Semiconductor laser

A semiconductor laser includes a semiconductor nanowire of a first conductivity type provided over a substrate, a light emitting layer provided around the semiconductor nanowire and insulated at an upper end and a lower end thereof, a cladding layer of a second conductivity type different from the first conductivity type, the cladding layer being provided at an outer periphery of the light emitting layer, a first electrode electrically coupled to an end portion of the semiconductor nanowire, a second electrode electrically coupled to an outer periphery of the cladding layer, a first reflection mirror provided at a one-end portion side of the semiconductor nanowire, and a second reflection mirror provided at the other end portion side of the semiconductor nanowire.

FIELD

The embodiments discussed herein are related to a semiconductor laser.

BACKGROUND

In recent years, a very small laser light source that allows downsizing of an apparatus and high-density integration and has a good light emission characteristic is demanded.

On the other hand, a semiconductor nanowire formed in a bottom-up design has good crystallinity, and therefore, application thereof to nanodevices is expected.

For example, it seems a possible idea to interpose, in a semiconductor nanowire100, a light emitting layer102extending in a direction parallel to the front face of a substrate101(in a substrate in-plane direction) as depicted inFIG. 20to implement a very small semiconductor laser. This is hereinafter referred to as first technology.

Also it seems a possible idea, for example, to provide a light emitting layer extending in a direction perpendicular to the front face of a substrate on a semiconductor nanowire, namely, to provide a light emitting layer around a semiconductor nanowire, to implement a very small semiconductor laser. This is hereinafter referred to as second technology.

SUMMARY

According to an aspect of the embodiment, a semiconductor laser includes a semiconductor nanowire of a first conductivity type provided over a substrate, a light emitting layer provided around the semiconductor nanowire and insulated at an upper end and a lower end thereof, a cladding layer of a second conductivity type different from the first conductivity type, the cladding layer being provided at an outer periphery of the light emitting layer, a first electrode electrically coupled to an end portion of the semiconductor nanowire, a second electrode electrically coupled to an outer periphery of the cladding layer, a first reflection mirror provided at a one-end portion side of the semiconductor nanowire, and a second reflection mirror provided at the other end portion side of the semiconductor nanowire.

DESCRIPTION OF EMBODIMENTS

However, since the first technology described above fails to achieve a sufficient gain, it is difficult to implement a laser.

Further, it is difficult to implement a very small semiconductor laser having a good light emission characteristic only if the light emitting layer is provided simply around the semiconductor nanowire in the second technology described above. For example, if an end port ion of the light emitting layer contacts with and is electrically coupled to a substrate that functions as an electrode, then since recoupling of carriers is concentrated in the proximity of the substrate interface, it is difficult to implement a very small semiconductor laser having a good light emission characteristic.

Therefore, it is demanded to implement a very small semiconductor laser having a good light emission characteristic.

In the following, a semiconductor laser according to an embodiment of the present invention is described below with reference toFIGS. 1A to 12Hof the drawings.

The semiconductor laser according to the present embodiment is a semiconductor laser of a very small in-plane size in which a semiconductor nanowire having a diameter of, for example, approximately 10 μm or less is used. Therefore, the semiconductor laser according to the present embodiment is suitable for downsizing and high-density integration of an apparatus. It is to be noted that the semiconductor laser is hereinafter referred to also as nanowire laser or semiconductor nanowire laser.

In particular, as depicted inFIGS. 1A and 1B, the present semiconductor laser includes a substrate1, a semiconductor nanowire2, a light emitting layer3, an insulating film4, a cladding layer5, a p-side electrode6, an n-side electrode7, an upper reflection mirror8and a lower reflection mirror9.

Here, the substrate1is a semiconductor substrate having a first conductivity type, namely, a conductive semiconductor substrate. Here, the substrate1is an n-type semiconductor substrate. In particular, the substrate1is an n-type GaAs substrate.

The semiconductor nanowire2is a semiconductor nanowire of the first conductivity type, namely, a conductive semiconductor nanowire, provided on the substrate1and extending in a perpendicular direction to the front face of the substrate1(in a vertical direction). Here, the semiconductor nanowire2is an n-type semiconductor nanowire provided vertically on the n-type semiconductor substrate1. Therefore, a lower end portion of the semiconductor nanowire2contacts with the front face of the substrate1. In particular, the semiconductor nanowire2is an n-type GaAs nanowire. In this manner, a semiconductor material configuring the semiconductor nanowire2includes GaAs.

It is to be noted that, where the entirety of the semiconductor nanowire2and the light emitting layer3and cladding layer5provided around the semiconductor nanowire2is regarded as a nanowire, the semiconductor nanowire is referred to also as nanowire core. In this case, since each of the components just described is configured from a semiconductor layer, the semiconductor nanowire2, light emitting layer3and cladding layer5are referred to also as first semiconductor layer, second semiconductor layer and third semiconductor layer, respectively. Further, since the semiconductor nanowire2and the cladding layer5are individually configured from a conductive semiconductor material, each of them is referred to as conductive semiconductor layer.

The insulating film4is provided on the front face of the substrate1and contacts with part of a side face of the semiconductor nanowire2while a lower end portion of the light emitting layer3contacts with part of the front face of the insulating film4. Therefore, the lower end of the light emitting layer3is insulated by the insulating film4. It is to be noted that, in the present embodiment, also a lower end portion of the cladding layer5contacts with part of the front face of the insulating film4.

The light emitting layer3is a semiconductor light emitting layer of a cylindrical shape provided around the semiconductor nanowire2. In particular, the light emitting layer3extends in a perpendicular direction to the front face of the substrate1along the side face of the semiconductor nanowire2and contacts with and covers the side face (side wall) of the semiconductor nanowire2. Here, the light emitting layer3covers a region of the side face of the semiconductor nanowire2other than the region covered with the insulating film4. In other words, the light emitting layer3is provided so as to cover part of the side face of the semiconductor nanowire2. More particularly, the light emitting layer3is an InGaAs light emitting layer. In this manner, a semiconductor material configuring the light emitting layer3includes InGaAs.

The cladding layer5is a conductive semiconductor cladding layer configured from a semiconductor material of a second conductivity type different from the first conductivity type, and is a cylindrical semiconductor cladding layer provided at the outer periphery of the light emitting layer3. In particular, the cladding layer5extends in a direction perpendicular to the front face of the substrate1along the side face of the light emitting layer3and contacts with and covers the side face (side wall) of the light emitting layer3. Here, the cladding layer5is a p-type semiconductor cladding layer. More particularly, the cladding layer5is a p-type AlGaAs cladding layer. In this manner, the semiconductor material configuring the cladding layer5includes AlGaAs.

The p-side electrode6is a metal electrode and is provided on the outer periphery of the cladding layer5. In particular, the p-side electrode6is electrically coupled to the outer periphery of the cladding layer5. Here, the p-side electrode6is provided on the insulating film4and extends in a direction perpendicular to the front face of the substrate1along the side face of the cladding layer5, and contacts with and covers the side face of the cladding layer5. In the present embodiment, the p-side electrode6covers a region of the side face of the cladding layer5other than the region covered with the insulating film4. In other words, the p-side electrode6is provided so as to cover part of the side face of the cladding layer5. It is to be noted that the p-side electrode6is referred to also as second electrode. Further, since the p-side electrode6is formed from a metal film on the insulating film4and the cladding layer5, this is referred to also as metal electrode film or metal electrode layer.

The upper reflection mirror8is a multilayer film reflection mirror covering an upper end portion of the semiconductor nanowire2, an upper end portion of the light emitting layer3and an upper end portion of the cladding layer5. In particular, the upper reflection mirror8is a dielectric multilayer film reflection mirror. Consequently, the semiconductor laser can oscillate with lower threshold current. Further, by setting the reflectance of the upper reflection mirror8lower than the reflectance of the lower reflection mirror9hereinafter described, laser light can be extracted from an upper face thereof. In this case, the upper end of the light emitting layer3is insulated by the dielectric multilayer film reflection mirror8. Further, the upper reflection mirror8is provided at the upper end portion side of the semiconductor nanowire2, namely, at the tip end side of the semiconductor nanowire2. It is to be noted that the upper reflection mirror8is referred to also as first reflection mirror.

