JP2014027135A - p-TYPE ZnO-BASED SEMICONDUCTOR SINGLE CRYSTAL LAYER, AND ZnO-BASED SEMICONDUCTOR ELEMENT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a p-type ZnO-based semiconductor single crystal layer doped with Cu or/and Ag with high concentration and uniformly in the thickness direction.SOLUTION: In the p-type ZnO-based semiconductor single crystal layer where (i) a group IB element of Cu or/and Ag, and (ii) one or more group IIIB element selected from a group consisting of B, Ga, Al and In are codoped, the concentration of group IB element is 1×10cmor more, and substantially constant in the thickness direction of layer.

Description

  The present invention relates to a p-type ZnO-based semiconductor single crystal layer and a ZnO-based semiconductor element.

Zinc oxide (ZnO) is a direct transition type 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 p-type ZnO-based semiconductor single crystal layer in which Cu or / and Ag are uniformly doped in a high concentration and in the thickness direction.

  Moreover, it is providing the ZnO type | system | group semiconductor element provided with this p-type ZnO type semiconductor single crystal layer.

According to one aspect of the present invention, (i) a group IB element that is Cu or / and Ag, and (ii) one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In A p-type ZnO-based semiconductor single-crystal layer that is a co-doped p-type ZnO-based semiconductor, wherein the concentration of the group IB element is 1 × 10 ¹⁹ cm ⁻³ or more, and is substantially constant in the thickness direction of the layer A single crystal layer is provided.

According to another aspect of the present invention, the n-type ZnO based semiconductor layer, the ZnO based semiconductor active layer formed above the n-type ZnO based semiconductor layer, and the ZnO based semiconductor active layer are formed. a p-type ZnO-based semiconductor layer, an n-side electrode electrically connected to the n-type ZnO-based semiconductor layer, and a p-side electrode electrically connected to the p-type ZnO-based semiconductor layer, The p-type ZnO-based semiconductor layer is a single crystal layer, and includes (i) a group IB element that is Cu or / and Ag, and (ii) one or more selected from the group consisting of B, Ga, Al, and In. Provided is a ZnO-based semiconductor device that is co-doped with a group IIIB element, the concentration of the group IB element is 1 × 10 ¹⁹ cm ⁻³ or more, and is substantially constant in the thickness direction of the p-type ZnO-based semiconductor layer Is done.

  According to the present invention, it is possible to provide a p-type ZnO-based semiconductor single crystal layer in which Cu or / and Ag are uniformly doped in a high concentration and in the thickness direction.

  In addition, a ZnO-based semiconductor element including the p-type ZnO-based semiconductor single crystal layer can be provided.

FIG. 1 is a schematic cross-sectional view showing an MBE apparatus. FIG. 2A is a schematic cross-sectional view of a sample before annealing, and FIG. 2B is a time chart showing a shutter sequence of Zn cells, O cells, Ga cells, and Cu cells when forming an alternately laminated structure, 2C is a schematic cross-sectional view of the alternately laminated structure 54, and FIG. 2D is a schematic cross-sectional view of the Ga-doped ZnO single crystal layer 54a and the Cu layer 54b. FIG. 3 is a list of graphs showing the depth profiles of CV characteristics and impurity concentration for the alternately laminated structure of the sample before annealing. FIG. 4 is a list of graphs showing CV characteristics and depth profiles of impurity concentrations of the annealed samples. FIG. 5 is a list of graphs showing the depth profiles of the absolute Cu concentration [Cu] and the absolute Ga concentration [Ga] after the end of annealing by secondary ion mass spectrometry. FIG. 6A is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device according to the first embodiment, and FIG. 6B is a schematic cross-sectional view of an alternate stacked structure 5A. FIG. 7 is a time chart showing an example of a shutter sequence of Zn cells, Mg cells, O cells, Ga cells, and Cu cells when forming an alternately laminated structure. FIG. 8A is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device according to the second embodiment, FIG. 8B is a schematic cross-sectional view showing another example of the active layer 15, and FIG. It is a schematic sectional drawing of structure 16A. FIG. 9 is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device according to the third embodiment. FIG. 10 is a table summarizing the film forming conditions of the Ga-doped n-type Mg _x Zn _1-x O single crystal film in manufacturing the ZnO-based semiconductor light emitting devices according to 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.

  A Zn source gun 72, an Mg source gun 74, a Cu source gun 75, and a Ga source gun 76 are Knudsen 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 including 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. Under constant O radical beam irradiation conditions (for example, RF power 300 W, O ₂ flow rate ₂ sccm), Zn flux is changed to grow ZnO, and the Zn flux dependence of the ZnO 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 previous application (Japanese Patent Application No. 2012-41096), the inventors of the present application proposed a novel technique for doping, for example, Cu into 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) A method for producing a Cu-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer that alternately repeats the process of supplying Cu on the single crystal film was proposed in the previous application. According to the manufacturing method according to the previous application, a Cu-doped p-type Mg _x Zn _1-x O single crystal layer having high flatness and good crystallinity can be obtained.

The p-type ZnO-based semiconductor single crystal layer and the ZnO-based semiconductor element according to the present application are manufactured by, for example, a method improved from the proposal according to the previous application. In the p-type ZnO-based semiconductor single crystal layer of the present invention, for example, monovalent Cu ⁺ that functions as an acceptor more effectively than the p-type Mg _x Zn _1-x O single crystal layer manufactured by the method according to the previous application is included. Exist.

  First, an experiment conducted by the inventors will be described. The inventors of the present application have found that a Ga-doped ZnO single crystal layer (alternate stacked structure) in which Cu is supplied on the layer becomes p-type by annealing. Hereinafter, description will be made along four samples of Sample 1 to Sample 4. 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 0.17 nm / s (J _Zn = 1.1 × 10 ¹⁵ 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 0.17 nm / s (J _Zn = 1.1 × 10 ¹⁵ 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, Zn, O and Ga, and Cu were supplied at different timings to form an alternate stacked structure 54. The formation temperature of the alternately laminated structure 54 was 300 ° C.

