JP2014236017A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device capable of efficiently recovering current collapse.SOLUTION: A semiconductor device comprises: a substrate; a nitride semiconductor layer having a heterojunction part formed on the substrate, and bonded with semiconductor layers having bandgap energies different from each other, and generating a two-dimensional carrier gas in the vicinity of a bonded interface of the semiconductor layer with a lower bandgap energy, of the semiconductor layers, and a light-emission part formed on the substrate and irradiating the heterojunction part with generated light; a plurality of electrodes formed on a part of an upper part of the nitride semiconductor layer, and applying a voltage to the heterojunction part and the light-emission part; and a protection layer formed on the nitride semiconductor layer and the electrodes. The protection layer contains a wavelength conversion material absorbing light emitted from the light-emission part, and emitting light having a wavelength longer than that of the absorbed light. The material configuring the protection layer has a lower absorption rate to wavelength of the light emitted from the wavelength conversion material rather than to the wavelength of the light emitted from the light-emission part.

Description

  The present invention relates to a semiconductor device.

  Wide band gap semiconductors are very attractive as materials for semiconductor devices for high temperature environments, high power, or high frequency because they have high breakdown voltage, good electron transport properties, and good thermal conductivity. Typical wide band gap semiconductors include GaN, AlN, InN, BN, or a nitride semiconductor that is a mixed crystal of two or more of these. For example, in a semiconductor device having an AlGaN / GaN heterojunction structure, two-dimensional electron gas (2DEG) is generated at the heterojunction interface due to the piezoelectric effect. This 2DEG has high electron mobility and carrier density. Therefore, a semiconductor device having such an AlGaN / GaN heterojunction structure, such as a Schottky barrier diode (SBD) or a field effect transistor (FET), has a high breakdown voltage, a low on-resistance, and a high speed. It has switching speed and is very suitable for power switching application.

  Further, in the GaN-based semiconductor device, a current collapse phenomenon in which the on-resistance increases when a high voltage is applied is known. This current collapse phenomenon is not preferable because it causes an increase in power consumption and a decrease in reliability. The current collapse phenomenon is considered to be caused by the trapping of electrons as carriers in the interface state of the heterojunction, the deep level of the semiconductor layer, or the like.

  As a countermeasure against the deterioration of the performance of the semiconductor device due to such a current collapse phenomenon, a method of irradiating the semiconductor device with ultraviolet to visible light from an LED (Light Emitting Diode) and releasing carriers trapped in the interface state or the like There is. As a result, current collapse is recovered, and an increase in on-resistance due to the current collapse phenomenon can be reduced (see, for example, Patent Document 1).

JP 2008-198731 A

Here, a semiconductor device is generally formed with a protective layer made of polyimide, SiO ₂ or the like on the surface for the purpose of improving the mechanical strength of the semiconductor device or ensuring the insulation on the surface of the semiconductor device. It is. However, in the known method for recovering current collapse, when the semiconductor device is irradiated with light from the LED, a part of the light is absorbed by the protective layer, and the current collapse cannot be recovered efficiently.

  The present invention has been made in view of the above, and an object of the present invention is to provide a semiconductor device capable of efficiently recovering current collapse.

  In order to solve the above-described problems and achieve the object, a semiconductor device according to the present invention includes a substrate and a semiconductor layer formed on the substrate and having different band gap energies. A heterojunction that generates a two-dimensional carrier gas in the vicinity of the interface where the semiconductor layers with lower band gap energy are joined; and a light emitting part that is formed on the substrate and that emits light emitted to the heterojunction A plurality of electrodes formed on a part of the nitride semiconductor layer and applying a voltage to the heterojunction portion and the light emitting portion, and the nitride semiconductor layer and the electrode The protective layer includes a wavelength conversion material that absorbs light emitted by the light emitting portion and emits light having a longer wavelength than the absorbed light, and the protective layer. The material constituting the layers, than the wavelength of light which the light emitting unit emits light, the wavelength converting material to the wavelength of light emitted, characterized in that a low absorption rate.

  The semiconductor device according to the present invention is characterized in that, in the above invention, an increase in on-resistance due to a current collapse phenomenon is reduced by light emitted from the wavelength conversion material.

  In the semiconductor device according to the present invention as set forth in the invention described above, the light emitting portion is a pn junction between a p-type semiconductor and an n-type semiconductor.

  The semiconductor device according to the present invention is characterized in that, in the above invention, the light emitting portion is a heterojunction portion.

  The semiconductor device according to the present invention is characterized in that, in the above invention, the light emitting portion includes a quantum well structure.

  The semiconductor device according to the present invention is characterized in that, in the above invention, the heterojunction portion and the light emitting portion are the same or are stacked in the semiconductor stacking direction.