It is to be noted that, where a condition of a mode I in which the electric field of light hereinafter described is confined in the semiconductor nanowire2and the light emitting layer3is satisfied, the upper reflection mirror8may be provided at least over the upper end portion of the semiconductor nanowire2and the upper end portion of the light emitting layer3. On the other hand, where another condition of a mode II in which the electric field of light hereinafter described is confined in the light emitting layer is satisfied, the upper reflection mirror8may be provided at least over the end portion of the light emitting layer3. In this manner, the upper reflection mirror8may be provided at least over the upper end portion of the light emitting layer3.

The n-side electrode7and the lower reflection mirror9are configured from a metal film provided on the back face of the substrate1. In particular, the metal film provided on the back face of the substrate1functions as an n-side electrode and a lower reflection mirror. Therefore, the n-side electrode7is a metal electrode. Here, since the n-type semiconductor nanowire2is provided on the n-type semiconductor substrate1as described hereinabove, the n-side electrode7is electrically coupled to a lower end portion of the n-type semiconductor nanowire2through the n-type semiconductor substrate1. It is to be noted that the n-side electrode7is referred to also as first electrode. Further, the lower reflection mirror9is a metal film reflection mirror. It is to be noted that the lower reflection mirror9is provided at the lower end portion side of the semiconductor nanowire2, namely, at the substrate side of the semiconductor nanowire2. It is to be noted that the lower reflection mirror9is referred to also as second reflection mirror.

It is to be noted that, where the condition of the mode I in which the electric field of light hereinafter described is confined in the semiconductor nanowire2and the light emitting layer3is satisfied, the lower reflection mirror9may be provided at least under a lower end portion of the semiconductor nanowire2and a lower end portion of the light emitting layer3. On the other hand, where the condition of the mode II in which the electric field of light hereinafter described is confined in the light emitting layer3is satisfied, the lower reflection mirror9may be provided at least under the lower end portion of the light emitting layer3. In this manner, the lower reflection mirror9may be provided at least under the lower end portion of the light emitting layer3.

Particularly, it is possible to obtain a favorable laser characteristic by setting the reflectance of the upper reflection mirror8and the lower reflection mirror9to approximately 95% or more and setting the length of the semiconductor nanowire2to approximately 1 μm or more. Further, while a more favorable laser characteristic can be obtained as the length of the semiconductor nanowire2increases, it is preferable to set the length of the semiconductor nanowire2to approximately 10 μm or less in order for the semiconductor nanowire2to have sufficient mechanical strength. In other words, it is preferable to configure the upper reflection mirror8and the lower reflection mirror9so as to have a reflectance of 95% or more and configure the semiconductor nanowire2so as to have a length of 1 μm or more but 10 μm or less.

Incidentally, in the present embodiment, the n-type semiconductor nanowire2, p-type cladding layer5and light emitting layer3sandwiched by them extend in the perpendicular direction to the front face of the substrate1as described hereinabove. Further, the light emitting layer3provided around the semiconductor nanowire2is insulated at the upper end and the lower end thereof. Especially, while the semiconductor nanowire2contacts with the n-type semiconductor substrate1, the lower end portion of the light emitting layer3contacts with the front face of the insulating film4but does not contact with the n-type semiconductor substrate1. Consequently, current can be injected uniformly into the light emitting layer3. In other words, a favorable current injection structure can be implemented using the semiconductor nanowire2. Consequently, a very small semiconductor laser having a favorable light emission characteristic (output) can be implemented.

Further, in the present embodiment, by combining such a favorable light confinement structure as hereinafter described with such a very small semiconductor laser having a favorable current injection structure as described hereinabove, a very small semiconductor laser having a more favorable light emission characteristic is implemented.

First, where the refractive index of the semiconductor material configuring the semiconductor nanowire2, the refractive index of the semiconductor material configuring the light emitting layer3and the refractive index of the semiconductor material configuring the cladding layer5are represented by n1, n2and n3as depicted inFIG. 2B, respectively, the present semiconductor laser is configured such that a relationship of n3<n1<n2is satisfied. Consequently, the semiconductor laser having a favorable light confinement structure is implemented.

Further, in order to implement a semiconductor laser having a more favorable light confinement structure, a condition for implementing an optical confinement state in which light is confined in the semiconductor nanowire2and the light emitting layer3in the present semiconductor laser as depicted in an optical electric field intensity distribution ofFIG. 2Ahas been found. Such an optical confinement state as just described is hereinafter referred to as mode I and the condition just described is hereinafter referred to as condition of the mode I.

Here, light is confined more as the refractive index difference between the semiconductor material configuring the semiconductor nanowire2and the semiconductor material configuring the light emitting layer3increases. Therefore, light is confined more as the variation ratio Δn=(n2−n1)/n1of the refractive index n2of the semiconductor material configuring the light emitting layer3with respect to the refractive index n1of the semiconductor material configuring the semiconductor nanowire2increases.

Further, light is confined more as the thickness of the light emitting layer3increases. Therefore, where the radius of the semiconductor nanowire2and the distance from the center of the semiconductor nanowire2to the outer peripheral face (outer wall) of the light emitting layer3are represented by r1and r2, respectively, as depicted inFIG. 2B, light is confined more as the ratio δ=(r1−r1)/r1of the thickness (r2−r1) of the light emitting layer3with respect to the radius r1of the semiconductor nanowire2increases.

It is to be noted here that, while the radius of the semiconductor nanowire2is used in the calculation of δ in order to simplify the description, the factor to be used for the calculation is not limited to this. For example, where the sectional shape of the semiconductor nanowire2is a polygon (here, a hexagon) as depicted inFIG. 1B, the distance from the center to the sides of the semiconductor nanowire2may be used in place of the radius of the semiconductor nanowire2. In other words, the sectional shape of the semiconductor nanowire2may be a circular shape or a polygon, and in any case, the distance from the center to the outer peripheral face may be used.

Further, light is confined more as the radius r1of the semiconductor nanowire2increases.

Further, light is confined more as the wavelength λ of light decreases, namely, as the wave number k0=2π/λ of light increases.

Therefore, in the present embodiment, the refractive indexes n1and n3, radius r1of the semiconductor nanowire2and wave number k0are first set to certain values to determine a standardized frequency V0of the nanowire structure. Then, based on a graph indicating a variation of a standardized cutoff frequency V with respect to δ of each refractive index n2of the semiconductor material configuring the light emitting layer3in this case, a minimum value of δ with which the standardized cutoff frequency V coincides with the standardized frequency V0, namely, with which light can be confined, is calculated. Then, taking the refractive index difference between the semiconductor material configuring the semiconductor nanowire2and the semiconductor material configuring the light emitting layer3into consideration, the condition of the mode I is defined using the product Δn·δ of Δn and δ and the product r1·k0of r1and the wave number k0in order to generalize the foregoing.

Here, the standardized frequency V0can be represented as the following expression (1):

Further, a graph indicating a variation of the standardized cutoff frequency V with respect to δ of each refractive index of the semi conductor material configuring the light emitting layer3is obtained by performing numerical calculation using the following relational expression (2) of a cutoff condition:

Where J0and J1are Bessel functions of the first kind of the zeroth order and the first order, respectively, and Y0and Y1are Bessel functions of the second kind of the zeroth order and the first order, respectively. Further, V1and V2are calculated by the following expressions (3) and (4), respectively:

In this manner, the relational expressions of the cutoff condition are functions of U, δ and V. In this case, if a real number with which the relational expression of the cutoff condition is satisfied exists when U is varied from 0 to V at a certain value of δ, then this signifies that light is confined. Then, since a lower limit value of the real number with which the relational expression is satisfied becomes the standardized cutoff frequency V, by plotting the lower limit value, a graph indicating the variation of the standardized cutoff frequency V with respect to δ for each refractive index of the semiconductor material configuring the light emitting layer3can be obtained.

