JP2019102585A - Optical device - Google Patents

Abstract

To improve the internal quantum efficiency of an optical device with a lateral pin structure.SOLUTION: An optical device includes, on a substrate 101, a first semiconductor layer 102, a second semiconductor layer 103, an active layer 104, a third semiconductor layer 105, a fourth semiconductor layer 106, and a fifth semiconductor layer 107. The second semiconductor layer 103 and the fifth semiconductor layer 107 are composed of a compound semiconductor having a larger band gap than the active layer 104. The third semiconductor layer 105 and the fourth semiconductor layer 106 are composed of a compound semiconductor having a lower refractive index and a larger band gap than the active layer 104. The first semiconductor layer 102 is composed of a compound semiconductor having a larger band gap than the second semiconductor layer 103, the third semiconductor layer 105, and the fourth semiconductor layer 106.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical device composed of a semiconductor.

  In recent years, with the increase of communication capacity in a data center or the like, reduction in power consumption of an optical device for short distance optical communication is required. In order to meet this demand, optical devices having a buried heterostructure (BH) structure have been developed (see Non-Patent Documents 1 to 5). In the embedded heterostructure, the active layer made of a semiconductor having a high refractive index and a small band gap is sandwiched between upper, lower, right, and left layers of a semiconductor having a refractive index lower than that of the active layer and a large band gap. ing. This structure makes it possible to improve the light confinement coefficient to the active layer which largely contributes to various performances of the optical device.

  The optical device having such a buried heterostructure typically has a semiconductor multilayer structure with a thickness of about 250 nm to 500 nm, and is characterized in that it is devised to reduce power consumption by reducing the volume of the active layer. is there. In addition, a multiple quantum well (MQW) structure excellent in carrier coupling efficiency is adopted for the active layer.

  In such an optical device, the semiconductor multilayer structure is made thinner in order to achieve stronger light confinement by bringing a layer to be a cladding having different refractive index closer to an active layer serving as a core. Thus, in the configuration in which the semiconductor layer is thin, in order to apply an electric field to the optical device and to inject current, the semiconductor layers above and below the active layer are not a general vertical pin structure having p-type and n-type. A lateral pin structure is adopted in which the left and right semiconductor layers of the active layer are p-type and n-type.

  In the vertical pin structure, an electrode for current injection is disposed above the active layer. However, when the semiconductor layer is thinned, the distance between the electrode and the active layer becomes short, so that the active layer can be guided. The light will be influenced by the electrodes. On the other hand, the lateral pin structure makes it possible to shift the electrode from the upper portion of the active layer and to arrange the electrode away from the active layer, thereby solving the above-mentioned problems.

S. Matsuo et al. "Directly modulated buried heterostructure DFB laser on SiO2 / Si substrate fabricated by regrowth of InP using bonded active layer", Optics Express, vol. 22, no. 10, pp. 12139-12147, 2014. T. Okamoto et al., "Optically pumped membrane BH-DFB lasers for low-threshold and single-mode operation", IEEE Journal of Selected Topics in Quantum Electronics, vol. 9, no. 5, pp. 1361-1366, 2003 . S. Matsuo et al., "Room-temperature continuous-wave operation of lateral current injection wavelength-scale embedded active-region photonic-crystal laser", Optics Express, 2012, 20, (4), pp. 377-3780. S. Matsuo et al., "High-speed ultracompact buried heterostructure photonic-crystal laser with 13 fJ of energy consumed per bit transmitted", Nature Photonics, vol. 4, no. 9, pp. 648-654, 2010. K. Hasebe, et al., "High-Speed Modulation of Lateral Diode Structure Electro-Absorption Modulator Integrated With DFB Laser", Journal of Lightwave Technology, vol. 33, no. 6, pp. 1235-1240, 2015.

  By the way, one of the important indexes for driving an optical device with low power consumption is internal quantum efficiency. The internal quantum efficiency is a dimensionless number that represents the ratio of carriers that have contributed to light emission in the active layer among the carriers generated inside the semiconductor layer by current injection. Hereinafter, a semiconductor laser will be described by way of example with reference to FIG. FIG. 4 is a plot of the threshold current (Threat Current) and the light output (Output Power) at the same current injection as a function of the internal quantum efficiency. As the internal quantum efficiency increases, the light output increases proportionally and the threshold current decreases inversely.

