JP2010232425A - Semiconductor laser element and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized, low-cost, and high-performance semiconductor laser element which reduces a speckle noise, and also to provide a method for manufacturing the same. <P>SOLUTION: This semiconductor laser element is equipped with: a double hetero structure part stacking an n-type clad layer 103, an active layer 105, and a p-type clad layer 109 sequentially; a pair of laser resonator ends formed across the active layer 105; and reflection films 113 formed in the laser resonator ends for absorbing an oscillated light from the laser resonator ends. This semiconductor laser element is composed of a wurtzite type semiconductor. The laser resonator ends are formed on a C face (0001). When a band gap of the active layer 105 is Eg<SB>av</SB>, and a band gap of the reflection film 113 is Eg<SB>r</SB>, the following formula (1) is satisfied: (1) 1&times;Eg<SB>r</SB>&le;Eg<SB>av</SB>&le;1.2&times;Eg<SB>r</SB>. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a semiconductor laser device and a manufacturing method thereof.

  The group III nitride semiconductor material has a sufficiently large forbidden band width and a direct transition type between band transitions. Therefore, application to a short wavelength light emitting element has been actively studied. In particular, since the middle of the 1990s, the performance of light emitting diodes (LEDs) in the ultraviolet, blue, and green wavelength regions using this material for lighting and various display applications has improved dramatically. As a result, the application range of LEDs using this material has been greatly expanded to form a very large market. This material is also important as a light source for next-generation high-density optical disks. Therefore, research and development of a semiconductor laser diode (LD) with an oscillation wavelength of 405 nm has been vigorously advanced, and commercialization has already started.

  LDs using this material are also being studied as light sources for projection displays and the like. For example, good laser oscillation characteristics are obtained by the inner stripe laser structure on the GaN substrate disclosed in Patent Document 1.

  Further, Patent Document 2 can be cited as a related technique of the present invention. Patent Document 2 describes an air ridge type GaN semiconductor laser device having a lower threshold current value and a lower operating voltage than a conventional air ridge type GaN semiconductor laser device.

  Further, Patent Document 3 can be cited as a related technique of the present invention. Patent Document 3 describes that a protective layer having a band gap larger than the optical energy of oscillation light is provided on the laser end face. Thus, it is described that a highly reliable and long-life nitride semiconductor laser device can be obtained even during high-power transmission. Further, it is described that the reflective layer may serve as an odd multiple of λ / 4n.

  Further, Patent Document 4 can be cited as a related technique of the present invention. In Patent Document 4, a protective film is brought into contact with the nitride semiconductor layer on the resonator surface, and a protective film having a crystal structure different from the protective film is brought into contact with the second main surface of the substrate from the resonator surface. It is described that the adhesion of the protective film to the resonator surface can be improved by forming the protective film. Further, it is described that the adhesion between the protective film and the resonator surface can be improved by forming the protective film as a nitride film coaxial with the resonator surface. The resonator plane is preferably a plane selected from the group consisting of M-plane (1-100), A-plane (11-20), C-plane (0001), or R-plane (1-102), particularly M-axis orientation. It is described.

JP 2003-78215 A JP 2003-179111 A JP 2000-49410 A JP 2008-227002 A

  However, when the semiconductor laser described in Patent Documents 1 to 4 is used as a display light source, “flickering” caused by the coherence of laser light, that is, reduction of speckle noise becomes an important issue. Conventionally, in order to reduce this speckle noise, it is necessary to superimpose a plurality of independent laser beams or to use an optical element for changing the phase in time and space, which reduces the size and cost of the light source. It was difficult.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a small-sized, low-cost and high-performance semiconductor laser device with reduced speckle noise and a method for manufacturing the same.

According to the present invention,
A double heterostructure part in which a first cladding layer, an active layer, and a second cladding layer are sequentially stacked;
A pair of resonator end faces formed across the active layer;
A reflective film that is formed on at least one of the resonator end faces and absorbs oscillation light oscillated from the resonator end faces;
With
At least the active layer and the reflective film are made of a wurtzite semiconductor,
The resonator end surface is formed on a surface having polarity,
Provided is a semiconductor laser device that satisfies the following formula (1), where Eg _av is the band gap of the active layer and Eg _r is the band gap of the reflective film.
(1) 1 × Eg _r ≦ Eg _av ≦ 1.2 × Eg _r

Moreover, according to the present invention,
Laminating a first cladding layer, an active layer, and a second cladding layer in order;
Forming a pair of resonator end faces sandwiching the active layer;
Laminating a reflection film that absorbs oscillation light oscillated from the resonator end face on at least one of the resonator end faces;
Including
At least the active layer and the reflective film are formed of a wurtzite semiconductor,
In the step of forming the cavity end face, the cavity end face formed on the surface having a polarity, the band gap of the active layer and Eg _av, when the band gap of the reflective film and Eg _r, the following equation A method of manufacturing a semiconductor laser device that satisfies (1) is provided.
(1) 1 × Eg _r ≦ Eg _av ≦ 1.2 × Eg _r

  According to the present invention, it is possible to provide a small-sized, low-cost and high-performance semiconductor laser device with reduced speckle noise and a manufacturing method thereof.

