JP3149026B2 - Manufacturing method of semiconductor light receiving element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for manufacturing a semiconductor light receiving element suitable for constituting a receiver in an optical communication system using light having a wavelength of 1 [μm] band. Good quality I between carrier multiplication layer
Forming an nGaAsP graded layer to improve the frequency characteristics of this type of light-receiving device, and supply the raw material from the gas line onto the substrate by applying metal-organic vapor phase deposition. To grow a light absorbing layer made of InGaAs, and then successively supply a source gas from the same gas line as the gas line and grow a graded layer made of InGaAsP while changing the composition,
Next, a step of continuously supplying a source gas from the same gas line as the gas line to grow a carrier multiplication layer made of InP is provided.

[Industrial applications]

The present invention relates to a method for manufacturing a semiconductor light receiving element suitable for forming a receiver in an optical communication system using light having a wavelength of 1 [μm].

Generally, in a long-distance optical communication system, light having a wavelength of 1 [μm] band is often used due to a waveguide or the like, and an avalanche photo diode (APD) is used. ) Is said to be optimal for constructing a high-sensitivity receiver because it has an amplification function inside.

At present, to deal with the increase in capacity of optical communication systems, AP
Development and research has been done on making D faster. An APD used in the 1 [μm] band is basically composed of a light absorption layer of an InGaAs layer lattice-matched to an InP substrate, and a carrier multiplication layer of an InP layer grown thereon. In order to improve the frequency response by facilitating hole injection by eliminating sharp differences in band discontinuity between the light absorption layer and the InP carrier multiplication layer, the InGaAs light absorption layer and the InP carrier A thin film made of a quaternary mixed crystal such as InGaAsP is interposed between the multiplication layer,
The effect is not so good, and it seems to be applicable to ultra-high-speed optical communication systems targeting 10 [Gbit / s].
APD has not been realized.

An APD having a promising configuration for ultra-high speed has been proposed in which an InGaAsP graded layer whose composition slowly changes is interposed between an InGaAs light absorption layer and an InP carrier multiplication layer.

However, there is no technology that can easily manufacture such an APD, and thus it has not been realized yet.

[Conventional technology]

Usually, InGaAs / InP-based APDs use liquid phase growth (liquid phase growth).
epitaxy: LPE method, or metalorganic vapor phase epitaxy (metalor
It is often manufactured using epitaxially grown crystals grown by the ganic vapor phase epitaxy (MOVPE) method.

However, by applying LPE method or MOVPE method, InGaAsP
No graded layer is formed.

Among them, it is very difficult to form an InGaAsP layer whose composition is gradually graded by the LPE method, and it is considered that it is almost impossible in the near future. In addition, when the MOVPE method is used, the InGaAsP graded layer should be formed in principle by controlling the flow rate of the source gas, but in practice, it is difficult to control the graded layer.
Not realized.

[Problems to be solved by the invention]

In the present invention, by applying the MOVPE method, InGaA
Good quality InGaAsP between s light absorbing layer and InP carrier multiplication layer
A graded layer is formed to improve the frequency characteristics of this type of light receiving element.

[Means for solving the problem]

In general, the In _1-x Ga _x As _y P _1-y mixed crystal is obtained from the longest wavelength InGaAs (photoluminescence wavelength λ _PL = 1.67 [μm]) under the condition of lattice matching with InP. It is a useful material covering up to InP (photoluminescence wavelength λ _PL = 0.94 [μm]).

Figure 1 is, in the case of growing the該混crystallize become known lattice matching conditions for in various compositions to the coverage of _{In 1-x Ga x As y} P 1-y mixed crystal, FIG. 3 is a diagram showing the relationship between the raw material gas flow rate and the solid phase composition of P (1-y), wherein the vertical axis represents the raw material gas flow rate, and the horizontal axis represents the solid phase composition of P (1-y). y) is taken respectively.

In the figure, TMI is trimethylindium, ie, (C
H ₃ ) ₃ In, TEG is triethylgallium, that is, (C ₂ H ₅ ) ₃ G
a, respectively, and it goes without saying that AsH ₃ (arsine) is a raw material of As and PH ₃ (phosphine) is a raw material of P. Note that under lattice matching conditions, There is a relationship.