  There are two major causes for the internal quantum efficiency to fall below 1.

  First, it is due to the contribution of the thermal relaxation process due to non-radiative recombination. As the temperature of the semiconductor layer increases, the rate of non-radiative recombination increases, so the internal quantum efficiency decreases.

  Second, it is due to the occurrence of carrier recombination in places other than the active layer due to the presence of a current leak path in the structure of the semiconductor layer, and the like. If there is a current leak, the current injection efficiency (hereinafter simply referred to as injection efficiency) to the active layer is lowered, and as a result, the internal quantum efficiency is lowered.

  FIG. 5 shows injection current dependence of light output in two semiconductor lasers having different internal quantum efficiencies. In FIG. 5, the solid line shows the characteristics of the semiconductor laser with high internal quantum efficiency. Further, in FIG. 5, dotted lines indicate the characteristics of the semiconductor laser having low internal quantum efficiency. A laser with high internal quantum efficiency oscillates at a low threshold current first compared to a low laser, secondly, the rate of increase in light output per unit injection current is large, and third, the temperature at high injection current Since the rise is small, there is a feature that output decrease is unlikely to occur.

  Hereinafter, the injection efficiency of the above-described semiconductor laser in an optical device having a lateral pin structure will be described. In the lateral pin structure, carriers are injected from the left and right into the active layer region in which the semiconductor layers are stacked in the vertical direction which is the normal direction of the substrate plane. FIG. 6 shows a schematic view of carrier bonding that can occur other than in the active layer 203. In FIG. 6, solid arrows indicate the flow of electrons, and dotted arrows indicate the flow of holes.

  The first semiconductor layer 202 is formed on the substrate 201, and the active layer 203 is formed on the first semiconductor layer 202. In addition, the second semiconductor layer 204 is formed on the active layer 203. The first semiconductor layer 202 and the second semiconductor layer 204 are made of, for example, non-doped InP. Further, a p-type semiconductor layer 205 and an n-type semiconductor layer 206 are formed on the first semiconductor layer 202 so as to sandwich the active layer 203. Although not shown, for example, as a structure of a resonator, a diffraction grating is formed on or under the active layer 203.

  In this semiconductor laser, the first semiconductor layer 202 and the second semiconductor layer 204 above and below the active layer 203 serve as leak paths, and carrier coupling occurs in regions other than the active layer 203, and the injection efficiency is lowered. Therefore, in a semiconductor laser using a thin film semiconductor structure having a lateral pin structure, there is a problem that a desired internal quantum efficiency (about 80%) can not be obtained.

  The present invention has been made to solve the above problems, and its object is to improve the internal quantum efficiency of an optical device having a lateral pin structure.

  An optical device according to the present invention comprises a first semiconductor layer made of a compound semiconductor formed on a substrate, a second semiconductor layer made of a compound semiconductor formed on the first semiconductor layer, and a second semiconductor layer. An active layer formed of a compound semiconductor formed thereon, a third semiconductor layer formed of a p-type compound semiconductor formed on the second semiconductor layer with the active layer sandwiched in the plane direction of the substrate, and an n-type compound semiconductor And a fifth semiconductor layer formed of a compound semiconductor formed on the active layer, wherein the second semiconductor layer and the fifth semiconductor layer are formed of a compound semiconductor having a band gap larger than that of the active layer. The third semiconductor layer and the fourth semiconductor layer are made of a compound semiconductor having a refractive index lower than that of the active layer and a band gap larger than that of the active layer, and the first semiconductor layer is a second semiconductor layer, a third semiconductor layer And and a larger compound semiconductor band gap than the fourth semiconductor layer.

  The optical device further includes a first electrode connected to the third semiconductor layer and a second electrode connected to the fourth semiconductor layer.

  In the above optical device, the active layer may have a multiple quantum well structure.