1 is a perspective sectional view of a semiconductor laser device according to an embodiment. It is a figure which shows an example of the mirror loss spectrum of the reflecting film of the semiconductor laser element which concerns on embodiment. It is a figure which shows an example of the gain spectrum of the semiconductor laser element which concerns on embodiment. It is a figure which shows an example of the net gain spectrum of the semiconductor laser element which concerns on embodiment. (A) It is a figure which shows the relationship between the net gain and wavelength of the active layer of the 1st state of the semiconductor laser element which concerns on embodiment. (B) It is a figure which shows the relationship between the net gain and wavelength of the active layer of the 2nd state of the semiconductor laser element which concerns on embodiment. (C) It is a figure which shows the relationship between the mirror loss of the reflective film of the 1st state of the semiconductor laser element which concerns on embodiment, and a wavelength. (D) It is a figure which shows the relationship between the mirror loss and wavelength of the reflective film of the 2nd state of the semiconductor laser element which concerns on embodiment. (E) It is a figure which shows the relationship between the gain and wavelength of the semiconductor laser element of the 1st state which concerns on embodiment. (F) It is a figure which shows the gain and wavelength relationship of the semiconductor laser element of the 2nd state which concerns on embodiment. It is a perspective sectional view of a semiconductor laser device of a comparative example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

FIG. 1 is a schematic perspective sectional view showing the semiconductor laser device of the present embodiment. This semiconductor laser element includes a double heterostructure part in which an n-type cladding layer 103 (first cladding layer), an active layer 105, and a p-type cladding layer 109 (second cladding layer) are sequentially stacked, and an active layer 105. A pair of end faces of the laser resonator formed sandwiched and a reflection film 113 formed on the end face of the laser resonator and absorbing oscillation light oscillated from the end face of the laser resonator. This semiconductor laser element is made of a wurtzite semiconductor. The end face of the laser resonator is formed on the C plane (0001). The band gap of the active layer 105 and _{Eg av,} the band gap of the reflective film 113 when the Eg _r, satisfy the following formula (1).
(1) 1 × Eg _r ≦ Eg _av ≦ 1.2 × Eg _r

  The semiconductor laser device of this embodiment is fabricated on the {1-100} plane (m-plane, nonpolar plane) of the n-type substrate 101 (semiconductor substrate). The reflective film 113 is made of a wurtzite semiconductor and is laminated in the resonator direction, that is, in the C-axis direction [0001] direction. Therefore, the reflective film 113 in the state 1 that does not absorb oscillation light has a polarization electric field in the direction of the resonator due to the piezoelectric field. The reflective film 113 is designed so that the band gap of the reflective film 113 is reduced by this piezoelectric field compared to the band gap of the material constituting the reflective film 113.

In this element, the band gap between the active layer 105 and the reflective film 113 satisfies the above formula (1). Thereby, in the initial state before the laser oscillation starts, the absorption edge wavelength of the reflective film 113 and the wavelength of the oscillation light become substantially the same. Therefore, when light is oscillated from the end face of the resonator, the reflective film 113 absorbs part of the oscillated light. As a result, excited carriers are generated in the reflective film 113, and the internal electric field is screened (shielded) as the density of excited carriers increases. Therefore, the band gap energy increases, the mirror loss α _m of the reflective film 113 decreases (broken line 2 in FIG. 2), and the wavelength of the laser light emitted from the element becomes a long wave (broken line 2 in FIG. 3). On the other hand, the reflection film 113 in the state 2 that absorbs oscillation light has a large band gap energy, so that the absorption edge wavelength is shortened and the amount of oscillation light absorbed from the active layer 105 is decreased. As a result, the carrier density in the reflective film 113 gradually decreases, and the internal electric field is not screened (shielded). As a result, the band gap energy of the reflective film 113 decreases, and the mirror loss α _m increases to be the same as the mirror loss of the reflective film 113 in the state 1 (solid line 1 in FIG. 2). Therefore, the wavelength of the laser light emitted from the laser element becomes a short wave (solid line 1 in FIG. 3). Thereafter, periodically, the state 1 and the state 2 are fluctuated, and the mirror loss spectrum is fluctuated between the state 1 and the state 2. Thus, the reflection film 113 vibrates when irradiated with the oscillation light.

