JP2021114594A - Optical semiconductor element - Google Patents

Abstract

To provide an optical semiconductor element in which the variation in light output in a wafer surface is reduced.SOLUTION: An optical semiconductor element includes a substrate, a light-emitting layer, and a distribution Bragg reflector. The light-emitting layer includes an AlGaAs multiple quantum well layer. The distribution Bragg reflector is disposed between the substrate and the light-emitting layer, and pairs of a first layer and a second layer are stacked periodically. The first layer includes AlxGa1-xAs. The second layer includes Inz(AlyGa1-y)1-zP. The refractive index n1 of the first layer is higher than the refractive index n2 of the second layer. Assuming that the center wavelength of the band in the wavelength distribution of the reflectance of the distribution Bragg reflector is λ0, the first layer has a thickness larger than λ0/(4n1) and the second layer has a thickness smaller than λ0/(4n2).SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to opto-semiconductor devices.

When a distributed Bragg reflector (DBR) is provided between the light emitting layer and the substrate, the light from the light emitting layer toward the substrate can be reflected and high-power infrared light can be emitted upward.

In a DBR in which two layers having different refractive indexes are laminated, the wavelength at which the reflectance of the DBR is maximized changes because the crystal growth temperature fluctuates within and between lots, and the in-plane light of the optical semiconductor device wafer changes. The output fluctuates.

Japanese Unexamined Patent Publication No. 2016-129189

Provided is an optical semiconductor device in which fluctuations in optical output within the wafer surface are reduced.

The optical semiconductor device of the embodiment of the present invention includes a substrate, a light emitting layer, and a distributed Bragg reflector. The light emitting layer has an AlGaAs multiple quantum well layer. The distributed Bragg reflector is provided between the substrate and the light emitting layer, and pairs of the first layer and the second layer are periodically laminated. The first layer contains Al _x Ga _1-x As, and the second layer contains In _z (Al _y Ga _1-y ) _1-z P. The refractive index n ₁ of the first layer is higher than _{the refractive index n 2 of the second layer.} It said first layer having a distributed Bragg reflector of the center wavelength of the band in the wavelength distribution of reflectance as λ0 λ0 / (4n ₁₎ greater than the thickness. The second layer has a thickness less than _{λ0 / (4n 2).}

FIG. 1A is a schematic cross-sectional view of the optical semiconductor device according to the first embodiment, and FIG. 1B is a partial schematic side view of the distributed reflector. It is a simulation graph figure which shows the relative film thickness change rate dependence with respect to the fluctuation of a crystal growth temperature. FIG. 3A is a schematic cross-sectional view of the optical semiconductor device according to the comparative example, and FIG. 3B is a partial schematic side view of the distributed reflector. It is a graph which shows the average value of the chip optical output by lot of the comparative example. It is a simulation graph which shows the relative film thickness change rate dependence of _{In z} Ga _1-z P with respect to the fluctuation of a crystal growth temperature. It is a simulation graph figure which shows the relative film thickness change rate dependence of _{In z} Al _1-z P with respect to the crystal growth temperature fluctuation. FIG. 5 is a simulation graph showing the DBR relative reflectance dependence of In _z Al _{1-z P with respect to the In mixed crystal ratio z.} FIG. 8A shows a simulation graph of the DBR relative reflectance at z = 0.50 of the second embodiment, and FIG. 8B shows the DBR relative reflectance at z = 0.45 of the second embodiment. It is a simulation graph diagram.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1A is a schematic cross-sectional view of the optical semiconductor device according to the first embodiment, and FIG. 1B is a partial schematic side view of the distributed reflector.
The optical semiconductor element 10 includes a substrate 20, a light emitting layer 30, and a distributed Bragg reflector 40. The light emitting layer 30 has an Al _x Ga _1-x As multi-quantum well layer (MQW) structure. MQW _{includes a well layer containing Al x} Ga _1-x As and a barrier layer.

The Distributed Bragg Reflector (DBR) 40 is provided between the substrate 20 and the light emitting layer 30, and has a first layer (refractive index n ₁ ) 52 and a second layer (refractive index n _2). ) 54 and the pair 53 are periodically laminated. In the period of the pair 53, the phase difference at the center wavelength λ0 of the band in the wavelength distribution of the reflectance in the air of the distributed Bragg reflector 40 corresponds to 180 °. The first layer 52 contains Al _x Ga _1-x As, and the second layer 54 contains In _z (Al _y Ga _1-y ) _1-z P. Further, it is assumed that the center wavelength λ0 is 700 nm or more.

