US 20050180485 A1
A semiconductor laser device includes a QW active layer structure including a GaxIn1-xAs1-ySby layer wherein 0.3≦1-x and 0.003≦y≦0.008, or a QW active layer structure including a GaxIn1-xAs1-y2Ny1Sby2 layer wherein 0.3≦1-x, 0<y1<0.03 and 0.002≦y2≦0.06. The semiconductor laser device suppresses the three-dimensional epitaxial growth, and has superior optical characteristics including a low threshold current.
7. A method of making a QW layer for a semiconductor laser comprising depositing a layer of Ga, In, As, and Sb onto a GaAs substrate, wherein said In is included at an atomic ratio of 30% or more relative to Group-III elements, and wherein said depositing is performed with a partial pressure of Sb that is sufficient to form an active layer of about 0.3% to about 0.8% in atomic ratio of Sb relative to Group-V elements.
8. A method of making a QW layer for a semiconductor laser comprising depositing a layer of Ga, In, N, As, and Sb onto a GaAs substrate, wherein said In is included at an atomic ratio of 30% or more relative to Group-III elements, and wherein said depositing is performed with a partial pressure of Sb that is sufficient to form an active layer of about 0.2% to about 6% in atomic ratio of Sb relative to Group-V elements.
9. The method of
10. The method of
24. A method of making a semiconductor laser comprising:
depositing a first barrier layer of GaNzAs1-z onto a substrate;
depositing an active layer of GaxIn1-xAs1-y1-y2Ny1Sby2 over said first barrier layer; and depositing a second barrier layer of GaNzAs1-z over said active layer.
25. The method of
26. The semiconductor laser of
27. The semiconductor laser of
28. The method of
29. The method of
30. The method of
31. A method for manufacturing a semiconductor laser device comprising:
forming a laser structure by depositing a QW active layer structure over a substrate, wherein said QW active layer structure includes at least one QW layer comprising GaxIn1-xAs1-y1-y2Ny1Sby2, wherein 0.3≦1-x, wherein 0≦y1≦0.007, and wherein 0.002≦y2≦0.06, and
heat treating said laser structure, after growth of said QW active layer structure at a temperature of about 570 to 630 degrees C.
32. A method for manufacturing a semiconductor laser device comprising:
forming a laser structure by depositing a QW active layer structure over a substrate, wherein said QW active layer structure includes at least one QW layer comprising GaxIn1-xAs1-y1-y2Ny1Sby2, wherein 0.31-x, wherein 0.007≦y1≦0.03, and wherein 0.002≦y2≦0.06, and
heat treating said laser structure, after growth of said QW active layer structure at a temperature of about 670 to 730 degrees C.
(a) Field of the Invention
The present invention relates to a semiconductor laser device having a lower threshold current.
(b) Description of the Related Art
Semiconductor laser devices operating at a wavelength band between 1.2 μm and 1.3 μm now attract larger attention for use as light sources in optical communication scriber lines.
Although a GaInAsP semiconductor laser device formed on an InP substrate is conventionally developed as a semiconductor laser device having an emission wavelength of 1.3 μm band, it has been a problem that the semiconductor materials used in the GaInAsP laser device has a poor characteristic temperature of the threshold current as low as 50 K to 70 K, which degrades the temperature characteristics of the laser device.
In order to dispose a semiconductor laser device in each of households as a light source, it is desired that the semiconductor laser module have a longer wavelength band and a superior temperature characteristic without using a cooling device, and also can be manufactured at a lower cost.
Thus, a variety of semiconductor laser devices having improved temperature characteristics and longer emission wavelengths have been developed. It is reported in “Jpn. J. Appl. Phys., vol. 35(1996)”, pp. 1273-1275 by M. Kondow et al. that one of the semiconductor laser devices thus developed may have a temperature characteristic as high as about 180 K. Also it is assured therein by an experiments that a prototype semiconductor laser device achieved a higher temperature characteristic around 130 K to 270 K.
