JP2672404B2 - Semiconductor laser device and driving method thereof - Google Patents

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 used in a laser beam printer, an optical pickup, etc. and a driving method thereof.

[0002]

2. Description of the Related Art Generally, a semiconductor laser device is constructed by laminating a semiconductor layer including a laser emission layer on a semiconductor substrate, and as shown in FIG. 3, the temperature Tc of the emission region (Tc = 0 in this example). The forward current I-optical output Po characteristic shifts in accordance with the temperatures of 25 ° C., 25 ° C., and 50 ° C. (at the same time, the threshold current Ith of laser oscillation indicated by the arrow in the figure also shifts). Since the temperature Tc of the light emitting region rises with the passage of the energization time, when driven with a constant current, the light output Po decreases with the passage of the energization time, as shown in FIG. This phenomenon is called droop, and it causes the print quality of a laser beam printer using a semiconductor laser device to deteriorate and the S / N ratio of an optical pickup to decrease.

In order to suppress this droop, conventionally, the fabrication parameter of the semiconductor layer constituting the semiconductor laser device is changed to reduce the slope η of the forward current I-optical output Po characteristic. Further, when the semiconductor laser device is driven, a bias current that does not exceed the threshold current Ith is supplied during a period in which the device does not emit light (non-emission period) so that the device actually emits light (emission period). There is also known a method in which the temperature Tc of the light emitting region does not change so much.

[0004]

However, when the manufacturing parameters of the semiconductor layer are changed in order to suppress the droop, the effect of suppressing the droop is small, and it is difficult to manufacture the device and the device characteristics are impaired. is there
(In the worst case, it may shorten the life of the device.). Further, in the case of the method of supplying the bias current that does not exceed the threshold current Ith even during the non-light emitting period, there is a problem that it is difficult to set the bias current to a value equal to or less than Ith and effective for increasing the temperature. When the bias current is set to a value extremely smaller than Ith, the effect of raising the temperature of the light emitting region of the element is not obtained during the non-light emitting period. On the other hand, when the bias current is set to a value close to Ith, This is because the element emits light due to the decrease in Ith even during the non-light emitting period. It is more difficult to change the bias current according to the temperature change of Ith because the driving circuit becomes complicated.

Therefore, an object of the present invention is to provide a semiconductor laser device which can be easily manufactured and driven and which can effectively reduce droop without deteriorating the device characteristics. Another object of the present invention is to provide a method of driving such a semiconductor laser device.

[0006]

In order to achieve the above object, a semiconductor laser device according to a first aspect of the present invention is such that a semiconductor layer including a laser emitting layer is laminated on a substrate, and from the surface of the semiconductor layer to the surface of the substrate. A semiconductor laser device in which the semiconductor layer is divided into a plurality of regions by a groove reaching to each of the regions so that the respective regions are independently energized, and a specific region of the plurality of regions is a region of the semiconductor layer. While lasing at a threshold current according to a manufacturing parameter, the threshold current of laser oscillation in a neighboring region of the plurality of regions adjacent to the specific region sandwiching the groove is It is characterized by being set to a value larger than the threshold current.

According to a second aspect of the present invention, there is provided a method of driving a semiconductor laser device, wherein the semiconductor laser device is driven by the semiconductor laser device according to the first aspect. A current lower than the threshold current of the neighboring region is applied, and a drive current equal to or higher than the threshold current for causing the specific region to emit light is applied only to the specific region in the light emitting period following the non-light emitting period. Characterize.

[0008]

The semiconductor laser device according to the first aspect of the invention is driven as follows. First, the magnitude of the drive current that should be applied to the specific region during the light emission period (the period during which the element emits light) is
It is set to a value between the threshold current of the specific region and the threshold current of the neighboring region (set to a value larger than the threshold current of the specific region). During the non-light-emission period (the period in which the element does not emit light), the specific region is not energized, and the bias current having the same magnitude as the drive current is supplied to the neighboring region. At this time, since the specific region is not energized, neither light emission nor heat generation occurs.
On the other hand, the vicinity region does not emit light because the magnitude of the bias current is smaller than the threshold current of this region, and heat is generated according to the magnitude of the bias current. As a result, the specific region receives the heat of the neighboring region and rises to the same temperature as when the drive current of the set magnitude is supplied. Subsequently, during the light emission period, the drive current of the set magnitude is supplied to the specific region and the neighboring region is not energized. At this time, the specific area is
Light is emitted (becomes a light emission output of the element) and heat is generated according to the magnitude of the drive current. On the other hand, since the above-mentioned neighboring region is not energized, neither light emission nor heat generation occurs. As a result, the specific region does not receive heat from the neighboring region, and heat is generated only by the drive current. Here, the drive current and the bias current applied to the vicinity region during the non-light emission period are set to have substantially the same magnitude as described above. Therefore, the temperature of the specific region (and the neighboring region) is kept substantially constant throughout the non-light emitting period and the light emitting period.
Therefore, the forward current-light output characteristics of the specific region hardly shift, and droop is effectively suppressed.