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

  In forming the alternate laminated structure 54, a Zn cell shutter, an O cell shutter, and a Ga cell shutter are opened, a Cu cell shutter is closed, a Ga-doped ZnO single crystal layer growth step, a Zn cell shutter, an O cell shutter, and a Ga cell are formed. The Cu adhesion step (Cu layer forming step) in which the shutter was closed and the Cu cell shutter was opened was repeated alternately. By supplying Ga when growing the ZnO single crystal layer, it is expected that Ga enters the Zn site in the ZnO single crystal layer and functions as a donor. Since the step of growing the Ga-doped ZnO single crystal layer and the step of depositing Cu on the Ga-doped ZnO single crystal layer are provided separately and the open period of the O cell shutter and the open period of the Cu cell shutter are not overlapped, O radical and Cu are not supplied simultaneously.

  In the Ga-doped ZnO single crystal layer growth step, the O cell shutter and the Ga cell shutter are opened and closed simultaneously, and the open period of the Zn cell shutter is extended before and after the open periods of the O cell shutter and the Ga cell shutter. That is, the open period of the Zn cell shutter includes the open periods of the O cell shutter and the Ga cell shutter. In addition to not supplying the O radical and Cu simultaneously, by covering the surface of the Ga-doped ZnO single crystal layer with Zn before and after the Cu deposition step (by suppressing the exposure of O), the direct O radical and Cu Suppresses the reaction.

  In the preparation of the sample 1 before annealing of the sample 1, the open period of each of the O cell shutter and the Ga cell shutter is 16 seconds, and the open period of the Zn cell shutter is set before and after the open period of the O cell shutter and the Ga cell shutter. Extended by 1 second. The open period per time of the Zn cell shutter is 18 seconds. A period of 16 seconds during which the Zn cell shutter, the O cell shutter, and the Ga cell shutter are all opened is a Ga-doped ZnO single crystal layer growth period per time. The opening period per time of the Cu cell shutter was 10 seconds.

The Ga-doped ZnO single crystal layer growth step and the Cu deposition step were alternately repeated 140 times, thereby obtaining an alternately laminated structure 54 having a thickness of 480 nm. Zn flux F _Zn in the Ga-doped ZnO single crystal layer growth step is 0.17 nm / s (J _Zn = 1.1 × 10 ¹⁵ atoms / cm ² s), O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate. 2.0 sccm (J 2 _O = 8.1 × 10 ¹⁴ atoms / cm ² s), and the Ga cell temperature T _Ga was 490 ° C. The VI / II flux ratio is 0.74 (Zn rich condition). The Cu cell temperature T _Cu in the Cu adhesion step was 930 ° C., and the Cu flux F _Cu was 0.0015 nm / s.

  FIG. 2C is a schematic cross-sectional view of the alternately laminated structure 54. The alternate laminated structure 54 has a laminated structure in which Ga-doped ZnO single crystal layers 54a and Cu layers 54b are alternately laminated. This stacked structure can be considered as 140 layers of Ga-doped ZnO single crystal layer 54a to which Cu is supplied on the layers stacked in the thickness direction.

  The Ga-doped ZnO single crystal layer 54a has a thickness of about 3.3 nm, and the Cu layer 54b has a thickness (Cu deposition thickness) of 1 atomic layer or less, for example, about 1/20 atomic layer. In this case, the Cu coverage on the surface of the Ga-doped ZnO single crystal layer 54a is about 5%.

  FIG. 2D shows a schematic cross-sectional view of the Ga-doped ZnO single crystal layer 54a and the Cu layer 54b. For example, the Cu layer 54b having a thickness of about 1/20 atomic layer is formed of Cu adhering to a part of the surface of the Ga-doped ZnO single crystal layer 54a as shown in FIG. Hereinafter, for the sake of simplification of the drawing, the alternate laminated structure including the Cu deposition mode is represented by the layer structure of FIG. 2C.

FIG. 3 is a list of graphs showing the depth profiles of CV characteristics and impurity concentration for the alternately laminated structure of the sample before annealing. The graph showing the CV characteristics is shown in the upper row, and the graph showing the depth profile is shown in the lower row. The measurement was performed by an ECV method using an electrolytic solution as a Schottky electrode. The graph shows the results of analysis using a parallel model. The leftmost column is a graph relating to Sample 1. In addition, about the sample 1-sample 4 in order from the left column also including the graph about the sample mentioned later. The horizontal axis of the graph showing the CV characteristic 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. The horizontal axis of the graph showing the depth profile represents the position in the depth (thickness) direction of the sample in the unit of “nm”. 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.

Reference is made to the graph showing the CV characteristics of Sample 1. A curve that rises to the right (a relationship in which 1 / C ² increases as the voltage increases) is obtained. This indicates that the Ga-doped ZnO single crystal layer 54a (alternate stacked structure 54) supplied with Cu on the layer has n-type conductivity. Cu localized on the Ga-doped ZnO single crystal layer 54a is considered not to function as an acceptor. Note that the slope corresponds to the resistance value.

Reference is made to the graph showing the depth profile of Sample 1. As shown in this figure, the impurity concentration (donor concentration) _{N d} of Sample 1 before annealing samples alternate stacked structure 54 is 1.0 × ¹⁰ 20 ^{cm -3.}

  Next, the sample 1 was annealed. After annealing at 650 ° C. for 30 minutes in the atmosphere, annealing was further performed four times at that temperature for 10 minutes.

  FIG. 4 is a list of graphs showing CV characteristics and depth profiles of impurity concentrations of the annealed samples. The CV characteristic and depth profile at the position where the alternate laminated structure 54 is formed are shown. The leftmost column is a graph relating to Sample 1. Similar to FIG. 3, the samples 1 to 4 are related to the annealed samples in order from the left column, including a graph of the samples described later.

  Refer to Sample 1 column. In the upper column, a graph showing CV characteristics after annealing at 650 ° C. for 30 minutes is shown. The meanings of both axes of the graph are the same as those in the graph of the CV characteristic shown in FIG. When compared with the sample before annealing, the formation position of the alternately laminated structure 54 (Ga-doped ZnO single crystal layer 54a with Cu supplied on the layer) is increased in resistance. It is considered that Cu functions as a p-type impurity and offsets the function of the n-type impurity Ga.

  See below. The lower column shows graphs showing the CV characteristics and depth profiles of samples that were annealed at 650 ° C. for 30 minutes, and then annealed for 10 minutes 4 times, and then annealed at 650 ° C. for a total of 70 minutes. And listed in the bottom row. The meanings of both axes of the graph are the same as those of the graph shown in FIG.

