Optical Devices

Abstract

To provide an optical device capable of monitoring the output of a laser diode in real time using a photodetector.SOLUTION: An optical device 1 comprises a laser diode 10 formed on a nitride semiconductor substrate 100 and having a first nitride semiconductor laminate 11, and a photodetector 20 formed on a nitride semiconductor substrate 100 and having a second nitride semiconductor laminate 21, the laser diode 10 has an n-type contact electrode 12 disposed on a part of the exposed region of the n-type cladding layer 111 of the first nitride semiconductor laminate 11, and a p-type contact electrode 13 disposed on the p-type cladding layer 115 of the first nitride semiconductor laminate 11, and the photodetector 20 has two p-type contact electrodes 23 disposed on the p-type cladding layer 215 of the second nitride semiconductor laminate 21.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to optical devices. [Background technology]

[0002] A laser device including a laser diode and a photodetector that monitors the output of the laser diode is described in Patent Document 1. Also, Non-Patent Documents 1 and 2 describe ultraviolet laser diodes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-82045 A [Non-patent literature]

[0004] [Non-Patent Document 1] Zhang et al., Applied Physics Express 12, 124003(2019) [Non-Patent Document 2] Zhang et al., Applied Physics Letters117, 152104(2020) Summary of the Invention [Problem to be solved by the invention]

[0005] It is important for the stable light emission operation of a laser diode to monitor the output of the laser diode in real time using a light receiving element and adjust the driving conditions of the laser diode based on the monitoring results. In particular, in order to achieve a configuration that is inexpensive and suitable for mass production, it is desirable to monolithically provide the laser diode and the light receiving element on the same substrate.

[0006] In the ultraviolet laser diode structures described in Non-Patent Documents 1 and 2, the depletion layer formed by the pn junction does not coincide with the light-emitting layer. Therefore, if the ultraviolet laser diode structures described in Non-Patent Documents 1 and 2 are used as they are as a light-receiving element, the electron-hole pairs generated by receiving light in the light-emitting layer will recombine and disappear before being extracted as a photocurrent, since no electric field is applied to them. Therefore, there is a problem that the output of the laser diode cannot be monitored by the light-receiving element.

[0007] That is, an object of the present disclosure is to provide an optical device capable of monitoring the output of a laser diode in real time using a light receiving element. [Means for solving the problem]

[0008] In order to achieve the above object, an optical device according to one aspect of the present invention includes a nitride semiconductor substrate containing aluminum, a laser diode formed on the nitride semiconductor substrate and having a first nitride semiconductor stack, and a light-receiving element formed on the nitride semiconductor substrate and having a second nitride semiconductor stack, each of the first nitride semiconductor stack and the second nitride semiconductor stack including a first conductive type cladding layer including a nitride semiconductor layer having a first conductive type conductivity, a light-emitting layer disposed on the first conductive type cladding layer and formed of a nitride semiconductor layer including one or more quantum wells, and a second conductivity type cladding layer including a nitride semiconductor layer having a second conductivity type conductivity and disposed on the first nitride semiconductor laminate, and a second conductivity type contact layer disposed on the second conductivity type cladding layer, the laser diode having a first conductivity type contact electrode disposed in a part of an exposed region of the first conductivity type cladding layer of the first nitride semiconductor laminate, and a second conductivity type contact electrode disposed on the second conductivity type cladding layer of the first nitride semiconductor laminate, and the light receiving element having two or more second conductivity type contact electrodes disposed on the second conductivity type cladding layer of the second nitride semiconductor laminate. The light receiving element is disposed at a position facing a reflecting surface located opposite to a laser irradiation surface of the laser diode, and the second conductive type cladding layer is an Al cladding layer having an Al composition ratio e that decreases with increasing distance from the nitride semiconductor substrate. e Ga 1-e N (0.1≦e≦1) and having a narrower band gap than the light emitting layer. do. Effect of the Invention

[0009] According to one aspect of the present invention, the output of a laser diode can be monitored in real time using a light receiving element. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing an example of a schematic configuration of an optical device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0012] <Optical devices> The optical device according to the present embodiment includes a nitride semiconductor substrate including aluminum (Al), a laser diode formed on the nitride semiconductor substrate and having a first nitride semiconductor stack, and a light receiving element formed on the nitride semiconductor substrate and having a second nitride semiconductor stack, each of the first nitride semiconductor stack and the second nitride semiconductor stack including a first conductive type cladding layer having a nitride semiconductor layer having a first conductive type conductivity, a light emitting layer disposed on the first conductive type cladding layer and formed of a nitride semiconductor layer including one or more quantum wells, and a second conductive type a second conductivity type cladding layer including a nitride semiconductor layer having conductivity, and a second conductivity type contact layer on the second conductivity type cladding layer, the laser diode has a first conductivity type contact electrode arranged in a part of an exposed region of the first conductivity type cladding layer of the first nitride semiconductor laminate, the light receiving element has a second conductivity type contact electrode on a mesa portion of the second conductivity type cladding layer, and the second nitride semiconductor laminate has two or more second conductivity type contact electrodes arranged on the second conductivity type cladding layer of the second nitride semiconductor laminate of the second nitride semiconductor laminate. A structure from the first conductivity type cladding layer to the second conductivity type contact layer of the first nitride semiconductor laminate is identical to a structure from the first conductivity type cladding layer to the second conductivity type contact layer of the second nitride semiconductor laminate.

[0013] (substrate) The substrate provided in the optical device according to this embodiment includes a nitride semiconductor containing Al. The nitride semiconductor containing Al is, for example, aluminum nitride (AlN). That is, the substrate is preferably an AlN single crystal substrate. The nitride semiconductor containing Al is not limited to AlN, and may be, for example, aluminum gallium nitride (AlGaN). For example, when the substrate is a nitride semiconductor single crystal substrate such as AlN or AlGaN, the difference in lattice constant between the substrate and the nitride semiconductor layer formed on the substrate becomes small, and the nitride semiconductor layer can be grown in a lattice-matched system. This makes it possible to reduce threading dislocations in the substrate. The threading dislocation density of the substrate is 5×10 4 cm -2It is preferable that the threshold value of the oscillation current is 1×10 or less. 3 cm -2 More than 1×10 4 cm -2 The following is more preferred:

[0014] Here, the wording "comprises" in the expression "the substrate comprises a nitride semiconductor..." means that the layer mainly contains a nitride semiconductor, but this expression also includes cases where other elements are included. Specifically, this expression also includes cases where the composition of the nitride semiconductor layer is slightly changed by adding a small amount of other elements (for example, a few percent or less of elements such as gallium (Ga) (when Ga is not the main element), indium (In), arsenic (As), phosphorus (P), or antimony (Sb)). In expressions regarding the composition of other layers, the wording "comprises" has the same meaning. Also, the small amount of elements contained is not limited to the above.

[0015] The substrate may be doped with donor or acceptor impurities to be n-type or p-type. The substrate may be made of a nitride semiconductor such as AlN or sapphire (Al 2 O 3 ), silicon (Si), silicon carbide (SiC), magnesium oxide (MgO), gallium oxide (Ga 2 O 3 ), zinc oxide (ZnO), gallium nitride (GaN), or indium nitride (InN).

[0016] The substrate preferably has a thickness of 100 μm or more and 600 μm or less, for example. The surface orientation of the substrate may be c-plane (0001), a-plane (11-20), m-plane (10-10), etc., and a c-plane (0001) substrate is more preferable. Furthermore, the laser diode and the light receiving element can be formed on a surface tilted at some angle (for example, -4° to 4°, preferably -0.4° to 0.4°) from the normal direction of the c-plane (0001), but this is not limited thereto.

[0017] (First conductive type cladding layer) The first conductivity type clad layer provided in the optical device according to this embodiment is a layer of a nitride semiconductor containing Al and Ga. The first conductivity type clad layer is formed on a substrate. Here, for example, in the expression "the first conductivity type clad layer is formed on the substrate", the word "on" means that the first conductivity type clad layer is formed on the substrate. Further, the above expression also includes the case where another layer further exists between the substrate and the first conductivity type clad layer. In the relationship between other layers as well, the word "above" has the same meaning. For example, when the second conductivity type clad layer is formed via an electron blocking layer on a p-type waveguide layer, it is also included in the expression "the second conductivity type clad layer is formed on the p-type waveguide layer".