In particular, where n1=3.2, n3=3.1, r1=500 nm and λ=1.2 μm (k0=0.00523 nm−1), the standardized frequency V0is 2.08 from the expression (1). This is indicated by a solid line X inFIG. 3. If the value of the standardized cutoff frequency V is at the upper side than the solid line X, then light is not confined.

Further, if r2is varied to vary the value of δ individually at n2=3.3, 3.4 and 3.5, then a graph indicating the variation of the standardized cutoff frequency V with respect to δ in the case of each refractive index is indicated by solid lines A to C as depicted inFIG. 3, respectively. Here, inFIG. 3, the solid lines A, B and C indicate the variations in the cases of n2=3.3, n2=3.4 and n2=3.5, respectively.

Therefore, if the value of the standardized cutoff frequency V with respect to δ indicated by each of the solid lines A to C inFIG. 3is at the upper side than the solid line X, then light is not confined. For example, where n2=3.4 as indicated by the solid line B, the minimum value of δ with which light is confined is 0.05. In other words, where n2=3.4, if δ is equal to or higher than 0.05, then light is confined. Further, where n2=3.3 as indicated by the solid line A, the minimum value of δ with which light is confined is 0.09. In other words, where n2=3.3, if δ is equal to or higher than 0.09, then light is confined. In those cases, if the product Δn·δ of the values just mentioned and Δn=(n2−n1)/n1is calculated in order to generalize the foregoing taking the refractive index difference into consideration, then 0.003 and 0.002 are obtained as a result of the calculation. Thus, if Δn·δ is equal to or higher than 0.003 adopting the severer condition, then light is confined.

Further, the standardized frequency V0(=2.08) is calculated from the expression (1) given hereinabove and includes the radius r1of the semiconductor nanowire2and the wave number k0. Then, light is confined more as the radius r1of the semiconductor nanowire2increases as described hereinabove. Further, light is confined more as the wavelength λ of light decreases, namely, as the wave number k0=2π/λ of light increases. Therefore, if the product r1·k0of the factors described hereinabove is equal to or higher than 2.61 that is the product r1·k0of the factors in the particular example, then light is confined.

Accordingly, if the condition is satisfied that Δn·δ is equal to or higher than 0.003 and r1·k0is equal to or higher than 2.61, then light is confined in the semiconductor nanowire2and the light emitting layer3. In other words, the condition that Δn·δ is equal to or higher than 0.003 and r1·k0is equal to or higher than 2.61 is the condition of the mode I.

It is to be noted that it has been found that, where the condition of the mode I is satisfied, namely, where the optical confinement state described hereinabove is implemented, the radius of the semiconductor nanowire2has a lower limit. In particular, where δ is 2.0 inFIG. 3, while the thickness of the light emitting layer3is twice with respect to the radius of the semiconductor nanowire2, this is a limit to the film thickness of the light emitting layer3with which the light emitting layer3can be formed on the side face of the semiconductor nanowire2. Then, from the expression (1) given hereinabove, where the standardized cutoff frequency V is the lower limit value, the radius r1of the semiconductor nanowire2is the lower limit value. Therefore, inFIG. 3, the lower limit value to the standardized cutoff frequency V is 0.41 where δ is 2.0 at the refractive index n2=3.5 indicated by the solid line C. Then, if the radius r1of the semiconductor nanowire2is calculated from the expression (1) given hereinabove using the value of 0.41 and n1=3.2, n3=3.1 and λ=1.2 μm (k0=0.00523 nm−1), then the radius r1is 100 nm.

Further, where the wavelength λ=1.4 μm (wave number k0=0.00448 nm−1) is used in place of λ=1.2 μm (k0=0.00523 nm−1) in the particular example described hereinabove, the standardized frequency V0is 1.78 from the expression (1) given hereinabove. This is indicated by a solid line X inFIG. 4. If the value of the standardized cutoff frequency V is at the upper side than the solid line X, then light is not confined.

Further, if r2is varied to vary the value of δ individually at n2=3.3, 3.4 and 3.5, then the graphs indicating the variations of the standardized cutoff frequency V with respect to δ in the case of each refractive index are indicated by solid lines A to C inFIG. 4, respectively. Here, the solid lines A, B and C indicate the variations in the cases of n2=3.3, n2=3.4 and n23.5, respectively.

Therefore, if the values of the standardized cutoff frequency V with respect to δ indicated by the solid lines A to C are at the upper side than the solid line X inFIG. 4, then light is not confined. For example, where n2=3.4 as indicated by the solid line B, the minimum value of δ with which light is confined is 0.12. In other words, where n2=3.4, if δ is equal to or higher than 0.12, then light is confined. Further, where n2=3.3 as indicated by the solid line A, the minimum value of δ with which light is confined is 0.17. In other words, where n2=3.3, if δ is equal to or higher than 0.17, then light is confined. In those cases, if the product Δn·δ of the values just mentioned and Δn=(n2−n1)/n1is calculated in order to generalize the foregoing taking the refractive index difference into consideration, then 0.007 and 0.005 are obtained as a result of the calculation. Therefore, if Δn·δ is equal to or higher than 0.007 adopting the severer condition, then light is confined.

Further, the standardized frequency V0(=1.78) used for determining the condition is calculated from the expression (1) given hereinabove and includes the radius r1of the semiconductor nanowire2and the wave number k0. Then, light is confined more as the radius r1of the semiconductor nanowire2increases as described hereinabove. Further, light is confined more as the wavelength Δ of light decreases, namely, as the wave number k0=2π/λ of light increases. Therefore, if the product r1·k0of the factors mentioned above is equal to or higher than 2.24 that is the product r1·k0of the factors in the present modification, then light is confined.

Accordingly, if the condition is satisfied that Δn·δ is equal to or higher than 0.007 and r1·k0is equal to or higher than 2.24, then light is confined in the semiconductor nanowire2and the light emitting layer3. In particular, the condition that Δn·δ is equal to or higher than 0.007 and r2·k0is equal to or higher than 2.24 is the condition of the mode I.

Further, where r1=200 nm is used in place of r1=500 nm in the particular example described hereinabove, the standardized frequency V0at the wavelength 1.2 μm is 0.83 from the expression (1) given hereinabove. This is indicated by a solid line X inFIG. 5. If the value of the standardized cutoff frequency V is at the upper side than the solid line X, then light is not confined.

Further, if r2is varied to vary the value of δ individually at n3=3.3, 3.4 and 3.5, then the graphs indicating the variations of the standardized cutoff frequency V with respect to δ in the case of each refractive index are indicated by solid lines A to C inFIG. 5, respectively. Here, inFIG. 5, the solid lines A, B and C indicate the variations in the cases of n2=3.3, n2=3.4 and n2=3.5, respectively.

Therefore, if the values of the standardized cutoff frequency V with respect to δ indicated by the solid lines A to C inFIG. 5are at the upper side than the solid line X, then light is not confined. For example, where n2=3.4 as indicated by the solid line B, the minimum value of δ with which light is confined is 0.93. In particular, if δ is equal to or higher than 0.93 where n2=3.4, then light is confined. Further, where n2=3.3 as indicated by the solid line A, the minimum value of δ with which light is confined is 1.25. In other words, if δ is equal to or higher than 1.25 where n2=3.3, then light is confined. In those cases, if the product Δn·δ of the values just described and the Δn=(n2−n1)/n1is calculated in order to generalize the foregoing taking the refractive index difference into consideration, then 0.058 and 0.039 are obtained as a result of the calculation. Therefore, if Δn·δ is equal to or higher than 0.058 adopting the severer condition, then light is confined.

