JPH0637350A - Light signal receiver - Google Patents

Abstract

PURPOSE:To improve the nonlinear distortion of an avalanche photodiode. CONSTITUTION:A carrier doubling layer 7 of an avalanche photodiode 1 comprises a superlattice semiconductor layer in which well layers made of In1-(x+y)AlxGayAs1-zPz (where, 0<=x<1, 0<y<=1, 0<=z<1) and barrier layers made of In1-uAluAs (where, 0<u<1) are laminated sequentially and alternately. When the ionization rates of electrons and holes of carrier doubling layer are alphaand beta and the current amplification factor is M and natural logarithm is In for the avalanche photodiode, the light absorption layer 9 has the thickness of less than 1mum with the thickness of W=(1/alpha) In (M/(1+M(beta/alpha)). The avalanche photodiode has means of taking in a light signal from the side of a semiconductor substrate 5 and means of reflecting an incident light signal at the opposite side of the semiconductor substrate when seen from the light absorption layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal receiver using an avalanche photo diode.

[0002]

2. Description of the Related Art Conventionally, a carrier multiplication layer and a light absorption layer are laminated on a semiconductor substrate made of InP,
In addition, an avalanche photodiode configured to receive an analog-modulated optical signal and output a photocurrent corresponding to the intensity of the signal is used, and the carrier multiplication layer has an In
Various optical signal receivers have been proposed, which are composed of a single semiconductor layer of P.

According to the optical signal receiver using such an avalanche photodiode, since the avalanche photodiode used therein has a carrier multiplication layer, it is incident from the avalanche photodiode. The photocurrent corresponding to the intensity of the optical signal that is output is multiplied and output.Therefore, the optical signal is compared with the case of an optical signal receiver that uses a simple photodiode without a carrier multiplication layer. , With high sensitivity, can be received.

[0004]

However, in the case of the above-mentioned conventional optical signal receiver, the carrier multiplication layer of the avalanche photo diode used therein is composed of a single semiconductor layer of InP. , The ratio α / β of the electron ionization rate α of the avalanche photodiode to the ionization rate of the hole is close to 1, and therefore the current multiplication factor of the avalanche photodiode changes the intensity of the incident optical signal. Therefore, the photocurrent output from the avalanche photo diode is accompanied by a large non-linear distortion with respect to the incident optical signal.
It has the drawback of being accompanied by a large non-linear distortion due to the non-linear distortion of the photocurrent output from the avalanche photo diode.

The present invention therefore proposes a new optical signal receiver without the above-mentioned drawbacks.

[0006]

The optical signal receiver according to the present invention, as in the case of the conventionally proposed optical signal receiver, has a semiconductor layer as a carrier multiplication layer and an optical layer on a semiconductor substrate made of InP. An avalanche photodiode having a structure in which a semiconductor layer as an absorption layer is laminated in that order, and configured to receive an analog-modulated optical signal and output a photocurrent corresponding to its intensity. However, the semiconductor layer as the carrier multiplication layer of the avalanche photo diode is In _{1- (x + y)} Al _x G
a _y As _{1- z} P _z (where 0 ≦ x <1, 0 <y ≦ 1,
0 ≦ z <1), a semiconductor layer as a well layer, and In
It is a superlattice semiconductor layer having a structure in which _1-u Al _u As (however, 0 <u <1) semiconductor layers as barrier layers are alternately laminated. In this case, the semiconductor layer as the light absorption layer of the avalanche photo diode,
It is acceptable that it is made of InGaAs and has a thickness of 1 μm or less.

Further, the avalanche photodiode is provided with a means for making the optical signal incident on the side of the semiconductor substrate opposite to the semiconductor layer side as the light absorption layer,
It is possible to have means for reflecting the light of the incident optical signal on the side opposite to the semiconductor substrate side as viewed from the semiconductor layer as the light absorption layer.

Further, the avalanche photodio
In the semiconductor layer as the carrier multiplying layer, the ionization rates of electrons and holes in the semiconductor layer as the carrier multiplying layer are determined by α and β, respectively, and the ionization rates of the electrons and holes are determined by α and β. When the current multiplication factor of the avalanche photo diode is M and the natural logarithm is In, W = (1 / α) In (M / (1 + M (β /
It is acceptable to have a thickness W given in α))). Is acceptable.

[0009]

According to the optical signal receiver of the present invention, the nonlinear distortion of the photocurrent output from the avalanche photo diode is significantly smaller than that of the conventional optical signal receiver. Non-linear distortion due to non-linear distortion of the photocurrent output from the avalanche photodiode is smaller than that in the case of the conventional optical signal receiver in receiving the optical signal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an optical signal receiver according to the present invention will be described with reference to FIGS.