In the graph of the CV characteristic shown in the upper stage, a downward-sloping curve (a relationship in which 1 / C ² decreases as the voltage increases) is obtained. This indicates that the formation position of the alternate stacked structure 54 has p-type conductivity. The Cu concentration per unit volume at the position where the alternately laminated structure 54 is formed is higher than the Ga concentration, and it is considered that when the diffusion of Cu proceeds, the concentration of the p-type impurity Cu increases after Ga is compensated. Showing the depth profile, referring to the lower graph, the impurity concentration (acceptor concentration) of alternate stacked structure 54 forming positions in the sample after annealing of the sample 1 _{N a} is ^{2.0 × 10 17 cm -3 ~1.0 ×} 10 It turns out that it is ¹⁹ cm- ³ .

FIG. 5 is a list of graphs showing the depth profiles of the absolute Cu concentration [Cu] and the absolute Ga concentration [Ga] after the end of annealing by secondary ion mass spectrometry (SIMS). The leftmost graph is related to Sample 1. Similar to FIGS. 3 and 4, the sample 1 to sample 4 are annealed in order from the left, including graphs of samples to be described later. The horizontal axis of the graph represents the position in the depth direction of the sample after annealing, and the vertical axis represents the Cu concentration [Cu] and the Ga concentration [Ga]. The position in the depth direction of the sample after annealing is indicated by the unit “μm” for the samples 1 to 3 and the unit “nm” for the sample 4. The unit of [Cu] and [Ga] is “cm ⁻³ ”.

See Sample 1 column. The depth range of 0.0 μm to 0.48 μm is the p-type layer formation position corresponding to the formation position of the alternately laminated structure 54. The Cu concentration [Cu] is 2.2 × 10 ²⁰ cm ⁻³ and the Ga concentration [Ga] is 3.4 × 10 ¹⁹ cm ⁻³ , both of which are almost constant throughout the thickness direction of the p-type layer. Recognize. In the present specification and claims, “substantially constant” in terms of concentration means 50% to 150% of the average value of concentration (2.2 × 10 ²⁰ cm ^{−3 in} the case of [Cu] in FIG. 1). % Range (1.1 × 10 ²⁰ cm ^{−3 to} 3.3 × 10 ²⁰ cm ^{−3 in} the case of [Cu] of sample 1 in the figure). Cu is diffused uniformly. [Cu] is larger than [Ga], and the value of [Cu] / [Ga], which is the ratio of [Cu] to [Ga], is 6.5. [Cu] and [Ga] may not be accurately measured near the surface of the p-type layer due to, for example, the influence of surface adsorbate. For example, in the case of sample 1, it is measured at a low value.

  Next, Sample 2 to Sample 4 will be described. Samples 2 to 4 are samples in which, for example, the supply amounts of Cu and Ga are adjusted at the time of producing an alternately laminated structure, and [Cu] / [Ga] are set to values different from those of sample 1, respectively.

  Samples 2 to 4 are the same as those of Sample 1 shown in FIG. 2A in that a ZnO buffer layer, an undoped ZnO layer, and an alternately laminated structure are sequentially formed on the ZnO substrate 51. However, the growth conditions of the layers formed on the ZnO substrate 51 are different.

In the preparation of the samples 2 and 3 before annealing, the growth temperature of the ZnO buffer layer was 300 ° C. and the growth time was 5 minutes. A ZnO buffer layer having a thickness of 40 nm was grown at a Zn flux F of _Zn of 0.16 nm / s, an O radical beam irradiation condition of RF power of 300 W, and an O ₂ flow rate of 2.0 sccm. Thereafter, annealing was performed at 900 ° C. for 15 minutes.

The growth temperature of the undoped ZnO layer was 900 ° C. and the growth time was 15 minutes. An undoped ZnO layer having a thickness of 120 nm was grown with Zn flux F _Zn of 0.16 nm / s, O radical beam irradiation conditions of RF power of 300 W, and O ₂ flow rate of 2.0 sccm.

The alternate laminated structure was formed at a growth temperature of 300 ° C. In the Ga-doped ZnO single crystal layer growth step, the Zn flux F _Zn was 0.16 nm / s, the O radical beam irradiation conditions were RF power 300 W, and O ₂ flow rate 2.0 sccm. The VI / II flux ratio is smaller than 1 and is a Zn-rich condition. The cell temperature T _Ga of _Ga was 498 ° C. in the production of sample 2 and 505 ° C. in the case of sample 3. The growth period of the Ga-doped ZnO single crystal layer per one time was set to 16 seconds. The Cu cell temperature T _Cu in the Cu adhesion step was 930 ° C., and the Cu flux F _Cu was 0.0015 nm / s. The opening period per time of the Cu cell shutter was 10 seconds. The Ga-doped ZnO single crystal layer growth step and the Cu adhesion step were alternately repeated 60 times to obtain an alternately laminated structure. The growth time is 30 minutes. The thickness of the alternately laminated structure was 207 nm for sample 2 and 199 nm for sample 3. In this way, samples 2 and 3 were prepared before annealing.

  The method of preparing the sample 4 before annealing is different from that of the sample 2 and the sample 3 in the growth conditions of the alternately laminated structure.

The alternately laminated structure of Sample 4 was formed at a growth temperature of 300 ° C. Zn flux in Ga-doped ZnO single crystal layer growing step _{F Zn} is 0.15 nm / s, O radical beam irradiation conditions RF power 300 W, and the _{O 2} flow rate 2.0 sccm. The VI / II flux ratio is smaller than 1 and is a Zn-rich condition. The cell temperature TGa of _Ga was 525 ° C. The growth period of the Ga-doped ZnO single crystal layer per one time was set to 16 seconds. The Cu cell temperature T _Cu in the Cu adhesion step was 930 ° C., and the Cu flux F _Cu was 0.0015 nm / s. The open period per time of the Cu cell shutter was 50 seconds. The Ga-doped ZnO single crystal layer growth step and the Cu deposition step were alternately repeated 30 times to form an alternating laminated structure having a thickness of 90 nm, and a sample 4 sample before annealing was produced.

Reference is made to the column of sample 2 to sample 4 in FIG. According to the graph showing the CV characteristics in the upper stage, as in Sample 1, Sample 1 to Sample 4 also have a relationship in which 1 / C ² increases as the voltage increases in the alternate stacked structure. That is, it can be seen that in the samples before annealing of Sample 2 to Sample 4, the alternately laminated structure (Ga-doped ZnO single crystal layer with Cu supplied on the layer) has n-type conductivity.

