JP4114223B2 - Operation method of self-oscillation type semiconductor laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a self-oscillation type semiconductor laser and a method for operating the same.
[0002]
[Prior art]
In applying a semiconductor laser as a light source for an optical disk recording / reproducing apparatus or the like, it is important how to suppress return light noise. As one of the countermeasures for suppressing the return light noise, a so-called self-pulsation type semiconductor laser that has been made multi-mode by self-excited oscillation of the semiconductor laser is conventionally known.
[0003]
Conventionally, in such a self-pulsation type semiconductor laser, for example, an n-type cladding layer, an active layer, and a p-type cladding layer are sequentially stacked on an n-type GaAs substrate, and the upper layer portion of the p-type cladding layer is provided. An index guide type semiconductor having a current confinement structure in which an n-type current confinement layer is embedded on both sides of the provided stripe portion, and a difference in refractive index between the portion corresponding to the stripe portion and the portions on both sides thereof It is smaller than the laser and the lateral light confinement is moderated. In operation, self-excited oscillation has been realized by causing the portions corresponding to both sides of the stripe portion in the active layer to act as a saturable absorber.
[0004]
[Problems to be solved by the invention]
However, in the conventional self-pulsation type semiconductor laser, when the operating conditions change, specifically, for example, when the operating temperature rises to a high temperature of about 70 ° C., the blocking rate of current by the n-type current confinement layer becomes room temperature. Compared with the time of operation, the carrier passes through the n-type current confinement layer, and the spread of the carrier in the lateral direction (perpendicular to the resonator length direction and parallel to the junction) increases. There is a problem in that the proper state of the light distribution and the carrier distribution collapses, and the portion that has been acting as a saturable absorber so far cannot play its role, and self-excited oscillation stops. As described above, in the conventional self-pulsation type semiconductor laser, the operating conditions capable of self-oscillation are limited to a narrow range, and the stability and reliability of self-excited oscillation with respect to changes in the operating conditions are lacking. there were.
[0005]
By the way, as a technique for suppressing the spread of the current in the lateral direction due to an increase in operating temperature or the like, when manufacturing a self-excited oscillation type semiconductor laser, the thickness or impurity concentration of the n-type current confinement layer, or the p-type cladding layer Although it is conceivable to control the thickness (particularly, the thickness on both sides of the stripe portion) and the impurity concentration, none of them are perfect and are limited. Specifically, for example, in order to suppress the spread of current in the lateral direction, it is effective to reduce the thickness of the p-type cladding layer on both sides of the stripe portion. It is difficult to strictly control the thickness of the portion, and inconveniences such as a decrease in the margin for self-excited oscillation and changes in other parameters of the laser occur, making design difficult.
[0006]
Therefore, an object of the present invention is to control the spread of the current in the lateral direction by a simple method, so that the range of operating conditions capable of self-oscillation can be widened, and stability against changes in operating conditions is achieved. Another object of the present invention is to provide a self-pulsation type semiconductor laser capable of realizing highly reliable self-pulsation and an operation method thereof.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the first invention of the present invention provides:
A first cladding layer of a first conductivity type;
An active layer on the first cladding layer;
A second cladding layer of the second conductivity type on the active layer,
In a self-pulsation type semiconductor laser having a current confinement structure in which a current confinement layer is embedded in both sides of a stripe portion provided in an upper layer portion of a second cladding layer,
An electrode electrically isolated from the laser driving electrode is connected to the current confinement layer
It is characterized by this.
[0008]
The second invention of this invention is:
A first cladding layer of a first conductivity type;
An active layer on the first cladding layer;
A second cladding layer of the second conductivity type on the active layer;
A current confinement layer having a striped opening on the second cladding layer;
In a self-pulsation type semiconductor laser having a second conductivity type third clad layer provided on the second clad layer in the opening portion of the current confinement layer,
An electrode electrically isolated from the laser driving electrode is connected to the current confinement layer
It is characterized by this.
[0009]
The third invention of the present invention is:
A first cladding layer of a first conductivity type;
An active layer on the first cladding layer;
A second cladding layer of the second conductivity type on the active layer,
A current confinement structure in which a current confinement layer is embedded in both sides of the stripe portion provided in the upper layer portion of the second cladding layer;
An operation method of a self-pulsation type semiconductor laser in which an electrode electrically isolated from a laser driving electrode is connected to a current confinement layer,
A laser driving voltage is applied to the laser driving electrode from the outside, and a predetermined voltage is applied to the current confinement layer independently of the laser driving voltage through the electrode.
It is characterized by this.
[0010]
The fourth invention of the present invention is:
A first cladding layer of a first conductivity type;
An active layer on the first cladding layer;
A second cladding layer of the second conductivity type on the active layer;
A current confinement layer having a striped opening on the second cladding layer;
A third clad layer of the second conductivity type provided on the second clad layer in the opening portion of the current confinement layer,
An operation method of a self-pulsation type semiconductor laser in which an electrode electrically isolated from a laser driving electrode is connected to a current confinement layer,
A laser driving voltage is applied to the laser driving electrode from the outside, and a predetermined voltage is applied to the current confinement layer independently of the laser driving voltage through the electrode.
It is characterized by this.
[0011]
In the present invention, the current confinement layer is typically of the first conductivity type, but in some cases, this current confinement layer may be insulative or semi-insulating.
[0012]
In the third and fourth aspects of the invention, the voltage applied to the current confinement layer may be controlled according to the operating conditions of the self-pulsation type semiconductor laser, such as the operating temperature. .