[0018] Also, in the description of this embodiment, "the first conductivity type" and "the second conductivity type" each mean a semiconductor indicating a different conductivity type. For example, when one of "the first conductivity type" and "the second conductivity type" is n-type conductivity, the other of "the first conductivity type" and "the second conductivity type" is p-type conductivity. Although not particularly limited, the first conductivity type clad layer is, for example, Al a Ga (1-a) N (0 < a < 1). Thus, when forming a material corresponding to the bandgap energy in the deep ultraviolet region as the light-emitting layer, it is possible to enhance the crystallinity of the light-emitting layer and improve the light-emitting efficiency. From the viewpoint of realizing high light-emitting efficiency, the nitride semiconductor constituting the first conductivity type clad layer is preferably a mixed crystal of AlN and GaN.

[0019] Also, from the viewpoint of growing with complete strain with respect to the substrate, the first conductivity type clad layer is more preferably formed of Al a Ga (1-a) N (0.6 ≤ a ≤ 0.8). When the first conductivity type clad layer is an n-type conductive semiconductor layer, group V elements other than N such as P, As, Sb, and impurities such as C, H, F, O, Mg, Si may be mixed, but the types of impurity elements are not limited to this.

[0020] From the viewpoint of reducing electrical resistance and the ease of obtaining raw materials, the impurity contained in the first conductive type cladding layer is preferably Si, and the impurity concentration is 5×10 18 cm -3 5×10 or more 19 cm -3 It is preferable that:

[0021] From the viewpoints of relaxation and film resistance, the first conductivity type cladding layer preferably has a layer thickness of 200 nm or more and 800 nm or less, more preferably 300 nm or more and 750 nm or less, and further preferably 300 nm or more and 500 nm or less.

[0022] The first-conductivity-type cladding layer may be a gradient layer in which the Al composition ratio increases in the direction away from the substrate for the purpose of controlling the longitudinal conductivity, etc. In this case, the above-mentioned limitation on the Al composition ratio can be the Al composition ratio averaged over the thickness of the first-conductivity-type cladding layer at each position in the thickness direction of the first-conductivity-type cladding layer, and a similar embodiment can be adopted.

[0023] (Waveguide layer) From the viewpoint of light confinement, the optical device according to the present embodiment may include a first-conductivity-type waveguide layer disposed between the first-conductivity-type cladding layer and the light-emitting layer to confine light in the light-emitting layer, and a second-conductivity-type waveguide layer disposed between the second-conductivity-type cladding layer and the light-emitting layer to confine light in the light-emitting layer.

[0024] The waveguide layers are formed above and below the light emitting layer, sandwiching it between them, and have the effect of confining the light emitted from the light emitting layer within the light emitting layer. In other words, the waveguide layer is composed of two layers: a portion on the first conductive type cladding layer side of the light emitting layer (first conductive type waveguide layer), and a portion on the second conductive type cladding layer side of the light emitting layer (second conductive type waveguide layer).

[0025] From the perspective of optical confinement, the waveguide layer is preferably a nitride semiconductor containing at least one of Al and Ga having a higher bandgap than the light-emitting layer. The waveguide layer preferably has an Al composition ratio and a film thickness capable of increasing the overlap between the electric field intensity distribution of the light standing in the device and the light-emitting layer. In particular, the film thickness ratio between the first-conductivity-type waveguide layer and the second-conductivity-type waveguide layer can vary depending on the optical confinement in the light-emitting layer and the Al composition ratio of AlGaN in the first-conductivity-type cladding layer and the second-conductivity-type cladding layer. From the perspective of carrier confinement in the light-emitting layer, the light-emitting layer is Al b Ga (1-b) N (0 < b < 1), and when the waveguide layer is Al c Ga (1-c) N (0 < c < 1), the Al composition ratio is more preferably b < c and c ≥ b + 0.05. For example, when taking the light-emitting layer with an emission wavelength of 265 nm as an example, b = 0.52, and c is preferably 0.57 or more. Also, from the perspectives of optical confinement and sheet resistance, the film thickness of each of the first-conductivity-type waveguide layer and the second-conductivity-type waveguide layer is preferably 70 to 150 nm.

[0026] The Al composition ratios of the first-conductivity-type waveguide layer and the second-conductivity-type waveguide layer are preferably uniform in the film thickness direction, but this is not the case. In order to avoid light absorption by the metal present on the second-conductivity-type contact, the Al composition ratio of the second-conductivity-type waveguide layer may be higher than that of the first-conductivity-type waveguide layer. For the same purpose, the film thickness of the second-conductivity-type waveguide layer may be thicker than that of the first-conductivity-type waveguide.

[0027] When the first-conductivity-type waveguide layer is an n-type conductive semiconductor layer, for the purpose of obtaining the same conductivity type as the first-conductivity-type cladding layer, in addition to N, group V elements other than N such as P, As, Sb, and impurities such as H, C, O, F, Mg, Si may be mixed in, but this is not the case.

[0028] (Light-emitting layer)

[0029] The light-emitting layer is a layer of a nitride semiconductor containing Al and Ga, sandwiched between a first-conductivity-type waveguide layer and a second-conductivity-type waveguide layer. From the viewpoint of achieving high luminous efficiency, the nitride semiconductor contained in the light-emitting layer is preferably, for example, a mixed crystal of AlN and GaN, for example, Al b Ga (1-b) N (0 < b < 1). In addition to N, the light-emitting layer may contain impurities such as group V elements other than N such as P, As, and Sb, and impurities such as C, H, F, O, Mg, and Si, but this is not limiting.

[0030] Also, the light-emitting layer can have either a multiple quantum well structure or a single quantum well structure. Although it depends on the longitudinal conductivity of each of the first-conductivity-type cladding layer and the second-conductivity-type cladding layer, the number of quantum well structures is preferably either 1 or 3. For the purpose of reducing the influence of crystal defects in the light-emitting layer, elements such as Si, Sb, and P are contained in part or all of the light-emitting layer at an impurity concentration of 1×10 15 cm -3 or higher.

[0031] (Second-conductivity-type cladding layer) The second-conductivity-type cladding layer is formed on the light-emitting layer and the waveguide layer, and is a nitride semiconductor layer containing Al and Ga having second-conductivity-type conductivity. The second-conductivity-type cladding layer is formed, for example, by A d Ga (1-d) N (0 < d < 1). Thereby, such a second-conductivity-type cladding layer is easily lattice-matched to the waveguide layer, and it is possible to suppress the threading dislocation density.

[0032] The second-conductivity-type cladding layer has conductivity sufficient to inject holes into the light-emitting layer, and is not particularly limited as long as it can increase the overlap between the electric field intensity distribution of the stationary optical mode in the optical device and the light-emitting layer (that is, increase the optical confinement). For example, it may be p-type AlGaN doped with Mg. Also, when the second-conductivity-type cladding layer is a p-type conductive semiconductor layer, impurities such as group V elements other than N such as P, As, and Sb, and impurities such as C, H, F, O, Mg, and Si may be mixed therein, but the types of impurity elements are not limited to this.

[0033] From the viewpoint of more efficiently injecting holes into the light-emitting layer, the second conductive type clad layer has a composition gradient such that the Al composition ratio e decreases in the direction away from the upper surface of the substrate (i.e., the Al composition ratio becomes smaller as it moves away from the substrate), and is composed of Al e Ga (1-e) N formed composition gradient layer (second conductive type vertical conductive layer (e.g., p-type vertical conductive layer), and Al f Ga (1-f) It preferably has a second conductive type lateral conductive layer (e.g., p-type lateral conductive layer) containing N (0 < f ≦ 1). The profile (gradient) of the Al composition ratio f in the second conductive type vertical conductive layer may decrease continuously or discontinuously. Here, "decreasing discontinuously" means including a portion in the film of the second conductive type vertical conductive layer where the Al composition ratio e is the same. That is, the second conductive type vertical conductive layer may include a portion where the Al composition ratio e does not decrease in the direction away from the substrate, but does not include an increasing portion. Further, the second conductive type vertical conductive layer may have a film thickness of less than 0.5 μm.

[0034] From the viewpoint of efficiently converting light into electron-hole pairs in the light-receiving element, the second conductive type vertical conductive layer preferably has a bandgap that is at least narrower than that of the light-emitting layer. That is, from this viewpoint, the second conductive type vertical conductive layer is preferably a layer formed of Al e Ga (1-e) N (0.1 ≦ e ≦ b) and is at least smaller than the bandgap of the light-emitting layer.

