JP6100590B2 - P-type ZnO-based semiconductor layer manufacturing method, ZnO-based semiconductor element manufacturing method, and n-type ZnO-based semiconductor multilayer structure - Google Patents

Description

  The present invention relates to a method for manufacturing a p-type ZnO-based semiconductor layer, a method for manufacturing a ZnO-based semiconductor element, and an n-type ZnO-based semiconductor multilayer structure.

  Zinc oxide (ZnO) is a direct-transition semiconductor having a band gap energy of 3.37 eV at room temperature, and has a relatively high exciton binding energy of 60 meV. In addition, the raw materials are inexpensive and have a feature of little influence on the environment and the human body. For this reason, realization of a light-emitting element using ZnO with high efficiency, low power consumption and excellent environmental performance is expected.

  However, the ZnO-based semiconductor is difficult to control the p-type conductivity because of the self-compensation effect due to strong ionicity. For example, as an acceptor impurity, a p-type having practical performance using a group VA element such as N, P, As, and Sb, a group IA element such as Li, Na, and K, and a group IB element such as Cu, Ag, and Au. Research on ZnO-based semiconductors has been conducted (see, for example, Patent Documents 1 to 5).

JP 2001-48698 A JP 2001-68707 A JP 2004-221132 A JP 2009-256142 A Japanese Patent No. 4365530

  An object of the present invention is to provide a novel method for manufacturing a p-type ZnO-based semiconductor layer, a method for manufacturing a ZnO-based semiconductor element, and an n-type ZnO-based semiconductor multilayer structure.

According to one aspect of the present invention, (a) a step of forming a _first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, and (b) the first Mg _x Zn Forming a group IB element layer containing a group IB element of Cu or / and Ag on the _1-xO (0 ≦ x ≦ 0.6) single crystal layer without supplying O ; c) forming a second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer on the group IB element layer; and (d) the second Mg _x Zn _{1− A} group IIIB containing one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In on the _x O (0 ≦ x ≦ 0.6) single crystal layer without supplying O A step of forming an element layer, (e) a step of repeating the steps (a) to (d) to form a laminated structure, and (f) annealing the laminated structure, Method for producing a p-type ZnO based semiconductor layer and a step wherein a group element group IIIB element to form a co-doped p-type _{Mg x Zn 1-x O (} 0 ≦ x ≦ 0.6) layer is provided The

According to another aspect of the present invention, the step of forming an n-type ZnO-based semiconductor layer above the substrate and the step of forming a p-type ZnO-based semiconductor layer above the n-type ZnO-based semiconductor layer are provided. And forming the p-type ZnO-based semiconductor layer includes: (a) forming a first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer; and (b) On the first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, without supplying O , an IB group element layer containing a IB group element that is Cu or / and Ag (C) forming a second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer on the group IB element layer, and (d) the first on the second _{Mg x Zn 1-x O (} 0 ≦ x ≦ 0.6) single crystal layer, selection without the supply of O, B, Ga, Al, and from the group consisting of in A step of forming a group IIIB element layer containing one or more group IIIB elements, (e) a step of repeating the steps (a) to (d) to form a layered structure, and (f) the layered structure And a step of forming a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer co-doped with the group IB element and the group IIIB element. A method is provided.

Further, according to another aspect of the present invention, a first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer and the first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) a group IB element layer containing a group IB element of Cu or / and Ag formed on the single crystal layer, and a second Mg _x Zn formed on the group IB element layer B, Ga formed on the _1-x O (0 ≦ x ≦ 0.6) single crystal layer and the second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer. And a group IIIB element layer containing one or more group IIIB elements selected from the group consisting of Al, In, and In, and the first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) unit crystal layer, wherein the group IB element layer, the second _{Mg x Zn 1-x O (} 0 ≦ x ≦ 0.6) single crystal layer, and the group IIIB element layer, is repeated in this order Layer n-type ZnO-based semiconductor multilayer structure is provided.

  According to the present invention, a novel method for manufacturing a p-type ZnO-based semiconductor layer, a method for manufacturing a ZnO-based semiconductor element, and an n-type ZnO-based semiconductor multilayer structure can be provided.

FIG. 1 is a schematic cross-sectional view showing an MBE apparatus. 2A is a schematic cross-sectional view of a sample before annealing, and FIG. 2B is a time chart showing a shutter sequence of a Zn cell, an O cell, a Cu cell, and a Ga cell when forming the alternately laminated structure 54. 2C is a schematic cross-sectional view of the alternately laminated structure 54, and FIG. 2D is a schematic cross-sectional view of the ZnO single crystal layer 54a, the Cu layer 54b, and the Ga layer 54c. FIGS. 3A and 3B are graphs showing the CV characteristics and the depth profile of the impurity concentration for the alternately laminated structure 54 of the sample 1 before annealing, respectively. FIG. 3C shows the alternately laminated structure 54 of the sample 1 before annealing of the sample 1. 3D is a graph showing a depth profile by SIMS of the absolute concentration [Cu] of Cu and the absolute concentration [Ga] of Ga, and FIG. 3D is viewed from the [11-20] direction of the alternately laminated structure 54 of Sample 1. It is a RHEED image. 4A and 4B are graphs showing the CV characteristics and the depth profile of the impurity concentration at the position where the alternately laminated structure 54 of the sample after annealing of the sample 1 is formed, respectively. 5A and FIG. 5B are graphs showing the CV characteristics and the depth profile of the impurity concentration for the alternately laminated structure 54 of the sample 2 before annealing, respectively, and FIG. 5C shows the alternately laminated structure 54 of the sample 2 before annealing of the sample 2. 5D is a graph showing the depth profile by SIMS of the absolute Cu concentration [Cu] and the absolute Ga concentration [Ga], and FIG. 5D is viewed from the [11-20] direction of the alternately laminated structure 54 of Sample 2. It is a RHEED image. 6A and 6B are graphs showing the CV characteristics and the depth profile of the impurity concentration at the position where the alternately laminated sample 54 of the sample 2 is formed, respectively, and FIG. It is a graph which shows the depth profile by SIMS of the absolute density | concentration [Cu] of Cu and the absolute density | concentration [Ga] of Ga in the structure 54 formation position. 7A to 7C are flowcharts illustrating an outline of a method for manufacturing a ZnO-based semiconductor light emitting device according to an embodiment. FIG. 8A is a schematic cross-sectional view of a ZnO-based semiconductor light-emitting device manufactured by the manufacturing method according to the first embodiment, and FIG. 8B is a schematic cross-sectional view of an alternate stacked structure 5A. FIG. 9 illustrates a Zn cell, an Mg cell, an O cell, and a Cu cell formed when an alternating multilayer structure is formed when a Cu, Ga co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer is formed. It is a time chart which shows an example of the shutter sequence of Cu cell and Ga cell. 10A is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device manufactured by the manufacturing method according to the second embodiment, and FIG. 10B is a schematic cross-sectional view showing another example of the active layer 15. FIG. 10C is a schematic cross-sectional view of the alternately laminated structure 16A. FIG. 11 is a schematic cross-sectional view of a ZnO based semiconductor light emitting device manufactured by the manufacturing method according to the third embodiment. FIG. 12 is a table summarizing the film forming conditions in steps (a) and (c) of the first to third examples.

  First, a crystal manufacturing apparatus used for growing a ZnO-based semiconductor layer or the like will be described. In the experiments and examples described below, molecular beam epitaxy (MBE) is used as a crystal manufacturing method. Here, the ZnO-based semiconductor contains at least Zn and O.

  FIG. 1 is a schematic cross-sectional view showing an MBE apparatus. In the vacuum chamber 71, a Zn source gun 72, an O source gun 73, an Mg source gun 74, a Cu source gun 75, and a Ga source gun 76 are provided.

  The Zn source gun 72, the Mg source gun 74, the Cu source gun 75, and the Ga source gun 76 are Knudsen cells that contain solid sources of Zn (7N), Mg (6N), Cu (9N), and Ga (7N), respectively. A Zn beam, Mg beam, Cu beam, and Ga beam are emitted by heating the cell.

The O source gun 73 includes an electrodeless discharge tube that uses a radio frequency of 13.56 MHz, for example, and plasmas O ₂ gas (6N) in the electrodeless discharge tube to emit an O radical beam. As the discharge tube material, alumina or high-purity quartz can be used.