The optical signal receiver according to the invention shown in FIGS. 1 and 2 has, as shown in FIG. 1, a demodulator 4 known per se on the output side, an amplifier 3 known per se.
Is connected to the avalanche photocoupler for receiving the incident analog-modulated optical signal LS via the known optical fiber 2 and outputting the photocurrent LI corresponding to the intensity of the optical signal LS to the amplifier 3. It has a configuration using a diode 1.

[0012] In this case, avalanche photodiode - de 1, as shown in FIG. 2, on the semiconductor substrate 5 and having a n ⁺ -type becomes in InP, semiconductor as a buffer layer and having a n ⁺ -type becomes in InP The layer 6, the semiconductor layer 7 as a carrier multiplication layer described later, and the p ⁺ type by being made of InP and having a relatively high p type impurity concentration of 8 × 10 ¹⁷ cm ⁻³ and having a p ⁺ type conductivity
A semiconductor layer 8 having a relatively thin thickness, such as A,
A semiconductor layer 9 as a light absorption layer described later, and GaA
s and having a relatively high p-type impurity concentration of, for example, 2 × 10 ¹⁷ cm ⁻³ , thereby having p ⁺ type and having a thickness of, for example, 500 A.
0, for example InP and for example 1 × 10 ¹⁸ cm ⁻³
The semiconductor layer 11 has ap ⁺ type by having such a relatively high p-type impurity concentration and has a thickness of, for example, 1000 A, and is made of, for example, InGaAs-based, for example, In _0.53 Ga _0.47 As and is, for example, 1 × 10.
By having a relatively high p-type impurity concentration such as ¹⁸ cm ⁻³ , it has p ⁺ -type and has, for example, 1000
The semiconductor layer 12 having a thickness of A is formed by laminating in that order.

The avalanche photo diode 1
Has an electrode layer 15 provided on the semiconductor substrate 5 on the side opposite to the side of the semiconductor layer 9 as a light absorbing layer and having a light incident window 14 through which the optical signal LS is incident, and the semiconductor layer 9 as a light absorbing layer. From the viewpoint, an electrode also serving as a light reflection layer that is provided on the semiconductor layer 12 on the side opposite to the semiconductor substrate 5 side so as to face the light incident window 14 and that reflects the light of the incident optical signal LS. And layer 13.

Further, in the avalanche photo diode 1 described above, the semiconductor layer 7 as the carrier multiplication layer described above is In _{1- (x + y)} Al _x Ga _y As _1-z P
_z (where 0 ≦ x <1, 0 <y ≦ 1, 0 ≦ z <1), for example, In _{1- (x + y)} Al _x Gay _y As _1-z P _z
Of In _0.53 Ga _0.47 As in which x is 0, y is 0.47, and z is 0, and is 10
The semiconductor layer 7a as a well layer having a thin thickness such as 0A and In _1-u Al _u As (where 0 <u <
1), but _{u of} In _1-u Al _u As is 0.4, for example.
Becomes 8 to In _{0.5 2} Al _0.48 As, a semiconductor layer 7b as a barrier layer are laminated sequentially and alternately, for example, 22 times and having a thin thickness such as for example 100A,
In addition, the superlattice semiconductor layer has a structure in which neither n-type impurities nor p-type impurities are intentionally introduced.

In the avalanche photo diode 1 described above, the semiconductor layer 7 as the carrier multiplication layer made of the superlattice semiconductor layer described above is used as a carrier multiplication layer for the electrons and holes in the semiconductor layer 7. The ionization rates are α and β, respectively, and those of electrons and holes are α
And avalanche photodiode 1 determined by β
Where M is the current multiplication factor and In is the natural logarithm, W = (1 / α) In (M / (1 + M (β / α))) ………………………… (1) Have. In this case, specifically, the thickness W is the ratio α of the ionization rates α and β of electrons and holes when the semiconductor layer 7 as the carrier multiplication layer is the superlattice semiconductor layer having the above-described configuration. / Β can be set to, for example, “10”, which is significantly larger than “1” when the semiconductor layer 7 as the carrier multiplication layer is a single semiconductor layer made of InP. Ionization rate of holes α
And β in the equation (2), which is the reciprocal of the ratio α / β
Can be set to, for example, “0.1”, and when x and x ′ are distances in the thickness direction of the semiconductor layer 7 as a carrier multiplication layer, the current multiplication factor M is Depending on the ionization rates α and β,

[Equation 1] Since it is given by (2), the current multiplication factor M can be set to, for example, “10” in accordance with β / α that can be set to “0.1”, for example. So that β / α and M
Is calculated from the equation (1) using, for example, 0.44 μm
Has a value of.