[0035] From the viewpoint of lattice matching, the second conductive type vertical conductive layer is preferably 500 nm or less. Further, from the viewpoints of light confinement and carrier injection, the second conductive type vertical conductive layer is more preferably 250 nm or more and 450 nm or less, and even more preferably 300 nm or more and 400 nm or less.

[0036] For the purpose of suppressing the diffusion of impurities, it is preferable that the second conductivity type vertical conduction layer is not intentionally mixed with impurities such as H, Mg, Be, Zn, Si, B, etc. in the region close to the second conductivity type waveguide layer, that is, it is preferable that it is in an undoped state. In other words, the second conductivity type vertical conduction layer may have an undoped region in a certain range including the interface with the second conductivity type waveguide layer in the thickness direction of the second conductivity type cladding layer. Here, the term "undoped" means that the above elements are not intentionally supplied to the target layer as elements in the process of forming the target layer, but it is also preferable that elements derived from raw materials and manufacturing equipment are not intentionally supplied to the target layer, for example, in a range of 10 16 cm -3 This does not apply when the second conductive type vertical conduction layer is mixed in the following range. The undoped region of the second conductive type vertical conduction layer includes at least the boundary with the second conductive type waveguide layer, but the size is not limited. For example, the entire region of the second conductive type vertical conduction layer may be undoped. As another example, 50% of the region of the second conductive type vertical conduction layer closer to the second conductive type waveguide layer than the second conductive type lateral conduction layer in the thickness direction of the second conductive type cladding layer may be undoped. As another example, about 10% of the region of the second conductive type vertical conduction layer closer to the second conductive type waveguide layer in the thickness direction of the second conductive type cladding layer may be undoped.

[0037] In this way, even in an undoped state, holes are generated in the second conductive vertical conductive layer due to polarization. From the viewpoint of carrier injection efficiency in a laser diode and photocurrent in a light receiving element, the hole concentration (carrier concentration) of the second conductive cladding layer is set to 1×10 -17 cm -3 More than 1×10 -19 cm -3 It is preferable that:

[0038] The second conductive type lateral conductive layer is formed on the second conductive type vertical conductive layer and is made of Al f Ga (1-f)It is a layer containing N(0 < f ≤ 1). The second-conductivity-type lateral conduction layer can be intentionally doped with impurities such as H, Mg, Be, Zn, Si, B, etc. for the purpose of controlling the longitudinal resistivity of the second-conductivity-type lateral conduction layer. The amount of the doped impurities can be, for example, 1×10 19 cm -3 or more and 5×10 21 cm -3 or less.

[0039] From the viewpoint of facilitating the quantum tunneling of the penetrating carriers, the second-conductivity-type lateral conduction layer preferably has a film thickness of 20 nm or less, more preferably may have a film thickness of 10 nm or less, and even more preferably may have a film thickness of 5 nm or less.

[0040] At the adjacent surface (i.e., the interface) between the second-conductivity-type lateral conduction layer and the second-conductivity-type longitudinal conduction layer, the Al composition ratio f may be larger than the minimum value of the Al composition ratio e in the second-conductivity-type longitudinal conduction layer. Furthermore, the second-conductivity-type lateral conduction layer is preferably completely strained with respect to the substrate. Such a second-conductivity-type lateral conduction layer can improve the lateral conductivity by making the net internal electric field accumulated on the surface and near the surface of the second-conductivity-type lateral conduction layer negative, thereby inducing holes at the interface.

[0041] Each of the first nitride semiconductor laminate and the second nitride semiconductor laminate is disposed between the second-conductivity-type longitudinal conduction layer and the second-conductivity-type waveguide layer and may have an Al g Ga 1-g N(0 < g ≤ 1.0) layer. An Al g Ga 1-gThe intermediate layer formed of N (0 < g ≤ 1.0) layers may be configured such that the Al composition ratio g increases in the direction away from the upper surface of the substrate. By having such an Al composition ratio g in the intermediate layer, at least one of the effects of improving the conductivity between the second conductivity type vertical conduction layer and the second conductivity type waveguide layer and the effect of being able to form the second conductivity type lateral conduction layer and the second conductivity type contact layer with complete strain can be obtained. The intermediate layer provided between the second conductivity type vertical conduction layer and the second conductivity type waveguide layer may be a mixed crystal that is not a bandgap that does not absorb light of a desired emission wavelength, and preferably has a film thickness of 50 nm or less, and may be an undoped layer.

[0042] The second conductivity type vertical conduction layer has the action of generating holes by the polarization doping effect and efficiently injecting the holes into the active layer in the light emitting layer. Therefore, by providing the second conductivity type vertical conduction layer between the light emitting layer and the second conductivity type contact layer, the carrier injection efficiency of the laser diode can be increased and the threshold voltage can be reduced. The second conductivity type lateral conduction layer has the effect of spreading the hole distribution narrowed by the electric field concentrated under the electrode in the lateral direction. By this effect, the carrier injection efficiency can be increased in the same manner as the second conductivity type vertical conduction layer.

[0043] (Second conductivity type contact layer) The nitride semiconductor laminate of the optical device according to the present embodiment may further include a second conductivity type contact layer disposed on the second conductivity type clad layer. The nitride semiconductor constituting the second conductivity type contact layer is formed of, for example, GaN, AlN, or InN and mixed crystals containing them. The second conductivity type contact layer may be mixed with impurities such as group V elements other than N such as P, As, Sb, carbon (C), helium (H), fluorine (F), oxygen (O), Mg, Si, beryllium (Be). From the versatility of the source gas, it is preferable that the impurity contained in the second conductivity type contact layer is Mg. From the viewpoint of reducing the contact resistance between the second conductivity type contact layer and the second conductivity type clad layer, the concentration of Mg is 8×10 19 cm -3 or more and 5×10 21 cm -3More preferably, the Mg concentration is 5×10 20 cm -3 5×10 or more 21 cm -3 It would be better if it was less than this.

[0044] In addition, the thickness of the second conductive type contact layer is 1 nm or more and 20 nm or less. The thinner the second conductive type contact layer is, the more efficient the carrier injection of the laser diode is. Conversely, the thicker the second conductive type contact layer is, the more efficient the carrier injection of the laser diode is.

[0045] (Electron Block Layer) The nitride semiconductor stack of the optical device according to this embodiment may further include an electron blocking layer having a band gap larger than that of the second conductivity type waveguide layer, inside the second conductivity type waveguide layer, between the second conductivity type waveguide layer and the light emitting layer (for example, at the middle), between the second conductivity type waveguide layer and the second conductivity type vertical conductive layer (for example, at the middle), or in a part of the second conductivity type waveguide layer. The film thickness of the electron blocking layer is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less so that holes can easily quantum penetrate the electron blocking layer.

[0046] (Mesa structure) The optical device according to this embodiment has a first mesa structure formed to electrically isolate a second conductivity type layer and a first conductivity type layer in a laser diode having a first nitride semiconductor stack, and a second mesa structure formed to isolate the first nitride semiconductor stack and the second nitride semiconductor stack, respectively.

[0047] From the viewpoint of current confinement of the laser and amplification by reflection at the end facet, the first mesa structure is preferably rectangular in plan view, has long and short sides, and the long sides are preferably parallel to the <1-100> direction. The reason why the long sides of the first mesa structure are preferably parallel to the <1-100> direction is that when the resonator mirror end face of the laser resonator is obtained by various methods such as cleavage and etching, the atomically flat (1-100) plane can be most easily formed. In other words, it is preferable that the first mesa structure has a resonator in which the mesa end face that is parallel to the (1-100) plane in plan view with respect to the crystal orientation of the nitride semiconductor substrate serves as the resonator mirror end face, and the laser diode is an edge-emitting laser diode that emits light in the <1-100> direction.

[0048] The nitride semiconductor laminate may have a plurality of mesa structures. That is, the nitride semiconductor laminate may have a form having a plurality of discontinuous side surfaces. From the viewpoint of efficiently injecting power into the light emitting layer, it may be preferable to have a mesa structure (also called a ridge portion) in which the second conductive type contact layer, or the second conductive type contact layer and the second conductive type cladding layer are partly or entirely removed except for the vicinity of the second electrode. In this case, the ridge portion is different from the mesa structure for exposing the first conductive type cladding layer, and for example, the side surface of the ridge portion is understood to be different from the side surface of the mesa structure.

