JP3668005B2 - Semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device including a semiconductor light emitting element and a light receiving element that receives an output thereof.
[0002]
[Prior art]
A light emitting element such as a semiconductor laser element or a light emitting diode for optical communication is used as a light source when light emission is required at a single wavelength or a wavelength close thereto. In general, when the output of the light emitting element is kept constant, automatic output control is performed in which the output of the light emitting element is detected by the light receiving element to control the operation of the light emitting element.
[0003]
By the way, the output wavelength of the semiconductor light emitting element slightly changes due to an increase in internal temperature due to its operation or a change in operating environment temperature. However, such a change adversely affects the automatic output control. Sometimes. That is, a transparent film is provided on the light receiving surface of the light receiving element, and the amount of light transmitted through the film varies depending on the wavelength. When the wavelength changes due to the temperature change, and the amount of light passing through the film changes accordingly, the detection output of the light receiving element also changes, and the sensitivity looks as if it changes with temperature.
[0004]
FIG. 2 shows the transmittance (a) of light of wavelength λ0 (790 nm), the transmittance (b) of light of wavelength λ1 (800 nm), and the transmission of wavelength λ1 with respect to the film thickness (t) of the coating (silicon oxide). The difference (c) between the transmittances of both wavelengths obtained by subtracting the transmittance of the wavelength λ0 from the rate is shown. In the transmittance difference (c) characteristic, in the film thickness where the transmittance difference is a negative value, the transmittance decreases when the standard wavelength λ0 changes to the wavelength λ1 due to the temperature rise. When the film of the light receiving element is set to such a film thickness, feedback that the light receiving output is reduced due to the temperature rise occurs, and the driving current of the light emitting element increases. As a result, the output of the light emitting element increases, and deterioration of the light emitting element itself tends to be induced.
[0005]
Also, in a semiconductor laser element, the output increases due to an increase in drive current, which tends to cause self-excited oscillation to become non-self-excited oscillation. When this laser element is mounted on an optical pickup or the like, the return light from the recording medium There is also a problem that noise due to the above becomes easy to occur.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a semiconductor light-emitting device that is not easily affected by a temperature rise in consideration of the above-described points. Another object is to provide a semiconductor light emitting device in which the detection output of the light receiving element does not decrease even if the wavelength of the light emitting element fluctuates due to temperature rise. Another object is to prevent deterioration of a semiconductor light emitting element. In addition, when a semiconductor laser is used as the semiconductor light emitting element, it is an object to prevent fluctuations in the oscillation state.
[0007]
[Means for Solving the Problems]
The semiconductor light emitting device of the present invention includes a semiconductor light emitting element in which the standard wavelength is set to λ0 and the wavelength at a temperature set as the upper limit of the operation guarantee range varies to λ1, and the light output from the light emitting element through the surface coating. In a semiconductor light emitting device including a light receiving element for receiving light, a difference in transmittance at which light of wavelength λ0 and light of wavelength λ1 of the light emitting element transmits through the film is obtained by changing the thickness of the film, and the transmittance The difference is in the positive range (when the wavelength increases from λ0 to λ1 and the amount of light passing through the film increases), the transmittance difference is in the negative range due to the film thickness variation of the film. The film thickness of the coating film is set within the range of the film thickness that takes an intermediate value between 0 and the maximum value so as to prevent the fluctuation.
[0008]
The semiconductor light emitting device of the present invention includes a semiconductor light emitting element in which the standard wavelength is set to λ0 and the wavelength at a temperature set as the upper limit of the operation guarantee range varies to λ1, and the light output from the light emitting element through the surface coating. In a semiconductor light emitting device including a light receiving element for receiving light, a difference in transmittance at which light of wavelength λ0 and light of wavelength λ1 of the light emitting element transmits through the film is obtained by changing the thickness of the film, and the transmittance The difference is in the positive range (when the wavelength increases from λ0 to λ1 and the amount of light passing through the film increases), the transmittance difference is in the negative range due to the film thickness variation of the film. Among the two regions that take an intermediate value between 0 and the maximum value that are located across the maximum value so as to prevent fluctuations, the film in the region on the side where the light transmittance of the wavelength λ0 of the light emitting element is large The film thickness is set within the thickness range. The features.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings, taking as an example the case where a semiconductor laser element is used as the semiconductor light emitting element. As shown in FIG. 1, the semiconductor light emitting device 1 is provided with a metal header 3 integrally on a metal stem 2, and a semiconductor is mounted on a side surface of the header 3 via a submount 4 such as silicon. A semiconductor laser element 5 as a light emitting element is arranged. On the stem 2, a light receiving element 6 for monitoring the rear output of the semiconductor laser element 5 is disposed directly below the semiconductor laser element 5.
