JP2015046593A - p-TYPE ZnO-BASED SEMICONDUCTOR LAYER MANUFACTURING METHOD AND ZnO-BASED SEMICONDUCTOR ELEMENT MANUFACTURING METHOD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a p-type ZnO-based semiconductor layer having a high acceptor concentration.SOLUTION: A p-type ZnO-based semiconductor layer manufacturing method comprises the steps of: (a) forming an n-type ZnO-based semiconductor single crystal structure including a group IB element which is Cu or/and Ag, and one or more group IIIB elements selected from a group consisting of B, Ga, Al and In; (b) performing first annealing on the n-type ZnO-based semiconductor single crystal structure under ordinary pressure and a first oxidizer atmosphere to form a p-type ZnO-based semiconductor layer co-doped with the group IB element and the group IIIB element; and (c) performing second annealing on the p-type ZnO-based semiconductor layer under a second oxidizer atmosphere which has an oxidizability higher than that under the ordinary pressure and the first oxidizer atmosphere to increase an acceptor concentration in the p-type ZnO-based semiconductor layer.

Description

  The present invention relates to a method for manufacturing a p-type ZnO-based semiconductor layer and a method for manufacturing a ZnO-based semiconductor element. A ZnO-based semiconductor means a semiconductor containing at least Zn and O.

  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 for realizing a ZnO-based semiconductor has been conducted.

The inventors of the present invention have found that an n-type ZnO-based semiconductor structure in which ZnO: Ga layers and Cu layers are alternately stacked becomes p-type by annealing, and is doped with a group IIIB n-type impurity such as Ga. A structure in which Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers and Cu or Ag, for example, Cu layers are alternately stacked is grown, the alternating stack structure is annealed, and Cu and Ga are A method for producing a co-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer is proposed.

Japanese Patent Laid-Open No. 2014-27137

  The inventors of the present application have continued intensive research and found a method for manufacturing a p-type ZnO-based semiconductor layer having a high acceptor concentration.

  An object of the present invention is to provide a method for manufacturing a p-type ZnO-based semiconductor layer having a high acceptor concentration and a method for manufacturing a ZnO-based semiconductor element including a p-type ZnO-based semiconductor layer having a high acceptor concentration.

  According to one aspect of the present invention, (a) an n-type comprising a group IB element that is Cu or / and Ag, and one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In A step of forming a ZnO-based semiconductor single crystal structure; and (b) subjecting the n-type ZnO-based semiconductor single crystal structure to a first annealing in a normal pressure first oxidant atmosphere to provide the Group IB element and the Group IIIB element. Forming a p-type ZnO based semiconductor layer co-doped with (c) a second oxidant in the second oxidant atmosphere having a higher oxidizing power than the normal pressure first oxidant atmosphere. A method for manufacturing a p-type ZnO-based semiconductor layer is provided.

  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 the step of forming the p-type ZnO-based semiconductor layer includes (a) one or more IIIB selected from the group consisting of a group IB element that is Cu or / and Ag, and B, Ga, Al, and In Forming an n-type ZnO-based semiconductor single crystal structure containing a group element; and (b) subjecting the n-type ZnO-based semiconductor single crystal structure to a first annealing in an atmospheric pressure first oxidant atmosphere to perform the IB A step of forming a p-type ZnO-based semiconductor layer co-doped with a group element and the group IIIB element; and (c) a second oxide having a higher oxidizing power than the first atmospheric oxidant atmosphere in the p-type ZnO-based semiconductor layer. And a second annealing process in an oxidant atmosphere. That the production method of the ZnO-based semiconductor device is provided.

  A method for manufacturing a p-type ZnO-based semiconductor layer having a high acceptor concentration and a method for manufacturing a ZnO-based semiconductor element including a p-type ZnO-based semiconductor layer having a high acceptor concentration can be provided.

1A is a schematic cross-sectional view showing an MBE apparatus, FIG. 1B is an atmospheric annealing apparatus, and FIG. 1C is a reduced pressure radical annealing apparatus. FIG. 2A is a schematic cross-sectional view of a sample on which an epitaxial layer has been grown, 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 stacked 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 ZnO: Ga layer 54a and the Cu layer 54b. FIGS. 3A and 3B are graphs showing the depth profile of CV characteristics and impurity concentration measured for the alternately laminated structure 54 of the as-grown sample, and FIG. 3C shows the absolute Cu concentration [Cu] in the alternately laminated structure 54. 2 is a graph showing a depth profile by SIMS of Ga and Ga absolute concentration [Ga]. FIG. 4A and FIG. 4B are graphs showing temperature changes over time of the first annealing and the second annealing of the first type two-stage annealing. FIGS. 5A and 5B are graphs showing CV characteristics and depth profiles of impurity concentrations measured for the positions where the alternately laminated structure 54 is formed in the sample after the first annealing of the first type two-stage annealing. 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 formation position of the alternating lamination structure 54 of the sample after 1st annealing of 1st type | mold 2 step annealing. FIG. 6A shows the CV characteristics and the CV characteristics at the position where the alternate laminated structure 54 is formed (p-type layer formation position) of the sample, measured as time elapses from the end of the first annealing of the first type two-step annealing to the start of the second annealing. It is a graph which shows the depth profile of impurity concentration. FIG. 6B shows an absolute Cu concentration [Cu] and an absolute Ga concentration [Ga] at the formation position (p-type layer formation position) of the alternately laminated structure 54 of the sample after the second annealing of the first type two-step annealing. It is a graph which shows the depth profile by SIMS. Figure 7 is a graph showing a change in acceptor concentration N _a of the sample was measured with time after the start of the second annealing from a first annealing at the end of the first kind of two-step annealing. FIG. 8 shows the second type two-step annealing, FIG. 8A is a graph showing the temperature change with respect to time of the atmospheric pressure oxygen annealing of the first annealing, and FIG. 8B is the time course of the reduced pressure oxygen radical annealing of the second annealing. FIG. 9 is a graph showing depth profiles of CV characteristics and impurity concentrations after first annealing and second annealing after as-grown and second-type two-stage annealing. 10A and 10B are flowcharts illustrating an outline of a method for manufacturing a ZnO-based semiconductor light-emitting device according to the first example. FIG. 11A is a schematic cross-sectional view of a ZnO-based semiconductor light-emitting element manufactured by the manufacturing method according to the first example, and FIG. 11B is a schematic cross-sectional view of an alternate stacked structure 5A. FIG. 12 shows a Zn cell, an Mg cell, an O cell, and a Ga cell for forming an alternate stacked structure when forming a Cu, Ga co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer. It is a time chart which shows the example of the shutter sequence of a cell and Cu cell. FIG. 13A is a schematic cross-sectional view of a ZnO-based semiconductor light-emitting element manufactured by the manufacturing method according to the second example, and FIG. 13B is a schematic cross-sectional view showing another example of the active layer 15. 13C is a schematic cross-sectional view of the alternately laminated structure 16A. FIG. 14 is a schematic cross-sectional view of a ZnO-based semiconductor light-emitting device manufactured by the manufacturing method according to the third example. 15A to 15D are schematic cross-sectional views showing examples of an n-type ZnO-based semiconductor single crystal structure capable of forming a p-type ZnO-based semiconductor single crystal layer.