[0013]
In the third aspect of the invention, when the second clad layer is a p-type clad layer and the conductivity type of the current confinement layer is n-type, a positive voltage is applied to the current confinement layer, When the current cladding layer is a p-type cladding layer and the current confinement layer is insulative or semi-insulating, a negative voltage is applied to the current confinement layer. On the other hand, in the third invention of the present invention, when the second cladding layer is an n-type cladding layer and the conductivity type of the current confinement layer is p-type, a negative voltage is applied to the current confinement layer, When the second cladding layer is an n-type cladding layer and the current confinement layer is insulative or semi-insulating, a positive voltage is applied to the current confinement layer.
[0014]
In the fourth invention of the present invention, when the second cladding layer and the third cladding layer are p-type cladding layers and the conductivity type of the current confinement layer is n-type, a positive voltage is applied to the current confinement layer. When the second cladding layer and the third cladding layer are p-type cladding layers and the current confinement layer is insulative or semi-insulating, a negative voltage is applied to the current confinement layer To do. On the other hand, in the fourth invention of the present invention, when the second cladding layer and the third cladding layer are n-type cladding layers and the conductivity type of the current confinement layer is p-type, the current confinement layer is negative. When the second and third cladding layers are n-type cladding layers and the current confinement layer is insulative or semi-insulating, a positive voltage is applied to the current confinement layer. Apply.
[0015]
According to the present invention configured as described above, since the electrode electrically isolated from the laser driving electrode is connected to the current confinement layer, during operation, the current confinement layer is passed through this electrode. On the other hand, a predetermined voltage can be applied from the outside independently of the laser driving voltage. In this way, by applying a predetermined voltage to the current confinement layer, a fixed charge is generated in the current confinement layer. Further, the electrostatic induction effect due to the fixed charge generated in the current confinement layer As a result, a fixed charge of the opposite polarity is generated in the second cladding layer or in both the second cladding layer and the third cladding layer, so that the current flowing in the element is at the center of the stripe portion. Become focused. For this reason, even if the operating conditions change, the lateral expansion of the carriers injected into the active layer is suppressed, and as a result, the portions corresponding to both sides of the stripe portion in the active layer are allowed. The saturated absorption region is formed stably, and for example, when the operating temperature is high, self-excited oscillation can be performed under severe operating conditions that were conventionally impossible.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
First, a first embodiment of the present invention will be described. FIG. 1 shows an AlGaAs self-pulsation type semiconductor laser according to the first embodiment. This AlGaAs self-oscillation semiconductor laser has an SCH (Separate Confinement Heterostructure) structure, and the active layer has a multiple quantum well (MQW) structure.
[0018]
As shown in FIG. 1, in the AlGaAs self-pulsation semiconductor laser according to the first embodiment, for example, an n-type Al is formed on an n-type GaAs substrate 1. _x2 Ga _1-x2 N-type Al through the As buffer layer 2 _x1 Ga _1-x1 As cladding layer 3, n-type Al _x2 Ga _1-x2 As optical waveguide layer 4, non-doped Al _x3 Ga _1-x3 MQW structure active layer 5 with As layer as quantum well layer, p-type Al _x2 Ga _1-x2 As optical waveguide layer 6, p-type Al _x1 Ga _1-x1 As cladding layer 7, non-doped Al _x2 Ga _1-x2 As optical waveguide layer 8 and p-type Al _x1 Ga _1-x1 As cladding layers 9 are sequentially stacked.
[0019]
Al _x2 Ga _1-x2 As optical waveguide layer 8 and p-type Al _x1 Ga _1-x1 The As cladding layer 9 has a ridge stripe shape with a predetermined width extending in one direction. For example, n-type Al is formed on both sides of the ridge stripe portion. _x1 Ga _1-x1 An n-type current confinement layer 10 composed of an As cladding layer 10a and an n-type GaAs layer 10b thereon is buried. In this case, the n-type current confinement layer 10 is provided on the entire surface including the portion on the ridge stripe portion, and the p-type Al is formed on the predetermined portion on the ridge stripe portion. _x1 Ga _1-x1 A stripe-shaped opening 10c having a predetermined width reaching the As cladding layer 9 is provided. Here, of the n-type current confinement layer 10, the upper n-type GaAs layer 10 b has a role for making good contact with an electrode (described later) provided thereon.
[0020]
P-type Al in the portion of the n-type current confinement layer 10 and the opening 10c excluding part of both ends in the lateral direction _x1 Ga _1-x1 A p-type GaAs cap layer 11 is provided on the As cladding layer 9 so as to fill the opening 10c.
[0021]
Where n-type Al _x1 Ga _1-x1 As cladding layer 3, p-type Al _x1 Ga _1-x1 As cladding layer 7, p-type Al _x1 Ga _1-x1 As cladding layer 9 and n-type Al _x1 Ga _1-x1 X1 in the As layer 10a is n-type Al. _x2 Ga _1-x2 As buffer layer 2, n-type Al _x2 Ga _1-x2 As optical waveguide layer 4, p-type Al _x2 Ga _1-x2 As optical waveguide layer 6 and Al _x2 Ga _1-x2 It is made larger than x2 in the As optical waveguide layer 8, and this x2 is Al as the quantum well layer of the active layer 5. _x3 Ga _1-x3 It is larger than x3 in the As layer. That is, x1>x2> x3. For example, x1 = 0.47, x2 = 0.3, and x3 = 0.13.
[0022]
In this AlGaAs self-pulsation type semiconductor laser, p-type Al _x1 Ga _1-x1 As cladding layer 7 and p-type Al _x1 Ga _1-x1 Al between the As cladding layer 9 _x2 Ga _1-x2 Since the As optical waveguide layer 8 is inserted, a step-shaped refractive index distribution is created in the lateral direction, and thereby the optical waveguide in the lateral direction is performed. In this case, the ridge stripe portion The refractive index difference between the high-refractive index portion and the low-refractive index portions on both sides thereof is smaller than that of a normal index guide type semiconductor laser, and the lateral light confinement is moderated.