  A stage 77 having a substrate heater holds the substrate 78. Each of the source guns 72 to 76 includes a cell shutter. By opening / closing each cell shutter, it is possible to switch between a state where each beam is irradiated onto the substrate 78 and a state where each beam is not irradiated. By irradiating a desired beam on the substrate 78 at a desired timing, a ZnO-based compound semiconductor layer having a desired composition can be grown.

By adding Mg to ZnO, the band gap can be widened. However, since ZnO has a wurtzite structure (hexagonal crystal) and MgO has a rock salt structure (cubic crystal), phase separation occurs when the Mg composition is too high. In Mg _x Zn _1-x O in which the Mg composition of MgZnO is specified as x, the Mg composition x is preferably 0.6 or less in order to maintain the wurtzite structure. Note that the notation Mg _x Zn _1-x O includes ZnO to which Mg is not added when x = 0.

  The n-type conductivity of the ZnO-based semiconductor can be obtained without doping impurities. Impurities such as Ga can be doped to increase n-type conductivity. The p-type conductivity of the ZnO-based semiconductor can be obtained by doping with a p-type impurity.

  A film thickness meter 79 using a crystal resonator is provided in the vacuum chamber 71. From the adhesion rate measured by the film thickness meter 79, the flux intensity of each beam is obtained.

  A gun 80 for reflection high energy electron diffraction (RHEED) and a screen 81 for displaying an RHEED image are attached to the vacuum chamber 71. From the RHEED image, the surface flatness and growth mode of the crystal layer formed on the substrate 78 can be evaluated.

  When the crystal is two-dimensionally grown and the surface is epitaxially grown (single crystal growth), the RHEED image shows a streak pattern, and when the crystal is three-dimensionally grown and the surface is not flat (single crystal growth), the RHEED image is A spot pattern is shown. In the case of polycrystalline growth, the RHEED image becomes a ring pattern.

Next, the VI / II flux ratio in Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) crystal growth will be described. The flux intensity of Zn beam _J Zn, the flux intensity of the Mg beam _{J Mg,} the flux intensity of O radical beam expressed as _{J O.} A beam of Zn or Mg, which is a metal material, contains atoms or clusters of Zn or Mg containing a plurality of atoms. Both atoms and clusters are effective for crystal growth. The O beam, which is a gas material, contains atomic radicals and neutral molecules. Here, the flux intensity of atomic radicals effective for crystal growth is considered.

An adhesion coefficient indicating the ease with which Zn adheres to the crystal is represented by k _Zn , an adhesion coefficient indicating the ease with which Mg is deposited is represented by k _Mg , and an adhesion coefficient indicating the ease with which O is deposited is represented by k _O. Zn adhesion coefficient k _Zn and flux strength J _Zn product k _Zn J _Zn , Mg adhesion coefficient k _Mg and flux strength J _Mg product k _Mg J _Mg , and O adhesion coefficient k _O and flux strength J _O The product k _O J _O corresponds to the number of Zn atoms, Mg atoms, and O atoms attached to the unit area of the substrate per unit time, respectively.

k _Zn J _Zn and _k Mg to the sum of _{J Mg} is the ratio of _{k O J O k O J O} / a _{(k Zn J Zn + k Mg} J Mg), defined as VI / II flux ratio. When the VI / II flux ratio is smaller than 1, the group II rich condition (simply Zn rich condition when Mg is not included), when the VI / II flux ratio is equal to 1, the stoichiometric condition, and the VI / II flux ratio is The case where it is larger than 1 is called VI group rich condition (or O rich condition).

In the crystal growth on the Zn plane (+ c plane), if the substrate surface temperature is 850 ° C. or lower, the adhesion coefficients k _Zn , k _Mg and k 2 _O can be regarded as 1, and the VI / II flux ratio is J _{O 2} / (J _Zn + J _Mg ).

The VI / II flux ratio can be calculated by the following procedure, for example, in the growth of ZnO. The Zn flux is measured as a _Zn deposition rate F _Zn (nm / s) at room temperature by a film thickness monitor using a crystal resonator. The Zn flux is converted from F _Zn (nm / s) to J _Zn (atoms / cm ² s).

On the other hand, O radical flux is calculated | required as follows. ZnO is grown by changing the Zn flux under constant O radical beam irradiation conditions (for example, RF power 300 W, O ₂ flow rate 2.0 sccm), and the Zn flux growth rate is experimentally determined. By fitting the result using the approximate expression of ZnO growth rate G _ZnO : G _ZnO = [(k _Zn J _Zn ) ^-1 + (k _O J _O ) ^-1 ] ^-1 , O radicals under the conditions flux _{J O} is calculated. From Zn flux _{J Zn} and O radical flux _{J O} thus obtained, it is possible to calculate the VI / II flux ratio.

  In the first application (Japanese Patent Application No. 2012-41096) filed earlier, the inventors of the present application proposed a novel technique of doping Cu into, for example, a ZnO-based semiconductor. This is because when Zn, O and Cu are supplied simultaneously and a Cu-doped ZnO film is grown by the MBE method, three-dimensional growth occurs, a polycrystalline film having a rough surface is obtained, and Cu is doped uniformly in the film thickness direction. This is a proposal made based on the experimental results and the like.

  By supplying Zn, O and Cu at the same time, the inventors of the present application promote the reaction between the active O radical and Cu, and CuO is formed as another crystal phase more than Cu replaces the Zn site. As a result, it was considered that ZnO growth was inhibited and polycrystallization occurred.

When a Cu-doped ZnO film is grown by simultaneously supplying Zn, O radicals and Cu, CuO (II) is likely to be formed due to the fact that Cu easily reacts with active O radicals. It is thought that the formation of valence Cu ²⁺ becomes dominant. In addition, since the temperature at which CuO (II) is thermally decomposed into Cu ₂ O (I) is higher than the growth temperature of the Cu-doped ZnO film, divalent Cu ²⁺ is unlikely to become monovalent Cu ⁺ , and in ZnO It is considered that Cu that does not function as an acceptor becomes dominant.

The inventors of the present application have two-dimensional growth and p-type conductivity as long as monovalent Cu ⁺ is more easily produced than divalent Cu ²⁺ , and Cu is a method for forming a Cu-doped ZnO layer that easily replaces a Zn site. For example, a step of forming a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film and a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) In the first application, a method for producing a Cu-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer, in which the steps of supplying Cu on the single crystal film are alternately repeated, was proposed. According to the manufacturing method according to the first application, a Cu-doped p-type Mg _x Zn _1-x O single crystal layer having high flatness and good crystallinity can be obtained.

Furthermore, the inventors of the present application discovered that the Ga-doped ZnO single crystal layer supplied with Cu on the layer becomes p-type by annealing, and the second application (Japanese Patent Application No. 2012-166837) filed earlier. Proposed a method for producing a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer co-doped with Cu and Ga, for example. The p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer according to the second application has high flatness and good crystallinity, and is obtained by the manufacturing method according to the first application. It contains more monovalent Cu ⁺ that effectively functions as an acceptor than the p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer.

  The invention according to the present application is a method for manufacturing a p-type ZnO-based semiconductor layer, a method for manufacturing a ZnO-based semiconductor element, and an n-type ZnO-based semiconductor multilayer structure, which are different from the proposals according to the first and second applications made earlier. About.

  First, an experiment conducted by the inventors will be described. As a result of diligent research, the inventors of the present application have determined that an n-type stacked structure in which ZnO single crystal layers supplied with Cu on the layers and ZnO single crystal layers supplied with Ga on the layers are alternately stacked ( It was discovered that the (alternate layered structure) becomes p-type by annealing. Hereinafter, description will be given along Sample 1 and Sample 2. In the description, a sample before annealing is described as a sample before annealing, and a sample after annealing is described as a sample after annealing.

  A method for manufacturing the sample 1 before annealing will be described. FIG. 2A shows a schematic cross-sectional view of the sample before annealing.

After performing thermal cleaning at 900 ° C. for 30 minutes on a Zn-faced ZnO (0001) substrate (hereinafter referred to as a ZnO substrate in this specification) 51 having n-type conductivity, the temperature of the substrate 51 was lowered to 300 ° C. At that temperature (growth temperature 300 ° C.), Zn flux F _Zn is 0.13 nm / s (J _Zn = 8.5 × 10 ¹⁴ atoms / cm ² s), O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate. The ZnO buffer layer 52 having a thickness of 30 nm was grown on the ZnO substrate 51 at 2.0 sccm (J 2 _O = 8.1 × 10 ¹⁴ atoms / cm ² s). In order to improve the crystallinity and surface flatness of the ZnO buffer layer 52, annealing was performed at 900 ° C. for 10 minutes.

