JP2005101536A - Nitride semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser element for oscillating in a short wavelength range. <P>SOLUTION: The nitride semiconductor laser element comprises, on a substrate: an n-type cladding layer and an n-type optical-guide layer both composed of a nitride semiconductor containing Al; an active layer composed of a nitride semiconductor containing In and Al and having a quantum-well structure with a well layer; and a p-type optical-guide layer and a p-type cladding layer both composed of a nitride semiconductor containing Al, wherein the well layer of the active layer is composed of Al<SB>x</SB>In<SB>y</SB>Ga<SB>1-x-y</SB>N (0.02≤x≤0.05, 0.005≤y≤0.03, x+y<1); a first barrier layer and a second barrier layer, which interpose the active layer, are composed of Al<SB>u</SB>Ga<SB>1-u</SB>N (0.10≤u≤0.17); and the film thickness of the well layer is larger than those of the barrier layers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

Today, semiconductor lasers using nitride semiconductors are considered capable of oscillating in a wide wavelength range from the ultraviolet to the red, and their application range is high-capacity and high-density information recording and playback such as DVDs. It is expected not only for use in an optical disc system capable of recording, but also as a light source for laser printers, optical networks, and the like.
Further, in the nitride semiconductor laser element, light emission and oscillation in a wavelength region of 365 nm or less are more important. This is because a nitride semiconductor laser element which is harmless to the environment can be put into practical use as an alternative product such as a mercury lamp or an application product thereof by shortening the wavelength to 365 nm or less.

In order to obtain light having a short wavelength in a nitride semiconductor laser element or the like, it is conceivable to change the In mixed crystal ratio in the active layer. However, it is difficult to use InGaN for the light emitting layer at a wavelength of 370 nm or less, which is the band gap of GaN. Further, when the wavelength is shortened, a loss due to light absorption occurs in the guide layer in the waveguide, and the threshold current increases.
As an attempt to shorten the wavelength of such a nitride semiconductor device, there is one using a quantum well structure such as AlInGaN. Thus, theoretically, by changing the Al composition ratio in the well layer, a laser element or a light emitting element having a desired emission wavelength can be obtained.
JP-A-10-270756

  However, in the case where a nitride semiconductor containing Al such as AlInGaN as shown in Patent Document 1 is used for a laser element, cracks are likely to occur compared to other nitride semiconductors not containing Al. If the generation of this crack is not prevented, it will not operate as a nitride semiconductor device. For this reason, the shortening of the wavelength containing Al and the prevention of crack generation have an exclusive relationship. Furthermore, in order to shorten the wavelength, GaN has a light absorption edge at 365 nm, and since it has a high absorption coefficient even in a region having a wavelength as long as 10 nm, laser elements and light emission in this short wavelength region of 370 m or less. Use in an element becomes difficult.

  In addition, since the element characteristics of the active layer in the laser element greatly depend on the crystallinity, the crystallinity of the conductive type layers disposed above and below the active layer is an extremely important factor for improving the element characteristics. Usually, a nitride semiconductor light emitting device has a structure in which an n-type layer, an active layer, and a p-type layer are stacked in this order on a substrate. Therefore, it is necessary to improve the crystallinity in the n-type layer on the substrate and the p-type layer on the active layer.

  Therefore, the present invention improves the crystallinity of a nitride semiconductor and suppresses the generation of cracks in a nitride semiconductor laser element having an ultraviolet to blue color, for example, an oscillation wavelength of 350 nm to 367 nm, particularly 352 nm to 365 nm. An object of the present invention is to form an element structure having a reduced threshold current density.

The nitride semiconductor laser device of the present invention can achieve the object of the present invention with the following configuration.
(1) A first nitride semiconductor laser element according to the present invention includes an n-type cladding layer and an n-type light guide layer made of a nitride semiconductor containing Al on a substrate, and a well made of a nitride semiconductor containing In and Al. In a nitride semiconductor laser device including an active layer having a quantum well structure having a layer, a p-type light guide layer made of a nitride semiconductor containing Al, and a p-type cladding layer, the well layer of the active layer is made of Al _x In _y Ga _1-xy N (0.02 ≦ x ≦ 0.05, 0.005 ≦ y ≦ 0.03, x + y <1), the first barrier layer and the second layer sandwiching the active layer The barrier layer is made of Al _u Ga _1-u N (0.10 ≦ u ≦ 0.17), and the thickness of the well layer is larger than that of the barrier layer.

If the well layer of the active layer is a quaternary mixed crystal, it is theoretically possible to emit light in a short wavelength region, but in this case, a crack is generated from the periphery of the active layer. Therefore, in the present invention, the well layer is made of Al _x In _y Ga _1-xy N (0.02 ≦ x ≦ 0.05, 0.005 ≦ y ≦ 0.03, x + y <1). The generation of cracks in the upper and lower layers of the well layer is suppressed. In particular, in a quaternary mixed crystal, by setting In to the range of 0.005 to 0.03, the strain is relieved around the well layer. Even if the quaternary mixed crystal well layer is in the above range, the crystallinity is lowered depending on the consistency with the barrier layers stacked above and below the well layer. In view of this, the present invention achieves good alignment between the well layer and the barrier layer by forming the barrier layer sandwiching the well layer from Al _u Ga _1-u N (0.10 ≦ u ≦ 0.17). It is possible to keep the crystallinity from being lowered.

When the well layer and the barrier layer are stacked at the above mixed crystal ratio, the occurrence of cracks around the active layer can be effectively suppressed by making the well layer thicker than the barrier layer. Although the active layer has been described as a single quantum well layer, it may be a multiple quantum well layer, and the final layer may be formed of a well layer or a barrier layer.
(2) In the above configuration, the n-type and p-type cladding layers include a _first layer made of Al _c Ga _1-c N (0.07 ≦ c ≦ 0.10), and Al _d Ga _1-d N ( It is preferable that the superlattice layer is a second layer composed of 0.11 ≦ d ≦ 0.14).

  Even when the active layer is grown with good crystallinity under the conditions described above, a laser element cannot be formed if a crack has already occurred in the lower layer. The same applies to the upper layer grown on the active layer. In particular, in a nitride semiconductor laser element with an oscillation wavelength of 365 nm or less, the compatibility between the active layer and its upper and lower layers, and the crystallinity of these upper and lower layers appear as a significant difference in element characteristics. Therefore, by forming the n-type and p-type cladding layers as superlattice layers composed of the first layer and the second layer in which the Al mixed crystal is in the above range, generation of cracks in the cladding layer can be suppressed.

(3) In the above configuration, the n-type and p-type light guide layers are preferably made of AlcGa1-cN (0.055 ≦ c ≦ 0.075). As a result, the generation of cracks in the guide layer and at the interface between the guide layer and the layer in contact with this layer can be suppressed.
(4) In the above configuration, it is preferable that a nitride semiconductor layer containing Al having a larger band gap energy than the active layer is interposed between the active layer and the p-type light guide layer. The nitride semiconductor layer containing Al functions as a p-type carrier confinement layer.

  (5) In the above configuration, it is preferable that the substrate has a low dislocation region at least immediately below the optical waveguide region. By providing the substrate with an underlayer with few crystal defects, the active layer grown on the underlayer has less dislocation propagation from below, and the lifetime characteristics of the laser device are greatly improved. The area of the base layer with few crystal defects for growing the active layer may be a low dislocation region in the narrow range of the optical waveguide. Further, by using the substrate, it is possible to suppress the occurrence of cracks at the interface between the substrate and the nitride semiconductor layer.

  (6) In the above configuration, the substrate includes a periodic stripe-shaped, lattice-shaped, or island-shaped first nitride semiconductor layer on a surface of a heterogeneous substrate, an upper surface of the first nitride semiconductor layer, and It is preferable that the second nitride semiconductor layer cover the entire surface of the heterogeneous substrate by growing using the side surface as a nucleus. With such a substrate, not only can a low dislocation region be formed in a wide range, but also a cavity can be formed between the first nitride semiconductor layers, thereby reducing the warpage of the substrate and reducing cracks. Occurrence can be suppressed.

