JP5823304B2 - Method for producing p-type ZnO, ZnO electroluminescent semiconductor element - Google Patents

Description

  The present invention relates to a method for producing p-type ZnO and a ZnO semiconductor film, and more particularly to a method for producing p-type ZnO capable of realizing a light emitting element related to light having a wavelength ranging from blue to ultraviolet light with ZnO, and a ZnO semiconductor film. .

  Conventionally, the material of the light emitting element in the blue to ultraviolet region is composed of compound semiconductors such as InGaN and GaN. In order to obtain such a compound semiconductor, an expensive crystal growth apparatus is required, and since many of the additives are rare materials, they are expensive. For this reason, research and development of electroluminescence (EL) elements using ZnO having a band gap close to these as materials replacing InGaN and GaN have been actively conducted. This ZnO is an abundant and inexpensive resource on the earth. In addition, this ZnO has an advantage that it can be easily synthesized, for example, a single crystal wafer can be obtained, and a film having a uniaxial crystal orientation can be formed on a glass substrate.

  In order to manufacture such an EL element, formation of a pn junction is indispensable. N-type ZnO is an n-type semiconductor and can be easily manufactured by doping a group III element such as aluminum or a halogen element.

  However, p-type ZnO, which is a p-type semiconductor, has been conventionally difficult to manufacture. Patent Document 1 discloses nitrogen-doped ZnO, which is p-type ZnO, but is insufficient in stability because nitrogen is easily desorbed. The present condition is that the preparation method of stable p-type ZnO has not been established.

Japanese Patent Application Laid-Open No. 2005-217035

  Therefore, the present invention has been devised in view of the above-described problems, and the object of the present invention is to newly provide a method for producing p-type ZnO, which has been conventionally difficult to produce. In addition, the present invention provides a ZnO semiconductor film manufactured by such a method for manufacturing p-type ZnO.

  A p-type ZnO manufacturing method to which the present invention is applied includes forming an n-layer composed of an n-type ZnO substrate and a pseudo p-layer in which nitrogen is implanted as a p-type dopant in the n-type ZnO substrate, and a forward bias voltage. To generate a diffusion current in the n layer and the pseudo p layer, and based on Joule heat generated by the generated diffusion current, a dopant distribution of nitrogen implanted in any one or more of the pseudo p layers In addition to repeating the change, the forward bias voltage causes an inversion distribution in the conduction band and valence band in the active layer, and near-field light is generated based on the nitrogen dopant distribution after the change, Reduces the diffusion current by causing electrons in the conduction band forming the population inversion to be induced and emitted in multiple steps based on a non-adiabatic process. Allowed to lower the Joule heat, characterized in that it constituted by fixing the dopant distribution of nitrogen in the pseudo p layer in the pseudo p layer as a p-type ZnO.

  At this time, at the time of applying the forward bias voltage, at least the pseudo p layer may be irradiated with guide light having any wavelength in the ultraviolet band to the blue band from the outside.

  According to the present invention having the above-described configuration, since most of the implanted nitrogen is not fixed at a position in the crystal that should function as an acceptor, a forward bias is applied in a pseudo-p layer that does not function stably as a p-layer. By applying a voltage, the fluidity of the pseudo p layer due to the generation of Joule heat is increased. Then, the near-field light is generated when the distribution of the dopant in the vicinity of the n layer in the pseudo p layer randomly changes and a certain specific dopant distribution is formed. And in the area | region where the said near field light generate | occur | produced, light emission arises by stimulated emission. In a region where light emission due to the generation of such near-field light occurs, the fluidity is lowered, the processing is stopped, and the dopant distribution is fixed. In a state where this dopant is fixed, light emission occurs when a forward bias voltage is applied, so that it functions as a so-called pn junction. That is, it means that the dopant in the vicinity of the n layer in the pseudo p layer has moved to a position in the crystal that should function as an acceptor and is fixed.

  Although the pseudo p layer 12 is composed of ZnO from the beginning, when nitrogen as a dopant in the pseudo p layer 12 moves to a position in the crystal that should function as an acceptor, ZnO becomes a p-type semiconductor. Will function.