Further, the semiconductor layer 9 as the light absorption layer is
It is made of InGaAs-based In _0.53 Ga _0.47 As and has a relatively low p-type impurity concentration of 2 × 10 ¹⁵ cm ⁻³ , thereby having p ⁻ type and having a thickness of 1 μm or less, for example, 0.8 μm. Having a D.

The above is the configuration of the embodiment of the optical signal receiver according to the present invention.

The optical signal receiver according to the present invention having the above-mentioned structure is used in the avalanche photo diode 1 which uses (i) the semiconductor layer 7 as a carrier multiplication layer thereof.
Is a single layer of a semiconductor layer which is InP and does not have the thickness W specified by the formula (2), and (ii) the semiconductor layer 9 as the light absorption layer has a thickness of 1 μm or less. (Iii) a light incident window is provided in the electrode layer 13 provided on the semiconductor layer 12 instead of the light incident window 14 provided in the electrode layer 15 provided on the semiconductor substrate 5. If the optical signal LS is made to enter through the entrance window, it has the same configuration as the conventionally proposed optical signal receiver.

Therefore, according to the optical signal receiver according to the present invention shown in FIGS. 1 and 2, although detailed description is omitted, as in the case of the conventionally proposed optical signal receiver, the electrode layer 1 is formed.
The optical signal LS is supplied to the avalanche photodiode 1 from the side of the amplifier 3 through the load of the avalanche photodiode 1 provided in the amplifier 3 between the amplifier 3 and the InGaAs system. Is effectively absorbed by the semiconductor layer 9 as the light absorption layer, but the other semiconductor substrate 5, the semiconductor layer 6 as the buffer layer,
Provided in the optical fiber 2 and the electrode layer 15 as light having a wavelength of, for example, 1.55 μm, which is hardly absorbed by the semiconductor layer 7, the semiconductor layer 8, the semiconductor layer 10, the semiconductor layer 11 and the semiconductor layer 12 as the carrier multiplication layer. Light incident window 1
When the light is input from the semiconductor substrate 5 side via 4, the light of the optical signal LS is absorbed by the semiconductor layer 9 as the light absorption layer, and accordingly, the light is emitted to the semiconductor layer 9 as the light absorption layer. A mechanism in which a hole pair is generated and the electron / electron in the hole is avalanche amplified by injecting into the semiconductor layer 7 as a carrier multiplication layer, and an optical signal is output from the avalanche photo diode 1. The photocurrent LI corresponding to the intensity of LS is output to the amplifier 3, which is amplified in the amplifier 3 and supplied to the demodulator 4, and thus the demodulator 4
Can obtain an analog demodulated signal of the optical signal LS, and therefore has a function of receiving the analog-modulated optical signal LS as in the case of the conventionally proposed optical signal receiver.

However, in the case of the optical signal receiver according to the present invention shown in FIGS. 1 and 2, the semiconductor layer 7 as the carrier multiplication layer of the avalanche photodiode 1 is In
_{1-xy Al x Ga y As} 1-z P z ( however, 0 ≦ x <
1, 0 <y ≦ 1, 0 ≦ z <1, a semiconductor layer 7a as a well layer, and In _1-u Al _u As (where 0 <u <
It is a superlattice semiconductor layer having a structure in which the semiconductor layer 7b serving as the barrier layer formed in 1) is sequentially and alternately laminated.

Therefore, the ratio α of the ionization rates α and β of electrons and holes in the semiconductor layer 7 as the carrier multiplication layer is α.
/ Β is equal to I as in the conventional optical signal receiver described above when the semiconductor layer 7 as the carrier multiplication layer is described above.
thickness W which is nP and is specified by the equation (1)
Compared with the case where the semiconductor layer is a single layer that does not have, it can be made significantly larger, for example, “10”.

By the way, the ratio α of the ionization rates α and β of electrons and holes in the semiconductor layer 7 as the carrier multiplication layer is α.
As / β increases, the change in the current multiplication factor M given by equation (2) given by dM / dα when the ionization rate α of electrons changes accordingly decreases.

