JP4901068B2 - Nitride-based semiconductor laser device and optical information processing apparatus including the same - Google Patents

Description

  The present invention relates to an improvement in a nitride semiconductor laser element and an optical information processing apparatus including the nitride semiconductor laser element. In the present specification, the optical information processing apparatus means an apparatus capable of performing at least one process of recording, reproducing, and erasing information with respect to an optical recording medium.

  In an optical information processing apparatus, a semiconductor laser element capable of generating a high-power and stable laser beam is eagerly desired in response to a demand for an increase in information recording speed. Furthermore, along with a demand for higher information recording density in a recording medium, a semiconductor laser element capable of emitting laser light having a short wavelength is eagerly desired.

  In general optical information processing devices, a recording method that uses the crystal phase change or magnetic phase transition of the material constituting the recording layer of the recording medium is employed, and the energy of the laser beam is used as a heat source during information recording. Has been. Therefore, in order to realize a high information recording speed, it is necessary to increase the light output of the laser element.

  However, it is known that when the amount of current injection is increased in order to increase the optical output of the semiconductor laser device, the semiconductor laser device oscillates not only in the basic horizontal horizontal mode but also in the high horizontal horizontal mode. . As a result, it becomes difficult to focus the laser beam on a small spot, the spot of the converged laser beam is likely to be displaced, and the recording density is reduced.

  The horizontal mode includes a horizontal horizontal mode and a vertical horizontal mode, but the problem is high-order mode oscillation in the horizontal horizontal mode. This is because the processing dimension accuracy in the manufacturing process of the laser element is higher in the stacking direction (vertical direction) of the semiconductor layers constituting the laser structure than in the direction orthogonal to the semiconductor layer (horizontal direction), and the layer thickness can be controlled with high accuracy. This is because it is possible to form an element structure that can oscillate only the basic vertical transverse mode without oscillating the higher-order vertical transverse mode.

  As semiconductor laser elements that emit laser light with a short wavelength, GaN, InN, AlN, and nitride semiconductor materials typified by their mixed crystal semiconductors are used as active layers, and laser light in the blue to ultraviolet region is emitted. Nitride-based semiconductor laser elements that can be used are listed, and in recent years, the trial production thereof has been carried out. A laser beam having a short wavelength can be focused to a spot that is smaller than a laser beam having a long wavelength. Therefore, an optical information processing apparatus using a nitride-based semiconductor laser element as a light source is attracting attention as a next-generation high-density information processing apparatus that can increase the recording density on a recording medium as compared with the conventional one.

  The known technology improves the unstable state due to the asymmetrical shape of the horizontal carrier distribution and horizontal light intensity distribution in the stripe region, and oscillates to a high output in a single horizontal transverse mode (basic horizontal transverse mode only). For this purpose, there is known an AlGaAs semiconductor laser element employing a so-called real refractive index waveguide type (ridge stripe structure) optical waveguide. In order to oscillate only in the basic next horizontal transverse mode up to high output, it is effective to reduce the width of the optical waveguide (hereinafter referred to as the stripe width). However, it is known that if it is made too narrow, the optical confinement action of the waveguide with respect to the light of the fundamental horizontal / horizontal mode becomes weak, and the threshold voltage of the semiconductor laser element increases. Therefore, there is a preferred range for the stripe width.

  The technique for optimizing the stripe width can also be applied to a nitride semiconductor laser element. However, since the optimum value of the stripe width is substantially proportional to the wavelength of the laser oscillation, the nitride semiconductor laser element has a smaller value of 2.0 μm or less than the AlGaAs semiconductor laser element. The effect of the stripe width on the characteristics of the nitride-based semiconductor laser device becomes more prominent as the design value width becomes narrower. As a result, in order to sufficiently reduce the influence on the characteristics of the nitride-based semiconductor laser element, a technique for forming the stripe width with an accuracy within ± 0.1 μm from the design value is required. However, it is extremely difficult in terms of process technology to be within this accuracy range. Therefore, it is difficult for a nitride-based semiconductor laser device to oscillate to a high output in a single horizontal transverse mode (basic next horizontal transverse mode only) only by adjusting the stripe width.

  FIG. 11 is a schematic cross-sectional view showing a conventional laminated structure of a typical nitride-based semiconductor laser device, and the direction orthogonal to the drawing is the resonator direction (axial direction). In this nitride semiconductor laser device, a lower cladding layer 3002, a lower optical waveguide layer 3003, an active layer 3004 having a triple quantum well structure, a carrier stop layer 3005, and an upper optical waveguide layer 3006 are formed on a substrate 3001. The upper cladding layer 3007 and the contact layer 3008 are sequentially stacked.

  The upper clad layer 3007 has a striped protrusion at the center, and its cross-sectional shape is a convex shape. The contact layer 3008 is formed only on the protruding portion of the upper cladding layer 3007. That is, the ridge stripe structure of the nitride-based semiconductor laser device in FIG. 11 is constituted by the protruding portion of the upper cladding layer 3007 and the contact layer 3008. This ridge stripe structure can be formed using a photolithography technique and an etching technique. Then, the light generated in the active layer 3004 is confined in the striped waveguide structure to cause a laser oscillation operation.

  Further, the nitride-based semiconductor laser device of FIG. 11 includes a buried layer 3009 formed on both sides of the ridge stripe and substantially transparent to light having an oscillation wavelength, and an electrode formed so as to cover the contact layer and the buried layer. 3010 and an electrode 3011 formed to cover the lower surface of the substrate. Both end surfaces in the longitudinal direction of the ridge stripe structure are resonator end surfaces that function as mirrors of the resonator.

In the conventional nitride-based semiconductor laser device shown in FIG. 11, the buried layer 3009 is formed of a material that absorbs light generated in the active layer 3004, thereby forming a single horizontal transverse mode (basic next horizontal transverse mode). (Only mode) is known to oscillate to high output. This method is described in, for example, Tsuyoshi Tojyo et al: Jpn.J.Appl.Phys.Vol.41 (2002) pp.1829-1833. In the nitride-based semiconductor laser device described in this document, the buried layer 3009 in FIG. 11 includes a silicon oxide (SiO ₂ ) layer that is transparent to light having a laser oscillation wavelength, and a silicon (Si) layer that exhibits absorption. Are formed in a two-layer structure.

In the nitride-based semiconductor laser device described in the document of Tsuyoshi Tojyo et al, absorption of light with the laser oscillation wavelength is achieved by adjusting the thickness of the SiO ₂ layer transparent to the light with the laser oscillation wavelength. The distance between the Si layer shown and the semiconductor layer is adjusted. When the distance between the Si layer and the semiconductor layer is reduced, the absorption of the laser beam is increased, and the operating current of the nitride semiconductor laser element necessary for obtaining a constant light output is increased. Further, if the distance between the Si layer and the semiconductor layer is increased, linear IL (current / light output) characteristics cannot be maintained up to a high output. Therefore, there is a preferable value for the distance between the Si layer and the semiconductor layer, that is, the thickness of the SiO ₂ layer, which is on the order of several tens of nm.
Tsuyoshi Tojyo et al: Jpn.J.Appl.Phys.Vol.41 (2002) pp.1829-1833

As described above, in the nitride semiconductor laser element in which the buried layer is composed of the SiO ₂ layer and the Si layer, it is necessary to strictly adjust the thickness of the SiO ₂ layer. That is, the SiO ₂ layer needs to be formed with a thickness on the order of several tens of nm. If a film thickness error of ± 5 nm or more occurs, the characteristics of the nitride-based semiconductor laser device, particularly the operating current and optical output Adversely affects the upper limit. However, it is difficult to suppress the thickness of the SiO ₂ layer to an error within ± 5 nm for each production lot of laser elements, and there is a problem that the production yield is lowered.

  In view of such problems, an object of the present invention is to provide a semiconductor laser device capable of realizing a stable transverse mode oscillation up to a high output while suppressing an increase in operating current at a high yield, and thus information at high speed and high density. Another object of the present invention is to provide an optical information processing apparatus capable of recording, reproducing and erasing data.

First, a nitride semiconductor generally means a crystal made of Al _p In _q Ga _{1-p type qN} (0 ≦ p ≦ 1, 0 ≦ q ≦ 1, 0 ≦ p + q ≦ 1). A nitride-based semiconductor does not mean only a crystal consisting of Al _p In _q Ga _{1-p type q} N alone, but a part of group III atoms (Al, In, Ga) (20 atomic% or less). Crystals substituted with B, Cr, V, Ti, Nb, Ta, Zr, Sc, Tl, Gd, La, etc., or a part of N atoms that are group V atoms (20 atomic% or less) are converted to P, As, Including crystals substituted with Sb and the like, and impurities such as B, Al, In, Tl, P, As, Sb, Be, Mg, Cd, Zn, C, Si, Ge, Sn, O, S, Se, Te, H, Sc, Cu, Fe, Ti, V, Cr, Y, Zr, Nb, lanthanoids, etc. are added. May be. The n-type nitride semiconductor and the p-type nitride semiconductor mean that the nitride semiconductor contains an impurity that defines a conductivity type.

