JPH11330612A - Semiconductor laser and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser which is capable of reducing return light noises to an irreducible minimum, when it is used as a light source for an optical disk device and an optical disk device equipped with a semiconductor laser as a light source. SOLUTION: A semiconductor laser is equipped with an active layer 4 sandwiched between an N-side clad layer 3 and a P-side clad layer 5, wherein a part of the P-side clad layer 5,100 nm or below apart from its interface with the active layer 4, is doped with an impurity such as Zn at a does between 1×10<18> cm<-3> and the doping saturation concentration, and a region of the P-side clad layer 5 ranging from its interface with the active layer 3 to the prescribed distance of 100 nm or below is kept undoped. The N-side clad layer 3 is subjected to the same process with the P-side clad layer 5, where the N-side clad layer 3 is doped with an N-type impurity such as Se at a does above 5×10<17> cm<-3> and below the doping saturation concentration. In addition, the active layer 4 has a multiple quantum well structure whose number of well layers is five or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser and an optical disk device using the semiconductor laser as a light source.

[0002]

2. Description of the Related Art In a semiconductor laser, p
Forming an n-junction is a fundamental requirement. At this time, the setting of the amount and position of doping of impurities for forming the p-type semiconductor layer and the n-type semiconductor layer forming the pn junction affects various characteristics of the semiconductor laser. I can say. In particular, from the standpoint of reliability, doping impurities in an excessively large amount or doping in a position close to the active layer may lead to the incorporation of impurities into the active layer, which becomes a non-radiative recombination center. Is often avoided. On the other hand, with respect to static characteristics such as the oscillation threshold value and the differential efficiency, the influence of the doped impurity does not appear so strongly. Doping is often performed at a distance of about 5 × 10 ¹⁷ cm ⁻³ ) and a little away from the active layer (away from the interface between the cladding layer and the active layer by more than 100 nm). These methods are referred to as weak doping (for example, JP-A-6-237038).

On the other hand, if a semiconductor laser is applied to a light source of an optical disk device or the like, it is necessary to minimize return light to the semiconductor laser. For this reason, by performing high-frequency superposition from outside or causing self-pulsation (also referred to as self-excited oscillation), the oscillation spectrum is multimode and has a wide spectrum width, and the coherence of the laser light is reduced. A method of improving a noise level with respect to return light is often used.

[0004] Here, when comparing the noise level at the time of high-frequency superposition of a semiconductor laser in which the doping is set weaker and a semiconductor laser in which the doping is set higher, the semiconductor laser in which the doping is set higher has a better noise level. Therefore, if the reliability can be ensured by another method, it is effective to set the doping as high as possible from the viewpoint of reducing the return optical noise.

[0005] In view of the further increase in the density of optical discs in the future, it is certain that the demand for return light noise of semiconductor lasers for optical disc devices will be even more severe, and further noise reduction is an important issue. It is.

[0006]

However, no effective technique has been proposed so far for further reducing the return light noise of the semiconductor laser for the optical disk device, and the noise reduction has its limit. there were.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a semiconductor laser which has very little return light noise when used as a light source of an optical disk device, and an optical disk device using this semiconductor laser as a light source.

[0008]

Means for Solving the Problems The present inventor has conducted intensive studies from an experimental and theoretical point of view in order to solve the above-mentioned problems of the prior art. The results of the study will be described below.

The present inventor has conducted a detailed study on the noise characteristics of an AlGaInP-based semiconductor laser used as a light source for an optical pickup of an optical disk device, particularly a digital video disk (DVD) device. This AlGaInP-based semiconductor laser has an active layer having a multiple quantum well (MQW) structure. Here, the relative noise intensity (Relative Intensity Noise, R
IN) and examined how the RIN correlates with various characteristics and structural parameters of the semiconductor laser.

The method used to evaluate RIN will be described as follows. That is, since a semiconductor laser used as a light source of an optical pickup of an optical disk device, particularly a DVD device, is usually a refractive index guided semiconductor laser, high frequency superposition is performed during reproduction of an optical disk. By the way, as shown in FIG. 1, the RIN of a semiconductor laser on which high-frequency superposition has been performed fluctuates periodically as the optical output increases. Since the optical output at the position of the noise "knot" differs depending on the semiconductor laser, the relative evaluation cannot be performed with the RIN fixed at a specific optical output and measured.
Therefore, here, attention is paid to the P2 noise corresponding to the second “lumps” (noises generated due to the appearance of the second peak of the relaxation oscillation) in FIG. 1, and RIN (I (intrinsic) ) -RIN) value and RIN (OFB (optical fe
edback) -RIN) value. Note that the return light distance periodically varies with respect to RIN.
Distance to make N the worst (OFB-RIN at this time is ma
x OFB-RIN) and other distances (OFB-RIN at this time is represented by min OFB-RIN)
And both have been measured. The high frequency superposition was performed at a strong amplitude of 330 MHz (approximately 30 mA amplitude) used for an optical pickup of a DVD device. The RIN rating was 3
Performed at the MHz center.

