JPH0537085A - Semiconductor laser device - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a semiconductor laser device that is easy to use by reducing the slope efficiency of the InGaAlP-based red semiconductor laser device and improving the temperature characteristics including droop characteristics. The semiconductor laser device according to the present invention uses a quaternary mixed crystal, and the Al composition of the active layer and the clad layer quaternary mixed crystal sandwiching the active layer is X <0.6 ≦ W. Here one of them is X and the other is W. The thickness of the active layer is 0.03 μm or less, and a coating surface is formed so that the reflectance of at least the mirror surface constituting the emission surface is 50% or more. As a result, the slope efficiency can be reduced, the droop characteristics and the temperature characteristics can be improved, and the reliability can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and in particular, is suitable for a light source of an information processing device such as a laser beam printer.

[0002]

2. Description of the Related Art In a semiconductor laser device, in order to effectively use light, it is general that the reflectance on the emitting surface side is equal to or less than 32% which is equivalent to that of the cleaved surface. However, in recent years, In which emits a laser beam in the wavelength range of 670 nm band
The GaAlP-based semiconductor laser is used as a light source of a laser beam printer, and it is required to satisfy droop characteristics of 10% or less. Further, since this semiconductor laser can use a high-sensitivity photosensitizer, it has an advantage that it is suitable for high speed and high precision.

This type of semiconductor laser, that is, a refractive index guide type laser SBR (Selective-ery Burie)
In the structure of d Ridge), a clad layer of the same conductivity type and a clad layer of a different conductivity type are stacked in this order on a GaAs substrate, and an active layer is provided between the clad layers. Further, a part of the different conductivity type clad layer is removed to form a stripe-shaped current path, a current block layer is deposited on the removed part, and then a contact layer is provided on the current path and the current block layer. To do.

The characteristics of this semiconductor laser are that current and light are confined in a part of the active layer by forming a current path, and Al is 0.6 or more as a composition of the clad layer.

[0005]

As described above, in the semiconductor laser device used as the light source of the laser printer, the light output of the semiconductor laser may decrease due to heat generation while applying a constant current pulse of several tens of msec. It has become a problem. Also, it is composed of a refractive index guide type laser,
The red semiconductor laser mainly composed of 1P has a poor thermal conductivity and has a low threshold value due to the reduction of the reactive current, but has a high slope efficiency and a poor temperature characteristic. Furthermore, the SBR laser has 10% or more of the droop characteristic, which is known as a characteristic representing the phenomenon that the optical output decreases when the semiconductor laser is pulse-driven, and thus satisfies the requirement for the light source of the laser printer. It was difficult.
Furthermore, the slope efficiency on the IL curve is 0.4.
Since it was 5 (W / A) or more, it was difficult to drive with constant power.

The present invention has been made under such circumstances, and in particular, the slope efficiency of the InGaAlP semiconductor laser is reduced, the temperature characteristics of the semiconductor laser device including the droop characteristics are improved, and the semiconductor laser is easy to use. The purpose is to provide a device.

[0007]

A semiconductor substrate of a first conductivity type, a clad layer of the first conductivity type and a second conductivity type formed on the semiconductor substrate in the following order, and sandwiched between the clad layers. And an active layer with a thickness of 0.03 μm or less,
A striped current path formed by removing a part of the second conductivity type clad layer and remaining, a current block layer formed by filling the removed part, and a current path and a current block layer And the electrode formed on the exposed portion of the semiconductor substrate and the contact layer, the long side of the current path, the active layer, and the crystal plane orthogonal to the first-conductivity-type and second-conductivity-type cladding layers. Consists of and
The semiconductor laser device according to the present invention is characterized in that it has a mirror surface having a reflectance of 50% or more on the emitting surface side that utilizes laser light.

Further, in the semiconductor laser device according to the present invention, the active layer and the clad layer are made of In _1-y Ga _{1-x, respectively.}
It is also characterized in that it is composed of Al _x ) _y P and In _1-z (Ga _1-w Al _w ) _z P, and X <0.6 ≦ W.