[0023]
An example of the thickness of each semiconductor layer constituting the AlGaAs self-pulsation type semiconductor laser is n-type Al. _x2 Ga _1-x2 The thickness of the As buffer layer 2 is 1 μm, n-type Al _x1 Ga _1-x1 The thickness of the As cladding layer 3 is 1.5 μm, n-type Al _x2 Ga _1-x2 As optical waveguide layer 4, p-type Al _x2 Ga _1-x2 As optical waveguide layer 6 and Al _x2 Ga _1-x2 The As optical waveguide layer 8 has a thickness of 70 nm and p-type Al. _x1 Ga _1-x1 The thickness of the As cladding layer 7 is 0.35 μm, p-type Al _x1 Ga _1-x1 The thickness of the As cladding layer 9 is 1.3 μm, and the n-type Al of the n-type current confinement layer 10 is _x1 Ga _1-x1 The thickness of the As layer 10a is 0.8 μm, the thickness of the n-type GaAs layer 10b is 0.5 μm, and the thickness of the p-type GaAs cap layer 11 is 1.5 μm.
[0024]
On the p-type GaAs cap layer 11, a p-side electrode 12 such as a Ti / Pt / Au electrode is provided in ohmic contact. In addition, an electrode 13 such as an AuGe / Ni electrode is connected to the n-type GaAs layer 10b at a predetermined portion on the n-type current confinement layer 10 that is not covered with the p-type GaAs cap layer 11 at both lateral ends. Provided in ohmic contact. On the other hand, an n-side electrode 14 such as an AuGe / Ni electrode is provided in ohmic contact with the back surface of the n-type GaAs substrate 1. As described above, in this AlGaAs self-pulsation type semiconductor laser, the electrode 13 separated from the p-side electrode 12 and the n-side electrode 14 is provided on the n-type current confinement layer 10, so that it is externally provided. A predetermined voltage can be applied to the n-type current confinement layer 10 through the electrode 13 independently of the laser driving voltage.
[0025]
Next, the operation of the AlGaAs self-pulsation type semiconductor laser configured as described above will be described.
[0026]
That is, when this AlGaAs self-pulsation type semiconductor laser is oscillated, for example, a positive voltage of about 2 to 3 V is applied to the p-side electrode 12 and the n-side electrode 14 is grounded. Here, the operation when the operating temperature is about room temperature and no voltage is applied to the electrode 13 will be described. In this case, as shown in FIG. 2, in the active layer 5, a current (here, n-type Al with respect to the active layer 5) _x1 Ga _1-x1 Electrons e injected from the As cladding layer 3 side ^- The light spreads almost over the portion corresponding to the ridge stripe portion, whereas the light spreads beyond the portion corresponding to the ridge stripe portion due to the gentle lateral confinement. Saturable absorption regions 15 are formed in portions corresponding to both sides of the ridge stripe portion in the active layer 5. Therefore, when the operating temperature is about room temperature, the saturable absorption region 15 is formed in the active layer 5 as described above, so that this AlGaAs self-oscillation is not required even if no voltage is applied to the electrode 13. Type semiconductor lasers self-oscillate.
[0027]
On the other hand, when the operating temperature rises from room temperature and reaches a high temperature of about 70 ° C., for example, if no voltage is applied to the electrode 13, the current blocking rate by the n-type current confinement layer 10 is at room temperature operation. As a result, the current spread in the lateral direction in the active layer 5 becomes larger than that at the time of room temperature operation, and carriers are injected also into the portion where the saturable absorption region 15 was formed at the time of room temperature operation. As a result, the self-excited oscillation stops. Therefore, in this AlGaAs self-pulsation type semiconductor laser, when the operating temperature rises, a predetermined positive voltage is applied to the n-type current confinement layer 10 through the electrode 13 independently of the laser driving voltage. In addition, the spread of current in the lateral direction due to an increase in operating temperature is suppressed.
[0028]
When a positive voltage is applied to the n-type current confinement layer 10 through the electrode 13, electrons are attracted to the electrode 13 side in the n-type current confinement layer 10 as shown in FIG. A positive (+) fixed charge is left behind. On the other hand, p-type Al in the vicinity of the junction with the n-type current confinement layer 10 _x1 Ga _1-x1 As cladding layer 7, p-type Al _x1 Ga _1-x1 In the As cladding layer 9 and the p-type GaAs cap layer 11, holes are repelled by the electrostatic induction effect due to the positive (+) fixed charge generated in the n-type current confinement layer 10, and as a result, the negative is caused by the p-type impurity. A fixed charge (−) is generated. For this reason, of the carriers, e ^- Is p-type Al _x1 Ga _1-x1 As cladding layer 7, p-type Al _x1 Ga _1-x1 It is repelled by the influence of negative (−) fixed charges generated in the As clad layer 9 and the p-type GaAs cap layer 11 and is concentrated in the center of the ridge stripe portion, and the hole (not shown) is an n-type. The electron e is repelled by the influence of positive (+) fixed charges generated in the current confinement layer 10. ^- In the same way as in the case of, it is concentrated at the center of the ridge stripe portion.
[0029]
As described above, in this AlGaAs self-pulsation type semiconductor laser, by applying a predetermined positive voltage to the n-type current confinement layer 10, the current spread is increased even when the operating temperature rises. Since it can be suppressed, saturable absorption regions 15 are formed in portions corresponding to both sides of the ridge stripe portion in the active layer 5 as in the room temperature operation, and stable self-excited oscillation is possible. In the case of this AlGaAs self-oscillation type semiconductor laser, when the operating temperature is 70 ° C., a positive voltage of about 5 to 10 V is applied to the electrode 13 to enable self-oscillation to an output of about 5 mW. Become.