FIG. 2 shows a metal organic chemical vapor deposition (MOCV).
D) Doping position of Zn used as a p-type impurity when growing the p-side cladding layer in the growth of the semiconductor layer forming the laser structure by the method (from the interface between the active layer and the p-side cladding layer to the p-side cladding layer) Distance to the position where Zn doping starts) and max OFB-RIN, minOF
The relationship between B-RIN and I-RIN is shown. However,
The measurement sample fixes a Zn flow rate during growth (specifically, a flow rate setting value of a mass flow controller of dimethyl zinc (DMZ) flowing as a p-type dopant during growth) to 2 cc, and a reference position O for doping is: About 25 from active layer
The position of the bottom surface of the ridge structure in FIG. 17 is intentionally controlled at a position in the p-side cladding layer of 0 nm, and the reliability is all good. As shown in FIG. 2, the correlation between the Zn-doped position and I-RIN is ambiguous, but the Zn-doped position and max OFB-RIN and min OFB
A correlation with -RIN is seen. FIG. 2 shows that Zn doping tends to have a stronger return light when started from a position closer to the active layer. In particular, when starting from a position within 100 nm from the active layer, noise is considerably reduced. .
Further, although not clearly shown in FIG.
When the Zn doping is started from a position within 0 nm, the noise becomes lower.

FIG. 3 shows the Zn flow rate and the max OFB-RI.
The relationship between N, min OFB-RIN and I-RIN is shown. As shown in FIG.
B-RIN, min OFB-RIN and I-RIN
Both tend to be low. Also, max OFB-R
Looking closely at the dependence of IN and min OFB-RIN on the Zn flow rate, it seems that there is an optimum value for a certain Zn flow rate, and in this figure, there appears to be an optimum value per 2 cc. Zn
The actual flow rate of cc is determined by the off-angle of the off-substrate used for growing the semiconductor layer, the growth temperature, and the V of the raw material during the growth.
/ III ratio, etc., and cannot be stated with just this data. It can be said that the tendency is that the higher the Zn flow rate is, the lower the risk is. However, attention is needed when the Zn flow rate is lower. In this case, there is a high possibility that the light will be very weak to the return light.

As can be seen from the above, Zn doping of the p-side cladding layer has a considerable amount and position in each RIN.
It can be seen that this has been affected. Basically, doping Zn more and nearer to the active layer,
It is considered good for improving N.

Next, the influence of Zn doping on various characteristics of a semiconductor laser will be described.

In order to consider why Zn doping affects RIN, consider what effect Zn doping has on laser characteristics. First, FIG. 4 shows the relationship between the differential efficiency D1, the threshold current I _th , the differential resistance R _s, and the operating voltage V _op with respect to the optical output 5 mW during DC driving, which have a strong correlation with the Zn doping position. However, for the measurement,
An AlGaInP-based semiconductor laser having a cavity length of 500 μm and an end face reflectance of 30% to 75% was used.

As shown in FIG. 4, as the Zn doping position becomes closer to the active layer, I _th monotonically decreases and D 1 monotonically increases. This is considered to be because the band gap (E _g ) of the p-side cladding layer is increased by doping Zn to the vicinity of the active layer, and overflow of injected carriers from the active layer is suppressed. actually,
As will be described later, the characteristic temperature T ₀ is greatly improved. Also, R
_Although both _s and V _op have a strong correlation with the Zn doping position (naturally because V _op = E _g + R _s × I _op ), when the Zn doping position is closer to the active layer, the p side since the drop resistance of the cladding layer, the total R _s is reduced. It can be seen that V _op sharply decreases due to the synergistic effect of the decrease in R _{s and} the decrease in I _op .

As described above, the Zn doping position has a great influence on the static characteristics of the semiconductor laser.
The flow rate does not significantly affect the static characteristics.