  In the semiconductor device according to the present invention as set forth in the invention described above, the electrode is formed electrically separated from the heterojunction portion and the light emitting portion.

  In the semiconductor device according to the present invention, in the above invention, the protective layer is substantially transparent to at least one of light emitted from the light emitting unit and light emitted from the wavelength conversion material. It is characterized by that.

In the semiconductor device according to the present invention as set forth in the invention described above, the protective layer is made of any one of polyimide, SiO ₂ , and SiN _x .

  In the semiconductor device according to the present invention as set forth in the invention described above, the wavelength conversion material is a dye.

  In the semiconductor device according to the present invention, in the above invention, the reflective film that reflects the light emitted from the wavelength conversion material on at least one of the upper side of the protective layer and the lower side of the light emitting unit. It is characterized by providing.

  According to the present invention, a semiconductor device that can efficiently recover current collapse can be realized.

FIG. 1 is a schematic cross-sectional view of a semiconductor device according to Embodiment 1 of the present invention. FIG. 2 is a diagram for explaining how current collapse is recovered in the semiconductor device shown in FIG. FIG. 3 is a diagram illustrating an example of the transmittance of polyimide. FIG. 4 is an explanatory diagram illustrating a state in which the wavelength is converted by the wavelength conversion material. FIG. 5 is an explanatory diagram illustrating a state in which the wavelength is converted by the wavelength conversion material. FIG. 6 is a schematic cross-sectional view of a semiconductor device according to Embodiment 2 of the present invention. FIG. 7 is a diagram for explaining how current collapse is recovered in the semiconductor device shown in FIG. 6. FIG. 8 is a schematic cross-sectional view of a semiconductor device according to Embodiment 3 of the present invention. FIG. 9 is a diagram for explaining how current collapse is recovered in the semiconductor device shown in FIG. 8. 10 is a diagram illustrating an example of a method of manufacturing the semiconductor device illustrated in FIG. FIG. 11 is a diagram illustrating an example of a manufacturing method of the semiconductor device illustrated in FIG. FIG. 12 is a diagram illustrating an example of a manufacturing method of the semiconductor device illustrated in FIG. FIG. 13 is a diagram illustrating an example of a manufacturing method of the semiconductor device illustrated in FIG. FIG. 14 is a diagram illustrating an example of a manufacturing method of the semiconductor device illustrated in FIG. FIG. 15 is a diagram illustrating an example of a method of manufacturing the semiconductor device illustrated in FIG.

  Embodiments of a semiconductor device according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments. In the description of the drawings, the same or corresponding elements are appropriately denoted by the same reference numerals. It should be noted that the drawings are schematic, and the relationship between the dimensions of each element, the ratio of each element, and the like may differ from the actual situation. Even between the drawings, there are cases in which portions having different dimensional relationships and ratios are included.

(Embodiment 1)
First, the semiconductor device according to the first embodiment of the present invention will be described. FIG. 1 is a schematic cross-sectional view of a semiconductor device according to Embodiment 1 of the present invention. As shown in FIG. 1, in the semiconductor device 100, a buffer layer 102, a u-GaN layer 103, and an n-AlGaN layer 104 are sequentially stacked on a substrate 101. Further, a p-GaN layer 105 is stacked on a part of the n-AlGaN layer 104, and an anode electrode 106a is formed so as to straddle the n-AlGaN layer 104 and the p-GaN layer 105. A cathode electrode 106c is formed on the layer 104 so as to be separated from the p-GaN layer 105 and the anode electrode 106a. A protective layer 107 containing the wavelength conversion material 107a is uniformly formed thereon, and a reflective film 108 is formed on the top.

  Here, the interface between the u-GaN layer 103 and the n-AlGaN layer 104 is a heterojunction part in which semiconductor layers having different band gap energies are joined. The interface between the n-AlGaN layer 104 and the p-GaN layer 105 is a pn junction between a p-type semiconductor and an n-type semiconductor, and is a light emitting portion. The semiconductor device 100 functions as an SBD using a 2DEG layer 103a formed at the interface between the u-GaN layer 103 and the n-AlGaN layer 104 as a current path.

  In the GaN-based semiconductor device, the substrate 101 is preferably made of a material that is substantially transparent to the GaN emission wavelength of 365 nm, and is made of, for example, sapphire. Further, the substrate 101 may be silicon, SiC, ZnO, AlN, GaN, or the like, but it is more preferable that the substrate 101 has a small absorption and is transparent with respect to the wavelength emitted by the light emitting portion. The buffer layer 102 is, for example, an AlN layer having a thickness of about 100 nm, but may have a configuration in which a plurality of AlN layers and GaN layers are alternately stacked.