[0049] The second mesa structure is not particularly limited as long as it can electrically separate the first nitride semiconductor laminate and the second nitride semiconductor laminate. From the viewpoint of reducing the influence of heat generated from the first nitride semiconductor laminate, it is preferable that at least a part of the n-clad is exposed. More preferably, a part of the substrate is exposed. That is, the first mesa structure can be formed first, and then a part of the laminate can be covered with a protective layer, and then the second mesa structure can be formed, or the first mesa structure can be formed by forming the second mesa structure first and then covering a part of the laminate with a protective layer. When the optical device has such a first mesa structure and a second mesa structure, the laser diode and the light receiving element are electrically separated from each other except for the nitride semiconductor substrate and a part of the first conductive type clad layer.

[0050] From the viewpoint of monitoring the intensity of the laser light irradiated from the first nitride semiconductor laminate, the second mesa structure is preferably disposed on the opposite side of the surface irradiated with the laser and receives the leakage light of the reflection. From the viewpoint of receiving as much laser light as possible, the second mesa structure is preferably a rectangle long in the direction of laser irradiation. From the viewpoint of chip yield, the second mesa structure is preferably the same width as the mesa structure of the laser diode, but is not limited thereto. Furthermore, the second mesa structure may have a material or shape processed on the side to facilitate absorption of the laser light. From the viewpoint of absorption of the laser light, the distance between the first mesa structure and the second mesa structure is preferably 1 μm or more and 1000 μm or less. That is, the distance between the laser diode and the light receiving element may be 1 μm or more and 1000 μm or less. In this case, the distance means the shortest distance from the reflecting surface located opposite the laser irradiated surface included in the first mesa structure to the second mesa structure when measured horizontally.

[0051] (electrode) Electrical contact to the optical device according to the present embodiment is achieved in the first nitride semiconductor stack by a second electrode disposed on the second conductivity type cladding layer and a first electrode disposed in contact with the first conductivity type cladding layer. For example, the electrical contact can be made by disposing an electrode on the backside of the substrate. Alternatively, the electrical contact can be made by removing, for example by chemical or dry etching, various upper layers of the laser diode to expose the first conductivity type cladding layer in one or more regions adjacent the second conductivity type cladding layer, and disposing an electrode on the exposed first conductivity type cladding layer.

[0052] When the first conductive type cladding layer is an n-type cladding layer, the first electrode is made of a metal such as Al, titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), Zr, or a mixed crystal thereof, or indium oxide (ITO) or Ga 2 O 3 The conductive oxide may be used.

[0053] When the second conductive type cladding layer is a p-type cladding layer, the second electrode is made of a metal such as Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Ir, Zr, or a mixed crystal thereof, or ITO or Ga 2 O 3 The conductive oxide may be used.

[0054] The arrangement area and shape of the electrode are not limited as long as electrical contact is obtained with the first conductive type cladding layer and the second conductive type contact layer, respectively. From the viewpoint of internal loss, the second electrode is preferably arranged in an area on the second conductive type cladding layer that is 5 μm or more away from the side surface of the mesa structure in a plan view.

[0055] Electrical contact with the second nitride semiconductor laminate is achieved by at least two or more second conductivity type contact electrodes (third electrodes) formed on the second conductivity type cladding layer. When the second conductivity type cladding layer is a p-type cladding layer, the third electrodes are made of metals such as Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Ir, Zr, or mixed crystals thereof, or ITO or Ga 2 O 3From the viewpoint of efficiently extracting photocurrent, the third electrode is preferably an ohmic electrode with respect to the nitride semiconductor layer (the second conductive cladding layer in this embodiment) with which it is in contact. The term "ohmic electrode" as used here means that when the voltage-current characteristics between the two electrodes are measured, the voltage obtained by extrapolating from the slope at the point where the change is most linear is 0.5 V or less. In addition, in this case, the contact resistance between the third electrode and the second conductive cladding layer is 1×10 -4 Ωcm 2 More than 1×10 -2 Ωcm 2 From the viewpoint of efficiently extracting photocurrent, it is preferable that the distance between two or more third electrodes is 2 μm or more and 20 μm or less. The shape of the third electrodes is not particularly limited, and is not limited to a circular, rectangular, comb-shaped, or the like. The number of third electrodes is also not particularly limited as long as a voltage can be applied between the third electrodes, and two or more third electrodes may be connected in series. From the viewpoint of the manufacturing process, it is preferable to arrange two third electrodes opposite each other.

[0056] (Photodetector) The light receiving element provided in the optical device according to this embodiment has two or more second conductive type contact electrodes on the second conductive type cladding layer. In general laser diodes and light emitting diodes (LEDs), a depletion layer is often formed in the light emitting layer sandwiched between a p-type layer and an n-type layer. Therefore, two or more identical laser diodes can be arranged on the same substrate, and one of them can be used as a light receiving element. That is, by injecting a current into the pn junction of the laser diode and applying a voltage between the pn junction of the laser diode used as the light receiving element, the light irradiated from the laser diode can be received and extracted as a photocurrent. On the other hand, since the optical device according to this embodiment has a structure having a composition gradient layer in the second conductive type cladding layer, the depletion layer is formed on the second conductive type cladding layer side, not in the light emitting layer. Since the light irradiated from the laser diode is light equivalent to the band gap of the light emitting layer, if a depletion layer is not formed in the light emitting layer, the light is received by the light emitting layer, and the generated electron-hole pairs are recombined and disappear without being extracted as a photocurrent. When two or more electrodes are disposed on the second conductive cladding and a voltage is applied between the two or more electrodes, the electrical resistance of the second conductive cladding layer can be read as a current value (a voltage value when converted by resistance). When light is irradiated from the light emitting layer, the second conductive cladding layer is a composition gradient layer and has a layer having a band gap narrower than the band gap of the light emitting layer. Therefore, excited electron-hole pairs are generated in the second conductive cladding layer. This causes a change in the electrical resistance of the second conductive cladding layer, and the change can be read as a current between the two or more electrodes. The current between the two or more electrodes can be read by various methods, such as a method of directly reading it as a current value, or a method of amplifying the voltage drop of a resistor element connected between a voltage source that generates a voltage to be applied between the two or more electrodes and these electrodes and reading it as a voltage. In other words, it can be used as a photoconductor type light receiving element that monitors the change in the electrical resistance of the second conductive cladding layer. In this way, the light receiving element provided in the optical device according to this embodiment is a photoconductor type sensor.

[0057] By forming the light receiving element and the laser diode on the same substrate, it is possible to significantly reduce manufacturing costs. In addition, the positioning of the laser diode and the light receiving element, which is important in an optical device that has a light receiving element and a laser diode monolithically, is also very simple because it is uniquely determined by the photomask during the process. Furthermore, regarding temperature characteristics, since they are formed on the same substrate, there is an advantage that correction by offset processing etc. can be easily performed.

[0058] (Optical device manufacturing method) The optical device according to this embodiment is manufactured through a process of forming each layer on a substrate. The substrate is formed by a general substrate growth method such as a vapor phase growth method, such as a sublimation method or a hydride vapor phase epitaxy (HVPE) method, or a liquid phase growth method.

[0059] The process of forming each layer on the substrate can be performed by, for example, molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), metal organic chemical vapor deposition (MOCVD), or the like.

[0060] Here, among the layers formed on the substrate, the nitride semiconductor layer is formed from an Al source containing, for example, trimethylaluminum (TMAl), a Ga source containing, for example, trimethylgallium (TMGa) or triethylgallium (TEGa), or ammonia (NH 3 ) can be used as a N source material.

[0061] Optical devices are manufactured by a process of removing unnecessary portions of each layer formed on a substrate by etching, which can be performed, for example, by inductively coupled plasma (ICP) etching.

[0062] The optical device can also be manufactured through a process of forming electrodes, which can be performed in a variety of ways, for example by depositing metals by electron beam deposition (EB).

[0063] Here, the optical device is manufactured by dividing the substrate on which each layer has been formed through the above-mentioned steps into individual pieces by dicing.

[0064] The electrodes are formed by, but not limited to, resistance heating deposition, electron gun deposition, sputtering, or the like. The electrodes may be formed as a single layer or as a laminate of multiple layers. After the layers are formed, the electrodes may be heat-treated in an oxygen, nitrogen, or air atmosphere.

[0065] Next, the optical device according to this embodiment will be described in more detail with reference to the drawings.

[0066] <Embodiment> 1 is a schematic cross-sectional view of an optical device 1 according to one embodiment of the present invention. A laser diode 10 includes a first nitride semiconductor stack 11 on a nitride semiconductor substrate 100. A light-receiving element 20 includes a second nitride semiconductor stack 21 on the nitride semiconductor substrate 100. The first nitride semiconductor stack 11 and the second nitride semiconductor stack 21 have the same layer configuration.