Refer to the lower graph showing the depth profile. The donor concentrations N _d of the alternately stacked structures of Sample 2, Sample 3, and Sample 4 are 1.0 × 10 ²⁰ cm ⁻³ , 1.0 × 10 ²⁰ cm ⁻³ , and 7.0 × 10 ²⁰ cm ⁻³ , respectively. is there.

  Subsequently, the samples 2 to 4 were annealed.

  Reference is made to the column of sample 2 in FIG. Sample 2 was divided into two parts, one of which was annealed at 650 ° C. for 10 minutes in the atmosphere, and the other was annealed at 650 ° C. for 30 minutes in the atmosphere. The upper column is a graph showing the CV characteristics of Sample 2 that was annealed at 650 ° C. for 10 minutes. The formation position of the alternately laminated structure (Ga-doped ZnO single crystal layer with Cu supplied on the layer) is higher than before the annealing.

  The lower column shows the CV characteristics and the depth profile of the impurity concentration of Sample 2 that was annealed at 650 ° C. for 30 minutes.

In the upper graph showing the CV characteristics, a relationship in which 1 / C ² decreases as the voltage increases is obtained. As a result, it can be seen that the formation position of the alternately laminated structure is p-type. Showing the depth profile, referring to the lower graph, the acceptor concentration _{N a} of the alternate stacked structure forming position in the sample 2 was annealed for 30 minutes at ^{650 ℃ 1.0 × 10 17 cm -3} ~7.0 × It turns out that it is 10 ^{< 18} > cm ^<-3 >.

The column of Sample 2 in FIG. 5 shows the depth profiles of Cu concentration [Cu] and Ga concentration [Ga] by SIMS of the sample annealed at 650 ° C. for 30 minutes. The Cu concentration [Cu] is 1.7 × 10 ²⁰ cm ⁻³ and the Ga concentration [Ga] is 3.7 × 10 ¹⁹ cm ^{−3 in} the range corresponding to the formation position of the alternately laminated structure (formation position of the p-type layer). It can be seen that both are substantially constant over the entire thickness of the p-type layer. The value of [Cu] / [Ga] is 4.6.

  Reference is made to the column of sample 3 in FIG. Sample 3 was also annealed in air. After 10 times of annealing at 550 ° C. for 7 times, 4 times of annealing for 10 minutes at 570 ° C., 3 times of annealing for 10 minutes at 580 ° C. and once for 5 minutes, Further, an annealing treatment was performed at 590 ° C. for 12 minutes. The total annealing time is 157 minutes.

  The upper column is a graph showing the CV characteristics after performing annealing at 550 ° C. for 10 minutes three times (total 30 minutes). The position where the alternate laminated structure is formed is higher than before the annealing.

  The lower column shows the CV characteristics and the depth profile of the impurity concentration of the sample subjected to annealing at 590 ° C. for 12 minutes (total annealing of 157 minutes).

In the upper graph showing the CV characteristic, a relationship in which 1 / C ² decreases as the voltage increases is obtained, and it can be seen that the formation position of the alternate stacked structure has become p-type. Showing the depth profile, referring to the lower graph, the acceptor concentration _{N a} of the alternate stacked structure forming position in the sample after annealing of the sample 3 is ^{6.0 × 10 17 cm -3 ~1.0 ×} 10 19 cm -3 I know that there is.

Refer to the column for sample 3 in FIG. The Cu concentration [Cu] is 1.2 × 10 ²⁰ cm ⁻³ and the Ga concentration [Ga] is 6.0 × 10 ¹⁹ cm ^{−3 in} the range (p-type layer formation position) corresponding to the formation position of the alternately laminated structure. It can be seen that both are substantially constant over the entire thickness of the p-type layer. The value of [Cu] / [Ga] is 2.0.

  Reference is made to the column of sample 4 in FIG. Sample 4 was annealed in air at 500 ° C. for 10 minutes, 525 ° C. for 10 minutes, and 550 ° C. for 10 minutes, and then further annealed at 600 ° C. for 10 minutes for 5 times. The total annealing time is 80 minutes.

  The upper column is a graph showing the CV characteristics after annealing at 550 ° C. for 10 minutes. The position where the alternate laminated structure is formed is higher than before the annealing.

  The lower column shows the CV characteristics and the depth profile of the impurity concentration of the sample that was annealed at 600 ° C. for 50 minutes (5 times for 10 minutes) (total annealing for 80 minutes).

In the upper graph showing the CV characteristic, a relationship in which 1 / C ² decreases as the voltage increases is obtained, and it can be seen that the formation position of the alternate stacked structure has become p-type. Showing the depth profile, referring to the lower graph, the acceptor concentration _{N a} of the alternate stacked structure forming position in the sample after annealing of the sample 4 is ^{8.0 × 10 17 cm -3 ~1.0 ×} 10 19 cm -3 I know that there is.

Refer to the column for sample 4 in FIG. The Cu concentration [Cu] is 3.5 × 10 ²⁰ cm ⁻³ and the Ga concentration [Ga] is 2.0 × 10 ²⁰ cm ^{−3 in} the range corresponding to the formation position of the alternately laminated structure (formation position of the p-type layer). It can be seen that both are substantially constant over the entire thickness of the p-type layer. The value of [Cu] / [Ga] is 1.8.

From the above experiments conducted by the inventors of the present application, the alternately laminated structure (Ga-doped ZnO single crystal layer) of Sample 1 to Sample 4 is as-grown and n-type (see FIG. 3), and the resistance is increased by annealing (see FIG. 3). It is understood that the p-type is obtained (refer to the lower column of FIG. 4). By performing the annealing treatment, Cu in the Cu layer is uniformly diffused in the Ga-doped ZnO single crystal layer. With the diffusion of Cu (generation of Cu ⁺ functioning as an acceptor), the alternate stacked structure (Ga-doped ZnO single crystal layer) is increased in resistance (the donor concentration _Nd is decreased), and further, Cu and Ga are co-doped. The p-type ZnO single crystal layer is considered to be p-type.

  From the comparison of Sample 1 to Sample 4, the annealing conditions (temperature, time, atmosphere, etc.) for making p-type are as follows: the thickness of the alternate laminated structure, Ga doped ZnO single crystal layer, Cu concentration [Cu] in the alternate laminated structure , Ga concentration [Ga], [Cu] to [Ga] ratio [Cu] / [Ga], etc.