Next, the interface between the u-GaN layer 103 and the n-AlGaN layer 104 is a heterojunction part constituting a heterojunction. First, the u-GaN layer 103 is made of undoped GaN and functions as an electron transit layer. The n-AlGaN layer 104 is a layer made of n-type AlGaN and functions as an electron supply layer. AlGaN is a mixed crystal of AlN and GaN, and has a larger band gap energy than GaN of the u-GaN layer 103, and the characteristics of the band gap, spontaneous polarization, and piezo polarization change depending on the composition ratio. The n-AlGaN layer 104 is a single layer of, for example, Al _0.25 Ga _0.75 N. However, the n-AlGaN layer 104 is not limited to an AlGaN single layer, and may be a pseudo mixed crystal layer in which a plurality of AlN layers and GaN layers are alternately stacked. In that case, the band gap energy when the pseudo mixed crystal layer is averaged in the thickness direction may be larger than that of the u-GaN layer 103. Further, the thickness of the AlN layer and the GaN layer may be adjusted so that the 2DEG layer does not occur in the pseudo mixed crystal layer.

  Then, in the vicinity of the interface between the n-AlGaN layer 104 and the u-GaN layer 103 whose band gap energy is lower than that of the n-AlGaN layer 104, by controlling the Al composition ratio and thickness of the n-AlGaN layer 104, A 2DEG layer 103a, which is a two-dimensional carrier gas with a controlled concentration, is formed. The 2DEG layer 103a serves as a current path through which electrons flow. Since the 2DEG layer 103 a has a small electron impurity scattering, the 2DEG layer 103 a becomes an electrically conductive layer with high mobility and low resistance, and provides a current path between the electrodes formed on the n-AlGaN layer 104.

  The p-GaN layer 105 is formed on a part of the n-AlGaN layer 104 and has a band gap energy smaller than that of the n-AlGaN layer 104. For example, the p-GaN layer 105 is made of p-type GaN and serves as a field plate layer that relaxes electric field concentration. Function. However, the p-GaN layer 105 may be replaced with a layer made of AlGaN or the like having a lower band gap energy than the n-AlGaN layer 104 and a low Al composition ratio.

  The interface between the n-AlGaN layer 104 and the p-GaN layer 105 forms a pn junction. Therefore, when a positive voltage is applied, electrons are supplied from the n side, holes are supplied from the p side, and light is emitted by combining the electrons and the holes. As a result, the pn junction functions as a light emitting unit. The wavelength of light emitted from the light emitting unit is, for example, 365 nm, which is the emission wavelength of GaN, but by increasing the Al composition ratio of the n-AlGaN layer 104, light having a shorter wavelength can be obtained.

  Furthermore, in order to form the SBD, an anode electrode 106a that is in Schottky contact with the n-AlGaN layer 104 and the p-GaN layer 105 and a cathode electrode 106c that is in ohmic contact with the n-AlGaN layer 104 are formed on the semiconductor layer. Has been. The anode electrode 106a is made of, for example, Ni / Au, and the cathode electrode 106c is made of, for example, Ti / Al.

  The protective layer 107 protects the semiconductor layer and the electrode below the protective layer 107 from external force, external heat, voltage, water wetting, and the like. Therefore, although the protective layer 107 is made of polyimide having excellent mechanical strength and insulation, a material can be appropriately selected depending on the use of the semiconductor device. The protective layer 107 includes a wavelength conversion material 107a that absorbs light emitted from the light emitting portion and emits light having a longer wavelength than the absorbed light. The material constituting the protective layer 107 is a material having a lower absorptance with respect to the wavelength of light emitted from the wavelength conversion material 107a than the wavelength of light emitted from the light emitting portion.

  The reflection film 108 may be a mirror made of various metals, but may be a dielectric multilayer film mirror made of a dielectric multilayer film. Furthermore, the structure which reflects using the refractive index difference of each layer of a semiconductor may be sufficient.

  Next, the operation of the semiconductor device 100 will be described. When a voltage is applied to the anode electrode 106a and the cathode electrode 106c of the semiconductor device 100, a current flows with respect to a positive voltage from the anode electrode 106a toward the cathode electrode 106c. On the other hand, with respect to the reverse voltage, the semiconductor device 100 that is an SBD does not flow current due to the Schottky barrier of the anode electrode 106a.

  When a high voltage is applied to such a GaN-based SBD, electrons as carriers are trapped in the interface states or deep levels in the semiconductor due to the current collapse phenomenon, and due to the negative charges of the trapped electrons, It is considered that the electron concentration of the 2DEG layer 103a decreases. When a positive voltage is applied to the semiconductor device 100 in a state where this current collapse occurs, the on-resistance increases because the electron concentration of the 2DEG layer 103a, which is the current path of the SBD, decreases.