The item where the Zn flow rate has a correlation is the relaxation oscillation frequency _fr , and the correlation is stronger than the Zn doping position. This relationship is shown in FIG. Here, f _r (P2) of FIG. 5A f _r of the optical output P2, in Figure 5B f _r (5 mW) represents the f _r of the optical output 5 mW. From FIG. 5, f _r as Zn flow increases it can be seen that high. That is, f
Similarly to RIN, _r also shows a tendency that the doping amount of Zn doping is relatively large and that the doping position is higher when the doping position is closer to the active layer.

FIG. 6 shows the relationship between the Zn doping position and the optical output P2 corresponding to the second noise bump at the time of high-frequency superimposition. The correlation is strong. It can be seen that P2 has increased.
This is also one of the effects of Zn doping on laser characteristics.

FIG. 7 shows the correlation between T ₀ and max OFB-RIN. When T ₀ is high, OFB-RIN tends to be low, and improvement of T ₀ is a good guideline against noise. This is consistent with the effect of Zn doping.

Next, the correlation with the number of well layers constituting the active layer is examined. FIG. 8 shows the number of well layers constituting the active layer and OF.
The correlation with B-RIN is shown. From FIG. 8, it can be seen from the overall tendency that the larger the number of well layers is, the better the return optical noise is. If the number of well layers is 5 or more, more preferably 7 or more, max OFB-RIN and min OFB-R
IN can be made sufficiently low. FIG. 9 shows the correlation between the number of well layers and I-RIN. These correlations are also strong. The correlation is similar to that of OFB-RIN, and the larger the number of well layers, the better the I-RIN.

From FIG. 10, it can be considered that the well structure has a very strong correlation with P2, which has an effect on each RIN. The tendency is that the number of well layers is larger than P2.
Will be higher.

[0023] Next, a description will be given of the correlation between the R _s. One dynamic characteristic and closely related parameters in the static characteristics of the semiconductor laser is R _s. This is conventionally used as an index as a parameter that affects the modulation amplitude ΔI _th when performing high-frequency superposition. Then, R
_s is prepared samples with various values to examine the relationship between the major characteristics and R _s of the semiconductor laser. First, given two examples of correlation R _s appears most plainly. FIG. 11 shows the correlation between R _s and V _op . As discussed earlier, V _op is expressed by the following relational expression: V _op = E _g + R _s · I _op (1) where E _g (eV) = 1.24 / λ (μm): band gap of active layer _Is connected to Rs.

Now, since E _g is almost constant (1.9 eV), if I _op does not greatly change, a strong correlation is obtained, which is a natural result.

The next interesting correlation is the correlation between R _s and ΔI _th shown in FIG. 12, which also showed a very strong correlation. In an environment where the stray capacitance is the same, it is basically better to apply the high frequency superimposition, so that it can be said that a lower R _s is better.

FIG. 13 and FIG. 14 show whether or not R _s is a good index for noise. Although these have a none strong correlation, each RIN as R _s is low is improved.

[0027] Figure 15 shows the correlation between R _s and f _r. f _r
It can be seen that the dynamic characteristic strongly correlates with R _s .

The correlation of R _s with T ₀ shown in FIG. As shown in FIG. 16, as R _s is smaller, T ₀
Is expensive. This is thought to be the result of a higher T ₀ and a lower R _s when Zn is sufficiently doped near the active layer. The cause is apparently Zn doping.

In view of the above experimental results, the reasons for the contribution of parameters considered important in laser design to noise are summarized as follows.

(1) When the Zn doping is increased, the OFB-R
This the IN is improved, "Zn-doped is strong" → "R _s is lowered, T ₀
Rise "→" superposition amplitude increases "→" wavelength chirping Δν increases "→" becomes insensitive to return light "or" Zn doping is strong "
→ “P2 increases” → “I-RIN decreases”
→ This is due to the relationship that “OFB-RIN becomes smaller”.

(2) Regarding the well structure of the active layer, the OFB-RIN is improved by increasing the number of well layers. This is because “the number of well layers is large” → “P2 is increased” →
This is considered to be due to the relationship that “I-RIN decreases” → “OFB-RIN also decreases”.

As described above, the noise of the index-guided semiconductor laser was experimentally investigated in detail with and without return light under the high-frequency superimposed driving conditions usually used for this type of semiconductor laser. As a result of the study, it was concluded that the following countermeasures were effective in reducing the return optical noise.

1. The activation doping position of Zn to the p-side cladding layer (more generally, the p-type impurity activation doping (position where doping is performed and the impurity is determined after diffusion)) is within 100 nm from the interface between the p-side cladding layer and the active layer. Preferably 50n
m and a doping saturation concentration of 1 × 10 ¹⁸ cm ⁻³ or more (for example,
3 × 10 ¹⁸ cm ⁻³ ) or less, preferably 2 × 10 ¹⁸ cm ⁻³ or less.