[0067] The first nitride semiconductor stack 11 has an n-type cladding layer 111 including a nitride semiconductor layer having n-type conductivity (an example of a first conductivity type), a light emitting layer 113 disposed on the n-type cladding layer 111 and formed of a nitride semiconductor layer including one or more quantum wells, a p-type cladding layer 115 disposed on the light emitting layer 113 and including a nitride semiconductor layer having p-type conductivity (an example of a second conductivity type), and a p-type contact layer 116 disposed on the p-type cladding layer 115. The p-type contact layer 116 has a nitride semiconductor including, for example, GaN.

[0068] Moreover, first nitride semiconductor stack 11 has n-type waveguide layer 112 disposed between n-type cladding layer 111 and light emitting layer 113 to confine light in light emitting layer 113, and p-type waveguide layer 114 disposed between p-type cladding layer 115 and light emitting layer 113 to confine light in light emitting layer 113. The n-type waveguide layer 112 and p-type waveguide layer 114 are suitable configurations for operating first nitride semiconductor stack 11 as part of a laser diode.

[0069] The second nitride semiconductor stack 21 has an n-type cladding layer 211 including a nitride semiconductor layer having n-type conductivity, a light emitting layer 213 disposed on the n-type cladding layer 211 and formed of a nitride semiconductor layer including one or more quantum wells, a p-type cladding layer 215 disposed on the light emitting layer 213 and including a nitride semiconductor layer having p-type conductivity, and a p-type contact layer 216 disposed on the p-type cladding layer 215.

[0070] The second nitride semiconductor stack 21 has an n-type waveguide layer 212 disposed between the n-type cladding layer 211 and the light emitting layer 213 to confine light in the light emitting layer 213, and a p-type waveguide layer 214 disposed between the p-type cladding layer 215 and the light emitting layer 213 to confine light in the light emitting layer 213. If the first nitride semiconductor stack 11 does not have the n-type waveguide layer 112 and the p-type waveguide layer 114, the second nitride semiconductor stack 21 also does not have the n-type waveguide layer 212 and the p-type waveguide layer 214.

[0071] The n-type cladding layers 111, 211 correspond to the above-mentioned first-conductivity-type cladding layer. The n-type waveguide layers 112, 212 correspond to the above-mentioned first-conductivity-type waveguide layer. The light-emitting layers 113, 213 correspond to the above-mentioned light-emitting layer. The p-type waveguide layers 114, 214 correspond to the above-mentioned second-conductivity-type waveguide layer. The p-type cladding layers 115, 215 correspond to the above-mentioned second-conductivity-type cladding layer. The p-type contact layers 116, 216 correspond to the above-mentioned second-conductivity-type contact layer.

[0072] The laser diode 10 has an n-type contact electrode 12 disposed on a part of the exposed region of the n-type cladding layer 111, and a p-type contact electrode 13 disposed on the p-type cladding layer 115. For ease of understanding, a voltage source that generates a voltage applied between the n-type contact electrode 12 and the p-type contact electrode 13 is illustrated in FIG.

[0073] The light receiving element 20 has two or more (two in this embodiment) p-type contact electrodes 23 on the p-type cladding layer. For ease of understanding, a voltage source that generates a voltage applied between the two p-type contact electrodes 23 to read out a current change based on a change in the electrical resistance of the p-type cladding layer 215 is illustrated in FIG.

[0074] The n-type contact electrode 12 corresponds to the above-mentioned first electrode, the p-type contact electrode 13 corresponds to the above-mentioned second electrode, and the p-type contact electrode 23 corresponds to the above-mentioned second conductivity type contact electrode (i.e., third electrode).

[0075] In the laser diode 10, by applying a bias between the n-type contact electrode 12 and the p-type contact electrode 13, electrons and holes are supplied to the light emitting layer 113 and recombined to generate light with a wavelength according to the band gap of the light emitting layer 113. The light generated in the light emitting layer 113 of the laser diode 10 causes stimulated emission, and is amplified and oscillated in the resonator structure.

[0076] When the light emitted from the laser diode 10 enters the p-type cladding layer 215 of the light receiving element 20, electrons and holes are generated in the p-type cladding layer 215, which changes the resistance of the p-type cladding layer 215. At this time, if a constant bias is applied between the two p-type contact electrodes 13 of the light receiving element 20, it is possible to detect the change in resistance of the p-type cladding layer 215. In the optical device 1, it becomes possible to monitor the output of the laser diode 10 from the detected change in resistance of the p-type cladding layer 215.

[0077] (Measurement of impurity and doping concentrations) The concentrations of dopants and impurities contained in each layer constituting the nitride semiconductor substrate 100, the first nitride semiconductor stack 11, and the second nitride semiconductor stack 21 provided in the optical device 1 can be measured by secondary ion mass spectrometry (SIMS).

[0078] When the concentration of dopants and impurities contained in each layer is measured by SIMS after being processed into the optical device 1, the measurement can be performed in a state in which the n-type contact electrode 12, the p-type contact electrode 13, and the p-type contact electrode 23 are removed by chemical etching or physical polishing. The concentration of dopants and impurities contained in each layer can also be measured by sputtering from the front side of both sides of the nitride semiconductor substrate 100 on which the n-type contact electrode 12, the p-type contact electrode 13, and the p-type contact electrode 23 are not formed.

[0079] Specifically, SIMS measurements are performed under the measurement conditions provided by Evans Analytical Group (EAG), Inc. A cesium (Cs) ion beam with an energy of 14.5 keV is used to sputter the sample during the measurements.

[0080] (Layer thickness measurement method) The thickness of each layer constituting the optical device 1 can be measured by cutting out a predetermined cross section perpendicular to the nitride semiconductor substrate 100, observing the cross section with a transmission electron microscope (TEM), and using the length measurement function of the TEM. As a measurement method, first, a cross section perpendicular to the main surface of the nitride semiconductor substrate 100 of the optical device 1 (i.e., the surface on which the first nitride semiconductor laminate 11 and the second nitride semiconductor laminate 21 are formed) is observed with the TEM. Specifically, for example, the observation width is set to a range of 2 μm or more in a direction parallel to the main surface of the nitride semiconductor substrate 100 in a TEM image showing a cross section perpendicular to the main surface of the nitride semiconductor substrate 100 of the optical device 1. Within this observation width, contrast is observed at the interface between two layers with different compositions, so the thickness up to this interface is observed in a continuous observation region with a width of 200 nm. The thickness of each layer can be obtained by calculating the average thickness of each layer contained within this 200 nm wide observation region from five locations arbitrarily selected from the observation width of 2 μm or more described above.

[0081] (Method of measuring atomic concentration of each layer) The atomic concentration of each layer and hillock constituting the optical device 1 can be measured by reciprocal space mapping (RSM) using X-ray diffraction (XRD). Specifically, the lattice relaxation rate and Al composition relative to the substrate can be obtained by analyzing reciprocal space mapping data in the vicinity of a diffraction peak obtained using an asymmetric plane as a diffraction plane. Examples of the diffraction plane include the (10-15) plane and the (20-24) plane.

[0082] In addition, for layers that do not provide sufficient reflection intensity by XRD, such as compositionally graded layers and hillocks contained in the light-emitting layers 113, 213 and the p-type cladding layers 115, 215, the layer thicknesses can be measured by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and electron energy loss spectroscopy (EELS).

[0083] In EELS, the composition of a sample is analyzed by measuring the energy lost when an electron beam passes through the sample. Specifically, for example, the energy loss spectrum of the intensity of the transmitted electron beam is measured and analyzed for a thin-sectioned sample used in TEM observation. The peak position of the peak that appears near the energy loss of 20 eV changes depending on the composition of each layer, and the composition can be obtained from the peak position. In the same way as the layer thickness calculation method using TEM observation described above, the Al composition of each layer is obtained by calculating the average value of the Al composition in an observation width of 200 nm from five points arbitrarily selected from an observation area of ​​2 μm or more.

[0084] In EDX, characteristic X-rays generated by an electron beam in a thin-sectioned sample used in the above-mentioned TEM observation, etc. are measured and analyzed. In the same manner as the method for calculating layer thickness using TEM observation described above, the Al composition of each layer is obtained by calculating the average value of the Al composition in an observation width of 200 nm from five points arbitrarily selected from an observation region of 2 μm or more.