On the ZnO buffer layer 52, the growth temperature is 900 ° C., the Zn flux F _Zn is 0.13 nm / s (J _Zn = 8.5 × 10 ¹⁴ atoms / cm ² s), the O radical beam irradiation condition is RF power 300 W, An undoped ZnO layer 53 having a thickness of 100 nm was grown at an O ₂ flow rate of 2.0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s). The undoped ZnO layer 53 is an n-type ZnO layer. On the undoped ZnO layer 53, the alternately laminated structure 54 was formed by changing the supply period of Zn and O, the supply period of Cu, and the supply period of Ga from each other. The formation temperature of the alternately laminated structure 54 was 250 ° C.

  FIG. 2B is a time chart showing a shutter sequence of Zn cells, O cells, Cu cells, and Ga cells when forming the alternately laminated structure 54.

In forming the alternate laminated structure 54, a (P ₁ ) ZnO single-crystal layer growth process in which a Zn cell shutter and an O cell shutter are opened and a Cu cell shutter and a Ga cell shutter are closed, (P ₂ ) Zn cell shutter, O cell shutter , And closing the Ga cell shutter and opening the Cu cell shutter Cu attaching step (Cu layer forming step), (P ₃ ) closing the Ga cell shutter, closing the O cell shutter and the Cu cell shutter and opening the Ga cell shutter (Ga layer forming step) is repeated in the order of, for example, (P ₁ ), (P ₂ ), (P ₁ ), (P ₃ ). In _{(P 1)} and _{(P 2),} ZnO single crystal layer Cu is supplied is formed on the layer, _{(P 1)} and in _{(P 3),} ZnO single crystal layer Ga is supplied onto the layer Is formed.

Since the steps (P ₁ ) to (P ₃ ) are provided separately and the open period of the O cell shutter and the open period of the Cu cell shutter are not overlapped, the O radical and Cu are not supplied simultaneously.

In the step (P ₁ ), the open period of the Zn cell shutter is extended before and after the open period of the O cell shutter. That is, the open period of the Zn cell shutter includes the open period of the O cell shutter. In addition to not supplying O radicals and Cu simultaneously, by covering the surface of the ZnO single crystal layer with Zn (by suppressing the exposure of O), the direct reaction between the O radicals and Cu is performed before the Cu deposition step. Suppress.

  In the preparation of the sample 1 before annealing, the open period of each O cell shutter was 10 seconds, and the open period of the Zn cell shutter was extended by 1 second before and after the open period of the O cell shutter. The open period per time of the Zn cell shutter is 12 seconds. 10 seconds during which both the Zn cell shutter and the O cell shutter are opened is the ZnO single crystal layer growth period per time. The open period per time of the Cu cell shutter was 100 seconds, and the open period per time of the Ga cell shutter was 16 seconds.

30 sets of the steps of performing (P ₁ ), (P ₂ ), (P ₁ ), and (P ₃ ) in this order were repeated to obtain an alternately laminated structure 54 having a thickness of about 100 nm. Zn flux F _Zn in the process (P ₁ ) is 0.13 nm / s (J _Zn = 8.5 × 10 ¹⁴ atoms / cm ² s), O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate 2.0 sccm ( J _O = 8.1 × 10 ¹⁴ atoms / cm ² s). The VI / II flux ratio is 0.95 (Zn rich condition). The cell temperature T _Cu of Cu in the step (P ₂ ) was 950 ° C., and the cell temperature T _Ga of Ga in the step (P ₃ ) was 540 ° C.

  FIG. 2C is a schematic cross-sectional view of the alternately laminated structure 54. The alternate stacked structure 54 has a structure in which a ZnO single crystal layer 54a, a Cu layer 54b, a ZnO single crystal layer 54a, and a Ga layer 54c are repeated in this order, and 30 layers are stacked. In this stacked structure, it is considered that a ZnO single crystal layer supplied with Cu on the layer and a ZnO single crystal layer supplied with Ga on the layer are alternately stacked by 30 layers in the thickness direction. Is also possible.

  The thickness of the ZnO single crystal layer 54a is about 1.7 nm, the thickness of the Cu layer 54b (Cu deposition thickness) is 1 atomic layer or less, for example, about 1/3 atomic layer, the thickness of the Ga layer 54c (Ga The deposition thickness) is 1 atomic layer or less, for example about 1/5 atomic layer. The Cu coverage on the surface of the ZnO single crystal layer 54a is about 33%, and the Ga coverage is about 20%.

  FIG. 2D shows a schematic cross-sectional view of the ZnO single crystal layer 54a, the Cu layer 54b, and the Ga layer 54c. As shown in this figure, for example, the Cu layer 54b having a thickness of about 1/3 atomic layer is formed of Cu adhering to a part of the surface of the ZnO single crystal layer 54a. Further, for example, the Ga layer 54c having a thickness of about 1/5 atomic layer is formed of Ga adhering to a part of the surface of the ZnO single crystal layer 54a. Hereinafter, in order to simplify the drawing, the alternate laminated structure 54 including the Cu and Ga deposition modes is represented by the layer structure of FIG. 2C.

3A and 3B are graphs showing the CV characteristics and the depth profile of the impurity concentration for the alternately laminated structure 54 of the sample 1 before annealing, respectively. The measurement was performed by an electrochemical CV measurement (ECV) method using an electrolytic solution as a Schottky electrode. The graph shows the results of analysis using a parallel model. The horizontal axis of the graph of FIG. 3A represents the voltage in the unit “V”, and the vertical axis represents “1 / C ² ” in the unit “cm ⁴ / F ² ”. Both axes use a linear scale. Also, the horizontal axis of the graph of FIG. 3B represents the position in the depth (thickness) direction of the sample in the unit “nm”, and the vertical axis represents the impurity concentration in the unit “cm ⁻³ ”. The horizontal axis uses a linear scale, and the vertical axis uses a logarithmic scale.

Referring to the graph of FIG. 3A, a curve that rises to the right (a relationship in which 1 / C ² increases as the voltage increases) is obtained, and an alternate stacked structure 54 (a ZnO single crystal layer 54a in which Cu is supplied on the layer), and It is shown that the ZnO single crystal layer 54a) with Ga supplied on the layer has n-type conductivity. Note that the slope corresponds to the resistance value.

Referring to the graph of FIG. 3B, the impurity concentration (donor concentration) of alternate stacked structure 54 _{N d} is found to be about 1.0 × ¹⁰ 21 ^{cm -3.}

FIG. 3C shows the depth by secondary ion mass spectrometry (SIMS) of the absolute concentration [Cu] of Cu and the absolute concentration [Ga] of Ga in the alternately laminated structure 54 of the sample 1 before annealing. It is a graph which shows a profile. The horizontal axis of the graph represents the position in the depth direction of the sample in the unit “μm”, and the vertical axis represents the Cu concentration [Cu] and the Ga concentration [Ga] in the unit “cm ⁻³ ”. The horizontal axis uses a linear scale, and the vertical axis uses a logarithmic scale.

It can be seen that the Cu concentration [Cu] in the alternately laminated structure 54 is 1.0 × 10 ²¹ cm ⁻³ and the Ga concentration [Ga] is 6.0 × 10 ²⁰ cm ⁻³ . The value of [Cu] / [Ga] is 1.7.

  FIG. 3D is a RHEED image viewed from the [11-20] direction of the alternate stacked structure 54. The RHEED image shows a streak pattern, which indicates that a single crystal layer having a flat surface and good crystallinity is formed.

  Next, the sample 1 was annealed. Annealing was performed at 600 ° C. for 10 minutes in an oxygen atmosphere at a flow rate of 1 L / min.

  4A and 4B are graphs showing the CV characteristics and the depth profile of the impurity concentration at the position where the alternately laminated structure 54 of the sample after annealing of the sample 1 is formed, respectively. The meanings of both axes of the graph are equal to those of the graphs shown in FIGS. 3A and 3B, respectively.

In the graph of FIG. 4A, a downward-sloping curve (a relationship in which 1 / C ² decreases as the voltage increases) is obtained, and it is shown that the formation position of the alternately laminated structure 54 has p-type conductivity.