  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.

  FIG. 1A shows a schematic cross-sectional view of an MBE apparatus. In the vacuum chamber 71, a Zn source gun 72, an O source gun 73, an Mg source gun 74, a p-type impurity Cu source gun 75, and an n-type impurity Ga source gun 76 are provided. Guns are provided as needed. For example, a p-type impurity Ag source gun can be provided instead of or in addition to the p-type impurity Cu source gun. In the first sample, since Cu is used as the p-type impurity, it is assumed that the Cu source gun 75 is 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.

O source gun 73 includes, for example, an electrodeless discharge tube using a 13.56MHz radio frequency (RF) power, _{O 2} gas in the electrodeless discharge tube (6N) into plasma and emits O radical beam. As the discharge tube material, alumina, high-purity quartz or the like can be used.

  A stage 77 having a heater holds, for example, a ZnO 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.

When Mg is added to ZnO to form a MgZnO mixed crystal, 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 expressed as x, the Mg composition x is preferably 0.6 or less in order to maintain the wurtzite structure. _{Incidentally,} Mg _{x Zn 1-x} O includes ZnO without Mg as the case of 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 a ZnO-based semiconductor requires p-type impurity doping.

  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 single crystal grows two-dimensionally and an epitaxial layer with a flat surface grows, the RHEED image shows a streak pattern. When a single crystal grows three-dimensionally and an epitaxial layer with a non-flat surface grows, the RHEED image shows a spot pattern. In the case of polycrystalline growth, the RHEED image becomes a ring pattern.

  A film thickness meter 79 using a crystal resonator is provided in the vacuum chamber 71. The film thickness can be obtained from the vibration frequency, and the film formation speed can be obtained from the time change of the film thickness. Using the adhesion rate measured by the film thickness meter 79, the flux intensity of each beam can be obtained. The flux means the amount flowing per unit time and unit area. The flux intensity is the beam intensity in MBE.

The flux intensity of Zn beam _J Zn, the flux intensity of the Mg beam _{J Mg,} the flux intensity of O radical beam and _{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 beam of O which is a gas material contains atomic radicals and neutral molecules. Here, the flux intensity of atomic radicals effective for crystal growth is considered.

In crystal growth, the adhesion coefficient indicating the ease of adhesion of Zn to the base is k _Zn , the adhesion coefficient indicating the ease of _Mg adhesion is _kmg , and the adhesion coefficient indicating the ease of _O adhesion is 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 , O adhesion coefficient k _O and flux strength J _O 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.

k _O of _{J O, k Zn} J Zn and _k Mg _{J Mg} sum of the _{(k Zn J Zn + k Mg} J Mg), is the ratio _{k O J O / (k Zn} J Zn + k Mg J Mg), VI / II flux ratio. When the VI / II flux ratio is less than 1, the group II rich condition (or Zn rich condition), when the VI / II flux ratio is equal to 1, the stoichiometric condition, and when the VI / II flux ratio is greater than 1, VI This is called the 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 / It can be expressed as ( _JZn + _JMg ).

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

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. The result is obtained by using the approximate expression of ZnO growth rate G _ZnO : G _ZnO = [(k _Zn J _Zn ) ^-1 + (k _O J _O ) ^-1 ] ^-1 , so that k _O = By fitting with 1 and fitting, the O radical flux J _{O under} that condition 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.

  An experiment conducted by the present inventors will be described. The state after crystal growth (before annealing) is referred to as as-grown.

  FIG. 2A shows a schematic cross-sectional view of an as-grown sample. On a Zn-faced ZnO (0001) substrate (hereinafter referred to as a ZnO substrate) 51 having n-type conductivity, a ZnO buffer layer 52, an undoped ZnO layer 53, and an alternate stacked structure 54 are stacked in an epitaxial state.

A method for manufacturing the sample will be described. The substrate 51 is loaded on the stage 77 of the MBE apparatus shown in FIG. 1A, the chamber 71 is closed, evacuated, the substrate is heated, and thermal cleaning is performed at 900 ° C. for 30 minutes. The temperature of the substrate 51 is lowered to 300 ° C., and a Zn flux F _Zn is supplied at a growth temperature of 300 ° C. at 0.17 nm / s (J _Zn = 1.1 × 10 ¹⁵ atoms / cm ² s), and O radical beam irradiation is performed. The conditions are an RF power of 300 W, an O ₂ flow rate of 2.0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s), and a low-temperature grown ZnO buffer layer 52 having a thickness of 30 nm is grown on the ZnO substrate 51. After the growth, the substrate 51 is heated and annealed at 900 ° C. for 10 minutes. The crystallinity and surface flatness of the low temperature grown ZnO buffer layer 52 will be improved.

On the ZnO buffer layer 52, the substrate 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 conditions are RF power 300 W, An undoped ZnO layer 53 having a thickness of 100 nm is 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 becomes an n-type ZnO layer.

  After growing the undoped ZnO layer 53, the substrate temperature is lowered to 250 ° C. Zn, O, n-type impurity Ga, and p-type impurity Cu are supplied at different timings on the undoped ZnO layer 53 at a substrate temperature of 250 ° C., thereby forming an alternately laminated structure 54 of ZnO: Ga layers and Cu layers. To do. ZnO: Ga indicates ZnO doped with impurity Ga. Later, the thickness of the ZnO: Ga layer is limited so that the p-type impurity Cu can diffuse into the ZnO: Ga layer and function as a p-type impurity. However, the thickness should be sufficient for the ZnO: Ga layer to exhibit good crystallinity and continuity.

  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. A high level indicates shutter open and a low level indicates shutter close.

  When the Zn cell shutter is opened, the O cell shutter and the Ga cell shutter are also opened. A ZnO: Ga crystal layer grows. In the ZnO: Ga growth process, the Cu cell shutter is closed. In the ZnO: Ga layer growth step, the O cell shutter and the Ga cell shutter are simultaneously opened and closed, and the Zn cell shutter is opened in synchronization with the O cell shutter and the Ga cell shutter, and the open period is extended before and after. For example, the opening period of each O cell shutter and Ga cell shutter is set to 10 seconds, and the opening period of the Zn cell shutter is extended by 1 second before and after the opening period of the O cell shutter and Ga cell shutter. The ZnO: Ga layer growth period per time is considered to be 10 seconds. The outermost surface of the ZnO: Ga layer becomes a Zn plane and suppresses the direct association of O and Cu.