  As described above, according to the present invention, the first semiconductor layer formed of the second semiconductor layer, the third semiconductor layer, and the compound semiconductor having a band gap larger than that of the fourth semiconductor layer is disposed under the active layer. The excellent effect is obtained that the internal quantum efficiency of the optical device of the lateral pin structure is improved.

FIG. 1 is a cross-sectional view showing the configuration of an optical device according to an embodiment of the present invention. FIG. 2 is a band diagram showing a band structure in the optical device in the embodiment of the present invention. FIG. 3A is a cross-sectional view showing a state in the middle of the process for describing the method of manufacturing an optical device according to the embodiment of the present invention. FIG. 3B is a cross-sectional view showing a state in the middle of the process for describing the method of manufacturing an optical device according to the embodiment of the present invention. FIG. 3C is a cross-sectional view showing a state in the middle of the process for describing the method of manufacturing an optical device according to the embodiment of the present invention. FIG. 3D is a cross-sectional view showing a state in the middle of the process for describing the method of manufacturing an optical device according to the embodiment of the present invention. FIG. 3E is a cross-sectional view showing a state in the middle of the process for describing the method of manufacturing an optical device according to the embodiment of the present invention. FIG. 3F is a cross-sectional view showing a state in the middle of the process for describing the method of manufacturing an optical device according to the embodiment of the present invention. FIG. 4 is a characteristic diagram showing the threshold current of the semiconductor laser having a lateral pin structure and the light output at the same current injection as a function of the internal quantum efficiency. FIG. 5 is a characteristic diagram showing the injection current dependency of the light output in two semiconductor lasers having different internal quantum efficiencies. FIG. 6 is a cross-sectional view showing the configuration of a semiconductor laser having a lateral pin structure. FIG. 7 is a band lineup obtained by calculating energy levels in the optical device according to the embodiment of the present invention.

  Hereinafter, an optical device according to an embodiment of the present invention will be described with reference to FIG. The optical device includes a first semiconductor layer 102, a second semiconductor layer 103, an active layer 104, a third semiconductor layer 105, a fourth semiconductor layer 106, and a fifth semiconductor layer 107 on a substrate 101. Each semiconductor layer is made of a compound semiconductor.

  The first semiconductor layer 102 is made of a compound semiconductor, and in the embodiment, is formed on the substrate 101 via the lower cladding layer 110. The second semiconductor layer 103 is formed on the first semiconductor layer 102. On the second semiconductor layer 103, the active layer 104 is sandwiched between the third semiconductor layer 105 and the fourth semiconductor layer 106 in a direction parallel to the plane of the substrate 101. The third semiconductor layer 105 is made of a p-type compound semiconductor, and the fourth semiconductor layer 106 is made of an n-type compound semiconductor.

  In the embodiment, first, the second semiconductor layer 103 and the fifth semiconductor layer 107 are made of a compound semiconductor having a band gap larger than that of the active layer 104. The third semiconductor layer 105 and the fourth semiconductor layer 106 are made of a compound semiconductor having a refractive index lower than that of the active layer 104 and a large band gap. In addition, the first semiconductor layer 102 is made of a compound semiconductor having a band gap larger than that of the second semiconductor layer 103.

  The optical device includes a first electrode 111 electrically connected to the third semiconductor layer 105 and a second electrode 112 electrically connected to the fourth semiconductor layer 106. The first electrode 111 may be formed directly on the third semiconductor layer 105, or the first electrode 111 may be formed via a contact layer. Similarly, the second electrode 112 may be formed directly on the fourth semiconductor layer 106, or the second electrode 112 may be formed via the contact layer. The contact layer may be made of a semiconductor in which an impurity is introduced at a higher concentration and whose band gap is smaller than that of the third semiconductor layer 105 and the fourth semiconductor layer 106.

  For example, the substrate 101 is made of high resistance InP. The lower cladding layer 110, the second semiconductor layer 103, and the fifth semiconductor layer 107 are made of non-doped InP (i-InP). The third semiconductor layer 105 is made of Zn-doped p-type InP (p-InP), and the fourth semiconductor layer 106 is made of Si-doped n-type InP (n-InP) It is done.