  Hereinafter, the principle of the semiconductor laser according to the present embodiment will be described in more detail with reference to FIGS. 2, 5 (c) and (d) have the mirror loss spectrum of the reflective film 113. In FIG. 2, the horizontal axis represents the energy (Eg) of light absorbed by the reflective film 113. 5C and 5D, the horizontal axis indicates the absorption edge wavelength (λ) of the reflective film 113. 3, 5 (e) and (f) have the gain spectrum of the semiconductor laser of the present embodiment. 3, the horizontal axis indicates the energy (Eg) of the emitted light, and in FIGS. 5 (e) and 5 (f), the horizontal axis indicates the wavelength (λ) of the emitted light. 4, 5 (a) and (b) have the net gain spectrum of the active layer 105. 4, the horizontal axis indicates the energy (Eg) of the oscillation light, and in FIGS. 5A and 5B, the horizontal axis indicates the wavelength (λ) of the oscillation light. 5A, 5C, and 5E show a first state in which the reflective film 113 does not absorb oscillation light, and FIGS. 5B, 5D, and 5F show the reflective film 113. FIG. Shows a second state in which oscillation light is absorbed.

The net gain G ′ is defined by the following formula (1).
G ′ = Γ × g−α _i (1)
Where Γ is a confinement factor of the active layer 105, g is a gain coefficient (cm ⁻¹ ), and α _i is an absorption coefficient (cm ⁻¹ ) for the total loss of the semiconductor laser device.

The gain G is defined by the following formula (2).
G = G′−α _m (2)

  As shown in FIGS. 4, 5 (a) and 5 (b), the net gain spectrum of the active layer 105 does not change between the state 1 and the state 2. In other words, the band gap of the active layer 105 does not change before and after the light oscillation.

In this element, the band gap between the active layer 105 and the reflective film 113 satisfies the above formula (1). Therefore, it is designed so that the absorption edge wavelength of the reflective film 113 and the wavelength of the oscillation light of the active layer 105 are substantially the same. It is preferable that the absorption edge wavelength AE of the reflective film 113 and the wavelength γ of the oscillation light satisfy 1 / AE ≦ 1 / γ ≦ 1.2 / AE, and 1 / AE ≦ 1 / γ ≦. It is more preferable to satisfy 1.1 / AE. When the materials of the active layer 105 and the reflective film 113 are made of the same element, the band gaps of the active layer 105 and the reflective film 113 can easily satisfy the above formula (1). The reflective film 113 is designed to absorb the oscillation light so as to shield the piezoelectric field and increase the band gap energy. Therefore, as shown in FIG. 2, in the state 2, the mirror loss spectrum is shifted to the high energy side. On the other hand, as described above, the net gain spectrum does not change before and after the oscillation of light. Therefore, as shown in FIG. 3, the gain spectrum shifts to the low energy side. Therefore, immediately after laser oscillation, laser light is emitted at a wavelength λ ₁ (FIG. 5 (e), solid line 1 in FIG. 3). However, the reflection film 113 absorbs the oscillation light having the wavelength λ ₁ , thereby increasing the wavelength. A long wave λ ₂ (λ ₁ <λ ₂ ) is emitted (FIG. 5 (f), broken line 2 in FIG. 3).

As shown in FIG. 5 (d), the In state 2, the absorption edge wavelength AE ₂ is shorter than the absorption edge wavelength AE ₁ state 1. Therefore, in the reflective film 113 in the state 2, the amount of oscillation light absorbed becomes small, and the excited carrier density decreases. As a result, the piezo electric field is not shielded, whereby the band gap of the reflective film 113 is reduced, and the mirror loss spectrum of the reflective film 113 returns to the low energy side again (state 1, solid line 1 in FIG. 2). As a result, the gain spectrum is shifted to the higher energy side, and the wavelength of the emitted light is shifted to λ ₁ (solid line 1 in FIG. 3). Thereafter, the wavelength fluctuates between the state 1 and the state 2 periodically, and the wavelength of the emitted laser light fluctuates between λ ₁ and λ ₂ .

  In order to generate the switching of the wavelength of the emitted light as described above, the wavelength λ of the emitted light and the absorption edge AE of the reflective film are designed so as to satisfy the following formula (3).

λ ₁ <AE ₂ ≦ λ ₂ <AE ₁ (3)

The difference (Δw) between AE ₁ and λ ₂ is preferably 5 nm to 50 nm. The difference (Δλ) between λ ₁ and λ ₂ is preferably 5 nm to 20 nm, and particularly preferably 10 nm. Further, the wavelength variation period is about several MHz to several tens of MHz, and at this time, the intensity of the laser beam may be modulated simultaneously. By doing so, speckle noise can be effectively suppressed.