Moreover, it is also reported by F. Koyama et al., in IEEE Photon. Technol. Lett., vol. 12(2000) pp. 125-127 that a characteristic temperature as high as around 140 K-170 K was realized by using a high-strained GaInAs semiconductor laser device operating at an emission wavelength band of 1.2 μm. It is to be noted that since the commercial single mode (SM) optical fiber has a cutoff for fundamental mode at 1.2 μm wavelength, the semiconductor laser device is expected for use as a light source in a local area network (LAN).
The conventional high-strained semiconductor laser device as described above suffers from the higher amount of strain and a poor mixing capability of the constituent element, nitrogen (N), into the V-group elements due to the fact that nitrogen has a smaller radius of atoms. This involves an undesirable three-dimensional growth and a large number of crystal defects unless the growth temperature is lowered to a minimum, which however degrades the optical quality for the crystal structure.
It is also noted that the high strained layer is difficult to grow with involving a longer-distance migration by using a molecular beam epitaxy (MBE) generally used for growing semiconductor layers.
In view of the above problem in the conventional semiconductor laser device, it is an object of the present invention to provide a GaInNAs semiconductor laser. device and a high-strained GaInAs semiconductor laser device with an improved optical quality.
It is another object of the present invention to provide a method for manufacturing such a GaInNAs semiconductor device.
The present invention provides a semiconductor laser device including a GaAs substrate and a laser structure overlying thereon and including a quantum well (QW) active layer structure, said QW active layer structure including a GaxIn1-xAs1-ySby well layer wherein 0.3≦1-x and 0.003≦y≦0.008 or a GaxIn1-xAs1-y1-y2Ny1Sby2 well layer wherein 0.3≦1-x, 0<y1<0.03 and 0.002≦y2≦0.06.
In the semiconductor laser device of the present invention, it is preferable to suppress the migration of Group-III atoms to some extent because the Group-III atoms may grow in a three-dimensional structure due to agglomeration during growth of the same as a high-strained layer if the migration distance of the Group-III atoms is large.
The present invention also provides a method for manufacturing the semiconductor device including the step of heat treating the layer structure of the laser structure at temperatures depending on the composition of the active layer, after epitaxial growth of the GaxIn1-xAs1-y1-y2Ny1Sby2 well layer. The heat treatment is conducted at a temperature of 570 degrees C. to 630 degrees C. when 0<y1<0.007 or at a temperature of 670 degrees C. to 730 degrees C when 0.007<y1<0.03.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.
Before describing the preferred embodiments of the present invention, the principle of the present invention will be described for the sake of understanding.
With reference to
In the conventional semiconductor laser device of
In a conventional GaInNAs semiconductor laser device, in order to realize a low threshold current in a wavelength band of 1.3 μm, nitrogen (N) is generally added to a GaInAs layer, wherein In is about 40% in the Group-III elements, at about 0.6% in atomic ratio relative to the V-group elements, to obtain a strain of around 2.7% in the total strain of the GaInNAs semiconductor laser. This device, however, suffers from the higher amount of strain and from poor mixing capability of the constituent element, nitrogen, into the V-group elements due to nitrogen having a smaller radius of atoms. This device thus involves a three-dimensional growth and a large number of crystal defects unless the epitaxial growth is conducted at a lower temperature, which degrades the optical quality for the crystal structure however.
In general, there are a plurality of techniques for epitaxially growing a semiconductor layer having a high strain, the techniques including (a) a lower-temperature growth, (b) a higher atomic ratio of V-group elements to Group-III elements, (c) a higher growth rate, and (d) using a surfactant.
The technique using the surfactant is such that elements having a property of higher segregation feasibility, such as Sb, Te and Sn, are used in a MBE or MOCVD for reducing the surface energy and the surface diffusion length of the group-III atoms to thereby suppress the three-dimensional growth. This technique is described by M. Copel et al., in Phys. Rev. Lett. vol. 63(1989) pp. 632-635.