  The active layer 104 may be made of, for example, bulk InGaAsP. The active layer 104 may have a multiple quantum well structure in which well layers of InGaAsP and barrier layers are alternately stacked. The first semiconductor layer 102 may be made of InAlAs. The first semiconductor layer 102 may be made of InGaAlAs, AlGaAs, or a nitride semiconductor such as AlGaN or AlN.

  In order to improve the quality of each semiconductor layer, the first semiconductor layer 102, the second semiconductor layer 103, the active layer 104, the third semiconductor layer 105, the fourth semiconductor layer 106, and the fifth semiconductor layer 107 are lattice matched with one another. It should be selected according to the material to be As a combination satisfying this condition, for example, InP is used for the first semiconductor layer 102, the second semiconductor layer 103, the third semiconductor layer 105, the fourth semiconductor layer 106, and the fifth semiconductor layer 107, and the active layer 104 is bulky. There is an example using InGaAsP or InGaAlAs. On the other hand, when the active layer 104 has a multiple quantum well structure, it is not necessary for both the well layer and the barrier layer to be lattice matched with other adjacent semiconductor layers.

When the substrate 101 is made of SiO ₂ , the total film thickness of the lower cladding layer 110, the first semiconductor layer 102, the second semiconductor layer 103, the active layer 104, and the fifth semiconductor layer 107 is reduced to obtain the active layer 104. The optical confinement factor inside can be increased to improve the optical device characteristics. The total film thickness may be, for example, 400 nm or less. In order to increase the current injection efficiency while increasing the light confinement coefficient in the active layer 104, the width of the active layer 104 may be limited, and the width may be, for example, between 200 nm and 1000 nm.

  When the optical device in the embodiment is, for example, a laser, a resonant structure (not shown) may be provided. For example, if a diffraction grating is formed on the active layer 104, a distributed feedback laser can be obtained. In addition, on the front side and the back side of the paper surface of FIG. 1, if a core layer is formed continuously to the active layer 104 and a diffraction grating is formed on this core layer, a distributed Bragg reflector laser can be obtained. it can. Further, the external resonator structure may be combined to form a laser.

  As described above, according to the embodiment, the first semiconductor layer 102 made of a compound semiconductor having a larger band gap below the second semiconductor layer 103, the third semiconductor layer 105, and the fourth semiconductor layer 106. As a result, the formation of the current leak path on the substrate side of the active layer 104 is suppressed. This effect can be expected to be higher as the second semiconductor layer 103 is thinner, and the second semiconductor layer 103 may be omitted if there is no problem in fabrication. As a result, according to the embodiment, it is possible to improve the internal quantum efficiency of the optical device of the lateral pin structure.

  The effects described above will be described in more detail. In this optical device, the first current path (a), the second current path (b), and the third current path (c) are carriers (electrons and holes), as indicated by the dashed-dotted arrows in FIG. It can be considered as a path through which The band conditions for each of these current paths are as shown in FIG.

  (A) of FIG. 2 corresponds to the first current path (a) of FIG. 1 and is a band diagram when carriers flow into the active layer 104. Since the active layer 104 is formed of a semiconductor having a smaller band gap than the third semiconductor layer 105 and the fourth semiconductor layer 106, carriers are confined in the active layer 104 and recombination occurs efficiently.

  2B corresponds to the second current path (b) in FIG. 1 and is a band diagram in the case where carriers flow into the fifth semiconductor layer 107 on the upper part of the active layer 104. FIG. When the second semiconductor layer 103, the active layer 104, the third semiconductor layer 105, the fourth semiconductor layer 106, and the fifth semiconductor layer 107 are formed of the same semiconductor, there is no factor that inhibits the flow of carriers. Also in the semiconductor layer 107, constant recombination occurs.

