JPH0645689A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To enhance a barrier of a conduction band or a valence band from an active layer to a window layer, to suppress leakage of carrier from the active layer to the window layer and to prevent deterioration of an end face of a resonator by doping it with impurities, and enhancing carrier concentration of the window layer formed at the end face of the resonator in which a light is irradiated. CONSTITUTION:A p-type AlXGa1-XAs clad layer 11, a p-type AlXGa1-XAs active layer 12, an n-type AlXGa1-XAs clad layer 13 and an n-type GaAs contact layer 14 are sequentially laminated on a p-type GaAs substrate 10 by an organic metal vapor growing method. In this case, a stripe structure for confirming a current and a light is formed in an element by a photolithography method or a chemical etching method. An end face of the structure is formed at an end face 15 of a resonator by a cleavage method to become a laser light irradiating end face, and an AlXGa1-XAs window layer 16 is formed at the face 15 by an MOCVD method. Zn is doped in the layer 16 as p-type impurity to enhance carrier concentration.

Description

Detailed Description of the Invention

[0001]

The present invention has a high reliability,
The present invention relates to a high output semiconductor laser device.

[0002]

2. Description of the Related Art Conventionally, a laser beam emitted from a semiconductor laser element having excellent light-converging property and directivity has been used for an information processing device such as an optical disk device or a laser beam printer device. Recently, in order to increase the amount of information processed by an information processing apparatus and increase the speed of the information processing apparatus, a laser beam emitted from a semiconductor laser element is required to have a high output and high reliability of the semiconductor laser element is required.

A high-power semiconductor laser device having improved reliability by preventing light absorption at the end face from which light of the semiconductor laser device is emitted and preventing deterioration of the end face has been studied.
The applicant has proposed in Japanese Patent Application No. 3-236645 that an end face from which a light is emitted by forming a window layer made of a semiconductor having a forbidden band width larger than that of an active layer on the end face from which a light is emitted from a semiconductor laser device. A high-output semiconductor laser device having high reliability, which can prevent light absorption in the semiconductor layer and can alleviate lattice distortion between the window layer and the semiconductor layer on the end face because the window layer is a thin film, has been filed. FIG. 5 is a vertical cross-sectional view of the main part of the semiconductor laser device. This semiconductor laser device is a semiconductor laser device using an A1GaAs-based material, and includes a GaAs substrate 50 and an Al _0.45 Ga _0.55 As clad layer.
51, Al _0.15 Ga _0.85 As active layer 52, Al _0.45 Ga _0.55
An As clad layer 53 and a GaAs contact layer 54 are sequentially laminated, and a stripe structure for current confinement and light confinement is provided inside the semiconductor laser device. On the end face 55 of the resonator from which light is emitted, the Al mixed crystal ratio is equal to that of the active layer 52.
Window layer 56 made of a larger Al _0.5 Ga _0.5 As semiconductor
Are formed. Therefore, the window layer 56 has a wider band gap than the active layer 52 and does not absorb light. Moreover, since the thickness of the window layer 56 is as thin as 0.2 μm, the lattice distortion between the resonator end face 55 and the window layer 56 can be relaxed, and the resonator end face 55 and the window layer 56 can be relaxed.
Since a good interface is formed between and, non-radiative recombination is unlikely to occur.

[0004]

In the above semiconductor laser device, the carrier concentration of the window layer 56 formed on the end face 55 of the resonator from which light is emitted is not limited.

However, when the carrier concentration of the window layer 56 is low, the following problems occur in the characteristics of the semiconductor laser device. For example, the active layer 52 has a carrier concentration of 1
A case where a p-type semiconductor layer having a density of × 10 ¹⁸ cm ^-3 and a p-type semiconductor layer having a carrier concentration of 5 × 10 ¹⁶ cm ^-3 is used as the window layer 56 will be described below. FIG. 6 is a diagram showing an energy band structure before the active layer 52 and the window layer 56 are joined, and FIG. 7 is a diagram showing an energy band structure after the active layer 52 and the window layer 56 are joined. Is. Here, E _F (a) is the Fermi level of the active layer 52, E _F (w) is the Fermi level of the window layer 56, and ΔEc is the energy difference of the conduction band between the active layer 52 and the window layer 56. , △ E
v represents the energy difference in the valence band. As shown in FIG. 7, when the active layer 52 and the window layer 56 are stacked, the barrier Ebc from the active layer 52 to the window layer 56 in the conduction band is approximately represented by the following formula (1). (Refer to “Optical Communication Device Optics” by Yonezu) Ebc = ΔEc + (E _F (a) −E _F (w)) (1) When the carrier concentration of the window layer 56 is low, Since the Fermi level E _F (a) is located near the center of the energy band and approaches the Fermi level E _F (w) of the active layer 52,
The value of the second term of the above equation (1) becomes small, and therefore the value of the barrier Ebc becomes small. Therefore, when a current is passed through the semiconductor laser element to inject carriers into the active layer 52 from the clad layers 51 and 53, and the laser oscillation occurs, the electrons 70 injected into the active layer leak to the window layer 56. A surface level 71 is formed on the surface of the window layer 56 by oxidation, and the electrons 70 leaked to the window layer 56 are non-radiatively recombined with holes at the surface level 71. The recombination causes local heat generation, the width of the forbidden body near the end face 55 of the resonator is reduced, and the light absorption is increased, and the electrons generated by the light absorption are further non-radiatively coupled with the holes. Temperature rises further. By repeating this, the end face 55 of the resonator is melted and deteriorated.