In the ordinary growth technique using the surfactant, the growth step is stopped or interrupted to dispose the surfactant on the underlying layer in an amount of 1 ML or less before growing the high-strained layer. During the growth of the high-strained layer, the surfactant is not added, whereby the surfactant is floating on the surface of the high-strained layer without incorporating into the high-strained layer.
The present inventor noticed the effectiveness of addition of Sb in a minute amount of about 0.2% to 2.5% with respect to the amount of V-group elements together with addition of a Group-III element during the growth of the high strained layer, without disposing the surfactant on the underlying layer before growing the high-strained layer.
More specifically, a GalnAsSb layer is formed in a 1.2-μm band GaInAs semiconductor laser device, whereas a GaInNAsSb layer is formed in a 1.3-μm band GaInNAs semiconductor laser device. The experiments as detailed below and conducted by the inventor revealed the superiority of this technique to the conventional technique.
In the first experiments, Sb is added in a GaIn0.39As single quantum well (SQW) active layer, to thereby manufacture a 1.2-μm band semiconductor laser device.
The sample structure 60 shown in
A GaIn0.39As SQW layer has a higher compressive strain as high as 2.8%. The design thickness of the SQW layer structure is set at 7.3 nm, wherein the relationship between the critical thickness and the In content is calculated to obtain 4 nm for the critical thickness based on the theory presented by J. W. Matthews and A. E. Blakeslee for the GaInAs/GaAs semiconductor laser device.
In these experiments, Sb is added only to a GaIn0.39As SQW layer to form a GaInAsSb SQW layer. By changing the Sb flux (Torr) as a parameter, the photoluminescence (PL) dependency of the Sb flux was investigated. The results are shown in
The growth conditions of the GaInAsSb layer in the experiments are as follows:
In order to investigate the amount of incorporation of Sb into a GaInAs well layer, GaAsSb layers were grown with different amounts of Sb flux, and the Sb contents (%) in the GaAsSb layers were measured. The results is shown in
Sb was incorporated into the GaAs film in a linear relation with respect to the Sb flux up to 5×10−6 Torr, as shown in
The PL wavelength indicated relatively good coincidence to the calculation up to a Sb flux of 2×10−6 Torr.
At 2×10−7 Torr where the PL intensity becomes the maximum, as understood from the first experiments, the composition of the GaInAsSb film resulted in Ga0.61In0.39AS0.9968Sb0.0032, that means a minute amount of Sb was incorporated into the film. Thus, it is considered that Sb does not act as a surfactant, and that Sb is incorporated in the GaInAs film to act as a quasi-surfactant. Thus, it is considered that, in the area where the PL intensity is higher, a three-dimensional growth is suppressed and a two-dimensional growth is promoted. More specifically, it is considered that Sb has a function for lowering the surface energy, suppressing extension of the diffusion length, and suppressing the three-dimensional growth.
It is understood from
By changing the Sb flux (Torr) while fixing a specified condition, experiments for growing GaInNAsSb layers were conducted, and the results thus obtained are shown in
The well layer had a compressive strain of 2.7% when the well layer had no Sb content (or made of GaIn0.39AsN0.0044), and had a design thickness of 7.3 nm. In addition, the nitrogen radicals excited by a RF plasma source were used as the nitrogen source. In order to recover the excellent crystallinity, after growth of a GaInNAsSb layer, a semi-insulating GaAs wafer is mounted on the GaInAsSb layer in a nitrogen ambient, in a face-to-face contact with the epitaxial layer side thereof, followed by an annealing step at a temperature of 650 degrees C. for ten minutes. The semi-insulating GaAs wafer functions as a cap layer for preventing the escape of phosphorus atoms.
As described in connection with the second experiments for the growth of a GaAsSb layer, a Sb flux of 1×10−6 Torr provides a Sb content of 1.6% relative to the V-group elements, and the nitrogen content is calculated at 0.44% relative to the V-group elements based on the wavelength shift of the as-grown epitaxial layer occurring with the addition of nitrogen.