  The Zn cell shutter, O cell shutter, and Ga cell shutter are closed, and the Cu cell shutter is opened to form a Cu layer. Cu is an impurity and supplies only a limited amount. Since the Cu layer is less than one atomic layer, it may be referred to as a Cu adhesion step. The amount of Cu evaporation depends on the cell temperature and the shutter open period. For example, the cell temperature of Cu is set to 990 ° C., and the open period per time of the Cu cell shutter is set to 50 seconds. The ZnO: Ga layer growth step and the Cu layer formation step are alternately repeated. It was confirmed by RHEED that a single crystal grew.

For example, in the ZnO: Ga layer growth step, the Zn flux F _Zn is 0.13 nm / s (J _Zn = 8.6 × 10 ¹⁴ atoms / cm ² s), the 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 cell temperature T _Ga of _Ga was 600 ° C. (F _Ga was less than the detection lower limit). The Cu cell temperature T _Cu in the Cu adhesion step was 990 ° C., and the Cu flux F _Cu was 0.004 nm / s. The VI / II flux ratio is 0.94 (Zn rich condition).

  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 ZnO: Ga layers 54a and Cu layers 54b are alternately laminated. The ZnO: Ga layer growth step and the Cu deposition step were alternately repeated 60 times to obtain an alternately laminated structure 54 having a thickness of 120 nm. The thickness of the ZnO: Ga layer 54a is about 2.0 nm, and the thickness of the Cu layer 54b (Cu deposition thickness) is 1 atomic layer or less, for example, about 1/20 atomic layer. In this case, the Cu coverage on the surface of the ZnO: Ga layer 54a is about 5%.

  FIG. 2D shows a schematic cross-sectional view of the ZnO: Ga 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 ZnO: Ga 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 a layer structure as shown in FIG. 2C.

  3A and 3B are graphs showing CV characteristics and depth profiles of impurity concentrations measured for the alternately laminated structure 54 in the as-grown state of the sample. The measurement was performed by an electrochemical CV measurement method (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. Referring to the graph of FIG. 3A, a curve that rises to the right (the relationship in which 1 / C ² increases as the voltage increases) is obtained, indicating that the alternate stacked structure 54 has n-type conductivity. Note that the slope corresponds to the impurity concentration (resistance value).

The horizontal axis of the graph of FIG. 3B represents the position in the depth (thickness) direction of the sample (depletion layer depth from the sample surface) 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. 3B, the impurity concentration (donor concentration) of alternate stacked structure 54 _{N d} is seen to be about 1.0 × ¹⁰ 21 ^{cm -3.}

FIG. 3C is a graph showing a depth profile of the absolute Cu concentration [Cu] and the absolute Ga concentration [Ga] in the alternating layered structure 54 by secondary ion mass spectrometry (SIMS). . The horizontal axis of the graph represents the position in the depth direction of the sample in the unit “nm”, 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. The n-type impurity Ga and the p-type impurity Cu are doped almost uniformly over the entire thickness of the alternate laminated structure.

It can be seen that the Cu concentration [Cu] in the alternately laminated structure 54 is 2.8 × 10 ²¹ cm ⁻³ and the Ga concentration [Ga] is 9.4 × 10 ²⁰ cm ⁻³ . The value of [Cu] / [Ga], which is the ratio of [Cu] to [Ga], is 2.9. Note that the concentrations of [Cu] and [Ga] may not be accurately measured in the vicinity of the surface due to the influence of the adsorbate.

  In the as-grown state, Cu, which is a p-type impurity, has not yet been activated. In order for IB group Cu to function as a p-type impurity, it will be necessary for Cu to enter the Zn site. It is conceivable to anneal to diffuse Cu. Various annealings have been tried in the past, but satisfactory results have not yet been obtained. At most, p-type is obtained with CV characteristics.

  A ZnO-based crystal is considered to contain various vacancy: lattice defects (vacancies). In order for Cu and Ag, which are group IB elements, to function as p-type impurities, Cu and Ag occupy a Zn site which is a group II element, obtain one electron, and supply one hole. It will be necessary. On the other hand, oxygen (O) vacancies exist in the ZnO crystal. O vacancies function as donors. In order to obtain a better p-type crystal, it would be desirable to reduce the donor O vacancies.

  The present inventors considered activating p-type impurities and suppressing donor concentration in order to obtain good p-type conductivity. In order to diffuse and electrically activate the p-type impurity, first annealing is performed. As the first annealing, for example, annealing in an atmospheric oxygen atmosphere is performed. As the second annealing, second annealing is performed in which O vacancies are reduced and the donor concentration is suppressed. In order to reduce O vacancies, it is desired to supply mono-containing substances containing oxygen and having a strong oxidizing action into the crystal. If oxygen can be supplied to the O vacancies (if oxidation occurs), the O vacancies will decrease. As a method for causing oxidation, a method of supplying water vapor at normal pressure (first type) as used in wet oxidation of silicon, and supplying O radicals having a very strong oxidizing power under reduced pressure. A method (second type) was considered.

  FIG. 1B shows an atmospheric pressure annealing apparatus 30. The annealing chamber 36 has a susceptor 37 with a heater, and an inlet and an outlet for atmospheric pressure atmospheric gas. A sample substrate 78 is placed on the susceptor 37. A pipe connected to an oxygen supply source such as an oxygen cylinder and including valves V <b> 1 to V <b> 4 can supply oxygen to the annealing chamber 36. The valve V2r, which is linked to the valve V2 and takes the opposite state, forms a branch on the upstream side of the valve V2, and the branched pipe 32 forms a bubbler in the container 31 that stores the pure water 34. A pipe 33 that takes in oxygen containing water vapor above the liquid level of the pure water 34 joins a pipe downstream of the valve V3 via the valve V3r. The valve V3r takes a state opposite to that of the valve V3. When the valves V2 and V3 are closed and the valves V2r and V3r are opened, oxygen gas containing water vapor is supplied to the annealing chamber 36 through the bubbler. This gas supply system can supply either dry oxygen gas or wet oxygen gas to the annealing chamber 36.

  FIG. 1C shows a reduced pressure radical annealing apparatus 40. The annealing chamber 41 has an airtight structure, includes a susceptor 47 with a heater, and an electrodeless discharge tube 43 having an RF coil 44, and is connected to the vacuum exhaust devices 42a and 42b through exhaust valves. The electrodeless discharge tube 43 is connected to oxygen piping via valves V6 and V7 and a mass flow controller MFC. The substrate 78 is introduced into the annealing chamber 41, the inside of the chamber 41 is evacuated, the inside of the electrodeless discharge tube is set in a reduced pressure oxygen atmosphere, and RF power is supplied to generate oxygen plasma. Oxygen radicals can be supplied onto the sample 78 from the electrodeless discharge tube 43. A gas other than oxygen that can generate oxygen radicals may be used.

  In the first type experiment, the sample was introduced into the annealing apparatus 30 and the first type two-step annealing process was performed. In the first annealing, p-type impurities are diffused in an oxygen atmosphere, and in the second annealing, annealing is performed in an oxygen atmosphere containing water vapor, and oxygen is supplied to O vacancies in the crystal. First, Cu was used as a p-type impurity.