  (C) of FIG. 2 corresponds to the second current path (c) of FIG. 1, and is a band diagram in the case where carriers flow into the semiconductor layer on the substrate side from the active layer 104. In the case of a general lateral pin structure optical device, a band diagram similar to that of the upper portion of the active layer is formed and recombination occurs. On the other hand, according to the present invention, since the high band gap first semiconductor layer 102 is present under the active layer 104, carriers are substantially suppressed from flowing into the lower part of the active layer 104. Therefore, the carrier flow in the third current path of FIG. 1 can be substantially zero. As a result, according to the embodiment described above, the recombination efficiency in the active layer 104 is improved, and the characteristics of the optical device can be improved. In order to obtain this effect, the thickness of the first semiconductor layer 102 may be such that it does not cause a tunnel current, for example, 4 nm or more.

  In FIG. 2D, when InP is selected as the first semiconductor layer 102, the third semiconductor layer 105, and the fourth semiconductor layer 106 as an embodiment, and an InAlAs layer is selected as the lower cladding layer 110, It is a band figure corresponding to the 2nd current path (c) of FIG. The combination of InP and InAlAs is called a type II structure, and while the influx of carriers (holes) in the valence band can not be suppressed, the influx of carriers (electrons) in the conduction band is strongly suppressed. For this reason, although the holes are accumulated in the lower cladding layer 110 and the first semiconductor layer 102, the mobility of the holes in InP is as small as 1/20 or less of the electrons, so the influence on the leakage is small. On the other hand, since the flow of electrons having a large influence on the leak is strongly inhibited, the recombination efficiency in the active layer 104 is improved as in the case of FIG. 2C. FIG. 7 shows the case where InP is selected as the first semiconductor layer 102, the third semiconductor layer 105, and the fourth semiconductor layer 106, an InAlAs layer lattice-matched with InP as the lower cladding layer 110, and an InGaAlAs layer as the active layer 104. It is a band lineup in which energy levels are calculated, and it can be seen that the flow of carriers in the conduction band can be suppressed. In FIG. 7, the dotted line indicates the state of the heavy hole, and the alternate long and short dash line indicates the state of the light hole.

  In addition, the conductivity type may be changed by doping the first semiconductor layer 102 for the purpose of enhancing the above-described effects. For example, it is expected that current leakage to the lower cladding layer 110 can be more strongly suppressed by doping Fe to make it semi-insulating. Also, in the first semiconductor layer 102, a conductive type distribution structure may be formed in the vertical direction. For example, current leakage to the lower cladding layer 110 can be expected to be suppressed by forming an NPNP structure in which N-type and P-type are repeated two or more cycles in the vertical direction in the first semiconductor layer 102. In addition, in the first semiconductor layer 102, a conductive type distribution structure may be formed in the left-right direction. For example, even if the conductivity type below the third semiconductor layer 105 is different from that of the third semiconductor layer 105 and the conductivity type below the fourth semiconductor layer 106 is different from that of the fourth semiconductor layer 106, the current to the lower cladding layer 110 is It can be expected to suppress the leak.

Hereinafter, a method of manufacturing the optical device according to the embodiment will be described with reference to FIGS. 3A to 3F.
First, as shown in FIG. 3A, the lower cladding layer 110 is formed on the substrate 101. The lower cladding layer 110 may be formed by depositing a non-doped compound semiconductor or a semi-insulating compound semiconductor by known metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or the like. The lower cladding layer 110 formed on a separately prepared growth substrate may be bonded to the substrate 101 made of Si or the like by direct wafer bonding.

  Next, as shown in FIG. 3B, the first semiconductor layer 102, the second semiconductor layer 103, the active layer forming layer 104a, and the fifth semiconductor layer forming layer 107a are formed on the lower cladding layer 110. For example, the layers described above may be formed sequentially by epitaxial growth of a predetermined compound semiconductor by MOCVD, MBE, or the like. In addition, an n-type impurity, a p-type impurity, or an SI-type impurity may be introduced during the epitaxial growth of the first semiconductor 102 to change the conductivity type. Alternatively, after epitaxial growth of the first semiconductor 102, an n-type impurity or a p-type impurity may be introduced by ion implantation or thermal diffusion to change the conductivity type, and then the second semiconductor layer 103 may be regrown.