[0011]
The light receiving element 6 is composed of, for example, a photodiode, and as shown in an enlarged cross-sectional view of the main part in FIG. 1, a transparent film such as a protective film and a silicon oxide or silicon nitride film as an antireflection film is formed on the surface thereof. 7 is provided. The light-receiving element 6 uses an N-type silicon substrate 8 having a resistance value of 500 Ωcm or more, and a P-type conductive high-concentration impurity layer 9 is formed on the front side with a P-type impurity such as boron (B) along the light-receiving region. By diffusion, it is formed with a depth of 1 to 5 μm and an impurity concentration of about 1 × 10 ²⁰ cm ⁻³ , and an N-type conductive high-concentration impurity layer 10 is formed on the back side of the substrate with an N-type impurity such as phosphorus (P). By diffusing, it is formed with a depth of about 100 μm and an impurity concentration of about 1 × 10 ²⁰ cm ⁻³ , and an N-type ohmic electrode 11 is formed through this layer 10. On the coating 7, a P-type electrode 12 that reaches the layer 9 through a contact hole formed in the coating 7 is formed.
[0012]
Next, the film thickness (t) setting of the film 7 will be described. Here, the semiconductor laser element 5 has its standard oscillation wavelength (λ0) set to 790 nm (normal temperature: 25 ° C.), and the oscillation wavelength (70 ° C.) at the upper limit of the guaranteed temperature range (70 ° C.). Let λ1) be 800 nm. The film 7 on the surface of the light receiving element 6 is made of silicon oxide having a refractive index of 1.46, and the rear output of the laser element 5 is incident on the light receiving surface of the light receiving element 6 perpendicularly.
[0013]
When the film thickness (t) of the coating 7 is sequentially changed, as shown in FIG. 2, the transmittance (a) of the light having the standard wavelength (λ0) and the transmittance (b) of the light having the changed wavelength (λ1) are obtained. ) Varies with a sinusoidal characteristic that periodically repeats a maximum value (about 93%) and a minimum value (about 68%). The figure also shows a transmittance difference (c) obtained by subtracting the light transmittance at the wavelength (λ1) after the change from the light transmittance at the standard wavelength (λ0). This transmittance difference (c) also takes a value shown on the right axis of the graph and fluctuates in a sinusoidal characteristic that periodically repeats a maximum value and a minimum value (see the right axis of the graph). As t) becomes thicker, its amplitude increases.
[0014]
In the region where the value of the transmittance difference (c) is negative, the wavelength varies from λ0 to λ1, so that the amount of light passing through the coating 7 decreases, that is, the detection output of the light receiving element 6 decreases. It is shown that. When a circuit for detecting the output of the light receiving element 6 and keeping the output of the laser element 5 constant is provided, the coating 7 of the light receiving element 6 is set to a film thickness at which the transmittance difference (c) shows a negative value. If so, the drive current of the laser element 5 is increased with the decrease in the detection output of the light receiving element 6 as described above, the load on the laser element 5 is increased, and the element deterioration is accelerated. Further, as the output of the laser element 5 increases, the return light noise tends to increase from the self-excited oscillation state to the non-self-excited oscillation state.
[0015]
Therefore, the film thickness of the coating 7 of the light receiving element 6 is set in a range where the transmittance difference (c) takes a positive value. If the film thickness (t) is set in this way, when the wavelength varies from λ0 to λ1, the amount of light passing through the coating 7 increases and the detection output of the light receiving element 6 increases. When a circuit that detects the output of the light receiving element 6 and keeps the output of the laser element 5 constant is provided, the drive current of the laser element 5 is reduced as the output of the light receiving element 6 increases. The load on the laser element 5 is reduced to prevent element deterioration. Further, since the laser element 5 maintains the self-excited oscillation state, it can be made less susceptible to the influence of return light noise.
[0016]
The first condition for the film thickness (t) of the coating 7 is that the transmittance difference (c) is set in a positive range. The second condition is that the transmittance (a) (or (b) ) Is set to such a film thickness that takes a value close to the maximum value. If the value of the transmittance (a) (or (b)) is small, if the output of the element 5 is small, a sufficient detection output by the light receiving element 6 may not be obtained. It is preferable to set to. According to this condition, for example, it is preferable to set the film thickness (t) selected from 1350 to 2000 mm, 4150 to 4700 mm, and 6800 to 7400 mm.
[0017]
Here, in the film thickness at which the value of the transmittance (a) (or (b)) is a maximum value, the transmittance difference (c) is a value near 0, and due to the film thickness variation of the coating film 7 due to manufacturing error or the like. Since the transmittance difference (c) may fluctuate in the negative range, a condition for preventing this is necessary. The third condition for this is to set the film thickness (t) such that the transmittance difference (c) takes an intermediate value between the maximum value and zero. By setting in this way, it is possible to effectively prevent the transmittance difference (c) from fluctuating in the negative range due to the film thickness fluctuation of the coating 7. According to this condition, for example, it is most preferable to set the film thickness to a thickness selected from 1500 to 1800 mm, 4250 to 4600 mm, and 6900 to 7300 mm.
[0018]
As described above, it is desirable to satisfy either the second or third condition after satisfying the first condition, and it is most preferable to satisfy the three conditions at the same time.