  4A and 4B are graphs showing the contents of the first annealing and the second annealing of the first type experiment. The horizontal axis shows the passage of time, and the vertical axis shows the temperature. As shown in FIG. 4A, the first annealing is performed in an oxygen gas atmosphere in the chamber, the temperature is raised from room temperature to 570 ° C., annealing is performed for 10 minutes, and the temperature is lowered to room temperature. As shown in FIG. 2C, impurities Ga and Cu are present at different positions in the crystal. In the first annealing, at least Cu is diffused and moved to the vicinity of Ga. For this reason, the temperature of the first annealing is a relatively high temperature.

As shown in FIG. 4B, after the first annealing, the second annealing is performed by switching the atmosphere in the chamber to an oxygen atmosphere containing water vapor, raising the temperature from room temperature to 350 ° C., and performing annealing for 45 minutes, Subsequently, the temperature is raised to 400 ° C. and annealing is performed for 15 minutes. When the second annealing is performed at a high temperature, impurity diffusion and O escape may occur. Therefore, the second annealing is performed at a relatively low temperature (at least a temperature lower than the first annealing) and a high oxidizing power. It is preferable to carry out. As an example, the first annealing is performed in an oxygen atmosphere at a flow rate of 1 L / min for 10 minutes at 570 ° C., and the second annealing is performed by adding water vapor to oxygen at a flow rate of 1 L / min and at 350 ° C. for 45 minutes and 400 ° C. For 15 minutes. Note that bubbling was performed by passing O ₂ gas through boiling pure water.

5A and 5B are graphs showing the CV characteristics and the depth profile of the impurity concentration at the position where the alternately laminated structure 54 is formed after the first annealing of the sample, 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. 5A, 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. 5B, the impurity concentration (acceptor concentration) _{N a} of alternate stacked structure 54 formed position after first annealing sample (p-type layer formation position) is the order of 6.0 × ¹⁰ 17 ^{cm -3} I understand that.

FIG. 5C shows a SIMS depth profile of the Cu absolute concentration [Cu] and the Ga absolute concentration [Ga] at the position where the alternate laminated structure 54 is formed (p-type layer formation position) after the first annealing. It is a graph. The meaning of both axes of the graph is equal to that of FIG. 3C. In the measurement, since an electrode is provided on the p-type layer, accurate measurement is not performed near the surface (shallow position). Cu concentration [Cu] is 1.8 × 10 ²¹ cm ⁻³ , Ga concentration [Ga] is 9.0 × 10 ²⁰ cm ^{−3 at} the position where the alternate stacked structure 54 is formed (p-type layer formation position), and the measurement is accurate. It can be seen that both are substantially constant throughout the thickness direction of the p-type layer except for the vicinity of the surface which is not performed. Cu and Ga are uniformly diffused in the p-type layer. The value of [Cu] / [Ga] is about 2.0. In this specification, “almost constant” with respect to the concentration means a range of 50% to 150% of an average value of concentration (for example, 1.8 × 10 ²¹ cm ^{−3 in} the case of [Cu] in the figure). .

FIG. 6A is a graph showing a depth profile of CV characteristics and impurity concentration at the position where the alternate laminated structure 54 is formed (p-type layer formation position) after the second annealing of the sample. The graph showing the CV characteristics in the upper column and the depth profile of the impurity concentration is shown in the lower column. The meanings of both axes of the graph are equal to those of the graphs shown in FIGS. 3A and 3B. Referring to the graph showing the CV characteristics, a downward-sloping curve (a relationship in which 1 / C ² decreases as the voltage increases) is obtained during the second annealing period, and the formation position (p-type layer) of the alternate stacked structure 54 is obtained. It can be seen that the p-type conductivity at the formation position is maintained.

Referring to the graph indicating the depth profile of the impurity concentration, acceptor concentration _{N a} of 15 minutes after the start of the second annealing (during annealing practice of 350 ° C. for 15 minutes) is about 6.8 × ¹⁰ 17 ^{cm -3.} The acceptor concentration _{N a} is about 8.3 × ¹⁰ 17 ^{cm -3} of 30 minutes after the start of the second annealing (during annealing performed a total of 30 minutes at 350 ° C.), in addition, 45 minutes after the start of the second annealing (350 ° C. acceptor concentration _{N a} of annealing time of execution) of a total of 45 minutes is seen to increase to about 1.1 × ¹⁰ 18 ^{cm -3.} Further, the acceptor concentration _{N a} of 60 minutes after the start of the second annealing (350 ° C. in a total of 45 minutes of annealing and 400 ° C. sample was annealed for 15 minutes at) increases to about 2.5 × ¹⁰ 18 ^{cm -3} .

  FIG. 6B shows a SIMS depth profile 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 after the second annealing is completed. It is a graph. The meaning of both axes of the graph is equal to that of FIG. 3C. Further, in the measurement, since an electrode was placed on the p-type layer, accurate measurement was not performed in the vicinity of the surface, as in the case of the sample after the first annealing shown in FIG. 5C.

The Cu concentration [Cu] at the position where the alternately laminated structure 54 is formed (p-type layer formation position) is 1.6 × 10 ²¹ cm ⁻³ , the Ga concentration [Ga] is 7.5 × 10 ²⁰ cm ⁻³ , and the measurement is accurate. It can be seen that both are substantially constant over the entire thickness of the p-type layer, except near the surface where it is not performed. The distribution of Cu and Ga in the p-type layer is uniform. The value of [Cu] / [Ga] is about 2.1.

Figure 7 is a graph showing temporal changes in the acceptor concentration N _a after the first annealing of the sample. The horizontal axis of the graph represents each of the annealing conditions and the vertical axis, the acceptor concentration N _a, shown in the unit of "cm ^-3".

The second annealing, the acceptor concentration N _a of the alternate stacked structure 54 formation position (p-type layer formation position) is increased. Specifically, in the second annealing before starting (after the first annealing finished), the acceptor concentration _{N a} of about 6.0 × ¹⁰ 17 ^{cm -3} is, after completion of the second anneal, about 2.5 × It has increased to 10 ¹⁸ cm ⁻³ . Increase in the acceptor concentration _{N a} is about 1.9 × ¹⁰ 18 ^{cm -3,} the acceptor concentration _{N a} after completion of the second anneal is 4.2 times that of prior to the start second annealing. In the experiment, as the time to perform the second annealing is longer, it is seen also acceptor concentration N _a is increased.

  It is understood that the sample alternately stacked structure (ZnO: Ga layer) is as-grown and n-type (see FIG. 3A) and is p-typed by the first annealing (see FIG. 5A). By performing the first annealing, Cu and Ga are preferably diffused uniformly in the alternately laminated structure. With the diffusion of Cu and Ga, the alternate laminated structure is considered to become a p-type ZnO single crystal layer co-doped with Cu and Ga (to be p-type). That is, the first annealing can be said to be an annealing in which Cu and Ga are diffused to make the alternate laminated structure p-type.