From the second and third experiments, it was confirmed that the optical property of the GaInNAs layer is improved by the addition of Sb at an amount of 0.8 to 1.6% in terms of the Sb content.
In order to further investigate the property of GaInNAsSb SQW lasers, samples having a variety of Sb contents were observed by using a transmission electron microscope (TEM).
The SQW layer grown in a Sb flux of 2×10−7 Torr, as shown in
In addition, in order to increase the laser emission wavelength up to 1.3 μm, the nitrogen content should be increased to some extent, which necessitates increase of the Sb content. Although the optimum Sb content depends on the composition of the layer, a larger N content generally increases the optimum Sb content.
In the third experiments, although the PL wavelength after the heat treatment is 1.24 μm for a nitrogen content of 0.44% and a Sb flux of 1×10−6 Torr, the emission wavelength is desirable to be increased up to 1.35 μm in consideration that WDM (wavelength division multiplexing) system is expected to develop into a 1.3 μm band wavelength. In such a case, the nitrogen content should be increased up to around 1.5% depending on the In content.
The upper limit (UL) of Sb content is calculated from the maximum value (Mx=1.6%) of the optimum Sb content in the third experiments, the nitrogen content (Nc1=1.5%) necessary for achieving the 1.35 μm wavelength and the nitrogen content (Nc2=0.44%) obtained in the third experiments, as follows:
The lower limit (LL) of Sb content is calculated from the minimum value (Min=0.8%) of the optimum Sb content in the third experiments, the minimum nitrogen content (Nc3=0.1%) for achieving the 1.3 μm band wavelength by increasing the In content and the nitrogen content (Nc2=0.44%) obtained in the third experiments, as follows
The fourth experiments are such that the wavelength is increased up to 1.3 μm by using a GaInNAsSb well layer. We observed that the use of both GaInNAsSb well layer and GaAs barrier layer involved a problem in that the PL intensity in the vicinity of 1.3 μm decreases down to 1/20 compared to the PL intensity in the vicinity of 1.2 μm, as shown by the graphs (1) to (5) in
For preparing the graphs (1) to (5), a plurality of laser structures were formed each including an n-GaAs buffer layer having a thickness of 0.2 μm, an n-In0.47Ga0.53P cladding layer having a thickness of 0.25 μm, a GaAs optical confinement layer having a thickness of 0.1 μm, a SQW active layer structure including a GaAs barrier layer having a thickness of 0.03 μm, a SQW layer having a thickness of 7.3 nm, and a GaAs barrier layer having a thickness of 0.03 μm, a GaAs optical confinement layer having a thickness of 0.1 μm, and a p-In0.47Ga0.53P cladding layer having thickness of 0.25 μm, which were consecutively formed in this order on a (100) plane of an n-GaAs substrate. The SQW layer is made of GaxIn1-xN1-y-0.016AsySb0.016.
Some samples of the laser structures were formed at a growth temperature of 460 degrees C. for the well layers and the barrier layers, with the In content in the GaInNAsSb well layer being 37%, the nitrogen flow rate being varied at 0.05 sccm, 0.10 sccm and 0.15 sccm. The other samples of the laser structures were also formed with the In content in the GaInNAsSb well layer being 39%, and the nitrogen flow rate at 0.05 sccm and 0.10 sccm, with the other conditions being maintained similar to the some samples. These samples of the laser structures were subjected to a heat treatment at a temperature of 500 to 700 degrees C. in a nitrogen ambient for ten minutes for improvement of the crystallinity after the epitaxial growth.
The resultant laser structures having those well layers and barrier layers are subjected to measurements of the PL wavelength and the PL intensity thereof. The results of the measurements are by the graphs (1) to (5) shown in
Tables 1 to 5 show the measured values plotted on the graphs (1) to (5), respectively.