Referring to the graph of FIG. 4B, the impurity concentration (acceptor concentration) _{N a} of alternate stacked structure 54 forming positions in the sample after annealing of the sample 1 (p-type layer formation position) is the order of 1.0 × ¹⁰ 18 ^{cm -3} I understand that.

The Cu concentration [Cu] at the position where the alternate stacked structure 54 is formed (p-type layer formation position) is about 8.0 × 10 ²⁰ cm ⁻³ and the Ga concentration [Ga] is about 5.0 × 10 ²⁰ cm ⁻³ . The value of [Cu] / [Ga] is expected to be about 1.6.

  Next, sample 2 will be described. Sample 2 is a sample in which the thickness of the ZnO single crystal layer 54a, the Cu layer 54b, and the Ga layer 54c is about ½ when compared with Sample 1. Except for the alternately laminated structure 54, the layers were formed under the same growth conditions as those of the sample 1 before annealing.

In the preparation of the sample 2 before annealing for sample 2, the process of performing (P ₁ ), (P ₂ ), (P ₁ ), and (P ₃ ) in this order is repeated 60 sets, and an alternate stacked structure having a thickness of about 110 nm 54 was obtained. Zn flux F _Zn in the process (P ₁ ) is 0.12 nm / s (J _Zn = 7.9 × 10 ¹⁴ atoms / cm ² s), O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate 2.0 sccm ( J _O = 8.1 × 10 ¹⁴ atoms / cm ² s). The VI / II flux ratio is 1.0 (stoichiometric conditions). The cell temperature T _Cu of Cu in the step (P ₂ ) was 950 ° C., and the cell temperature T _Ga of Ga in the step (P ₃ ) was 540 ° C.

  The open period per O cell shutter was 5 seconds, and the open period of the Zn cell shutter was extended by 1 second before and after the open period of the O cell shutter. The open period per time of the Zn cell shutter is 7 seconds. 5 seconds when both the Zn cell shutter and the O cell shutter are in the open state is a ZnO single crystal layer growth period per time. The open period per time of the Cu cell shutter was 50 seconds, and the open period per time of the Ga cell shutter was 8 seconds.

  The alternate laminated structure 54 of Sample 2 has a structure in which 60 layers of ZnO single crystal layers 54a, Cu layers 54b, ZnO single crystal layers 54a, and Ga layers 54c are repeated in this order.

  The thickness of the ZnO single crystal layer 54a is about 0.9 nm, the thickness of the Cu layer 54b (Cu deposition thickness) is 1 atomic layer or less, for example, about 1/5 atomic layer, the thickness of the Ga layer 54c (Ga The deposition thickness) is 1 atomic layer or less, for example about 1/15 atomic layer. The Cu coverage on the surface of the ZnO single crystal layer 54a is about 21%, and the Ga coverage is about 6.7%.

  5A and 5B are graphs showing the CV characteristics and the depth profile of the impurity concentration for the alternately laminated sample 54 of the sample 2 before annealing, respectively. The meanings of both axes in each graph are equal to those in FIGS. 3A and 3B.

Referring to the graph of FIG. 5A, a curve that rises to the right (the relationship in which 1 / C ² increases as the voltage increases) is obtained, and an alternate stacked structure 54 (a ZnO single crystal layer 54a to which Cu is supplied on the layer), and It is shown that the ZnO single crystal layer 54a) with Ga supplied on the layer has n-type conductivity.

Referring to the graph of FIG. 5B, the impurity concentration (donor concentration) of alternate stacked structure 54 _{N d} is found to be about 1.7 × ¹⁰ 21 ^{cm -3.}

  FIG. 5C is a graph showing a SIMS depth profile of the Cu absolute concentration [Cu] and the Ga absolute concentration [Ga] in the alternately laminated structure 54 of the sample 2 before annealing. The meaning of both axes of the graph is equal to that of FIG. 3C.

It can be seen that the Cu concentration [Cu] in the alternately laminated structure 54 is 1.1 × 10 ²¹ cm ⁻³ and the Ga concentration [Ga] is 3.5 × 10 ²⁰ cm ⁻³ . The value of [Cu] / [Ga] is 3.14.

  FIG. 5D is an RHEED image viewed from the [11-20] direction of the alternately laminated structure 54. A spot streak pattern is shown. Although a single crystal layer is formed, for example, it is spot-like compared to the RHEED image shown in FIG. 3D, and it can be seen that the surface has irregularities.

  Next, the sample 2 was annealed. Annealing was performed at 600 ° C. for 10 minutes in an oxygen atmosphere at a flow rate of 1 L / min.

  6A and 6B are graphs showing the CV characteristics and the depth profile of the impurity concentration at the positions where the alternately laminated structure 54 of the sample 2 after annealing of the sample 2 is formed, respectively. The meanings of both axes of the graph are equal to those of the graphs shown in FIGS. 3A and 3B, respectively.

In the graph of FIG. 6A, a downward-sloping curve (a relationship in which 1 / C ² decreases as the voltage increases) is obtained, and it is shown that the formation position of the alternately laminated structure 54 has p-type conductivity.

Referring to the graph of FIG. 6B, the impurity concentration (acceptor concentration) _{N a} of alternate stacked structure 54 forming positions in the sample after annealing of the sample 2 (p-type layer formation position) is the order of 8.0 × ¹⁰ 17 ^{cm -3} I understand that.

  6C is a graph showing SIMS depth profiles of the Cu absolute concentration [Cu] and the Ga absolute concentration [Ga] at the formation position (p-type layer formation position) of the alternately laminated structure 54 of the sample 2 after annealing. It is. The meaning of both axes of the graph is equal to that of FIG. 3C.

The Cu concentration [Cu] is 8.0 × 10 ²⁰ cm ⁻³ and the Ga concentration [Ga] is 5.0 × 10 ²⁰ cm ^{−3 at} the position where the alternately laminated structure 54 is formed (p-type layer formation position). It can be seen that it is substantially constant over the entire thickness direction. In this specification, “almost constant” with respect to the concentration means a range of 50% to 150% of the average value of concentration (for example, 8.0 × 10 ²⁰ cm ^{−3 in} the case of [Cu] in the figure). . Cu and Ga are uniformly diffused. The value of [Cu] / [Ga] is 1.6.

  From the above experiments conducted by the inventors of the present application, the alternately laminated structure 54 of Sample 1 and Sample 2 (ZnO single crystal layer 54a with Cu supplied to the layer and ZnO single crystal with Ga supplied to the layer) It is understood that the layer 54a) is as-grown and n-type (see FIGS. 3A and 5A) and becomes p-type by annealing (see FIGS. 4A and 6A). By performing the annealing treatment, Cu in the Cu layer 54b and Ga in the Ga layer 54c are uniformly diffused into the ZnO single crystal layer 54a. With the diffusion of Cu and Ga, the alternate laminated structure 54 is considered to become a p-type ZnO single crystal layer co-doped with Cu and Ga (to be p-type). In the p-type ZnO single crystal layer, Cu is in a monovalent state, Ga is in a trivalent state, Zn sites are substituted, and Cu and Ga are considered to exert an electrical attractive force on each other.

  The annealing conditions (temperature, time, atmosphere, etc.) for the p-type are as follows: the thickness of the alternate stacked structure 54 and the ZnO single crystal layer 54a, the Cu concentration [Cu], the Ga concentration [Ga], [ The ratio of [Cu] to Ga] will vary depending on [Cu] / [Ga] and the like.

In the experiment, as shown in FIG. 6C, a p-type layer having substantially constant Cu concentration [Cu] and Ga concentration [Ga] was obtained over the entire thickness direction of the layer. For example, in the case of Sample 2, the Cu concentration [Cu] in the p-type layer was 8.0 × 10 ²⁰ cm ⁻³ .

From this result, an n-type stacked structure (alternate stacked structure 54) in which ZnO single crystal layers 54a supplied with Cu on the layers and ZnO single crystal layers 54a supplied with Ga on the layers are alternately stacked. Is uniformly doped in the thickness direction to a concentration of 1.0 × 10 ¹⁹ cm ⁻³ or higher, which is a high concentration, and to a concentration of at least less than 1.0 × 10 ²¹ cm ^−3. I think it can be done. Further, according to this method, for example, a method for manufacturing a p-type layer according to the second application filed earlier (as an example, a Ga-doped ZnO single crystal layer supplied with Cu on the layer is annealed, and Cu, Ga Compared with a method of manufacturing a co-doped p-type ZnO single crystal layer), since the ZnO single crystal layer 54a is not directly doped with Ga, a p-type ZnO semiconductor single crystal layer doped with Ga and Cu at a higher concentration Easy to manufacture. Furthermore, the Ga and Cu concentrations can be controlled by the open period of the cell shutter.