(7) In the above structure, it is preferable that a low dislocation region is formed in the second nitride semiconductor layer. As a result, the life characteristics of the laser element are greatly improved.
(8) In the above configuration, the number of dislocations in the low dislocation region of the substrate is preferably 1 × 10 ⁷ pieces / cm ² or less. The crystallinity of the substrate is inherited by each layer grown on it, but if the number of dislocations in the low dislocation region is 1 × 10 ⁷ / cm ² or less, the crystallinity of each layer grown thereon is stabilized.

As the substrate, a heterogeneous substrate made of a material different from the nitride semiconductor can be used. Insulating substrate such as sapphire, spinel (MgA1 ₂ O ₄ ) whose principal surface is C-plane, R-plane or A-plane, oxide substrate lattice-matched with nitride semiconductor, and others such as Si, SiC, etc. This is a conductive substrate. Preferably, a pseudo-nitride semiconductor substrate in which a nitride semiconductor with few crystal defects is grown on the heterogeneous substrate, or a nitride semiconductor substrate in which a wafer is processed from a nitride bulk single crystal is used. If a nitride semiconductor substrate or a conductive substrate is used, a counter electrode structure can be obtained without being limited to a laser element structure in which electrodes are formed on the same surface.

  Further, in order to prevent the occurrence of fine cracks in the nitride semiconductor, the off-angle angle is formed in the following range on the dissimilar substrate. It is preferable that the C-plane of sapphire is off-angled stepwise and the off-angle angle θ is in the range of 0.01 ° to 0.3 °. If the off-angle angle θ is less than 0.01 °, fine cracks tend to occur inside the nitride semiconductor grown in the lateral direction, while if the off-angle angle exceeds 0.3 °, selective growth occurs. When the surface state of the nitride semiconductor becomes step-like and the device structure is grown thereon, the step is slightly emphasized, and the device tends to be short-circuited and the threshold value (Ith) is easily increased. Such fine cracks may cause a decrease in life characteristics. Therefore, it is preferable to use the off-angled substrate as described above in terms of preventing the occurrence of fine cracks.

(9) In the above configuration, the substrate is preferably a substrate made of Al _x Ga _1-x N (0 ≦ x ≦ 1). In addition, a GaN layer is laminated on the substrate by HVPE method or MOCVD method, a heterogeneous substrate is removed and only the GaN layer is removed, and single crystal GaN is formed on a GaN seed crystal in NH ₃ fluid. A GaN substrate formed by recrystallization can also be used.
(10) Further, the nitride semiconductor laser element may have a pair of resonator surfaces, and a dielectric multilayer film may be formed on a light emitting end surface of the resonator surface.

(11) The dielectric multilayer film can be formed of a laminated film of a silicon oxide film having a thickness of at least 5λ / 4n and a zirconium oxide film having a thickness of λ / 4n from the light emitting end face side.
(12) A second nitride semiconductor laser element of the present invention is formed on a substrate with an n-type cladding layer and an n-type light guide layer made of a nitride semiconductor containing Al, and a nitride semiconductor containing In and Al. A nitride semiconductor laser device comprising an active layer having a quantum well structure having a well layer, a p-type light guide layer made of a nitride semiconductor containing Al, and a p-type cladding layer, wherein the pair of nitride semiconductor laser devices is a pair A laminated film of a silicon oxide film having a thickness of at least 5λ / 4n or more and a zirconium oxide film having a thickness of λ / 4n from the light emitting end face side on the light emitting end face of the resonator face A dielectric multilayer film is formed.

  The nitride semiconductor laser device of the present invention forms an active layer and a waveguide structure capable of laser oscillation in a short wavelength region of 365 nm or less. In particular, in the AlInGaN well layer, by adopting the above-described configuration, the forbidden band width of a desired emission wavelength can be formed by changing the Al composition ratio, and a light emitting element and a laser element in a short wavelength region can be obtained.

A typical example of the nitride semiconductor laser element of the present invention is a laser element as shown in FIG. FIG. 1 is a schematic cross-sectional view showing a nitride semiconductor laser element according to an embodiment of the present invention.
An underlayer 102 using lateral growth is formed on a heterogeneous substrate 101 such as sapphire via a buffer layer (not shown), and an n-type contact made of a nitride semiconductor layer doped with an n-type impurity thereon. Layer 103, crack preventing layer 104 made of In _g Ga _1-g N (0.05 ≦ g ≦ 0.2) doped with n-type impurities, superlattice layer n-type cladding layer 105, and bandgap than cladding layer An n-type guide layer 106 made of a low-energy nitride semiconductor layer (AlGaN), an active layer 107 having a quantum well structure having a well layer made of AlInGaN, Al _d Ga _1-d N doped with p-type impurities (0 < at least one p-type electron confinement layer (can be omitted) consisting of d ≦ 1), and a nitride semiconductor layer (AlGaN) having a smaller band gap energy than the cladding layer A p-type guide layer 109, a p-type cladding layer 110 of a superlattice layer, and a p-type contact layer 111 made of a nitride semiconductor layer doped with a p-type impurity. It is.

A second protective film (buried layer) 162 is formed on the side surface of the ridge.
A p-electrode 120 is formed on the p-type contact layer 111 that is the uppermost layer of the ridge-shaped stripe, and an n-electrode 121 is formed on the n-type contact layer 103.
Furthermore, a laminated film 164 is formed on the side surfaces of the p electrode 120 and the n electrode 121 except for the formation surface of the p pad electrode 122 and the n pad electrode 123. A p pad electrode 122 and an n pad electrode 123 are formed on the p electrode 120 and the n electrode 121, respectively.

Although not shown in FIG. 1, a protective film made of an inorganic material to be described later is formed on the light emitting surface side of the resonator surface, and a dielectric multilayer film is formed thereon. .
(Substrate 101)
As a substrate used for the nitride semiconductor laser device of the present invention, a different type substrate different from the nitride semiconductor may be used, or a nitride semiconductor substrate may be used. Examples of the heterogeneous substrate include, for example, an insulating substrate such as sapphire, spinel (MgA1 ₂ O ₄ ) having any one of the C-plane, R-plane, and A-plane, SiC (including 6H, 4H, and 3C), A nitride semiconductor such as an oxide substrate lattice-matched with ZnS, ZnO, GaAs, Si, and a nitride semiconductor can be grown, and a conventionally known substrate material can be used. Among them, sapphire and spinel are mentioned. The substrate may have at least a surface having an off-angle angle of about 0.01 to 0.3 ° and a step-like off-angle angle. Thereby, generation | occurrence | production of a fine crack can be prevented inside the nitride semiconductor layer and active layer which comprise an element.

When a nitride semiconductor substrate (for example, a GaN substrate) is used, the underlying layer (including a protective layer for performing lateral growth), the n contact layer, and the like are not necessarily formed and are omitted. be able to.
(Underlayer 102)
A base layer 102 made of a nitride semiconductor is preferably formed on the heterogeneous substrate 101 through a buffer layer (not shown).

As the buffer layer, for example, InαAlβGa _1- α _- βN (0 ≦ α, 0 ≦ β, α + β ≦ 1) or the like (for example, AlN, GaN, AlGaN, InGaN, etc., preferably GaN) is 300 ° C. or higher and 900 ° C. or lower. Examples include those grown at a film thickness of several tens of angstroms to several hundreds of angstroms. This buffer layer is preferable for alleviating the lattice constant irregularity between the heterogeneous substrate and the high-temperature-grown nitride semiconductor layer and preventing the occurrence of dislocations.