  In particular, in the present invention, the vicinity of the n layer in the pseudo p layer is made to flow once based on Joule heat, and then the dopant is moved and solidified to a state where the function as a p-type semiconductor can be exhibited. Thereby, the diffused and fixed dopant is stably fixed in a state capable of exhibiting a function as a p-type semiconductor in ZnO. For this reason, it becomes possible to change the pseudo p layer into a p layer that exhibits the function as an original p-type semiconductor. That is, according to the present invention, it is possible to stably produce p-type ZnO.

It is a block diagram of the preparation apparatus of p-type ZnO to which this invention is applied. It is an energy band figure of n layer and pseudo p layer. It is a figure which shows the example after the distribution change of a dopant arises. It is the figure which showed the non-adiabatic process with the model which replaced the coupling | bonding of atoms with the spring. (A) is an example in which an inversion distribution based on the difference in electron density is formed in the vicinity of the n layer in the pseudo-p layer, and (b) is based on a non-adiabatic process of electrons in the conduction band by near-field light. It is a figure which shows the example made to light-emit by making it discharge | release. Depending on the wavelength of the incident light, an intermediate vibration order as shown in FIG. 6 is formed. It is a figure which shows the example in which the micro area | region B of substantially the same distribution as the micro area | region A is formed.

  Hereinafter, a method for producing p-type ZnO to which the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of a p-type ZnO manufacturing apparatus 10 to which the present invention is applied. The manufacturing apparatus 10 includes a pn junction 1 and a power supply 41 for applying a voltage to the pn junction 1.

  The pn junction 1 is made of ZnO and includes an n layer 11 and a pseudo p layer 12. The n layer 11 is an n-type semiconductor composed of an n-type ZnO substrate. The n layer 11 is obtained by doping a group III element such as aluminum or a halogen element with respect to an n-type ZnO substrate.

The pseudo p layer 12 is an n-type ZnO substrate implanted with nitrogen as a p-type dopant with high density and high energy. The pseudo p layer 12 may have a doping density of about 10 ¹⁹ in the vicinity of, for example, 700 KeV and 500 nm from the surface. Incidentally, since nitrogen as a dopant lacks stability, the pseudo p layer 12 often does not stably act as a so-called p-type semiconductor. That is, most of the nitrogen as a dopant in the pseudo p layer 12 is not fixed at a position in the crystal that should function as an acceptor. However, since nitrogen is added as a p-type dopant, it is defined as a pseudo p layer 12 as a pseudo p layer.

  In the method for producing p-type ZnO to which the present invention is applied, the dopant distribution of nitrogen as a dopant in ZnO of the pseudo p layer 12 in the pn junction 1 is changed. The change in the dopant distribution here is a concept including all phenomena caused by annealing, such as a change in the position of initially implanted nitrogen or a diffusion of the implanted nitrogen.

  In the pseudo p layer 12, a dopant 14 made of nitrogen is implanted. However, this dopant distribution is unstable and cannot function as a so-called p-type semiconductor.

  Actually, a forward bias voltage is applied to the pn junction 1. As a result, it is possible to produce the p-type ZnO according to the present invention based on the following mechanism.

  FIG. 2 shows an energy band diagram of the n layer 11 and the pseudo p layer 12. When a forward bias voltage is applied, holes in the pseudo p layer 12 move to the n layer 11 side, and electrons in the n layer 11 move to the pseudo p layer 12 side. As a result, a diffusion current flows by mutual cancellation of electrons and holes. When the forward bias voltage is high, Joule heat is generated due to the movement of the electrons. The particularly large generation site of the Joule heat is centered on the interface between the n layer 11 and the pseudo p layer 12 that generates a large potential difference. However, at least in the vicinity of the n layer 11 in the pseudo p layer 12, the potential difference is large. Occurs. By increasing this forward bias voltage, an avalanche breakdown occurs in the vicinity of the n layer 11 in the pseudo p layer 12, and current flows at once. As a result, heat generation due to Joule heat is promoted by such avalanche breakdown.

  As a result of the generation of the Joule heat, the fluidity increases in the pseudo p layer 12, particularly in the vicinity of the n layer 11, and the distribution of the dopant 14 changes. By continuing to apply the forward bias voltage described above, the distribution change of the dopant 14 continuously occurs.