  Here, FIG. 2 is a diagram for explaining how current collapse is recovered in the semiconductor device shown in FIG. As shown in FIG. 2, the interface between the n-AlGaN layer 104 and the p-GaN layer 105 of the semiconductor device 100 is a pn junction, and when a positive voltage is applied, electrons and holes are combined, for example, , Emits light l1 having a wavelength of 365 nm, and functions as a light emitting portion. When the light 11 is irradiated to the trapped electrons, the electrons are released from the trap and the current collapse is restored.

  However, general polyimide absorbs ultraviolet to visible light. FIG. 3 is a diagram illustrating an example of the transmittance of polyimide. As shown in FIG. 3, light having a wavelength of 365 nm or less is absorbed by the polyimide and hardly transmitted. Therefore, a part of the light 11 is absorbed by the protective layer 107 and cannot contribute to the recovery of current collapse. Thus, when the protective layer 107 is formed, the efficiency of recovering the current collapse is deteriorated.

  Here, the protective layer 107 of the semiconductor device 100 contains the wavelength conversion material 107a. Then, as shown in FIG. 2, when the light l1 is irradiated onto the wavelength conversion material 107a, the light l1 is absorbed by the wavelength conversion material 107a and emitted from the wavelength conversion material 107a as light l2 having a longer wavelength. As a result, the ratio of the light absorbed by the protective layer 107 out of the light emitted from the light emitting unit can be reduced, and the light emitted from the light emitting unit can be efficiently utilized for recovery of current collapse. .

  Next, FIG. 4 is explanatory drawing showing a mode that a wavelength is converted with the wavelength conversion material. As shown in FIG. 4, for example, 365 nm of light 11 is emitted by the light emitting unit, and when the wavelength conversion material 107 a made of, for example, a coumarin compound is irradiated, light 12 having a wavelength of about 480 nm is emitted. It will be. At this time, the polyimide has a sufficiently large transmittance for the light l2. Therefore, the light l2 can be efficiently used to recover the current collapse without being absorbed by the protective layer 107.

  In the current collapse phenomenon, the level for trapping electrons as carriers is mainly at a position of 1.9 to 2.6 eV from the conductor. These levels are negatively charged by trapping electrons, the electron concentration of the 2DEG layer 103a is lowered, and the on-resistance is increased. Therefore, by irradiating light corresponding to 1.9 to 2.6 eV and having a wavelength of about 475 to 655 nm, electrons are released from the trap and current collapse is recovered.

  As such a wavelength conversion material 107a that emits light having a wavelength of about 475 to 655 nm, for example, a coumarin compound or a rhodamine dye can be used. In addition, it may be an inorganic compound or an organic compound, but it absorbs light emitted by the light emitting portion, emits light having a wavelength longer than the absorbed light, and emits light The material is not limited to this as long as the wavelength is about 475 to 655 nm.

  Furthermore, the semiconductor device 100 includes a reflective film 108 on the top surface, and the reflective film 108 reflects the light 11 or the light l2. Thus, light that is emitted from the upper surface of the semiconductor device 100 to the outside of the semiconductor device 100 is eliminated, and the current collapse is efficiently recovered.

  Thus, the reflective film 108 reflects the light emitted from the wavelength conversion material 107a, and more preferably reflects the light emitted by the light emitting unit. As a result, the reflective film can keep the light emitted from the wavelength conversion material 107a and the light emitted from the light emitting unit within the semiconductor device, and contribute to more efficient recovery of current collapse. Therefore, the reflective film may be formed not only on the uppermost surface of the semiconductor device 100 but also on the bottom surface of the substrate 101. Moreover, you may form in the arbitrary positions which pinch | interpose a light emission part and a protective layer. Furthermore, the structure which becomes a resonator with respect to a specific wavelength by making these reflective films into a fixed space | interval may be sufficient.

  In a known method of recovering current collapse, a semiconductor device having a 2DEG layer formed by a heterojunction portion and an LED that irradiates light to the semiconductor device are formed monolithically. On the other hand, in the semiconductor device 100 according to the first embodiment, the heterojunction portion and the light emitting portion are formed by being stacked in the semiconductor stacking direction. Therefore, it is not necessary to newly form a semiconductor layer in order to configure a light emitting unit such as an LED, and to realize a semiconductor device that can efficiently recover current collapse by a simple method that does not increase the number of steps. There is an effect that can be.