2. For the n-side cladding layer, for example, S
e, more generally the activation doping position of the n-type impurity is n
It is separated from the interface between the side cladding layer and the active layer by a predetermined distance within 100 nm, preferably within 50 nm, and the concentration of the doped portion is 5 × 10 ¹⁷ cm ⁻³ or more and the doping saturation concentration (for example, 1 × 10 ¹⁸ cm ^−3). cm ⁻³ ) or less.

3. The active layer has a multiple quantum well structure in which the number of well layers is at least 5 or more, preferably 7 or more.

It should be noted that, in addition to these countermeasures, the relaxation oscillation 2
It is also effective to set the optical output P2 corresponding to the noise bump generated due to the appearance of the third peak to 3 mW or more.

The present invention has been devised based on the above study by the present inventors.

That is, in order to achieve the above object, a first invention of the present invention relates to a semiconductor laser having a structure in which an active layer is sandwiched between an n-side cladding layer and a p-side cladding layer. The p-type impurity is doped to a concentration of 1 × 10 ¹⁸ cm ⁻³ or more and a doping saturation concentration or less at a portion within a predetermined distance of 100 nm or less from the interface between the p-side cladding layer and the active layer. A portion of the cladding layer that is less than a predetermined distance from the interface between the p-side cladding layer and the active layer is not doped with a p-type impurity, and the active layer is a multiple quantum well having at least five or more well layers. It has a structure.

According to a second aspect of the present invention, there is provided a semiconductor laser having a structure in which an active layer is sandwiched between an n-side cladding layer and a p-side cladding layer. N-type impurities are doped at a concentration of 5 × 10 ¹⁷ cm ⁻³ or more and a doping saturation concentration or less at a portion within a predetermined distance of 100 nm or less from the interface with the n-side cladding layer of the n-side cladding layer. A portion less than a predetermined distance from the interface with the active layer is not doped with an n-type impurity, and the active layer has a multiple quantum well structure in which the number of well layers is at least 5 or more. is there.

According to a third aspect of the present invention, there is provided an optical disc device using a semiconductor laser as a light source, wherein the semiconductor laser has a structure in which an active layer is sandwiched between an n-side cladding layer and a p-side cladding layer, A portion of the cladding layer which is separated from the interface between the p-side cladding layer and the active layer by a predetermined distance within 100 nm or more is doped with a p-type impurity at a concentration of 1 × 10 ¹⁸ cm ⁻³ or more and a doping saturation concentration or less. The portion of the p-side cladding layer that is less than a predetermined distance from the interface between the p-side cladding layer and the active layer is not doped with a p-type impurity, and the active layer has at least five or more well layers. It has a multiple quantum well structure.

According to a fourth aspect of the present invention, in an optical disk device using a semiconductor laser as a light source, the semiconductor laser has a structure in which an active layer is sandwiched between an n-side cladding layer and a p-side cladding layer. An n-type impurity is doped to a concentration of 5 × 10 ¹⁷ cm ⁻³ or more and a doping saturation concentration or less in a portion of the cladding layer which is separated from the interface between the n-side cladding layer and the active layer by a predetermined distance within 100 nm or more. A portion of the n-side cladding layer less than a predetermined distance from the interface between the n-side cladding layer and the active layer is not doped with an n-type impurity, and the active layer has at least 5 or more well layers. It has a multiple quantum well structure.

In the first and third aspects of the present invention, preferably, a portion of the p-side cladding layer which is separated from the interface between the p-side cladding layer and the active layer by a predetermined distance within 50 nm or more is provided. Is doped to a concentration of 1 × 10 ¹⁸ cm ⁻³ or more and a doping saturation concentration or less. The doping saturation concentration of the p-type impurity is, for example, about 3 × 10 ¹⁸ cm ⁻³ . Preferably, the doping concentration of the p-type impurity is 2 × 10
¹⁸ cm ^-3 or more. The p-type impurity is typically Zn, but may be other.

In the second and fourth aspects of the present invention, preferably, the n-type cladding layer is provided with a n-type impurity at a portion within a predetermined distance of 50 nm or less from an interface between the n-side cladding layer and the active layer. To a concentration of 5 × 10 ¹⁷ cm ⁻³ or more and a doping saturation concentration or less. The doping saturation concentration of the n-type impurity is, for example, about 1 × 10 ¹⁸ cm ⁻³ .
The n-type impurity is typically Se, but may be another material such as Si.