  FIG. 3 shows an example after the distribution change of the dopant 14 occurs. The generation of Joule heat increases the fluidity in the pseudo p layer 12, particularly in the vicinity of the n layer 11. As a result, the distribution of the dopant in the vicinity of the n layer 11 in the pseudo p layer 12 changes randomly. As a result of repeated changes in the surface shape and dopant distribution, for example, a specific dopant distribution is formed in the fine region A. The specific dopant distribution in the fine region A is a distribution that is more suitable for generating near-field light based on incident light. The conditions for forming this specific dopant distribution are not established, and as a result of random changes of the dopant in the vicinity of the n layer 11 in the pseudo p layer 12 due to the generation of Joule heat, it occurs by chance under a certain probability. Is formed.

  When such a specific dopant distribution in the fine region A is formed, if the above-described forward bias voltage is further loaded, near-field light is generated in the specific dopant distribution. The near-field light here includes the meaning of a virtual electromagnetic field, and therefore the formation of a virtual electromagnetic field is understood as meaning the generation of near-field light. The generation of the near-field light is generated by spontaneous emission of the injected charge and stimulated emission based on it when the forward current is injected, even in the absence of the induced light. Generation of this near-field light causes a non-adiabatic process described below. Incidentally, the generation position of the near-field light is generated at a place where the specific dopant distribution is generated, but may naturally occur at other places.

  This non-adiabatic process can be considered by a model in which the bonds between atoms are replaced by springs as shown in FIG. In general, the wavelength of propagating light is much larger than the size of the molecule, so it can be regarded as a spatially uniform electric field at the molecular level. As a result, as shown in FIG. 4A, adjacent electrons are vibrated with the same amplitude and the same phase by the spring. Since the atomic nucleus of ZnO is heavy, it cannot follow the vibrations of the electrons, and molecular vibrations are extremely difficult to occur in the propagating light. In this way, in propagation light, it can be ignored that molecular vibrations are involved in the excitation process of electrons, so this process is called adiabatic process.

  On the other hand, the spatial electric field gradient of near-field light drops very steeply. For this reason, near-field light gives different vibrations to adjacent electrons, and as shown in FIG. 4B, the heavy nuclei are also vibrated by the vibrations of the different electrons. The occurrence of molecular vibration in the near-field light corresponds to energy taking the form of molecular vibration. Therefore, in the near-field light, an excitation process (non-adiabatic process) via the vibration level is possible. In this way, the excitation process via the vibration level of the nucleus is called a non-adiabatic process because the nucleus moves in response to the adiabatic process, which is a normal optical response.

Further, by continuing to apply the forward bias voltage described above, the electron density n ₁ in the conduction band is overwhelmingly higher than the hole density n ₂ in the lower level. As a result, an inversion distribution based on the difference in electron density is formed in the vicinity of the n layer 11 in the pseudo p layer 12 between the conduction band and the lower level, as shown in FIG. Next, due to this inversion distribution, electrons in the conduction band are virtually transitioned to a vibration level located in the middle of the band gap based on a non-adiabatic process by near-field light. Can be made. The fact that the electrons were able to transit to the vibration level based on the non-adiabatic process was realized because near-field light was generated at that location. This near-field light is generated by a change in dopant that occurs with a certain probability due to the flow due to Joule heat. The electrons that have transitioned to the vibration level travel around the virtual field (dressed photon-phonon level) virtually generated by the near-field light, and then return from the vibration level to the conduction band. The electrons returning to the conduction band contribute to Joule heat due to the diffusion current.

  Thus, at the stage where the near-field light is simply generated, the electrons in the conduction band are virtually transitioned to the vibration level and returned to the conduction band again. The electrons returning to the conduction band contribute to Joule heat, and the Joule heat does not decrease, and the distribution change of the dopant in the vicinity of the n layer 11 in the pseudo p layer 12 continues.

  As a result of the change in the distribution of the dopant due to Joule heat, when the generation mode of the near-field light further changes, as shown in FIG. Based on a non-adiabatic process by light, light is emitted by virtually transitioning to a vibration level located in the middle of the band gap and emitting electrons therefrom. Further, light is emitted by stimulated emission of electrons in the conduction band in a plurality of steps based on such near-field light.