The window layer 56 has a carrier concentration of 5 × 10 5.
^When an n-type semiconductor layer of ¹⁶ cm ^-3 is used, the active layer
When carriers are injected into 52 and laser oscillation is occurring, the barrier E from the active layer 52 to the window layer 56 in the valence band
bv is approximately represented by the following equation (2).

[0007] _{Ebv = △ Ev + (E F} (w) -E F (a)) - Vj ··· (2) where, Vj is biased in the connection between the active layer 52 and the window layer 56 potential Indicates. When the carrier concentration of the window layer 56 is low, the value of the second term of the above formula (2) becomes small similarly to the above, so that the barrier Ebv becomes small and the holes injected into the active layer 56 become Leak to 52. Also in this case, as in the above case, non-radiative recombination occurs on the surface of the window layer 56, thereby inducing deterioration of the end face 55.

Even when the active layer 52 is an n-type and non-doped semiconductor layer, in the state where carriers are injected into the active layer 52 and laser oscillation occurs, the window layer 56 is exposed to the same as in the above case. Due to carrier leakage, the end surface 55 is deteriorated.

The present invention solves the above problems,
The purpose is to provide a high-power semiconductor laser with high reliability.

[0010]

A semiconductor laser device of the present invention comprises a resonator having an active layer sandwiched between a pair of clad layers, and an end face from which light amplified in the active layer of the resonator is emitted. And a window layer formed of a semiconductor having a bandgap larger than that of the active layer and having an increased carrier concentration by doping impurities, thereby achieving the above object.

Preferably, the carrier concentration of the window layer is
It is 1 × 10 ¹⁷ cm ^-3 or more.

[0012]

In the semiconductor laser device of the present invention, the carrier concentration of the window layer formed on the end face of the resonator from which light is emitted is increased. As a result, the barrier of the conduction band or valence band from the active layer to the window layer becomes high, and the leakage of carriers from the active layer to the window layer is suppressed. Therefore, the end face of the resonator is less likely to deteriorate.

[0013]

EXAMPLES Examples of the present invention will be described below.

(Embodiment 1) FIG. 1 is a diagram showing a semiconductor laser device of the present invention. This semiconductor laser device comprises a p-type GaAs substrate 10 and a p-type Al _x Ga _1-x As clad layer.
11, p-type Al _x Ga _{1 -x} As active layer 12, n-type Al _x Ga _{1 -x}
An As clad layer 13 and an n-type GaAs contact layer 14 are sequentially laminated by a metal organic chemical vapor deposition method (MOCVD method). At this time, a stripe structure for current confinement and light confinement is formed inside the element by a photolithography method or a chemical etching method. The end face of this stripe structure is made into the end face 15 of the resonator by the cleavage method. An end face 15 of the resonator serves as a laser light emitting end face, and an Al _x Ga _{1 -x} As window layer 16 is formed on the end face 15 by MOCVD. The window layer 16 is doped with Zn as a p-type impurity to increase the carrier concentration.

FIG. 2 shows an energy band structure before the active layer 12 and the window layer 16 are joined, and FIG. 3 shows the Fermi level in which the window layer 12 and the active layer 16 are joined. This is the energy band structure of time.

The electron barrier Ebc in the conduction band from the active layer 12 to the window layer 16 is approximately represented by the following equation (1).

[0017] _{Ebc = △ Ec + (E F} (a) -E F (w)) ··· (1) window layer 16, an impurity is doped carrier concentration of the p-type is enhanced. Therefore, the Fermi level of the window layer 16 approaches the valence band, and the value of the second term of the above formula (1) becomes large. Therefore, from the active layer 12 shown in the above formula (1) to the window layer
The electron barrier Ebc of the conduction band to 16 becomes larger. Therefore, a current is passed through the semiconductor laser element to inject carriers into the active layer 12, and the active layer 12 is oscillated under the condition of laser oscillation.
The leakage of the electrons 30 from the window layer 16 to the window layer 16 can be reduced. Therefore,
Non-radiative recombination of electrons 30 and holes at the surface level 31 of the window layer 16 does not occur. Therefore, deterioration of the end surface 15 can be suppressed.

FIG. 4 shows the relationship between the maximum light output of the semiconductor laser device and the carrier concentration of the window layer 16. In particular, when the carrier concentration of the window layer 16 is 1 × 10 ¹⁷ cm ⁻³ or more, the deterioration of the end face 15 is suppressed and the maximum light output is improved. Further, since the deterioration of the end surface 15 is suppressed, the reliability at the time of high output operation is improved.

Details of the semiconductor layer of this embodiment are shown below.