[0085] In XPS, the evaluation of the depth direction is possible by performing XPS measurement while performing sputter etching using an ion beam. The ion beam is generally Ar +However, other ion species such as Ar cluster ions may be used as long as they can be irradiated by an etching ion gun mounted on the XPS device. The XPS peak intensities of Al, Ga, and N are measured and analyzed to obtain the depth profile of the Al composition in each layer. Instead of sputter etching, the laser diode may be obliquely polished so that a cross section perpendicular to the main surface of the nitride semiconductor substrate 100 is enlarged and exposed, and the exposed cross section may be measured by XPS.

[0086] The composition of each layer can be measured not only by XPS but also by Auger Electron Spectroscopy (AES). In this case, the composition can be measured by Auger Electron Spectroscopy on a cross section exposed by sputter etching or oblique polishing. The composition of each layer can also be measured by SEM-EDX measurement of a cross section exposed by oblique polishing.

[0087] (Optical device application fields) The optical device 1 according to this embodiment is applicable to devices in, for example, the medical and life science fields, the environmental field, the industrial and manufacturing fields, the lifestyle and home appliances fields, the agricultural field, and other fields. The optical device 1 is applicable to devices for synthesizing and decomposing medicines or chemical substances, devices for sterilizing liquids, gases, and solids (containers, food, medical equipment, etc.), devices for cleaning semiconductors, etc., devices for modifying the surfaces of films, glass, metals, etc., exposure devices for manufacturing semiconductors, FPDs, PCBs, and other electronic products, printing and coating devices, adhesive and sealing devices, transfer and molding devices for films, patterns, mockups, etc., and devices for measuring and inspecting banknotes, wounds, blood, chemical substances, etc.

[0088] Examples of liquid sterilization equipment include, but are not limited to, automatic ice makers, ice trays and ice storage containers in refrigerators, water tanks for ice makers, freezers, ice makers, humidifiers, dehumidifiers, cold water tanks, hot water tanks and flow piping for water servers, freezer-type water purifiers, portable water purifiers, water supply units, hot water heaters, wastewater treatment equipment, garbage disposers, toilet drain traps, washing machines, water sterilization modules for dialysis, connector sterilizers for peritoneal dialysis, and disaster water storage systems.

[0089] Examples of gas sterilization devices include, but are not limited to, air purifiers, air conditioners, ceiling fans, floor or bedding vacuum cleaners, futon dryers, shoe dryers, washing machines, clothes dryers, indoor germicidal lamps, storage ventilation systems, shoe boxes, chests of drawers, etc.

[0090] Examples of solid sterilization equipment (including surface sterilization equipment) include, but are not limited to, vacuum packing machines, belt conveyors, hand tool sterilization equipment for medical, dental, barber, and beauty salon use, toothbrushes, toothbrush holders, chopstick cases, cosmetic pouches, drain covers, toilet spot cleaners, and toilet lids.

[0091] Next, examples and comparative examples of the optical device 1 according to this embodiment will be described. Table 1 is a list summarizing the main parts of Examples 1 to 9 and Comparative Examples 1 to 3 of the optical device 1.

[0092] [Table 1]

[0093] [Example 1] As the nitride semiconductor substrate 100, an AlN single crystal substrate having a thickness of 550 μm and a (0001) plane was annealed using a metal-organic chemical vapor deposition (MOCVD) apparatus. The annealing process was carried out by placing the AlN single crystal substrate in an environment of 1300° C. and annealing the NH 3 Anneal for 5 min in H 2 Two sets of treatments were carried out, each set consisting of 5 minutes of annealing in the atmosphere.

[0094] Next, an AlN layer, which is a homoepitaxial layer, was formed on the AlN single crystal substrate. The AlN layer was formed to a thickness of 500 nm in an environment at 1200°C. At this time, the ratio of the supply rate of the group III element source gas to the supply rate of the nitrogen source gas (V / III ratio) was set to 50. The degree of vacuum in the chamber in which the annealing was performed was set to 50 mbar. The growth rate of the AlN layer was set to 0.5 μm / hr. Trimethylaluminum (TMAl) was used as the Al source, and ammonia (NH 3 ) was used.

[0095] On the AlN layer formed as described above, a first conductive type cladding layer was formed, a part of which would eventually become the n-type cladding layer 111, 211. The first conductive type cladding layer was an n-type AlGaN layer (Al: 70%, i.e., Al 0.70 Ga 0.30 The first conductive type cladding layer was formed to a thickness of 350 nm under the conditions of a temperature of 1080°C, a degree of vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the first conductive type cladding layer was 0.4 μm / hr. Trimethylaluminum (TMAl) was used as the Al raw material, triethylgallium (TEGa) was used as the Ga raw material, and ammonia (NH 3 ) was used as the silicon source. 4 ) was used.

[0096] Next, a first conductive type waveguide layer, a part of which will eventually become the n-type waveguide layer 112, 212, was formed on the first conductive type cladding layer. The first conductive type cladding layer was an n-type AlGaN layer (Al: 63%, i.e., Al 0.63 Ga 0.37The first conductive type waveguide layer was formed to a thickness of 60 nm under the conditions of a temperature of 1080°C, a degree of vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the first conductive type cladding layer was 0.35 μm / hr. Trimethylaluminum (TMAl) was used as the Al raw material, triethylgallium (TEGa) was used as the Ga raw material, and ammonia (NH 3 ) was used.

[0097] Next, a light emitting layer, a portion of which will eventually become the light emitting layer 113, 213, was formed on the first conductive type cladding layer. The light emitting layer was formed by depositing a film so as to have a multiple quantum well structure in which quantum well layers and barrier layers were laminated three times. Here, the quantum well layer was an AlGaN layer (Al: 52%, i.e., Al 0.52 Ga 0.48 The barrier layer having a thickness of 6.0 nm was an AlGaN layer (Al: 63%, i.e., Al 0.63 Ga 0.37 N layer).

[0098] The light-emitting layer was formed under conditions of a vacuum degree of 50 mbar and a V / III ratio of 4000. The growth rate of the quantum well layer was 0.18 μm / hr, and the growth rate of the barrier layer was 0.15 μm / hr.

[0099] Next, a second conductive type waveguide layer, a part of which will eventually become the p-type waveguide layer 114, 214, was formed on the light emitting layer. The second conductive type waveguide layer was an AlGaN layer containing no dopant (Al: 63%, i.e., Al 0.63 Ga 0.37 The second conductive type waveguide layer was formed to a thickness of 60 nm under the conditions of a temperature of 1080°C, a degree of vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the second conductive type waveguide layer was 0.35 μm / hr. Trimethylaluminum (TMAl) was used as the Al raw material, and triethylgallium (TEGa) was used as the Ga raw material.

[0100] Next, a second-conductivity-type cladding layer (graded layer), a part of which will eventually become the p-type cladding layer 115, 215, was formed on the second-conductivity-type waveguide layer. The second-conductivity-type cladding layer has a laminated structure of an AlGaN layer having a thickness of 20 nm, in which the Al composition is distributed in the direction away from the AlN single crystal substrate and changes from Al=0.63 to 1.0, and an AlGaN layer having a thickness of 350 nm, in which the Al composition is distributed in the direction away from the AlN single crystal substrate and changes from Al=1.0 to 0.3. The second-conductivity-type cladding layer was formed under the conditions of a temperature of 1080°C, a degree of vacuum of 50 mbar, and a V / III ratio of 4000. The growth rate of the second-conductivity-type cladding layer at this time was 0.3 to 0.5 μm / hr. Trimethylaluminum (TMAl) was used as the Al raw material. Triethylgallium (TEGa) was used as the Ga raw material.

[0101] Next, a nitride semiconductor layer having p-type conductivity (p-type contact layer) was formed on the second conductivity type cladding layer, a portion of which would eventually become the p-type contact layers 116, 216. Here, the p-type contact layer was a layer having a laminated structure of an AlGaN layer having a thickness of 30 nm and varying Al=0.7 to 0.4 using Mg as a dopant impurity, and a GaN layer having a thickness of 10 nm (i.e., Al: 0%).

[0102] The p-type contact layer was formed under the conditions of a temperature of 950° C., a degree of vacuum of 150 mbar, and a V / III ratio of 3650. The growth rate of the p-type contact layer at this time was 0.2 μm / hr.

