the speed becomes slow. Second
The reason for this is that the normal HPT is not provided with a base electrode, and the speed becomes slow due to the effect of accumulating excess carriers in the base. In order to solve these two points, the light receiving function and the amplifying function may be shared by different elements (photodiode and HBT), and the respective structures may be optimized and then integrated in the same IC chip. The present invention not only provides a structure for simply integrating a photodiode and an HBT, but also provides an integrated structure in which the photodiode and the HBT have a structure suitable for high-speed operation. An optical integrated circuit having a function and high speed can be realized.

Means for Solving the Problems In order to solve the above problems, the present invention provides a semiconductor substrate,
A light absorbing layer and a light transmitting layer sequentially stacked on the semiconductor substrate, a diffusion region formed in a partial region of the light absorbing layer and the light transmitting layer, and a region other than the diffusion region of the light transmitting layer. A base and an emitter (or a collector) sequentially laminated on a partial region; a photodiode formed by the light absorption layer and the light transmission layer in the diffusion region; the emitter (or collector), the base and the An optical integrated circuit is configured with a structure including a hetto-junction bipolar transistor formed by the light transmitting layer immediately below the base.

Action The optical integrated circuit of the present invention can operate at a higher speed than the HPT because the light receiving function and the amplifying function are separated and the structure of the photodiode and the HBT is optimized with respect to two points of the laminated structure and the device area. It is a thing. That is, in the laminated structure, the light absorption layer of the photodiode and the base of the HBT are independent semiconductor layers, and the thickness and the carrier concentration can be optimized so as to speed up each device. Regarding the device area, make sure that the photodiode area is large enough to receive light, and then
Can be speeded up by miniaturization. Also,
Since the number of integrated HBTs is not limited to one,
It also becomes possible to integrate a photodiode and an amplifier circuit composed of multiple HBTs. Since the base electrode is naturally provided also in the first stage HBT connected to the photodiode, another appropriate base bias current of the photocurrent from the photodiode can flow. This also accelerates the speed.

Embodiment FIG. 1 is a sectional view showing an embodiment of the optical integrated circuit of the present invention. An n ⁻ type InGaAs light absorption layer 7 and an n type InP light transmission layer 8 are stacked on a semi-insulating InP substrate 6, and a pin photodiode 10 is formed together with a p type diffusion region 9 formed by Zn vapor phase diffusion or the like. I am configuring. A ring-shaped P-side electrode 11 and an n-type electrode 12 are vapor-deposited on the photodiode 10,
A region inside the P-side electrode 11 serves as a light receiving surface. For example, Cr / Pt / Au is used as the P-side electrode, and Au is used as the n-side electrode.
Use -Sn. On the other hand, the light transmission layer 8 other than the region where the photodiode 10 is formed serves as a collector 13, on which a p-type InGaAsP base 14 and an n-type InP emitter 15 are laminated to form an HBT 16. In addition to the collector electrode 17 and the emitter electrode 18, a base electrode 20 via a graft base 19 is vapor-deposited on the HBT 16. Graft base 19
Is a region in which a part of the emitter 15 is inverted to p-type by vapor phase diffusion of Zn or the like.

The photodiode 10 and the HBT 16 are electrically separated by a separation diffusion region 21 in which a partial region of the light transmission layer 8 and the light absorption layer 7 is inverted to p-type. Although not shown in FIG. 1, a wiring made of wiring metal is provided between the photodiode and the HBT electrode. For example, Ti / Au is used as the wiring metal, and wiring is performed on the insulating film 22 such as the SiN film that covers the substrate surface.
Although only one HBT is shown in FIG. 1, two or more HBTs may be integrated, or an integrated circuit of an amplifier circuit and a photodiode in which a plurality of HBTs are wired. Further, part or all of the HBT may be used as the reverse transistor. The reverse transistor is the HBT in Fig. 1.
The collector is used as the emitter and the emitter is used as the collector.