(Modification)
As a modification of the semiconductor device 100, two types of wavelength conversion materials may be added to the protective layer 107. As a result, as shown in FIG. 5, the light 11 emitted from the light emitting unit is rescued by one wavelength conversion material and emitted as light 12 having a longer wavelength, and the light 12 is absorbed by the other wavelength conversion material. Thus, a two-stage wavelength conversion is performed in which light 13 having a longer wavelength is emitted. At this time, the light 13 that has undergone the two-stage wavelength conversion has a higher transmittance with respect to polyimide, and can more efficiently recover the current collapse. Alternatively, two types of wavelength conversion materials may be added, and the light 11 may be wavelength-converted into two different wavelengths by the two types of wavelength conversion materials. Furthermore, two or more types of wavelength conversion materials may be used.

  As described above, since the wavelength conversion material is added to the protective layer 107, the semiconductor device 100 suppresses absorption of the light emitted from the light emitting portion into the protective layer 107, and efficiently recovers current collapse. be able to. Therefore, the semiconductor device 100 according to the first embodiment is a semiconductor device that can efficiently recover the current collapse.

(Embodiment 2)
Next, a semiconductor device according to the second embodiment of the present invention will be described. FIG. 6 is a schematic cross-sectional view of a semiconductor device according to Embodiment 2 of the present invention. As illustrated in FIG. 6, in the semiconductor device 200 according to the second embodiment, a buffer layer 202, a u-GaN layer 203, and a u-AlGaN layer 211 are sequentially stacked on a substrate 201. Further, a p-AlGaN layer 212 is laminated on a part of the u-AlGaN layer 211, and a gate electrode 213g is formed thereon. On the u-AlGaN layer 211, a source electrode 213s and a drain electrode 213d are formed apart from each other so as to sandwich the p-AlGaN layer 212. A protective layer 207 containing the wavelength conversion material 207a is uniformly formed thereon, and a reflective film 208 is formed on the top. Here, the interface between the u-GaN layer 203 and the u-AlGaN layer 211 is a heterojunction part in which semiconductor layers having different band gap energies are joined. The semiconductor device 200 uses a 2DEG layer 203a, which is a two-dimensional carrier gas, formed near the interface between the u-GaN layer 203 and the u-AlGaN layer 211, which has a lower band gap energy than the u-AlGaN layer 211, as a current path. It functions as a GIT (Gate Injection Transistor).

  Next, the operation of the semiconductor device 200 will be described. First, the p-AlGaN layer 212 is formed in a state where the gate voltage is not applied to the gate electrode 213g and the 2DEG layer 203a thereunder is depleted as shown in FIG. . Thus, when the gate voltage is off, the source electrode 213s and the drain electrode 213d are not conductive. Therefore, the semiconductor device 200 is a normally-off device. On the other hand, when the gate voltage is turned on and a positive gate voltage is applied to the gate electrode 213g, depletion of the 2DEG layer 203a caused by the p-AlGaN layer 212 is eliminated, and the source electrode 213s, The electrode 213d is electrically connected. Further, when a high positive gate voltage is applied, holes are injected from the gate electrode 213g into the 2DEG layer 203a. As a result, approximately the same number of electrons as the injected holes flow from the source electrode 213s to the holes, and further flow to the drain electrode 213d by the drain voltage. Thus, the semiconductor device 200 operates as a GIT that is normally off and has low on-resistance.

  When a high voltage is applied to the semiconductor device 200 that operates as such a GIT, electrons as carriers are trapped in an interface level or a deep level in the semiconductor due to a current collapse phenomenon, and the trapped electrons are negatively charged. It is considered that the electron concentration of the 2DEG layer 203a decreases due to the electric charge. When a positive drain voltage is applied to the semiconductor device 200 in a state where this current collapse occurs, the on-resistance increases because the electron concentration of the 2DEG layer 203a that is the current path of the GIT decreases.

  Here, FIG. 7 is a diagram for explaining how current collapse is recovered in the semiconductor device shown in FIG. 6. As shown in FIG. 7, the interface between the u-GaN layer 203 and the u-AlGaN layer 211 of the semiconductor device 200 is a heterojunction, but when a positive high gate voltage is applied to the gate electrode 213g as described above. Then, holes h are injected from the gate electrode 213g into the 2DEG layer 203a. Since the mobility of the hole h is about two orders of magnitude smaller than that of electrons, the hole h stays almost directly below the gate electrode 213g. When electrons e flow from the source electrode 213s, some of the electrons e and holes h are combined to emit light l1. That is, this heterojunction part also has a function as a light emitting part. When the light 11 is irradiated to the trapped electrons, the electrons are released from the trap and the current collapse is restored.

  Here, the wavelength conversion material 207 a is added to the protective layer 207 of the semiconductor device 200. When the light conversion material 207a is irradiated with the light l1, the light l1 is absorbed by the wavelength conversion material 207a, and light 12 having a longer wavelength is emitted from the wavelength conversion material 207a. As a result, absorption of light emitted from the light emitting portion into the protective layer 207 is suppressed, and current collapse can be efficiently recovered. Therefore, the semiconductor device 200 according to the second embodiment is a semiconductor device that can efficiently recover the current collapse.