  Further, in this specification, “width of the ridge stripe structure” and “stripe width” represent an average value of the upper side width and the lower side width of the substantially trapezoidal shape of the ridge stripe cross section. When the ridge stripe width is locally changed in the resonator direction, it means the average value of the average value of the upper side width and the average value of the lower side width over the entire resonator length.

  “Vertical direction” refers to the thickness direction of the semiconductor layer. The “horizontal direction” means a direction perpendicular to the longitudinal direction of the resonator and orthogonal to the thickness direction of the semiconductor layer.

  The “local equivalent refractive index Nin within the stripe” means an equivalent refractive index determined by a normal electric field distribution calculation in a virtual slab waveguide having a vertical refractive index distribution in the stripe. . Similarly, the “local equivalent refractive index Nout outside the stripe” means a virtual slab waveguide having a vertical refractive index distribution outside the stripe, and an equivalent refractive index obtained by normal electric field distribution calculation in the structure. Means. The “local absorption coefficient αout outside the stripe” is a value obtained by (imaginary part Im [Nout] of the local equivalent refractive index outside the stripe) × 2 × 2π / (laser oscillation wavelength [cm]).

  The “horizontal transverse mode” refers to a virtual slab waveguide having a local equivalent refractive index distribution n (y) represented by the following formula (1) with respect to the stripe width W, and a normal electric field in the structure. It shall mean the mode obtained by distribution calculation.

n (y) = Nin (| y | ≦ W); n (y) = Nout (| y |> W) (1)
“Basic horizontal horizontal mode” and “primary horizontal horizontal mode” mean a basic horizontal mode and a primary mode of horizontal horizontal mode, respectively. “Basic order mode absorption coefficient” is a value obtained by (imaginary part of equivalent refractive index of basic order horizontal transverse mode) × 2 × 2π / (laser oscillation wavelength [cm]). “First order mode absorption coefficient” A value obtained by (imaginary part of equivalent refractive index of primary horizontal transverse mode) × 2 × 2π / (laser oscillation wavelength [cm]).

  Further, the “horizontal confinement coefficient Γ‖” is defined as the following formula (2), where the horizontal light intensity distribution of the horizontal transverse mode is defined as I (y) and the stripe width of the laser element is defined by the following formula (2). The amount defined in 3).

  Electric field distribution calculation means normal electric field distribution calculation in the slab waveguide. For the calculation method, for example, M.J.Bergmann and H.C.Casey, Jr .: J.Appl.Phys., Vol.84, 1998, pp.1196-1203 can be referred to. The refractive index n of each material related to the oscillation wavelength λ [nm], which is a parameter in the electric field distribution calculation, is obtained by calculation. At that time, the oscillation wavelength λ can be in the range of 300 to 800 nm. For example, a parameter (energy band gap) Eg [eV] of a nitride semiconductor material is given by the following equation.

For In _s Ga _1-s N (0 ≦ s ≦ 1)
Eg = Eg1 [s] = 3.42 (1-s) + 2.65s-3.94s (1-s)
For Al _t Ga _1-t N (0 ≦ t ≦ 1),
Eg = Eg2 [t] = 3.42 (1-t) + 6.2t-1.057t (1-t)
_{For,; In s Al t Ga 1} -st N (0 <t <1 0 <s <1)
Eg = {s · Eg1 [s + t] + t · Eg2 [s + t]} / (s + t)
Thereby, a refractive index is calculated | required according to following Formula.

p [λ] = 1 / [1 / λ- (Eg-3.42) /1239.852]
Anyway,
When p [λ]> 360.7
n (p [λ]) = [4.3663801 + p-type ² / (p-type ² -295.9 ^-2 )] ^-0.5
When p [λ] ≦ 360.7
n (p [λ]) = c0 + c1, q + c2, q- ² + c3, q- ³ + c4, q- ⁴
q = p [λ] -360
c0 = 2.718
c1 = 9.976e ^-3
c2 = 3.005e ^-4
c3 = 4.584e ^-6
c4 = 2.596e ^-8
In the electric field distribution calculation in this specification, the calculation is performed on the assumption that there is no absorption except for the absorption coefficient of the buried layer that absorbs light having a visible wavelength.

  Under the premise and conditions as described above, the nitride semiconductor laser element of the present invention includes an active layer made of a nitride semiconductor on a substrate, a ridge stripe structure for confining light in the horizontal direction, And a buried layer formed in contact with both sides of the ridge stripe, and the buried layer has an absorption function for light having a visible wavelength.

The buried layer preferably has a layer thickness of 0.1 μm or more over a range where the distance from each side surface of the ridge stripe is at least 0.5 μm. A second buried layer made of a material different from that of the buried layer may be provided on the buried layer, and an electrode may be provided on the second buried layer. The absorption coefficient of the buried layer is preferably 3 × 10 ⁴ [cm ⁻¹ ] or more.

The width of the ridge stripe is preferably 1.0 μm or more and 2.0 μm or less. The difference in mode absorption coefficient between the horizontal basic primary mode and the horizontal primary horizontal mode due to the buried layer is preferably 5 [cm ⁻¹ ] or more. Further, the mode absorption coefficient of the horizontal fundamental order transverse mode by the buried layer is preferably 20 [cm ⁻¹ ] or less.

When the width of the ridge stripe is W [μm], the full width at half maximum of the far field pattern is θ‖ [°], the real part of the refractive index of the buried layer is R, and the absorption coefficient is α [cm ⁻¹ ], R and α are {(R−R0) / a} ² + {(α−α0) / b} ² ≦ 1;
{(R−R0 ′) / a ′} ² + {(α−α0 ′) / b ′} ² ≧ 1;
R>0; and α> 0
It is preferable that R0 = 28.182 × αout ^−0.3945 ;
a = 3948 × αout ^−1.6089 ;
α0 = 12381 × αout ^-1.828 ;
b = 19959 × αout ^−1.7896 ;
R0 ′ = 28.182 × αout2 ^−0.3945 ;
a ′ = 3948 × αout2 ^−1.6089 ;
α0 ′ = 12381 × αout2 ^-1.828 ;
b ′ = 19959 × αout2 ^−1.7896 ;
αout = 10/10 × exp [−0.226834−0.73435W−0.0921402θ‖ + 0.393325W · θ‖]; and αout2 = 5/5 × exp [4.26705-2.31818W−0.35138θ‖ + 0.48567W · θ‖]
It is.

  The width of the ridge stripe structure is not less than 1.9 μm and less than 2.0 μm, the full width at half maximum of the horizontal direction of the far field pattern is not less than 9 ° and not more than 10 °, and the buried layer has Si, GaAs, InP, GaP, and It can be formed of any material of InAs.

  Further, the width of the ridge stripe structure is 1.8 μm or more and less than 1.9 μm, the horizontal full width at half maximum of the far field pattern is 9 ° or more and 10 ° or less, and the buried layer is made of Si, GaAs, SiO, InP. , Ge, InAs, Au, Ti, Pt, Mo, and W.

  Further, the width of the ridge stripe structure is 1.7 μm or more and less than 1.8 μm, the horizontal full width at half maximum of the far field pattern is 9 ° or more and 10 ° or less, and the buried layer is made of Si, GaAs, SiO, InP , InAs, Al, Ag, Rh, Ir, Cu, Ir, Pt, Ni, Ti, Au, Mo, and W.

  Further, the width of the ridge stripe structure is 1.6 μm or more and less than 1.7 μm, the full width at half maximum in the horizontal direction of the far field pattern is 9 ° or more and 10 ° or less, and the buried layer is made of SiO, amorphous Si, SiO, It can be formed of any material of GaAs, InP, Al, Ag, Rh, Ir, Pt, Ni, Cu, Ti, Au, Mo, and W.

  Further, the width of the ridge stripe structure is 1.5 μm or more and less than 1.6 μm, the horizontal full width at half maximum of the far field pattern is 9 ° or more and 10 ° or less, and the buried layer is formed of Ge, SiO, Al, Ag. , Rh, Ir, Pt, Ni, Cu, Ti, Au, Mo, and W.

  Further, the width of the ridge stripe structure is 1.4 μm or more and less than 1.5 μm, the horizontal full width at half maximum of the far field pattern is 9 ° or more and 10 ° or less, and the buried layer is made of Al, Ag, Rh, Ir , Cu, Pt, Ni, Ti, and Au.

  Further, the width of the ridge stripe structure is 1.0 μm or more and less than 1.4 μm, the horizontal full width at half maximum of the far field pattern is 9 ° or more and 10 ° or less, and the buried layer is made of Al, Ag, and Rh. It can be formed of any material.