  Further, in Sample 1 to Sample 3 in which both the Cu concentration [Cu] and the Ga concentration [Ga] are in a narrow numerical range, when attention is paid to the value of [Cu] / [Ga], Sample 1> Sample 2> Sample 3 In relation, it is recognized that the smaller the value of [Cu] / [Ga], the lower the annealing temperature necessary for p-type conversion or the shorter the processing time. For example, formation of donor point defects such as oxygen vacancies by high-temperature annealing, reduction of Cu concentration or Ga concentration in the p-type layer due to external diffusion from the p-type layer, and application of Cu or Ga to the underlying layer (n-type layer) Considering the possibility of occurrence of defects such as deterioration of pn interface steepness due to diffusion, the value of [Cu] / [Ga] is desirably less than 100, for example, and more desirably 50 or less. Let's go.

  Furthermore, if it is considered that Cu and Ga are compensated by 1: 1 in an alternate stacked structure (a structure composed of a Ga-doped ZnO single crystal layer and Cu supplied thereon), [Cu] / [Ga]> 1 In this case, p-type conversion will be possible. For example, when [Cu] / [Ga] ≧ 2, it is likely that a practical p-type conductivity is easily obtained by annealing.

  Therefore, for example, if 1 <[Cu] / [Ga] <100, the alternate laminated structure can be made p-type by relatively low-temperature annealing, and if 2 ≦ [Cu] / [Ga] ≦ 50. It may be possible to obtain practical p-type conductivity by annealing at a lower temperature.

In the experiment, for example, as shown in FIG. 5, a p-type layer having substantially constant Cu concentration [Cu] and Ga concentration [Ga] was obtained over the entire thickness direction of the layer. The Cu concentration [Cu] in the p-type layer was 1.2 × 10 ²⁰ cm ⁻³ (in the case of sample 3) to 3.5 × 10 ²⁰ cm ⁻³ (in the case of sample 4).

From this result, for example, by a method of annealing a Ga-doped n-type ZnO single crystal layer to which Cu is supplied on the layer, Cu is concentrated to a concentration of 1.0 × 10 ¹⁹ cm ⁻³ or more, which can be said to be a high concentration. In Sample 4, it can be considered that doping can be uniformly performed in the thickness direction to a concentration of the order of 10 ²⁰ cm ⁻³ to a concentration of at least less than 1.0 × 10 ²¹ cm ⁻³ .

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]. With consideration of this knowledge, by annealing the Ga-doped n-type ZnO single crystal layer Cu is supplied onto the layer, the acceptor concentration is 1.0 × ¹⁰ 17 ^{cm -3} or more, 1.0 × ¹⁰ 19 cm ^{- It} can be said that a p-type layer of less than ³ is obtained. In fact, the depth profile of the lower column of FIG. 4, (in the case of sample 2) acceptor concentration _{N a} of samples 1 to ^{4, 1.0 × 10 17 cm -3 ~1.0} × 10 19 cm -3 (In the case of sample 1, sample 3, and sample 4).

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 a Ga-doped ZnO single crystal layer supplied with Cu on the layer, Cu is doped at a high concentration and uniformly in the entire thickness direction of the layer, and is practical p-type conductivity. Cu, Ga co-doped ZnO single crystal layer having the above can be produced. Further, it can be manufactured by annealing at a low temperature.

  The alternate laminated structure (Ga-doped ZnO single crystal layer with Cu supplied on the layer) showing n-type conductivity is converted to p-type by increasing the resistance by annealing. In the experiment, for example, in the case of Sample 1, after annealing at 650 ° C. for 30 minutes to produce a high resistance sample (see the graph in the upper column of FIG. 4), that is, after undergoing an apparent high resistance Furthermore, p-type conversion was performed by carrying out an annealing treatment for 40 minutes (see the graph in the lower column of FIG. 4). However, even when the sample before annealing was continuously subjected to annealing at 650 ° C. for 70 minutes, alternating lamination was performed. The structure becomes p-type. At this time, it can be said that the alternate laminated structure is made p-type through a potential increase in resistance. Similarly, the sample 2 before annealing at 650 ° C. for 30 minutes, the sample 3 before annealing at 590 ° C. for 12 minutes, and the sample 4 before annealing at 600 ° C. for 50 minutes in the atmosphere. By implementing in, it is possible to p-type after alternately increasing the resistance of the alternately laminated structure of each sample.

  In addition, it can also be considered that the alternately laminated structure is converted into a p-type through further insulation after a potential or actual high resistance. It may be possible to make the insulation manifest by setting the annealing conditions. Therefore, it can be said that the alternately laminated structure is made p-type through a potential or an apparent increase in resistance and further through a potential or an apparent insulation.

  The inventors of the present application have discovered that further annealing of the p-type alternate laminated structure can have n-type conductivity again. Therefore, the annealing process may be terminated, for example, after the alternate laminated structure is made p-type through increasing the resistance and before becoming the n-type layer again.

  Through experiments conducted by the inventors of the present application, annealing treatment was performed on a Ga-doped ZnO single crystal layer (alternate laminated structure in which Ga-doped ZnO single crystal layer growth step and Cu adhesion step were alternately formed) in which Cu was supplied on the layer. It was found that a p-type ZnO layer co-doped with Cu and Ga was obtained after increasing the resistance.

  Next, with reference to FIGS. 6A and 6B, a ZnO-based semiconductor light emitting device according to the first embodiment using a Cu, Ga co-doped ZnO layer as a p-type semiconductor layer will be described. The first example is a homostructure ZnO-based semiconductor light emitting device. 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.

  First, a method for manufacturing a ZnO-based semiconductor light emitting device according to the first embodiment will be described.

As shown in FIG. 6A, the ZnO substrate 1 above, and at a growth temperature of 300 ° C., the Zn flux _{F Zn} and _{0.15nm / s (J Zn = 9.9} × 10 14 atoms / cm 2 s), O radical beam The ZnO buffer layer 2 having a thickness of 30 nm was grown under the irradiation conditions of RF power of 300 W and 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 above the ZnO buffer layer 2 at a growth temperature of 900 ° C. to grow an n-type ZnO layer 3 having a thickness of 150 nm. 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 .