The inventors of the present application have found that the impurity concentration (acceptor concentration) of Cu in the ZnO-based semiconductor layer is about two orders of magnitude smaller than the absolute concentration of Cu [Cu]. Taking this knowledge into consideration, a p-type layer having an acceptor concentration of 1.0 × 10 ¹⁷ cm ⁻³ or more and less than 1.0 × 10 ¹⁹ cm ⁻³ can be obtained by the method of annealing the alternately laminated structure 54. it can. In the experiment, p-type layers having an acceptor concentration of 1.0 × 10 ¹⁸ cm ⁻³ (for sample 1) and 8.0 × 10 ¹⁷ cm ⁻³ (for sample 2) are obtained.

A p-type layer can be considered practical if the acceptor concentration is 1.0 × 10 ¹⁷ cm ⁻³ or more. Therefore, the p-type layer obtained by the experiment is a p-type ZnO-based semiconductor single crystal layer having practical p-type conductivity.

  According to the method of annealing the alternately laminated structure 54, Cu and Ga having a practical p-type conductivity are obtained in which Cu is highly concentrated and Cu and Ga are uniformly doped in the entire thickness direction of the layer. A doped ZnO single crystal layer can be produced.

  The inventors of the present application have discovered that further annealing of the p-type alternate laminated structure 54 can provide n-type conductivity again. Therefore, the annealing process may be terminated, for example, after the alternate laminated structure 54 becomes p-type and before it becomes an n-type layer again.

  Next, a first example of manufacturing a ZnO-based semiconductor light emitting device using a Cu, Ga co-doped ZnO layer as a p-type semiconductor layer will be described.

  7A to 7C are flowcharts illustrating an outline of a method for manufacturing a ZnO-based semiconductor light emitting device according to an embodiment. In addition, although an Example demonstrates a semiconductor light-emitting device, this invention is applicable not only to a light-emitting device but a semiconductor device widely.

  As shown in FIG. 7A, a method for manufacturing a ZnO-based semiconductor light emitting device according to an embodiment includes a step of forming an n-type ZnO-based semiconductor layer above a substrate (step S101), and an n-type ZnO-based semiconductor formed in step S101. A step (step S102) of forming a p-type ZnO-based semiconductor layer above the layer is included.

  Further, as shown in FIG. 7B, the p-type ZnO-based semiconductor layer forming step of Step S102 includes four steps of Step S102a, Step S102b, Step S102c, and Step S102d.

In the p-type ZnO-based semiconductor layer forming step (step S102), first, an n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer to which Cu is supplied is formed on the layer ( Step S102a). Next, an n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer to which Ga is supplied is formed thereon (step S102b). Step S102a and step S102b are alternately repeated to form a stacked structure (step S102c). Then, the stacked structure formed in step S102c is annealed to form a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer co-doped with Cu and Ga (step S102d).

More specifically, as shown in FIG. 7C, in the p-type ZnO-based semiconductor layer forming step (step S102), first, Zn, O, and Mg as necessary are supplied, and n-type Mg _x Zn _{1 -x O (0 ≦ x ≦ 0.6} ) to form a single crystal layer (step S102a _1). Next, step S102a n-type are formed in _{1 Mg x Zn 1-x O} (0 ≦ x ≦ 0.6) on the single crystal layer to form a Cu layer (Step S102a _2). Subsequently, Zn, O, and Mg as necessary are supplied, and an n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer is formed on the Cu layer (step S102b ₁ ). Further, step S102b n-type are formed in _{1 Mg x Zn 1-x O} (0 ≦ x ≦ 0.6) on the single crystal layer to form a Ga layer (Step S102b _2). Step S102a ₁ ~ a repeated Step S102b ₂ to form a laminated structure (step S102c). Then, the stacked structure formed in step S102c is annealed to form a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer co-doped with Cu and Ga (step S102d).

Incidentally, n-type ZnO-based semiconductor stacked structure according to the embodiment is manufactured by the process of step S102a~ step S102c of FIG. 7B (step S102a ₁ ~ step S102c of FIG. 7C).

  With reference to FIGS. 8A and 8B, a first embodiment for producing a ZnO-based semiconductor light emitting device having a homo structure will be described in detail. FIG. 8A is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device manufactured by the manufacturing method according to the first embodiment.

On the ZnO substrate 1, the growth temperature is 300 ° C., the Zn flux F _Zn is 0.15 nm / s (J _Zn = 9.9 × 10 ¹⁴ atoms / cm ² s), and the O radical beam irradiation condition is RF power 300 W, The ZnO buffer layer 2 having a thickness of 30 nm was grown at an O ₂ flow rate of 2.0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s). In order to improve the crystallinity and surface flatness of the ZnO buffer layer 2, annealing was performed at 900 ° C. for 10 minutes.

Zn, O and Ga were simultaneously supplied on the ZnO buffer layer 2 at a growth temperature of 900 ° C. to grow the n-type ZnO layer 3 having a thickness of 150 nm (for example, step S101 in FIG. 7A). Zn flux F _Zn is 0.15 nm / s (J _Zn = 9.9 × 10 ¹⁴ atoms / cm ² s), O radical beam irradiation conditions are RF power 250 W, O ₂ flow rate 1.0 sccm (J _O = 4.0). × 10 ¹⁴ atoms / cm ² s), and the cell temperature of Ga was 460 ° C. The Ga concentration of the n-type ZnO layer 3 is, for example, 1.5 × 10 ¹⁸ cm ⁻³ .

On the n-type ZnO layer 3, the growth temperature is 900 ° C., the Zn flux F _Zn is 0.03 nm / s (J _Zn = 2.0 × 10 ¹⁴ atoms / cm ² s), the O radical beam irradiation conditions are RF power 300 W, An undoped ZnO active layer 4 having a thickness of 15 nm was grown at an O ₂ flow rate of 2.0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s).

  Subsequently, a Cu and Ga co-doped p-type ZnO layer 5 was formed on the undoped ZnO active layer 4 (step S102 in FIG. 7A).

First, the substrate temperature was set to 250 ° C., and an alternately laminated structure was formed by a shutter sequence (see FIG. 2B) that was the same as that in Sample 1 before annealing. Specifically, a step of supplying Zn and O to grow a ZnO single crystal layer (step S102a _{1 in} FIG. 7C), a step of supplying Cu on the ZnO single crystal layer (step S102a _{2 in} FIG. 7C), Zn And the step of supplying Zn and O to grow a ZnO single crystal layer (step S102b _{1 in} FIG. 7C) and the step of supplying Ga onto the ZnO single crystal layer (step S102b _{2 in} FIG. 7C) are repeated 30 times in this order. An alternating laminated structure having a thickness of about 100 nm was formed (step S102c in FIG. 7C). The ZnO single crystal layer growth period per time is 10 seconds, the Cu supply period per time is 100 seconds, and the Ga supply period per time is 16 seconds. ZnO Zn flux _{F Zn} in single-crystal layer growth step _{0.13nm / s (J Zn = 8.5} × 10 14 atoms / cm 2 s), O radical beam irradiation conditions RF power 300 W, _{O 2} flow rate 2. It was set to 0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s). The VI / II flux ratio is 0.95. The Cu cell temperature T _Cu in the Cu supply step was 950 ° C., and the Ga cell temperature T _Ga in the Ga supply step was 540 ° C.

FIG. 8B is a schematic cross-sectional view of the alternately laminated structure 5A. The alternate stacked structure 5A has a stacked structure in which a ZnO single crystal layer 5a, a Cu layer 5b, a ZnO single crystal layer 5a, and a Ga layer 5c are stacked in this order. The thickness of the ZnO single crystal layer 5a is about 1.7 nm, the thickness of the Cu layer 5b is 1 atomic layer or less, for example, about 1/3 atomic layer, and the thickness of the Ga layer 5c is 1 atomic layer or less, for example, about 1 / 5 atomic layers. The Cu coverage on the surface of the ZnO single crystal layer 5a is about 33%, and the Ga coverage is about 20%. The alternate stacked structure 5A exhibits n-type conductivity, and the donor concentration _Nd is, for example, 1.0 × 10 ²¹ cm ⁻³ .