After growing the buffer layer, the first nitride semiconductor layer is partially grown, and further, the second nitride semiconductor layer is grown using the first nitride semiconductor layer as a growth nucleus, thereby lateral growth. It is preferable to form the base layer 102 in which dislocations are reduced by using. The underlayer is preferably a nitride semiconductor represented by the general formula Al _x Ga _1-x N (0 ≦ x ≦ 1), and preferably has a thickness of 3 to 30 μm. Further, the laterally grown region (low dislocation region) has a dislocation number as small as 1 × 10 ⁷ pieces / cm ² or less, preferably 1 × 10 ⁶ pieces / cm ² or less, or a region with a small amount. What you have is appropriate. Further, even if this underlayer contains an n-type impurity (for example, Si, Sn, Ge, Se, C, Ti, etc.) in the range of about 1 × 10 ^{16 to} 5 × 10 ²¹ cm ^−3, for example. Good.

In order to form the first nitride semiconductor layer partially (selectively), a photomask having a predetermined shape is produced using photolithography technology, and the predetermined shape is formed through the photomask. A protective film is formed. By forming the protective film in a shape such as a dot, stripe, grid surface, mesh, or mesh, the first nitride semiconductor layer can be etched into a desired pattern. The protective film may be, for example, an oxide such as silicon oxide (SiO _x ), titanium oxide (TiO _x ), zirconium oxide (ZrO _x ), nitride such as silicon nitride (Si _x N _y ) or titanium nitride, nitriding In addition to silicon oxide or these multilayer films, refractory metals having a melting point of 1200 ° C. or higher, such as tungsten, titanium, and tantalum, can be given.

  In addition, when the first nitride semiconductor layer is formed in a stripe shape, the relation between the stripe width A and the width B of the portion where no nucleus is formed (window portion) is 2 to 200 μm, preferably 15 ˜100 μm and width B is 2 to 200 μm, preferably 2 to 100 μm. When a laser element structure is formed on a nitride semiconductor obtained by selective growth and a ridge-shaped stripe is formed on the uppermost layer of the p-type nitride semiconductor layer, the ridge-shaped stripe is formed on the low dislocation region. Preferably it is formed. As a result, a nitride semiconductor laser device having excellent lifetime characteristics and the like can be realized.

In the case of using a heterogeneous substrate, after growing a nitride semiconductor serving as an underlayer before forming the device structure on the heterogeneous substrate, the heterogeneous substrate is removed by a method such as polishing, and a single substrate of nitride semiconductor The element structure may be formed as follows, and the heterogeneous substrate may be removed during or after the element structure is formed.
Examples of the nitride semiconductor substrate include a substrate made of a nitride semiconductor described later.

(Nitride semiconductor layer)
In the nitride semiconductor laser device of the present invention, the nitride semiconductor is a group III-V nitride semiconductor (InαAlβGa ₁ -α _- βN, 0 ≦ α, 0 ≦ β, α + β ≦ 1). Furthermore, a mixed crystal can be obtained in which B is used as a group III element or a part of N is substituted with P or As as a group V element. Note that a nitride semiconductor containing Al is β> 0, and a nitride semiconductor containing In is α> 0. The nitride semiconductor can be formed by any method known in the art, such as MOVPE (metal organic vapor phase epitaxy), HVPE (halide vapor phase epitaxy), MBE (molecular beam vapor phase epitaxy). .

  As the n-type impurity used in the nitride semiconductor layer, a group IV or group VI element such as Si, Ge, Sn, S, O, Ti, Zr, or the like can be used, preferably Si, Ge, Sn, Most preferably, Si is used. The p-type impurity is not particularly limited, and examples thereof include Be, Zn, Mn, Cr, Mg, and Ca, and Mg is preferably used. Thereby, each conductivity type nitride semiconductor layer is formed, and each conductivity type layer mentioned below is constituted.

In the present invention, the clad layer and the like are described as an n-type layer and a p-type layer. However, all the layers do not contain an n-type impurity or a p-type impurity. In some cases, a layer disposed on the n-type layer side from the active layer is referred to as an n-type layer, and a layer disposed on the p-type layer side from the active layer is referred to as a p-type layer.
First, an n-type contact layer 103 made of Al _d Ga _1-d N (0 <d ≦ 0.5) is grown on the base layer 102. The doping amount of the n-type impurity is preferably 5 × 10 ¹⁷ / cm ^{3 to} 5 × 10 ¹⁸ / cm ³ . The thickness of the n-type contact layer is 0.5 to 10 μm, preferably 2 to 5 μm. In the subsequent process, an n-electrode 121 is formed on the n-type contact layer.

Subsequently, a crack prevention layer 104 is grown on the n-type contact layer 103. As the crack prevention layer 104, Si-doped In _g Ga _1-g N (0.05 ≦ g ≦ 0.20) is grown, and preferably In _g Ga _{1-g with} g of 0.08 to 0.12. Grow N. Although this crack prevention layer can be omitted, when the crack prevention layer is formed on the n-type contact layer, the occurrence of cracks in the nitride semiconductor element can be prevented. In particular, in a short-wavelength laser element of 365 nm or less, since a crack is likely to occur near the active layer, it is preferable to form a crack prevention layer in the range of In shown above. The doping amount of Si is 5 × 10 ¹⁷ / cm ^{3 to} 5 × 10 ¹⁹ / cm ³ . The thickness of the crack prevention layer is a thickness that does not impair the crystallinity, and specifically, for example, 0.10 to 0.20 μm.

Next, an n-type cladding layer 105 is grown on the crack prevention layer 104. The n-type cladding layer 105 includes Al _a Ga _1-a N (0.07 ≦ a ≦ 0.10) as a first layer and Al _b Ga _1-b N (0.11 ≦ b ≦ 0. A superlattice layer consisting of 14) is preferred. The first layer and the second layer can be formed by stacking layers having a single layer thickness of 100 angstroms or less, preferably 70 angstroms or less, more preferably 40 angstroms or less, preferably 10 angstroms or more. By using such a superlattice layer, the occurrence of cracks can be prevented and the crystallinity can be improved despite containing Al. The total film thickness of the n-type cladding layer is preferably 0.45 to 0.65 μm.

The average composition is preferably formed as Al _e Ga _1-e N (0.07 ≦ e ≦ 0.14). If the average composition of Al is within this range, cracks can be suppressed, and a sufficient difference in refractive index from the laser waveguide can be obtained. The doping amount of the n-type impurity is preferably 1 × 10 ¹⁷ / cm ^{3 to} 5 × 10 ¹⁸ / cm ³ . When the n-type impurity is doped in this range, the resistivity can be lowered and the crystallinity is not impaired.

An n-type guide layer 106 is grown on the n-type cladding layer 105. Examples of the n-type guide layer 106 include Al _c Ga _1-c N (0.055 ≦ c ≦ 0.075). The thickness of the n-type guide layer is 0.05 to 0.25 μm, preferably 0.14 to 0.16 μm. It is preferable to grow with this film thickness because cracks do not occur and the threshold value (I _th ) decreases.
An active layer 107 is grown on the n-type guide layer 106. As the active layer 107, the well layer is made of Al _x In _y Ga _1-xy N (0.02 ≦ x ≦ 0.05, 0.005 ≦ y ≦ 0.03, x + y <1). In addition, the first barrier layer formed on the n layer side with the active layer interposed therebetween and the second barrier layer formed on the p layer side are formed of Al _u Ga _1-u N (0.10 ≦ u ≦ 0.17). ). The well layer is preferably thicker than the barrier layer. Further, impurities may be doped into one or both of the well layer and the barrier layer constituting the active layer. Preferably, the barrier layer is preferably doped with an impurity because the threshold value is lowered. The thickness of the well layer is 50 to 150 angstroms, preferably 90 to 110 angstroms. Regarding the thickness of the barrier layer, the first barrier layer is 30 to 150 angstroms, preferably 60 to 80 angstroms. The second barrier layer is 10 to 150 angstroms, preferably 30 to 60 angstroms. If the active layer is formed in the above range, the occurrence of cracks in the vicinity of the active layer can be suppressed.