In FIG. 1 (b), the thickness of the first layer 52 is T1, the phase change portion passing through the thickness of T1 is α ₁ (°), and the refractive index is n ₁ . At the center wavelength λ0 (in free space), the phase change component α ₁ is represented by Eq. (1).

α ₁ (°) = 90 ° × T1 / (λ0 / 4n ₁ ) Equation (1)

Further, the thickness of the second layer 54 is T2, the phase change portion passing through the thickness of T2 is α ₂ (°), and the refractive index is n ₂ . At the center wavelength λ0, the phase change α ₂ is represented by the equation (2).

α ₂ (°) = 90 ° × T2 / (λ0 / 4n ₂ ) Equation (2)

_{Here, the refractive index n 1} (@ λ0) of the first layer 52 (hereinafter referred to as “@ λ0”) at the wavelength λ0 _{is larger than the refractive index n 2} (@ λ0) of the second layer 54. (N ₁ > n 2). At this time, the light L1 emitted from the light emitting layer 30 and reflected at the interface between the first layer 52 and the second layer 54, and the first layer 52 and the second layer 54 one pair below the light L1 The phase difference between the light L2 reflected at the interface and the light L2 is _{designed to be (α 1} + α ₂ ) = 180 ° (@ λ0). Therefore, the optical path difference between the light L1 and the light L2 is 360 °, and the reflected light strengthens each other. As a result, by increasing the number of stacked DBRs, the upward reflectance due to the DBR can be increased and the light output can be increased.

In the first embodiment, the first layer 52 has a thickness T1 larger than a quarter wavelength (in-medium wavelength) at the center wavelength λ0, and the second layer 54 has a quarter wavelength at the center wavelength. It has a thickness T2 smaller than the wavelength (wavelength in the medium). That is, the phase change component α ₁ > the phase change component α ₂ is set.

Further, the optical semiconductor element 10 includes a substrate 20, a buffer layer 32 provided between the substrate 20 and the DBR 40, a first clad layer 34 provided between the DBR 40 and the light emitting layer 30, and a light emitting layer 30. A second clad layer 36 provided above and a contact layer 38 can be further included. The light 11 is emitted upward by providing the upper electrode 60 on the contact layer 38 and the lower electrode 62 on the back surface of the substrate 20 and injecting a current into the light emitting layer 30.

The buffer layer 32 includes n-type GaAs and the like. It is assumed that the first layer 52 of the DBR 40 includes an n-type Al _x Ga _1-x As (0 ≦ x ≦ 1) and the like. A second layer 54 of DBR40 is, n-type _{In z (Al y Ga 1-} y) 1-z P (0 ≦ y ≦ 1,0 ≦ z ≦ 1) is intended to include like. The first clad layer 34 is formed of n-type Al _x Ga _1-x As, or In _z (Al _y Ga _1-y ) _1-z P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). ) Etc. shall be included. It is assumed that the light emitting layer 30 includes an i-Al _x Ga _1-x As (0 ≦ x ≦ 1) multiple quantum well layer and the like. The second clad layer 36 is an n-type Al _x Ga _1-x As, or an In _z (Al _y Ga _1-y ) _1-z P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). ) Etc. shall be included.

The DBR is formed by using a vapor phase growth method such as the MOCVD (Metal Organic Chemical Vapor Deposition) method. When the MOCVD method is used, the film thickness fluctuates due to the temperature fluctuation during crystal growth. Therefore, the reflectance of the DBR fluctuates with respect to the design value. For example, when the DBR is laminated with 10 pairs or the like, the film thickness variation is accumulated, the reflectance of the DBR is lowered, and the light output is lowered.

Next, it will be described that the film thickness fluctuation in the DBR can be reduced by setting _{α 1} > α _2.
FIG. 2 is a simulation graph showing the dependence of the relative film thickness change rate on the fluctuation of the crystal growth temperature.
The vertical axis is the relative film thickness change rate (%), and the horizontal axis is the fluctuation range of the crystal growth temperature (° C.). The relative film thickness changes of In _0.5 Al _0.5 P and In _0.5 Ga _0.5 P are as large as ± 5% and ± 4%, respectively, within the allowable range of the crystal growth temperature of ± 5 ° C. .. On the other hand, _{the relative film thickness change rate of Al 0.5} Ga _0.5 As is as small as ± 2.5%. The inventors have found that the relative film thickness change rate can be reduced by reducing the In composition ratio z of the second layer constituting the DBR. For example, the relative film thickness change rate within the permissible range is as small as about 2% or less for GaAs and 1.7% or less for GaP. Further, for example, in In _0.5 Al _0.5 P, when the In mixed crystal ratio z is in the range of 0.45 to 0.5, the relative film thickness change rate with respect to the allowable range of crystal growth temperature ± 5 ° C. Was found to be about ± 5%. In this embodiment, the permissible range of temperature fluctuation during crystal growth is within ± 5 ° C. with respect to the set temperature.