As the wurtzite type semiconductor constituting the semiconductor laser device of this embodiment, a group III nitride semiconductor or a group II oxide semiconductor can be used, and a desired oscillation wavelength can be obtained by arbitrarily selecting the composition of the material. be able to. In particular, the group III nitride semiconductor is more preferable in that it can emit light efficiently. As the group III nitride semiconductor, one having a general formula of In _x Al _y Ga _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) can be used. Further, the oscillation wavelength of the active layer 105 and the absorption edge wavelength of the reflective film are controlled by changing the composition and thickness of the double heterostructure portion including the cladding layers 103 and 109 and the active layer 105 and the reflective film 113, respectively. be able to. For _example, the In _{z Ga 1-z} N, it can be a band gap energy to a desired one by using the following equation (4) (phys.stat.sol. (B ) 230, No2, R4-R6 (2002 )).
Eg (z) = 3.493-2.843z−2.5 × (1-z) (4)
However, in this embodiment, the absorption edge wavelength of the reflective film 113 is designed in consideration of the influence of the piezoelectric field.

Further, by making the elements constituting the reflective film 113 and the active layer 105 the same, the absorption edge wavelength and the oscillation wavelength of the reflective film 113 can be controlled with higher accuracy. For example, by making the reflective film 113 and the active layer 105 a layer made of In _z Ga _1-z N (0 <z <1), a laser that emits light efficiently in the blue to green band can be obtained.

  The reflective film 113 is preferably a single crystal. By doing so, the absorption edge wavelength of the reflective film 113 can be controlled with high accuracy.

The reflective film 113 may be doped with silicon. By doing so, it is possible to easily control the fluctuation range of the absorption edge wavelength. The amount of silicon to be doped is preferably 1 × 10 ¹⁶ to 1 × 10 ²⁰ cm ⁻³ .

  The reflective film 113 preferably has a heterostructure. With a structure having a large difference in refractive index, the reflectance of the reflective film 113 can be increased. Therefore, it becomes possible to control the wavelength of the emitted laser light with higher accuracy. The reflectance is preferably 80 to 99%.

By constructing the reflective film 113 and the active layer 105 with In _z Ga _1-z N (0 <z <1) and Al _n Ga _1-n N (0 <n <1), speckle noise is effectively reduced. A reduced laser emitting light in the blue to green band can be manufactured.

  Subsequently, as an example of the semiconductor laser element of the present embodiment, a nitride semiconductor laser element will be described as an example and will be described below with reference to FIG. This nitride semiconductor laser device includes an n-type GaN substrate 101, an n-side buffer layer 102, an n-type cladding layer 103, an n-type optical confinement layer 104, a quantum well layer (active layer) 105, p-type light. It has a confinement layer 106, a current confinement layer 107, a p-type cladding layer 109, a p-side contact layer 110, a p-type electrode 111, and an n-type electrode 112. In addition, a reflection film 113 is provided on the end face of the laser resonator.

  As shown in FIG. 1, the main surface of the n-type GaN substrate 101 is a (1-100) plane, and a resonator is formed in the <0001> direction. Further, the end face of the laser resonator is a {0001} plane, which is formed perpendicular to laser light (oscillation light) emitted by cleavage or dry etching.

Next, the layer structure of the nitride semiconductor laser device will be described in more detail. An n-side buffer layer 102 is formed on the n-type GaN substrate 101. The n-side buffer layer 102 is made of, for example, Si-doped n-type GaN (Si concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 1 μm = 1000 nm).

An n-type cladding layer 103 is formed so as to cover the Si-doped n-type GaN buffer layer 102. The n-type cladding layer 103 is made of, for example, Si-doped n-type Al _0.07 Ga _0.93 N (Si concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 2 μm = 2000 nm).

An n-type optical confinement layer 104 is formed so as to cover the n-type cladding layer 103. The n-type optical confinement layer 104 is made of, for example, Si-doped n-type GaN (Si concentration: 4 × 10 ¹⁷ cm ⁻³ , thickness: 100 nm).

A quantum well layer 105 is formed so as to cover the n-type optical confinement layer 104. The quantum well layer 105 is, for example, a two-period multiple quantum well (MQW) layer composed of an In _0.17 Ga _0.83 N (thickness 3 nm) well layer and an undoped GaN (thickness 10 nm) barrier layer. It is.

A cap layer (not shown) and a p-type optical confinement layer 106 are formed so as to cover the quantum well layer 105. The cap layer is made of, for example, Mg-doped p-type Al _0.2 Ga _0.8 N. The p-type optical confinement layer 106 is made of, for example, Mg-doped p-type GaN (Mg concentration 1 × 10 ¹⁹ cm ⁻³ , thickness 100 nm).