In the first, second, third and fourth aspects of the present invention, the number of well layers in the active layer is preferably seven or more.

In the present invention, the optical disk device includes:
Various devices such as an optical disk reproducing device, an optical disk recording device, an optical disk recording and reproducing device, and the like are included.

According to the first and third aspects of the present invention, the doping position of the p-type impurity in the p-side cladding layer is sufficiently close to the active layer, and the doping concentration is also sufficient. In addition, since the active layer has a multiple quantum well structure in which the number of well layers is 5 or more, it is possible to significantly reduce return optical noise.

According to the second and fourth aspects of the present invention, the doping position of the n-type impurity in the n-side cladding layer is sufficiently close to the active layer, and the doping concentration is also sufficient. In addition, since the active layer has a multiple quantum well structure in which the number of well layers is 5 or more, it is possible to significantly reduce return optical noise.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 17 shows an index-guided AlGaInP semiconductor laser having a ridge structure according to an embodiment of the present invention.

As shown in FIG. 17, in the AlGaInP-based semiconductor laser according to this embodiment, the n-type Ga
On an As substrate 1, an n-type GaAs buffer layer 2, n-side (A
l _x Ga _1-x ) _1-y In _y P clad layer 3, active layer 4,
p-side (Al _x Ga _1-x ) _1-y In _y P cladding layer 5, p
GaInP intermediate layer 6 and p-type GaAs cap layer 7
Are sequentially laminated. p-side (Al _x Ga _1-x ) _1-y I
The upper part of the n _y P cladding layer 5, the p-type GaInP intermediate layer 6, and the p-type GaAs cap layer 7 have a stripe shape extending in one direction. An n-type GaAs current block layer 8 is buried in both sides of the stripe portion, thereby forming a current confinement structure. On the p-type GaAs cap layer 7 and the n-type GaAs current block layer 8, a p-side electrode 9 made of, for example, a Ti / Pt / Au electrode is provided in ohmic contact with the p-type GaAs cap layer 7. On the back surface of the n-type GaAs substrate 1, an n-side electrode 10 made of, for example, an AuGe / Ni electrode is provided in ohmic contact with the n-type GaAs substrate 1.

As the n-type GaAs substrate 1, for example,
Those having a (100) plane orientation and those having a plane which is off by, for example, 5 to 15 ° from the (100) plane are used. The n-side (Al _x Ga _1-x ) _1-y In _y P cladding layer 3
The composition ratios x and y of the p-side (Al _x Ga _1-x ) _1-y In _y P cladding layer 5 are such that these layers are n-type GaAs.
The value is selected so as to lattice-match with the substrate 1, and specifically, for example, x = 0.7 and y = 0.5.

For example, as shown in FIG. 18, the active layer 4 has a GaInP / AlGaInP MQW structure in which undoped GaInP layers as well layers and undoped AlGaInP layers as barrier layers are alternately stacked. That is, the number of undoped GaInP layers is at least 5 or more, preferably 7 or more. The active layer 4
The part in contact with the n-side (Al _x Ga _1-x ) _1-y In _y P cladding layer 3 and the p-side (Al _x Ga _1-x ) _1-y In _y P cladding layer 5 is an optical waveguide layer. Undoped A as
It consists of an lGaInP layer.

N-side (Al _x Ga _{1 -x} ) _{1 -y} In _{y In the} P cladding layer 3, the n-side (Al _x Ga _{1 -x} ) _{1 -y} In
_The portion 3a located at a predetermined distance within 100 nm from the interface between the yP cladding layer 3 and the active layer 4, for example, less than 50 nm, is undoped, and the portion 3b located at a distance of 50 nm or more from this interface has an n-type impurity, for example. Se is 5 × 1
It is doped to an impurity concentration of 0 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ and is n-type. Also, the p-side (Al _x Ga _1-x )
The p-side (Al _x G) of the _1-y In _y P clad layer 5
_{a 1-x) 1-y} In y P cladding layer 5 and the predetermined distance within 100nm from the interface between the active layer 4, for example, the portion 5a in less than 50nm is undoped, 50n from the interface
The portion 3b located at a distance of m or more is doped with, for example, Zn as a p-type impurity at an impurity concentration of 1 × 10 ^{18 to} 3 × 10 ¹⁸ cm ⁻³ , and becomes a p-type impurity.