  Note that, in the semiconductor device 200 according to the second embodiment, the heterojunction portion and the light emitting portion have the same configuration. Therefore, it is not necessary to newly form a semiconductor layer in order to configure a light emitting unit such as an LED, and to realize a semiconductor device that can efficiently recover current collapse by a simple method that does not increase the number of steps. There is an effect that can be.

(Embodiment 3)
Next, a semiconductor device according to the third embodiment of the present invention will be described. FIG. 8 is a schematic cross-sectional view of a semiconductor device according to Embodiment 3 of the present invention. As shown in FIG. 8, a semiconductor device 300 according to the third embodiment includes an HFET 300a including a heterojunction in which semiconductor layers having different band gap energies are bonded on a substrate 301, and electrons and electrons when a voltage is applied. The LED 300b including a light-emitting portion having a quantum well structure that emits light by being combined with holes is formed monolithically, but each electrode of the HFET 300a and each electrode of the LED 300b are formed electrically apart from each other. .

In the semiconductor device 300, a buffer layer 302 and an n-GaN layer 321 are sequentially stacked on a substrate 301. First, in an HFET (Hetero-FET) 300a, a u-GaN layer 303 and a u-AlGaN layer 311 are sequentially stacked on an n-GaN layer 321. Here, the interface between the u-GaN layer 303 and the u-AlGaN layer 311 is a heterojunction part in which semiconductor layers having different band gap energies are joined. This HFET 300a is an HFET having a 2DEG layer 303a, which is a two-dimensional carrier gas formed in the vicinity of the interface between the u-GaN layer 303 and the u-AlGaN layer 311 having a lower band gap energy than the u-AlGaN layer 311, as a current path. Function. Next, in the LED 300b, an n-cladding layer 322, a light emitting layer 323, a p-cladding layer 324, and a contact layer 325 are sequentially stacked on the n-GaN layer 321. Further, a SiO ₂ film 326 is formed thereon as a protective insulating film, and the source electrode 313s, the drain electrode 313d, and the gate electrode 313g of the HFET 300a are electrically separated from each other at the opening of the SiO ₂ film 326, and A p-type electrode 327p and an n-type electrode 327n of the LED 300b are formed. A protective layer 307 containing the wavelength converting material 307a is uniformly formed thereon, and a reflective film 308 is formed on the top. Further, the reflective film 308 is also formed on the bottom surface of the substrate 301.

  The light emitting layer 323 of the LED 300b may have, for example, an InGaN / GaN quantum well structure, and may have a multiple quantum well structure. In addition, a separate confinement heterostructure (SCH) structure may be provided. Further, the light-emitting layer 323 is not limited to this, and a material and a light emission wavelength can be selected as appropriate.

  Next, the operation of the semiconductor device 300 will be described. First, in the HFET 300a, the u-AlGaN layer 311 of the u-GaN layer 303 is in a state where the interface between the u-GaN layer 303 and the u-AlGaN layer 311 is a heterojunction and no voltage is applied to the gate electrode 313g. A 2DEG layer 303a is formed at the interface with the. Therefore, the HFET 300a is a normally-on device. On the other hand, when a negative gate voltage is applied to the gate electrode 313g, the 2DEG layer 303a immediately below the gate electrode 313g is depleted, and the source electrode 313s and the drain electrode 313d are not conductive.

  Next, in the LED 300b, when a voltage is applied to the p-type electrode 327p and the n-type electrode 327n, holes are supplied from the p-type electrode 327p and electrons are supplied from the n-type electrode 327n to the light-emitting layer 323, which is a light-emitting portion. , Holes and electrons combine to emit light.

  When a high voltage is applied to the HFET 300a of such a semiconductor device 300, electrons as carriers are trapped in the interface states or deep levels in the semiconductor due to the current collapse phenomenon, and the negative charge of the trapped electrons causes the 2DEG layer. It is thought that the electron concentration of 303a decreases. When a positive drain voltage is applied to the HFET 300a in a state where this current collapse occurs, the on-resistance increases because the electron concentration of the 2DEG layer 303a, which is the current path of the HFET 300a, decreases.

  Here, FIG. 9 is a diagram for explaining how current collapse is recovered in the semiconductor device shown in FIG. As shown in FIG. 9, when a voltage is applied to the LED 300b which is a light emitting unit, light l1 is emitted by light emission. When the light 11 is irradiated to the trapped electrons, the electrons are released from the trap and the current collapse is restored, but the protective layer 307 made of polyimide, for example, absorbs the light 11.