  As a result, it is possible to realize light emission by emitting electrons from the pn junction 1. In the specific dopant distribution, near-field light continues to be generated, so that a non-adiabatic process can be generated. In stimulated emission by this non-adiabatic process, electrons are emitted through vibration levels. At this time, even in the light having a wavelength longer than the absorption edge wavelength corresponding to the band gap width, electrons in the conduction band can be emitted in a multi-step transition, and as a result, electrons in the conductor are reduced. Is possible.

The multistage stimulated emission caused by such a non-adiabatic process causes the electron density n ₁ in the conduction band to decrease. As a result, the amount of electrons moving to the n layer 13 is reduced in the region where the peculiar dopant distribution in which such near-field light is generated is formed, and the diffusion current is reduced. And the Joule heat falls about the area | region in which the said specific dopant distribution was formed. That is, stimulated emission takes away energy of electrons and holes, and the fluidity in the vicinity of the n layer 11 in the pseudo p layer 12 decreases. As a result, the change in dopant distribution is suppressed in the vicinity of the n layer 11 in the pseudo p layer 12. Such a dopant distribution is fixed without change.

  Further, when light emission occurs as shown in FIG. 5B, near-field light due to a specific dopant distribution is likely to be generated based on the light emission. The generated near-field light further tends to cause a non-adiabatic process in each part, and the fixation of the specific dopant distribution and the light emission are promoted.

  Moreover, the mechanism described above is continuously generated by continuing to apply the forward bias voltage as described above.

  In the fine region A, the near-field light continues to be generated as it is, and the stimulated emission by the non-adiabatic process described above is continuously generated. As a result, the temperature is lowered, and the fine region A continues to be fixed in this state. In addition, since the near-field light is not generated in the portions other than the fine region A, the fluidity in the vicinity of the n layer 11 in the pseudo p layer 12 is increased by generating Joule heat as it is without being cooled. The dopant distribution in the vicinity of the n layer 11 in the pseudo p layer 12 changes randomly. As a result of this random change in dopant distribution, as shown in FIG. 6, a fine region B having the same distribution as the fine region A may be formed. Similar to the fine region A, the specific dopant distribution in the fine region B is a more suitable distribution for generating near-field light. The conditions for forming this specific dopant distribution are not established, and as a result of random changes of the dopant in the vicinity of the n layer 11 in the pseudo p layer 12 due to the generation of Joule heat, it occurs by chance under a certain probability. Is formed.

  When such a specific dopant distribution in the fine region B is formed, if the forward bias voltage described above is further applied, near-field light is generated in the specific dopant distribution. The generation of the near-field light is generated by spontaneous emission of the injected charge and stimulated emission based on it when the forward current is injected, even in the absence of the induced light. The generation of the near-field light causes a similar non-adiabatic process in the fine region B.

  Also in the fine region B, the diffusion current is reduced due to multistage stimulated emission due to the non-adiabatic process. And about the micro area | region B in which the said specific dopant distribution was formed, Joule heat will fall and fluidity | liquidity will fall. As a result, also in the fine region B, the change in the dopant distribution is suppressed in the vicinity of the n layer 11 in the pseudo p layer 12. Such a dopant distribution is fixed without change.

  When such processing is repeatedly executed, ideally, many dopant distributions identical to those in the fine regions A and B in which near-field light is suitably generated when a forward bias voltage is applied are created. The change in the dopant distribution is suppressed, and the processing by improving the fluidity is stopped. As a result, the luminous efficiency can be dramatically improved.

  Thus, in the present invention, since most of the implanted nitrogen is not fixed at a position in the crystal that should function as an acceptor, a forward bias voltage is applied in the pseudo-p layer 12 that does not function stably as a p-layer. As a result, the fluidity of the pseudo p-layer 12 due to the generation of Joule heat is increased. Then, the near-field light is generated when the distribution of the dopant in the vicinity of the n layer 11 in the pseudo p layer 12 randomly changes and a specific dopant distribution is formed. And in the area | region where the said near field light generate | occur | produced, light emission arises by stimulated emission. In a region where light emission due to the generation of such near-field light occurs, the fluidity is lowered, the processing is stopped, and the dopant distribution is fixed.