[0103] In this manner, a nitride semiconductor stack was formed on the AlN single crystal substrate, a portion of which would eventually become the first nitride semiconductor stack 11 and the second nitride semiconductor stack 21. When reciprocal lattice mapping measurement was performed by XRD on this nitride semiconductor stack, it was found that pseudomorphic growth without relaxation had occurred from the first conductivity type cladding layer to the p-type contact layer.

[0104] The nitride semiconductor laminate produced as described above is 2 The resistance of the p-type contact layer was further reduced by annealing in the atmosphere at 700° C. for 10 minutes or more.

[0105] Using ICP, 2 A first nitride semiconductor laminate 11 having a first mesa structure in which the first conductive type cladding layer is exposed in a rectangular region parallel to the <1-100> direction and long in the <1-100> direction was formed by dry etching using a gas containing . The formed first mesa structure had a length of 600 μm in the <1-100> direction and a length of 40 μm in the <11-20> direction. The end surface of the first mesa structure was treated using a TMAH solution heated to 80°C. As a result of this treatment, the end surface of the first mesa structure was formed at an angle of 90°±3° with respect to the AlN single crystal substrate.

[0106] Next, while the first mesa structure was protected with a mask, Cl was injected using ICP. 2 A second nitride semiconductor laminate 21 having a second mesa structure in which the AlN single crystal substrate is exposed in a rectangular region parallel to the <1-100> direction and long in the <1-100> direction was formed by dry etching using a gas containing the compound. The distance between the first mesa structure and the second mesa structure was 20 μm.

[0107] On the p-type contact layer 116 in the first mesa structure, a rectangular electrode metal region (second electrode) containing Ni or Au, which was parallel to the <1-100> direction and long in the <1-100> direction, was formed as a p-type contact electrode 13. At this time, the second electrode had a width of 5 μm and a length of 600 μm.

[0108] Furthermore, on the p-type contact layer 216 in the second mesa structure, two rectangular electrode metal regions (third electrodes) containing Ni or Au, parallel to the <1-100> direction and elongated in the <1-100> direction, were formed as p-type contact electrodes 23. In this case, each of the third electrodes had a width of 15 μm and a length of 500 μm, and the distance between the two third electrodes was 5 μm.

[0109] In addition, in the region where the first conductivity type cladding layer is exposed, multiple rectangular electrode metals (first electrodes) made of V, Al, Ni, Ti or Au and parallel to the <1-100> direction and elongated in the <1-100> direction are formed as n-type contact electrodes 12.

[0110] In this manner, an optical device 1 was obtained that monolithically had a laser diode structure having the same structure as the laser diode 10 and a sensor structure having the same structure as the light receiving element 20. From the TEG pattern formed in the wafer and the Transmission Line Model (TLM) method, the third electrode of the light receiving element 20 had a contact resistance of 1×10 -3 Ωm 2 (See Table 1.) Furthermore, the carrier concentration in the second conductive clad layer formed in the TEG pattern was 1×10 18 cm -3 (See Table 1).

[0111] For the obtained optical device 1, edge emission intensity was measured by injecting a current into the laser diode 10. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes 23) of the light receiving element 20. In addition, the current value and light receiving sensitivity of the light receiving element 20 were calibrated using a Xe lamp and a spectrometer whose emission intensity was known in advance.

[0112] As shown in Table 1, in the optical device 1 according to the first embodiment, the dark current is 1×10 -9 A. Also, as shown in Table 1, the injection current density was 15 kA / cm 2 When , the photocurrent is 1×10 -3 A, and the converted peak emission intensity was 10 mW. The peak emission intensity was calculated from a calibration curve obtained by using a pre-calibrated power meter to show the correlation between the light emitted from the laser irradiation surface of the laser diode 10 and the leaked light from the reflection surface located opposite the laser irradiation surface.

[0113] [Example 2] On the p-type contact layer in the second mesa structure, two rectangular electrode metal regions (third electrodes) containing Ni or Au parallel to the <1-100> direction and elongated in the <1-100> direction were formed as p-type contact electrodes 23, and each of the third electrodes had a plurality of comb shapes, and each of the comb teeth had a width of 2 μm and a length of 500 μm. The distance between the two third electrodes was 5 μm. The optical device according to Example 2 was formed in the same manner as the optical device according to Example 1, except for the shape of the third electrode. Although the shape of the third electrode was different, when measured in the same manner as in Example 1, the third electrode of the light receiving element 20 had a contact resistance of 1×10 -3 Ωm 2 (See Table 1).

[0114] For the obtained optical device 1, edge emission intensity was measured by injecting a current into the laser diode 10. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes 23) of the light receiving element 20. As shown in Table 1, in the optical device 1 according to Example 2, the dark current was 1×10 -9 A. The injection current density was 15 kA / cm 2 When , the photocurrent is 5×10 -2 A (see Table 1), and the converted peak emission intensity was 10 mW.

[0115] [Example 3] The optical device 1 according to Example 3 was formed in the same manner as the optical device 1 according to Example 1, except that the distance between the first mesa structure and the second mesa structure was 50 μm. For the obtained optical device 1, an edge emission intensity measurement was carried out by injecting a current into the laser diode 10. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes 23) of the light receiving element 20. As shown in Table 1, in the optical device 1 according to Example 3, the dark current was 1×10 when the laser was not oscillating. -9 A. The injection current density was 15 kA / cm 2 When , the photocurrent is 5×10-4 A (see Table 1), and the converted peak emission intensity was 10 mW.

[0116] [Example 4] The optical device 1 according to Example 4 was formed in the same manner as the optical device 1 according to Example 1, except that the distance between the first mesa structure and the second mesa structure was 1 μm. For the obtained optical device 1, an edge emission intensity measurement was carried out by injecting a current into the laser diode 10. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes 23) of the light receiving element 20. As shown in Table 1, in the optical device 1 according to Example 4, the dark current was 1×10 when the laser was not oscillating. -9 A. The injection current density was 15 kA / cm 2 When , the photocurrent is 5×10 -6 A (see Table 1), and the converted peak emission intensity was 10 mW.

[0117] [Example 5] In the optical device 1 according to the fifth embodiment, the contact resistance of the third electrode of the light receiving element 20 is 8×10 -3 Ωm 2 (See Table 1). Except for this, the optical device was formed in the same manner as the optical device 1 according to Example 1.

[0118] The edge emission intensity of the obtained optical device 1 was measured by injecting a current into the laser diode. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes 23) of the light receiving element 20. As shown in Table 1, in the optical device 1 according to Example 5, the dark current was 5×10 -10 A. The injection current density was 15 kA / cm 2 When , the photocurrent is 5×10 -4 A (see Table 1), and the converted peak emission intensity was 10 mW.

[0119] [Example 6] In the optical device 1 according to the sixth embodiment, the contact resistance of the third electrode of the light receiving element 20 is 2×10 -4 Ωm 2 (See Table 1). Except for this, the optical device was formed in the same manner as the optical device 1 according to Example 1.

[0120] The edge emission intensity of the obtained optical device 1 was measured by injecting a current into the laser diode. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes 23) of the light receiving element 20. As shown in Table 1, when the laser was not oscillating, the dark current was 1×10 -8 A. The injection current density was 15 kA / cm 2 When , the photocurrent is 5×10 -2 A (see Table 1), and the converted peak emission intensity was 10 mW.

[0121] [Example 7] The optical device 1 of Example 7 was formed in the same manner as the optical device 1 of Example 1, except that the width of each of the third electrodes was 15 μm, the length of each of the third electrodes was 500 μm, and the distance between the third electrodes was 1 μm (see Table 1).

[0122] The edge emission intensity of the obtained optical device 1 was measured by injecting a current into the laser diode. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes 23) of the light receiving element 20. As shown in Table 1, when the laser was not oscillating, the dark current was 1×10 -8 A. The injection current density was 15 kA / cm 2 When , the photocurrent is 1×10 -2 A (see Table 1), and the converted peak emission intensity was 10 mW.

[0123] [Example 8] The optical device 1 of Example 8 was formed in the same manner as the optical device 1 of Example 1, except that the width of each of the third electrodes was 12 μm, the length of each of the third electrodes was 500 μm, and the distance between the third electrodes was 10 μm (see Table 1).

[0124] The edge emission intensity of the obtained optical device 1 was measured by injecting a current into the laser diode. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes 23) of the light receiving element 20. As shown in Table 1, when the laser was not oscillating, the dark current was 5×10 -10 A. The injection current density was 15 kA / cm 2 When , the photocurrent is 5×10 -4 A (see Table 1), and the converted peak emission intensity was 10 mW.