The p-side (Al _x Ga) having a stripe shape
_1-x ) _1-y In _y P-type GaIn upper part of P clad layer 5
The width of the P intermediate layer 6 and the p-type GaAs cap layer 7, that is, the lowermost portion of the stripe portion is, for example, 4 μm or more, and the uppermost width of the stripe portion is, for example, 3.5 μm or more. At this time, θ‖ ≦ 7.5 °.

One example of the thickness of each semiconductor layer constituting the AlGaInP-based semiconductor laser is n-type GaAs.
Buffer layer 2 is 0.3 μm, n-side (Al _x Ga _1-x )
_{The 1-y} In _y P cladding layer 3 is 1 μm, p-side (Al _x Ga
_1-x ) _1-y In _y P clad layer 5 is 1 μm, p-type GaI
The nP intermediate layer 6 is 0.1 μm, and the p-type GaAs cap layer 8
Is 0.3 μm.

The end face of the cavity of this AlGaInP-based semiconductor laser is coated with an end face, and the reflectance R _f of the end face on the front side is 30% or more, preferably 40%.
More preferably, the reflectance R _r of the rear end face is at least 70%, preferably at least 80%, more preferably at least 90%.
It is set above. The resonator length L is, for example, 25
0 μm.

Next, a method of manufacturing the AlGaInP-based semiconductor laser according to this embodiment configured as described above will be described.

To manufacture an AlGaInP-based semiconductor laser according to this embodiment, first, an n-type GaAs substrate 1 is formed.
An n-type GaAs buffer layer 2, an n-side (Al _x Ga _1-x ) _1-y In _y P clad layer 3, an active layer 4 having an MQW structure, and a p-type (Al _x Ga _1-x) )
_{A 1-y} In _y P clad layer 5, a p-type GaInP intermediate layer 6, and a p-type GaAs cap layer 8 are sequentially grown. Here, the n-side (Al _x Ga _1-x ) _1-y In _y P cladding layer 3
During the growth, until a predetermined thickness is performed grown while doping the Se concentration N _n, to grow the remaining portion is then stopped dope Se. In addition, the p-side (Al _x G
_{a 1-x) 1-y} In y P During the growth of the cladding layer 5, up to a predetermined thickness without doping of Zn, to grow while subsequently doped with Zn to a concentration N _p.

Next, a stripe-shaped resist pattern (not shown) extending in one direction is formed on the p-type GaAs cap layer 7 by lithography, and this resist pattern is used as a mask to form a p-side (Al _x Ga _{1−). x} ) _1-y
The In _y P clad layer 5 is etched by a wet etching method to a halfway depth in the thickness direction, and the p-side (Al _x G
a _1-x ) _1-y In _y P clad layer 5, p-type GaI
The nP intermediate layer 6 and the p-type GaAs cap layer 7 are patterned in a stripe shape. Here, in this wet etching, an etching solution made of, for example, sulfuric acid is used.

Next, after removing the resist pattern used as a mask in the above-mentioned wet etching, for example, M
The n-type GaAs current block layer 8 is selectively grown by the OCVD method to bury the portions on both sides of the stripe portion.

Next, p-type GaAs is formed by, for example, a vacuum evaporation method.
A p-side electrode 9 is formed on the entire surface of the s cap layer 7 and the n-type GaAs block layer 8, and the n-type GaAs substrate 1
Similarly, an n-side electrode 10 is formed on the back surface.

Next, the n-type GaAs substrate 1 on which the laser structure is formed as described above is cleaved in a bar shape to form both resonator end faces, and these end faces are coated with end faces. The bar is cleaved into chips.

Thereafter, the laser chip obtained as described above is packaged. As described above, the intended AlGaInP-based semiconductor laser is manufactured.

As described above, according to this embodiment,
Both the n-side (Al _x Ga _1-x ) _1-y In _y P cladding layer 3 and the p-side (Al _x Ga _1-x ) _1-y In _y P cladding layer 5 are located at positions sufficiently close to the active layer 4. Since the impurity is appropriately doped at a high concentration and the number of the well layers in the active layer 4 is at least 5 or more, the structure is optimal for reducing the return light noise, and the reliability is sufficiently secured. The return optical noise can be greatly reduced as compared with the conventional AlGaInP-based semiconductor laser. In addition, since high-frequency superimposition is likely to occur, the output of the high-frequency superimposition circuit can be reduced. Further, the temperature characteristics can be improved by increasing T ₀ . Further, the threshold current density can be reduced.

Next, the AlGaI according to the above-described embodiment is used.
An optical disk reproducing apparatus using an nP semiconductor laser as a light source will be described. FIG. 19 shows the configuration of the optical disk reproducing apparatus.