Further, the standardized frequency V0(=0.83) used for determining the condition is calculated from the expression (1) given hereinabove and includes the radius r1of the semiconductor nanowire2and the wave number k0. Then, light is confined more as the radius r1of the semiconductor nanowire2increases as described hereinabove. Further, light is confined more as the wavelength λ of light decreases, namely, as the wave number k0=2π/Δ of light increases. Therefore, if the product r1·k0of the factors described above is equal to or higher than 1.046 that is the product r1·k0of the factors in the modification, then light is confined.

Accordingly, if the condition is satisfied that Δn·δ is equal to or higher than 0.058 and r1·k0is equal to or higher than 1.046, then light is confined in the semiconductor nanowire2and the light emitting layer3. In particular, the condition that Δn·δ is equal to or higher than 0.058 and r1·k0is equal to or higher than 1.046 is the condition of the mode I.

Further, where r1=200 nm is used in place of r1=500 nm and the wavelength λ=1.4 μm (wave number k0=0.00448 nm−1) is used in place of λ=1.2 μm (k0=0.00523 nm−1) in the particular example described hereinabove, the standardized frequency V0is 0.71 from the expression (1) given hereinabove. This is indicated by the solid line X inFIG. 6. If the value of the standardized cutoff frequency V is at the upper side than the solid line X, then light is not confined.

Further, if r2is varied to vary the value of δ individually at n2=3.3, 3.4 and 3.5, then the graphs indicating the variations of the standardized cutoff frequency V with respect to δ in the case of each refractive index are indicated by solid lines A to C inFIG. 6, respectively. Here, inFIG. 6, the solid lines A, B and C indicate the variations in the cases of n2=3.3, n2=3.4 and n2=3.5, respectively.

Therefore, if the values of the standardized cutoff frequency V with respect to δ indicated by the solid lines A to C are at the upper side than the solid line X inFIG. 6, then light is not confined. For example, where n2=3.4, the minimum value of δ with which light is confined is 1.21 as indicated by the solid line B. In other words, if δ is equal to or higher than 1.21 where n2=3.4, then light is confined. Further, where n2=3.3, the minimum value of δ with which light is confined is 1.65 as indicated by the solid line A. In other words, if δ is equal to or higher than 1.65 where n2=3.3, then light is confined. In those cases, the product Δn·δ of the values just mentioned and Δn=(n2−n1)/n1is calculated in order to generalize the foregoing taking the refractive index difference into consideration, then 0.075 and 0.051 are obtained as a result of the calculation. Therefore, if Δn·δ is equal to or higher than 0.075 adopting the severer condition, then light is confined.

Further, the standardized frequency V0(=0.71) used for determining the condition is calculated from the expression (1) given hereinabove and includes the radius r1of the semiconductor nanowire2and the wave number k0. Then, light is confined more as the radius r1of the semiconductor nanowire2increases as described hereinabove. Further, light is confined more as the wavelength λ of light decreases, namely, as the wave number k0=2π/λ of light increases. Therefore, if the product r1·k0of the factors described hereinabove is equal to or higher than 0.896 that is the product r1·k0of the factors in the present modification, then light is confined.

Accordingly, if the condition is satisfied that Δn·δ is equal to or higher than 0.075 and r1·k0is equal to or higher than 0.896, then light is confined in the semiconductor nanowire2and the light emitting layer3. In other words, the condition that Δn·δ is equal to or higher than 0.075 and r1·k0is equal to or higher than 0.896 is the condition of the mode I.

In short, if one of the condition that Δn·δ is equal to or higher than 0.003 and r1·k0is equal to or higher than 2.61, the condition that Δn·δ is equal to or higher than 0.007 and r1·k0is equal to or higher than 2.24, the condition that Δn·δ is equal to or higher than 0.058 and r1·k0is equal to or higher than 1.046 and the condition that Δn·δ is equal to or higher than 0.075 and r1·k0is equal to or higher than 0.896 is satisfied, then the optical confinement state in which the optical electric field is confined in the semiconductor nanowire2and the light emitting layer3is implemented. In other words, the semiconductor laser which can satisfy the condition of the mode I and has a more favorable light confinement structure can be implemented.

In the present embodiment, the semiconductor nanowire2, light emitting layer3and cladding layer5are configured as a GaAs nanowire, an InGaAs light emitting layer and an AlGaAs cladding layer as described hereinabove, respectively. In this case, for example, if the radius of the GaAs nanowire2, the In composition of the InGaAs light emitting layer3and the film thickness of the In0.3Ga0.7As light emitting layer3are set to approximately 500 nm, 0.3 and approximately 50 nm, respectively, then, at the wavelength 1.2 μm, Δn·δ and the product Δn·δ are 0.032, 0.1 and 0.0032, respectively. Further, r1·k0is 2.615. In other words, Δn·δ is equal to or higher than 0.003 and r1·k0is equal to or higher than 2.61, and the condition of the mode I is satisfied. It is to be noted that, in this case, the film thickness of the AlGaAs cladding layer5may be set, for example, to approximately 150 nm.

Incidentally, a condition for implementing an optical confinement state with which light is confined in the light emitting layer3has been found as indicated by an optical electric field intensity distribution ofFIG. 7in order to implement a semiconductor laser having a more favorable light confinement structure in the present semiconductor laser. Such an optical confinement state as just described is referred to as mode II and a condition for the optical confinement state is referred to as condition of the mode II.

A graph indicating the variation of the standardized cutoff frequency V with respect to δ for each refractive index of the semiconductor material configuring the light emitting layer3can be obtained by performing numerical calculation using the following expression (5) of a cutoff condition:

where K0and K1are modified Bessel functions of the zeroth and first orders, respectively; J0and J1are Bessel functions of the first kind of the zeroth and first orders, respectively; and Y0and Y1are Bessel functions of the second kind of the zeroth and first orders, respectively. Further, V1, V2and W are calculated by the following expressions (6), (7) and (8), respectively:

In this manner, the relational expressions of the cutoff condition are functions of U, δ and V. In this case, if a real number with which the relational expressions of the cutoff condition are satisfied exists when U is varied from 0 to V at a certain value of δ, then this signifies that light is confined. Then, since a lower limit value to the real number with which the relational expressions are satisfied is the standardized cutoff frequency V, by plotting the lower limit value, a graph indicating the variation of the standardized cutoff frequency V with respect to δ for each refractive index of the semiconductor material configuring the light emitting layer3can be obtained.

In particular, where n1=3.2, n3=3.1, r1=500 nm and λ=1.2 μm (k0=0.00523 nm−1), the standardized frequency V0is 2.08 from the expression (1). This is indicated by a solid line X inFIG. 8. If the value of the standardized cutoff frequency V is at the upper side than the solid line X, then light is not confined.

Further, if r2is varied to vary the value of δ individually at n2=3.3, 3.4 and 3.5, then graphs indicating the variations of the standardized cutoff frequency V with respect to δ in the case of each refractive index are indicated by solid lines A to C as depicted inFIG. 8, respectively. Here, inFIG. 8, the solid lines A, B and C indicate the variations in the cases of n2=3.3, n2=3.4 and n2=3.5, respectively.

Therefore, if the values of the standardized cutoff frequency V with respect to δ indicated by the solid lines A to C inFIG. 8are at the upper side than the solid line X, then light is not confined. For example, where n2=3.5 as indicated by the solid line C, the minimum value of δ with which light is confined is 0.27. In other words, where n2=3.5, if δ is equal to or higher than 0.27, then light is confined. Further, where n2=3.4 as indicated by the solid line B, the minimum value of δ with which light is confined is 0.4. In other words, where n3=3.4, if δ is equal to or higher than 0.4, then light is confined. In those cases, if the product Δn·δ of the values just mentioned and Δn=(n2=n1)/n1is calculated in order to generalize the foregoing taking the refractive index difference into consideration, then 0.025 and 0.025 are obtained as a result of the calculation. Thus, if Δn·δ is equal to or higher than 0.025, then light is confined.