The reason is that the avalanche photodio
The electric field intensity in the semiconductor layer 1, particularly the electric field intensity in the semiconductor layer 7 as the carrier multiplication layer and the semiconductor layer 9 as the light absorption layer is the distribution of electrons and holes in the semiconductor layers 7 and 9, that is, the space. It changes depending on the electric charge, but as described above, the change is caused by the avalanche photodiode.
The electrons in the electron-hole pairs generated in the semiconductor layer 9 as the light absorption layer due to the incidence of the optical signal LS on the gate 1 are injected into the semiconductor layer 7 as the carrier multiplication layer to be avalanche multiplied. At this time, holes are injected from the semiconductor layer 7 as the carrier multiplication layer into the semiconductor layer 9 as the light absorption layer, and the charge in the semiconductor layer 9 becomes excessive,
Even if the semiconductor layer 9 changes in the increasing direction, the semiconductor layer 7 changes in the decreasing direction. Therefore, the ionization rates α and β of the electrons and holes are correspondingly decreased, whereby the current multiplication factor is increased. This is because M becomes small.

From the above, in the case of the optical signal receiver according to the present invention shown in FIGS. 1 and 2, the nonlinear distortion of the photocurrent LI output from the avalanche photodiode 1 with respect to the optical signal LS is caused by the carrier multiplication. The semiconductor layer 7 as a layer,
It is remarkably small as compared with the case of a single semiconductor layer which is made of InP and does not have the thickness W specified by the formula (1).

Further, in the case of the optical signal receiver according to the present invention shown in FIGS. 1 and 2, the semiconductor layer 9 as the light absorption layer of the avalanche photodiode 1 is made of InGaAs but is made of InGaAs. The semiconductor has only a thin thickness D of 1 μm or less, which is thinner than the wavelength (for example, 1.55 μm) of light (of the optical signal LS) that is effectively absorbed by the semiconductor.

By the way, as described above, the electrons in the electron-hole pairs generated in the semiconductor layer 9 as the light absorption layer by the incidence of the optical signal LS to the avalanche photodiode 1 serve as the carrier multiplication layer. When avalanche multiplication is performed by injecting into the semiconductor layer 7, holes are injected from the semiconductor layer 7 as a carrier multiplication layer into the semiconductor layer 9 as a light absorption layer. If the semiconductor layer 9 as a thin layer is thin, the amount of holes injected from the semiconductor layer 7 as a carrier multiplication layer into the semiconductor layer 9 as a light absorption layer is accordingly small. Since the electric field strength of the semiconductor layer 9 as the absorption layer does not become large and the electric field strength of the semiconductor layer 7 as the carrier multiplication layer does not become small by this amount, such a change in the electric field strength due to the space charge effect may occur. Small.

Therefore, in the case of the optical signal receiver according to the present invention shown in FIGS. 1 and 2, the non-linear distortion of the photocurrent LI output from the avalanche photodiode 1 with respect to the optical signal LS is caused by the light absorption layer. It is smaller than when the semiconductor layer 9 has a thickness greater than a thin thickness D of 1 μm or less.

In the case of the optical signal receiver according to the present invention shown in FIGS. 1 and 2, the light incident window 14 of the avalanche photodiode 1 is different from the side of the semiconductor layer 9 serving as the light absorption layer of the semiconductor substrate 5. An electrode layer 13 is provided on the side opposite to the semiconductor substrate 5 side as viewed from the semiconductor layer 9 which is provided on the opposite side as a means for making the optical signal LS incident and which is the light absorption layer of the avalanche photodiode 1. Since it is provided also as a reflection layer for reflecting the light of the received optical signal LS, the light of the optical signal LS incident on the semiconductor layer 9 as the light absorbing layer through the light incident window 14 is used as the light absorbing layer. Part of the light that has not passed through the semiconductor layer 9 and has passed through the semiconductor layer 9 serving as the light absorbing layer is reflected by the electrode layer 13 and re-enters the semiconductor layer 9 serving as the light absorbing layer.

Therefore, in the case of the optical signal receiver according to the present invention shown in FIGS. 1 and 2, the semiconductor layer 9 as the light absorption layer is used.
However, even if the thickness D is as thin as 1 μm or less as described above, the quantum efficiency corresponding to the case where the thickness D is smaller than the thickness D can be obtained.

Further, in the case of the optical signal receiver according to the present invention shown in FIGS. 1 and 2, the avalanche photo diode 1 is used.
The semiconductor layer 7 as the carrier multiplication layer has the thickness W given by the above-mentioned formula (1).

By the way, the avalanche photodiode with respect to the change dV of the voltage V applied to the semiconductor layer 7 as the carrier multiplication layer due to the effect of the space charge described above.
Given by the change dM of the current multiplication factor M of the channel 1, (dM /
dV) / M is the semiconductor layer 7 as the carrier multiplication layer,
It has a minimum when it has the thickness W given by the above equation (1).