[0125] [Example 9] The optical device 1 of Example 9 was formed in the same manner as the optical device 1 of Example 1, except that the width of each of the third electrodes was 8 μm, the length of each of the third electrodes was 500 μm, and the distance between the third electrodes was 20 μm (see Table 1).

[0126] The edge emission intensity of the obtained optical device 1 was measured by injecting a current into the laser diode. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes 23) of the light receiving element 20. As shown in Table 1, when the laser was not oscillating, the dark current was 1×10 -10 A. The injection current density was 15 kA / cm 2 When , the photocurrent is 1×10 -4 A (see Table 1), and the converted peak emission intensity was 10 mW.

[0127] [Comparative Example 1] The optical device according to Comparative Example 1 was formed in the same manner as the optical device 1 according to Example 1, except that the first mesa structure and the second mesa structure have the same shape, and the second mesa structure includes a first electrode and a second electrode similar to the first mesa structure in this embodiment. That is, the optical device according to Comparative Example 1 has a part of the n-type cladding layer exposed, a second electrode disposed on the exposed part of the n-type cladding layer, and one first electrode disposed on the p-type contact electrode of the light receiving element.

[0128] The edge emission intensity of the obtained optical device was measured by injecting a current into the laser diode. At this time, a voltage of 5 V was applied between the first and second electrodes of the light receiving element. As shown in Table 1, when the laser was not oscillating, the dark current was equivalent to noise and could not be measured. In addition, when the injected current density was 15 kA / cm 2 At this time, the photocurrent also corresponded to noise (see Table 1) and could not be measured.

[0129] [Comparative Example 2] The optical device according to Comparative Example 2 was formed in the same manner as the optical device 1 according to Example 1, except that an n-type electrode similar to the first electrode was formed as the third electrode. The contact resistance between the TEG pattern formed in the wafer and the n-type electrode formed on the light receiving element by the TLM method could not be measured (see Table 1).

[0130] The edge emission intensity of the obtained optical device was measured by injecting a current into the laser diode. At this time, a voltage of 5 V was applied between the two n-type electrodes of the light receiving element. As shown in Table 1, when the laser was not oscillating, the dark current was equivalent to noise and could not be measured. In addition, when the injected current density was 15 kA / cm 2 At this time, the photocurrent also corresponded to noise (see Table 1) and could not be measured.

[0131] [Comparative Example 3] The optical device according to Comparative Example 3 was formed in the same manner as in Example 1, except that the second cladding layer was removed by ICP etching when the second mesa structure was formed. The contact resistance of the third electrode of the light receiving element could not be measured from the TEG pattern formed in the wafer and the TLM method (see Table 1).

[0132] The edge emission intensity of the obtained optical device was measured by injecting a current into the laser diode. At this time, a voltage of 5 V was applied between the two third electrodes (p-type contact electrodes) of the light receiving element. As shown in Table 1, when the laser was not oscillating, the dark current was equivalent to noise and could not be measured. In addition, when the injected current density was 15 kA / cm 2 At this time, the photocurrent also corresponded to noise (see Table 1) and could not be measured. [Explanation of symbols]

[0133] 1. Optical Devices 10 Laser Diode 11 First nitride semiconductor laminate 12 n-type contact electrode 13 p-type contact electrode 20 Photodetector 21 Second nitride semiconductor laminate 23 p-type contact electrode 100 Nitride semiconductor substrate 111,211 n-type cladding layer 112,212 n-type waveguide layer 113,213 Emitting layer 114,214 p-type waveguide layer 115,215 p-type cladding layer 116,216 p-type contact layer

Claims

1. a nitride semiconductor substrate containing aluminum; a laser diode formed on the nitride semiconductor substrate and having a first nitride semiconductor stack; a light receiving element formed on the nitride semiconductor substrate and having a second nitride semiconductor stack; Equipped with Each of the first nitride semiconductor stack and the second nitride semiconductor stack is a first conductivity type cladding layer including a nitride semiconductor layer having a first conductivity type; a light emitting layer disposed on the first conductive type cladding layer and formed of a nitride semiconductor layer including one or more quantum wells; a second conductive type cladding layer disposed on the light emitting layer and including a nitride semiconductor layer having a second conductive type conductivity; a second conductivity type contact layer disposed on the second conductivity type cladding layer; the laser diode has a first conductivity type contact electrode disposed in a part of an exposed region of the first conductivity type cladding layer of the first nitride semiconductor stack, and a second conductivity type contact electrode disposed on the second conductivity type cladding layer of the first nitride semiconductor stack, the light receiving element has two or more second-conductivity-type contact electrodes disposed on the second-conductivity-type cladding layer of the second nitride semiconductor stack, the light receiving element is disposed at a position facing a reflecting surface located opposite to a laser irradiation surface of the laser diode, The second conductive type cladding layer is made of Al e Ga 1-e N (0.1≦e≦1) in which the Al composition ratio e decreases with increasing distance from the nitride semiconductor substrate, and has a composition gradient layer having a narrower band gap than the light emitting layer. Optical devices.

2. The laser diode and the light receiving element are electrically isolated from each other except for the nitride semiconductor substrate and a part of the first conductive type cladding layer. The optical device according to claim 1 .

3. The second conductivity type contact electrode disposed on the second nitride semiconductor stack is an ohmic electrode.

3. An optical device according to claim 1 or 2.

4. The contact resistance between the second conductive type contact electrode disposed in the second nitride semiconductor stack and the second conductive type contact layer of the second nitride semiconductor stack is 1×10 －４ Ω cm ２ Above 1 x 10 －２ Ω cm ２ is less than or equal to An optical device according to any one of claims 1 to 3.

5. The second conductive type cladding layer has a carrier concentration of 1×10 －１７ cm －３ Above 1 x 10 －１９ cm －３ is less than or equal to An optical device according to any one of claims 1 to 4.

6. The second conductivity type contact electrode disposed on the second nitride semiconductor stack contains at least nickel or gold. An optical device according to any one of claims 1 to 5.

7. The light receiving element is a photoconductor type sensor. An optical device according to any one of claims 1 to 6.

8. The distance between the two or more second conductivity type contact electrodes arranged on the second nitride semiconductor stack is 2 μm or more and 20 μm or less. An optical device according to any one of claims 1 to 7.

9. The nitride semiconductor substrate is an aluminum nitride single crystal substrate. An optical device according to any one of claims 1 to 8.

10. Each of the first nitride semiconductor stack and the second nitride semiconductor stack is a first conductivity type waveguide layer disposed between the first conductivity type cladding layer and the light emitting layer to confine light in the light emitting layer; a second conductive type waveguide layer disposed between the second conductive type cladding layer and the light emitting layer to confine light in the light emitting layer; An optical device according to any one of claims 1 to 9.

11. the second conductivity type contact layer provided on each of the first nitride semiconductor stack and the second nitride semiconductor stack has a nitride semiconductor containing gallium nitride; The second conductive type cladding layer has a thickness of less than 0.5 μm and is a composition gradient layer disposed on the nitride semiconductor substrate side. The second conductive type vertical conductive layer is an Al ｆ G 1-ｆ N (0<f≦1), and a second conductivity type lateral conduction layer disposed on the second conductivity type contact electrode side.

11. The optical device of claim 10.

12. Each of the first nitride semiconductor stack and the second nitride semiconductor stack is disposed between the second conductive type vertical conduction layer and the second conductive type waveguide layer, and includes an Al ｇ G 1-ｇ N layers, where 0<g≦1.0; 12. The optical device of claim 11.

13. The thickness of the second conductive type vertical conductive layer is 250 nm or more and 450 nm or less.

13. An optical device according to claim 11 or 12.

14. the second conductivity type vertical conduction layer has an undoped region in a certain range including an interface with the second conductivity type waveguide layer in a thickness direction of the second conductivity type cladding layer; An optical device according to any one of claims 11 to 13.

15. The first conductive type cladding layer is made of Al ａ G 1-ａ N (0.6<a≦0.8), the second conductive type vertical conduction layer and the second conductive type lateral conduction layer are fully strained with respect to the nitride semiconductor substrate; An optical device according to any one of claims 11 to 14.

16. the second conductive type lateral conduction layer has an Al composition ratio f that is greater than a minimum value of the Al composition ratio e at a surface adjacent to the second conductive type vertical conduction layer; 16. An optical device according to any one of claims 11 to 15.

17. The distance between the laser diode and the light receiving element is 1 μm or more and 1000 μm or less.

17. An optical device according to any one of claims 1 to 16.

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