Further, the standardization frequency V0(=2.08) used for determining the condition is calculated from the expression (1) given hereinabove and includes the radius r1of the semiconductor nanowire2and the wave number k0. Then, light is confined more as the radius r1of the semiconductor nanowire2increases as described above. Further, light is confined more as the wavelength λ of light decreases, namely, as the wave number k0=2π/λ of light increases. Therefore, if the product r1·k0of the factors mentioned above is equal to or higher than 2.61 that is the product r1·0of the factors in the particular example, then light is confined.

Accordingly, if the condition is satisfied that Δn·δ is equal to or higher than 0.025 and r1·k0is equal to or higher than 2.61, then light is confined in the light emitting layer3. In other words, the condition that Δn·δ is equal to or higher than 0.025 and r1·k0is equal to or higher than 2.61 is the condition of the mode II.

Further, where the wavelength λ=1.4 μm (wave number k0=0.00448 nm−1) is used in place of λ=1.2 μm (k0=0.00523 nm−1) in the particular example described above, the standardization frequency V0is 1.78 from the expression (1) given above. This is indicated by a solid line X inFIG. 9. If the value of the standardized cutoff frequency V is at the upper side than the solid line X, then light is not confined.

Further, if r2is varied to vary the value of δ individually at the n2=3.3, 3.4 and 3.5, then graphs indicating the variations of the standardized cutoff frequency V with respect to δ in the case of each refractive index are indicated by solid lines A to C inFIG. 9, respectively. Here, inFIG. 9, the solid lines A, B and C indicate the variations in the cases of n2=3.3, n3=3.4 and n2=3.5, respectively.

Therefore, if the values of the standardized cutoff frequency v with respect to δ indicated by the solid lines A to C are at the upper side than the solid line X inFIG. 9, then light is not confined. For example, where n2=3.5 as indicated by the solid line C, the minimum value of δ with which light is confined is 0.34. In other words, where n2=3.5, if δ is equal to or higher than 0.34, then light is confined. Further, where n2=3.4 as indicated by the solid line B, the minimum value of δ with which light is confined is 0.5. In other words, where n2=3.4, if δ is equal to or higher than 0.5, then light is confined. In those cases, if the product Δn·δ of the values just mentioned and Δn=(n2=n1)/n1is calculated in order to generalize the foregoing taking the refractive index difference into consideration, then 0.031 and 0.031 are obtained as a result of the calculation. Therefore, if Δn·δ is equal to or higher than 0.031, then light is confined.

Further, the standardization frequency V0(=1.78) used for determining the condition is calculated from the expression (1) given hereinabove and includes the radius r1of the semiconductor nanowire2and the wave number k0. Then, light is confined more as the radius r1of the semiconductor nanowire2increases as described above. Further, light is confined more as the wavelength λ of light decreases, namely, as the wave number k0=2π/λ of light increases. Therefore, if the product r1·k0of the factors mentioned above is equal to or higher than 2.24 that is the product r1·k0of the factors in the present modification, then light is confined.

Accordingly, if the condition is satisfied that Δn·δ is equal to or higher than 0.031 and r1·k0is equal to or higher than 2.24, then light is confined in the light emitting layer3. In other words, the condition that Δn·δ is equal to or higher than 0.031 and r1·k0is equal to or higher than 2.24 is the condition of the mode II.

Further, where r1=200 nm is used in place of r1=500 nm in the particular example described above, the standardization frequency V0in the case of the wavelength 1.2 μm is 0.83 from the expression (1) given above. This is indicated by a solid line X inFIG. 10. If the value of the standardized cutoff frequency V is at the upper side than the solid line X, then light is not confined.

Further, if r2is varied to vary the value of δ individually at n2=3.3, 3.4 and 3.5, then the graphs indicating the variations of the standardized cutoff frequency V with respect to δ in the case of each refractive index are indicated by solid lines A to C inFIG. 10, respectively. Here, inFIG. 10, the solid lines A, B and C indicate the variations in the cases of n=3.3, n2=3.4 and n2=3.5, respectively.

Therefore, if the values of the standardized cutoff frequency V with respect to δ indicated by the solid lines A to C are at the upper side than the solid line X inFIG. 10, then light is not confined. For example, where n2=3.5 as indicated by the solid line C, the minimum value of δ with which light is confined is 0.98. In other words, where n2=3.5, if δ is equal to or higher than 0.98, then light is confined. Further, where n2=3.4 as indicated by the solid line B, the minimum value of δ with which light is confined is 1.45. In other words, where n2=3.4, if δ is equal to or higher than 1.45, then light is confined. In those cases, if the product Δn·δ of the values mentioned above and Δn=(n2=n1)/n1is calculated in order to generalize the foregoing taking the refractive index difference into consideration, then 0.091 and 0.090 are obtained as a result of the calculation. Therefore, if Δn·δ is equal to or higher than 0.091 adopting the severer condition, then light is confined.

Further, the standardization frequency V0(=0.83) used for determining the condition is calculated from the expression (1) given hereinabove and includes the radius r1of the semiconductor nanowire2and the wave number k0. Then, light is confined more as the radius r1of the semiconductor nanowire2increases as described above. Further, light is confined more as the wavelength λ of light decreases, namely, as the wave number k0=2π/λ of light increases. Therefore, if the product r1·k0of the factors mentioned above is equal to or higher than 1.046 that is the product r1·k0of the factors in the present modification, then light is confined.

Accordingly, if the condition is satisfied that Δn·δ is equal to or higher than 0.091 and r1·k0is equal to or higher than 1.046, then light is confined in the light emitting layer3. In other words, the condition that Δn·δ is equal to or higher than 0.091 and r1·k0is equal to or higher than 1.046 is the condition of the mode II.

Further, where r1=200 nm is used in place of r1=500 nm and the wavelength λ=1.4 μm (wave number k0=0.00448 nm−1) is used in place of λ=1.2 μm (k0=0.00523 nm−1) in the particular example described above, the standardization frequency V0in the case of the wavelength 1.4 μm is 0.71 from the expression (1) given hereinabove. This is indicated by a solid line X inFIG. 11. If the value of the standardized cutoff frequency V is at the upper side than the solid line X, then light is not confined.

Further, if r2is varied to vary the value of δ individually at n2=3.3, 3.4 and 3.5, then graphs indicating the variations of the standardized cutoff frequency V with respect to δ in the case of each refractive index are indicated by solid lines A to C inFIG. 11, respectively. Here, inFIG. 11, the solid lines A, B and C indicate the variations in the cases of n2=3.3, n2=3.4 and n2=3.5, respectively.

Therefore, if the values of the standardized cutoff frequency V with respect to δ indicated by the solid lines A to C are at the upper side than the solid line X inFIG. 11, then light is not confined. For example, where n2=3.5 as indicated by the solid line C, the minimum value of δ with which light is confined is 1.26. In other words, where n2=3.5, if δ is equal to or higher than 1.26, then light is confined. Further, where n2=3.4 as indicated by the solid line B, the minimum value of δ with which light is confined is 1.87. In other words, where n2=3.4, if δ is equal to or higher than 1.87, then light is confined. In those cases, if the product Δn·δ of the values mentioned above and Δn=(n2=n1)/n1is calculated in order to generalize the foregoing taking the refractive index difference into consideration, then 0.118 and 0.116 are obtained as a result of the calculation. Therefore, if Δn·δ is equal to or higher than 0.118 adopting the severer condition, then light is confined.