The multi-quantum well structure of the active layer starts with a barrier layer and ends with a well layer, starts with a barrier layer and ends with a barrier layer, starts with a well layer and ends with a barrier layer, and starts with a well layer and ends with a well layer. It may end. It is preferable to start with a barrier layer and repeat a pair of a well layer and a barrier layer 1 to 5 times to lower the threshold value and improve the life characteristics.
A p-type carrier confinement layer 108 is grown on the active layer 107. The p-type carrier confinement layer 108 is a nitride semiconductor layer containing Al having a larger band gap energy than the active layer. The p-type carrier confinement layer 108 is formed by growing at least one layer made of Mg-doped Al _d Ga _1-d N (0 <d ≦ 1). Preferably d is in the range of 0.1 to 0.5, and more preferably d is in the range of 0.25 to 0.35. This is because if d is less than 0.1, the laser element does not function as a sufficient electron confinement layer, and if it is 0.25 or more, sufficient electron confinement (carrier confinement) is made, resulting in carrier overflow. It is because it suppresses.

In addition, when it is 0.35 or less, it is possible to grow while suppressing the generation of cracks, and it is possible to grow with good crystallinity. The thickness of the p-type carrier confinement layer is 10 to 200 angstroms, preferably 50 to 150 angstroms. When the film thickness is in the above range, electrons in the active layer 108 can be confined well, and the generation of cracks can also be suppressed. Further, the bulk resistance is preferably low. The doping amount of Mg in the p-type electron confinement layer 109 is 1 × 10 ¹⁹ / cm ³ to 1 × 10 ²¹ / cm ³ . When the doping amount is within this range, in addition to lowering the bulk resistance, Mg is well diffused into a p-type guide layer grown by undoped described later, and 1 × Mg is added to the p-type guide layer which is a thin film layer. 10 ¹⁶ / cm ³ can be contained in a range of ~1 × 10 ¹⁸ / cm ^3. The p-type electron confinement layer 109 is preferably grown at a low temperature, for example, a temperature similar to the temperature at which the active layer is grown at about 900 to 1000 ° C., because it can prevent decomposition of the active layer.

  The p-type electron confinement layer may be composed of two layers, a low temperature growth layer and a high temperature layer, for example, a layer grown at a temperature about 100 ° C. higher than the growth temperature of the active layer. Thus, when it is composed of two layers, the low temperature growth layer prevents the active layer from being decomposed, and the high temperature growth layer reduces the bulk resistance. The thickness of each layer when the p-type electron confinement layer is composed of two layers is not particularly limited, but the low temperature growth layer is preferably 10 to 50 Å, and the high temperature growth layer is preferably 50 to 150 Å. Here, the carrier confinement layer may be formed of a single film or a multilayer film having a different composition.

This p-type electron confinement layer is for confining carriers in an active layer or well layer. In a laser element, a high-power light-emitting element, etc., the carrier is activated by an increase in temperature and current density due to element driving. It is possible to prevent the carrier from overflowing, and the carrier can be efficiently injected into the active layer.
Next, the p-type guide layer 109 is grown on the p-type electron confinement layer 108. An example of the p-type guide layer 109 is a nitride semiconductor layer made of Al _c Ga _1-c N (0.055 ≦ c ≦ 0.075). The thickness of the p-type guide layer is 0.05 to 0.25 μm, preferably 0.14 to 0.16 μm. Within this range, the threshold value is preferably lowered. As described above, the p-type guide layer is grown as an undoped layer, but Mg doped in the p-type electron confinement layer is diffused to 1 × 10 ¹⁶ / cm ³ to 1 × 10 ¹⁸ / cm ^3. Mg is contained in the range. Moreover, even if the film thicknesses of the n-type guide layer and the p-type guide layer are asymmetric in the vertical direction, the occurrence of cracks can be suppressed within the above film thickness range.

A p-type cladding layer 110 is grown on the p-type guide layer 109. The p-type cladding layer 110 preferably has a multilayer structure in which nitride semiconductor layers having different compositions are stacked. For example, the first layer is made of Al _a Ga _1-a N (0.07 ≦ a ≦ 0.10), and the second layer is made of Al _b Ga _1-b N (0.11 ≦ b ≦ 0.14). A lattice layer is mentioned. The doping amount of the p-type impurity is preferably 1 × 10 ¹⁷ / cm ³ to 1 × 10 ¹⁹ / cm ³ . It is preferable that the p-type impurity is doped in this range because the doping amount is such that the crystallinity is not impaired and the bulk resistance is lowered. Such a multilayer film can be formed by stacking layers having a single layer thickness of 100 angstroms or less, preferably 70 angstroms or less, more preferably 40 angstroms or less, preferably 10 angstroms or more. By forming the p-type cladding layer with a superlattice structure, it is possible to realize a 365 nm oscillation laser element while suppressing the occurrence of cracks. The total film thickness of the p-type cladding layer 110 is 0.4 to 0.55 μm, and this range is preferable for reducing the forward voltage (Vf). The average composition of Al in the entire p-type cladding layer is 0.07 to 0.14. This value is preferable for suppressing the occurrence of cracks and obtaining a difference in refractive index from the laser waveguide.

A p-type contact layer 111 is grown on the p-type cladding layer 110. The p-type contact layer is preferably formed by growing a nitride semiconductor layer made of Mg-doped GaN. A film thickness of about 10 to 200 angstroms is appropriate. The doping amount of Mg is 1 × 10 ¹⁹ / cm ³ to 1 × 10 ²² / cm ³ . By adjusting the film thickness and the Mg doping amount in this way, the carrier concentration of the p-type contact layer is increased, and an ohmic contact with the p-electrode 120 is easily obtained.

(Ridge formation)
After the nitride semiconductors are stacked in this way, a ridge is formed. The ridge-shaped stripe is etched from the p-type contact layer to the lower side (substrate side) than the p-type contact layer, and at least to the p-type cladding layer, and the ridge stripe is formed above the active layer. Is appropriate. For example, a stripe formed by etching from the p-type contact layer to the middle of the p-type guide layer as shown in FIG.

In order to form a stripe-shaped waveguide region, a protective film made of Si oxide (mainly SiO ₂ ) is formed with a film thickness of 0.5 μm on almost the entire surface of the uppermost p-type contact layer by a CVD apparatus. Thereafter, a mask having a predetermined shape is formed on the protective film, and a stripe-shaped protective film is formed by, for example, a photolithography technique using CHF ₃ gas with an RIE apparatus. Using this protective film as a mask, the semiconductor layer is etched by, for example, SiCl ₄ gas.

The width of the ridge is in the range of 1 to 15 μm, preferably 1.5 to 5.0 μm.
(Formation of first insulating film)
A first insulating film is formed on the surface of the p-type semiconductor layer with the SiO ₂ mask remaining. The first insulating film may be provided on the entire surface of the semiconductor layer by masking the n electrode formation surface. Further, it is preferable to provide a portion where an insulating film is not formed so that it can be easily divided later. The first insulating film is made of a material having a value smaller than the refractive index of the laser waveguide region, and has a refractive index of about 1.6 to 2.3, Si, V, Zr, Nb, Examples include oxides containing at least one element selected from the group consisting of Hf and Ta, BN, AlN, and the like. Preferably, any one or more elements of Zr and Hf oxides, BN, particularly preferable Is ZrO ₂ or SiO ₂ .

After forming the first insulating film, it is immersed in a buffered solution to dissolve and remove the SiO ₂ formed on the upper surface of the ridge stripe, and on the p-type contact layer together with SiO ₂ by the lift-off method (and also the n-type contact). The first insulating film on the layer is removed. Thereby, the upper surface of the ridge is exposed and the side surface of the ridge is covered with the first insulating film.
The wafer is then heat treated at 600 ° C. In the case where a material film other than SiO ₂ is formed as the first insulating film, after the first insulating film is formed, it is 300 ° C. or higher, preferably 400 ° C. or higher, and below the decomposition temperature of the nitride semiconductor (1200 ° C.). By performing the heat treatment, the first insulating film can be hardly dissolved in the dissolved material of the mask (mainly SiO ₂ or the like) in the subsequent process.