Above 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 above the undoped ZnO active layer 4.

  First, the substrate temperature is set to 300 ° C., and Zn, O, Ga, and Cu are supplied at different timings in a shutter sequence (see FIG. 2B) that is the same as that for sample 1 before annealing. A supplied Ga-doped n-type ZnO single crystal film was prepared. Specifically, a process of supplying Zn, O, and Ga to grow a Ga-doped ZnO single crystal film and a process of supplying Cu on the Ga-doped ZnO single crystal film are alternately repeated 140 times each to obtain a thickness of 480 nm. The alternate laminated structure was formed. It can be considered that the alternately laminated structure is formed by stacking 140 Ga-doped n-type ZnO single crystal films supplied with Cu on the film in the thickness direction.

The growth period of the Ga-doped ZnO single crystal film per time was 16 seconds, and the Cu supply period per time was 10 seconds. Zn flux F _Zn in the Ga-doped ZnO single crystal film growth step is 0.17 nm / s (J _Zn = 1.1 × 10 ¹⁵ atoms / cm ² s), O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate. 2.0 sccm (J 2 _O = 8.1 × 10 ¹⁴ atoms / cm ² s), and the Ga cell temperature T _Ga was 490 ° C. The VI / II flux ratio is 0.74. Further, the cell temperature _{T Cu} of Cu in the Cu supplying step and 930 ° C., and the Cu flux _{F Cu} and 0.0015 / s.

FIG. 6B is a schematic cross-sectional view of the alternately laminated structure 5A. The alternately laminated structure 5A is a structure in which Ga-doped ZnO single crystal films 5a and Cu layers 5b are alternately laminated (a structure in which Ga-doped ZnO single crystal films 5a supplied with Cu are laminated in the thickness direction). Have The thickness of the Ga-doped ZnO single crystal film 5a is about 3.3 nm, and the thickness of the Cu layer 5b is 1 atomic layer or less, for example, about 1/20 atomic layer (Cu coverage on the surface of the Ga-doped ZnO single crystal film 5a is 5). %). The alternately laminated structure 5A (Ga-doped ZnO single crystal film 5a with Cu supplied on the film) exhibits n-type conductivity, and the donor concentration _Nd is, for example, about 1.0 × 10 ²⁰ cm ⁻³ .

  Next, the Ga-doped ZnO single crystal film 5a (alternate laminated structure 5A) supplied with Cu on the film is annealed, and a p-type film doped with Cu (Cu, Ga co-doped p-type ZnO layer 5) and did. For example, by performing annealing at 650 ° C. for 70 minutes in the atmosphere, Cu in the Cu layer 5b is diffused into the Ga-doped ZnO single crystal film 5a, and the alternate stacked structure 5A exhibiting n-type conductivity is made p-type. be able to. Under this annealing condition, the Ga-doped ZnO single crystal film 5a is made p-type through a potential increase in resistance.

  For example, after annealing at 650 ° C. for 30 minutes in the atmosphere to increase the resistance of the Ga-doped ZnO single crystal film 5a, the annealing is further performed in air at 650 ° C. for 40 minutes. The Ga-doped ZnO single crystal film 5a may be made p-type.

  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. . Thus, a ZnO-based semiconductor light emitting device according to the first example was manufactured.

  FIG. 6A is a schematic cross-sectional view of a ZnO based semiconductor light emitting device according to the first embodiment. The ZnO-based semiconductor light emitting device according to the first embodiment includes an n-type ZnO-based semiconductor layer (n-type ZnO layer 3), a ZnO-based semiconductor active layer (undoped ZnO active layer 4) formed above the n-type ZnO-based semiconductor layer, A p-type ZnO-based semiconductor layer (Cu, Ga co-doped p-type ZnO layer 5) formed above the ZnO-based semiconductor active layer, and an n-side electrode (n-side electrode 6n) electrically connected to the n-type ZnO-based semiconductor layer And a p-side electrode (p-side electrode 6p) electrically connected to the p-type ZnO-based semiconductor layer.

The Cu and Ga co-doped p-type ZnO layer 5 is a p-type ZnO-based single crystal layer co-doped with Cu and Ga. In the Cu and Ga co-doped p-type ZnO layer 5, the Cu concentration [Cu] is 1.0 × 10 ¹⁹ cm ⁻³ or more and less than 1.0 × 10 ²¹ cm ⁻³ , for example, 2.2 × 10 ²⁰ cm ^{−. 3,} which is substantially constant in the layer thickness direction. The Ga concentration [Ga] is, for example, 3.4 × 10 ¹⁹ cm ⁻³ and is substantially constant in the layer thickness direction. The Cu concentration [Cu] and the Ga concentration [Ga] satisfy the relationship [Ga] <[Cu]. The Cu and Ga co-doped p-type ZnO layer 5 of the semiconductor light emitting device according to the first embodiment is a p-type ZnO layer in which Cu is doped at a high concentration and uniformly throughout the thickness direction.

In the experiment and the first example, a Cu and Ga co-doped p-type ZnO layer was formed (x = 0 in Mg _x Zn _1-x O notation), but Ga-doped n-type Mg _x in which Cu was supplied onto the film. By annealing a Zn _1-x O (0 <x ≦ 0.6) single crystal film, a p-type film doped with Cu (Cu, Ga co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal film) can be obtained (x ≠ 0 in the Mg _x Zn _1-x O notation).

As an example of preparing a Ga-doped n-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal film supplied with Cu on the film, a Ga-doped n-type Mg _x Zn _1-x O (0 <X ≦ 0.6) The case of forming an alternate stacked structure in which single crystal films and Cu layers are alternately stacked will be described.

  FIG. 7 is a time chart showing an example of a shutter sequence of Zn cells, Mg cells, O cells, Ga cells, and Cu cells when forming an alternately laminated structure.

In the formation of the alternately laminated structure, a Ga-doped Mg _x Zn _1-x O (0 <x ≦ 0.6) that opens a Zn cell shutter, an Mg cell shutter, an O cell shutter, and a Ga cell shutter and closes a Cu cell shutter. The single crystal film growth step and the Cu deposition step of closing the Zn cell shutter, Mg cell shutter, O cell shutter, and Ga cell shutter and opening the Cu cell shutter are alternately repeated.