  A current confinement layer 107 is formed so as to cover the p-type optical confinement layer 106. The current confinement layer 107 is made of, for example, AlN.

A p-type cladding layer 109 is formed so as to cover the current confinement layer 107. The p-type cladding layer 109 is made of, for example, Mg-doped p-type Al _0.07 Ga _0.93 N (Mg concentration 1 × 10 ¹⁹ cm ⁻³ , thickness 500 nm).

A p-side contact layer 110 is formed so as to cover the p-type cladding layer 109. The p-side contact layer 110 is made of, for example, Mg-doped p-type GaN (Mg concentration 2 × 10 ²⁰ cm ⁻³ or less, thickness 20 nm). A p-type electrode 111 is provided on the p-side contact layer 110. An n-type electrode 112 is provided below the n-type GaN substrate 101.

Further, a reflection film 113 is formed on the end face of the laser resonator. The reflective film 113 is composed of, for example, eight cycles of In _0.12 Ga _0.88 N (thickness 40 nm) / Al _0.28 Ga _0.72 N (thickness 47 nm).

  Next, a method for manufacturing the semiconductor laser device of this embodiment will be described. First, the n-type cladding layer 103, the active layer 105, and the p-type cladding layer 109 are sequentially stacked on the nonpolar plane (for example, (1-100) plane) of the substrate 101 to form a double heterostructure.

  At this time, an n-type optical confinement layer 104 may be formed between the n-type cladding layer 103 and the active layer 105. Further, the p-type optical confinement layer 106 and the current confinement layer 107 may be formed between the active layer 105 and the p-type cladding layer 109.

  The current confinement layer 107 can be formed by the following process. First, an amorphous layer is formed by low temperature deposition. Thereafter, a stripe-shaped opening is provided in the amorphous layer by etching. The opening can be formed by lithography such as light exposure or electron beam exposure and selective etching using, for example, a phosphoric acid-based liquid described in Patent Document 1. Thereafter, the p-type cladding layer 109 and the upper layer are formed at a temperature higher than the amorphous layer formation temperature. In this way, the current confinement layer 107 can be converted from an amorphous layer to a crystalline layer. At this time, the opening is filled with the p-type cladding layer 109, but for convenience of description of the manufacturing process, the portion that was the opening is distinguished and referred to as a buried portion 108.

  Next, a p-type electrode 111 is formed on the double heterostructure, and an n-electrode 112 is formed on the surface of the substrate 101 opposite to the surface where the double heterostructure is formed. Next, a pair of resonator end faces are formed by cleaving in a polar plane (for example, <0001> direction) and sandwiching the active layer 105.

Next, the reflective film 113 is laminated on the resonator end face. The reflective film 113 can be formed by, for example, a molecular beam epitaxy (MBE) method. In the case of forming the reflective film 113 made of a nitride semiconductor made of In _x Al _y Ga _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), Ga, In In addition, each metal is used as a molecular beam by using an ordinary effusion cell as a raw material for Al, and a nitrogen raw material is supplied as a nitrogen radical beam by an RF plasma cell. The composition and film thickness of the reflective film 113 can be controlled by adjusting the molecular beam intensity and nitrogen radical beam intensity of Ga, In, and Al.

  It continues and demonstrates the effect of embodiment. In the present embodiment, the resonator end face is formed on a surface having polarity, the reflection film 113 is formed on the resonator end face, and the absorption end wavelength is made substantially the same as the wavelength of the oscillation light. By doing so, the reflective film 113 has a polarization electric field by a piezoelectric field, and the polarization electric field is screened by absorption of light. Therefore, the band gap of the reflective film 113 can be changed between a state where the oscillation light is not absorbed and a state where the oscillation light is absorbed. Furthermore, when the absorption edge wavelength of the reflection film 113 is shortened by light absorption, the absorption edge wavelength of the reflection film 113 is vibrated by the irradiation of oscillation light. That is, by periodically changing the amount of light absorbed by the reflective film 113, the mirror loss of the reflective film 113 can be periodically changed. As a result, the wavelength of the laser light emitted from the element is periodically changed. Will fluctuate. Therefore, according to the element of the present embodiment, the speckle noise can be reduced because the coherence of the laser beam is lowered.

  Further, in this semiconductor laser element, speckle noise can be reduced without using an optical element for superimposing oscillation light or changing a phase in space and time. Therefore, it is possible to realize a high-performance semiconductor laser device capable of reducing the size and cost of the light source.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable. For example, in the embodiment, an example has been described in which the reflective film is oriented in the same crystal axis direction as the resonator end face, that is, in the C-axis direction [0001] direction. However, it may be a plane having polarity, and may be a semipolar plane such as a (1-101) plane or a (11-22) plane. In addition, as shown in the embodiment, by using the (0001) plane as the resonator end surface, a good internal electric field can be applied to the reflective film 113, but the plane direction of the resonator end surface includes a <0001> component. Any semipolar surface or polar surface may be used. Moreover, it is good also as a semipolar surface whose angle | corner with {0001} planes other than the {0001} plane of a laser end surface is less than 90 degree | times. The n-type may be p-type and the p-type may be n-type. In the embodiment, the example in which the double hetero structure is formed on the substrate has been described. However, the double hetero structure may be formed on the template.