[0030]
When this AlGaAs self-oscillation type semiconductor laser is used as a light source for an optical disk recording / reproducing apparatus, for example, it is positively applied to the n-type current confinement layer 10 through the electrode 13 during reproduction in which self-excited oscillation operation is required. A voltage is applied, and the AlGaAs self-pulsation semiconductor laser is self-oscillated with an output of 5 mW, for example. At this time, for example, a combination of a temperature sensor and a microprocessor is used to constantly monitor the operating temperature of the AlGaAs self-excited oscillation type semiconductor laser and control the voltage applied to the n-type current confinement layer 10 according to the operating temperature. (Specifically, by controlling the voltage applied to the n-type current confinement layer 10 to increase as the operating temperature rises), the AlGaAs self-pulsation semiconductor laser is changed in operating temperature. Regardless of this, self-excited oscillation is possible in a substantially constant state. On the other hand, since it is not necessary to perform a self-oscillation operation during recording, the application of voltage to the n-type current confinement layer 10 is stopped, and this AlGaAs-based self-oscillation semiconductor laser is driven at a high output of 20 to 30 mW, for example. Operate the output.
[0031]
Next, a manufacturing method of the AlGaAs self-pulsation type semiconductor laser according to the first embodiment configured as described above will be explained.
[0032]
That is, in order to manufacture this AlGaAs self-pulsation type semiconductor laser, first, as shown in FIG. 4, an n-type Al is formed on an n-type GaAs substrate 1. _x2 Ga _1-x2 As buffer layer 2, n-type Al _x1 Ga _1-x1 As cladding layer 3, n-type Al _x2 Ga _1-x2 As optical waveguide layer 4, MQW structure active layer 5, p-type Al _x2 Ga _1-x2 As optical waveguide layer 6, p-type Al _x1 Ga _1-x1 As cladding layer 7, Al _x2 Ga _1-x2 As optical waveguide layer 8 and p-type Al _x1 Ga _1-x1 The As cladding layer 9 is sequentially grown by, for example, the MOCVD method.
[0033]
Next, p-type Al _x1 Ga _1-x1 For example, the CVD method is used on the entire surface of the As cladding layer 9 to form SiO. ₂ After forming the film and the SiN film, they are patterned by etching to form a stripe-shaped mask (not shown) having a predetermined width, and using this mask as an etching mask, p-type Al is formed by wet etching. _x1 Ga _1-x1 Etching is performed until the surface of the As cladding layer 6 is exposed. As a result, as shown in FIG. _x2 Ga _1-x2 As optical waveguide layer 8 and p-type Al _x1 Ga _1-x1 The As cladding layer 9 is patterned into a ridge stripe shape having a predetermined width extending in one direction. Thereafter, the mask used as an etching mask is removed.
[0034]
Next, as shown in FIG. 6, n-type Al as the n-type current confinement layer 10 is formed on the entire surface. _x1 Ga _1-x1 The As layer 10a and the n-type GaAs layer 10b are sequentially grown by, for example, the MOCVD method. Next, by selectively etching the n-type current confinement layer 10 in a predetermined portion on the ridge stripe portion, an opening 10c is formed in this portion. Next, the p-type GaAs cap layer 11 is grown on the entire surface by, for example, the MOCVD method so as to fill the opening 10c of the n-type current confinement layer 10.
[0035]
Next, as shown in FIG. 7, the p-side electrode 12 is formed on the entire surface of the p-type GaAs cap layer 11.
[0036]
Next, the entire surface of the p-side electrode 12 is made of SiO by, eg, CVD. ₂ After forming a film or SiN film, this is patterned by etching to cover a portion corresponding to the vicinity of the ridge stripe portion, and a mask (not shown) having a predetermined shape having openings at both ends in the lateral direction. Form. Next, using this mask as an etching mask, etching is performed until the surface of the n-type current confinement layer 10 is exposed, whereby the p-type GaAs cap layer 11 and the p-side electrode 12 are patterned into a predetermined shape as shown in FIG. To do.
[0037]
Next, a portion excluding a predetermined portion on the n-type current confinement layer 10 exposed at both ends in the lateral direction is covered with a resist pattern (not shown), and an AuGe / Ni film is formed on the entire surface. By removing (lifting off) together with the upper AuGe / Ni film, an electrode 13 is formed at a predetermined portion on the n-type current confinement layer 10 as shown in FIG.
[0038]
Next, the n-type GaAs substrate 1 is lapped from its back surface side to have a predetermined thickness. Thereafter, as shown in FIG. 1, an n-side electrode 14 is formed on the back surface of the n-type GaAs substrate 1. Thus, the target AlGaAs self-pulsation type semiconductor laser is manufactured.
[0039]
As described above, according to the first embodiment, the electrode 13 electrically isolated from the p-side electrode 12 and the n-side electrode 14 is connected to the n-type current confinement layer 10, and this electrode 13 is in operation. When a predetermined positive voltage is applied to the n-type current confinement layer 10 independently of the laser driving voltage, the operating condition changes, for example, when the operating temperature rises. Even if it exists, the spread to the horizontal direction of the carrier inject | poured in the active layer 5 can be suppressed. For this reason, according to the first embodiment, the range of operating conditions in which the AlGaAs self-oscillation semiconductor laser can perform self-oscillation can be widened compared to the conventional one, and the n-type current confinement layer By controlling the voltage applied to 10 according to the operating conditions, it is possible to maintain the self-excited oscillation state even when the operating conditions change. In addition, the reliability can be improved.