Further, since the temperatures in the specific region and the neighboring region are kept substantially constant, the threshold currents in both regions hardly shift. Therefore, the magnitude of the bias current can be easily set to a value (constant value) between the threshold currents of the both regions, in which the neighboring region does not emit unnecessary light and the necessary heat generation amount is obtained. To be done. Therefore, this semiconductor laser device can be easily driven by a simple driving circuit.

Further, the semiconductor layer constituting this semiconductor laser device may be formed with standard manufacturing parameters,
Grooves that divide the semiconductor layer into a plurality of regions are easily formed by etching. Furthermore, the threshold current in the above-mentioned vicinity region is set by applying an overcurrent to this region,
It is easily set (deteriorated) to a value larger than the threshold current of the specific region. Therefore, this semiconductor laser device is easily manufactured. Further, since the semiconductor layer is formed with standard manufacturing parameters, the characteristics of the manufactured device are not impaired.

According to the method of driving the semiconductor laser device of claim 2, as described above, a simple driving circuit is used.
The semiconductor laser device can be driven, and droop can be effectively suppressed.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The semiconductor laser device and its driving method of the present invention will be described in detail below with reference to the embodiments shown in the drawings.

As shown in FIG. 1, this semiconductor laser device comprises a p-type GaAs as a semiconductor layer on an n-type GaAs substrate 21.
Layer 20, n-type GaAs layer 19, p-type Ga _1- x AlxAs layer (laser emission layer) 18, p-type Ga _1- yAlyAs layer 17, p-type Ga _1- yAlyAs
A layer 17, a p-type GaAs _1- xAlxAs layer 16, and an n-type GaAs layer 15 are sequentially laminated, and the semiconductor layer is formed into a plurality of regions 2, 1, by grooves 4, 5 extending from the surface of the n-type GaAs layer 15 to the surface of the substrate 21. Three
The structure is divided into. The regions 2, 1, 3 are energized independently of each other by the electrodes 14, 22. Reference numerals 7, 6, and 8 denote stripe-shaped grooves (extending perpendicularly to the element cross section shown in FIG. 1) that narrow the current-carrying paths of the regions 2, 1, and 3, and In the laser emitting layer 18, the portions 12, 11, and 13 near the grooves 7, 6, and 8 respectively perform laser oscillation (light emission) or heat generation. Central area
(Specific region) 1 oscillates with a threshold current Ith1 according to the manufacturing parameters of the semiconductor layer, while regions on both sides
(Neighboring regions) 2 and 3 are set to a value Ith2, which is larger than the threshold current Ith1 in the region 1 because the threshold current for laser oscillation is supplied with overcurrent.

The semiconductor laser device of the present invention is driven as follows.

First, the magnitude of the drive current Iop to be applied to the region 1 during the light emission period (the period in which the device emits light) is determined by the threshold current Ith1 of the region 1 and the threshold current Ith2 of the regions 2 and 3. Set to a value between and.

As shown in FIG. 2, the region 1 is not energized during the non-light-emission period (the period in which the device does not emit light), and the regions 2 and 3 have the same magnitude as the drive current Iop. Bias current Ib is passed. At this time, since the region 1 is not energized, neither light emission nor heat generation occurs. On the other hand, areas 2, 3
Does not emit light because the magnitude of the bias current Ib is smaller than the threshold current Ith2 in this region, and heat is generated according to the magnitude of the bias current Ib. As a result, the area 1 receives the heat of the areas 2 and 3 and rises to the same temperature as when the drive current Iop of the set magnitude is supplied.

Subsequently, during the light emission period, as shown in FIG. 2, the drive current Iop having the set magnitude is set in the region 1 as described above.
To prevent current from being applied to the areas 2 and 3. At this time, the area 1 emits light according to the magnitude of the drive current.
(It becomes the light emission output of the element) and heat is generated. On the other hand, since the regions 2 and 3 are not energized, neither light emission nor heat generation occurs.
As a result, the area 1 does not receive heat from the areas 2 and 3, and heat is generated only by the drive current Iop. here,
The drive current Iop and the bias currents applied to the regions 2 and 3 in the non-light emitting period are set to the same magnitude as described above. Therefore, the temperature of the region 1 (and the regions 2 and 3) is kept substantially constant throughout the non-light emitting period and the light emitting period. Therefore, the forward current-optical output characteristics of the region 1 can be hardly shifted, and droop can be effectively suppressed.