  The fifth semiconductor layer forming layer 107a, the active layer forming layer 104a, the second semiconductor layer 103, and the first semiconductor layer 102 are formed by MOCVD, MBE or the like on a separately prepared growth substrate, and these are formed of Si or the like. Alternatively, the growth substrate may be removed by direct wafer bonding to the substrate 101 configured as described above. In this case, the lower cladding layer 110 may be omitted.

  Next, as shown in FIG. 3C, a mask pattern 151 is formed on the fifth semiconductor layer forming layer 107a by known photolithography technology and etching technology. The mask pattern 151 is made of, for example, an inorganic insulating material such as silicon oxide. Then, using the mask pattern 151 as a mask, the fifth semiconductor layer forming layer 107a and the active layer forming layer 104a are patterned using a known dry etching technique or wet etching technique or the like to form a predetermined shape as shown in FIG. 3D. The active layer 104 and the fifth semiconductor layer 107 are formed. For example, the active layer 104 and the fifth semiconductor layer 107 are formed in a stripe shape extending from the front to the back of the paper surface of FIG. 3D.

  Next, as shown in FIG. 3D, the third semiconductor layer 105 and the fourth semiconductor layer 106 are formed on the second semiconductor layer 103 lateral to the active layer 104 and the fifth semiconductor layer 107.

  For example, using the mask pattern 151 made of silicon oxide as a selective growth mask, InP is regrown on the exposed second semiconductor layer 103. Next, a p-type impurity is introduced into one of the regrown InP layers by ion implantation or thermal diffusion to form a third semiconductor layer 105. Further, an n-type impurity is introduced into the regrown layer of the other InP by ion implantation or thermal diffusion to form a fourth semiconductor layer 106.

  Further, in regrowth using the mask pattern 151 as the selective growth mask, first, in a state where the formation region of the fourth semiconductor layer 106 is masked, a source gas of an impurity that becomes p-type in the formation region of the third semiconductor layer 105 P-type InP is regrown to form the third semiconductor layer 105. After the third semiconductor layer 105 is formed in this manner, n-type InP is used in the formation region of the fourth semiconductor layer 106 also using the source gas of the impurity to be the n-type in a state where the third semiconductor layer 105 is masked. The fourth semiconductor layer 106 is formed by regrowth. Alternatively, after the third semiconductor layer 105 and the fourth semiconductor layer 106 are regrown to have the same conductivity type, doping for reversing one of the conductivity types may be performed by ion implantation or thermal diffusion. In addition, after the third semiconductor layer 105 and the fourth semiconductor layer 106 are regrown to have the same conductivity type, the semiconductor layer is removed again by etching with one of the masks masked, and the regrowth is performed to have a different conductivity type. good.

  After forming the respective semiconductor layers as described above, the mask pattern 151 is removed, whereby the optical device according to the embodiment can be obtained as shown in FIG. 3F. Thereafter, the first electrode 111 is formed on the third semiconductor layer 105, and the second electrode 112 is formed on the fourth semiconductor layer 106, whereby the optical device described with reference to FIG. 1 can be obtained.

  By the way, in the step of forming the active layer forming layer 104a, in the case of selecting mixed crystals (such as InGaAlAs) containing Al as a material, it is important to keep the oxygen concentration in the film forming chamber of the film forming apparatus low. This is because Al is a material that is extremely easily oxidized, and the use of a mixed crystal containing oxidized Al in the active layer significantly reduces the luminous efficiency. However, crystals such as InP and GaAs are less susceptible to oxidation than Al. Therefore, when oxygen is present in the deposition chamber, there is a problem that oxygen in the deposition chamber is easily taken into the growing semiconductor layer at the growth stage of the mixed crystal compound semiconductor containing Al. is there.

  On the other hand, the problem described above can be solved by continuously growing the active layer forming layer 104 a in the same deposition chamber after forming the first semiconductor layer 102. In general, the first semiconductor layer 102 having a band gap higher than that of the other layers is made of a material containing Al, such as InAlAs, InGaAlAs, AlGaAs, AlGaN, or AlN. Therefore, by growing the first semiconductor layer 102, oxygen in the deposition chamber is taken into the first semiconductor layer 102, and as a result, the oxygen concentration in the deposition chamber is reduced. If the active layer forming layer 104a is grown in this state, oxygen is not taken into the active layer forming layer 104a.