  Next, the alternate stacked structure 5A was annealed to form a p-type ZnO single crystal layer co-doped with Cu and Ga (step S102d in FIG. 7C). For example, by performing annealing at 600 ° C. for 10 minutes in an oxygen atmosphere at a flow rate of 1 L / min, the Cu of the Cu layer 5b and the Ga of the Ga layer 5c are diffused into the ZnO single crystal layer 5a, and the n-type conductivity The alternately laminated structure 5A showing the property can be a ZnO single crystal layer (Cu, Ga co-doped p-type ZnO layer 5) having p-type conductivity.

  Thereafter, an n-side electrode 6 n was formed on the back surface of the ZnO substrate 1. A p-side electrode 6p was formed on the Cu and Ga co-doped p-type ZnO layer 5, and a bonding electrode 7 was formed on the p-side electrode 6p. The n-side electrode 6n can be formed by stacking an Au layer having a thickness of 500 nm on a Ti layer having a thickness of 10 nm. The p-side electrode 6p is formed by laminating a 10 nm thick Au layer on a 1 nm thick Ni layer having a size of 300 μm □, and the bonding electrode 7 is formed by an Au layer having a size of 100 μm □ and a thickness of 500 nm. . In this manner, a ZnO-based semiconductor light emitting device was fabricated by the method according to the first example.

The Cu and Ga co-doped p-type ZnO layer 5 of the ZnO-based semiconductor light-emitting device manufactured by the manufacturing method according to the first embodiment is a p-type ZnO-based semiconductor single crystal layer in which Cu and Ga are co-doped. The Cu concentration [Cu] is 1.0 × 10 ¹⁹ cm ⁻³ or more and less than 1.0 × 10 ²¹ cm ⁻³ , for example, 8.0 × 10 ²⁰ cm ⁻³ , and is substantially constant in the layer thickness direction. is there. The Ga concentration [Ga] is, for example, 5.0 × 10 ²⁰ cm ⁻³ and is substantially constant in the layer thickness direction. In the Cu and Ga co-doped p-type ZnO layer 5 of the first example, [Cu] / [Ga] is 1.6.

  According to the manufacturing method according to the first embodiment, for example, Cu is highly doped, and Cu and Ga are uniformly doped throughout the thickness direction, and have practical p-type conductivity. The type ZnO layer 5 can be manufactured.

Experiments and In the first embodiment, Cu, to form a Ga co-doped p-type ZnO layer (e.g. _{Mg x Zn 1-x O x} = 0 in representation of steps S102a ₁ ~ Step S102d in Fig. 7C) is, n-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer growth step, Cu adhesion step, n-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer growth step, Ga By annealing the alternately laminated structure formed by repeating the deposition steps in this order, a Cu, Ga co-doped Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer exhibiting p-type conductivity is obtained. (For example, x ≠ 0 in the Mg _x Zn _1-x O notation in steps S102a ₁ to S102d in FIG. 7C).

FIG. 9 illustrates a Zn cell, an Mg cell, an O cell, and a Cu cell formed when an alternating multilayer structure is formed when a Cu, Ga co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer is formed. It is a time chart which shows an example of the shutter sequence of Cu cell and Ga cell.

In the formation of the alternating layered structure, Mg _x Zn _1-x O (0 <x ≦ 0... 0) opens (Q ₁ ) Zn cell shutter, Mg cell shutter, and O cell shutter and closes Cu cell shutter and Ga cell shutter. 6) Single crystal layer growth process, (Q ₂ ) Cu deposition process (Cu layer formation process), which closes the Zn cell shutter, Mg cell shutter, O cell shutter, and Ga cell shutter and opens the Cu cell shutter, (Q ₃ ) For example, (Q ₁ ), (Q ₂ ), (Q ₁ ) is a Ga deposition step (Ga layer forming step) in which the Zn cell shutter, Mg cell shutter, O cell shutter, and Cu cell shutter are closed and the Ga cell shutter is opened. , (Q ₃ ) in this order. In the step (Q ₁ ) and the step (Q ₂ ), an Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer to which Cu is supplied is formed on the layer, and the steps (Q ₁ ) and (Q ₁ ) and In the step (Q ₃ ), an Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer supplied with Ga is formed on the layer.

In the example shown in this figure, the open period of the Zn cell shutter in the Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer growth step includes the open period of the Mg cell shutter and the O cell shutter. Is set to Specifically, the opening and closing of the Mg cell shutter and the O cell shutter are performed simultaneously, and the opening period of the Zn cell shutter is extended before and after the opening periods of the Mg cell shutter and the O cell shutter.

For example, the open period per time of the Mg cell shutter and the O cell shutter is 10 seconds. The open period of the Zn cell shutter is extended by 1 second before and after the open period of the Mg cell shutter and the O cell shutter, and the open period per time of the Zn cell shutter is set to 12 seconds. 10 seconds when all of the Zn cell shutter, Mg cell shutter, and O cell shutter are in the open state is the Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer growth period. The open period per time of the Cu cell shutter was 100 seconds, and the open period per time of the Ga cell shutter was 16 seconds.

In addition to not supplying the O radical and Cu simultaneously, the surface of the Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer is covered with Zn before the Cu deposition step, so that the O radical and Cu The direct reaction of is suppressed.

In the case of supplying Mg together with Zn, from the viewpoint of suppressing the reaction between O radicals and Cu, for example, at least one of the open period of the Zn cell shutter and the open period of the Mg cell shutter has the open period of the O cell shutter. It should be included. From the viewpoint of improving the controllability of the Mg composition of the Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer, for example, the open period of the Zn cell shutter is the open period of the Mg cell shutter and the O cell shutter. It is thought that it should be included.

Next, a second example of manufacturing a double heterostructure ZnO-based semiconductor light-emitting device including a Cu, Ga co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer and A third embodiment will be described.

  FIG. 10A is a schematic cross-sectional view of a ZnO based semiconductor light emitting device manufactured by the manufacturing method according to the second embodiment.

Zn and O were simultaneously supplied on the ZnO substrate 11 to grow, for example, a ZnO buffer layer 12 having a thickness of 30 nm. As an example, the growth temperature may be 300 ° C., the Zn flux F _Zn may be 0.15 nm / s, the O radical beam irradiation conditions may be RF power 300 W, and the O ₂ flow rate 2.0 sccm. In order to improve the crystallinity and surface flatness of the ZnO buffer layer 12, annealing was performed at 900 ° C. for 10 minutes.

Zn, O, and Ga were simultaneously supplied on the ZnO buffer layer 12 to grow an n-type ZnO layer 13 having a thickness of 150 nm at a growth temperature of 900 ° C., for example. Zn flux F _Zn was 0.15 nm / s, O radical beam irradiation conditions were RF power 250 W, O ₂ flow rate 1.0 sccm, and Ga cell temperature was 460 ° C. The Ga concentration of the n-type ZnO layer 13 is, for example, 1.5 × 10 ¹⁸ cm ⁻³ .

Zn, Mg and O were simultaneously supplied on the n-type ZnO layer 13 to grow, for example, an n-type MgZnO layer 14 having a thickness of 30 nm. The growth temperature can be 900 ° C., Zn flux F _Zn can be 0.1 nm / s, Mg flux F _Mg can be 0.025 nm / s, O radical beam irradiation conditions can be RF power 300 W, and O ₂ flow rate 2.0 sccm. The Mg composition of the n-type MgZnO layer 14 is, for example, 0.3.

Zn and O were simultaneously supplied on the n-type MgZnO layer 14 to grow a ZnO active layer 15 having a thickness of 10 nm at a growth temperature of 900 ° C., for example. Zn flux F _Zn was 0.1 nm / s, O radical beam irradiation conditions were RF power 300 W, and O ₂ flow rate 2.0 sccm.

  As shown in FIG. 10B, the active layer 15 may employ a quantum well structure in which MgZnO barrier layers 15b and ZnO well layers 15w are alternately stacked instead of a single ZnO layer.