[0040]
Further, according to the first embodiment, the self-oscillation operation is controlled and maintained by a simple method of applying a positive voltage to the n-type current confinement layer 10 during operation. Compared to the structure of a normal self-oscillation type semiconductor laser, it is only necessary to change the electrode 13 to the n-type current confinement layer 10, so that the development cost is low and the margin for self-oscillation is increased. Therefore, it is easy to manufacture, and the control of the self-excited oscillation operation is realized only by suppressing the lateral spread of the current flowing in the element. It also has the advantage of increasing the degree of freedom.
[0041]
Next explained is the second embodiment of the invention. FIG. 10 is a cross-sectional view of an AlGaAs self-pulsation semiconductor laser according to the second embodiment. This AlGaAs self-pulsation type semiconductor laser has an SCH structure, and the active layer has an MQW structure.
[0042]
As shown in FIG. 10, in the AlGaAs self-pulsation type semiconductor laser according to the second embodiment, for example, an n-type Al is formed on an n-type GaAs substrate 21. _x2 Ga _1-x2 N-type Al via the As buffer layer 22 _x1 Ga _1-x1 As cladding layer 23, n-type Al _x2 Ga _1-x2 As optical waveguide layer 24, non-doped Al _x3 Ga _1-x3 MQW structure active layer 25 with As layer as quantum well layer, p-type Al _x2 Ga _1-x2 As optical waveguide layer 26 and p-type Al _x1 Ga _1-x1 As cladding layers 27 are sequentially stacked.
[0043]
p-type Al _x1 Ga _1-x1 On the As cladding layer 27, for example, n-type Al _x1 Ga _1-x1 An n-type current confinement layer 28, which is composed of an As cladding layer 28a and an n-type GaAs layer 28b on the As cladding layer 28a and has a stripe-shaped opening 28c having a predetermined width extending in one direction, is laminated. The p-type Al in the n-type current confinement layer 28 and its opening 28c excluding part of both ends in the lateral direction. _x1 Ga _1-x1 On the As cladding layer 27, non-doped Al _x2 Ga _1-x2 P-type Al through the As optical waveguide layer 29 _x1 Ga _1-x1 An As cladding layer 30 is laminated. This p-type Al _x1 Ga _1-x1 A p-type GaAs cap layer 31 is provided on the As cladding layer 30.
[0044]
Where n-type Al _x1 Ga _1-x1 As cladding layer 23, p-type Al _x1 Ga _1-x1 As cladding layer 27, n-type Al _x1 Ga _1-x1 As layer 28a and p-type Al _x1 Ga _1-x1 X1 in the As cladding layer 30 is n-type Al. _x2 Ga _1-x2 As buffer layer 22, n-type Al _x2 Ga _1-x2 As optical waveguide layer 24, p-type Al _x2 Ga _1-x2 As optical waveguide layer 26 and Al _x2 Ga _1-x2 It is made larger than x2 in the As optical waveguide layer 29, and this x2 is Al as the quantum well layer of the active layer 25. _x3 Ga _1-x3 It is larger than x3 in the As layer. That is, x1>x2> x3. For example, x1 = 0.47, x2 = 0.3, and x3 = 0.13.
[0045]
In this AlGaAs self-pulsation type semiconductor laser, p-type Al in the opening 28c is used. _x1 Ga _1-x1 As cladding layer 27 and p-type Al _x1 Ga _1-x1 Al between the As cladding layer 30 _x2 Ga _1-x2 By inserting the As optical waveguide layer 29, a step-shaped refractive index distribution is created in the lateral direction, and thereby the optical waveguide in the lateral direction is performed. In this case, the difference in refractive index between the high refractive index portion in the ridge stripe portion and the low refractive index portion on both sides thereof is smaller than in the case of a normal index guide type semiconductor laser, and the light in the lateral direction is reduced. Confinement is relaxed.
[0046]
An example of the thickness of each semiconductor layer constituting the AlGaAs self-pulsation type semiconductor laser is n-type Al. _x2 Ga _1-x2 The thickness of the As buffer layer 22 is 1 μm, n-type Al _x1 Ga _1-x1 The thickness of the As cladding layer 23 is 1.5 μm, n-type Al _x2 Ga _1-x2 As optical waveguide layer 24, p-type Al _x2 Ga _1-x2 As optical waveguide layer 26 and Al _x2 Ga _1-x2 The As optical waveguide layer 29 has a thickness of 70 nm and p-type Al. _x1 Ga _1-x1 The As cladding layer 27 has a thickness of 0.35 μm, and of the n-type current confinement layer 28, n-type Al _x1 Ga _1-x1 The As layer 28a is 0.4 μm thick, the n-type GaAs layer 28b is 0.3 μm thick, p-type Al _x1 Ga _1-x1 The As clad layer 30 has a thickness of 1 μm, and the p-type GaAs cap layer 31 has a thickness of 0.5 μm.
[0047]
On the p-type GaAs cap layer 31, a p-side electrode 32 such as a Ti / Pt / Au electrode is provided in ohmic contact. Further, at both lateral ends, the p-type GaAs cap layer 31, p-type Al _x1 Ga _1-x1 As cladding layer 30 and Al _x2 Ga _1-x2 An electrode 33 such as an AuGe / Ni electrode, for example, is provided in ohmic contact with the n-type GaAs layer 28b at a predetermined portion on the n-type current confinement layer 28 that is not covered with the As optical waveguide layer 29. On the other hand, an n-side electrode 34 such as an AuGe / Ni electrode is provided in ohmic contact with the back surface of the n-type GaAs substrate 21. As described above, in this AlGaAs self-pulsation type semiconductor laser, the electrode 33 separated from the p-side electrode 32 and the n-side electrode 34 is provided on the n-type current confinement layer 28, so that it is externally provided. A predetermined voltage can be applied to the n-type current confinement layer 28 through the electrode 33 independently of the laser driving voltage.