[0019]
In the above embodiment, the case where the output of the element 5 is perpendicularly incident on the light receiving element 6 (incident angle θ = 0 °) has been described as an example. However, the output of the element 5 is incident on the light receiving element 6 within a predetermined range of incident angles (θ _The present invention can also be applied to the case of oblique incidence with _{MAX to} θ _MIN ). The characteristic shown in FIG. 3 is that the arrangement of the laser element 5 and the light receiving element 6 having the same characteristics as those described above is such that the incidence on the light receiving surface of the light receiving element 6 is oblique and the incident angle θ is 82.5 degrees (θ _MAX ) to 73.5 degrees (θ _MIN ), when the incident angle θ is changed in increments of 0.5 degrees from θ _MAX to θ _MIN for each of the wavelengths λ0 and λ1. The total transmittance (a) of wavelength λ0, the total transmittance (b) of wavelength λ1, and the transmittance difference (c) obtained by subtracting the total transmittance (b) from the total transmittance (a) The film thickness (t) is obtained by sequentially changing. Also in this case, the film thickness (t) of the film 7 can be set under the same conditions as described above, and the total transmittance of the wavelength λ0 is assumed on the precondition that the transmittance difference (c) is a positive value. (A) is in the range of 2000 to 2300 mm or 5850 to 6250 mm in which the maximum is near, and the transmittance difference (c) is most preferably in the range of 2100 to 2200 mm or 5950 to 6150 mm in the vicinity of the intermediate value between the maximum value and 0. The film thickness (t) of the film 7 is set as the range.
[0020]
In FIG. 4, only the element 5 shown in FIG. 1 is changed as follows, that is, a red laser in which the standard emission wavelength λ0 is set to 670 nm and the wavelength λ1 at the upper limit temperature of the operation guarantee range varies to 680 nm. FIG. 3 is a characteristic diagram in the case of a change (characteristic diagram similar to the characteristic diagram of FIG. 2). In this case, the film thickness (t) of the film 7 is preferably selected from 2800 to 3400 mm, 5200 to 5800 mm, and 7400 to 8000 mm, and is selected from 3000 to 3300 mm, 5300 to 5700 mm, and 7500 to 7900 mm. Is most preferred.
[0021]
In the above embodiment, the semiconductor laser element is used as the semiconductor light emitting element. However, the present invention is also applied to the case where a light emitting diode whose emission wavelength is set to a substantially single wavelength is used as the light emitting element. be able to.
[0022]
【The invention's effect】
As described above, according to the present invention, a semiconductor light-emitting device including a light-emitting element and a light-receiving element can be configured to be hardly affected by temperature rise. In addition, it is possible to provide a semiconductor light emitting device in which the sensitivity of the light receiving element does not decrease even when the wavelength of the light emitting element varies due to temperature rise. In addition, deterioration of the semiconductor light emitting element can be prevented. In addition, when a semiconductor laser is used as the semiconductor light emitting element, fluctuations in the oscillation state can be prevented.
[Brief description of the drawings]
FIG. 1 is a front view showing an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing one example of the relationship between the film thickness and the transmittance or transmittance difference according to the present invention.
FIG. 3 is a characteristic diagram showing another example of the relationship between the film thickness and the transmittance or transmittance difference according to the present invention.
FIG. 4 is a characteristic diagram showing another example of the relationship between the film thickness and the transmittance or transmittance difference according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor light-emitting device 5 Semiconductor laser element (semiconductor light-emitting device)
6 Light receiving element 7 Coating

Claims (2)

A semiconductor light emitting element in which the wavelength at a temperature at which the standard wavelength is set to λ0 and the upper limit of the operation guarantee range is changed to λ1 and a light receiving element that receives light output from the light emitting element through a surface coating are provided. In the semiconductor light emitting device, the difference in transmittance between the light of the light emitting element having the wavelength λ0 and the light having the wavelength λ1 transmitted through the coating is obtained by changing the thickness of the coating, and the transmittance difference is in a positive range (positive and negative). (In the case where the amount of light passing through the film increases as the wavelength varies from λ0 to λ1) , and this transmittance difference is prevented from varying in the negative range due to the film thickness variation of the film. A film thickness of the coating film is set within a range of film thickness that takes an intermediate value between 0 and a maximum value. A semiconductor light emitting element in which the wavelength at a temperature at which the standard wavelength is set to λ0 and the upper limit of the operation guarantee range is changed to λ1 and a light receiving element that receives light output from the light emitting element through a surface coating are provided. In the semiconductor light emitting device, the difference in transmittance between the light of the light emitting element having the wavelength λ0 and the light having the wavelength λ1 transmitted through the coating is obtained by changing the thickness of the coating, and the transmittance difference is in a positive range (positive and negative). (In the case where the amount of light passing through the film increases as the wavelength varies from λ0 to λ1) , and this transmittance difference is prevented from varying in the negative range due to the film thickness variation of the film. The film is within the range of the film thickness of the region on the side where the transmittance of light of the wavelength λ0 of the light emitting element is large, out of the two regions having a maximum value between 0 and the maximum value located between the maximum value and A semiconductor light emitting device characterized by setting a film thickness of .

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