  Furthermore, the width of the ridge stripe structure is 1.6 μm or more and 1.7 μm or less, the full width at half maximum in the horizontal direction of the far field pattern has a value of more than 10 ° and 11 ° or less, and the buried layer has Si, SiO, InP, It can be formed of any material of GaAs, Ge, InAs, Au, Ti, Ni, Cu, Pt, Mo, and W.

  Further, the width of the ridge stripe structure is 1.5 μm or more and 1.6 μm or less, and the full width at half maximum in the horizontal direction of the far field pattern has a value of more than 10 ° and 11 ° or less, and the buried layer is made of Si, SiO, InP, It can be formed of any material of GaAs, Ge, InAs, Al, Ag, Rh, Cu, Au, Ti, Ni, Ir, Pt, Mo, and W.

  Further, the width of the ridge stripe structure is 1.4 μm or more and less than 1.5 μm, the full width at half maximum in the horizontal direction of the far field pattern is greater than 10 ° and 11 ° or less, and the buried layer is amorphous Si, SiO, GaAs , Ge, InAs, Al, Ag, Rh, Cu, Au, Ti, Ni, Ir, Pt, Mo, and W.

  Further, the width of the ridge stripe structure is 1.6 μm or more and 1.7 μm or less, the full width at half maximum in the horizontal direction of the far field pattern is greater than 11 ° and 12 ° or less, and the buried layer is formed of GaP, InP, and Si It can be formed of any of these materials.

  Further, the width of the ridge stripe structure is 1.5 μm or more and less than 1.6 μm, the full width at half maximum in the horizontal direction of the far field pattern has a value of more than 11 ° and 12 ° or less, and the buried layer has Si, SiO, InP, It can be made of any material of GaAs, Ge, InAs, and W.

  Further, the width of the ridge stripe structure is not less than 1.4 μm and less than 1.5 μm, the full width at half maximum in the horizontal direction of the far field pattern has a value greater than 11 ° and not more than 12 °, and the buried layer has Si, SiO, GaAs, It can be made of any material of Ge, InAs, InP, Al, Ag, Rh, Cu, Au, Ti, Ni, Ir, Pt, Mo, and W.

  Furthermore, the optical information processing apparatus according to the present invention has at least one function for recording, reproducing, and erasing information with respect to an optical recording medium, and for one or more functions of those recording, reproduction, and erasure A light emission control means that includes at least one nitride-based semiconductor laser element according to the present invention as a light source, emits laser light from the laser element at a predetermined output, and condensing light that condenses the laser light emitted from the laser element. And an irradiation position control means for irradiating a predetermined position of the optical recording medium with the laser beam condensed by the condensing means for processing of recording, reproducing or erasing information. Yes.

  The nitride-based semiconductor laser element according to the present invention can also be used as a light source of an optical information transmission device that emits an optical signal to an optically transmitting medium such as an optical fiber. Examples of such an optical information transmission device include a device that converts information given by an electrical signal into an optical signal and emits it to a medium, and a device that relays an optical signal.

  According to the present invention, by providing buried layers made of a predetermined material on both sides of a ridge stripe of a nitride semiconductor laser element, it is possible to realize a stable transverse mode oscillation up to a high output while suppressing an increase in operating current. Semiconductor laser elements can be manufactured with a high yield. In particular, the thickness of the buried layer only needs to be 0.1 μm or more, and the effect of eliminating the need for highly accurate layer thickness control is also obtained.

  FIG. 1 is a schematic cross-sectional view showing an example of the structure of a nitride-based semiconductor laser device according to the present invention, and shows a cross section perpendicular to the cavity direction of the laser device. In this nitride semiconductor laser element, a plurality of nitride semiconductor layers 102-109 including at least an active layer 105 are formed on a first conductivity type substrate 101. A ridge stripe is formed by etching from the second conductivity type side (upper side) of the nitride-based semiconductor layer, thereby forming a stripe shape having a role of horizontal light confinement of the nitride-based semiconductor laser device. A waveguide is formed. Furthermore, a buried layer 110 made of a single layer or a plurality of layers is formed on the entire surface of the region 113 etched on both sides of the ridge stripe. Both end faces in the longitudinal direction of the stripe function as mirrors to form an optical resonator. The first conductivity type and the second conductivity type mean p-type or n-type. When the first conductivity type is p-type, the second conductivity type is n-type, and the first conductivity type is n-type. In the case of a type, the second conductivity type is a p-type.

[Embodiment 1]
The structure of the nitride-based semiconductor laser device according to the first embodiment of the present invention will be described with reference to FIG. In this nitride-based semiconductor laser device, an n-type GaN base layer 102 (film thickness 0.1 to 10 μm), n-type Al _x Ga _1-x N (film thickness 30 to 300 μm), and n-type Al _x Ga _1-x N ( 0.05 ≦ x ≦ 0.2) lower cladding layer 103 (film thickness of 0.4 μm or more), n-type GaN lower optical waveguide layer 104 (film thickness of 0 to 0.15 μm), and n-type In _v stacked alternately. An active layer 105 (oscillation wavelength of 370 to 430 nm) having a multiple quantum well structure including a Ga _1-v N (0 ≦ v <w) barrier layer and an In _w Ga _1-w N (v <w ≦ 0.2) well layer. , Total film thickness 5 to 60 nm), p-type Al _z Ga ₁ -z N carrier blocking layer 106 (film thickness 0 to 0.02 μm), p-type GaN upper optical waveguide layer 107 (film thickness 0.05 to 0.15 μm) ), P-type Al _y Ga _1-y N (0.05 <y <0.2) upper cladding layer 108 (thickness 0.02) 10 μm) and a p-type GaN contact layer 109 (film thickness 0.01 to 10 μm) are sequentially stacked.

  In addition, a ridge stripe structure is formed by etching from the p-side (upper side) of the nitride-based semiconductor layer to the p-type upper cladding layer, the p-type upper optical waveguide layer, the carrier block layer, or the active layer, Horizontal light confinement is performed in the waveguide portion of the nitride-based semiconductor laser device.

  Furthermore, a buried layer 110 is formed on the substantially entire surface of the etched region 113. The positive electrode 111 is formed so as to cover the exposed surface of the p-type GaN contact layer 109 and the buried layer 110. The negative electrode 112 is formed so as to cover the lower surface of the n-type GaN substrate 101. Both end faces of the stripe function as mirrors and constitute an optical resonator.

  Next, an example of a method for manufacturing the nitride-based semiconductor laser device in the present embodiment will be described below.

(substrate)
First, an n-type GaN substrate 101 (having a thickness of 100 to 500 μm) having a (0001) C plane as a crystal growth main surface is cleaned. The cleaned GaN substrate 101 is introduced into the MOCVD apparatus, and cleaning is performed at a high temperature of about 1100 ° C. in an H ₂ atmosphere.

(Low temperature growth buffer layer)
Thereafter, the temperature of the substrate is lowered, SiH ₄ is introduced at 10 nmol / min while flowing hydrogen (H ₂ ) as a carrier gas at 10 l / min, and NH ₃ and trimethylgallium (TMG) are each 5 l / min at a substrate temperature of 600 ° C. Introduced at min and 20 mol / min, a low-temperature growth buffer layer made of n-type GaN having a thickness in the range of 0 to 10 μm (for example, 100 nm) is deposited. Here, the thickness of 0 μm means that the low temperature growth buffer layer can be omitted in some cases. Further, the method for forming the low-temperature growth buffer layer made of n-type GaN has been described. However, the method is not limited to n-type GaN, and may be GaN with an SiH ₄ introduction amount of 0 mol / min, and further formed with AlGaInN containing Al or In. May be. When Al is included, an appropriate amount of trimethylaluminum (TMA) is introduced at the time of film formation, and when In is included, an appropriate amount of trimethylindium (TMI) may be introduced at the time of film formation.

(N-type GaN layer)
Next, the substrate is heated to about 1050 ° C. while flowing N ₂ and NH ₃ at a rate of 5 l / min. After the temperature rise, the carrier gas is changed from N ₂ to H ₂ , SiG ₄ is introduced at 10 nmol / min while TMG is introduced at 100 μmol / min, and the n-type GaN layer 102 has a thickness of 0.1 to 10 μm. (For example, about 4 μm).

(N-type buffer layer)
Next, the supply of TMG and SiH ₄ was stopped, the carrier gas was changed from H ₂ to N ₂ , the substrate temperature was lowered to about 800 ° C., TMG was adjusted to 15 μmol / min, and SiH ₄ was changed to 10 nmol / While introducing Tmin, a constant amount of TMI is allowed to flow, and an n-type buffer layer made of n-type In _r Ga _1-r N (for example, r = 0.07) is grown to a thickness of 0 to 200 nm. The thickness of 0 nm in this case also means that the n-type buffer layer can be omitted in some cases.