Further, the standardization frequency V0(=0.71) used for determining the condition is calculated from the expression (1) given hereinabove and includes the radius r1of the semiconductor nanowire2and the wave number k0. Then, light is confined more as the radius r1of the semiconductor nanowire2increases as described above. Further, light is confined more as the wavelength λ of light decreases, namely, as the wave number k0=2π/λ of light increases. Therefore, if the product r1·k0of the factors mentioned above is equal to or higher than 0.896 that is the product r1·k0of the factors in the present modification, then light is confined.

Accordingly, if the condition is satisfied that Δn·δ is equal to or higher than 0.118 and r1·k0is equal to or higher than 0.896, then light is confined in the light emitting layer3. In other words, the condition that Δn·δ is equal to or higher than 0.118 and r2·k0is equal to or higher than 0.896 is the condition of the mode II.

After all, if one of the condition that Δn·δ is equal to or higher than 0.025 and besides r1·k0is equal to or higher than 2.61, the condition that Δn·δ is equal to or higher than 0.031 and besides r1·k0is equal to or higher than 2.24, the condition that Δn·δ is equal to or higher than 0.091 and besides r1·k0is equal to or higher than 1.046 and the condition that Δn·δ is equal to or higher than 0.118 and besides r1·k0is equal to or higher than 0.896 is satisfied, then an optical confinement state in which an electric field of light is confined in the light emitting layer3is established. In other words, it is possible to implement a semiconductor laser that satisfies the condition of the mode II and has a more favorable light confinement structure. Especially, since an electric field of light is confined strongly in the light emitting layer3and has a strong overlap with the light emitting layer3, oscillation with a lower threshold value can be achieved.

In order to satisfy the condition of the mode II when an AlGaInAs-based material is used as in the present embodiment, the following is preferable. In particular, it is preferable to form the semiconductor nanowire2from an AlGaAs nanowire, form the light emitting layer3from an InGaAs light emitting layer and form the cladding layer5from an AlGaAs cladding layer because the film thickness of the InGaAs light emitting layer3can be reduced to obtain a high value of Δn·δ. In this instance, for example, if the radius of the AlGaAs nanowire2is set to approximately 500 nm and the Al composition of the AlGaAs nanowire2is set to 0.3 while the In composition of the InGaAs light emitting layer3is set to 0.3 and the film thickness of the InGaAs light emitting layer3is set to approximately 150 nm, then Δn is 0.085 and δ is 0.3 at the wavelength of 1.2 μm, and the product Δn·δ of them is 0.0255. Further, r1·k0is 2.61. In other words. Δn·δ is equal to or higher than 0.025 and besides r1·k0is equal to or higher than 2.61, and consequently, the condition of the mode II is satisfied. It is to be noted that, in this case, for the AlGaAs cladding layer5, the Al composition may be set to 0.4, and the film thickness may be set, for example, to approximately 250 nm.

Now, a fabrication method for the semiconductor laser according to the present embodiment is described with reference toFIGS. 12A to 12H.

First, a metal particulate (catalytic metal)10and a SiO2film4A as the insulating film4, namely, a SiO2insulating film (SiO2mask), are provided on an n-type GaAs substrate1as depicted inFIG. 12A. In particular, a SiO2insulating film4A having an opening in a region in which a semiconductor nanowire2is to be grown is formed on an n-type GaAs substrate1, and a metal particulate10is provided in the opening. A semiconductor nanowire growing substrate is fabricated in this manner. Here, the impurity concentration of the n-type GaAs substrate1may be, for example, approximately 5 x 1017to 1×1019cm−3. It is to be noted that the opening may have a size corresponding to the diameter of the semiconductor nanowire2.

Then, an n-type GaAs nanowire as the semiconductor nanowire2is grown on the n-type GaAs substrate1in such a manner as to extend in a direction perpendicular to the front face of the n-type GaAs substrate1, for example, by a metal organic vapor phase epitaxy (MOVPE) method. In this case, the SiO2insulating film4A (4) contacts with part of a side face of the n-type GaAs semiconductor nanowire2. Here, as the raw material of GaAs, for example, triethylgallium (TEG) or arsine (AsH4) may be used. Meanwhile, as the n-type dopant, for example, Si may be used, and as the raw material therefor, for example, disilane (Si2H4) may be used. Further, the impurity concentration may be, for example, approximately 5 x 1017to approximately 1 x 1019cm−3.

After the n-type GaAs nanowire2is formed in this manner, the metal particulate10is removed as depicted inFIG. 12C, and an InGaAs layer as the light emitting layer3, namely, an InGaAs light emitting layer, is formed on the SiO2insulating film4A (4) in such a manner as to cover the side face (periphery) of the n-type GaAs nanowire2, for example, by an MOVPE method. In this case, a lower end portion of the InGaAs light emitting layer3contacts with the front face of the SiO2insulating film4A (4).

Then, a p-type AlGaAs layer as the cladding layer5, namely, a p-type AlGaAs cladding layer, is formed on the SiO2insulating film4A (4) in such a manner as to cover a side face (periphery) of the InGaAs light emitting layer3, for example, by an MOVPE method. In this case, a lower end portion of the p-type AlGaAs cladding layer5contacts with the front face of the SiO2insulating film4A (4). Here, as the p-type dopant, for example, Zn may be used, and as the raw material therefor, for example, diethyl zinc (DEZ) may be used. Meanwhile, the impurity concentration may be, for example, approximately 5×1017to approximately 1×1019cm−3. Further, as the raw material for GaAs, for example, triethylgallium (TEG) or arsine (AsH4) may be used. Meanwhile, as the Al raw material, for example, trimethyl aluminum (TMAl) may be used. Especially, in order to obtain a good conductivity, the Al composition of the p-type AlGaAs cladding layer5is preferably set to approximately 0.1 to approximately 0.4. However, the Al composition of the p-type AlGaAs cladding layer5is not limited to this.

It is to be noted that, in order to couple, after the p-type AlGaAs cladding layer5is formed in this manner, the cladding layer5to the p-side electrode6in low resistance, a contact layer not depicted may be formed in such a manner as to cover a side face (periphery) of the p-type AlGaAs cladding layer5. For example, a p-type GaAs contact layer of a thickness of approximately 1 nm to approximately 10 nm may be formed.

Then, after a SiO2film4B as the insulating film4, namely, a SiO2insulating film, is formed on the front surface as depicted inFIG. 12D, the resist11is patterned as depicted inFIG. 12E, and part of the SiO2film4B, namely, a portion of the SiO2film4B which covers the side face of the cladding layer5, is removed by etching as depicted inFIG. 12F. The side face of the p-type AlGaAs cladding layer5is exposed in this manner.

Then, after the resist11is removed, a metal film as the p-side electrode6, namely, a p-side metal electrode, is formed in such a manner as to cover a side face of the p-type AlGaAs cladding layer5and the front face of the SiO2insulating film4B (4) as depicted inFIG. 12G.

Thereafter, after the back face of the substrate1is worked, metal films that serve as both of the lower reflection film9and the n-side electrode7, namely, a metal film reflection film and an n-type metal electrode, are formed in such a manner as to cover the back face of the substrate1as depicted inFIG. 12H. Further, a dielectric multilayer film as the upper reflection mirror8, namely, a dielectric multilayer reflection film, is formed at upper end portions of the n-type GaAs semiconductor nanowire2, InGaAs light emitting layer3and p-type AlGaAs cladding layer5.

The semiconductor layer according to the present embodiment can be fabricated in this manner.

Accordingly, with the semiconductor layer according to the present embodiment, there is an advantage that a very small semiconductor laser having a good light emitting characteristic can be implemented.

In particular, in a very small semiconductor layer that is suitable for downscaling and high integration of an apparatus and has a small in-plane size and that uses a semiconductor nanowire of a diameter, for example, equal to or smaller than approximately 10 μm. Especially, in a semiconductor laser that is good in matching property with a Si-based passive device and emits laser light of a long wavelength equal to or greater than 1.2 μm, a good light emitting characteristic can be implemented.