  Here, a wavelength conversion material 307 a is added to the protective layer 307 of the semiconductor device 300. When the light conversion material 307a is irradiated with the light l1, the light l1 is absorbed by the wavelength conversion material 307a and light having a longer wavelength is emitted from the wavelength conversion material 307a. As a result, absorption of light emitted from the light emitting portion into the protective layer 307 is suppressed, and current collapse can be efficiently recovered. Therefore, the semiconductor device 300 according to the third embodiment is a semiconductor device that can efficiently recover the current collapse.

  Next, an example of a method for manufacturing a semiconductor device according to the third embodiment of the present invention will be described. 10 to 15 are diagrams illustrating an example of a manufacturing method of the semiconductor device illustrated in FIG. In the following, the growth of each semiconductor layer may be an MOCVD method, or an HVPE method or an MBE method. Each electrode may be formed using a lift-off method.

First, as shown in FIG. 10, a buffer layer 302 made of AlN having a thickness of about 100 nm and an n-GaN layer 321 having a thickness of about 2 to 4 μm are sequentially laminated on a substrate 301 made of sapphire, A dielectric film 331 made of SiO _{2 having a} thickness of about 1 μm is laminated. Then, a photoresist R is applied thereon, and the photoresist R is formed in a region other than the region where the HFET 300a is to be formed by exposure and development.

  Next, as shown in FIG. 11, using the photoresist R as a mask, the dielectric film 331 in the region where the HFET 300a is to be formed is removed, and further the photoresist R is removed. Here, the u-GaN layer 303 and the u-AlGaN layer 311 are sequentially stacked on the n-GaN layer 321 exposed by removing the dielectric film 331.

  Next, as shown in FIG. 12, a dielectric film 331 is formed in a region other than the region where the LED 300b is to be formed, in the same manner as the method using the above-described photoresist. Here, as shown in FIG. 13, an n-cladding layer 322, a light emitting layer 323, a p-cladding layer 324, and a contact layer are formed on the n-GaN layer 321 in a region where the dielectric film 331 is not formed. 325 are sequentially stacked.

Next, as shown in FIG. 14, an SiO ₂ film 326 is formed using a photoresist again so as to cover areas other than the regions where the respective electrodes are to be formed. Then, as shown in FIG. 15, the source electrode 313s of the HFET 300a, the drain electrode 313d, the gate electrode 313g, and the p-type electrode 327p of the LED 300b are electrically separated from each other in the opening of the SiO ₂ film 326. The n-type electrode 327n is formed. Thereafter, the protective layer 307 is uniformly formed thereon, and the reflective film 308 is formed on the top and the bottom surface of the substrate 301, whereby the semiconductor device 300 is manufactured.

  In the semiconductor device 300 according to the third embodiment, the timing for applying the gate voltage to the HFET 300a or the timing for applying the drain voltage may be synchronized with the timing for applying the voltage to the LED 300b. A voltage may be applied at an independent timing. Furthermore, the on-resistance of the HFET 300a may be measured, and control may be performed so that a voltage is applied to the LED 300b when the on-resistance exceeds a predetermined threshold.

Further, the light emitting unit is not limited to the LED, and may be a self-luminous body having a radioisotope and a light emitting substance. The self-luminous substance functions as a light emitting unit by emitting light when radiation accompanying nuclear decay of a radioisotope brings the luminescent substance into an excited state and the luminescent substance returns from the excited state to the ground state. The self-luminous material includes, for example, any one of ³ H, ¹⁴ C, ¹⁴⁷ Pm, and ⁶³ Ni as a radioisotope, and any one of ZnS, ZnTe, ZnSe, GaN, and Si as a light-emitting substance. Including.

  As described above, according to the above embodiment, a semiconductor device that can efficiently recover current collapse can be provided.

In the above embodiment, the protective layer is polyimide, but a material having necessary physical characteristics can be appropriately selected in accordance with the use of the semiconductor device. SiO ₂ and SiN _x are excellent in mechanical strength and insulation and are suitable as a protective layer.

  In the above embodiment, the protective layer may be a material that has little absorption and is substantially transparent to the light 11 emitted from the light emitting unit or the light 12 emitted from the wavelength conversion material. For example, a polyimide material having a transmittance exceeding 80% for light having a wavelength of 365 nm has been reported. When such a material is used for the protective layer, light absorption by the protective layer is small, and current collapse can be efficiently recovered. In such a case, since the material such as polyimide has a higher transmittance as the wavelength becomes longer as shown in FIG. 3, when the wavelength of the light l1 is converted into the light l2 having a longer wavelength by the wavelength conversion material, Light absorption by the protective layer can be reduced, and current collapse can be efficiently recovered.