FIG. 3A is a schematic cross-sectional view of the optical semiconductor device according to the comparative example, and FIG. 3B is a partial schematic side view of the distributed reflector.
The thickness TT2 of _Al x _{Ga 1-x} thickness TT1 is a quarter wavelength of the first layer 152 consisting of _{As, In z (GaAl) 1} -z second layer 154 made of P of DBR140 4 minutes It is set to one wavelength of. The thickness TT2 of the second layer 154 of the comparative example is larger than the film thickness T2 of the second layer 54 of the first embodiment. Therefore, in the comparative example, the absolute value of the thickness variation of the second layer 154 represented by the relative film thickness change rate × TT2 is the relative film thickness change rate of the second layer 54 of the first embodiment ×. It is larger than the absolute value of the thickness variation of T2.

FIG. 4 is a graph showing the average value of the chip optical output for each lot of the comparative example.
The vertical axis is the relative value of the average value of the chip optical output (measured value), and the horizontal axis is the crystal growth lot number. The fluctuation range of the DBR film thickness distribution becomes large due to the fluctuation of the crystal growth temperature. Therefore, the fluctuation range of the relative reflectance of the DBR for each lot becomes large, and the relative value of the chip light output fluctuates greatly between 0.75 and 1.15.

On the other hand, in the first embodiment, the thickness T2 of the second layer 54 is smaller than the quarter wavelength, and the thickness T1 of the first layer 52 is larger than the quarter wavelength. Then, the phase change (α ₁ + α ₂ ) is kept at 180 °. Even if the thickness T1 of the first layer 52 is 1/4 wavelength or more, the relative film thickness change rate is as small as 2.5% or less, so that the relative film thickness change rate of the DBR as a whole is higher than that of the comparative example. Can be reduced. Therefore, in the first embodiment, the fluctuation of the relative reflectance of the DBR is reduced with respect to the fluctuation allowable range of the crystal growth temperature, and the fluctuation of the light output between lots is reduced.

For example, assuming that the first layer 52 is Al _0.2 Ga _0.8 As, the refractive index n ₁ is about 3.55 at 770 nm, and the wavelength in the medium is about 54.2 nm. Further, when the second layer 54 is In _0.5 Al _0.5 P, the refractive index n ₂ is about 3.12 at 770 nm, and the wavelength in the medium is about 61.7 nm. When the DBR is composed of such layers, n ₁ > n ₂ can be set. For example, if the thickness T2 of the second layer 54 is 56.1 nm (corresponding to α2 = 82 °), the thickness T1 of the first layer 52 is 59 nm ( _{corresponding to α 1} = 98 °). .. The reflectance can be increased by setting the phase change of one pair of DBR to 180 °.

The phase change amount α ₂ can be set to, for example, 30 ° or more and smaller than 90 ° by the second layer 54. If the phase change component α ₂ is too small, the DBR reflection characteristic with respect to the wavelength may deteriorate. Therefore, _{the lower limit of the phase change component α 2} is set to, for example, 30 °.

_{FIG. 5 is a simulation graph showing the dependence of Inz} Ga _1-z P on the relative film thickness change rate with respect to the fluctuation of the crystal growth temperature.
The In mixed crystal ratio z decreases from 0.5 to 0.42, and the relative film thickness change rate decreases from 4% to 2.8%. That is, the smaller the In mixed crystal ratio z, the smaller the relative film thickness change rate within the allowable range of crystal growth temperature fluctuation (set temperature ± 5 ° C.) in the first layer 52 constituting the DBR.

_{FIG. 6 is a simulation graph showing the dependence of Inz} Al _1-z P on the relative film thickness change rate with respect to the fluctuation of the crystal growth temperature.
The In mixed crystal ratio z decreases from 0.5 to 0.42, and the relative film thickness change rate decreases from 5% to 3.3%. That is, the smaller the In mixed crystal ratio z, the smaller the relative film thickness change rate within the allowable range of crystal growth temperature fluctuation (set temperature ± 5 ° C.) in the first layer 52 constituting the DBR. The second layer 54 was designated as In _z Ga _1-z P in FIG _{. 5 and In z} Al _1-z P in FIG. Even if the second layer 54 is In _z (Al _y Ga _1-y ) _1-z P, the fluctuation range of the relative film thickness change rate is almost the same as in FIGS. 5 and 6.