(N-type cladding layer)
Next, the supply of TMI, TMG, and SiH ₄ is stopped, the temperature of the substrate is raised again to 1050 ° C., the carrier gas is changed from N ₂ to H ₂ again, and the flow rate of TMG is adjusted to 50 μmol / min. , While introducing a certain amount of TMA and flowing SiH ₄ at 10 nmol / min, the n-type cladding layer 103 made of n-type Al _x Ga _1-x N (for example, x = 0.1) is 0.4 μm or more (for example, To a thickness of 1 μm).

(N-side optical waveguide layer)
When the growth of the n-type cladding layer 103 is completed, the supply of TMA is stopped, the TMG is adjusted to 100 μmol / min, and the n-type GaN optical waveguide layer 104 has a thickness of 0 to 0.15 μm (for example, 100 nm). Grow to become. The n-side optical waveguide layer 104 may be a non-doped optical waveguide layer.

(Active layer)
Thereafter, the supply of TMG was stopped, the carrier gas was changed from H ₂ to N ₂ again, the temperature of the substrate was lowered to 700 ° C., and trimethylindium (TMI), which is an indium raw material, was introduced in a constant amount while TMG was introduced. was introduced at _{15μmol / min, in v Ga 1} -v N ( eg v = 0.023) growing from consisting barrier layer. Thereafter, the supply of TMI is increased to a certain amount, and a well layer made of In _w Ga _1-w N (for example, w = 0.070) is grown. By repeating the growth of these InGaN barrier layers and InGaN well layers, a multiple quantum well active layer 105 having an alternate multilayer structure (barrier layer / well layer /... / Well layer / barrier layer) is formed. The InGaN mixed crystal ratio and film thickness of the barrier layer and the well layer are designed so that the emission wavelength is in the range of 370 to 430 nm, and the flow rate of TMI introduced during film growth is that of the In composition film equal to the design value. Adjust as you get. The number of well layers is preferably in the range of 2 to 6, and particularly preferably 3. The barrier layer and / or the well layer may be non-doped or n-type containing a dopant such as Si.

(P-type carrier block layer)
When the growth of the multi-quantum well active layer 105 is completed, the supply of TMI and TMG is stopped, the temperature of the substrate is raised again to 1050 ° C., the carrier gas is changed from N ₂ to H ₂ again, and TMG is changed to 50 μmol / p-type Al _z Ga _1-z that also serves as an evaporation preventing layer having a thickness of 0 to 20 nm by flowing an appropriate amount of min and TMA and flowing p-type doping raw material biscyclopentadienylmagnesium (Cp ₂ Mg) at 10 nmol / min. An N (for example, z = 0.2) carrier block layer 106 is grown. The p-type carrier block layer may be replaced with a non-doped carrier block layer.

(P-side optical waveguide layer)
When the growth of the evaporation prevention layer 106 is completed, the supply of TMA is stopped, the supply amount of TMG is adjusted to 100 μmol / min, and the optical waveguide layer 107 made of p-type GaN is 0.05 to 0.15 μm (for example, To a thickness of 0.1 μm). The p-side optical waveguide layer may be replaced with a non-doped optical waveguide layer.

(P-type cladding layer)
Thereafter, the supply of TMG is adjusted to 50 μm / min, a certain amount of TMA is introduced, and the first p-type cladding layer 108 made of p-type Al _y Ga _1-y N (for example, y = 0.07) is changed to 0 Growing to a thickness of 0.02 to 10 μm (eg 0.5 μm).

(P-type contact layer)
Finally, the supply of TMG is adjusted to 100 μmol / min, the supply of TMA is stopped, and a p-type contact layer 109 made of p-type GaN having a thickness of 0.01 to 10 μm (for example, 0.1 μm) is formed. Crystal growth of the light emitting device structure is terminated. When the crystal growth is completed, the supply of TMG and Cp ₂ Mg is stopped to cool the substrate, and the obtained wafer is taken out from the MOCVD apparatus at room temperature.

  Thereafter, using the photolithography technique and the reactive ion etching technique, the p-type GaN contact layer 109 is left in a stripe shape with a width of 1 to 4 μm (for example, 2 μm), and etching is performed up to the first p-type cladding layer 108. A ridge stripe for forming a waveguide is formed. At this time, the remaining film thickness of the first p-type cladding layer 108 in the etched region is in the range of the full width at half maximum θ‖ = 7 ° to 12 ° in the horizontal FFP (far field pattern) (for example, 9.5). Adjust the angle so that Thereafter, a buried layer is formed using a photolithography technique except for a portion where the p-type GaN contact layer 109 is in contact with the electrode.

  Thereafter, a positive electrode is formed so as to cover the exposed surface of the p-type contact layer 109. For example, Au / Ni, Au / Pd, Au / Mo / Pd, etc. may be used as the electrode material. Further, the negative electrode 112 is formed on the back surface of the n-type GaN substrate 101. For example, Al / Ti or Au / W may be used as the negative electrode material.

  Thereafter, the wafer is cleaved into a plurality of bars to form end faces that serve as resonator mirrors, and these bars are further divided into a plurality of chips to obtain the nitride-based semiconductor laser device shown in FIG.

In the graphs of FIGS. 2A, 2B, and 2C, the horizontal axis represents the off-strip local absorption coefficient [cm ⁻¹ ], the vertical axis represents the mode absorption coefficient [cm ⁻¹ ], and the graph The solid line and the broken line in the figure represent the results obtained by calculating the absorption coefficients of the basic horizontal horizontal mode and the primary horizontal horizontal mode by electric field distribution calculation. That is, in FIG. 2A, the solid line 201 and the broken line 202 represent the absorption coefficients of the basic horizontal horizontal mode and the primary horizontal horizontal mode when the stripe width is 2.0 μm, respectively. In FIG. 2B, the solid line 203 and the broken line 204 represent the absorption coefficients of the basic horizontal horizontal mode and the primary horizontal horizontal mode when the stripe width is 1.5 μm. Here, the real part of the local equivalent refractive index outside the stripe is determined so that the full width at half maximum in the horizontal direction of the FFP in each stripe width is 9.5 °. In FIG. 2C, the solid line 205 and the broken line 206 represent the absorption coefficients of the basic horizontal horizontal mode and the primary horizontal horizontal mode when the stripe width is 2.0 μm, respectively. The calculation is performed by determining the real part of the local equivalent refractive index outside the stripe so that the full width at half maximum is 12.0 °.

  As is apparent from FIG. 2, when the local absorption coefficient outside the stripe increases, the absorption coefficients of the basic horizontal horizontal mode and the primary horizontal horizontal mode show a monotonically increasing tendency. In addition, the absorption coefficient of the primary horizontal transverse mode is larger than that of the fundamental horizontal transverse mode. This is because the electric field distribution of the primary horizontal transverse mode is shifted to the region outside the stripe compared to the fundamental horizontal transverse mode. This is because a large amount of ooze out and is more affected by the local absorption coefficient outside the stripe. Furthermore, the narrower the stripe width, the larger the absorption coefficient. However, as the stripe width becomes narrower, the electric field distribution of each horizontal transverse mode oozes out to the area outside the stripe. Because it receives. Furthermore, the absorption coefficient increases as the horizontal full width at half maximum of the FFP becomes smaller. This is equivalent to the fact that the horizontal full width at half maximum of the FFP is smaller, which means that the horizontal confinement becomes worse. This is because the electric field distribution oozes out to the region outside the stripe and is more influenced by the local absorption coefficient outside the stripe.

Consider the case in which the FFP horizontal full width at half maximum is 7.0 °, 9.5 °, and 12.0 ° when the stripe width is 1.0 μm, 1.5 μm, and 2.0 μm, respectively. In each case, the local absorption coefficient outside the stripe where the difference between the absorption coefficient of the fundamental horizontal transverse mode and the primary horizontal transverse mode is 10 cm ⁻¹ or more, and the extra-strip local absorption where the fundamental order mode absorption coefficient is 5 cm ^−1. When the coefficient values are calculated in the manner shown in FIGS. 2A to 2C, the results shown in Table 1 are obtained.