  In addition, although the plane orientation of the main surface of the substrate is the m-plane, the surface orientation of the main surface of the substrate is not limited to other planes as long as the surface orientation of the resonator end surface includes a <0001> component and is a semipolar or polar surface. The effects of the invention can be obtained. Therefore, even in the case of a surface emitting laser in which the substrate main surface is a {0001} plane (c-plane) and the laser end surface is also a c-plane, the same effect can be generated by an appropriate combination of the reflective film and the active layer. It is possible. Specifically, instead of the {1-100} plane of the substrate main surface in the above embodiment, a {11-20} plane, a {11-22} plane, or a {1-101} plane may be used. However, it is preferable to form the double heterostructure portion on the nonpolar surface of the semiconductor substrate because the wavelength of the oscillation light can be made stable and constant.

  Further, it is sufficient that at least one of the resonator end faces has a polarity. As long as the reflection film is formed on the resonator end face having a polarity, the reflection film is provided on at least one of the resonator end faces. Just do it. Further, the wavelength, material, and composition of the semiconductor laser element can be selected other than those listed in the embodiment.

(Example)
Hereinafter, a specific embodiment according to the present invention will be described with reference to FIG. An n-type GaN (1-100) substrate 101 having an n-type carrier Si concentration of about 1 × 10 ¹⁸ cm ⁻³ was used.

An element structure was formed on the n-type GaN substrate 101 under a reduced pressure of 400 hPa by using a metal-organic vapor phase epitaxy (MOVPE) method. A mixed gas of hydrogen and nitrogen was used as the carrier gas. As supply sources of Ga, Al, and In, trimethylgallium (TMG), trimethylaluminum (TMA), and trimethylindium (TMI) were used, respectively. Silane (SiH ₄ ) was used as the supply source of the n-type dopant Si, and biscyclopentadienyl magnesium (Cp ₂ Mg) was used as the supply source of the p-type dopant Mg.

First, crystal growth of amorphous AlN or the like for the n-type cladding layer 103, the active layer, the p-type cladding layer 109, and the current confinement layer 107 was performed. Hereinafter, this process is referred to as an “active layer growth process”. After the n-type GaN substrate 101 was put into the growth apparatus, the temperature of the substrate was raised while supplying NH ₃ , and the growth was started when the growth temperature was reached. Si-doped n-type GaN buffer layer 102 (Si concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 1 μm), Si-doped n-type Al _0.07 Ga _0.93 N (Si concentration 4 × 10 ¹⁷ cm ⁻³ , thickness) 2 μm) n-type cladding layer 103, Si-doped n-type GaN (Si concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.1 μm) n-type optical confinement layer 104, In _0.2 Ga _0.8 N A two-period multiple quantum well (DQW) layer 105 composed of a (thickness 3 nm) well layer and an undoped GaN (thickness 10 nm) barrier layer, and a cap layer composed of Mg-doped p-type Al _0.2 Ga _0.8 N (not shown) 1), a p-type optical confinement layer 106 made of Mg-doped p-type GaN (Mg concentration 2 × 10 ¹⁹ cm ⁻³ , thickness 0.1 μm) was sequentially deposited.

Here, the substrate temperature is 1080 ° C., the TMG supply rate is 58 μmol / min, the NH ₃ supply rate is 0.36 mol / min, and the AlGaN growth is the substrate temperature of 1080 ° C., the TMA supply rate is 49 μmol / min, and the TMG supply rate is 58 μmol / min. min, NH _{3 was} supplied at 0.36 mol / min. The InGaN MQW growth was performed at a substrate temperature of 800 ° C., a TMG supply rate of 8 μmol / min, and an NH ₃ supply rate of 0.36 mol / min. The TMIn supply rate was 48 μmol / min for the well layer and 3 μmol / min for the barrier layer. After depositing these structures, the substrate temperature was lowered to about 400 ° C., and an amorphous AlN layer (which was later crystallized to become the current confinement layer 107) was deposited. The supply amounts of TMA and NH ₃ during the deposition of the amorphous AlN layer were 36 μmol / min and 0.36 mol / min, respectively, and the deposited film thickness was 0.1 μm.