(Formation of electrodes)
Next, a p-electrode 120 is formed on the ridge protrusion on the p-type contact layer 111 and the first insulating film by sputtering. The p electrode 120 preferably has, for example, a multilayer structure of metal layers, and specifically includes Ni / Au.
In addition, an n-electrode 121 that takes ohmic contact is also formed on the upper surface of the n-type contact layer 104. The n-electrode 121 is made of Ti / Al, and is formed in a stripe shape parallel to the ridge and having the same length. Note that the n-electrode is not necessarily formed on the upper surface of the n-type contact layer. For example, if the substrate used has conductivity and can ensure ohmic contact, the lower surface side of the substrate (what is the element structure? You may form in the other side.

After the p-electrode 120 and the n-electrode 121 are formed, heat treatment is performed in a mixed atmosphere of oxygen and / or nitrogen. The temperature is 1000 ° C. or lower, preferably 800 ° C. or lower, more preferably 600 ° C. or lower.
(Formation of second insulating film)
Next, a resist that covers the entire surface of the p-electrode 120 on the ridge and a part of the upper portion of the n-electrode 121 is formed, and a second insulating film 162 made of SiO ₂ is formed on the entire surface. Thereafter, by performing a lift-off method, a second insulating film 162 in which the entire upper surface of the p-electrode 120 and a part of the n-electrode 121 are exposed is formed.

In consideration of the subsequent division, the second insulating film 162 and the p and n electrodes 120 and 121 may not be formed in a stripe-shaped range having a width of about 10 μm across the division position.
(Pad electrode formation)
Next, the laminated film 164 is formed of a laminated film such as SiO ₂ or TiO ₂ so as to cover the electrodes. The laminated film 164 may be formed as a single layer. Thereafter, pad electrodes 122 and 123 are formed. The pad electrodes 122 and 123 are preferably formed so as to cover the second insulating film 162. The pad electrode is in contact with the p electrode and the n electrode in a stripe shape. The pad electrode is preferably a laminated body made of a metal such as Ni, Ti, Au, or Pt.

(Chip)
Next, the sapphire substrate on which the nitride semiconductor has grown is polished and adjusted to a film thickness of about 200 μm, and then a scribe groove is formed on the back surface of the substrate, braking from the nitride semiconductor layer side, and cleaving. Laser. Alternatively, a bar-shaped laser may be formed by etching such as RIE without polishing or removing the sapphire substrate. The cleavage surface or etching surface of the nitride semiconductor layer is an M surface (1-100 surface) of the nitride semiconductor, and this surface is a resonator surface.

The resonator surface is preferably covered with an insulating film. Examples of the insulating film include a film that functions as a protective film and / or a film that functions as a reflectance control film. As this insulating film, for example, a dielectric multilayer film is suitable.
The dielectric multilayer film is basically formed by alternately laminating inorganic materials having different reflectances. For example, the dielectric multilayer film is alternately laminated with a thickness of λ / 4n (λ: wavelength, n: refractive index). Can be changed. The type and thickness of each thin film of the dielectric multilayer film can be designed by appropriately selecting those inorganic materials according to the wavelength of the nitride semiconductor laser element to be oscillated. For example, as the inorganic material, Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, B, Ti and oxides and nitrides thereof (for example, AlN, AlGaN, BN, etc.) ) Or a compound such as fluoride is suitable from the viewpoint of efficiently resonating light generated in the active layer. In particular, one or more of TiO ₂ , ZrO ₂ , HfO ₂ , Sc ₂ O ₃ , Y ₂ O ₃ , MgO, Al ₂ O ₃ , Si ₃ N ₄ or ThO ₂ as a high refractive index material, low Examples of the refractive index material include one or more of SiO ₂ , ThF ₄ , LaF ₃ , MgF ₂ , LiF, NaF or Na ₃ AlF _6. These high refractive index materials, low refractive index materials, Are preferably used in appropriate combination.

  The insulating film can be formed by laminating one to several tens of layers with a thickness of several tens to several μm depending on the wavelength of oscillation.

Among them, a nitride semiconductor, a semiconductor when the laser element, a dielectric multilayer film formed on the cavity end face is at least 2 selected from SiO _2, TiO _2, ZrO ₂ which oscillates blue from outside the ultraviolet or near ultraviolet More than one kind is preferable, and a combination of SiO ₂ and ZrO ₂ is more preferable. These three types, particularly these two types of oxides, have little light absorption in the range of 360 nm to 460 nm, and can adhere very well to the nitride semiconductor to prevent peeling. Furthermore, it does not deteriorate even when light of a wavelength in this range is continuously irradiated for a long time, and it has excellent heat resistance against the heat generated by the semiconductor laser device, and has a long life regardless of the type of environmental atmosphere. Can be secured.

When using a combination of SiO ₂ and ZrO ₂ , it is preferable to first form a film having good adhesion to the nitride semiconductor as a protective film on the nitride semiconductor. For example, ZrO ₂ can be used as the protective film. When the insulating film that is in direct contact with the nitride semiconductor, particularly the dielectric multilayer film, has good adhesion to the nitride semiconductor, the protective film may not be provided. Thereby, the adhesiveness with a nitride semiconductor (especially GaN-type semiconductor etc.) can be ensured more. For example, on the ZrO _2, it is appropriate to laminating a SiO ₂ and ZrO ₂ are alternately. As described above, the film thickness in this case is suitably, for example, λ / 4n. In particular, the film thickness of SiO ₂ is preferably 5λ / 4n or more, and is preferably 5λ / 4n. Is more preferable. Note that in such a multilayer structure of insulating films, when two or more layers of SiO ₂ are stacked, only the side closest to the nitride semiconductor may have a thickness of 5λ / 4n.

These insulating films can be formed by a known method such as vapor deposition or sputtering. It is not always necessary to form the same material, the same laminated structure, and the same film thickness on the emission end face of the resonator face and the opposite face.
The nitride semiconductor laser device of the present invention can be mounted by either face-up mounting (that is, the substrate side is opposed to the submount substrate) or face-down mounting (that is, the ridge side is opposed to the submount substrate). Good. In the former case, wire bonding or the like is performed on the pad electrode and connected to the outside. In the latter case, metallized layers (bumps: Ag, Au, Sn, In, Bi, Cu, Zn, etc.) are formed on the p electrode and the n electrode, respectively. The metallized layer is connected to a pair of positive and negative external electrodes provided on the submount. Further, a wire or the like is wired to the submount substrate (external electrode). In the case of face-down mounting, the heat dissipation can be improved because the heat generating ridge side is located in the vicinity of the submount substrate.

Hereinafter, a laser element structure as shown in FIG. 1 will be described as an example.
(Example 1)
First, as a dissimilar substrate, the C-plane that is off-angled stepwise is the main surface, the off-angle angle θ = 0.02 °, the step difference is about 20 angstroms, the terrace width W is about 800 angstroms, and the orientation flat surface is the A-plane. Then, a sapphire substrate whose step is perpendicular to the A plane is prepared.

  The sapphire substrate is set in a reaction vessel, the temperature is set to 510 ° C., hydrogen is used as a carrier gas, ammonia and TMG (trimethylgallium) are used as a source gas, and a low-temperature growth buffer layer made of GaN on the sapphire substrate 101 102 is grown to a thickness of 200 Angstroms.

After the buffer layer growth, only TMG is stopped, the temperature is raised to 1050 ° C., and when it reaches 1050 ° C., TMG and ammonia are used as source gases, and a GaN layer made of undoped GaN is grown to a thickness of 2.5 μm. . The obtained GaN layer is processed to have a stripe width of 4 μm and a window width of 16 μm.
Thereafter, a first nitride semiconductor layer (not shown) made of undoped GaN is grown on the GaN layer processed into a stripe shape by about 3 μm, and a second nitride semiconductor layer is grown by about 15 μm on the first nitride semiconductor layer. Then, the base layer 102 is formed by planarization.