It is to be noted that the present invention is not limited to the configuration described in the foregoing description of the embodiment but can be modified in various forms without departing from the subject matter of the present invention.

For example, in the embodiment described above, the case in which the materials configuring the substrate1, semiconductor nanowire2, light emitting layer3and cladding layer5include GaAs, GaAs, InGaAs and AlGaAs, respectively, and AlGaInAs-based materials are used is taken as an example. However, the present invention is not limited to this. For example, InGaAsP-based materials may be used and the materials configuring the substrate1, semiconductor nanowire2, light emitting layer3and cladding layer5may include InP, InP, InGaAsP or InGaAs and InGaP, respectively.

In this case, for example, if the radius of the InP nanowire2is set to approximately 200 nm and the InGaAsP light emitting layer3is formed as an In0.85Ga0.15As0.33P0.67light emitting layer and besides the film thickness of this layer is set to approximately 250 nm, then at the wavelength of 1.2 μm, Δn becomes 0.0479 and δ becomes 1.25. Consequently, the product Δn·δ of them becomes 0.0598. Further, r1·k0becomes 1.046. In other words, Δn·δ becomes equal to or higher than 0.058 and besides r1·k0becomes equal to or higher than 1.046, and the condition of the mode I is satisfied. It is to be noted that, in this case, the film thickness of the InGaP cladding layer5may be set, for example, to approximately 100 nm.

Meanwhile, if the radius of the InP nanowire2is set to approximately 500 nm and the InGaAsP light emitting layer3is formed as an In0.85Ga0.15As0.33P0.67light emitting layer and besides the film thickness of this layer is set to approximately 250 nm, then at the wavelength of 1.2 μm, Δn becomes 0.0479 and δ becomes 0.5. Consequently, the product Δn·δ of them becomes 0.0284. Further, r1·k0becomes 2.615. In other words, Δn·δ becomes equal to or higher than 0.025 and besides and r1·k0becomes equal to or higher than 2.61, and the condition of the mode II is satisfied. It is to be noted that, in this case, the film thickness of the InGaP cladding layer5may be set, for example, to approximately 200 nm.

Further, while the light emitting layer3in the embodiment described hereinabove is formed as a bulk InGaAs layer, the light emitting layer3is not limited to this, but it may be formed, for example, as a quantum well light emitting layer having a quantum well structure as depicted inFIG. 13. This is referred to as first modification.

In this case, for example, the semiconductor nanowire2may be formed as an AlGaAs nanowire, and the light emitting layer3may be formed as a GaAs/InGaAs quantum well light emitting layer configured from a GaAs layer3A and an InGaAs layer3B stacked with each other while the cladding layer5is formed as an AlGaAs cladding layer. Here, the GaAs/InGaAs quantum well light emitting layer3is configured by providing, in the inside of the InGaAs layer3B (barrier layer; second semiconductor layer), the GaAs layer3A (well layer; fourth semiconductor layer) having a band gap smaller than that of the InGaAs layer38. In this case, the light emitting layer3includes InGaAs. Further, for example, if the Al composition of the AlGaAs nanowire2is set, for example, to 0.3 and the radius of the Al0.3Ga0.7As nanowire2is set to approximately 200 nm and besides the film thickness of the GaAs/InGaAs quantum well light emitting layer3in which five InGaAs layers3B are provided is set to approximately 230 nm (the total thickness of the GaAs layers3A is approximately 210 nm and the total film thickness of the InGaAs layers3B is 20 nm), then at the wavelength of 1.2 μm, Δn becomes 0.057 and δ becomes 1.15. Consequently, the product Δn·δ of them becomes 0.0655, and r1·k0becomes 1.046. In other words, Δn·δ is equal to or higher than 0.058 and r1·k0is equal to or higher than 1.046, and the condition of the mode I is satisfied. It is to be noted that, in this case, as regards the InGaAs layer3B configuring the GaAs/InGaAs quantum well light emitting layer3, the In composition is set to 0.6 and the film thickness is set to approximately 4 nm. Further, as the refractive index of the GaAs/InGaAs quantum well light emitting layer3, an average value weighted by the film thickness is used. Further, the Al composition of the AlGaAs cladding layer5may be set, for example, to approximately 0.4 and the film thickness of the same may be set, for example, to approximately 100 nm.

Further, for example, the semiconductor nanowire2may be formed as an InP nanowire, and the light emitting layer3may be formed as an InGaAs/InGaAsP quantum well light emitting layer configured from an InGaAs layer3A and an InGaAsP layer3B stacked with each other while the cladding layer5is formed as an InGaP cladding layer. Here, the InGaAs/InGaAsP quantum well light emitting layer3is configured by providing, in the inside of the InGaAsP layer3B (barrier layer; second semiconductor layer), the InGaAs layer3A (well layer; fourth semiconductor layer) having a band gap smaller than that of the InGaAsP layer3B. Further, for example, if the radius of the InP nanowire2is set to approximately 500 nm and the InGaAs/InGaAsP quantum well light emitting layer3is formed as an InGaAs/In0.85Ga0.15As0.33P0.67quantum well light emitting layer in which five InGaAs layers3B are provided and the film thickness of the same is set to approximately 250 nm (the total thickness of the InGaAsP layers3B is approximately 240 nm and the total film thickness of the InGaAs layers3A is 15 nm), then at the wavelength of 1.2 μm, Δn is 0.0518 and δ is 0.51. Consequently, the product Δn·δ of them is 0.0264, and r1·k0is 2.615. In other words, Δn·δ is equal to or higher than 0.025 and besides r1·k0is equal to or higher than 2.61, and the condition of the mode II is satisfied. It is to be noted that, in this case, the In composition of the InGaAs layer3A configuring the InGaAs/In0.85Ga0.15As0.33P0.67quantum well light emitting layer3is set to 0.56 and the film thickness is set to approximately 3 nm. It is to be noted here that, as the refractive index of the InGaAs/InGaAsP quantum well light emitting layer3, an average value weighted with the film thickness is used. Further, the film thickness of the InGaP cladding layer5may be set, for example, to approximately 200 nm.

Further, while the above-described embodiment is described taking the case in which the metal layers formed on the back face of the substrate serve as both of the lower reflection film9and the n-side electrode7as an example, the metal film is not limited to this. In other words, the position and the shape of the lower reflection mirror9and the position of the n-side electrode7are not limited to those of the embodiment described hereinabove.

For example, where the condition of the mode I described above is satisfied, the upper reflection mirror B may be provided at least over an upper end portion of the semiconductor nanowire2and an upper end portion of the light emitting layer3and the lower reflection mirror9may be provided at least under a lower end portion of the semiconductor nanowire2and a lower end portion of the light emitting layer3. On the other hand, where the condition of the mode II described hereinabove is satisfied, the upper reflection mirror8may be provided at least over an upper end portion of the light emitting layer3and the lower reflection mirror9may be provided at least under a lower end portion of the light emitting layer3. Further, the lower reflection mirror9may be a multilayer film reflection mirror provided at the substrate side of the semiconductor nanowire2.

In particular, the n-side electrode7may be provided not on the back face of the substrate1but on the front face of the substrate1, and the lower reflection mirror9may be formed as a multilayer film reflection mirror provided on the back face of the substrate1. This is referred to as second modification.

Here, the multilayer film reflection mirror9may be formed as a dielectric multilayer film reflection mirror. In this case, the semiconductor laser structured such that both of the p-side electrode6and the n-side electrode7are provided at the front face side of the substrate and have a current injection structure in which current is injected from the substrate front face side through the electrodes6and7and besides dielectric multilayer film reflection mirrors8and9with which a high reflectance is obtained with a small number of cycles are provided over and under the semiconductor nanowire2and the light emitting layer3. Further, one electrode (n-side electrode7) is electrically coupled to an end portion of the semiconductor nanowire2through the semiconductor substrate1.