From Table 1, using the stripe width W [μm] and the FFP horizontal half-value full angle θ‖ [°], the local area outside the stripe where the difference in absorption coefficient between the basic horizontal transverse mode and the primary horizontal transverse mode is xcm ^−1. The value of the absorption coefficient [cm ⁻¹ ] can be approximated by the following equation (4).

x / 10exp (−0.226834−0.73435W−0.0921402θ‖ + 0.393325W · θ‖) (4)
The value of the value in the basic mode absorption coefficient y [cm ^-1] become stripe outside the local absorption coefficient [cm ^-1] can be approximated by the following equation (5).

y / 5exp (4.26705-2.331018W-0.35138θ‖ + 0.48567W · θ‖) (5)
In order to maintain the basic horizontal transverse mode up to high output, the optimum horizontal lateral absorption coefficient αout [cm ⁻¹ ] outside the stripe is maintained at about y [cm ⁻¹ ] or less for the basic horizontal horizontal mode absorption coefficient. Since it is necessary to take the difference in absorption coefficient between the basic horizontal transverse mode and the primary horizontal transverse mode to about x [cm ⁻¹ ] or more, the range that αout [cm ⁻¹ ] should satisfy is the stripe width W [μm]. And the FFP horizontal half-value full angle θ‖ [°], it can be written as:

x / 10exp (−0.226834−0.73435W−0.0921402θ‖ + 0.393325W · θ‖) ≦ αout ≦ y / 5exp (4.26705-2.331018W−0.35138θ‖ + 0.48567W · θ‖)
For example, in order to make the absorption coefficient difference between the fundamental horizontal mode and the primary horizontal transverse mode 10 [cm ⁻¹ ] or more and make the absorption coefficient of the fundamental mode 5 [cm ⁻¹ ] or less, the stripe width W = 2.0 μm and nitride semiconductor laser element with θ ° = 9.5 °, the local absorption coefficient outside the stripe may be in the range of 135 ≦ αout ≦ 254 from the above equation. In the nitride-based semiconductor laser device in which the stripe width W = 1.5 μm and θ９ = 9.5 °, the local absorption coefficient outside the stripe may be in the range of 30 ≦ αout ≦ 80 from the above equation.

In the graph of FIG. 3, the horizontal axis represents the real part of the refractive index of the buried layer, and the vertical axis represents the local absorption coefficient outside the stripe [a. u. : Arbitrary unit], and the curve shows the result of calculation. That is, the solid curve 301 represents the case where the absorption coefficient of the buried layer is 100,000 [cm ⁻¹ ] and the layer thickness is infinite, and the dotted curve 302 represents the absorption coefficient of the buried layer of 100,000 [cm]. ⁻¹ ] represents the case where the layer thickness is 0.1 μm.

  As is clear from the shape of the solid curve 301 in FIG. 3, if the real part of the refractive index of the buried layer is increased from 0, the local absorption coefficient outside the stripe increases monotonously up to around 2.5, but 2 It shows a maximum near .5, and then tends to decrease monotonously. The reason for this tendency is as follows. That is, when the real part of the refractive index of the buried layer is as small as 2.5 or less, the vertical electric field distribution outside the stripe hardly penetrates into the buried layer, and as a result, the laser beam does not feel the absorption of the buried layer. In addition, the local absorption coefficient outside the stripe becomes small. However, if the real part of the refractive index of the buried layer is in the vicinity of 2.5 to 3.0, it becomes close to the equivalent refractive index of the laser oscillation light, so that the laser light propagates through the buried layer. The local absorption coefficient increases rapidly. Furthermore, when the real part of the refractive index of the buried layer becomes 3 or more, the non-stripe local absorption coefficient again shows a decreasing tendency.

A dotted curve 302 in FIG. 3 represents a case where the layer thickness is 0.1 μm, and shows a tendency to vibrate around the solid curve 301 when the layer thickness is infinite. This is because the laser beam interferes between the lower surface and the upper surface of the buried layer, and the amplitude becomes smaller as the absorption coefficient of the buried layer is larger or the buried layer is thicker. It is not preferable to exhibit such vibration characteristics because it causes variation in element characteristics when a large number of nitride semiconductor laser elements are manufactured. In order to avoid this situation, the absorption coefficient of the buried layer is preferably 30,000 [cm ⁻¹ ] or more, and more preferably 100,000 [cm ⁻¹ ] or more. The thickness of the buried layer is preferably 0.1 μm or more, and more preferably 0.2 μm or more. If the buried layer absorption coefficient is 30,000 [cm ⁻¹ ] or more and the buried layer thickness is 0.1 μm or more, the influence of variations in the buried layer thickness on the device characteristics can be virtually ignored. The effect of the present invention can be obtained.

In the graph of FIG. 4, the horizontal axis represents the real part of the refractive index of the buried layer, and the vertical axis represents the absorption coefficient [1e5 / cm ⁻¹ ] of the buried layer. Note that 1e5 represents 1 × 10 ⁵ . The curve in the graph shows the contour line of the local absorption coefficient outside the stripe. That is, the contour lines 401, 402, 403, 404, and 405 are respectively 30 [cm ⁻¹ ], 70 [cm ⁻¹ ], 100 [cm ⁻¹ ], 150 [cm ⁻¹ ], and 400 [cm ⁻¹ ]. ] Represents the off-triple local absorption coefficient.

Here, if the real part of the refractive index of the buried layer is R, and the absorption coefficient is α [× 10 ⁵ cm ⁻¹ ], the curve 401 can be approximated by the following equation.

{(R-8) /7.2} ² + {(α-6) / 12} ² = 1; R>0;α> 0
Similarly, curve 402 can be approximated by:

{(R−5.7) / 4} ² + {(α−4.5) /8.6} ² = 1; R>0;α> 0
Similarly, the curve 403 can be approximated by the following equation.

{(R-4.4) /2.5} ² + {(α−3) /5.5} ² = 1; R>0;α> 0
Similarly, curve 404 can be approximated by:

{(R-3.6) /1.3} ² + {(α−1.5) /3.1} ² = 1; R>0;α> 0
Similarly, curve 405 can be approximated by:

{(R-2.77) /0.25} ² + {(α−0.2) /0.4} ² = 1; R>0;α> 0
From the above results, a contour line having an out-of-strip local absorption coefficient αout [cm ⁻¹ ] can be expressed as the following equation (6).

{(R−R0) / a} 2 + {(α−α0) / b} 2 = 1, R> 0, α> 0 (6)
However, R0 = 28.182 × αout−0.3945
a = 3948 × αout−1.6089
α0 = 12381 × αout−1.828
b = 19959 × αout−1.7896
As shown in the flowchart of FIG. 5, the refractive index to be satisfied by the buried layer material used for the nitride-based semiconductor laser device can be obtained using the above-described equations (4) to (6). First, the stripe width W [μm] of the nitride-based semiconductor laser device and the FFP horizontal half-value full angle θ‖ [°] are determined. As described above, there is a preferable range for the stripe width W [μm], and the value depends on the crystal quality of the semiconductor multilayer film constituting the nitride semiconductor laser element, but is approximately 1.0 μm or more and 2.0 μm. Or less, more preferably 1.3 μm or more and 1.7 μm or less, and most preferably 1.45 μm or more and 1.65 μm or less. The FFP horizontal half-maximum angle θ‖ [°] is determined by a request from an optical information processing apparatus including a nitride semiconductor laser element, but is preferably approximately 7 ° to 12 °, and preferably 8 ° to 11 °. Is more preferable, and 9 ° or more and 10 ° or less is most preferable.

Further, a lower limit value x [cm ⁻¹ ] of an absorption coefficient difference between the basic horizontal horizontal mode and the primary horizontal horizontal mode and an upper limit value y [cm ⁻¹ ] of the basic horizontal horizontal mode absorption coefficient are determined. x may be a lower limit of a range in which the effect of maintaining the fundamental horizontal horizontal mode oscillation until a high output is obtained, and can be set to 5 [cm ⁻¹ ], for example, 10 [cm ⁻¹ ]. Is more preferable. y may be set to an upper limit within a range in which an increase in operating current is not problematic in practical use, and may be set to 20 [cm ⁻¹ ], for example, and more preferably 10 [cm ⁻¹ ]. ^-1 ] is most preferable.

When W, θ‖, x, and y are determined, the lower limit value of the absorption coefficient αout outside the stripe is determined from Expression (4) and the upper limit value is determined from Expression (5) according to the procedure shown in FIG. Furthermore, the real part R of the refractive index and the absorption coefficient α [cm ⁻¹ ] of the buried layer are determined by the equation (6) using the obtained αout range.

6, for example, W = 2.0μm, θ‖ = 9.5 ° , x = 10 [cm-1], and y = 5 in the case of [cm ^-1], the refractive index real part R and the buried layer It is a graph for demonstrating the procedure which determines absorption coefficient (alpha) [* 10 < ⁵ > cm < ^-1 >]. In FIG. 6A, curves 601 and 602 that are completely equivalent to the curves 201 and 202 in FIG. 2A are drawn. In this figure, the values of x and y are indicated by arrows x and y in the figure, respectively. Also, the values of the local absorption coefficient αout outside the stripe where the distance between the curve 601 and the curve 602 is x = 10 cm ⁻¹ and the value of the local absorption coefficient αout outside the stripe where the value of the curve 601 is y = 5 cm ⁻¹ are shown in FIG. 6 (a), indicated by arrows 603 and 604, respectively. The value 603 can be obtained from the equation (4), and the value 604 can be obtained from the equation (5). These values are 135 cm ⁻¹ and 254 cm ⁻¹ , respectively. From equation (6), a curve satisfying αout = 135 cm ⁻¹ is a curve 605 shown in FIG. 6B, and a curve satisfying αout = 254 cm ⁻¹ is a curve 606 shown in FIG. 6B. That is, a material having R and α within the range satisfying the following formula (7) is preferably used as the buried layer material.