[0048]
The AlGaAs self-pulsation type semiconductor laser according to the second embodiment configured as described above can perform the same operation as the AlGaAs self-pulsation type semiconductor laser according to the first embodiment.
[0049]
Next explained is a method for manufacturing the AlGaAs self-pulsation semiconductor laser according to the second embodiment configured as described above.
[0050]
That is, in order to manufacture this AlGaAs self-pulsation type semiconductor laser, first, as shown in FIG. 11, an n-type Al is formed on an n-type GaAs substrate 21. _x2 Ga _1-x2 As buffer layer 22, n-type Al _x1 Ga _1-x1 As cladding layer 23, n-type Al _x2 Ga _1-x2 As optical waveguide layer 24, active layer 25, p-type Al _x2 Ga _1-x2 As optical waveguide layer 26, p-type Al _x1 Ga _1-x1 N-type Al constituting the As cladding layer 27 and the n-type current confinement layer 28 _x1 Ga _1-x1 The As layer 28a and the n-type GaAs layer 28b are sequentially grown by, for example, the MOCVD method.
[0051]
Next, on the n-type current confinement layer 28, SiO ₂ A mask (not shown) made of a film, a SiN film or the like and having a stripe-shaped opening with a predetermined width extending in one direction is formed. Next, the n-type current confinement layer 28 is selectively etched by wet etching using this mask as an etching mask. As a result, as shown in FIG. 12, a stripe-shaped opening 28 c extending in one direction is formed in the n-type current confinement layer 28. Thereafter, the mask used for etching is removed.
[0052]
Next, as shown in FIG. 13, the opening 28c is embedded in the entire surface of the n-type current confinement layer 28, and Al _x2 Ga _1-x2 As optical waveguide layer 29 and p-type Al _x1 Ga _1-x1 As cladding layer 30 is grown sequentially by MOCVD, for example, and p-type Al _x1 Ga _1-x1 A p-type GaAs cap layer 31 is grown on the entire surface of the As cladding layer 30 by, for example, the MOCVD method.
[0053]
Next, as shown in FIG. 14, a p-side electrode 32 is formed on the entire surface of the p-type GaAs cap layer 31.
[0054]
Next, the entire surface of the p-side electrode 32 is made of SiO by, eg, CVD. ₂ After forming a film or SiN film, this is patterned by etching to cover a portion corresponding to the vicinity of the ridge stripe portion, and a mask (not shown) having a predetermined shape having openings at both ends in the lateral direction. Form. Next, by using this mask as an etching mask, etching is performed until the surface of the n-type current confinement layer 28 is exposed, as shown in FIG. _x2 Ga _1-x2 As optical waveguide layer 29, p-type Al _x1 Ga _1-x1 The As cladding layer 30, the p-type GaAs cap layer 31, and the p-side electrode 32 are patterned into a predetermined shape.
[0055]
Next, a portion excluding a predetermined portion on the n-type current confinement layer 28 exposed at both lateral ends is covered with a resist pattern (not shown), an AuGe / Ni film is formed on the entire surface, and then the resist pattern is applied to the resist pattern. By removing (lifting off) together with the upper AuGe / Ni film, an electrode 33 is formed at a predetermined portion on the n-type current confinement layer 28 as shown in FIG.
[0056]
Next, the n-type GaAs substrate 21 is lapped from the back surface side to have a predetermined thickness. Thereafter, as shown in FIG. 10, an n-side electrode 34 is formed on the back surface of the n-type GaAs substrate 21. Thus, the target AlGaAs self-pulsation type semiconductor laser is manufactured.
[0057]
According to the second embodiment, the same advantages as those of the first embodiment can be obtained.
[0058]
Next explained is the third embodiment of the invention. FIG. 17 is a sectional view of an AlGaAs self-pulsation type semiconductor laser according to the third embodiment. This AlGaAs self-pulsation type semiconductor laser is of a surface emitting type having a vertical resonator structure. 17, parts that are the same as or correspond to those in FIG. 10 are given the same reference numerals.
[0059]
As shown in FIG. 17, in this AlGaAs self-pulsation semiconductor laser, an n-type Al is formed on an n-type GaAs substrate 21. _x1 Ga _1-x1 Each semiconductor layer constituting the laser structure is stacked via the As buffer layer 22 in the same manner as the AlGaAs self-pulsation semiconductor laser according to the second embodiment. In this case, however, the n-type current confinement layer 28 is made of p-type Al. _x1 Ga _1-x1 An n-type GaAs layer 28d on the As cladding layer 27 and an n-type Al layer on the n-type GaAs layer 28d _x2 Ga _1-x2 As layer 28e. Here, in the n-type current confinement layer 28, the thickness of the n-type GaAs layer 28d is, for example, 0.1 μm. Further, in this AlGaAs self-pulsation type semiconductor laser, a reflecting mirror (not shown) is provided at a predetermined portion, whereby a resonator structure is formed in a direction perpendicular to the main surface of the n-type GaAs substrate 21. A groove 21a for extracting laser light is provided in a predetermined portion on the back side of the n-type GaAs substrate 21.
[0060]
In the AlGaAs self-pulsation type semiconductor laser, the p-type GaAs cap layer 31 is stacked on the n-type GaAs substrate 21 and then etched from the back side of the n-type GaAs substrate 21 to thereby obtain a lateral direction. The n-type GaAs layer 28d of the n-type current confinement layer 28 is exposed at both ends. Therefore, in this case, the electrode 33 is the p-type Al in the n-type current confinement layer 28. _x1 Ga _1-x1 The n-type GaAs layer 28d provided on the side in contact with the As cladding layer 27 is in contact.