Next, stripe openings 108 extending in the <0001> direction were formed in the amorphous AlN layer. Hereinafter, this process is referred to as a “stripe formation process”. After depositing 100 nm of SiO ₂ on the amorphous AlN layer and applying a resist, a stripe pattern with a width of 1.5 μm was formed by photolithography.

Next, SiO ₂ was etched using buffered hydrofluoric acid as a mask, after which the resist was removed with an organic solvent and washed with water. The amorphous AlN layer was not etched or damaged in each step of buffered hydrofluoric acid, organic solvent, and water washing. Next, the amorphous AlN layer was etched using SiO ₂ as a mask. As the etching solution, a solution in which phosphoric acid and sulfuric acid were mixed at a volume ratio of 1: 1 was used. The amorphous AlN layer in the region not covered with the SiO ₂ mask was removed by etching for 8.5 minutes in the solution kept at 90 ° C. Thereafter, SiO ₂ used as a mask was removed with buffered hydrofluoric acid. Thus, a stripe-shaped opening having a width of 1.5 μm was formed in the amorphous AlN layer.

A p-type AlGaN cladding layer 109 was buried and regrown on the amorphous AlN layer in which the opening was formed. Hereinafter, this process is referred to as a “p-type cladding layer regrowth process”. After charging the MOVPE apparatus, the temperature was raised to 1100 ° C., which is the growth temperature, at an NH ₃ supply rate of 0.36 mol / min. After reaching 1100 ° C., a p-type cladding layer 109 made of Mg-doped p-type Al _0.07 Ga _0.93 N (Mg concentration 1 × 10 ¹⁹ cm ⁻³ , thickness 0.5 μm) was deposited. As a result, the opening was filled with the p-type cladding layer 109. For convenience of description of the manufacturing process, the portion that was the opening is distinguished and referred to as an embedded portion 108. Thereafter, the substrate temperature was lowered to 1080 ° C., and then a p-type contact layer 110 made of Mg-doped p-type GaN (Mg concentration 1 × 10 ²⁰ cm ⁻³ , thickness 0.02 μm) was deposited. The deposition conditions of AlGaN and GaN were the same as those in the active layer growth process described above, except for the difference in dopant.

  A p-type electrode 111 was formed on the upper part of the laser diode (LD) wafer obtained as described above, and an n-type electrode 112 was formed on the lower part by vacuum deposition. This process is referred to as an “electrode formation process”. After the electrode formation, the bar was cleaved in the direction perpendicular to the stripe-shaped buried portion 108 to form an LD bar. A typical element length was 500 μm.

Next, the obtained LD bar was put into a molecular beam epitaxy (MBE) apparatus, and a reflective film 113 was formed. After turning on the MBE apparatus, the substrate temperature is set to about 700 ° C., each metal of purity 7N is used as a molecular beam by using an ordinary effusion cell as a raw material for Ga, In, and Al, and a nitrogen raw material is supplied by an RF plasma cell. A nitrogen radical beam was supplied onto the substrate. The molecular beam intensity of each raw material is adjusted so that the growth rate of each binary group III nitride is 1 μm / h for GaN, 0.12 μm / h for InN, and 0.28 μm / h for AlN. The beam intensity was adjusted so that the V / III ratio was approximately 1. Under the above conditions, the reflection film 113 having 8 periods of In _0.12 Ga _0.88 N (thickness 40 nm) / Al _0.28 Ga _0.72 N (thickness 47 nm) was formed on the end face of the laser resonator. An LD chip was obtained through the above steps.

(Comparative example)
The LD chip shown in FIG. 6 was produced. As shown in the figure, the structure is the same as that of the example except that the reflection film 113 is not formed on the end face of the resonator. The manufacturing method is the same as that of the example except that the reflective film 113 is not formed.

(Evaluation)
The LD chips obtained in the examples and comparative examples were each fused to a heat sink, and the light emission characteristics were examined. As a result, the LD chip of the example laser-oscillated in a longitudinal multimode with a current density of 4.0 kA / cm ² , a voltage of 5.0 V, and a center wavelength of 450 nm. Further, it was confirmed that the center wavelength vibrates between 455 nm and 445 nm with a cycle of 20 MHz. AE ₁ was 460 nm and AE ₂ was 450 nm. On the other hand, the oscillation spectrum of the LD chip of the comparative example is constant at the center wavelength of 445 nm, and no oscillation of the wavelength was observed.