The second annealing, the acceptor concentration N _a of the p-type ZnO single crystal layer Cu and Ga are co-doped is increased (see FIG. 6A and FIG. 7) It is understood. The Cu and Ga co-doped p-type ZnO single crystal layer after the first annealing has O vacancies that act as donor sources. By performing the second annealing, it is considered that O is supplemented to O vacancies and O vacancies are reduced.

In the first type of experiment, the second annealing was performed in an atmosphere in which water vapor (H ₂ O) was included in oxygen gas. H ₂ O functions as an oxidizing agent, and oxygen gas mainly functions as a carrier. A gas other than oxygen gas could be used as the carrier gas. Although there is no special restriction | limiting in carrier gas, it will be preferable to use oxygen from a viewpoint of reducing the oxygen detach | desorbed from a Cu and Ga co-doped p-type ZnO single crystal layer. By performing the second annealing in an atmosphere containing an oxidizing agent, to complement the O vacancies, it could increase the acceptor concentration N _a.

The annealing process in the atmosphere containing oxygen as the first annealing atmosphere and water vapor as the second annealing atmosphere has been described above. The atmosphere used for the first and second annealings has a large oxidizing power. Other than the above, NO ₂ , N ₂ O, ozone, methyl alcohol, ethyl alcohol, etc. could be used as the oxidizing agent if the relationship is selected so as to maintain the relationship of 1 oxidizing agent <second oxidizing agent.

  By applying the first type two-stage annealing treatment to the alternately laminated structure in which the ZnO: Ga layer growth process and the Cu adhesion process are alternately repeated, Cu and Ga are doped over the entire thickness direction of the layer, It was found that a Cu, Ga co-doped p-type ZnO layer (p-type ZnO-based semiconductor layer) having a high acceptor concentration can be obtained.

Cu, Ga co-doped p-type conductivity is performed by first annealing a structure in which Ga-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers and Cu layers are alternately stacked. A Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) 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. Instead of Cu or together with Cu, Ag, which is a group IB element capable of forming a plurality of valences, can be used.

  Next, the second type of experiment in which the second type of two-step annealing is performed will be described. Note that Ag was used as a p-type impurity in the sample in the second type experiment. The Cu layer in the cross-sectional views of FIGS. 2A, 2C, and 2D is replaced with an Ag layer 54b. The p-type impurity is Cu in the first type experiment, and Ag in the second type experiment is not limited. The p-type impurity can be appropriately selected from Cu and Ag. A process for forming a sample containing Ag as a p-type impurity will be described.

After performing the thermal cleaning on the ZnO substrate 51, the temperature of the substrate 51 is lowered to 250 ° C., the growth temperature is 250 ° C., the Zn flux F _Zn = 0.15 nm / s, the O ₂ supply amount is ₂ sccm, and the RF power is 300 W for 5 minutes. A low-temperature grown ZnO buffer layer 52 having a thickness of 30 nm was grown on the ZnO substrate 51. After the growth, annealing was performed at 950 ° C. for 30 minutes, and it was expected that the crystallinity and surface flatness of the low temperature growth ZnO buffer layer 52 would be improved. The substrate temperature at 950 ° C., on the ZnO buffer layer 52, Zn flux _{F Zn} to 0.15 nm / s, RF power 300 W, 15 minutes O radical beam with _{O 2} flow rate 2.0 sccm, was supplied, the thickness of 100nm An undoped ZnO layer 53 was grown. The undoped ZnO layer 53 is n-type.

After growing the undoped ZnO layer 53, the substrate temperature was lowered to 250 ° C. A substrate temperature of 250 ° C., Zn flux ^{_{F Zn = 0.15nm / s (J}} Zn = 9.9x10 14 atoms / cm 2 s), O 2 supply amount 2 sccm, RF power ^{_{300W (J O = 8.1 × 10}} 14 atoms / Cm ² s), VI / II flux ratio 0.82, Ag source temperature 830 ° C., Ga source temperature 550 ° C., 10 seconds ZnO: Ga layer growth and 40 seconds Ag layer growth on the undoped ZnO layer 53 Were alternately set to form an alternately laminated structure 54 having a thickness of 150 nm. The second type two-step annealing was performed on the second type sample thus formed. The first annealing is, for example, atmospheric pressure annealing in an oxygen atmosphere, like the first annealing of the first type two-stage annealing. The temperature is such that p-type impurities can be diffused. The second annealing is performed by irradiating oxygen radicals with strong oxidizing power in a reduced pressure atmosphere.

  FIG. 8A is a graph showing a second type of first annealing step. A sample containing Ag as a p-type impurity is loaded on a stage 37 in a chamber 36 of an atmospheric pressure annealing apparatus 30 as shown in FIG. 1B, and the temperature is raised from room temperature to 450 ° C. in an atmospheric pressure oxygen gas atmosphere. Annealing was performed for a minute, and the temperature was lowered to room temperature. The p-type impurity Ag diffused and showed p-type. Thereafter, the sample was taken out from the atmospheric pressure annealing apparatus 30 and loaded into the reduced pressure radical annealing apparatus 40.

FIG. 8B is a graph showing a second annealing process of the second type. In a reduced pressure oxygen atmosphere of 10 ⁻¹ Pa or less, for example, about 10 ⁻² Pa, the temperature is raised from room temperature to 350 ° C., an O ₂ flow rate of ₂ sccm, an RF power of 300 W (J 2 _O = 8.1 × 10 ¹⁴ atoms / cm ² s ), Oxygen plasma was generated, oxygen radicals were supplied onto the substrate 78 and irradiated with oxygen radicals for 30 minutes. Thereafter, the plasma is stopped, the temperature is lowered to room temperature, the vacuum is released, and the substrate is taken out.

  FIG. 9 shows the depth profile of the impurity concentration obtained from the as-grown, the first annealing, the CV characteristics after the second annealing, and the depletion layer width measured in the sample subjected to the second type two-step annealing.

The horizontal axis of the upper graph in FIG. 9 represents 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 lower graph in FIG. 9 represents the voltage in the unit “V”, 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.

In as-grown, the CV characteristic rises to the right, indicating n-type. The donor concentration was 9.0 × 10 ²⁰ cm ⁻³ . After the first annealing, the CV characteristic decreases to the right, indicating that it is inverted to p-type. The acceptor concentration was 7.0 × 10 ¹⁷ cm ⁻³ . After the second annealing, the acceptor concentration increased to 8.0 × 10 ¹⁸ cm ⁻³ . The second anneal resulted in an increase in acceptor concentration by about an order of magnitude. It is thought that the O radical supplemented the O vacancies and the donor concentration was reduced.

  Thus, it has been found that a p-type ZnO-based semiconductor layer having a high acceptor concentration can be manufactured by the first-type two-step annealing and the second-type two-step annealing. The first type experiment and the second type experiment can be used as the first example and the second example. Various ZnO-based semiconductor elements can be manufactured using the p-type ZnO-based semiconductor layer having a high acceptor concentration obtained by these Examples.