[0061]
Where n-type Al _x1 Ga _1-x1 As cladding layer 23, p-type Al _x1 Ga _1-x1 As cladding layer 27 and p-type Al _x1 Ga _1-x1 X1 in the As cladding layer 30 is n-type Al. _x2 Ga _1-x2 As buffer layer 22, n-type Al _x2 Ga _1-x2 As optical waveguide layer 24, p-type Al _x2 Ga _1-x2 As optical waveguide layer 26, n-type Al _x2 Ga _1-x2 As layer 28e and Al _x2 Ga _1-x2 It is made larger than x2 in the As optical waveguide layer 29, and this x2 is Al as the quantum well layer of the active layer 25. _x3 Ga _1-x3 It is larger than x3 in the As layer. That is, x1>x2> x3. For example, x1 = 0.47, x2 = 0.3, and x3 = 0.13.
[0062]
Since the other configuration of the AlGaAs self-pulsation semiconductor laser is the same as that of the AlGaAs self-pulsation semiconductor laser according to the second embodiment, the description thereof is omitted.
[0063]
The AlGaAs self-pulsation type semiconductor laser applies a predetermined positive voltage to the n-type current confinement layer 28 through the electrode 33 electrically separated from the p-side electrode 32 and the n-side electrode 34. The same operation as that of the AlGaAs self-pulsation type semiconductor laser according to the first embodiment can be performed.
[0064]
According to the third embodiment, the same advantages as those of the first embodiment can be obtained in the surface-emitting AlGaAs self-pulsation semiconductor laser having a vertical resonator structure.
[0065]
Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible. For example, the numerical values, materials, structures, and the like given in the embodiments are merely examples, and are not limited to these.
[0066]
Specifically, the n-type current confinement layers 10 and 28 in the first to third embodiments described above are formed of n-type Al. _x1 Ga _1-x1 Laminated structure of As layers 10a, 28a and n-type GaAs layers 10b, 28b, or n-type GaAs layer 28d and n-type Al _x2 Ga _1-x2 Although it has a laminated structure with the As layer 28e, these may be a single-layer n-type AlGaAs layer or n-type GaAs layer, for example.
[0067]
In place of the n-type current confinement layers 10 and 28 in the first to third embodiments, an insulating or semi-insulating current confinement layer may be used. Specifically, for example, when the current confinement layer is made semi-insulating, the current confinement layer is formed using a semi-insulating AlGaAs layer or GaAs layer doped with Co or Fe. In the first to third embodiments, when the current confinement layer is insulative or semi-insulating, a negative voltage is applied to the current confinement layer during operation. The operation principle at this time is the same as the operation principle described in the first embodiment. Specifically, for example, in the first embodiment, a case where a semi-insulating current confinement layer is used instead of the n-type current confinement layer 10 will be described as an example. By applying a negative voltage, a positive (+) charge is induced in the portion of the current confinement layer opposite to the electrode, while p-type Al in the vicinity of the junction with the current confinement layer. _x1 Ga _1-x1 As cladding layer 7, p-type Al _x1 Ga _1-x1 In the As cladding layer 9 and the p-type GaAs cap layer 11, holes are repelled by the electrostatic induction effect due to the positive (+) fixed charge generated in the current confinement layer, and as a result, a negative (−) fixed charge is generated. To do. For this reason, of the carriers, e ^- Is p-type Al _x1 Ga _1-x1 As cladding layer 7, p-type Al _x1 Ga _1-x1 It is repelled by the influence of negative (−) fixed charges generated in the As clad layer 9 and the p-type GaAs cap layer 11, and is concentrated in the center of the ridge stripe portion. Repelled by the influence of positive (+) fixed charges generated in the layer, the electron e ^- In the same way as in the case of, it is concentrated at the center of the ridge stripe portion.
[0068]
Further, for example, in the first to third embodiments described above, the conductivity types of the substrate and each semiconductor layer may be reversed. In this case, as the current confinement layer, a p-type conductivity type or an insulating or semi-insulating layer is used. When a p-type current confinement layer is used, a negative voltage is applied to the p-type current confinement layer during operation, and when an insulating or semi-insulating current confinement layer is used, In operation, a positive voltage is applied to the insulating or semi-insulating current confinement layer.
[0069]
In the first to third embodiments, the case where the present invention is applied to an AlGaAs self-pulsation semiconductor laser having an SCH structure has been described. However, the present invention is an AlGaAs self-oscillation having a DH (Double Heterostructure) structure. It is also possible to apply to an excitation oscillation type semiconductor laser. The active layer may have a structure other than the MQW structure.
[0070]
Furthermore, in the first to third embodiments, the case where the present invention is applied to an AlGaAs self-pulsation type semiconductor laser has been described. However, the present invention is not limited to an AlGaAs type self-pulsation type semiconductor laser, but includes an AlGaInP type. The present invention can also be applied to self-pulsation type semiconductor lasers, self-pulsation type semiconductor lasers using II-VI group compound semiconductors, and self-pulsation type semiconductor lasers using nitride III-V group compound semiconductors. In general, in a self-pulsation type semiconductor laser using a II-VI group compound semiconductor, Al is used as a material for the current confinement layer. ₂ O _Three In a self-pulsation type semiconductor laser using a nitride III-V compound semiconductor, SiO is used as a material for the current confinement layer. ₂ However, even when such an insulator is used as the material of the current confinement layer, the same effects as those described in the above embodiment can be obtained.