As mentioned above, although the structure of this invention was demonstrated, this invention is not restricted to this, Various aspects are included. The following is an example.
(1) A group III nitride semiconductor laser, wherein at least one laser end face is composed of a polar surface, and a reflective film having a polarity is formed thereon. .
(2) The nitride semiconductor laser according to (1), wherein the reflective film of the semiconductor laser is oriented in the same crystal axis direction as the laser end face.
(3) The nitride semiconductor laser according to (1) or (2), wherein the reflective film of the semiconductor laser is a single crystal.
(4) The nitride semiconductor laser according to (1) to (3), wherein an absorption edge mirror loss spectrum of the reflection film of the semiconductor laser is shifted to a high energy side by irradiation with laser oscillation light.
(5) The nitride semiconductor laser according to (1) to (4), wherein the oscillation wavelength of the semiconductor laser varies during operation.
(6) The nitride semiconductor laser according to (1) to (5), wherein the oscillation wavelength of the semiconductor laser varies periodically.
(7) The group III nitride semiconductor laser according to any one of (1) to (6), wherein the semiconductor laser is fabricated on a {1-100} plane substrate.
(8) The group III nitride semiconductor laser according to any one of (1) to (6), wherein the semiconductor laser is fabricated on a {11-20} plane substrate.
(9) The group III nitride semiconductor laser according to any one of (1) to (6), wherein the semiconductor laser is fabricated on a {11-22} plane substrate.
(10) The group III nitride semiconductor laser according to any one of (1) to (6), wherein the semiconductor laser is fabricated on a {0001} plane substrate.
(11) The group III nitride semiconductor laser according to any one of (1) to (10), wherein at least one of the semiconductor lasers has a (0001) plane.

101 n-type substrate 102 n-type buffer layer 103 n-type cladding layer 104 n-type optical confinement layer 105 active layer (quantum well layer)
106 p-type optical confinement layer 107 p-type current confinement layer 108 buried portion 109 p-type cladding layer 110 p-type contact layer 111 p-type electrode 112 n-type electrode 113 reflective film

Claims (16)

A double heterostructure part in which a first cladding layer, an active layer, and a second cladding layer are sequentially stacked;
A pair of resonator end faces formed across the active layer;
A reflective film that is formed on at least one of the resonator end faces and absorbs oscillation light oscillated from the resonator end faces;
With
At least the active layer and the reflective film are made of a wurtzite semiconductor,
The resonator end surface is formed on a surface having polarity,
A semiconductor laser device that satisfies the following formula (1), where Eg _av is the band gap of the active layer and Eg _r is the band gap of the reflective film.
(1) 1 × Eg _r ≦ Eg _av ≦ 1.2 × Eg _r   2. The semiconductor laser element according to claim 1, wherein the active layer and the reflective film are made of the same element. 3. The semiconductor laser device according to claim 1, wherein the active layer and the reflective film include In _z Ga _1-z N (0 <z <1).   4. In an initial state before laser oscillation starts, the absorption edge wavelength of the reflection film and the wavelength of oscillation light are substantially the same, and the reflection film vibrates when irradiated with oscillation light. The semiconductor laser device according to any one of the above.   The semiconductor laser device according to claim 1, wherein the reflective film is laminated in a resonator direction.   6. The semiconductor laser device according to claim 1, wherein the reflective film is a single crystal.   The semiconductor laser device according to claim 1, wherein the wurtzite semiconductor is a nitride semiconductor.   The semiconductor laser device according to claim 1, wherein the active layer and the reflective film have a heterostructure. The semiconductor laser device according to claim 8, wherein the heterostructure is composed of In _z Ga _1-z N (0 <z <1) and Al _n Ga _1-n N (0 <n <1).   The semiconductor laser device according to claim 1, wherein the double heterostructure portion is formed on a nonpolar surface of a semiconductor substrate.   11. The semiconductor laser device according to claim 1, wherein the resonator end surface on which the reflective film is formed is formed on a (0001) plane of a wurtzite semiconductor crystal.   The semiconductor laser device according to claim 1, wherein the double heterostructure portion is formed on a {1-100} plane of a semiconductor substrate.   The semiconductor laser device according to claim 1, wherein the double heterostructure portion is formed on a {11-20} plane of a semiconductor substrate.   The semiconductor laser device according to claim 1, wherein the double heterostructure portion is formed on a {11-22} plane of a semiconductor substrate.   The semiconductor laser device according to claim 1, wherein the double heterostructure portion is formed on a {0001} plane of a semiconductor substrate. Laminating a first cladding layer, an active layer, and a second cladding layer in order;
Forming a pair of resonator end faces sandwiching the active layer;
Laminating a reflection film that absorbs oscillation light oscillated from the resonator end face on at least one of the resonator end faces;
Including
At least the active layer and the reflective film are formed of a wurtzite semiconductor,
In the step of forming the cavity end face, the cavity end face formed on the surface having a polarity, the band gap of the active layer and Eg _av, when the band gap of the reflective film and Eg _r, the following equation A method of manufacturing a semiconductor laser device that satisfies (1).
(1) 1 × Eg _r ≦ Eg _av ≦ 1.2 × Eg _r

Images