In the example shown in the figure, the open period of the Zn cell shutter in the Ga-doped Mg _x Zn _1-x O single crystal film growth step is set to include the open periods of the Mg cell shutter, the O cell shutter, and the Ga cell shutter. Has been. Specifically, the Mg cell shutter, the O cell shutter, and the Ga cell shutter are simultaneously opened and closed, and the Zn cell shutter open period is set before and after the Mg cell shutter, O cell shutter, and Ga cell shutter open periods. Extended.

For example, the open period per time of the Mg cell shutter, O cell shutter, and Ga cell shutter is 16 seconds. The open period of the Zn cell shutter is extended by 1 second before and after the open periods of the Mg cell shutter, the O cell shutter, and the Ga cell shutter, and the open period of each Zn cell shutter is 18 seconds. A period of 16 seconds during which the Zn cell shutter, Mg cell shutter, O cell shutter, and Ga cell shutter are all open is a Ga-doped Mg _x Zn _1-x O single crystal film growth period. The opening period per time of the Cu cell shutter was 10 seconds.

In addition to not supplying the O radical and Cu simultaneously, covering the surface of the Ga-doped Mg _x Zn _1-x O single crystal film with Zn before and after the Cu deposition step suppresses the direct reaction between the O radical and Cu. The

When supplying Mg together with Zn, from the viewpoint of suppressing the reaction between O radicals and Cu, at least one of the open period of the Zn cell shutter and the open period of the Mg cell shutter includes the open period of the O cell shutter. This should be done. From the viewpoint of enhancing the controllability of the Mg composition of the Ga-doped Mg _x Zn _1-x O single crystal film, the open period of the Zn cell shutter should include the open periods of the Mg cell shutter and the O cell shutter. Conceivable.

By annealing a Ga-doped n-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal film (alternate laminated structure) supplied with Cu on the film, the resistance is increased, Cu, A Ga co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal film is produced.

Next, a second example and a second example of a ZnO-based semiconductor light emitting device having a double hetero structure including a Cu, Ga co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer are described. Three examples will be described.

  A method for manufacturing a ZnO-based semiconductor light emitting device according to the second embodiment will be described with reference to FIGS. 8A to 8C.

As shown in FIG. 8A, Zn and O were simultaneously supplied above 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 above 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 above 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 sccm. The Mg composition of the n-type MgZnO layer 14 is, for example, 0.3.

Zn and O were simultaneously supplied above 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. 8B, 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 substrate temperature is lowered to, for example, 300 ° C., and the Ga-doped MgZnO single crystal film growth process and the Cu deposition process are alternately repeated to form an alternate stacked structure above the active layer 15 (Ga-doped n-type with Cu supplied on the film) MgZnO single crystal film was prepared). The shutter sequence of the Zn cell, Mg cell, O cell, Ga cell, and Cu cell in forming the alternate stacked structure is the same as that shown in FIG. 7, for example.

For example, the growth period in a single Ga-doped MgZnO single crystal film growth step is 16 seconds, and the Cu supply period in a single Cu deposition step is 10 seconds. Zn flux F _Zn in the Ga-doped MgZnO single crystal film growth step is 0.15 nm / s, Mg flux F _Mg is 0.03 nm / s, O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate 2.0 sccm, The cell temperature TGa of _Ga is 498 ° C. The VI / II flux ratio is 0.72. The Cu cell temperature T _Cu in the Cu supplying step was 930 ° C., and the Cu flux F _Cu was 0.0015 nm / s. The Ga-doped MgZnO single crystal film growth step and the Cu deposition step were alternately repeated 60 times to obtain an alternate laminated structure having a thickness of 200 nm. The alternate stacked structure can be considered as 60 layers of Ga-doped n-type MgZnO single crystal films supplied with Cu stacked in the thickness direction.

FIG. 8C is a schematic cross-sectional view of the alternately laminated structure 16A. The alternate laminated structure 16A has a laminated structure in which Ga-doped MgZnO single crystal films 16a and Cu layers 16b are alternately laminated (a Ga-doped MgZnO single crystal film 16a supplied with Cu on the film is laminated in the thickness direction). Structure). The thickness of the Ga-doped MgZnO single crystal film 16a is about 3.3 nm, the thickness of the Cu layer 16b is 1 atomic layer or less, for example, about 1/20 atomic layer (the Cu coverage on the surface of the Ga-doped MgZnO single crystal film 16a is 5 %). The alternate stacked structure 16A (Ga-doped MgZnO single crystal film 16a with Cu supplied on the film) exhibits n-type conductivity, and the donor concentration _Nd is, for example, about 7.5 × 10 ¹⁹ cm ⁻³ .

  Next, the Ga-doped MgZnO single crystal film 16a (alternate stacked structure 16A) supplied with Cu on the film is annealed, and a Cu-doped p-type film (Cu, Ga co-doped p-type is formed above the active layer 15. An MgZnO layer 16) was formed. For example, by performing annealing at 650 ° C. for 20 minutes in the atmosphere, Cu in the Cu layer 16b is diffused into the Ga-doped MgZnO single crystal film 16a, and the alternate stacked structure 16A exhibiting n-type conductivity is made p-type. be able to. Under this annealing condition, the Ga-doped MgZnO single crystal film 16a is made p-type through a potential increase in resistance.

  For example, after annealing at 650 ° C. for 10 minutes in the atmosphere to increase the resistance of the Ga-doped MgZnO single crystal film 16a, the annealing is further performed in air at 650 ° C. for 10 minutes. The Ga-doped MgZnO single crystal film 16a may be made p-type.

  The Mg composition of the Cu and Ga co-doped p-type MgZnO layer 16 is, for example, 0.3.

  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. Thus, the ZnO-based semiconductor light emitting device according to the second embodiment is manufactured.

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.

  FIG. 8A is a schematic cross-sectional view of a ZnO based semiconductor light emitting device according to a second embodiment. The ZnO-based semiconductor light emitting device according to the second embodiment includes an n-type ZnO-based semiconductor layer (for example, an n-type ZnO layer 13), a ZnO-based semiconductor active layer (active layer 15) formed above the n-type ZnO-based semiconductor layer, ZnO P-type ZnO-based semiconductor layer (Cu, Ga co-doped p-type MgZnO layer 16) formed above the active semiconductor active layer, n-side electrode (n-side electrode 17n) electrically connected to the n-type ZnO-based semiconductor layer And a p-side electrode (p-side electrode 17p) electrically connected to the p-type ZnO-based semiconductor layer.