  In a state where this dopant is fixed, light emission occurs when a forward bias voltage is applied, so that it functions as a so-called pn junction. That is, it means that the dopant in the vicinity of the n layer 11 in the pseudo p layer 12 has moved and fixed to a position in the crystal that should function as an acceptor.

  Although the pseudo p layer 12 is composed of ZnO from the beginning, when nitrogen as a dopant in the pseudo p layer 12 moves to a position in the crystal that should function as an acceptor, ZnO becomes a p-type semiconductor. Will function. Therefore, it can be said that the fine regions A and B in which the near-field light is suitably generated in the pseudo p layer 12 are changed to so-called p-type ZnO.

  In particular, in the present invention, the n layer 11 and the vicinity thereof in the pseudo p layer 12 are once flowed based on Joule heat, and then the dopant is moved and solidified to a state where the function as a p-type semiconductor can be exhibited. Thereby, the diffused and fixed dopant is stably fixed in a state capable of exhibiting a function as a p-type semiconductor in ZnO. For this reason, it becomes possible to change the pseudo p layer 12 into a p layer that exhibits the function as an original p-type semiconductor. That is, according to the present invention, it is possible to stably produce p-type ZnO.

  The present invention is not limited to the embodiment described above. When the forward bias voltage is actually applied, the guide light may be incident on at least the vicinity of the n layer 11 in the pseudo p layer 12. As a result, an intermediate vibration rank is formed as shown in FIG. 6 according to the wavelength of the incident light. The electrons make a transition to the vibration order located in the middle and then make a transition to the lower level by stimulated emission, but the emission wavelength is actually the band gap between the vibration order located in the middle and the base order. Depends on the difference. The vibration order located in the middle greatly depends on the wavelength of the guide light emitted from the outside.

  FIG. 7 shows the actual spectral distribution of output light for the obtained pn junction 1. In this example, guide light having a wavelength of 407 nm is irradiated. As a result, the spectral distribution of the output light has a peak centered at 390 nm as shown in FIG. That is, the spectral distribution of the output light is very close to the incident guide light and wavelength. For this reason, it can be said that the wavelength of the output light is based on the wavelength of the incident guide light.

  You may make it irradiate the light of any wavelength in an ultraviolet band to a blue band as this guide light. Thereby, the obtained pn junction body 1 obtained can be configured as a device that emits light having a wavelength in the ultraviolet band to the blue band.

  Further, in the present invention, p-type ZnO corresponding to the p layer in the obtained pn junction 1 may be cut out and used, or used as a ZnO electroluminescent semiconductor element using such p-type ZnO as a p layer. Of course, you may make it do.

DESCRIPTION OF SYMBOLS 1 pn junction body 10 Preparation apparatus of p-type ZnO 11 N layer 12 Pseudo p layer 14 Dopant 41 Power supply

Claims (2)

forming an n layer composed of an n-type ZnO substrate and a pseudo-p layer in which nitrogen is implanted as a p-type dopant in the n-type ZnO substrate;
A diffusion current is generated in the n layer and the pseudo p layer by applying a forward bias voltage;
Based on the Joule heat generated by the generated diffusion current, repeatedly changing the dopant distribution of nitrogen implanted in any one or more of the pseudo-p layers, and the conduction band in the active layer by the forward bias voltage Causing an inversion distribution in the valence band,
In the place where the near-field light is generated based on the nitrogen dopant distribution after the change, by causing the electrons in the conduction band forming the inversion distribution to be stimulated emission in multiple stages based on a non-adiabatic process, A method for producing p-type ZnO, characterized in that the diffusion current is reduced to lower the Joule heat, the dopant distribution of nitrogen in the pseudo-p layer is fixed, and the pseudo-p layer is configured as p-type ZnO . 2. The p-type ZnO according to claim 1, wherein at the time of applying the forward bias voltage, at least the pseudo-p layer is irradiated with guide light having any wavelength in the ultraviolet band to the blue band from the outside. Manufacturing method.

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