  Hereinafter, an example of manufacturing a ZnO-based semiconductor light-emitting element using a Cu, Ga co-doped p-type ZnO-based semiconductor layer will be described. The Cu, Ga co-doped p-type ZnO semiconductor layer can be replaced with an Ag, Ga co-doped p-type ZnO based semiconductor layer. When Ag is used as the p-type impurity, Ag and oxygen may be supplied to form an AgO layer (AgO deposition step).

  10A and 10B are flowcharts illustrating an outline of a method for manufacturing a ZnO-based semiconductor light-emitting device according to the first example. In the first example, a semiconductor light emitting element will be described. However, the present invention is not limited to the light emitting element but can be widely applied to semiconductor elements. As shown in FIG. 10A, the manufacturing method of the ZnO-based semiconductor light emitting device according to the first example includes a step of forming an n-type ZnO-based semiconductor layer above the substrate (step S101) and an n-type ZnO-based formed in step S101. A step (step S102) of forming a p-type ZnO-based semiconductor layer above the semiconductor layer is included. As shown in FIG. 10B, the p-type ZnO-based semiconductor layer forming step of step S102 includes five steps of step S102a to step S102e.

In the p-type ZnO-based semiconductor layer forming step (step S102), first, Zn, O, Mg and Ga are supplied as necessary, and Ga-doped n-type Mg _x Zn _1-x O (0 ≦ 0). x ≦ 0.6) A single crystal layer is formed (step S102a). Next, Cu is supplied onto the Ga-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer formed in step S102a (step S102b). Step S102a and step S102b are alternately repeated to form a stacked structure (step S102c). Then, first annealing is performed on the stacked structure formed in step S102c to form a p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer co-doped with Cu and Ga (step S102d). . Further, the Cu, Ga co-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer formed in step S102d is annealed (second anneal) in an atmosphere containing an oxidizing agent, Cu, The acceptor concentration of the Ga co-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer is increased (step S102e).

FIG. 12 shows a Zn cell, an Mg cell, and an O cell in forming an alternate stacked structure in order to form a Cu, Ga co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) single crystal layer. 5 is a time chart illustrating an example of a shutter sequence of a Ga cell and a Cu cell. Compared to the shutter sequence shown in FIG. 2B, an Mg shutter is added. The Mg shutter is controlled to open and close in synchronization with the O shutter and the Ga shutter. The other points are the same.

  A first example of manufacturing a homo-structured ZnO-based semiconductor light-emitting device will be described with reference to FIGS. 11A and 11B.

FIG. 11A is a schematic cross-sectional view of a ZnO based semiconductor light emitting device manufactured by the manufacturing method according to the first example. Although the ZnO substrate 1 is used in the first example, a conductive substrate such as an MgZnO substrate, a GaN substrate, a SiC substrate, or a Ga ₂ O ₃ substrate may be used.

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, A ZnO buffer layer 2 having a thickness of 30 nm is 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 is performed at 900 ° C. for 10 minutes. On the ZnO buffer layer 2, Zn, O and Ga are simultaneously supplied at a growth temperature of 900 ° C. to grow the n-type ZnO layer 3 having a thickness of 150 nm (step S101 in FIG. 10A). For example, 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 0.0 × 10 ¹⁴ atoms / cm ² s), and the cell temperature of Ga is 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, The undoped ZnO active layer 4 having a thickness of 15 nm is grown at an O ₂ flow rate of 2.0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s). Subsequently, a Cu, Ga co-doped p-type ZnO layer 5 is formed on the undoped ZnO active layer 4 (step S102 in FIG. 10A).

First, the substrate temperature is set to 250 ° C., and Zn, O, Ga, and Cu are supplied at different timings to form an alternately laminated structure. Specifically, the step of supplying Zn, O, and Ga to grow a ZnO: Ga layer and the step of supplying Cu on the ZnO: Ga layer are repeated 60 times alternately to form an alternating stacked structure with a thickness of 120 nm. Form. For example, the ZnO: Ga layer growth period per time is 10 seconds, and the Cu supply period per time is 50 seconds. Zn flux F _Zn in the ZnO: Ga layer growth step is 0.13 nm / s (J _Zn = 8.6 × 10 ¹⁴ 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 is 600 ° C. The VI / II flux ratio is 0.94. Further, the cell temperature T _Cu of Cu in the Cu supplying step is set to 990 ° C., and the Cu flux F _Cu is set to 0.004 nm / s.

FIG. 11B is a schematic cross-sectional view of the alternately laminated structure 5A. The alternate laminated structure 5A has a laminated structure in which ZnO: Ga layers 5a and Cu layers 5b are alternately laminated. The thickness of the ZnO: Ga layer 5a is about 2.0 nm, the thickness of the Cu layer 5b is 1 atomic layer or less, for example, about 1/20 atomic layer (ZnO: Ga coverage on the surface of the Ga layer 5a is about 5%). is there. The alternate stacked structure 5A exhibits n-type conductivity, and the donor concentration _Nd is, for example, 1.0 × 10 ²¹ cm ⁻³ .

A first type of two-step annealing is performed on the alternate stacked structure 5A. First annealing is performed to make the alternate stacked structure 5A into p-type. For example, by performing annealing at 570 ° C. for 10 minutes in an oxygen atmosphere at a flow rate of 1 L / min, Cu and Ga are diffused, and an alternate stacked structure 5A exhibiting n-type conductivity is formed by co-doping Cu and Ga. Type ZnO single crystal layer. Acceptor concentration _{N a} of the p-type ZnO single crystal layer after completion of the first annealing is, for example, 6.0 × ¹⁰ 17 ^{cm -3.}

  In an atmosphere in which water vapor is included in oxygen at a flow rate of 1 L / min, the second annealing is performed at 350 ° C. for 45 minutes and at 400 ° C. for 15 minutes to supplement the O vacancies, and the Cu, Ga co-doped p-type ZnO layer 5 Form.

  Thereafter, the n-side electrode 6 n is formed on the back surface of the ZnO substrate 1. A p-side electrode 6p is formed on the Cu, Ga co-doped p-type ZnO layer 5, and a bonding electrode 7 is 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 is manufactured 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 example is co-doped with Cu and Ga, and has a high acceptor concentration N _a , for example, 2.5 × 10 ¹⁸ cm ^−3. A p-type ZnO-based semiconductor single crystal layer. For example, the Cu concentration [Cu] is 1.6 × 10 ²¹ cm ⁻³ and the Ga concentration [Ga] is 7.5 × 10 ²⁰ cm ⁻³ ([Cu] / [Ga] is 2.1). It is almost constant in the thickness direction.

  According to the manufacturing method according to the first example, a ZnO-based semiconductor light-emitting element including Cu and Ga co-doped p-type ZnO layer 5 in which Cu and Ga are uniformly doped throughout the thickness direction of the layer and has a high acceptor concentration is manufactured. be able to.

Next, a second example and a third example of manufacturing 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. An example will be described.