As shown in FIG. 19, this optical disk reproducing apparatus uses a semiconductor laser 101 as a light emitting element as a light source.
It has. As the semiconductor laser 101, the AlGaInP-based semiconductor laser according to the above-described embodiment is used. The optical disk reproducing apparatus also guides the light emitted from the semiconductor laser 101 to the optical disk D and reproduces the reflected light (signal light) from the optical disk D, that is, a known optical system, that is, a collimating lens 102, a beam splitter 103, 1/4 wavelength plate 104, objective lens 105, detection lens 106, light receiving element 1 for signal light detection
07 and a signal light reproducing circuit 108.

In this optical disk reproducing apparatus, the emitted light L of the semiconductor laser 101 is made parallel by the collimator lens 102, further passed through the beam splitter 103, and the degree of polarization is adjusted by the 波長 wavelength plate 104. The light is condensed by the lens 105 and is incident on the optical disk D. Then, the signal light L ′ reflected by the optical disc D is applied to the objective lens 105 and the 波長 wavelength plate 104.
After the light is reflected by the beam splitter 103 through the detection lens 106, the light is incident on the light receiving element 107 for signal light detection, where it is converted into an electric signal.
At 08, the information written on the optical disc D is reproduced.

According to this optical disk reproducing apparatus, the semiconductor laser 101 uses the AlGaInP-based semiconductor laser according to the above-described embodiment, whose return light noise is sufficiently lower than that of the conventional semiconductor laser. can do.

Although the embodiment of the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible. .

[0070]

As described above, according to the semiconductor laser of the present invention, return light noise can be extremely reduced when used as a light source of an optical disk device.

Further, according to the optical disk apparatus of the present invention, since the semiconductor laser used as the light source has very little return light noise, the optical disk can be reproduced and / or recorded with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the relationship between the optical output of a semiconductor laser and RIN.

FIG. 2 is a schematic diagram showing a relationship between RIN and a Zn doping position.

FIG. 3 is a schematic diagram illustrating a relationship between RIN and a Zn flow rate.

[4] D1, I _th, which is a schematic diagram showing the relationship between R _s and V _op and Zn-doped position.

5 is a schematic diagram illustrating a relationship between f _r and Zn flow.

FIG. 6 is a schematic diagram illustrating a relationship between P2 and a Zn doping position.

FIG. 7 is a schematic diagram illustrating a relationship between max OFB-RIN and T ₀ .

FIG. 8: max OFB-RIN and min OFB
FIG. 9 is a schematic diagram illustrating a relationship between −RIN and the number of well layers.

FIG. 9 is a schematic diagram illustrating a relationship between I-RIN and the number of well layers.

FIG. 10 is a schematic diagram illustrating a relationship between P2 and the number of well layers.

FIG. 11 is a schematic diagram illustrating a relationship between V _op and R _s .

FIG. 12 is a schematic diagram illustrating a relationship between R _s and ΔI _th .

FIG. 13 is a schematic diagram illustrating a relationship between R _s and I-RIN at P2.

FIG. 14 is a schematic diagram showing the relationship between R _s and min OFB-RIN and max OFB-RIN at P2.

Figure 15 is a schematic diagram showing the relationship between R _s and f _r.

FIG. 16 is a schematic diagram illustrating a relationship between R _s and T ₀ .

FIG. 17 shows an AlGaInP according to an embodiment of the present invention.
FIG. 2 is a perspective view showing a system semiconductor laser.

FIG. 18 shows an AlGaInP according to an embodiment of the present invention.
FIG. 3 is an energy band diagram of a semiconductor laser.

FIG. 19 shows an AlGaInP according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating an optical disk reproducing apparatus using a system semiconductor laser as a light source.

[Explanation of symbols]

1 · · · n-type GaAs substrate, 2 · · · n-type GaAs buffer layer, 3 · · · n-side _{(Al x Ga 1-x)} 1-y In y P
Cladding layer, 4 ... active layer, 5 ... p side (Al _x G
a _1-x ) _1-y In _y P clad layer, 6... p-type GaI
nP intermediate layer, 7 ... p-type GaAs cap layer, 8 ...
-N-type GaAs current blocking layer, 9 ... p-side electrode, 1
0 ... n-side electrode

Claims (13)