P-type GaAs substrate 10: thickness 100 μm p-type Al _x Ga _1-x As clad layer 11: Al _0.45 Ga _0.55
As, thickness 1.5 μm p-type Al _x Ga _1-x As active layer 12: Al _0.15 Ga _0.85 A
s, thickness 0.06 μm n-type Al _x Ga _1-x As clad layer 13: Al _0.45 Ga _0.55
As, thickness 1.5 μm n-type GaAs contact layer 14: thickness 1.5 μm p-type Al _x Ga _1-x As window layer 16: Al _0.5 Ga _0.5 As, thickness 0.2 μm, carrier concentration 1 × 10 ¹⁸ cm ^-3 Then, high-power optical oscillation of 600 mW was obtained,
No deterioration of the end face of the resonator was observed.

Example 2 Same as Example 1 except that the window layer 16 was doped with Se, which is an n-type impurity, as an impurity so that the carrier concentration of electrons in the window layer 16 was 1 × 10 ¹⁸ cm ^−3. Then, a semiconductor laser device was manufactured.

In the state where a current is passed through this semiconductor laser device to inject carriers into the active layer 12 and laser oscillation occurs, the barrier in the valence band from the active layer 12 to the window layer 16 is expressed by the following formula (2). Approximately shown.

[0023] _{Ebv = △ Ev + (E F} (w) -E F (a)) - Vj ··· (2) window layer 16, n-type impurity is doped with a carrier concentration is enhanced. Therefore, the Fermi level of the window layer 16 approaches the conduction band, and the value of the second term of the above equation (2) becomes large. Therefore, from the active layer 12 to the window layer 16 shown in the above formula (2).
The barrier Ebv of the valence band to the window is increased, and the leakage of holes from the active layer 12 to the window layer 16 can be reduced. Along with that,
Deterioration at the end surface 15 can also be suppressed.

Also in this case, the relationship between the maximum optical output of the laser and the carrier concentration is the same as that shown in FIG. 4, and particularly when the carrier concentration of the window layer 16 is 1 × 10 ¹⁷ cm ^-3 or more, the semiconductor laser device is used. The maximum light output of is improved and the reliability is also improved.

In this example, high-power optical oscillation of 600 mW was obtained, and deterioration of the end face of the resonator was not observed.

Although the p-type active layer is used in the above embodiment, similar effects can be obtained by using other n-type and non-doped active layers. Further, although Zn and Se are used as the impurities for doping the window layer 16, the same effect can be obtained by using other materials such as Mg, Be, Si and Te. The thickness of the window layer 16 is preferably 1.0 μm or less so that the lattice distortion between the end face 15 of the resonator and the window layer 16 can be relaxed.

The MOCVD method was used as the method for growing the window layer 16, but other molecular beam epitaxy method (MBE method) was used.
Method), metalorganic molecular beam epitaxy method (MOMBE
Method), an atomic layer growth method (ALE method) and the like. In addition to the cleavage method, a dry etching method, a chemical etching method, or the like may be used as a method for forming the end face of the resonator.

In the above embodiment, the AlGaAs semiconductor laser device is shown.
It can also be applied to an nGaAlP-based semiconductor laser device. Also, for the sake of simplicity, the semiconductor laser device having a double hetero structure is shown. However, an L having a guide layer provided on one side of the active layer is used.
OC (Large Optical Cavity) type, SCH (Separated Confinement Heterostructur) with guide layers on both sides
It can be applied to other structures such as the e) type, and further, GRIN (Graded Index) -SCH type in which the refractive index of the guide layer is gradually changed.

[0029]

As described above, in the semiconductor laser device of the present invention, the barrier of the conduction band or the valence band is increased by doping the window layer with impurities to increase the carrier concentration of the window layer, Carrier leakage from the active layer to the window layer can be suppressed. Therefore, it is possible to prevent light absorption of the active layer near the end face of the resonator from which light is emitted and suppress deterioration of the end face, improve the maximum optical output of the high-power laser, and improve reliability. it can.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a main part of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is an energy band structure diagram before a p-type window layer and an active layer of a semiconductor laser device of an example of the present invention are joined.

FIG. 3 is an energy band structure diagram after the p-type window layer and the active layer of the semiconductor laser device of the example of the present invention are joined.

FIG. 4 is a diagram showing the relationship between the maximum optical output of the semiconductor laser device and the carrier concentration of the window layer.

FIG. 5 is a longitudinal sectional view of a main part of a conventional semiconductor laser device.

FIG. 6 is an energy band structure diagram before a p-type window layer and an active layer of a conventional semiconductor laser device are stacked.

FIG. 7 is an energy band structure diagram after a p-type window layer and an active layer of a conventional semiconductor laser device are stacked.

[Explanation of symbols]

 12 Active layer 15 Resonator end face 16 Window layer

Claims (2)

[Claims] 1. A resonator having an active layer sandwiched between a pair of clad layers and an end face from which amplified light is emitted in the active layer of the resonator, the forbidden band width being larger than that of the active layer. A semiconductor laser device having a window layer made of a large semiconductor having a high carrier concentration by doping impurities. 2. The carrier concentration of the window layer is 1 × 10 ¹⁷ cm ^-3
The semiconductor laser device according to claim 1, which is as described above.