  FIG. 13A is a schematic cross-sectional view of a ZnO-based semiconductor light-emitting element manufactured by the manufacturing method according to the second example.

Zn and O are 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 is performed at 900 ° C. for 10 minutes.

Zn, O, and Ga are simultaneously supplied on the ZnO buffer layer 12 to grow an n-type ZnO layer 13 having a thickness of 150 nm, for example, at a growth temperature of 900 ° C. Zn flux F _Zn is 0.15 nm / s, O radical beam irradiation conditions are RF power 250 W, O ₂ flow rate 1.0 sccm, and Ga cell temperature is 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 are 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 are simultaneously supplied onto 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 is 0.1 nm / s, O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate 2.0 sccm.

  As shown in FIG. 13B, 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, 250 ° C., and the Ga-doped n-type MgZnO single crystal layer growth step and the Cu deposition step are alternately repeated to form an alternate stacked structure on the active layer 15. The shutter sequence of the Zn cell, Mg cell, O cell, Ga cell, and Cu cell in forming the alternate laminated structure is the same as that shown in FIG. 12, for example.

For example, the growth period in a single Ga-doped MgZnO single crystal layer growth step is 10 seconds, and the Cu supply period in a single Cu deposition step is 50 seconds. Zn flux F _Zn in the Ga-doped MgZnO single crystal layer growth step is 0.13 nm / s, Mg flux F _Mg is 0.04 nm / s, O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate 2.0 sccm, The cell temperature T _Ga of _Ga is 600 ° C. The VI / II flux ratio is 0.79. The Cu cell temperature T _Cu in the Cu supplying step is 990 ° C., and the Cu flux F _Cu is 0.004 nm / s. The Ga-doped MgZnO single crystal layer growth step and the Cu deposition step are alternately repeated 60 times to obtain an alternately laminated structure having a thickness of 120 nm.

FIG. 13C 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 layers 16a and Cu layers 16b are alternately laminated. The thickness of the Ga-doped MgZnO single crystal layer 16a is about 2.0 nm, and the thickness of the Cu layer 16b is 1 atomic layer or less, for example, about 1/20 atomic layer (Cu coverage on the surface of the Ga-doped MgZnO single crystal layer 16a is 5 %). Alternating structure 16A exhibits n-type conductivity, and donor concentration _Nd is, for example, 1.0 × 10 ²⁰ cm ⁻³ .

Next, the first type two-step annealing is performed on the alternate stacked structure 16A. First, p-type is formed by first annealing in an atmospheric pressure oxygen atmosphere. For example, by performing annealing at 570 ° C. for 10 minutes in an oxygen atmosphere at a flow rate of 1 L / min, Cu and Ga are diffused to form an alternate stacked structure 16A exhibiting n-type conductivity. Type MgZnO single crystal layer. Acceptor concentration _{N a} of the first annealing after completion p-type MgZnO single crystal layer is, for example, 3.0 × ¹⁰ 17 ^{cm -3.}

  Further, the second annealing is performed at 350 ° C. for 45 minutes and at 400 ° C. for 15 minutes in an atmosphere in which water vapor is included in oxygen at a flow rate of 1 L / min to supplement O vacancies, and Cu is formed on the active layer 15. A p-type MgZnO layer 16 codoped with Ga and Ga was formed. The Mg composition of the Cu, 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, 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 manner, a ZnO-based semiconductor light emitting device is manufactured by the method according to the second example.

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

Cu ZnO based semiconductor light emitting device according to the second example, Ga codoped p-type MgZnO layer 16, Cu and Ga are co-doped, p-type ZnO based with a high acceptor concentration _{N a} of example 1.0 × ¹⁰ 18 ^{cm -3} It is a semiconductor single crystal layer. For example, Cu concentration [Cu] is 3.0 × 10 ²⁰ cm ⁻³ , Ga concentration [Ga] is 1.59 × 10 ²⁰ cm ⁻³ ([Cu] / [Ga] is 1.89), both layers It is almost constant in the thickness direction.

  According to the manufacturing method according to the second example, a ZnO-based semiconductor light emitting device including Cu and Ga co-doped p-type MgZnO layer 16 in which Cu and Ga are uniformly doped throughout the thickness direction of the layer and has a high acceptor concentration is manufactured. be able to.

  FIG. 14 is a schematic cross-sectional view of a ZnO-based semiconductor light-emitting device manufactured by the manufacturing method according to the third example. In the first and second examples, crystals were grown on a conductive substrate to form a layer. In the third example, crystals grow 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 the case of the active layer 15 in the second example. Instead of the single ZnO layer, a quantum well structure may be adopted.

  A Cu, Ga co-doped p-type MgZnO layer 27 is formed on the active layer 26. Similarly to the second example, a Cu, Ga co-doped MgZnO layer 27 is formed, and the first type two-step annealing is performed to obtain a p-type. Other points are the same as in the second example.

  Since the c-plane sapphire substrate 21 of the third example 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, 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. Further, 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 example.

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

  In the example described above, the p-type ZnO-based semiconductor layer is formed of a ZnO-based semiconductor layer co-doped with Ga and Cu, and the first type two-step annealing is performed. As is apparent from the experimental results, a second type of two-step annealing is performed in which a second type of second annealing in which oxygen radicals are irradiated in a reduced pressure atmosphere is performed instead of the second annealing in a normal pressure atmosphere containing water vapor. You can also. Also, Ag can be used as a p-type impurity instead of Cu. By these combinations, 1) p-type impurity: Cu, first type two-step annealing, 2) p-type impurity: Ag, first type two-step annealing, 3) p-type impurity: Cu, second step, second type There are provided four methods for producing p-type ZnO-based layers: annealing, 4) p-type impurities: Ag, and second-stage two-stage annealing.

  In the case of using Ag, an AgO layer may be attached. It is preferable to adjust the temperature of the first annealing according to the element of the p-type impurity. Although Ga is used as the n-type impurity, one or more elements selected from the group consisting of B, Al, Ga, and In can be used. Various other changes, substitutions, combinations, etc. may be possible.

For example, in the experiments and examples, O radicals were used as the oxygen source of the MBE apparatus, but other gases having strong oxidizing power, such as ozone, H ₂ O, and polar oxidizers such as alcohol, can be used.

  In addition to Ga, B, Al, and In, which are Group IIIB elements as well as 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.

Furthermore, the inventors of the present application not only have a structure in which Ga-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers and Cu layers are alternately stacked, but also Cu (Group IB elements). ) And Ga (IIIB group element) are formed, and various n-type ZnO-based semiconductor single crystal structures are formed and subjected to first annealing, whereby Cu (IB group element) and Ga (IIIB group element) are codoped. A plurality of proposals have been made regarding a method of forming a p-type ZnO-based semiconductor layer and a method of manufacturing a ZnO-based semiconductor element using the p-type ZnO-based semiconductor layer. For even p-type ZnO based semiconductor layer according to these proposals, by performing the second annealing, it is possible to increase the acceptor concentration N _a.