Therefore, in the case of the optical signal receiver according to the present invention shown in FIGS. 1 and 2, the non-linear distortion of the photocurrent LI output from the avalanche photodiode 1 with respect to the optical signal LS is caused by the carrier multiplication layer. The semiconductor layer 7 is smaller than the case where the semiconductor layer 7 does not have the thickness W given by the equation (1).

From the above, according to the optical signal receiver of the present invention shown in FIGS. 1 and 2, the light incident on the avalanche photo diode 1 of the photocurrent LI output from the avalanche photo diode. The nonlinear distortion with respect to the signal LS is represented by 17 in the relation between the intensity of the optical signal LS and the photocurrent LI shown in FIG. The same structure as the optical signal receiver according to the present invention shown in FIGS. 1 and 2 except that the semiconductor layer 9 as a light absorbing layer has a thickness of 2 μm in the case of the same relationship between the two. Is smaller than the case of the same relation of the avalanche photodiode of the optical signal receiver which is not the optical signal receiver according to the present invention.

Therefore, according to the optical signal receiver according to the present invention shown in FIGS. 1 and 2, the conventional optical signal reception having the above-mentioned conventional configuration has the function of receiving the above-mentioned analog-modulated optical signal LS. It is possible to obtain the photocurrent LI output from the avalanche photo diode 1 which is smaller than that in the case of the device with a non-linear distortion caused by the non-linear distortion with respect to the optical signal LS and with high quantum efficiency.

In the above description, only one example of the optical signal receiver according to the present invention is shown, and the point is that a semiconductor layer as a carrier multiplication layer and a semiconductor as a light absorption layer are formed on a semiconductor substrate made of InP. An avalanche photo diode having a structure in which layers are laminated in that order and receiving an analog-modulated optical signal and outputting a photocurrent corresponding to the intensity thereof is used. It will be apparent that the present invention can be applied to various optical signal receivers to obtain the above-described effects of the present invention.

[Brief description of drawings]

FIG. 1 is a systematic connection diagram showing an embodiment of an optical signal receiver according to the present invention.

FIG. 2 is a schematic cross-sectional view showing an embodiment of an avalanche photodiode used in the optical signal receiver according to the present invention shown in FIG. 1 with an electric field intensity distribution diagram inside.

3 is an output photocurrent (ampere) with respect to the intensity (watt) of an incident optical signal of an avalanche photodiode used in the optical signal receiver according to the present invention shown in FIG. 2;
FIG. 6 is a diagram showing the above relationship with the same relationship of the avalanche photodiode used in the conventional optical signal receiver.

[Explanation of symbols]

 1 avalanche photodiode 2 optical fiber 3 amplifier 4 demodulator 5 semiconductor substrate 6 semiconductor layer as a buffer layer 7 semiconductor layer as a carrier multiplication layer 8 semiconductor layer 9 semiconductor layer as a light absorption layer 10, 11, 12 semiconductor Layer 13 Electrode Layer 14 Light Incident Window 15 Electrode Layer

Claims (3)

[Claims] 1. A structure in which a semiconductor layer as a carrier multiplication layer and a semiconductor layer as a light absorption layer are laminated in this order on a semiconductor substrate made of InP, and an analog modulated optical signal In an optical signal receiver using an avalanche photo diode configured to receive incident light and output a photocurrent according to its intensity, a semiconductor layer as a carrier multiplication layer of the avalanche photo diode, In _{1- (x + y)} Al _x Gay _y As _1-z
P _z (where 0 ≦ x <1, 0 <y ≦ 1, 0 ≦ z <1)
Layer as a well layer composed of In _1-u Al _u As
An optical signal receiver comprising a superlattice semiconductor layer having a structure in which semiconductor layers as barrier layers of 0 <u <1 are alternately laminated. 2. The optical signal receiver according to claim 1, wherein the semiconductor layer as the light absorption layer of the avalanche photo diode is made of InGaAs and has a thickness of 1 μm or less. -Seeing the means for injecting the optical signal on the side opposite to the semiconductor layer side as the light absorption layer of the semiconductor substrate and the semiconductor layer side as the light absorption layer, the side opposite to the semiconductor substrate side. Means for reflecting the light of the incident optical signal on the side, and an optical signal receiver. 3. The optical signal receiver according to claim 1, wherein the thickness W of the semiconductor layer as the carrier multiplication layer of the avalanche photodiode is such that electrons in the semiconductor layer as the carrier multiplication layer are When the ionization rates of holes are α and β, respectively, and the current multiplication factor of the avalanche photodiode determined by the ionization rates α and β of the electrons and holes is M and the natural logarithm is In, W = (1 / An optical signal receiver having a thickness W given by α) In (M / (1 + M (β / α))).