The step of lowering the substrate temperature to, for example, 250 ° C., supplying Zn, Mg, and O to grow an MgZnO single crystal layer (step S102a _{1 in} FIG. 7C), and supplying Cu on the MgZnO single crystal layer (FIG. 7C). Step S102a ₂ ), supplying Zn, Mg and O to grow a MgZnO single crystal layer (Step S102b _{1 in} FIG. 7C), supplying Ga on the MgZnO single crystal layer (Step S102b _{2 in} FIG. 7C) Were repeated 30 times in this order to form an alternately laminated structure having a thickness of about 100 nm on the active layer 15 (step S102c in FIG. 7C). The shutter sequence of the Zn cell, Mg cell, O cell, Cu cell, and Ga cell in forming the alternate stacked structure is the same as that shown in FIG. 9, for example.

For example, the growth period in the single MgZnO single crystal layer growth step is 10 seconds, the Cu supply period in one Cu supply step is 100 seconds, and the Ga supply period in one Ga supply step is 16 seconds. It was. The Zn flux F _Zn in the MgZnO single crystal layer growth step is 0.13 nm / s, the Mg flux F _Mg is 0.03 nm / s, the O radical beam irradiation conditions are RF power 300 W, and O ₂ flow rate 2.0 sccm. The VI / II flux ratio is 0.82. The Cu cell temperature T _Cu in the Cu supply step was 950 ° C., and the Ga cell temperature T _Ga in the Ga supply step was 540 ° C.

FIG. 10C is a schematic cross-sectional view of the alternately laminated structure 16A. The alternate stacked structure 16A has a stacked structure in which an MgZnO single crystal layer 16a, a Cu layer 16b, an MgZnO single crystal layer 16a, and a Ga layer 16c are stacked in this order. The MgZnO single crystal layer 16a has a thickness of about 1.7 nm, the Cu layer 16b has a thickness of 1 atomic layer or less, for example, about 1/3 atomic layer, and the Ga layer 16c has a thickness of 1 atomic layer or less, for example, about 1 / 5 atomic layers. The Cu coverage on the surface of the MgZnO single crystal layer 16a is about 33%, and the Ga coverage is about 20%. The alternate stacked structure 16A exhibits n-type conductivity, and the donor concentration _Nd is, for example, 8 × 10 ²⁰ cm ⁻³ .

  Next, the alternate stacked structure 16 </ b> A was annealed to form the p-type MgZnO layer 16 co-doped with Cu and Ga on the active layer 15. For example, by performing annealing at 600 ° C. for 10 minutes in an oxygen atmosphere at a flow rate of 1 L / min, Cu in the Cu layer 16b and Ga in the Ga layer 16c are diffused into the MgZnO single crystal layer 16a, and n-type conductivity The alternating laminated structure 16A exhibiting the property can be a single crystal layer (Cu, Ga co-doped p-type MgZnO layer 16) having p-type conductivity. The Mg composition of the Cu and Ga co-doped p-type MgZnO layer 16 is, for example, 0.3.

  Thereafter, an n-side electrode 17 n is formed on the back surface of the ZnO substrate 11, and a p-side electrode 17 p is formed on the Cu and Ga co-doped p-type MgZnO layer 16. Further, the bonding electrode 18 is formed on the p-side electrode 17p. For example, the n-side electrode 17n is formed by laminating a 500-nm thick Au layer on a 10-nm-thick Ti layer, and the p-side electrode 17p has a thickness of 300 μm □ and a 1-nm-thick Ni layer. It can be formed by laminating a 10 nm Au layer. The bonding electrode 18 is formed of an Au layer having a size of 100 μm □ and a thickness of 500 nm. In this way, a ZnO-based semiconductor light emitting device is manufactured by the method according to the second embodiment.

Although the ZnO substrate 11 is used in the second embodiment, a conductive substrate such as an MgZnO substrate, a GaN substrate, a SiC substrate, or a Ga ₂ O ₃ substrate can be used.

The Cu and Ga co-doped p-type MgZnO layer 16 of the ZnO-based semiconductor light-emitting device manufactured by the manufacturing method according to the second embodiment is a p-type ZnO-based semiconductor single crystal layer in which Cu and Ga are co-doped. The Cu concentration [Cu] is 1.0 × 10 ¹⁹ cm ⁻³ or more and less than 1.0 × 10 ²¹ cm ⁻³ , for example, 8.0 × 10 ²⁰ cm ⁻³ , and is substantially constant in the layer thickness direction. is there. The Ga concentration [Ga] is, for example, 5.0 × 10 ²⁰ cm ⁻³ and is substantially constant in the layer thickness direction. In the Cu and Ga co-doped p-type MgZnO layer 16 of the second embodiment, [Cu] / [Ga] is 1.6.

  According to the manufacturing method according to the second embodiment, for example, Cu is highly doped and Cu and Ga are uniformly doped over the entire thickness direction, and Cu and Ga co-doped p having practical p-type conductivity are provided. The type MgZnO layer 16 can be manufactured.

  FIG. 11 is a schematic cross-sectional view of a ZnO based semiconductor light emitting device manufactured by the manufacturing method according to the third embodiment. In the first and second embodiments, crystals are grown on a conductive substrate and a layer is formed. In the third embodiment, crystals are grown on an insulating substrate.

Mg and O are simultaneously supplied on the c-plane sapphire substrate 21 which is an insulating substrate, and an MgO buffer layer 22 having a thickness of, for example, 10 nm is grown. As an example, the growth temperature can be 650 ° C., the Mg flux F _Mg can be 0.05 nm / s, the O radical beam irradiation conditions can be RF power 300 W, and the O ₂ flow rate 2.0 sccm. The MgO buffer layer 22 functions as a polarity control layer for controlling the ZnO-based semiconductor thereon to grow with the Zn surface as the surface.

On the MgO buffer layer 22, for example, a growth temperature of 300 ° C., a Zn flux F _Zn of 0.15 nm / s, an O radical beam irradiation condition of an RF power of 300 W, an O ₂ flow rate of 2.0 sccm, and Zn and O are simultaneously supplied. A ZnO buffer layer 23 having a thickness of 30 nm is grown. The ZnO buffer layer 23 grows on the Zn plane. In order to improve the crystallinity and surface flatness of the ZnO buffer layer 23, annealing is performed at 900 ° C. for 30 minutes.

Zn, O, and Ga are simultaneously supplied on the ZnO buffer layer 23 to grow, for example, an n-type ZnO layer 24 having a thickness of 1.5 μm. As an example, the growth temperature is 900 ° C., the Zn flux F _Zn is 0.05 nm / s, the O radical beam irradiation condition is RF power 300 W, the O ₂ flow rate 2.0 sccm, and the Ga cell temperature is 480 ° C.

On the n-type ZnO layer 24, Zn, Mg and O are simultaneously supplied to grow, for example, an n-type MgZnO layer 25 having a thickness of 30 nm. The growth temperature can be 900 ° C., Zn flux F _Zn can be 0.1 nm / s, Mg flux F _Mg can be 0.025 nm / s, O radical beam irradiation conditions can be RF power 300 W, and O ₂ flow rate 2.0 sccm. The Mg composition of the n-type MgZnO layer 25 is, for example, 0.3.

  On the n-type MgZnO layer 25, for example, a ZnO active layer 26 having a thickness of 10 nm is grown. The growth conditions can be made equal to those of the active layer 15 in the second embodiment. Instead of the single ZnO layer, a quantum well structure may be adopted.

  A Cu and Ga co-doped p-type MgZnO layer 27 is formed on the active layer 26. The formation method is the same as that of the Cu and Ga co-doped p-type MgZnO layer 16 in the second embodiment, for example.

  Since the c-plane sapphire substrate 21 of the third embodiment is an insulating substrate, an n-side electrode cannot be formed on the back side of the substrate 21. Therefore, etching is performed from the upper surface of the Cu and Ga co-doped p-type MgZnO layer 27 until the n-type ZnO layer 24 is exposed, and an n-side electrode 28n is formed on the exposed n-type ZnO layer 24. A p-side electrode 28p is formed on the Cu, Ga co-doped p-type MgZnO layer 27, and a bonding electrode 29 is formed on the p-side electrode 28p.

  The n-side electrode 28n is formed by stacking a 500 nm thick Au layer on a 10 nm thick Ti layer, and the p side electrode 28p is formed by a 10 nm thick Au layer on a 0.5 nm thick Ni layer. It can be formed by stacking. The bonding electrode 29 is formed of an Au layer having a thickness of 500 nm. In this manner, a ZnO-based semiconductor light emitting device is manufactured by the method according to the third embodiment.