If the data shown in FIG. 1 is known, the target semiconductor layer configuration for APD can be realized by controlling the mass flow controller of the raw material gas so as to follow each flow rate curve shown in the figure. Can be.

As described above, in the method for manufacturing a semiconductor light receiving element according to the present invention, (1) a raw material from a gas line is applied to a substrate (for example, n ⁺ Type InP substrate 1)
A light absorbing layer made of InGaAs (e.g., n-type InGa
As light absorbing layer 2) is grown, and then the same gas line as said gas line
InGaAs while supplying source gas from line and changing composition
A graded layer made of P (for example, an n-type InGaAsP graded layer 3) is grown, and subsequently, the same gas line as the gas line is used.
Supplying a source gas from the line to grow a carrier multiplication layer made of InP (for example, an n-type InP carrier multiplication layer 4); or (2) the method according to (1), (3) In the step (1), the step of extending the growth time to alleviate the sudden rise of the source gas as the source of P when growing the graded InGaAsP layer is included. And growing a light absorbing layer made of InGaAsP instead of growing the light absorbing layer made of InGaAs.

[Action]

By taking the above measures, InGaAs or InGaAsP
InGa with good crystallinity and smooth composition change between the light absorption layer composed of InP and the carrier multiplication layer composed of InP
Since the holes are connected by a graded layer made of AsP, holes can be easily injected from the light absorption layer to the carrier multiplication layer at a low voltage, so that the frequency characteristics are improved, and
Dark current can be reduced, and a high-performance semiconductor light receiving element can be realized.

〔Example〕

FIG. 2 is a sectional side view for explaining a main part of a semiconductor layer formed according to an embodiment of the present invention.

In the figure, 1 is an n ⁺ -type InP substrate, 2 is an n-type InGaAs light absorbing layer, 3 is an n-type InGaAsP graded layer, and 4 is an n-type InP carrier multiplication layer. The light absorbing layer 2
May be InGaAsP.

The main data in this semiconductor layer configuration is exemplified as follows.

(A) About substrate 1 Impurity: S Impurity concentration: 4 × 10 ¹⁸ [cm ⁻³ ] (b) About light absorbing layer 2 Thickness: 1.5 [μm] Impurity: Si Impurity concentration: 2 × 10 ¹⁵ [cm ^−3] (C) Graded layer 3 Thickness: 0.1 [μm] Impurity: Si Impurity concentration: 2 × 10 ¹⁵ [cm ^-3 ] (d) Carrier multiplication layer 4 Thickness: 2.0 [μm] Impurity: Si Impurity concentration: 2 × 10 ^{17 for} the thickness of 0.05 [μm] on the substrate side
[Cm ^-3 ] The thickness of the surface side 1.95 [μm] is 5 × 10 ¹⁵
[Cm ^-3 ] By the way, the growth rate of each semiconductor layer shown in the drawing, that is, the growth rate of the InGaAsP-based mixed crystal including InGaAs and InP is 1.5 [μm / hour]. Since the thickness of the graded layer 3 is 0.1 [μm], the growth time is 240 [seconds].

As is apparent from Figure 1, among the four types of raw material gas, only PH ₃ is rise in InGaAs vicinity is steep. For this reason, after growing the InGaAs light absorbing layer 2, about 10
With a growth time of about [sec], a situation occurs where PH ₃ changes rapidly from 0 to 400 [cc / min], and P
Of the solid phase composition is as small as 0 → 0.04. As a result,
When the source gas is controlled as shown in FIG. 1, the gas flow is likely to be disturbed, and skill is required to obtain a good grade.

To avoid such problems, the rising steep region of PH _3, that is, at the region where the P composition changes to 0 → 0.04, it is preferable to increase the growth time.

Figure 3 represents a diagram for explaining an example of controlling the flow rate of PH _3, a raw material gas flow rate on the vertical axis and the horizontal axis are taking a growing time, respectively.

As is apparent from the figure, the rise of PH ₃ is 1/10 as compared with the normal case, that is, the P composition becomes 0
By setting the ratio to 0.04, a good graded layer can be formed without disturbance of the gas flow.

FIG. 4 shows an energy band diagram relating to the semiconductor layer structure shown in FIG. 2 formed by using the technique described with reference to FIG. 3, and the same symbols as those used in FIG. Shall represent or have the same meaning.

In FIG, E _v Section of the valence band, the E _c indicates the bottom of the conduction band, respectively.