[0009]

In the semiconductor laser device according to the present invention, the reflectance on the mirror surface side is 50% or more, and the thickness of the active layer is 0.03.
This is completed based on the fact that the slope efficiency is reduced, the droop characteristic is improved, the operating temperature is improved, and the reliability is improved by setting the thickness to be not more than μm. The mirror surface constituting the emitting surface side is coated, for example, so that the reflectance is 50% or more.

In order to further exhibit the function as a red semiconductor laser, the composition of the first and second cladding layers is In _1-y (Ga _1-x Al _x ) _y P for the former and In _{1-z for the} latter. (G
a _{1- w} Al _w ) _z P, and X <0.6 ≦ W is required, and therefore it is limited. However, it should be added that Y and Z may be set to approximately 0.5.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described with reference to FIGS. The main part of the refractive index guide type red laser (SBR laser) which is shown in a perspective view in FIG. 1 is formed by three times of epitaxial methods by MOCVD.
That is, an n-type G having a thickness of approximately 300 μm, that is, a first conductivity type G
The first conductivity type In _1-z (Ga _0.3 Al) is formed on the aAs substrate 1.
After depositing the first cladding layer 2 made of _0.7 ) _z P and having a thickness of approximately 1.2 μm, non-doped In _1-y (Ga _1-x Al
_x ) deposit an active layer 3 composed of _y P and having a thickness (denoted as d _{act in} FIG. 1) of approximately 0.03 μm. Further, a second clad layer 4 made of In _{1 -z} (Ga _0.3 Al _0.7 ) _z P of the second conductivity type and having a thickness of approximately 1.2 μm is deposited. Furthermore, a second conductivity type InGaP layer 12 is further formed thereon in an amount of 0.00
Deposit 5 μm.

Among these, the non-doped active layer 3 and the first
As for the composition of Al in the second cladding layers 2 and 4, the former is In _1-y Ga _1-x Al _x ) _y P in the claims.
The latter is described as In _1-z (Ga _1-w Al _w ) _z P, and X <0.6 ≦ W, and Y and Z are set to about 0.5.
In such a composition, in order to fully exhibit the function as a red semiconductor laser, it is the basis of limitation.

After the exposed surface of the second cladding layer 2 is covered with an etching mask of silicon dioxide, a part of the second cladding layer 2 is ablated by an isotropic etching process to form a striped pattern indicated by W in FIG. To form a current path 5. After that, a part of the GaAs6 current blocking layer of the first conductivity type having a thickness of approximately 0.5 μm is deposited so as to fill the side surface of the stripe-shaped current path 5.

As a result, the second conductivity type current blocking layer 6 is formed.
Then, a contact layer 7 made of GaAs of the second conductivity type and having a thickness of about 0.5 μm is entirely deposited on the flat surface formed by the exposed surface of the stripe-shaped current path 5.

The thickness of the n-type or first conductivity type GaAs substrate 1 is the thickest in each layer of the laminated structure, but in FIG.
The omission is indicated by a mark. Furthermore, the current path 4
Is 5 μm, and the distance h between the active layer 3 and the current block layer 6 is 0.2 μm.

After that, the first conductivity type GaAs substrate 1 side is polished and thinned until the entire thickness becomes 100 μm.

Next, an electrode 8 made of Au-Ge is formed on the exposed surface of the substrate 1, and an electrode 9 made of Au-Zn is formed on the exposed surface of the contact layer 7, that is, the exposed surface of the laminated body. The process moves to the mirror surface 10 process.

In other words, the crystal planes orthogonal to the stripe-shaped current passages 5, in other words, the substrate 1, the first and second active layers 2, 4, the active layer 3, the current blocking layer 6, the strasp-shaped current passages 5, and the contact layer 7, respectively. The end face is cleaved, and a dielectric multilayer film (not shown) is coated thereon to form the mirror surface 10. As the dielectric multilayer film, Al ₂ O ₃ / Si / Al ₂ O ₃ ; λ
/ 4 × 3) is applicable, and Si is used as other materials.
Combinations of O ₂ / Si and SiO ₂ / SiN can also be used. As a result, the reflectance of the mirror surface 10 becomes 50% or more.