[0071]
The technical idea similar to that of the present invention can also be applied to a normal semiconductor laser other than a self-excited oscillation type semiconductor laser. In this case, a predetermined voltage is applied to the current confinement layer during the operation of the semiconductor laser. By applying this, it is possible to cause a normal semiconductor laser to perform a self-oscillation operation. In addition, when the lateral refractive index difference Δn is small and light confinement is moderated as in a self-excited oscillation type semiconductor laser, the lateral light spread is caused by the injection of carriers into the active layer. Although it is hardly affected by the state, as in the case of an index guide type semiconductor laser, the lateral refractive index difference Δn is larger than that of a self-excited oscillation type semiconductor laser, and light confinement is strengthened. It is possible to directly control the beam shape by applying a voltage to the current confinement layer to change the state of carrier injection into the active layer. Specifically, in this case, by applying a voltage to the current confinement layer, the lateral spread of carriers in the active layer becomes smaller than when no voltage is applied (carrier injection region). Therefore, the beam divergence angle θ // in the horizontal direction of the far-field image (FFP) can be increased.
[0072]
【The invention's effect】
As described above, according to the present invention, since the electrode electrically isolated from the laser driving electrode is connected to the current confinement layer, the laser is applied to the current confinement layer from the outside through the electrode during operation. Self-excited oscillation can be controlled by a simple method of applying a predetermined voltage independent of the driving voltage. This allows a wide range of operating conditions in which self-excited oscillation is possible, and changes in operating conditions. Therefore, it is possible to realize a self-pulsation type semiconductor laser with high stability and reliability of self-pulsation against the above.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an AlGaAs self-pulsation type semiconductor laser according to a first embodiment of the invention.
FIG. 2 is a cross-sectional view for explaining the operation of the AlGaAs self-pulsation semiconductor laser according to the first embodiment of the invention.
FIG. 3 is a cross-sectional view for explaining the operation of the AlGaAs self-pulsation semiconductor laser according to the first embodiment of the invention.
FIG. 4 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation semiconductor laser according to the first embodiment of the invention.
FIG. 5 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation semiconductor laser according to the first embodiment of the invention.
6 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation type semiconductor laser according to the first embodiment of the invention. FIG.
7 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation semiconductor laser according to the first embodiment of the invention. FIG.
FIG. 8 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation semiconductor laser according to the first embodiment of the invention.
FIG. 9 is a sectional view of an AlGaAs self-pulsation type semiconductor laser according to a second embodiment of the invention.
FIG. 10 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation semiconductor laser according to the second embodiment of the invention.
11 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation semiconductor laser according to the second embodiment of the invention. FIG.
12 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation type semiconductor laser according to the second embodiment of the invention. FIG.
13 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation type semiconductor laser according to the second embodiment of the invention. FIG.
FIG. 14 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation type semiconductor laser according to the second embodiment of the invention.
FIG. 15 is a cross-sectional view for explaining the method of manufacturing the AlGaAs self-pulsation semiconductor laser according to the second embodiment of the invention.
FIG. 16 is a cross-sectional view for explaining the method for manufacturing the AlGaAs self-pulsation semiconductor laser according to the second embodiment of the invention.
FIG. 17 is a sectional view of an AlGaAs self-pulsation type semiconductor laser according to a third embodiment of the invention.
[Explanation of symbols]
1,21 ... n-type GaAs substrate, 3,23 ... n-type Al _x1 Ga _1-x1 As cladding layer, 4, 24 ... n-type Al _x2 Ga _1-x2 As optical waveguide layer, 5, 25 ... active layer, 6, 26 ... p-type Al _x2 Ga _1-x2 As optical waveguide layer, 7, 9, 27, 30... P-type Al _x1 Ga _1-x1 As cladding layer, 8, 29 ... Al _x2 Ga _1-x2 As optical waveguide layer, 10, 28... N-type current confinement layer, 10a, 28a... N-type Al _x1 Ga _1-x1 As layer, 10b, 28b, 28d ... n-type GaAs layer, 28e ... n-type Al _x2 Ga _1-x2 As layer, 11, 31 ... p-type GaAs cap layer, 12, 32 ... p-side electrode, 13, 33 ... electrode, 14, 34 ... n-side electrode

Claims (2)

A first cladding layer of a first conductivity type;
An active layer on the first cladding layer;
A second cladding layer of the second conductivity type on the active layer,
A current confinement structure in which a current confinement layer is embedded in portions on both sides of the stripe portion provided in the upper layer portion of the second cladding layer;
An operation method of a self-excited oscillation type semiconductor laser in which an electrode electrically isolated from a laser driving electrode is connected to the current confinement layer, and an optical waveguide layer is inserted under the stripe portion There,
A laser driving voltage is applied to the laser driving electrode from the outside, and a predetermined voltage is applied to the current confinement layer independently of the laser driving voltage through the electrode. A method for operating a self-excited oscillation type semiconductor laser, characterized in that control is performed so that the operating temperature of the excitation type semiconductor laser increases as the operating temperature rises . A first cladding layer of a first conductivity type;
An active layer on the first cladding layer;
A second conductivity type second cladding layer on the active layer;
A current confinement layer having a stripe-shaped opening on the second cladding layer;
A third clad layer of a second conductivity type provided on the second clad layer in the opening portion of the current confinement layer and the current confinement layer;
An electrode electrically isolated from the laser driving electrode is connected to the current confinement layer, and light is applied to the current confinement layer and the second cladding layer in the opening portion of the current confinement layer. An operation method of a self-pulsation type semiconductor laser in which the third cladding layer is provided via a wave layer,
A laser driving voltage is applied to the laser driving electrode from the outside, and a predetermined voltage is applied to the current confinement layer independently of the laser driving voltage through the electrode. A method for operating a self-excited oscillation type semiconductor laser, characterized in that control is performed so that the operating temperature of the excitation type semiconductor laser increases as the operating temperature rises .

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