Next, a buffer layer (not shown) made of Al _0.02 Ga _0.98 N is formed on the base layer 102 at a temperature of 1100 ° C. using TMG (trimethylgallium), TMA (trimethylaluminum), and ammonia. The film is grown with a thickness of 5 μm. This layer functions as a buffer layer between the AlGaN n-type contact layer and the nitride semiconductor substrate made of GaN.

An n-type contact layer 103 made of Al _0.02 Ga _0.98 N doped with Si at 1100 ° C. is grown to a thickness of 4 μm on the obtained buffer layer using TMG, TMA, ammonia, and silane gas as an impurity gas.
Next, a crack prevention layer 104 made of In _0.10 Ga _0.90 N doped with Si at 5 × 10 ¹⁸ / cm ³ at a temperature of 920 ° C. using TMG, TMI (trimethylindium), and ammonia is formed to a thickness of 0.15 μm. Grow in.

The temperature is set to 1000 ° C., TMA, TMG, and ammonia are used as source gases, an A layer made of undoped Al _0.13 Ga _0.87 N is grown to a thickness of 25 mm, and silane gas is used as an impurity gas. A B layer made of Al _0.09 Ga _0.91 N doped with 5 × 10 ¹⁸ / cm ³ is grown to a thickness of 25 mm. Then, the operation of alternately laminating the A layer and the B layer is repeated 120 times to laminate the A layer and the B layer, and the n-type cladding layer 105 made of a multilayer film (superlattice structure) having a total film thickness of 0.6 μm is formed. Grow. At this time, the average composition of Al in the cladding layer is 0.110.

On the cladding layer 105, TMG and ammonia are used as source gases at the same temperature, and an n-type light guide layer 106 made of Al _0.065 Ga _0.935 N and having a thickness of 0.15 μm is grown.
Next, the temperature is set to 970 ° C., TMI (trimethylindium), TMG, and TMA are used as source gases, a barrier layer made of Si-doped Al _0.15 Ga _0.85 N, and an undoped In _0.02 Al _0.03 Ga _0.95 A well layer made of N and a barrier layer made of undoped Al _0.15 Ga _0.85 N are stacked in the order of the first barrier layer / well layer / second barrier layer to form the active layer 107. At this time, the first barrier layer is 70 mm, the second barrier layer is 50 mm, the well layer is 100 mm, and the quantum well structure has a total film thickness of about 220 mm.

On the active layer 107, TMA, TMG, and ammonia were used as source gases, Cp ₂ Mg (cyclopentadienyl magnesium) was used as an impurity gas, and Mg was doped at 1 × 10 ¹⁹ / cm ³ at the same temperature. A p-type electron confinement layer 108 made of Al _0.3 Ga _0.7 N is grown to a thickness of 13 nm.
The temperature is set to 1000 ° C., TMG and ammonia are used as source gases, and a 0.15 μm thick p-type light guide layer 109 made of Al _0.065 Ga _0.935 N is grown. The p-type light guide layer 109 is doped with Mg by diffusion of Mg from adjacent layers such as the p-type electron confinement layer 108 and the p-type cladding layer 110 described later. It can be a doped layer.

Subsequently, an A layer made of undoped Al _0.13 Ga _0.87 N is grown to a thickness of 25 mm at 1000 ° C., and then a B layer made of Mg doped Al _0.09 Ga _0.91 N is grown to a thickness of 25 mm using Cp ₂ Mg. The p-type cladding layer 110 made of a superlattice layer having a total thickness of 0.45 μm is grown by repeating the operation of alternately stacking the A layer and the B layer 90 times.
Finally, a p-type contact layer 111 made of p-type GaN doped with Mg at 1 × 10 ²⁰ / cm ³ is grown on the p-type cladding layer 110 at a temperature of 1000 ° C. to a thickness of 150 mm. The p-type contact layer 111 can be composed of p-type In _X Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), preferably GaN or Al composition doped with p-type impurities If the AlGaN ratio is 0.3 or less, the most preferable ohmic contact with the p-electrode 120 can be obtained. Since the p-type contact layer 111 forms an electrode thereon, it is desirable to have a high carrier concentration of 1 × 10 ¹⁷ / cm ³ or more. If it is lower than 1 × 10 ¹⁷ / cm ^3, it tends to be difficult to obtain a preferable ohmic with the electrode. Furthermore, when the composition of the contact layer is GaN, a preferable ohmic with the electrode material is easily obtained. After the reaction is completed, the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.

After the nitride semiconductor is grown in this way to form a laminated structure, the wafer is taken out from the reaction vessel, and an etching mask made of SiO ₂ is formed on the surface of the uppermost p-type contact layer 111. The mask is processed into a predetermined shape, and a p-type semiconductor layer, an active layer, and a part of the n-type semiconductor layer are sequentially etched by RIE (reactive ion etching) using Cl ₂ gas to form an n electrode. Expose the surface of the mold contact layer. At this time, the surface of the n-type contact layer is exposed not only in the region where the n-electrode is formed, but also in the region including the position and / or the periphery where the nitride semiconductor element is cleaved or divided in a later step. .

Next, a ridge stripe is formed as the above-described stripe-shaped waveguide region. First, a first protective film made of Si oxide (mainly SiO ₂ ) is formed to a thickness of 0.5 μm on almost the entire surface of the uppermost p-type contact layer (upper contact layer) 111 by a PVD apparatus. . Next, a mask having a predetermined shape is formed on the first protective film, and the first protective film is formed with a stripe width of 1. with a RIE (reactive ion etching) apparatus using CF ₄ gas and photolithography. 6 μm. Subsequently, using the first protective film as a mask, the p-type contact layer 111, the p-type cladding layer 110, and a part of the p-type light guide layer 109 are etched, so that the film thickness of the p-type light guide layer 109 is increased. A ridge stripe is formed by etching to a depth of 0.1 μm.

After the ridge stripe is formed, the second protective film 162 made of Zr oxide (mainly ZrO ₂ ) is formed on the first protective film, and the p-type light guide exposed by etching on the first protective film. It is continuously formed on the layer 109 with a thickness of 0.2 μm.
After the formation of the second protective film 162, the wafer is heat-treated at 600 ° C. When a material other than SiO ₂ is formed as the second protective film 162 in this way, after the second protective film 162 is formed, it is 300 ° C. or higher, preferably 400 ° C. or higher, and below the decomposition temperature of the nitride semiconductor (1200 ° C. ), The second protective film 162 becomes difficult to dissolve in the dissolved material (hydrofluoric acid) of the first protective film, and it is more desirable to add this step.

  Next, the wafer is immersed in hydrofluoric acid, and the first protective film is removed by a lift-off method. As a result, the first protective film provided on the p-type contact layer 111 is removed, and the p-type contact layer is exposed. As described above, as shown in FIG. 1, the second protective film (embedded layer) 162 is formed on the side surface of the ridge stripe and on the plane continuous therewith (exposed surface of the p-type light guide layer 109).

Thus, after the first protective film provided on the p-type contact layer 112 is removed, as shown in FIG. 1, Ni / Au (100 Å / 100 mm) is formed on the exposed surface of the p-type contact layer 111. A p-electrode 120 made of 1500 Å) is formed. However, the p-electrode 120 is formed over the second protective film 162 with a stripe width of 100 μm, as shown in FIG.
Before or after the formation of the p-electrode 120, a striped n-electrode 121 made of Ti / Al (100Å / 5000Å) is formed in a direction parallel to the stripe on the surface of the n-type contact layer 103 that has already been exposed.

Next, in order to provide an extraction electrode on the p-electrode 120 and the n-electrode 121, a desired region is masked and a laminated film 164 made of SiO ₂ and TiO ₂ is provided. At this time, the width of the active layer 107 (width in the direction perpendicular to the resonator direction) is 160 μm, and SiO ₂ and the resonator surface (reflecting surface side) and the resonator surface (light emitting surface side) are paired. A laminated film 164 made of TiO ₂ is provided.
Thereafter, a pad electrode 122 made of RhO—Pt—Au (3000 to 1500 to 6000) is provided on the p electrode 120. A pad electrode 123 made of Ni—Ti—Au (1000 Å−1000 Å−8000 Å) is provided on the n electrode 121.