{(R−4.07) /1.48} ² + {(α−1.59) /3.09} ² ≦ 1;
{(R-3.17) /0.53} ² + {(α−0.50) /0.99} ² ≧ 1;
R>0; and α> 0 (7)
Such a range is indicated by a hatched area in FIG. Examples of materials corresponding to this range include GaP (R = 4.1; α = 80,000 cm ⁻¹ ), Si (R = 5.42; α = 129,000 cm ⁻¹ ), and the like.

FIG. 7 shows another example of the refractive index of the buried layer when W = 1.5 μm, θ‖ = 9.5 °, x = 10 [cm ⁻¹ ], and y = 10 [cm ⁻¹ ]. It is a graph for demonstrating the procedure which determines the real part R and absorption coefficient (alpha) [cm ^<-1 >]. In FIG. 7A, curves 701 and 702 which are completely equivalent to the curves 203 and 204 in FIG. 2B are drawn. In this figure, the values of x and y are shown. Further, the value of the local absorption coefficient αout outside the stripe where the distance between the curve 701 and the curve 702 is x = 10 cm ⁻¹ and the value of the local absorption coefficient αout outside the stripe where the value of the curve 701 is y = 10 cm ⁻¹ are shown in FIG. Indicated by arrows 703 and 704 in the middle. The value 703 can be obtained from equation (4), the value 704 can be obtained from equation (5), and these values are 30 cm ⁻¹ and 160 cm ⁻¹ , respectively. Further, from equation (6), a curve satisfying αout = 30 cm ⁻¹ is a curve 705 shown in FIG. 7B, and a curve satisfying αout = 160 cm ⁻¹ is a curve 706 shown in FIG. 7B. That is, a material having R and α [× 10 ⁵ cm ⁻¹ ] within the range satisfying the following formula (8) is preferably used as the buried layer material.

{(R−0.737) /16.6} ² + {(α−24.7) /45.4} ² ≦ 1;
{(R−5.00) /3.41} 2 + {(α−4.09) /7.81} 2 ≧ 1;
R>0; and α> 0 (8)
The range is indicated by the hatched area in FIG. A material applicable to the nitride semiconductor laser element of the first embodiment corresponding to this range includes SiO (R = 2.1; α = 31,000 cm ⁻¹ ).

  In the nitride semiconductor laser device of the present invention, the first conductivity type electrode and the second conductivity type electrode are not characteristic elements. However, in order to ensure electrical connection with voltage application (current supply) means for driving the nitride-based semiconductor laser element, the first conductivity type electrode and the second conductivity type electrode are usually used. Is formed in the nitride-based semiconductor laser device. The electrode for the first conductivity type and the electrode for the second conductivity type may be a single-layer electrode made of a single metal material or alloy material, or a stacked electrode made of a metal material or alloy material different from each other. Also good.

  In this embodiment, the buried layer 110 that absorbs visible wavelengths is formed so as to be in contact with both side surfaces of the ridge stripe. If the layer thickness of 0.1 μm or more exists in the range up to 5 μm, the effect of the present invention can be obtained. That is, for example, even if there are transparent buried layers in the vicinity of both side surfaces of the ridge stripe, the buried layer having an absorption with respect to visible wavelengths in a region within a distance of 0.5 μm from the ridge stripe has a thickness of 0. If the thickness is 1 μm or more, the effect of the present invention can be obtained. Further, for example, even if there is no buried layer having absorption with respect to a visible wavelength in a region away from 0.5 μm from the ridge stripe structure or there is a region having a layer thickness of less than 0.1 μm, the effect of the present invention is achieved. can get.

[Embodiment 2]
In FIG. 8, a nitride-based semiconductor laser device according to Embodiment 2 of the present invention is shown in a schematic cross-sectional view perpendicular to its resonator. This nitride-based semiconductor laser device includes an n-type GaN base layer 802 (film thickness 0.1 to 10 μm), n-type Al _x Ga ₁ , which are sequentially stacked on an n-type GaN substrate 801 (film thickness 30 to 300 μm). _-x N (0.05 ≦ x ≦ 0.2) lower clad layer 803 (film thickness of 0.4 μm or more) and n-type GaN lower optical waveguide layer 804 (film thickness of 0 to 0.15 μm) are alternately stacked. An active layer 805 having a multiple quantum well structure including an In _w Ga _1-w N (v <w ≦ 0.2) well layer and an n-type In _v Ga _1-v N (0 ≦ v <w) barrier layer ( Oscillation wavelength 370 to 430 nm, total film thickness 5 to 60 nm), p-type Al _z Ga ₁ -z N carrier block layer 806 (film thickness 0 to 0.02 μm), p-type GaN upper optical waveguide layer 807 (film thickness 0. 05-0.15 μm), p-type Al _y Ga _1-y N (0.05 <y <0.2) upper cladding layer 808 (A film thickness of 0.02 to 10 μm) and a p-type GaN contact layer 809 (a film thickness of 0.01 to 10 μm).

  A ridge stripe structure is formed by etching from the p-side (upper side) of the nitride-based semiconductor multilayer film to the p-type upper cladding layer, the p-type upper optical waveguide layer, the carrier block layer, or the active layer 805. As a result, the optical confinement in the horizontal direction of the waveguide portion of the nitride-based semiconductor laser device is performed.

  Further, buried layers 810 and 811 are formed on the substantially entire surface 814 of the etched region on both sides of the ridge stripe. The positive electrode 812 is formed so as to cover the exposed surface of the p-type GaN contact layer and the buried layer 811. The negative electrode 813 is formed so as to cover the lower surface of the n-type GaN substrate. Both end faces of the stripe function as mirrors and constitute an optical resonator.

  The method for manufacturing the nitride-based semiconductor laser device according to the second embodiment is the same as the method for manufacturing the nitride-based semiconductor laser device according to the first embodiment except that the buried layer is composed of two layers. Explanation is omitted.

  In the nitride-based semiconductor laser device according to the second embodiment, the buried layer formed on the substantially entire surface 814 of the etched region is buried with the buried layer 810 made of a material capable of absorbing light having a visible wavelength and insulating. Layer 811 is formed.

  In the nitride-based semiconductor laser device of the first embodiment, since the buried layer is composed of one layer, the adhesion between the two may be poor depending on the combination of the buried layer material and the positive electrode material. In this case, peeling is likely to occur between the electrode and the buried layer, causing problems that the operating voltage increases and the proportion of elements that do not oscillate laser increases. In the nitride-based semiconductor laser device of the second embodiment, such a problem can be solved by inserting a single layer of material having good adhesion between the buried layer and the positive electrode.

To give a specific example, when SiO is used as a buried layer material that absorbs light having a visible wavelength, and Pd, Ni, Mo, or Au is used as a positive electrode material existing on the buried layer, Adhesion between the buried layer and the positive electrode material is not sufficient. Therefore, as in the nitride-based semiconductor laser device of this embodiment, if a TiO ₂ film is formed to a thickness of 50 nm, for example, by a method such as sputtering, between SiO and TiO ₂ and TiO ₂ , Since the adhesion between the positive electrode and the positive electrode is good, the problem of peeling between SiO and the positive electrode can be solved.

  In the nitride-based semiconductor laser device of the first embodiment, since the buried layer is composed of one layer, when the buried layer is an electric conductor such as a metal, the current spreads over the entire active layer. In addition, the current density immediately below the ridge stripe cannot be increased, resulting in a significant increase in operating current. Therefore, such a problem can be solved by inserting a buried layer made of an insulating material as in the nitride-based semiconductor laser device of the second embodiment, that is, the current is directly under the ridge stripe. Can be constricted.

  In the nitride-based semiconductor laser device according to the second embodiment, if the thickness of the buried layer 810 having absorption is 0.1 μm or more as in the case of the nitride-based semiconductor laser device according to the first embodiment, the buried layer The influence of the thickness variation on the device characteristics can be virtually ignored, and the effects of the present invention can be obtained. In the second embodiment, the range to be satisfied by the refractive index and absorption coefficient of the buried layer is exactly the same as in the first embodiment.