Further, the mirror surface 10 having a reflectance of 50% or more.
Does not need to be installed on crystal planes that are orthogonal to the stripe-shaped current path 5 and face each other, and one side has a reflectance of 50%.
The above mirror surface 10 makes no difference.

FIGS. 5 and 6 shown to explain that the reflectance of the mirror surface 10 is 50% or more are shown in FIGS.
With the reflectance of the mirror surface 11 (see FIG. 1) facing to as the parameter, the front reflectance is taken on both horizontal axes, and the vertical axis is
The former shows the slope efficiency and the latter shows the threshold value. Therefore,% shown in both figures represents the back surface reflectance.

On the other hand, the slope efficiency required in a system using a semiconductor laser device is 0.4 W / A or less.

Here, the curve of FIG. 5 when the reflectances of the mirror surfaces 10 and 11 facing each other are symmetrical is exactly 0.4 W /
The slope efficiency of A is shown, which is the basis for setting the reflectance of the mirror surface 10 to 50% or more.

FIG. 6 shows how much the rear surface reflectance should be controlled when the front surface reflectance is 50% or more. The back surface reflectance has a correlation with the threshold value, and the lower the reflectance, the higher the threshold value.
If the reflectance of about 30%, which is the same as that of the cleaved surface, is controlled to have a reflection loss equivalent to that, it is considered that the threshold value of the semiconductor laser device is not affected.

For example, if the front surface has a reflectance of 50% and the rear surface has a reflectance of 18% or more, the threshold value will not increase.

Such a semiconductor laser is so-called J-Down after it is formed into one chip by a cleavage process.
A semiconductor laser device is obtained by mounting the substrate 1 on the envelope in a 9 mmΦ envelope.

As described above, in the semiconductor laser device according to the present invention, a stripe-shaped current path 5 is formed by removing a part of the second conductivity type clad layer and removing the remaining part, and the stripped part is filled with a current. The block layer 6 is installed.

As another semiconductor laser structure, an IS structure of a gain guide can be used, and its perspective view is shown in FIG. As is clear from the drawing, it is almost the same as that of FIG. 1, and the concrete numerical values are also the same, so that the explanation will be omitted.

[0028]

The quaternary mixed crystal semiconductor laser made of InGaAlP has conventionally been provided with a mirror surface coated with a thickness of λ / 2, and the active layer has a thickness d _act 0.0.
Slope efficiency ≧ 0.45 threshold current = 6μm =
35 mA, kink level of 14 mW, COD level of about 15 mW and droop characteristics of about 10% are obtained. On the other hand, Al ₂ O ₃ / Si / Al ₂ O ₃ (λ / 4 × 3
A high reflection coating of layer) gives a reflectance of about 60%.

FIG. 3 shows the characteristics of a, b, and c type semiconductor lasers in which the horizontal axis represents current and the vertical axis represents optical output. a is d _act = 0.06 μm, R _f = R _r = 32
%, B, d _act = 0.06 μm, R _f = R _r = 60
% And c relate to the present invention, and d _act = 0.03 μ
m, R _f = R _r = 60%.

According to FIG. 3, when the double-sided reflectance of the conventional semiconductor laser a is 60%, the slope efficiency is 0.3.
5. It is clearly shown that the kink level and the COD level decrease with the threshold current = 27 mA.

On the other hand, the C according to the present invention has a slope efficiency of 0.35, and the kink level and COD level are the same as those of the conventional a.

This will be described with reference to FIG. In this figure, the horizontal axis represents the mirror surface reflectance and the vertical axis represents the normalized power density (× 10
⁹ cm ² ) is used to explain the dependence of the mirror surface reflectance as a parameter that destroys the active layer thickness on the mirror surface, and the normalized power density varies depending on the difference in the active layer thickness. Is clear.