  After forming the n electrode 121 and the p electrode 120 as described above, the sapphire substrate 101 of the wafer is polished to 200 μm, and then the surface of the above-described resonator surface (light emitting surface side), that is, a stripe The stacked film 164 is removed by etching the surface in the direction perpendicular to the p- and n-electrodes 120 and 121, and the resonance surface (1-100 surface, surface corresponding to the side surface of the hexagonal column crystal = M surface) ).

Finally, the wafer was cut into chips in a direction parallel to the p-electrode to obtain a laser element (resonator length: 650 μm).
The obtained laser device was a nitride semiconductor device that continuously oscillates at a wavelength of 365 nm at room temperature. When CW (Continuous Wave) with an oscillation wavelength of 365 nm at 25 ° C. and APC driving with 3 mW were performed, a lifetime characteristic of 2000 hours or more was exhibited.
(Example 2)
A sapphire substrate similar to that in Example 1 is prepared as a different substrate.

  The sapphire substrate is set in a reaction vessel, the temperature is set to 510 ° C., hydrogen is used as a carrier gas, ammonia and TMG (trimethylgallium) are used as a source gas, and a low-temperature growth buffer layer made of GaN on the sapphire substrate 101 102 is grown to a thickness of 200 Angstroms.

After the buffer layer growth, only TMG is stopped, the temperature is raised to 1050 ° C., and when it reaches 1050 ° C., TMG and ammonia are used as source gases, and a GaN layer made of undoped GaN is grown to a thickness of 2.5 μm. . The obtained GaN layer is processed to have a stripe width of 4 μm and a window width of 16 μm.
Thereafter, a first nitride semiconductor layer (not shown) made of undoped GaN is grown on the GaN layer processed into a stripe shape by about 3 μm, and a second nitride semiconductor layer is grown by about 15 μm on the first nitride semiconductor layer. Then, the base layer 102 is formed by planarization.

Next, a buffer layer (not shown) made of Al _0.02 Ga _0.98 N is formed on the base layer 102 at a temperature of 1100 ° C. using TMG (trimethylgallium), TMA (trimethylaluminum), and ammonia. The film is grown with a thickness of 5 μm.
An n-type contact layer 103 made of Al _0.02 Ga _0.98 N doped with Si at 1100 ° C. is grown to a thickness of 4 μm on the obtained buffer layer using TMG, TMA, ammonia, and silane gas as an impurity gas.

Next, a crack prevention layer 104 made of In _0.10 Ga _0.90 N doped with Si at 5 × 10 ¹⁸ / cm ³ at a temperature of 920 ° C. using TMG, TMI (trimethylindium), and ammonia is formed to a thickness of 0.15 μm. Grow in.
The temperature is set to 1000 ° C., TMA, TMG, and ammonia are used as source gases, an A layer made of undoped Al _0.13 Ga _0.87 N is grown to a thickness of 25 mm, and silane gas is used as an impurity gas. A B layer made of Al _0.09 Ga _0.91 N doped with 5 × 10 ¹⁸ / cm ³ is grown to a thickness of 25 mm. Then, the operation of alternately laminating the A layer and the B layer is repeated 120 times to laminate the A layer and the B layer, and the n-type cladding layer 105 made of a multilayer film (superlattice structure) having a total film thickness of 0.6 μm is formed. Grow. At this time, the average composition of Al in the cladding layer is 0.110.

On the cladding layer 105, TMG and ammonia are used as source gases at the same temperature, and an n-type light guide layer 106 made of Al _0.065 Ga _0.935 N and having a thickness of 0.15 μm is grown.
Next, the temperature is set to 970 ° C., TMI (trimethylindium), TMG, and TMA are used as source gases, a barrier layer made of Si-doped Al _0.15 Ga _0.85 N, and an undoped In _0.02 Al _0.03 Ga _0.95 A well layer made of N and a barrier layer made of undoped Al _0.15 Ga _0.85 N are stacked in the order of the first barrier layer / well layer / second barrier layer to form the active layer 107. At this time, the first barrier layer is 70 mm, the second barrier layer is 50 mm, the well layer is 100 mm, and the quantum well structure has a total film thickness of about 220 mm.

On the active layer 107, TMA, TMG, and ammonia were used as source gases, Cp ₂ Mg (cyclopentadienyl magnesium) was used as an impurity gas, and Mg was doped at 1 × 10 ¹⁹ / cm ³ at the same temperature. A p-type electron confinement layer 108 made of Al _0.3 Ga _0.7 N is grown to a thickness of 13 nm.
The temperature is set to 1000 ° C., TMG and ammonia are used as source gases, and a 0.15 μm thick p-type light guide layer 109 made of Al _0.065 Ga _0.935 N is grown. The p-type light guide layer 109 is doped with Mg by diffusion of Mg from adjacent layers such as the p-type electron confinement layer 108 and the p-type cladding layer 110 described later. It can be a doped layer.

Subsequently, an A layer made of undoped Al _0.13 Ga _0.87 N is grown to a thickness of 25 mm at 1000 ° C., and then a B layer made of Mg doped Al _0.09 Ga _0.91 N is grown to a thickness of 25 mm using Cp ₂ Mg. The p-type cladding layer 110 made of a superlattice layer having a total thickness of 0.45 μm is grown by repeating the operation of alternately stacking the A layer and the B layer 90 times.
Finally, a p-type contact layer 111 made of p-type GaN doped with Mg at 1 × 10 ²⁰ / cm ³ is grown on the p-type cladding layer 110 at a temperature of 1000 ° C. to a thickness of 150 mm. The p-type contact layer 111 has a high carrier concentration of 1 × 10 ¹⁷ / cm ³ or more. After the reaction is completed, the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.

After the nitride semiconductor is grown in this way to form a laminated structure, the wafer is taken out from the reaction vessel, and an etching mask made of SiO ₂ is formed on the surface of the uppermost p-type contact layer 111. The mask is processed into a predetermined shape, and the p-type semiconductor layer, the active layer, and a part of the n-type semiconductor layer are sequentially etched by RIE using Cl ₂ gas, and the surface of the n-type contact layer for forming the n-electrode is formed. Expose. At this time, the surface of the n-type contact layer is exposed not only in the region where the n-electrode is formed, but also in the region including the position and / or the periphery where the nitride semiconductor element is cleaved or divided in a later step. .

Next, a ridge stripe is formed as the above-described stripe-shaped waveguide region. First, a first protective film made of Si oxide (mainly SiO ₂ ) is formed to a thickness of 0.5 μm on almost the entire surface of the uppermost p-type contact layer (upper contact layer) 111 by a PVD apparatus. . Next, a mask having a predetermined shape is formed on the first protective film, and the first protective film is formed with a stripe width of 1. with a RIE (reactive ion etching) apparatus using CF ₄ gas and photolithography. 6 μm. Subsequently, using the first protective film as a mask, the p-type contact layer 111, the p-type cladding layer 110, and a part of the p-type light guide layer 109 are etched, so that the film thickness of the p-type light guide layer 109 is increased. A ridge stripe is formed by etching to a depth of 0.1 μm.

After the ridge stripe is formed, the second protective film 162 made of Zr oxide (mainly ZrO ₂ ) is formed on the first protective film, and the p-type light guide exposed by etching on the first protective film. It is continuously formed on the layer 109 with a thickness of 0.2 μm.
After the formation of the second protective film 162, the wafer is heat-treated at 600 ° C.
Next, the wafer is immersed in hydrofluoric acid, and the first protective film is removed by a lift-off method. As a result, the first protective film provided on the p-type contact layer 111 is removed, and the p-type contact layer is exposed. As described above, as shown in FIG. 1, the second protective film (embedded layer) 162 is formed on the side surface of the ridge stripe and on the plane continuous therewith (exposed surface of the p-type light guide layer 109).