The Cu and Ga co-doped p-type MgZnO layer 16 is a p-type ZnO-based single crystal layer co-doped with Cu and Ga. In the Cu and Ga co-doped p-type MgZnO layer 16, the Cu concentration [Cu] is 1.0 × 10 ¹⁹ cm ⁻³ or more and less than 1.0 × 10 ²¹ cm ⁻³ , for example, 2.0 × 10 ²⁰ cm ^{−. 3,} which is substantially constant in the layer thickness direction. The Ga concentration [Ga] is, for example, 3.6 × 10 ¹⁹ cm ⁻³ and is substantially constant in the layer thickness direction. The Cu concentration [Cu] and the Ga concentration [Ga] satisfy the relationship [Ga] <[Cu]. The Cu and Ga co-doped p-type MgZnO layer 16 of the semiconductor light emitting device according to the second embodiment is a p-type MgZnO layer in which Cu is doped at a high concentration and uniformly throughout the thickness direction.

  With reference to FIG. 9, a method of manufacturing a ZnO-based semiconductor light emitting device according to the third embodiment will be described. In the first and second embodiments, the semiconductor layer is formed above the conductive substrate. In the third embodiment, the semiconductor layer is formed above the insulating substrate.

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

For example, Zn and O are simultaneously supplied above the MgO buffer layer 22 with a growth temperature of 300 ° C., a Zn flux F _Zn of 0.15 nm / s, an O radical beam irradiation condition of RF power of 300 W, and an O ₂ flow rate of 2.0 sccm. 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 above 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 sccm, and the Ga cell temperature is 480 ° C.

Zn, Mg and O are simultaneously supplied above the n-type ZnO layer 24 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 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. Thus, a ZnO-based semiconductor light emitting device according to the third embodiment is manufactured.

  FIG. 9 is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device according to the third embodiment. Similarly to the first and second embodiments, the ZnO-based semiconductor light emitting device according to the third embodiment also has an n-type ZnO-based semiconductor layer (for example, an n-type ZnO layer 24) and a ZnO formed above the n-type ZnO-based semiconductor layer. Electrically connected to a p-type semiconductor active layer (active layer 26), a p-type ZnO-based semiconductor layer (Cu, Ga co-doped p-type MgZnO layer 27) formed above the ZnO-based semiconductor active layer, and an n-type ZnO-based semiconductor layer And an n-side electrode (n-side electrode 28n) and a p-side electrode (p-side electrode 28p) electrically connected to the p-type ZnO-based semiconductor layer. The Cu and Ga co-doped p-type MgZnO layer 27 of the third embodiment has the same properties as the Cu and Ga co-doped p-type MgZnO layer 16 of the second embodiment.

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

For example, in manufacturing a ZnO-based semiconductor light emitting device according to the embodiment, O radicals were used as an oxygen source, but other gases having strong oxidizing power such as ozone, H ₂ O, and polar oxidizers such as alcohol may be used. it can. In addition, a Ga-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film in which Cu is supplied on the film is formed using the MBE method. For example, it is formed by vacuum deposition or sputtering. May be. Furthermore, although annealing was performed in the air, it may be performed in an oxygen atmosphere or the like.

In the experiments and examples, a Ga-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film in which Cu is supplied onto the film is annealed to form a p-type doped with Cu. Layer (Cu, Ga co-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer). By annealing the Ga (IIIB group element) doped n-type Mg _x Zn _1-x O single crystal film to which Cu (IB group element) is attached, Cu is a VIB group element O and monovalent (Cu ⁺ ) As a result, the monovalent Cu ⁺ functioning as an acceptor is more likely to be generated than the divalent Cu ²⁺ , and as a result, the Ga-doped n-type Mg _x Zn _1-x O single crystal film is considered to be 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 a (α) Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film proposed by the inventors of the present application (Japanese Patent Application No. 2012-41096), (Β) Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) Cu-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0), in which the step of supplying Cu on the single crystal film is repeated alternately. In the method for producing the 0.6) layer, the following findings (1) to (3) are obtained.

(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.

When a Ga-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film is grown also in manufacturing a ZnO-based semiconductor element according to the present application, the above (1) to ( By growing under the conditions shown in 3), it is possible to obtain a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) film having high flatness and good crystallinity.

FIG. 10 is a table summarizing the film forming conditions of the Ga-doped n-type Mg _x Zn _1-x O single crystal film in manufacturing the ZnO-based semiconductor light emitting devices according to the first to third examples.

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 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. The p-type Mg _x Zn _1-x O layer according to the example is a p-type ZnO-based semiconductor layer that is annealed and has improved flatness.

  The p-type ZnO-based semiconductor layer according to the embodiment can be used for, for example, a light emitting diode (LED) or a laser diode (LD) that emits light having a short wavelength (ultraviolet to blue wavelength region), and these applied products (various indicators). , LED display, CV / DVD light source, 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 Ga-doped ZnO single crystal film 5b Cu 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 structure 16a Ga-doped MgZnO single crystal Film 16b Cu 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 28p p-side electrode 29 Bonding electrode 51 ZnO substrate 52 ZnO buffer layer 53 Undoped ZnO layer 54 Alternating layered structure 54a Ga doped ZnO single crystal layer 54b Cu 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 (2)

A p-type ZnO-based semiconductor in which (i) a group IB element that is Cu or / and Ag and (ii) one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In are co-doped A single crystal layer,
A p-type ZnO-based semiconductor single crystal layer in which the concentration of the group IB element is 1 × 10 ¹⁹ cm ⁻³ or more and is substantially constant in the thickness direction of the layer. an n-type ZnO-based semiconductor layer;
A ZnO-based semiconductor active layer formed above the n-type ZnO-based semiconductor layer;
A p-type ZnO based semiconductor layer formed above the ZnO based semiconductor active layer;
An n-side electrode electrically connected to the n-type ZnO-based semiconductor layer;
A p-side electrode electrically connected to the p-type ZnO-based semiconductor layer,
The p-type ZnO based semiconductor layer is a single crystal layer,
(I) a group IB element that is Cu or / and Ag, and (ii) one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In, are co-doped,
The ZnO-based semiconductor device, wherein the concentration of the group IB element is 1 × 10 ¹⁹ cm ⁻³ or more and is substantially constant in the thickness direction of the p-type ZnO-based semiconductor layer.