Further, while, in the present second modification, the dielectric multilayer film reflection film9is provided in a recessed portion formed by working the back face of the substrate1, the reflection mirror is not limited to this. For example, a multilayer film reflection mirror as the lower reflection mirror9may be provided without working the back face of the substrate1as depicted inFIG. 15. This is referred to as third modification. It is to be noted that, also in the embodiment described hereinabove, metal films that function as the lower reflection mirror9and the n-side electrode7may be provided without working the back face of the substrate1similarly. However, it is preferable to form a recessed portion by working the back face of the substrate1in that the spread of light in the substrate1can be suppressed. It is to be noted that, since, in the configurations of the modifications, the lower reflection mirror9is provided under lower end portions of the semiconductor nanowire2, light emitting layer3and cladding layer5, the configuration described above can be applied in both of a case in which the condition of the mode I is satisfied and another case in which the condition of the mode II is satisfied.

Further, for example, the lower reflection mirror9may be formed as a multilayer film reflection mirror provided on the front face of the substrate1in place of the provision on the back face of the substrate1as depicted inFIG. 16. This is referred to as fourth modification.

Here, the multilayer film reflection mirror9may be formed as a conductive multilayer film reflection mirror provided at least between the substrate1and the semiconductor nanowire2and light emitting layer3. For example, the material configuring the multilayer film reflection mirror9may be a conductive semiconductor material. Further, the lower end portion of the semiconductor nanowire2may contact with the front face of the conductive multilayer film reflection mirror9. Further, the insulating film4may be provided on the front face of the conductive multilayer film reflection mirror9such that it contacts with part of a side face of the semiconductor nanowire2and besides a lower end portion of the light emitting layer3contacts with part of the front face of the insulating film4. Further, the n-side electrode7may be provided on the front face of the conductive multilayer film reflection mirror9. In this case, the semiconductor nanowire2is provided over the substrate1. Further, both of the p-side electrode6and the n-side electrode7are provided on the front face side of the substrate and a current injection structure in which current is injected from the substrate front face side through the electrodes is provided, and besides the multilayer film reflection mirrors8and9with which a high reflectance is obtained with a small number of cycles are provided over and under the semiconductor nanowire2and the light emitting layer3at the substrate front face side and have a structure in which the spread of light in the substrate1can be suppressed. Further, one (n-side electrode7) of the electrodes is electrically coupled to an end portion of the semiconductor nanowire2through the conductive multilayer film reflection mirror9and the semiconductor substrate1. Further, the lower reflection film9is provided at a lower end portion side of the semiconductor nanowire2.

Further, while, in the present fourth modification, the conductive multilayer film reflection mirror9is provided on the overall front face of the substrate1, the provision of the conductive multilayer film reflection mirror9is not limited to this. For example, as depicted inFIG. 17, the conductive multilayer film reflection mirror9may be provided partially on the front face of the substrate1while a conductive semiconductor layer12is provided in such a manner as to be coupled to the conductive multilayer film reflection mirror9and the n-side electrode7is provided on the front face of the conductive semiconductor layer12. This is referred to as fifth modification. As the conductive semiconductor layer12, preferably a low resistance semiconductor layer of a high impurity concentration is used. Here, the conductive multilayer film reflection mirror9may be provided at least between the substrate1and the semiconductor nanowire2and light emitting layer3. Here, the conductive multilayer film reflection mirror9is provided between the semiconductor nanowire2and the light emitting layer3and cladding layer5. In this manner, in a region on the front face of the substrate1other than the region in which the conductive multilayer film reflection mirror9is provided, the conductive semiconductor layer12may be provided in place of the conductive multilayer film reflection mirror9. In other words, a portion of the conductive multilayer film reflection mirror9at which the conductive multilayer film reflection mirror9contacts with the n-side electrode7may be replaced by the conductive semiconductor layer12. This makes it possible to implement a more favorable current injection structure. In this case, one (n-side electrode7) of the electrodes is electrically coupled to an end portion of the semiconductor nanowire2through the conductive semiconductor layer12, conductive multilayer film reflection mirror9and semiconductor substrate1.

It is to be noted that, while, in the configurations of the fourth and fifth modifications, the lower reflection film9is provided under lower end portions of the semiconductor nanowire2, light emitting layer3and cladding layer5, both configurations can be applied in both of a case in which the condition of the mode I is satisfied and in another case in which the condition of the mode II is satisfied.

Further, for example, the lower reflection film9may be formed as a dielectric multilayer film reflection mirror provided partially on the front face of the substrate1in place of the provision on the back face of the substrate1as depicted inFIG. 18. In other words, the lower reflection film9may be formed as a dielectric multilayer film reflection mirror that is provided at least between the substrate1and the light emitting layer3such that it contacts with part of a side face of the semiconductor nanowire2and besides a lower end portion of the light emitting layer3contacts with part of the front face of the dielectric multilayer film reflection mirror.

In this case, the lower end portion of the semiconductor nanowire2contacts with the front face of the substrate1. In other words, the semiconductor nanowire2is provided on the substrate1. In this case, the lower reflection film9is a partial reflection mirror that does not cover a lower end portion of the semiconductor nanowire2although it is provided at a lower end portion side of the semiconductor nanowire2. Meanwhile, the upper reflection mirror8may be provided in such a manner as to cover at least an upper end portion of the light emitting layer3. In this case, the upper end and the lower end of the light emitting layer3are insulated by the upper reflection mirror8and the lower reflection film9each configured from a dielectric multilayer film reflection mirror. Further, the n-side electrode7may be provided on the back face of the semiconductor substrate1and electrically coupled to an end portion of the semiconductor nanowire2through the semiconductor substrate1. In this case, while a current injection structure wherein current is injected from the p-side electrode6and the n-side electrode7provided at the front face side and the back face side of the substrate1, respectively, is implemented, a structure is implemented wherein the dielectric multilayer film reflection mirrors8and9with which a high reflectance is obtained with a small number of cycles are provided over and under the light emitting layer3at the front face side of the substrate and the spread of light in the substrate1can be suppressed. In this manner, in the configuration of the present sixth modification, the upper reflection mirror8is provided over upper end portions of the semiconductor nanowire2, light emitting layer3and cladding layer5. On the other hand, the lower reflection film9is provided merely under lower end portions of the light emitting layer3and cladding layer5but is not provided under a lower end portion of the semiconductor nanowire2. Therefore, the configuration of the sixth modification can be used in a case in which the condition of the mode II is satisfied.

In order to fabricate the semiconductor laser having the configuration of the sixth modification, the fabrication method of the embodiment described hereinabove may be modified such that it includes the following steps in place of the step of providing catalytic metal10and an insulating film4A (4) on a substrate1, namely, in place of the step of fabricating a semiconductor nanowire growing substrate. In particular, a dielectric multilayer film reflection mirror as the lower reflection film9is formed on a substrate1, for example, as depicted inFIGS. 19A and 198. Then, an opening is formed in a region of the dielectric multilayer film reflection mirror9, in which a semiconductor nanowire2is to be grown, using resist13patterned on the dielectric multilayer film reflection mirror9as depicted inFIG. 19C, for example, using a lithography technology. Then, after the catalytic metal10is deposited, the resist13is removed to fabricate a semiconductor nanowire growing substrate including the catalytic metal10and the dielectric multilayer film reflection mirror9on the substrate1as depicted inFIG. 19D. It is to be noted that the succeeding steps can be performed similarly as in the case of the embodiment described hereinabove.

It is to be noted here that, although the modifications are described as modifications to the embodiment described hereinabove, also it is possible to combine them arbitrarily. For example, the first modification described hereinabove may be applied to the second to sixth modifications described hereinabove.