FIG. 7 is _{a simulation graph showing the DBR relative reflectance dependence of In z} Al _1-z P with respect to the In mixed crystal ratio z.
The vertical axis is the DBR relative reflectance (%), and the horizontal axis is the In mixed crystal ratio z. The relative reflectance is 100% when the In mixed crystal ratio z = 0.50. As the In mixed crystal ratio z decreases (to the right on the horizontal axis), the DBR relative reflectance gradually decreases, and when z = 0.45, it decreases to about 93%. That is, when the mixed crystal ratio of the first layer (AlGaAs) 52 is fixed and _{the In mixed crystal ratio z of In z} Al _1-z P of the second layer 54 is changed, the smaller the In mixed crystal ratio z, the smaller the In mixed crystal ratio z. The relative reflectance of the DBR is decreasing.

FIG. 8A is a simulation graph of the DBR relative reflectance in the vicinity of z = 0.50 of the second embodiment, and FIG. 8B is a simulation graph of the DBR relative reflectance in the vicinity of z = 0.45 of the second embodiment. It is a simulation graph diagram showing.
The vertical axis is the DBR relative reflectance (%), and the horizontal axis is the In mixed crystal ratio z. The relative reflectance is 100% when z = 0.50. It is assumed that the first layer 52 contains Al _x Ga _1-x As and the second layer 54 contains In _z Al _1-z P. _{Further, it is assumed that the phase α 1} of the first layer 52 is represented by the equation (1), and the phase α ₂ of the second layer 54 is represented by the equation (2). As in FIG. 2, it was assumed that the volatility of the In composition ratio z was about ± 5% with respect to the fluctuation range of the crystal growth temperature of ± 5 ° C.

In FIG. 8A, assuming that the set value of the In mixed crystal ratio z is 0.5, the In mixed crystal ratio z fluctuates in the range of 0.475 to 0.525 within the fluctuation range of the crystal growth temperature. At this time, the relative reflectance is 96 to 104% (the fluctuation range is 8%). On the other hand, in FIG. 8B, assuming that the set value of the In mixed crystal ratio z is 0.45, the In mixed crystal ratio z fluctuates in the range of 0.4275 to 0.4725 in the fluctuation range of the crystal growth temperature. become. At this time, the relative reflectance is expected to be 90.0 to 95.5% (the fluctuation range is as small as 5.5%). However, when z <0.45, the lattice mismatch rate is higher than that of the GaAs substrate, so z ≧ 0.45.

Further, z ≦ 0.525. That is, as the In composition ratio z is lowered from 0.5 to 0.45, the fluctuation range of the relative reflectance can be reduced, and the fluctuation range of the light emission output in the wafer surface can be reduced.

According to the present embodiment, there is provided an optical semiconductor device in which fluctuations in optical output within the wafer surface are reduced within an allowable range of fluctuations in crystal growth temperature, and as a result, fluctuations in optical output between lots are reduced. .. The optical semiconductor device of the present embodiment is widely used in a photocoupler or a photorelay capable of transmitting a signal in a state where the input and output are electrically isolated.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

10 optical semiconductor device, 20 substrate, 30 light emitting layer, 40 distributed Bragg reflector (DBR), 52 first layer, 54 second layer, n ₁ first layer refractive index, n ₂ second layer Refractive index, λ0 center wavelength, T1 first layer thickness, T2 second layer thickness

Claims (4)

With the board
A light emitting layer having an AlGaAs multiple quantum well layer,
Provided between the substrate and the light emitting layer, pairs of the first layer and the second layer are periodically laminated, and the first layer contains Al _x Ga _1-x As, and the first layer is contained. Layer 2 contains a distributed Bragg reflector containing _{In z} (Al _y Ga _1-y ) _{1-z P, and}
With
The refractive index n ₁ of the first layer is higher than the refractive index n _{2 of the second layer.}
The first layer, the distribution center wavelength of the band in the wavelength distribution of the reflectivity of Bragg reflector as .lambda.0, have a thickness greater than λ0 / (4n _1),
The second layer is an optical semiconductor device having a thickness smaller than _{λ0 / (4n 2).} The optical semiconductor device according to claim 1, wherein the center wavelength is 700 nm or more. The optical semiconductor device according to claim 1 or 2, wherein the In mixed crystal ratio z of the second layer is 0.45 ≦ z ≦ 0.525. The optical semiconductor device according to any one of claims 1 to 3, wherein the substrate includes GaAs.

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