Further, since the temperatures of the regions 1 and 2 and 3 are kept substantially constant, the threshold currents Ith1 and Ith2 of the regions 1, 2 and 3 hardly shift. Therefore, the magnitude of the bias current Ib is a value (constant value) such that the regions 2 and 3 do not emit light unnecessarily and the required amount of heat generation is obtained between the threshold currents Ith1 and Ith2.
Can be set easily. Therefore, this semiconductor laser device can be easily driven by a simple driving circuit.

Further, the semiconductor layers 20, 19, 18, 17, 16 and 15 constituting this semiconductor laser device may be formed by standard fabrication parameters, and the grooves 4 and 5 for partitioning the semiconductor layer are etched. It can be easily formed.
Further, the threshold current Ith2 of the regions 2 and 3 is changed (deteriorated) to a value larger than the threshold current Ith1 of the region 1 by passing an overcurrent to the regions 2 and 3, and thus it is easy to perform. Can be set to. Therefore, this semiconductor laser device can be easily manufactured. Also,
Since the semiconductor layers 20, 19, 18, 17, 16 and 15 can be formed with standard manufacturing parameters, it is possible to prevent the characteristics of the manufactured device from being impaired.

[0020]

As is apparent from the above, the semiconductor laser device according to the first aspect has a structure in which a semiconductor layer including a laser emitting layer is laminated on a substrate and the semiconductor layer is formed by a groove extending from the surface of the semiconductor layer to the surface of the substrate. Is a semiconductor laser device in which each of the regions is energized independently of each other, and a specific region of the plurality of regions is a threshold according to a manufacturing parameter of the semiconductor layer. While lasing with a value current, a threshold current of laser oscillation in a neighboring region adjacent to the specific region of the plurality of regions with the groove interposed therebetween is larger than the threshold current of the specific region. Since it is set to a value, it can be easily manufactured and driven, and droop can be effectively reduced without impairing device characteristics. Therefore, the printing quality of the laser beam printer using this semiconductor laser device and the S / N ratio of the optical pickup can be greatly improved.

According to a second aspect of the present invention, there is provided a method of driving a semiconductor laser device, wherein during the non-light emitting period of the semiconductor laser device, a current lower than a threshold current of the near region is applied only to the near region to cause the non-light emitting. In the light emitting period following the period, a driving current equal to or higher than a threshold current for causing the specific region to emit light is applied only to the specific region, so that the semiconductor laser device according to claim 1 can be driven by a simple driving circuit. Droop can be effectively suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a method for driving the semiconductor laser device.

FIG. 3 is a diagram showing a general forward current-optical output characteristic of a semiconductor laser device.

FIG. 4 is a diagram illustrating a droop of a conventional semiconductor laser device.

[Explanation of symbols]

1 Specific region 2, 3 Neighboring region 4, 5 Groove 6, 7, 8 Striped groove 11, 12, 13 Light or heat generating location 14,22 Electrode 15 n-type GaAs layer 16 p-type Ga _1- xAlxAs layer 17 p Type Ga _1- yAlyAs layer 18 p type Ga _1- xAlxAs layer 19 n type GaAs layer 20 p type GaAs layer 21 n type GaAs substrate

Claims (2)

(57) [Claims] 1. A semiconductor layer including a laser emitting layer is laminated on a substrate, and the semiconductor layer is divided into a plurality of regions by a groove extending from the surface of the semiconductor layer to the surface of the substrate, and the regions are independently of each other. A semiconductor laser device that is made to be energized, wherein a specific region of the plurality of regions oscillates with a threshold current according to a manufacturing parameter of the semiconductor layer, while the specific region of the plurality of regions is A semiconductor laser device, wherein a threshold current for laser oscillation in a neighboring region adjacent to the region with the groove interposed therebetween is set to a value larger than the threshold current in the specific region. 2. The method for driving a semiconductor laser device according to claim 1, wherein in the non-light emitting period of the semiconductor laser device, a current lower than a threshold current of the neighboring region is applied only to the neighboring region. In the light emission period following the non-light emission period after energization,
A method of driving a semiconductor laser device, wherein a drive current equal to or more than a threshold current for causing the specific region to emit light is applied only to the specific region.