Thus, after the first protective film provided on the p-type contact layer 112 is removed, as shown in FIG. 1, Ni / Au (100 Å / 100 mm) is formed on the exposed surface of the p-type contact layer 111. A p-electrode 120 made of 1500 Å) is formed. However, the p-electrode 120 is formed over the second protective film 162 with a stripe width of 100 μm, as shown in FIG.
Before or after the formation of the p-electrode 120, a striped n-electrode 121 made of Ti / Al (100Å / 5000Å) is formed in a direction parallel to the stripe on the surface of the n-type contact layer 103 that has already been exposed.

Next, in order to provide an extraction electrode on the p-electrode 120 and the n-electrode 121, a desired region is masked and a laminated film 164 made of SiO ₂ and TiO ₂ is provided. At this time, the width of the active layer 107 (width in the direction perpendicular to the resonator direction) is 160 μm, and SiO ₂ and the resonator surface (reflecting surface side) and the resonator surface (light emitting surface side) are paired. A laminated film 164 made of TiO ₂ is provided.
Thereafter, a pad electrode 122 made of RhO—Pt—Au (3000 to 1500 to 6000) is provided on the p electrode 120. A pad electrode 123 made of Ni—Ti—Au (1000 Å−1000 Å−8000 Å) is provided on the n electrode 121.

  After forming the n electrode 121 and the p electrode 120 as described above, the sapphire substrate 101 of the wafer is polished to 200 μm, and then the surface of the above-described resonator surface (light emitting surface side), that is, a stripe The stacked film 164 is removed by etching the surface in the direction perpendicular to the p- and n-electrodes 120 and 121, and the resonance surface (1-100 surface, surface corresponding to the side surface of the hexagonal column crystal = M surface) ).

In the obtained laser device, the light emitted from the active layer is efficiently resonated at least on the emission surface side of the main laser beam, and the resonator surface on the opposite surface side is particularly refracted from the resonator surface on the light emission surface side. A protective film made of ZrO ₂ was formed using a sputtering apparatus so as to have a rate difference, and then a dielectric multilayer film (not shown) was formed by laminating SiO ₂ and ZrO ₂ .
Here, the film thicknesses of the SiO ₂ film and the ZrO ₂ film constituting the protective film and the dielectric multilayer film can be set to preferable thicknesses according to the emission wavelength from the active layer. For example, the ZrO ₂ film in the dielectric multilayer film is λ / 4n, and the SiO ₂ film is 5λ / 4n.

Finally, the wafer was cut into chips in a direction parallel to the p-electrode to obtain a laser element (resonator length: 650 μm).
It was confirmed that the obtained laser device had the same effect as in Example 1, had little light absorption, and adhered very well to the nitride semiconductor to prevent peeling. Furthermore, it does not deteriorate even if light is continuously irradiated for a long time, and it has excellent heat resistance against the heat generated by the semiconductor laser element, and can ensure a long life regardless of the type of environmental atmosphere. I knew it was possible.
(Example 3)
A laser device having the same configuration as in Example 1 is obtained except that an n-GaN substrate is used as a substrate, a crack prevention layer is arbitrarily formed on the GaN substrate, and an n-type cladding layer is further formed thereon. It was. Here, the impurity of the GaN substrate was oxygen and / or silicon.

  It was confirmed that the obtained laser element had the same effect as in Example 1.

  The present invention is used for light-emitting elements such as light-emitting diode elements (LEDs), laser diode elements (LD) and superphotoluminescence diodes, light-receiving elements such as solar cells and optical sensors, or electronic devices such as transistors and power devices. The present invention relates to a nitride semiconductor device using a group III-V nitride semiconductor, and relates to a nitride semiconductor light-emitting device having an ultraviolet to blue color, particularly an emission wavelength of 365 nm or less.

It is a schematic cross section explaining a laser device structure according to an embodiment of the present invention. It is an oscillation spectrum at 25 degreeC and CW2mW in the laser element which concerns on one Embodiment of this invention. It is IL and IV characteristics at 25 ° C. and CW of 2 mW in the laser device according to one embodiment of the present invention. It is an energization test result in 25 degreeC and CW3mW in the laser element which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Substrate, 102 ... Buffer layer, 103 ... N-type contact layer, 104 ... Crack prevention layer, 105 ... N-type cladding layer, 106 ... N-type light guide layer, 107 ... Active layer, 108 ... p-type electron confinement layer, 109 ... p-type light guide layer, 110 ... p-type cladding layer, 111 ... p-type contact layer, 120 ... p Electrode, 121... N electrode, 122... P pad electrode, 123... N pad electrode, 162... Second protective film (embedded layer), 164.

Claims (12)

An active layer having a quantum well structure having an n-type cladding layer and an n-type light guide layer made of a nitride semiconductor containing Al, a well layer made of a nitride semiconductor containing In and Al, and Al on the substrate In a nitride semiconductor laser device including a p-type light guide layer and a p-type cladding layer made of a nitride semiconductor,
The well layer of the active layer is made of Al _x In _y Ga _1-xy N (0.02 ≦ x ≦ 0.05, 0.005 ≦ y ≦ 0.03, x + y <1), and sandwiches the active layer The first barrier layer and the second barrier layer are made of Al _u Ga _1-u N (0.10 ≦ u ≦ 0.17),
The nitride semiconductor laser device, wherein the well layer is thicker than the barrier layer. The n-type and p-type cladding layers are _{a first} layer made of Al _a Ga _1-a N (0.07 ≦ a ≦ 0.10), and Al _b Ga _1-b N (0.11 ≦ b ≦ 0). 14. The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser device is a superlattice layer composed of a second layer composed of .14). 3. The nitride semiconductor laser device according to claim 1, wherein the n-type and p-type light guide layers are made of Al _c Ga _1-c N (0.055 ≦ c ≦ 0.075). 4. 4. The nitride semiconductor laser according to claim 1, wherein a nitride semiconductor layer containing Al having a band gap energy larger than that of the active layer is interposed between the active layer and the p-type light guide layer. element. 5. The nitride semiconductor laser device according to claim 1, wherein the substrate has a low dislocation region at least immediately below the optical waveguide region. The substrate includes a first nitride semiconductor layer having a periodic stripe shape, a lattice shape, or an island shape on a surface of a different substrate, and an upper surface and / or a side surface of the first nitride semiconductor layer as a nucleus. The nitride semiconductor laser element according to claim 1, further comprising a second nitride semiconductor layer that covers the entire surface of the different substrate by growing. The nitride semiconductor laser element according to claim 6, wherein a low dislocation region is formed in the second nitride semiconductor layer. 8. The nitride semiconductor laser device according to claim 7, wherein the number of dislocations in the low dislocation region of the substrate is 1 × 10 ₇ pieces / cm ₂ or less. The nitride semiconductor laser device according to claim 1, wherein the substrate is a substrate made of Al _x Ga _1-x N (0 ≦ x ≦ 1). 10. The nitride semiconductor laser element according to claim 1, wherein the nitride semiconductor laser element has a pair of resonator surfaces, and a dielectric multilayer film is formed on a light emitting end surface of the resonator surface. 11. The dielectric multilayer film according to claim 10, wherein the dielectric multilayer film is formed of a laminated film of a silicon oxide film having a thickness of at least 5λ / 4n or more and a zirconium oxide film having a thickness of λ / 4n from the light emitting end face side. Nitride semiconductor laser device. An active layer having a quantum well structure having an n-type cladding layer and an n-type light guide layer made of a nitride semiconductor containing Al, a well layer made of a nitride semiconductor containing In and Al, and Al on the substrate In a nitride semiconductor laser device including a p-type light guide layer and a p-type cladding layer made of a nitride semiconductor,
The nitride semiconductor laser element has a pair of resonator surfaces, and a silicon oxide film having a thickness of at least 5λ / 4n or more from the light emitting end surface side and a film thickness of λ / 4n on the light emitting end surface of the resonator surface. A nitride semiconductor laser element in which a dielectric multilayer film composed of a laminated film with a zirconium oxide film is formed.

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