The COD level indicating the point where the mirror surface destruction occurs depends on the internal light density on the mirror surface. Figure 4
The normalized power density shown as the vertical axis of the figure represents that of the light inside the crystal. For example, the internal power density is 5 MW / cm.
^In order to produce an output of 10 mW or more in a laser that generates COD at ² , the standardized power density is 5 × 10 ⁸ cm ^-2
Must be: However, if the front surface reflectance is increased, the amount of light returning to the inside increases, and the normalized power density increases.

On the other hand, when the thickness of the active layer is reduced, the amount of light leaking into the cladding layer is increased and the internal light density in the active layer is reduced.

The kink level is not determined only by the light density on the mirror surface, but shows the same tendency as COD with respect to the internal power density on the mirror surface.

Therefore, the slope efficiency can be lowered by increasing the front surface reflectance, and the threshold current _Itr can be lowered to improve the temperature characteristics.

At this time, the kink level and the COD level simultaneously decrease, but it is possible to compensate by reducing the internal power density by thinning the active layer.

As is apparent from FIG. 4, the active layer thickness d
_{If act} is 0.03 μm, slope efficiency = 0.35, I _tr = 30 mA, kink level 14 mW, and COD is about 15 mW even with a high reflectance of 60%.

However, it is a practically sufficient value for use with an optical output of about 5 mW, and the operating current at 50 ° C. and 5 mW also drops from the conventional 60 to 70 mA to 40 to 50 mA. The reliability can be greatly improved.

As described above, the mirror surface reflectance is 50% or more and the thickness of the active layer is reduced to reduce the power density on the mirror surface. As a result, the slope efficiency and threshold are lowered, and the kink level and COD are reduced. Improvement of level Furthermore, improvement of droop characteristics can be achieved, and by extension, reliability at an operation level of 5 mW can be greatly improved.

Therefore, a visible light semiconductor laser device having suitable characteristics for a laser beam printer can be manufactured with high yield.

If the front surface reflectance is increased, the front surface mirror loss becomes smaller, the light extraction efficiency becomes worse, and the slope efficiency at the front surface mirror surface becomes smaller.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment according to the present invention.

FIG. 2 is a perspective view showing another embodiment according to the present invention.

FIG. 3 is a diagram showing current light output characteristics of a semiconductor laser.

FIG. 4 is a diagram for explaining the dependence of the normalized power density on the end surface on the mirror surface reflectance with the active layer thickness as a parameter.

FIG. 5 is a diagram showing the relationship between the two, with the front surface reflectance on the horizontal axis and the slope efficiency on the vertical axis.

FIG. 6 is a diagram showing the relationship between the two values by taking the front surface reflectance on the horizontal axis and the threshold value on the vertical axis.

[Explanation of symbols]

1: substrate, 2, 4: clad layer, 3: Active layer, 5: Striped current path, 6: current blocking layer, 7: contact layer, 8, 9: electrodes, 10: Front mirror surface, 11: Rear mirror surface.

Claims (2)

[Claims] 1. A semiconductor substrate of a first conductivity type, a clad layer of a first conductivity type and a clad layer of a second conductivity type formed on the semiconductor substrate in the following order, and a thickness provided between both clad layers. A current blocking layer of a first conductivity type having an active layer having a thickness of 0.03 μm or less, and a current path consisting of a stripe-shaped opening formed so as to overlap with the second conductivity type clad layer, the current path and the current. A contact layer formed by stacking on a block layer, an electrode formed on the exposed portion of the semiconductor substrate and the contact layer, a long side of the current path, an active layer, a clad layer of a first conductivity type and a second conductivity type. A semiconductor laser device comprising a mirror surface composed of crystal planes orthogonal to each other and having a reflectance of 50% or more on the emission surface side utilizing laser light. 2. The active layer and the cladding layer are made of In, respectively.
_1-y (Ga _1-x Al _x ) _y P and In _1-z (Ga _1-w A
consist l _{w) z} P, the semiconductor laser device, characterized in that the X <0.6 ≦ W