In the nitride-based semiconductor laser device of the second embodiment, when W = 1.5 μm, θ‖ = 9.5 °, x = 10 [cm ⁻¹ ], and y = 10 [cm ⁻¹ ], the buried layer The condition to be satisfied by the real part R of the refractive index and the absorption coefficient α [× 10 ⁵ cm ⁻¹ ] of the material is as shown in Equation (8), and the nitride semiconductor of the second embodiment corresponds to this range. As materials applicable to the laser element, in addition to the materials described in the first embodiment, Al (R = 0.49; α = 1,500,000 cm ⁻¹ ), Rh (R = 1.41; α = 1) , 300,000 cm ⁻¹ ), Pt (R = 1.72; α = 890,000 cm ⁻¹ ), Ti (R = 1.55; α = 680,000 cm ⁻¹ ), Au (R = 1.658; α = 610,000 cm ⁻¹ ), Ni (R = 1.61; α = 740,000 cm ⁻¹ ), Cu (R = 1.18; ^{α = 670,000cm -1), Mo (} R = 3.03; there are metals such as α = 1,000,000cm ^-1).

  As described above, in the nitride semiconductor laser element of the first embodiment, a material that is an electric conductor or cannot be applied as the buried layer material because of poor adhesion to the positive electrode is used in the second embodiment. This nitride semiconductor laser device can be applied, and has the effect of widening the range of selection.

  In the second embodiment, the buried layer 810 that absorbs light having a visible wavelength and the buried layer 811 that has insulating properties are each composed of one layer, but each is formed of a plurality of layers. The effect of the present invention can be obtained if the buried layer 810 that absorbs visible wavelengths is formed so as to be in contact with the bottom surface of the ridge located on both sides of the ridge stripe.

[Embodiment 3]
In the nitride-based semiconductor laser device of the third embodiment, among the nitride-based semiconductor laser devices having the configuration of the first or second embodiment, 9 ° ≦ θ‖ ≦ 10 °, in particular the basic horizontal horizontal mode and the primary horizontal horizontal mode. Preferred buried layer materials are disclosed when the lower limit of the mode absorption coefficient difference is x = 10 [cm ⁻¹ ] and the upper limit of the fundamental horizontal transverse mode absorption coefficient is y = 5 [cm ⁻¹ ]. Here, an example of a material that can be used as the buried layer material is shown in the graph of FIG. 9, but the candidate for the buried layer material is not limited to those shown here. In the graph of FIG. 9, the horizontal axis represents the real part of the refractive index of the material used for the buried layer, and the vertical axis represents the absorption coefficient [× 10 ⁵ cm ⁻¹ ].

  For example, when the stripe width W is 1.9 μm or more and 2.0 μm or less, the material of the buried layer is preferably Si, GaAs, InP, GaP, or InAs as an insulator or semiconductor.

  When W is 1.8 μm or more and less than 1.9 μm, Si, GaAs, SiO, InP, Ge, or InAs is preferable for the insulator or semiconductor, and Au, Ti, Pt, Mo, or W is preferable for the metal.

  When W is 1.7 μm or more and less than 1.8 μm, Si, GaAs, SiO, InP, or InAs is preferable for the insulator or semiconductor, and Al, Ag, Rh, Ir, Cu, Ir, Pt, Ni, Ti are preferable for the metal. Au, Mo, or W is preferred.

  When W is 1.6 μm or more and less than 1.7 μm, SiO, amorphous Si, SiO, GaAs, or InP is preferable for an insulator or a semiconductor, and Al, Ag, Rh, Ir, Pt, Ni, Cu, Ti, for a metal, are preferable. Au, Mo, or W is preferred.

  When W is 1.5 μm or more and less than 1.6 μm, Ge or SiO is preferable for an insulator or a semiconductor, and Al, Ag, Rh, Ir, Pt, Ni, Cu, Ti, Au, Mo, or W is preferable for a metal. .

  When W is 1.4 μm or more and less than 1.5 μm, the metal is preferably Al, Ag, Rh, Ir, Cu, Pt, Ni, Ti, or Au.

  When W is 1.0 μm or more and less than 1.4 μm, the metal is preferably Al, Ag, or Rh.

  However, in these cases, when the buried layer is an insulator or a semiconductor, the nitride semiconductor laser element of any of the first or second embodiments may be used. However, when the buried layer is a metal, the embodiment of the second embodiment is used. It is necessary to produce a nitride semiconductor laser element.

[Embodiment 4]
In the nitride semiconductor laser element of the fourth embodiment, among the nitride semiconductor laser elements having the form of the first or second embodiment, W is particularly not less than 1.4 μm and not more than 1.7 μm, and 10 ° <θ‖ ≦ 11. °, the lower limit of the absorption coefficient difference between the fundamental horizontal transverse mode and the primary horizontal transverse mode is x = 10 [cm ⁻¹ ], and the upper limit of the fundamental horizontal transverse mode absorption coefficient is y = 5 [cm ⁻¹ ]. A preferred buried layer material is disclosed.

  For example, when the stripe width W is 1.6 μm or more and 1.7 μm or less, the material of the buried layer is preferably Si, SiO, InP, GaAs, Ge, or InAs for the insulator or semiconductor, and Au, Ti, Ni for the metal. Cu, Pt, Mo, or W is preferred.

  When W is 1.5 μm or more and less than 1.6 μm, Si, SiO, InP, GaAs, Ge, or InAs is preferable for an insulator or a semiconductor, and Al, Ag, Rh, Cu, Au, Ti, Ni, Ir is preferable for a metal. , Pt, Mo, or W is preferred.

  When W is 1.4 μm or more and less than 1.5 μm, amorphous Si, SiO, GaAs, Ge, or InAs is preferable for the insulator or semiconductor, and Al, Ag, Rh, Cu, Au, Ti, Ni, Ir, or the like is preferable for the metal. Pt, Mo, or W is preferred.

  However, even in these cases, the nitride semiconductor laser element according to any one of the first and second embodiments may be used when the buried layer is an insulator or a semiconductor. However, when the buried layer is a metal, the embodiment 2 may be used. It is necessary to produce a nitride-based semiconductor laser device.

[Embodiment 5]
In the nitride-based semiconductor laser device of the fifth embodiment, among the nitride-based semiconductor laser devices having the embodiments of the first or second embodiment, W is particularly 1.4 μm or more and 1.7 μm or less, and 11 ° <θ‖ ≦ 12. °, the lower limit of the absorption coefficient difference between the fundamental horizontal transverse mode and the primary horizontal transverse mode is x = 10 [cm ⁻¹ ], and the upper limit of the fundamental horizontal transverse mode absorption coefficient is y = 5 [cm ⁻¹ ]. A preferred buried layer material is disclosed.

  For example, when the stripe width W is 1.6 μm or more and 1.7 μm or less, the material of the buried layer is preferably GaP, InP, or Si crystal as an insulator or semiconductor.

  When W is 1.5 μm or more and less than 1.6 μm, Si, SiO, InP, GaAs, Ge, or InAs is preferable for an insulator or a semiconductor, and W is preferable for a metal.

  When W is 1.4 μm or more and less than 1.5 μm, Si, SiO, GaAs, Ge, InAs, or InP is preferable for the insulator or semiconductor, and Al, Ag, Rh, Cu, Au, Ti, Ni, Ir is preferable for the metal. , Pt, Mo, or W is preferred.

  However, even in these cases, the nitride semiconductor laser element according to any one of the first and second embodiments may be used when the buried layer is an insulator or a semiconductor. However, when the buried layer is a metal, the embodiment 2 may be used. It is necessary to produce a nitride-based semiconductor laser device.

[Embodiment 6]
FIG. 10 is a schematic block diagram illustrating an example of an optical information processing apparatus according to the sixth embodiment. This optical information processing apparatus includes the nitride-based semiconductor laser element according to the present invention as a light source for recording light, and a known configuration is used in addition to the light source.

  The optical information processing apparatus of FIG. 10 includes a nitride-based semiconductor laser device 1001 according to the present invention, a beam emission control means (not shown), a collimator lens 1002, a beam shaping prism 1003, a beam splitter 1004, an objective. A lens (light collecting means) 1005, an optical disk (optical recording medium) 1006, an irradiation position control means (not shown), and a light detection system (light detection means) 1007 for detecting light are included. In FIG. 10, parts (means) unnecessary for explaining the features of the present invention are not shown for the sake of simplification and clarification.

  In the optical information processing apparatus of FIG. 10, the nitride semiconductor laser element 1001 can also serve as a recording light source, a reproduction light source, and an erasing light source. The beam emission control means can emit light having different outputs, and controls to emit light at a lower output during the reproduction operation than the outputs of the recording light and the erasing light. obtain.