  The Cu and Ga co-doped p-type MgZnO layer 27 of the ZnO-based semiconductor light emitting device according to the third embodiment is a p-type ZnO-based semiconductor single layer having the same properties as the Cu and Ga co-doped p-type MgZnO layer 16 of the second embodiment. It is a crystal layer.

  As mentioned above, although this invention was demonstrated along experiment and an Example, this invention is not restrict | limited to these.

For example, in the manufacturing method according to the embodiment, O radicals are used as an oxygen source, but other gases having strong oxidizing power such as polar oxidizers such as ozone, H ₂ O, and alcohol can be used.

  In the manufacturing method according to the embodiment, annealing is performed in an oxygen atmosphere, but may be performed in the air.

Further, in the experiments and examples, an n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer supplied with Cu on the layer and an n-type Mg supplied with Ga on the layer. _{A structure in which x} Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers are alternately stacked is annealed, and Cu and Ga co-doped Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) A single crystal layer was formed (p-type). By annealing the alternately laminated structure containing Cu (IB group element) and Ga (IIIB group element), Cu becomes easy to bond with O which is a VIB group element in a monovalent (Cu ⁺ ) state, and as an acceptor. It is considered that the function of monovalent Cu ⁺ is more likely to occur than divalent Cu ²⁺ , and as a result, the alternate stacked structure becomes p-type. Therefore, Ag which is a group IB element capable of forming a plurality of valences similarly to Cu can be used instead of or together with Cu. Moreover, not only Ga but B, Al, and In which are IIIB group elements like Ga can be used. The group IIIB element used may be one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In.

  It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like can be made.

The step of forming the (α) Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film proposed by the inventors of the present invention in the first application made earlier, and (β) Cu-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6), in which the step of supplying Cu onto the Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film is alternately repeated. The following findings (1) to (3) have been obtained in the method for producing a) layer.

(1) Forming a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film having a thickness of 10 nm or less per step (α) in order to prevent deterioration of crystallinity. Is desirable.

(2) In order to obtain high flatness and good crystallinity, stoichiometry conditions (VI / II flux ratio is 1) or Group II rich conditions (VI / II flux ratio is less than 1) in step (α) ) Is desirable to form a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film under the condition that the VI / II flux ratio is 0.5 or more and less than 1. More desirable.

(3) In order to realize good crystal growth, in the step (α), the growth temperature (substrate temperature) is about 200 ° C. or more and 350 ° C. or less, and Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) It is desirable to grow a single crystal film.

In the present application, for example, (a) a step of forming a _first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, and (b) the first Mg _x Zn _1-x O ( (0 ≦ x ≦ 0.6) a step of forming a group IB element layer containing a group IB element of Cu or / and Ag on the single crystal layer, and (c) a second layer on the group IB element layer A step of forming a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer; and (d) the second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal. Forming a group IIIB element layer containing one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In on the layer; and (e) the steps (a) to (d). A step of repeatedly forming a laminated structure; and (f) annealing the laminated structure to co-doped the group IB element and the group IIIB element. Even when a p-type ZnO-based semiconductor layer is manufactured using a step of forming a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer, the above (1) to (3) are shown. By carrying out the steps (a) and (c) under conditions, a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer having high flatness and good crystallinity can be obtained. Is possible.

FIG. 12 shows the steps (a) and (c) (first and second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers of the first to third embodiments. It is the table | surface which put together the film-forming conditions in the process to carry out.

As shown in this table, the conditions shown in the above (1) to (3) are satisfied in all of the first to third embodiments. Therefore, the p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer manufactured by the manufacturing method according to the embodiment is a p-type ZnO-based semiconductor layer having high flatness and good crystallinity. .

As a result of the inventors performing surface observation with an atomic force microscope (AFM) image or the like, the surface of the p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer was observed. Was found to be flatter than the surface of the alternating layered structure. By performing the annealing treatment, a p-type Mg _x Zn _1-x O layer with improved flatness is manufactured.

  The p-type ZnO-based semiconductor layer manufactured by the manufacturing method according to the embodiment can be used for, for example, a light emitting diode (LED) or a laser diode (LD) that emits light of a short wavelength (ultraviolet to blue wavelength region). It can be used for application products (various indicators, LED displays, CV / DVD light sources, etc.). Furthermore, it can be used for white LEDs and their application products (lighting fixtures, various indicators, displays, backlights for various displays, etc.). Moreover, it can utilize for an ultraviolet sensor.

DESCRIPTION OF SYMBOLS 1 ZnO substrate 2 ZnO buffer layer 3 n-type ZnO layer 4 Undoped ZnO active layer 5 Cu, Ga co-doped p-type ZnO layer 5A Alternating structure 5a ZnO single crystal layer 5b Cu layer 5c Ga layer 6n n-side electrode 6p p-side electrode 7 Bonding electrode 11 ZnO substrate 12 ZnO buffer layer 13 n-type ZnO layer 14 n-type MgZnO layer 15 active layer 15b MgZnO barrier layer 15w ZnO well layer 16 Cu, Ga co-doped p-type MgZnO layer 16A Alternating stacked structure 16a MgZnO single crystal layer 16b Cu layer 16c Ga layer 17n n-side electrode 17p p-side electrode 18 bonding electrode 21 c-plane sapphire substrate 22 MgO buffer layer 23 ZnO buffer layer 24 n-type ZnO layer 25 n-type MgZnO layer 26 active layer 27 Cu, Ga co-doped p Type MgZnO layer 28n n-side electrode 28pp p-side electrode 9 Bonding electrode 51 ZnO substrate 52 ZnO buffer layer 53 Undoped ZnO layer 54 Alternating laminated structure 54a ZnO single crystal layer 54b Cu layer 54c Ga layer 71 Vacuum chamber 72 Zn source gun 73 O source gun 74 Mg source gun 75 Cu source gun 76 Ga Source gun 77 Stage 78 Substrate 79 Film thickness meter 80 RHEED gun 81 Screen

Claims (7)

(A) forming a _first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer;
(B) On the first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, IB containing a group IB element that is Cu or / and Ag without supplying O Forming a group element layer;
(C) forming a second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer on the group IB element layer;
(D) On the second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, selected from the group consisting of B, Ga, Al, and In without supplying O Forming a Group IIIB element layer comprising one or more Group IIIB elements,
(E) repeating the steps (a) to (d) to form a laminated structure;
(F) annealing the laminated structure to form a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer co-doped with the group IB element and the group IIIB element; A method for producing a p-type ZnO-based semiconductor layer.   The method for producing a p-type ZnO-based semiconductor layer according to claim 1, wherein the steps (a) and (c) are performed by a MBE method at a substrate temperature of 350 ° C or lower.   The method for producing a p-type ZnO-based semiconductor layer according to claim 1 or 2, wherein the steps (a) and (c) are performed under a condition that a VI / II flux ratio is 0.5 or more and 1 or less. Forming an n-type ZnO-based semiconductor layer above the substrate;
Forming a p-type ZnO-based semiconductor layer above the n-type ZnO-based semiconductor layer,
The step of forming the p-type ZnO-based semiconductor layer includes:
(A) forming a _first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer;
(B) On the first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, IB containing a group IB element that is Cu or / and Ag without supplying O Forming a group element layer;
(C) forming a second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer on the group IB element layer;
(D) On the second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, selected from the group consisting of B, Ga, Al, and In without supplying O Forming a Group IIIB element layer comprising one or more Group IIIB elements,
(E) repeating the steps (a) to (d) to form a laminated structure;
(F) annealing the laminated structure to form a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer co-doped with the group IB element and the group IIIB element; A method for manufacturing a ZnO-based semiconductor element.   The method for manufacturing a ZnO-based semiconductor element according to claim 4, wherein the steps (a) and (c) are performed at a substrate temperature of 350 ° C. or less by an MBE method.   The method for producing a ZnO-based semiconductor element according to claim 4 or 5, wherein the steps (a) and (c) are performed under a condition that a VI / II flux ratio is 0.5 or more and 1 or less. A first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer;
A group IB element layer including a group IB element of Cu or / and Ag formed on the first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer;
A second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer formed on the group IB element layer;
One or more group IIIB elements selected from the group consisting of B, Ga, Al, and In formed on the second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer A group IIIB element layer containing
The first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, the IB group element layer, the second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) An n-type ZnO-based semiconductor multilayer structure in which a single crystal layer and the group IIIB element layer are repeatedly laminated in this order.