In the figure, the dashed lines indicate the energy bands related to the semiconductor layer configuration obtained by the growth performed without applying the technique described with reference to FIG. 3, and there is almost no difference in the case according to the embodiment of the present invention. No problem for APD.

According to the present embodiment, a good graded layer can be grown without switching the gas line, in other words, without interrupting the growth.

Incidentally, the rise of PH ₃ was a problem for the first view, i.e., the amount of change in photoluminescence wavelength lambda _PL when a 0 → 0.04 at P composition is a very small, 1.67
[Μm] → 0.02 [μm] from 1.65 [μm]. Usually, the wavelength of the light source used for optical communication is 1.30 [μm],
Or 1.55 [μm], considering the light receiving element,
Even if the photoluminescence wavelength λ _PL of the light absorbing layer changes from 1.67 [μm] to 1.65 [μm], it does not cause a serious problem.

If this concept is introduced, the light absorption layer has a P composition of 0.
By using about 05 InGaAsP, a good graded layer can be formed without encountering a sudden change in the PH ₃ flow rate shown in FIG.

FIG. 5 shows a diagram for explaining an example of controlling the PH ₃ flow rate in the case where the above concept is introduced, in which the vertical axis represents the source gas flow rate, and the horizontal axis represents the growth time. It is taken.

As is clear from the figure, in the present embodiment, the composition of the light absorbing layer was merely changed from InGaAs to InGaAsP having a P composition of 0.04. In such a case, the graded layer laminated thereon had InGaAsP. In this case, the P composition is changed from 0.04 to 1 without any problem, and a good graded layer can be formed without the need for gas line switching.

〔The invention's effect〕

In the method for manufacturing a semiconductor light receiving element according to the present invention,
The material from the gas line is supplied onto the substrate by applying a metal organic chemical vapor deposition method to grow a light absorbing layer made of InGaAs, and then subsequently the same gas line as the gas line A raw material gas is supplied from and a graded layer made of InGaAsP is grown while changing the composition, and then a source gas is supplied from the same gas line as the gas line to form a carrier multiplication layer made of InP. Including the step of growing.

Depending on the configuration, InGaAs or InGaAsP
InGa with good crystallinity and smooth composition change between the light absorption layer composed of InP and the carrier multiplication layer composed of InP
Since the holes are connected by a graded layer made of AsP, holes can be easily injected from the light absorption layer to the carrier multiplication layer at a low voltage, so that the frequency characteristics are improved, and
Dark current can be reduced, and a high-performance semiconductor light receiving element can be realized.

[Brief description of the drawings]

Figure 1 is _{In 1-x Ga x As y} P diagram showing the relationship between the _1-y solid composition of the feed gas flow rate and P at the time of mixed crystal is grown (1-y), FIG. 2 main part sectional side view for explaining a semiconductor layer structure which is formed by a one embodiment the present invention, FIG. 3 is diagram for explaining an example of controlling the flow rate of PH _3, Fig. 4 a third energy band diagram relating to a semiconductor layer structure seen in Figure 2 formed by using the techniques described for Figure, Figure 5 shows a diagram for describing an example of controlling the PH ₃ flow rate, respectively. In the figure, 1 is an n ⁺ -type InP substrate, 2 is an n-type InGaAs light absorbing layer, 3 is an n-type InGaAsP graded layer, and 4 is an n-type InP carrier multiplication layer.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-133970 (JP, A) JP-A-59-136981 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/10-31/119

Claims (3)

(57) [Claims] The present invention relates to a method for producing a light absorbing layer of InGaAs by supplying a raw material from a gas line onto a substrate by applying a metal organic chemical vapor deposition method. InGaAsP while supplying source gas from the same gas line and changing the composition
Growing a graded layer consisting of: and then successively supplying a source gas from the same gas line as the gas line to grow a carrier multiplication layer made of InP. A method for manufacturing a semiconductor light receiving element. 2. The method according to claim 1, further comprising a step of extending a growth time to alleviate a sudden rise of a source gas as a source of P when growing the InGaAsP graded layer. A method for manufacturing a semiconductor light receiving element according to the above. 3. The method according to claim 1, further comprising the step of growing a light absorbing layer made of InGaAsP instead of growing the light absorbing layer made of InGaAs.