The photodiode of the present optical integrated circuit has a so-called windowed structure, and incident light is absorbed by the light absorption layer without being absorbed by the light transmission layer. Therefore, when the light transmitting layer is InP and the light absorbing layer is InGaAs as described above, there is sensitivity in the wavelength range of incident light of 0.9 to 1.6 μm. Conversely, for example, the wavelength
For the purpose of receiving light of 1.3 μm, the light transmission layer may be InGaAsP having a bandgap wavelength λg> 1.3 μm, and the light absorption layer may be InGaAsP having λg ≦ 1.3 μm. Further, a material having a band gap in the middle between the light transmitting layer and the light absorbing layer may be sandwiched between, for example, the InP light transmitting layer and the InGaA layer.
s An InGaAsP layer of λg = 1.3 μm may be provided between the light absorption layers. This intermediate layer not only improves the response speed of the photodiode, but also functions as an anti-meltback layer when crystal growth is performed by the liquid phase epitaxial (LPE) method. . The photodiode with a window has an advantage that the quantum effect is higher than that without a window, and in the case of a planar type in which a portion where the pn junction is exposed on the crystal surface is in the light transmission layer, a dark current is generated. There is also the effect of becoming smaller. This is because, for example, if the pn junction is exposed on the InGaAs surface, the leakage current through that portion becomes very large and unstable, whereas this does not occur on the InP surface.

The light transmitting layer of the present optical integrated circuit also plays a large role in manufacturing. That is, if there is no light transmission layer in the structure of FIG. 1, selective etching cannot be performed when performing mesa etching while leaving the emitter and base of the HBT. This is because there is no known etching solution that etches InGaAsP sufficiently faster than InGaAs. On the other hand, InGaAsP rather than InP
Since a H ₂ SO ₄ -based etchant is used to etch satisfactorily, selective etching is possible if there is a light-transmitting layer. Further, as an advantage in manufacturing the present optical integrated circuit, there is a point that the entire structure has a substantially planar structure.

As described above, this optical integrated circuit has the advantage that high speed can be achieved by integrating the photodiode and HBT individual elements, and the photodiode has a window with high quantum efficiency and low dark current. Further, it has an advantage that its manufacture is easy.

FIG. 2 is a sectional view showing a second embodiment of the optical integrated circuit of the present invention. Basically, it is the same as that shown in FIG. 1, and the same parts are given the same numbers. This embodiment is different from that shown in FIG. 1 in that the n ⁺ buried layer 23 is provided to reduce the series resistance of the n layer of the photodiode and the collector resistance of the HBT and the element isolation is performed by the dielectric 24. It is that you are. The material of the n ⁺ buried layer 23 is InP, InGaA
It may be either s or InGaAsP. As the dielectric 24, SiN, polyimide, silica glass, or the like is used. By using dielectric isolation, it is possible to reduce the parasitic capacitance, and it is possible to avoid the breakdown voltage failure between the n ⁺ buried layer and the isolation diffusion region which occurs in the case of diffusion isolation.

In the description of the above examples, the semiconductor material is In
Although the P-based material has been used, other semiconductor materials may be used. It is also possible to use a pin photodiode as an avalanche photodiode.

EFFECTS OF THE INVENTION As described above, according to the present invention, an optical integrated circuit capable of high-speed operation is obtained by integrating a photodiode and an HBT and optimizing the structure of the photodiode and the HBT with respect to two points of a laminated structure and a device area. Can be configured. Further, the integrated photodiode is a planar type with a window having high quantum efficiency and low dark current, and the optical integrated circuit itself has a substantially planar structure and is easy to manufacture.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical integrated circuit according to an embodiment of the present invention, and FIG.
FIG. 3 is a sectional view of an optical integrated circuit according to a second embodiment of the present invention, and FIG.
The figure is a cross-sectional view of a conventional heterojunction phototransistor. 6 ... Substrate, 7 ... Light absorbing layer, 8 ... Light transmitting layer, 10 ...
Photodiode, 13 ... Collector, 14 ... Base, 15 ...
… Emitter, 16 …… Heterojunction bipolar transistor (HBT).

Claims (1)

[Claims] 1. A semiconductor substrate, a light absorbing layer and a light transmitting layer sequentially stacked on the semiconductor substrate, and a diffusion region formed in a partial region of the light absorbing layer and the light transmitting layer.
A photodiode formed by the light absorption layer and the light transmission layer in the diffusion region, the base and the emitter (or the collector) sequentially stacked on a part of the light transmission layer other than the diffusion region; An optical integrated circuit comprising: a heterojunction bipolar transistor formed by the emitter (or collector), the base, and the light transmission layer immediately below the base.