  During the recording operation and the erasing operation, the laser light emitted from the nitride-based semiconductor laser device 1001 is converted into parallel light or a nearly parallel light beam by the collimator lens 1002, passes through the beam shaping prism 1003 and the beam splitter 1004, and is converted into the objective light. The light is condensed on the information recording surface of the optical disk 1006 by the lens 1005. Bit information is written on the information recording surface of the optical disc 1006 by magnetic modulation or refractive index modulation. During the reproducing operation, laser light emitted from the semiconductor laser device through the same process as that during recording and erasing is focused on the information recording surface of the optical disk 1006 on which recording is performed by unevenness, magnetic modulation, or refractive index modulation. The condensed laser light is reflected by the information recording surface, passes through the beam splitter 1004 through the objective lens 1005, enters the light detection system 1007, and converts the optically detected signal into an electrical signal. The recorded information is read.

In the optical information processing apparatus including the nitride semiconductor laser element of the present invention, a defect occurrence rate of 10 ⁻⁶ or less can be achieved during the recording operation. Further, during the reproducing operation, the written information can be read out with a bit reading error rate of 10 ⁻⁶ .

On the other hand, in an optical information processing apparatus equipped with a conventional nitride-based semiconductor laser element, the defect occurrence rate during the recording operation and the bit error rate during the reproducing operation are both on the order of 10 ⁻³ . This difference is due to the fact that a nitride-based semiconductor laser element having IL characteristics that maintains the fundamental horizontal horizontal mode until high output and has no kink until high output is used in the optical information processing apparatus. This is because the output of the laser beam focused on the laser beam can be high and stable.

  According to the present invention, by using an embedded layer made of a predetermined material, it is possible to provide a semiconductor laser that realizes stable transverse mode oscillation up to a high output with a high yield while suppressing an increase in operating current. By using such a semiconductor laser, an optical information processing apparatus capable of recording, reproducing, or erasing information at high speed and high density can be provided. In this case, the nitride-based semiconductor laser device of the present invention that can oscillate in the fundamental horizontal / horizontal mode up to a high output and whose ellipticity in the FFP is close to 1 is used. It is also possible to omit means, for example, a forming prism that has always been used.

1 is a schematic cross-sectional view showing a nitride-based semiconductor laser device according to an embodiment of the present invention. It is a graph which shows the relationship between the local absorption coefficient outside a stripe in a laser element, and a transverse mode absorption coefficient. It is a graph which shows the relationship between the real part of the refractive index of a buried layer, and a local absorption coefficient outside a stripe. It is a graph which shows the relationship between the real part of the refractive index of a buried layer, and the absorption coefficient of a buried layer. It is a flowchart which shows the process of calculating | requiring the refractive index which the material of a buried layer should satisfy | fill. It is a graph for demonstrating an example of the procedure which determines the refractive index real part R and absorption coefficient (alpha) of a buried layer. It is a graph for demonstrating the other example of the procedure which determines the refractive index real part R and absorption coefficient (alpha) of a buried layer. FIG. 6 is a schematic cross-sectional view showing a nitride-based semiconductor laser device according to another embodiment of the present invention. It is a graph which shows the example of the material which can be used for a buried layer. 1 is a schematic block diagram illustrating an example of an erasable optical information processing apparatus according to the present invention. It is typical sectional drawing which shows the conventional typical nitride type semiconductor laser element.

Explanation of symbols

101, 801 n-type GaN substrate, 102, 802 n-type GaN underlayer, 103, 803 n-type Al _x Ga _1-x N lower cladding layer, 104, 804 n-type GaN lower optical waveguide layer, 105, 805 alternately stacked An active layer having a multiple quantum well structure including an n-type In _v Ga _{1 -v} N barrier layer and an In _w Ga _{1 -w} N well layer, 106,806 p-type Al _z Ga ₁ -z N carrier blocking layer, 107, 807 p-type GaN upper optical waveguide layer, 108, 808 p-type Al _y1 Ga _1-y1 N upper cladding layer, 109, 809 p-type GaN contact layer, 110, 810, 811 buried layer, 111, 812 positive electrode, 112, 813 Negative electrode, 113, 814 Etched region.

Claims (6)

A nitride-based semiconductor laser device,
On the substrate
An active layer included in the nitride-based semiconductor laminate;
A ridge stripe structure formed by etching from the upper surface of the nitride-based semiconductor stacked body and confining light in the horizontal direction;
An embedded layer formed so as to be embedded in contact with the exposed surface by the etching except for the top surface of the ridge stripe,
The buried layer has an absorption effect on light having a visible wavelength, has an absorption coefficient of 3 × 10 ⁴ [cm ⁻¹ ] or more,
The buried layer has a layer thickness of 0.1 μm or more until the distance from each side surface of the ridge stripe exceeds at least 0.5 μm,
The following conditions (a) to (m):
(A) The width of the ridge stripe structure is 1.9 μm or more and less than 2.0 μm, and the full width at half maximum of the far field pattern is 9 ° or more and 10 ° or less, and the buried layer is made of GaAs, InP, Formed of any material of GaP and InAs;
(B) The width of the ridge stripe structure is not less than 1.8 μm and less than 1.9 μm, and the full width at half maximum in the horizontal direction of the far field pattern is not less than 9 ° and not more than 10 °, and the buried layer has G aAs , I formed of any material of nP, Ge, and InAs;
(C) The width of the ridge stripe structure is 1.7 μm or more and less than 1.8 μm, and the horizontal half-width of the far field pattern has a value of 9 ° or more and 10 ° or less, and the buried layer includes G aAs , I formed of any material of nP and InAs;
Width; (d) the ridge stripe structure is less than or 1.6 [mu] m 1.7 [mu] m, has a horizontal full angle at half maximum is 10 ° or less of 9 ° or more values of the far field pattern, wherein the buried layer is All G aA s And any material of InP;
(E) the width of the ridge stripe structure is less than 1.6μm or 1.5 [mu] m, has a horizontal full angle at half maximum is 10 ° or less of 9 ° or more values of the far-field pattern, the material of the buried layer G e Formed of;
(F) The width of the ridge stripe structure is 1.6 μm or more and 1.7 μm or less, and the horizontal full width at half maximum of the far field pattern is greater than 10 ° and less than or equal to 11 °, and the buried layer is made of InP, Formed of any material of GaAs, Ge, and InAs;
(G) The width of the ridge stripe structure is 1.5 μm or more and 1.6 μm or less, and the full width at half maximum in the horizontal direction of the far field pattern is greater than 10 ° and 11 ° or less, and the buried layer is InP, Formed of any material of GaAs, Ge, and InAs;
(H) The width of the ridge stripe structure is 1.4 μm or more and less than 1.5 μm, and the full width at half maximum in the horizontal direction of the far field pattern is greater than 10 ° and less than or equal to 11 °, and the buried layer is made of GaAs, Formed of any material of Ge and InAs;
(I) The width of the ridge stripe structure is 1.6 μm or more and 1.7 μm or less, and the full width at half maximum in the horizontal direction of the far field pattern is greater than 11 ° and less than or equal to 12 °, and the buried layer includes GaP and InP Formed of any of the following materials;
(J) The width of the ridge stripe structure is not less than 1.5 μm and less than 1.6 μm, the full width at half maximum in the horizontal direction of the far field pattern is greater than 11 ° and not more than 12 °, and the buried layer is InP, And (k) the width of the ridge stripe structure is 1.4 μm or more and less than 1.5 μm, and the horizontal full width at half maximum of the far field pattern is 11 A nitride having a value greater than 12 ° and less than or equal to 12 °, and satisfying any one condition that the buried layer is made of any material of GaAs, Ge, InAs, and InP Semiconductor laser element. A second buried layer made of a material different from the buried layer on the buried layer;
The nitride-based semiconductor laser device according to claim 1, further comprising an electrode on the second buried layer. The absorption coefficient of the buried layer is 1 × 10 ⁵ [cm ⁻¹ ] or more.
The nitride-based semiconductor laser device described in 1. The nitriding according to any one of claims 1 to 3, wherein a difference in mode absorption coefficient between the horizontal basic primary transverse mode and the horizontal primary transverse mode by the buried layer is 5 [cm ^-1 ] or more. Physical semiconductor laser device. 5. The nitride-based semiconductor laser device according to claim 1, wherein a mode absorption coefficient of a horizontal fundamental order transverse mode by the buried layer is 20 [cm ⁻¹ ] or less. An optical information processing apparatus capable of performing at least one process of recording, reproducing, and erasing information with respect to an optical recording medium,
Including one or more nitride-based semiconductor laser elements according to any one of claims 1 to 5 as a light source for one or more processes of the recording, the reproduction, and the erasure;
Light emission control means for emitting laser light from the laser element at a predetermined output;
Condensing means for condensing the laser light emitted from the laser element;
And irradiation position control means for irradiating a predetermined position of the optical recording medium with the laser beam condensed by the condensing means for the recording, reproducing, or erasing process. Optical information processing device.

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