By performing a high-temperature heat treatment to an epitaxial layer, photoluminescence (PL) intensity increases by several times compared to the as-grown epitaxial layer without the high-temperature heat treatment, with an effect of decrease of the GaInNAs(Sb) layer, however, in the bandgap wavelength.
For example, the relationship between the PL wavelength and the PL intensity for the case of an In content of 37% and a nitrogen flow rate of 0.05 sccm is such that shown by the graph (1) wherein the wavelength of the as-grown layer is 1.222 μm whereas the wavelengths of the epitaxial layers subjected to the heat treatments at 550 degrees C. and 650 degrees C. are 1.21 μm and 1.18 μm, respectively.
As understood from
Thus, the inventor examined the solution of the lower PL intensity by using a GaNAs barrier layers having the structure as will be detailed below.
An n-GaAs buffer layer having a thickness of 0.2 μm, an n-In0.47Ga0.53P cladding layer having a thickness of 0.25 μm, a GaAs optical confinement layer having a thickness 0.1 μm a GaNAs barrier layer having a thickness of 0.03 μm, a SQW layer having a thickness of 7.3 nm, a GaNAs barrier layer having a thickness of 0.03 μm, a GaAs optical confinement layer having a thickness of 0.1 μm and a p-InGaP cladding layer having thickness of 0.25 μm were consecutively grown on a (100) plane of an n-GaAs substrate to form a layer structure implementing a laser structure. A plurality of laser structures having the layer structure described above were formed.
The SQW layer is made of GaxIn1-xN1-y-0.016AsySb0.016 similarly to the laser structure having GaAs barrier layers. While changing the In content in the SQW layers, the nitrogen content is changed in accordance therewith between 0.66% and 1.8%, or between 0.05 sccm and 0.15 sccm in terms of the nitrogen flow rate, in the GaNAs barrier layer.
Some laser structures were formed with the In content in the GaInNAsSb well layer being fixed at 37%, with the nitrogen content being changed from 0.33% to 1.8% (or the nitrogen (N2) flow rate between 0.05 sccm and 0.15 sccm), and other laser structures were formed with the In content being fixed at 39% and with the nitrogen flow rate being fixed at 0.05 sccm. The layers of these laser structures were subjected to a heat treatment, and the PL intensity and the PL wavelength were measured before and after the heat treatment. The results of the measurements are shown by graphs (6) to (9) in
The values obtained by the measurements are shown in Tables 6 to 9.
Although the PL intensity of the as-grown epitaxial layers including a pair of GaNas barrier layers is lower, the PL intensity increases sharply after the heat treatment at 650 degrees C. or above.
For example, a heat treatment at 650 degrees C. after the growth of a SQW structure including a Ga0.63In0.37N0.009As0.975Sb0.016 well layer and a pair of GaN0.018As0.982 barrier layer achieved a PL wavelength of 1.30 μm and a PL intensity which is comparable to the PL intensity of the SQW structure including GaAs barrier layers and having an emission wavelength around 1.20 μm, as shown by the graph (8) in
It is to be noted that the growth of the SQW active layer structure including Ga0.63In0.37N0.009As0.975Sb0.016 well layer and a pair of GaN0.018As0.982 barrier layers and the subsequent heat treatment of the as-grown epitaxial structure at 650 degrees C. achieved a PL wavelength of 1.30 μm and a PL intensity similar to the PL intensity of the laser structure having GaAs barrier lasers and emitting at a wavelength in the vicinity of 1.20 μm.
The reason for the increase in the PL intensity due to the GaInNAsSb layer is considered to result from the fact that the presence of nitrogen both in the barrier layers and in the well layer achieves a quasi-homogeneous epitaxial growth to thereby improve the crystallinity of these layers.
Thus, a laser structure including SQW active layer structure having Ga0.63In0.37N0.009As0.975Sb0.016/GaN0.08As0.982 layers was fabricated as a broad contact laser, which exhibited a excellent lower threshold current as low as 570 A/cm2 for a cavity length of 900 μm.
