JPS627176A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To improve the reliability of a semiconductor photodetector by forming a semiconductor layer having larger forbidden band width than a light absorption layer on a photoreceiving region and a guardring region to flatten the upper surface of a semiconductor substrate, thereby eliminating a concentration of an electric field and the decrease of a breakdown voltage and enhancing the bondability of electrodes. CONSTITUTION:An N-type InP buffer layer 2, an N-type InGaAs photoabsorbing layer 3, an N-type InGaAsP layer 4, an N-type InP avalanche multiplier layer 5 are grown by a liquid-phase epitaxial growing method on an N<+> type InP substrate 1, a mask is formed on the layer 5, the layer 5 is selectively removed, and an N<-> type InP layer 6 is buried and grown thereat. Then, the mask is removed, an N-type InGaAsP layer 7 is grown on the substrate so that the upper surface becomes flat. Then, a P<+> type photoreceiving region 8 is formed from the layer 5 to the layer 6, a P-type guardring region 9 is further formed to form a P-type side electrode 10 and an N-type side electrode 11 on the substrate. Thus, a breakdown weak point is controlled out of the photoreceiving region to improve the reliability of the electrode.

Description

[Detailed Description of the Invention] [Summary] The present invention provides an avalanche photodiode having a guard ring layer grown in a buried manner, by providing a transparent semiconductor layer that flattens the upper surface of the semiconductor substrate, thereby achieving a break outside the light-receiving area. This is to improve performance such as preventing downtime.

[Industrial application field]

The present invention relates to an improvement in a semiconductor light receiving device, particularly a compound semiconductor avalanche photodiode in which a guard ring is formed in a semiconductor layer having a lower impurity concentration than an avalanche multiplication layer.

In optical communications where light is used as an information signal medium, avalanche photodiodes (hereinafter abbreviated as APDs), whose photocurrent is multiplied by avalanche breakdown, are highly effective in improving the signal-to-noise ratio of photodetectors.

In particular, for optical communication systems using silica-based fibers, indium phosphorus/indium gallium arsenide (phosphorus) (InP/I
Compound semiconductor APDs such as nGaAs(P)) systems are important, and in this APD, a guard ring to prevent breakdown outside the light-receiving area is formed in a buried semiconductor layer with a lower impurity concentration than the avalanche breakdown layer. There are many things. However, with conventional APDs having this structure, the desired guard ring effect is often not achieved, and improvements are needed.

[Conventional technology]

A semiconductor substrate of an InP/InGaAs (P) type APD having a buried structure has a structure as shown in a schematic side sectional view of FIG. 2, for example.

In the figure, 1 is a type 1 InP substrate, 2 is an n-type InP buffer layer, 3 is an n-type TnGaAs light absorption layer, and 5 is an n-type I
nP avalanche multiplication layer, 6 a 1-type InP layer, 8 a p-type light receiving region, 9 a p-type guard ring region, 10 a p-side electrode, 1
1 is an n-side electrode.

A high reverse bias voltage is applied to this APD, with the A-type 1nP substrate 1 having positive polarity and the P-type light dissipating region 8 having negative polarity.
The avalanche breakdown in which the holes excited by the input signal light are used as primary carriers in the aAs optical absorption N3 is expressed by the forbidden band width In
This is caused by the InP avalanche multiplier layer 5 which is larger than the GaAs light absorption layer 3.

In order to prevent breakdown from occurring around the p-type light-emitting region 8 at a voltage lower than this avalanche breakdown, an n-type 1nP layer 6 with a lower impurity concentration than the avalanche multiplication layer 5 is provided, and the p-type A guard ring region 9 is formed in contact with the outer periphery of the p-type dissipating region 8, which is generally circular.

This conventional example is manufactured, for example, as follows.

That is, by a normal liquid phase epitaxial growth method, an n-type InP buffer layer 2, an n-type 1nG
An aAs light absorption layer 3 and an n-type 1nP avalanche multiplier layer 5 are grown, a mask with a thickness of, for example, about 0.1 to 0.2μ is provided on the N5, and the n-type InP avalanche multiplier layer is formed by meltback or the like. 5 is selectively removed to a depth of about 2 to 3 mm, for example, and an f-type InP layer 6 is buried and grown there to form a semiconductor substrate.

For example, cadmium (Cd) is diffused into this semiconductor substrate to a depth of about 1 to 2p, and the p-type light-emitting region 8 is replaced with n-type In.
A p-type guard ring region is formed extending from the P avalanche multiplication layer 5 to the n-type InP layer 6, and by implanting, for example, ions of beryllium (Be) into the n-type InP layer 6 and performing activation heat treatment, a p-type guard ring region with a gentle p-n junction is formed. form 9.

[Problem that the invention seeks to solve]

In the above manufacturing method, the selective removal of the n-type InP avalanche multiplication layer 5 and the buried growth of the n-type 1nP layer 6 are carried out using a common mask. For reasons such as the fact that the growth rate of the mask is higher than that of the flat portion, a step 6^ is formed in the buried n-type InP layer 6, which is limited at the edge of the mask, as shown in the figure.

This step generated in the n-type InP layer 6 is reflected in the p-type light-emitting region 8 due to the above-mentioned Cd diffusion, and a curved portion 8A is formed on the p-n junction surface, and when a high reverse bias voltage is applied to the p-n junction, This causes electric field concentration here. As a result, the curved portion 8
Although A is formed in the n-type 1nP layer 6 with a lower impurity concentration than the avalanche multiplication N5, it may break down at a lower voltage than the avalanche breakdown.

Further, the level difference 6A on the upper surface of the semiconductor substrate may reduce the adhesion of the electrode material by vapor deposition or the like.