15A to 15D show examples of an n-type ZnO-based semiconductor single crystal structure capable of forming a p-type ZnO-based semiconductor single crystal layer having _a high acceptor concentration Na by performing the first annealing and the second annealing. It is a schematic sectional drawing. FIG. 15A shows an alternate stacked structure 61A in which Cu-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers 61a and Ga layers 61b are alternately stacked (for example, Japanese Patent Application No. 2013-2013). No. 036824).

For example, (i) Zn, (ii) O, (iii) supply an IB group element that is Mg, (iv) Cu, and / or Ag as needed, and the alternate stacked structure 61A is doped with the IB group element. Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, and Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer, The step of supplying one or more group IIIB elements selected from the group consisting of Ga, Al, and In can be alternately repeated.

FIG. 15B shows an n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer 62a, a Cu layer 62b, and an n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single. An alternating stacked structure 62A in which crystal layers 62a and Ga layers 62c are alternately stacked in this order is shown (for example, see Japanese Patent Application No. 2013-085380). The alternate stacked structure 62A includes, for example, a step of forming a _first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer and a first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) forming a group IB element layer containing a group IB element of Cu or / and Ag on the single crystal layer; and forming a second Mg _x Zn _1-x O ( 0 ≦ x ≦ 0.6) a step of forming a single crystal layer, and B, Ga, Al, and In on the second Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer The step of forming a group IIIB element layer containing one or more group IIIB elements selected from the group consisting of can be formed repeatedly.

FIG. 15C shows an alternate stacked structure 63A in which n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers 63a and Cu and Ga layers 63b are alternately stacked (for example, Japanese Patent Application No. 2013-2013). No. 085381). The alternate stacked structure 63A includes, for example, a step of forming a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer and a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal. A step of supplying a group IB element of Cu or / and Ag and one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In on the layer is alternately repeated. Is possible.

15D shows a Cu-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer 64a and a Ga-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single unit. An alternate laminated structure 64A in which crystal layers 64b are alternately laminated is shown (for example, see Japanese Patent Application No. 2013-138550). The alternate stacked structure 64A includes a step of forming a _first Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer doped with a group IB element such as Cu or / and Ag, 1 Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer doped with one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In 2 Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers can be formed alternately and repeatedly.

By performing the first-type two-stage annealing or the second-type two-stage annealing for these structures as well, Cu (IB element) and Ga (IIIB element) co-doped p-type having _a high acceptor concentration Na. A Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer can be formed. It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like can be made.

  The p-type ZnO-based semiconductor layer manufactured by the manufacturing method according to the example 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.

1, 11, 51 ZnO substrate, 2, 12, 52 ZnO buffer layer,
3, 13, 53 n-type ZnO layer 4 undoped ZnO active layer,
5 Cu, Ga co-doped p-type ZnO layer, 5A Alternating structure 5a ZnO: Ga layer, 5b Cu layer,
6n n-side electrode, 6pp p-side electrode,
7 Bonding electrode, 14 n-type MgZnO layer,
15 active layer 15b MgZnO barrier layer,
15w ZnO well layer, 16Cu, Ga co-doped p-type MgZnO layer,
16A alternating laminated structure 16a Ga-doped MgZnO single crystal layer,
16b Cu layer, 17n n-side electrode,
17 p 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, 28nn side electrode,
28p p-side electrode, 54 alternating laminated structure,
54a ZnO: Ga layer, 54b Cu layer,
61A-64A alternating laminated structure, 71 vacuum chamber,
72-76 source gun, 77 stages,
78 substrate, 79 film thickness meter,
80 RHEED gun, 81 screen.

Claims (12)

(A) Forming an n-type ZnO-based semiconductor single crystal structure containing a group IB element that is Cu or / and Ag and one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In Process,
(B) The n-type ZnO-based semiconductor single crystal structure is subjected to a first annealing in an atmospheric pressure first oxidant atmosphere to form a p-type ZnO-based semiconductor layer in which the IB group element and the IIIB group element are co-doped. And a process of
(C) Second annealing is performed on the p-type ZnO-based semiconductor layer in a second oxidizing agent atmosphere having higher oxidizing power than the normal-pressure first oxidizing agent atmosphere, and the acceptor concentration of the p-type ZnO-based semiconductor layer is increased. And a method for manufacturing a p-type ZnO-based semiconductor layer.   The method for manufacturing a p-type ZnO-based semiconductor layer according to claim 1, wherein the second annealing is performed at a temperature lower than that of the first annealing.   The method for producing a p-type ZnO-based semiconductor layer according to claim 1, wherein the normal-pressure first oxidant atmosphere is an oxygen atmosphere.   The method for producing a p-type ZnO-based semiconductor layer according to claim 1, wherein the second oxidant atmosphere is a normal pressure atmosphere containing water vapor.   The method for producing a p-type ZnO-based semiconductor layer according to claim 1, wherein the second oxidant atmosphere is a reduced pressure atmosphere containing oxygen radicals. The method for producing a p-type ZnO-based semiconductor layer according to any one of claims 1 to 3, wherein the pressure in the second oxidant atmosphere is 10 ^-1 Pa or less. The step (a)
(A1) (i) Zn, (ii) O, (iii) Supply one or more group IIIB elements selected from the group consisting of Mg, (iv) B, Ga, Al, and In as necessary. Forming a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer doped with the IIIB group element;
(A2) supplying a group IB element of Cu or / and Ag on the Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer;
(A3) The method for producing a p-type ZnO-based semiconductor layer according to any one of claims 1 to 6, comprising a step of alternately repeating the step (a1) and the step (a2) to form a laminated structure. . 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 an n-type ZnO-based semiconductor single crystal structure containing a group IB element that is Cu or / and Ag and one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In Process,
(B) The n-type ZnO-based semiconductor single crystal structure is subjected to a first annealing in an atmospheric pressure first oxidant atmosphere to form a p-type ZnO-based semiconductor layer in which the IB group element and the IIIB group element are co-doped. And a process of
(C) Second annealing is performed on the p-type ZnO-based semiconductor layer in a second oxidizing agent atmosphere having higher oxidizing power than the normal-pressure first oxidizing agent atmosphere, and the acceptor concentration of the p-type ZnO-based semiconductor layer is increased. And a method of manufacturing a ZnO-based semiconductor element.   The method for manufacturing a ZnO-based semiconductor element according to claim 8, wherein the second annealing is performed at a temperature lower than that of the first annealing.   The method for manufacturing a ZnO-based semiconductor element according to claim 8 or 9, wherein the atmospheric pressure first oxidant atmosphere is an oxygen atmosphere.   The method for manufacturing a ZnO-based semiconductor element according to any one of claims 8 to 10, wherein the second oxidant atmosphere is a normal pressure atmosphere containing water vapor.   The method for manufacturing a ZnO-based semiconductor element according to claim 8, wherein the second oxidant atmosphere is a reduced pressure atmosphere containing oxygen radicals.