By arranging the data shown in
From the above experiments and investigation of the results in the experiments, the optical properties of the GaInAs semiconductor laser devices having an emission wavelength of 1.2 μm band, wherein In is included at an atomic ratio of 30% or more relative to Group-III elements can be improved remarkably by adding Sb as a constituent element at an atomic ratio of 0.3% to 0.8% relative V-group elements during the epitaxial growth of the GaInAs layer. In the case of GaInNAs semiconductor laser devices, Sb is added at an atomic ratio of 0.2% to 2.5% relative to the V-group elements during the epitaxial growth of the GaInNAs layer.
In the above configuration, a higher nitrogen content may degrade the crystallinity of the semiconductor laser, and thus the practical upper limit of the nitrogen content is preferably below 3% relative to V-group elements.
As described before with reference to
Now, the present invention is more specifically described with reference to accompanying drawings, wherein similar constituent elements are designated by similar reference numerals.
The SQW active layer structure 20 includes a single well layer made of Ga0.61In0.39As0.9968Sb0.0032 having a compressive strain of 2.82%, and the thickness of the well layer is 7.3 nm.
The GaInAsSb well layer is grown under the following conditions in case of gas-source MBE growth:
Although not explicitly illustrated, the semiconductor laser device of the present embodiment is formed as a ridge waveguide semiconductor laser device by mesa-etching of the above layers to have an active layer width of 3 μm.
The semiconductor laser device also includes a p-side ohmix electrode made of metallic layers including Au-Zn or Ti/Pt/Au films on the contact layer 26, and an n-side ohmic electrode made of metallic layers including Au-Ge/Ni/Au films.
The semiconductor laser device has a cavity length of 200 μm, and includes a high reflective (HR)-coat having a reflectance of 78% at the front facet and a HR-coat having a reflectance of 95% at the rear facet.
A sample of the semiconductor laser device of the present embodiment was fabricated and subjected to measurements for characteristics of the optical output with respect to injected current after the bonding thereof. The results of the measurements were such that the threshold current at 20 degrees C. was 6 mA, the characteristic temperature of the threshold current between 20 and 70 degrees C. was 256 K, and CW emission wavelength was 1.20 μm at a room temperature. In short, the sample had a threshold current which is lowest among the high-strained GaInAs semiconductor laser devices reported heretofore and a characteristic temperature which is significantly higher than those of the conventional ones.
The SQW active layer structure 32 includes a single Ga0.61In0.39As0.9796N0.0044Sb0.016well layer having a thickness of 7.3 nm.
The GaInNAsSb well layer is grown under the following conditions:
A sample of the semiconductor laser device of the present embodiment was fabricated and subjected to measurements for characteristics of the optical output with respect to injected current after the bonding thereof. The results of the measurements were such that the threshold current at 20 degrees C. was 10 mA, the characteristic temperature of the threshold current between 20 and 85 degrees C. was 157 K, and the CW emission wavelength was 1.26 μm at a room temperature. In short, the sample had a threshold current which is the lowest among the high-strained GaInNAs semiconductor laser devices reported heretofore and a characteristic temperature which is significantly higher than those of the conventional ones.
Although the sample had a CW emission wavelength of 1.26 μm, a variation of the configuration of the second embodiment provides a semiconductor laser device having an emission wavelength of 1.3 μm by adjusting the nitrogen content and the Sb content and by additionally using barrier layers each having a composition of GaNyAs1-y(N<0.05). The semiconductor laser device of the present invention may be a MQW laser device instead of the SQW laser devices as used in the first and second embodiments. The In content may be preferably in the range between 15% and 45% although the In content in the embodiments was exemplified at 39%.
The GaAs or GaNAs barrier layers as used in the first or second embodiment may be GaInNAs(Sb) or GaInAsP layers, each of which may have a strain.