As explained above, in an APD having a buried structure, the step caused by the buried growth layer becomes a weak point such as breakdown, and it is desired to deal with this.

[Means for solving problems]

The problem is that, as in the embodiment shown in FIG. 1, for example, a second semiconductor of the first conductivity type, which has a larger forbidden band width than the first semiconductor N3, is placed on the first semiconductor layer 3 that performs photoelectric conversion. layer 5; a third semiconductor N6 of the first conductivity type, which has a larger forbidden band width than the first semiconductor layer 3 and is grown in a buried manner by selectively removing the second semiconductor layer; a fourth semiconductor layer 7 having a larger forbidden band width than the semiconductor layer 3 and having a flat top surface covering the second and third semiconductor layers 5.6; This problem is solved by the semiconductor light receiving device according to the present invention, in which a region 8 of the second conductivity type forming a pn junction is formed in the semiconductor M5.6 of No. 3.

[For production]

In the semiconductor light receiving device according to the present invention, a semiconductor layer having a larger forbidden band width than the light absorption layer, that is, transparent to the target light, is provided on the light receiving region and the guard ring region,
The top surface of the semiconductor substrate is flat.

Therefore, the pn junction is flat even under the stepped portion caused by buried growth, and the guard ring effect is ensured without causing electric field concentration or reduction in breakdown voltage as in the conventional example.

Moreover, the adhesion of the electrodes is not impaired, and high reliability can be obtained.

〔Example〕

The present invention will be specifically explained below with reference to an embodiment whose schematic side sectional view is shown in FIG.

The semiconductor substrate of this example is manufactured, for example, as follows.

For example, an n-type 1nP buffer layer 2,
Thickness is approximately 2.5- and impurity temperature is approximately 5X10'Scm-'
N-type InGaAs optical absorption N3, thickness approximately 0.5I! rn
n-type InG with an impurity temperature of about 1×10I6CI11-3
aAsP (for example, luminescence peak wavelength λg = 1.
3-) Layer 4, thickness of about 3 pm and impurity temperature of about 3×101
An n-type InP avalanche multiplier layer 5 of 6cI11-3 is grown. A mask with a thickness of approximately 0.15 mm is provided on this N5 using, for example, silicon nitride (Si, N4), and the n-type 1nP avalanche multiplication layer 5 is selectively formed, for example, by a melt bank to a depth of approximately 2.5 mm. Remove impurities here at a temperature of about 5X10”
Embed and grow cm-arch n-type InPJii6.

The mask is then removed and onto this substrate, for example λg =
1.15-1 n-type I with impurity concentration of approximately 5X10"cm-'
The nGaAsP layer 7 is grown so that its upper surface is flat.

The reason why InGaAsP is used for the layer 7 in this embodiment is that it is particularly suitable for alleviating and flattening the step when grown by liquid phase epitaxial growth, for example, on InP iJ having a step.

In addition, as is already known, InGaAsP iJ 4 eases the difference in level between the light absorption layer 3 and the avalanche multiplication layer 5 in the valence band and conduction band to facilitate carrier drift,
It has the effect of speeding up the response.

For example, cadmium (Cd) is diffused into this semiconductor substrate at a temperature of about 2 x 1010l1lC and to a depth of about 1.5- to a p+ type light receiving region 8n type 1nP avalanche multiplication layer 5 to n
- type TnP layer 6, and furthermore, for example, beryllium (Be) is formed at an energy of 140 keV and a dose of 15X.
Ions are implanted into the lnP layer 6 to a depth of approximately 10" 4, and an activation heat treatment is performed at a temperature of 700.degree. C. for approximately 20 minutes to form a p-type guard ring region 9.

Regarding this example in which the p-side electrode 10 and the n-side electrode 11 are formed on this semiconductor substrate, the breakdown voltage vB=68
v, bias voltage 0.9 for light with a wavelength of 1.3 μm
A multiplication factor M#30 is obtained in V, which is a remarkable effect compared to the APDO multiplication factor M of the conventional example, which is about 20 at most.

〔Effect of the invention〕

As described above, according to the present invention, the occurrence of breakdown weak points outside the light-receiving region is sufficiently suppressed, and avalanche multiplication is realized as designed. Furthermore, the reliability of the electrode is improved, and it becomes possible to manufacture APDs with good characteristics at an excellent yield.

[Brief explanation of drawings]

FIG. 1 is a schematic side sectional view of an embodiment of the present invention, and FIG. 2 is a schematic side sectional view of a conventional example. In the figure, 1 is a 1-type InP substrate, 2 is an n-type 1nP buffer layer, 3 is an n-type InGaAs light absorption layer, and 4 is an n-type 1nGaAsPN. 5 is an n-type 1nP avalanche multiplication layer, 6 is an n-type lnP buried layer, 7 is an n-type 1nGaAsP layer according to the present invention, 8 is a p-type light receiving region, 9 is a p-type guard ring region, 10 and 11 are electrodes shows.

Claims (1)

[Claims] A second semiconductor layer (5) of the first conductivity type having a larger forbidden band width than the first semiconductor layer (3), on the first semiconductor layer (3) that performs photoelectric conversion. , whose forbidden band width is larger than that of the first semiconductor layer (3), and whose forbidden band width is larger than that of the first semiconductor layer (3).
A third semiconductor layer (6) of the first conductivity type, which is grown by selectively removing the semiconductor layer (5) of a fourth semiconductor layer (7) having a flat top surface covering the second and third semiconductor layers (5) and (6); 6) A semiconductor light receiving device characterized in that a second conductivity type region (8) forming a pn junction is formed in step 6).