  The first semiconductor layer 102 does not contribute to light emission, and the incorporation of oxygen into this layer does not affect the device characteristics, and the quality of the active layer is maintained. As a result, an effect of obtaining an active layer having good light emission characteristics can be expected as compared with a general active layer growth procedure in which a high band gap layer is not inserted.

  In addition, in the growth of the active layer forming layer 104a, it is also known that oxygen is released from various members by setting the temperature in the film forming chamber to a temperature higher than the long temperature of the active layer forming layer 104a before this step. There is. This prevents the introduction of oxygen in the growth of the active layer forming layer 104a. However, such high temperature treatment causes re-evaporation of InP in the semiconductor layer made of InP which has already been formed, which causes a problem of inhibiting high quality crystal growth.

  Further, when the substrate 101 is made of a material whose physical property constants (lattice constant, thermal expansion coefficient) are significantly different from those of InP, residual strain and its distribution occur in the semiconductor layer made of InP. InP is a material that tends to cause mass transport phenomenon in which atoms move and rearrange in a high temperature environment so as to minimize surface energy. For this reason, there is also a problem that when the strained InP layer is exposed to a high temperature environment, the flatness is deteriorated.

  On the other hand, in the present invention, since the first semiconductor layer 102 having a higher band gap is disposed closer to the substrate than the active layer, the first semiconductor layer 102 can be a layer of InAlAs. The re-evaporation temperature of InAlAs is higher than that of InP, and mass transport is also less likely to occur. Therefore, when growing the first semiconductor layer 102, the temperature in the deposition chamber can be raised to a higher temperature, and any of the problems described above does not occur, and a high quality active layer can be obtained.

  As described above, according to the present invention, since the first semiconductor layer formed of a compound semiconductor having a band gap larger than that of the second semiconductor layer is disposed under the active layer, the internal quantum of the optical device having a lateral pin structure Efficiency can be improved.

The present invention is not limited to the embodiments described above, and many modifications and combinations can be made by those skilled in the art within the technical concept of the present invention. It is clear. For example, the substrate may be made of a material such as silicon, silicon oxide, GaAs, GaN, Al ₂ O ₃ or the like.

  The second semiconductor layer and the fifth semiconductor layer may be made of a semi-insulating semiconductor. The active layer may be made of InGaAs, InGaAlAs, InAlAs, InP, InGaAs, GaAs, InGaN, or GaN, or may have a multiple quantum well structure.

  DESCRIPTION OF SYMBOLS 101 ... Substrate, 102 ... 1st semiconductor layer, 103 ... 2nd semiconductor layer, 104 ... Active layer, 105 ... 3rd semiconductor layer, 106 ... 4th semiconductor layer, 107 ... 5th semiconductor layer, 110 ... Lower clad layer, 111 ... 1st electrode, 112 ... 2nd electrode.

Claims (3)

A first semiconductor layer made of a compound semiconductor formed on a substrate;
A second semiconductor layer made of a compound semiconductor formed on the first semiconductor layer;
An active layer made of a compound semiconductor formed on the second semiconductor layer;
A third semiconductor layer made of a p-type compound semiconductor and a fourth semiconductor layer made of an n-type compound semiconductor which are formed on the second semiconductor layer across the active layer in the planar direction of the substrate;
A fifth semiconductor layer made of a compound semiconductor formed on the active layer;
The second semiconductor layer and the fifth semiconductor layer are made of a compound semiconductor having a band gap larger than that of the active layer,
The third semiconductor layer and the fourth semiconductor layer are made of a compound semiconductor having a refractive index lower than that of the active layer and having a larger band gap than that of the active layer.
An optical device, wherein the first semiconductor layer is made of a compound semiconductor having a band gap larger than that of the second semiconductor layer, the third semiconductor layer, and the fourth semiconductor layer. In the optical device according to claim 1,
A first electrode connected to the third semiconductor layer;
And a second electrode connected to the fourth semiconductor layer. In the optical device according to claim 1 or 2,
An optical device characterized in that the active layer has a multiple quantum well structure.

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