The GaAs optical confinement layer having a SCH (Separate Confinement Heterostructure) configuration as used in the embodiments may be replaced by an AlxGa1-xAs layer having a GRIN (Graded Refractive Index)-SCH configuration. In addition, the cladding layer may be made of AlGaAs.
The semiconductor laser device 80 of the present embodiment includes an n-GaAs substrate 82 having a (100) plane, and a layer structure formed thereon, the layer structure including a 0.5-μm-thick n-GaAs buffer layer (n=1×1018cm−3) 84, a bottom DBR (Distributed Bragg Reflector) mirror 86 including 30 pairs of layers each including an n-GaAs/n-Al0.0Ga0.1As pair, a 150-nm-thick undoped GaAs lower cladding layer 88, a quantum well active layer structure 90, a 150-nm-thick undoped GaAs upper cladding layer 92, a top DBR mirror 94 having 25 pairs of layers each including a p-Al0.9Ga0.1As/p-GaAs pair, and a 10-nm-thick p-GaAs cap layer 96.
Each layer of the pair of layers in both the bottom DBR mirror and the top DBR mirror has a thickness corresponding to λ/4n, given λ and n being the emission wavelength of the laser device and the refractive index of the each layer, respectively.
More specifically, the pair of layers in the bottom DBR mirror includes a 94-nm-thick n-GaAs layer and a 110-nm-thick n-Al0.9Ga0.1As layer. The pair of layers in the top DBR mirror includes a 94-nm-thick p-GaAs layer and a 110-nm-thick p-Al0.9Ga0.1As layer.
The SQW active layer structure 90 includes two wells each including a 7-nm-thick Ga0.63In0.37N0.975Sb0.016, and a pair of 20-nm-thick GaN0.018As0.982 barrier layer. The GaInNAsSb well layers were grown under the following conditions:
Each pair in the top p-type DBR mirror includes a 110-nm-thick Al0.9Ga0.1As and a 94-nm-thick p-GaAs layer. The bottom of the top p-type DBR mirror is implemented by a 20-nm thick AlAs layer 98 and a 90-nm-thick Al0.9Ga0.1As layer instead of the 110-nm-thick Al0.9Ga0.1As layer.
The bottom layers form a current confinement structure implemented by a non-oxidized area of the AlAs layer 98 which functions as a current injection area 100, and an oxidized area of the AlAs layer 98 wherein Al in the AlAs layer 98 is oxidized.
Among the layer structure as described above, the top DBR mirror 94 is configured by a photolithographic etching technique to form a annular groove 102 having a width of, example, 50 μm. The annular groove 102 defines a cylindrical mesa post having a diameter of 20 μm. By oxidizing Al in the selected area of the AlAs layer 98 outside the periphery of the mesa post, the current confinement structure is formed which includes the current injection area 98 having a diameter of 8 μm and the Al-oxidized area 100.
A SiNx film 104 is formed as an insulation layer for the entire layer structure including the annular groove 102 and except for the top of the mesa post. An annular p-side electrode 106 is formed inside the SiNx film 104 in contact with the p-GaAs cap layer 96. An electrode pad 108 made of Ti/Pt/Au films is formed on the annular p-side electrode 106 and the SiNx film 104. The bottom of the GaAs substrate 82 is polished for allowing the GaAs substrate 82 to have a thickness of 100 μm. An n-side electrode 110 is formed on the bottom surface of the GaAs substrate 82.
With the configuration as described above, the semiconductor laser device mode at a threshold current of 2 mA and at a temperature of 100 degrees C. or above.
In the examples of the first through third embodiments, the semiconductor laser device had emission wavelengths of 1200 nm and 1250 to 1300 nm. The present invention cam be applied to a semiconductor laser device or VCSEL having emission wavelengths of 980 nm, 1480 nm, 550 nm, 1650 nm etc. by modifying the nitrogen content and the Sb content.
Since the above embodiments are described only for examples, the present invention is not limited to the above embodiments and various modifications or alterations can be easily made therefrom by those skilled in the art without departing from the scope of the present invention.