  In particular, when the protective layer is made of a material that is substantially transparent to the light l1 emitted from the light emitting unit, the light l1 emitted from the light emitting unit to the protective layer side has no reflective film. It is discharged from the upper surface to the outside of the semiconductor device. At this time, when the wavelength conversion material is added to the protective layer, the light l2 emitted from the wavelength conversion material is emitted in a direction of us. As a result, when the wavelength conversion material is added to the protective layer, there is an effect that the ratio of the light emitted to the outside of the semiconductor device can be reduced and the current collapse can be efficiently recovered.

  The current collapse phenomenon is considered to be caused by trapping of electrons as carriers at the interface level of the heterojunction or the deep level of the semiconductor layer. Therefore, the current collapse can be recovered more efficiently by irradiating light having a wavelength corresponding to the energy depending on the depth of the level contributing to the current collapse. Therefore, in the present invention, a semiconductor device capable of more efficiently recovering current collapse can be realized by appropriately selecting a dye.

  Moreover, in the said embodiment, the structure further provided with a light storage part may be sufficient. While the phosphorescent portion is emitting light, the current collapse is always recovered, so that an increase in on-resistance can be suppressed for a long time. In addition, since the light storage unit stores the light emitted by the light emitting unit, it is possible to control the time for applying the voltage to the light emitting unit to be shortened while suppressing an increase in on-resistance due to current collapse, and more efficiently. The current collapse can be recovered. The phosphorescent part may be a material used for a luminous paint such as zinc sulfide or strontium aluminate.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

100, 200, 300 Semiconductor device 101, 201, 301 Substrate 102, 202, 302 Buffer layer 103, 203, 303 u-GaN layer 103a, 203a, 303a 2 DEG layer 104 n-AlGaN layer 105 p-GaN layer 106a Anode electrode 106c Cathode electrode 107, 207, 307 Protective layer 107a, 207a, 307a Wavelength conversion material 108, 208, 308 Reflective film 211, 311 u-AlGaN layer 212 p-AlGaN layer 213d, 313d Drain electrode 213g, 313g Gate electrode 213s, 313s Source Electrode 300a HFET
300b LED
321 n-GaN layer 322 n-cladding layer 323 light-emitting layer 324 p-cladding layer 325 contact layer 326 SiO ₂ film 327 n n-type electrode 327 p p-type electrode 331 dielectric film e electron h holes l 1, l 2, l 3 light R photoresist

Claims (11)

A substrate,
A semiconductor layer formed on the substrate and having different band gap energies is bonded, and a heterogeneity that generates a two-dimensional carrier gas in the vicinity of the bonded interface of the semiconductor layers having the lower band gap energy among the semiconductor layers. A junction,
A light emitting unit formed on the substrate and irradiating the heterojunction with emitted light;
A nitride semiconductor layer comprising:
A plurality of electrodes formed on a portion of the nitride semiconductor layer and applying a voltage to the heterojunction portion and the light emitting portion;
A protective layer formed on the nitride semiconductor layer and the electrode;
With
The protective layer includes a wavelength conversion material that absorbs light emitted from the light emitting unit and emits light having a longer wavelength than the absorbed light, and the material constituting the protective layer is a light emitting unit that emits light. A semiconductor device characterized in that the absorptance is lower than the wavelength of light emitted by the wavelength conversion material.   The semiconductor device according to claim 1, wherein an increase in on-resistance due to a current collapse phenomenon is reduced by light emitted from the wavelength conversion material.   The semiconductor device according to claim 1, wherein the light emitting portion is a pn junction between a p-type semiconductor and an n-type semiconductor.   The semiconductor device according to claim 1, wherein the light emitting part is a heterojunction part.   The semiconductor device according to claim 1, wherein the light emitting unit includes a quantum well structure.   The semiconductor device according to claim 1, wherein the heterojunction portion and the light emitting portion are the same or are stacked in the semiconductor stacking direction.   The semiconductor device according to claim 1, wherein the electrode is formed to be electrically separated from the heterojunction portion and the light emitting portion.   The said protective layer is substantially transparent with respect to at least one among the light which the said light emission part light-emitted, and the light which the said wavelength conversion material discharge | released, The any one of Claims 1-7 characterized by the above-mentioned. The semiconductor device described in one. The semiconductor device according to claim 1, wherein the protective layer is made of any one of polyimide, SiO ₂ , and SiN _x .   The semiconductor device according to claim 1, wherein the wavelength conversion material is a pigment.   The reflective film for reflecting light emitted from the wavelength conversion material is provided on at least one of the upper side of the protective layer and the lower side of the light emitting unit. The semiconductor device as described in any one.

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