[Claims] 1. A semiconductor laser having a structure in which an active layer is sandwiched between an n-side cladding layer and a p-side cladding layer, wherein 100 nm from an interface between the p-side cladding layer of the p-side cladding layer and the active layer. The p-type impurity is doped at a concentration of 1 × 10 ¹⁸ cm ⁻³ or more and a doping saturation concentration or less at a portion separated by a predetermined distance or more, and the p-side cladding layer of the p-side cladding layer and the active material A portion which is less than the predetermined distance from the interface with the layer and which is not doped with a p-type impurity, and wherein the active layer has a multiple quantum well structure in which the number of well layers is at least 5 or more. laser. 2. A portion of the p-side cladding layer, which is at least a predetermined distance within 50 nm from an interface between the p-side cladding layer and the active layer, is doped with 1 × 10 ¹⁸ cm ⁻³ or more of p-type impurities. 2. The semiconductor laser according to claim 1, wherein the semiconductor laser is doped to a concentration lower than the concentration. 3. A p-type impurity in a portion of the p-side cladding layer which is separated from the interface between the p-side cladding layer and the active layer by a predetermined distance of 100 nm or less and 1 × 10 ¹⁸ cm ^−3.
2. The semiconductor laser according to claim 1, wherein the semiconductor laser is doped to a concentration of 3 × 10 ¹⁸ cm ⁻³ or less. 4. A p-type impurity at 2 × 10 ¹⁸ cm ^{−3 in} a portion of the p-side cladding layer that is separated from the interface between the p-side cladding layer and the active layer by a predetermined distance within 100 nm or more.
2. The semiconductor laser according to claim 1, wherein the semiconductor laser is doped to a concentration of 3 × 10 ¹⁸ cm ⁻³ or less. 5. The semiconductor laser according to claim 1, wherein said p-type impurity is Zn. 6. The active layer has at least 7 well layers.
2. The semiconductor laser according to claim 1, wherein the semiconductor laser has the multiple quantum well structure. 7. A semiconductor laser having a structure in which an active layer is sandwiched between an n-side cladding layer and a p-side cladding layer, wherein 100 nm from an interface between the n-side cladding layer and the active layer in the n-side cladding layer. The n-type impurity is doped at a concentration of 5 × 10 ¹⁷ cm ⁻³ or more and a doping saturation concentration or less at a portion separated by a predetermined distance or more, and the n-side cladding layer of the n-side cladding layer and the active A portion which is not doped with an n-type impurity in a portion less than the predetermined distance from the interface with the layer, and wherein the active layer has a multiple quantum well structure in which the number of well layers is at least 5 or more; laser. 8. An n-type impurity in a portion of the n-side cladding layer, which is at least a predetermined distance within 50 nm from an interface between the n-side cladding layer and the active layer, is doped with 5 × 10 ¹⁷ cm ⁻³ or more. 8. The semiconductor laser according to claim 7, wherein the semiconductor laser is doped to a concentration equal to or lower than the concentration. 9. An n-type impurity in a portion of the n-side cladding layer which is separated from the interface between the n-side cladding layer and the active layer by a predetermined distance within 100 nm or more and contains 5 × 10 ¹⁷ cm ^−3.
8. The semiconductor laser according to claim 7, wherein the semiconductor laser is doped to a concentration of 1 × 10 ¹⁸ cm ⁻³ or less. 10. The semiconductor laser according to claim 7, wherein said n-type impurity is Se or Si. 11. The semiconductor laser according to claim 7, wherein said active layer has a multiple quantum well structure having at least seven or more well layers. 12. An optical disk device using a semiconductor laser as a light source, wherein the semiconductor laser has a structure in which an active layer is sandwiched between an n-side cladding layer and a p-side cladding layer. The p-type impurity is 1 × 10 ¹⁸ cm at a portion within a predetermined distance of 100 nm or less from the interface between the p-side cladding layer and the active layer.
^-3 is doped to a concentration of not more than the doping saturation concentration, and a portion of the p-side cladding layer less than the predetermined distance from the interface between the p-side cladding layer and the active layer is doped with a p-type impurity. An optical disk device, wherein the active layer has a multiple quantum well structure in which the number of well layers is at least 5 or more. 13. An optical disk device using a semiconductor laser as a light source, wherein the semiconductor laser has a structure in which an active layer is sandwiched between an n-side cladding layer and a p-side cladding layer. The n-type impurity is 5 × 10 ¹⁷ cm at a portion within a predetermined distance of 100 nm or less from the interface between the n-side cladding layer and the active layer.
^-3 or more and a doping saturation concentration or less, and a portion of the n-side cladding layer less than the predetermined distance from the interface between the n-side cladding layer and the active layer is doped with an n-type impurity. An optical disc device, wherein the active layer has a multiple quantum well structure in which the number of well layers is at least 5 or more.