JP2016033935A - P-TYPE ZnO SEMICONDUCTOR LAYER MANUFACTURING METHOD AND ZnO SEMICONDUCTOR ELEMENT MANUFACTURING METHOD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide manufacturing methods of a high-quality p-type ZnO semiconductor layer and a high-quality ZnO semiconductor element.SOLUTION: A p-type ZnO semiconductor layer manufacturing method comprises the steps of: forming an Ag-containing n-type ZnO semiconductor single crystal structure (S102a); annealing the n-type ZnO semiconductor single crystal structure while irradiating Zn to form an Ag-doped p-type ZnO semiconductor layer (S102b); forming an n-type ZnO semiconductor layer on a substrate (S101); and forming a p-type ZnO semiconductor layer above the n-type ZnO semiconductor layer by the above-mentioned method (S102).SELECTED DRAWING: Figure 5

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.

  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, since the ZnO-based semiconductor has a self-compensation effect due to strong ionicity, it is difficult to control the p-type conductivity by a crystal growth method using a thermal equilibrium impurity doping method such as a normal thermal diffusion method. 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

In the previous application (Japanese Patent Application No. 2014-012015), the inventors of the present application have, for example, an n-type ZnO-based semiconductor structure (alternate stacked structure) in which Ga-doped ZnO single crystal layers and AgO layers are alternately stacked in the thickness direction. ) Was annealed to propose a method for producing a p-type ZnO-based semiconductor single crystal layer co-doped with Ag and Ga. In this specification, a silver oxide that can be expressed as AgO _x such as AgO (silver oxide (II)), Ag ₂ O (silver oxide (I)), or the like is referred to as “AgO”.

  With reference to FIGS. 9A to 9C, a method for manufacturing a p-type ZnO-based semiconductor single crystal layer according to the previous application will be described.

  FIG. 9A shows a schematic cross-sectional view of the sample before annealing. The sample before annealing is produced by, for example, an MBE apparatus described later.

After performing thermal cleaning at 900 ° C. for 30 minutes on an n-type conductive Zn-faced ZnO (0001) substrate (hereinafter referred to as a ZnO substrate in this specification) 51, the temperature of the substrate 51 is lowered to 250 ° C. At that temperature (growth temperature 250 ° C.), 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 300 W, O ₂ flow rate. The ZnO buffer layer 52 having a thickness of 30 nm is grown on the ZnO substrate 51 at 2.0 sccm (J 2 _O = 8.1 × 10 ¹⁴ atoms / cm ² s). The growth time is 5 minutes. In order to improve the crystallinity and surface flatness of the ZnO buffer layer 52, annealing is performed at 950 ° C. for 30 minutes.

On the ZnO buffer layer 52, a growth temperature is 950 ° C., Zn flux F _Zn is 0.15 nm / s, O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate 2.0 sccm, and an undoped ZnO layer 53 having a thickness of 100 nm. Grow. The growth time is 15 minutes. The undoped ZnO layer 53 is an n-type ZnO layer. On the undoped ZnO layer 53, an alternate stacked structure 54 having a thickness of 150 nm is formed. The formation temperature of the alternately laminated structure 54 is 250 ° C.

  FIG. 9B 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 AgO layers 54b are alternately laminated.

The Ga-doped ZnO single crystal layer 54a has a Zn flux F _Zn of 0.15 nm / s, an O radical beam irradiation condition of RF power of 300 W, an O ₂ flow rate of 2.0 sccm, a Ga cell temperature T _Ga of 550 ° C. (Ga flux F _Ga is grown as less than the lower limit of detection). The growth time of the Ga-doped ZnO single crystal layer 54a per layer is 10 seconds. The VI / II flux ratio is 0.81.

The AgO layer 54b is grown under the O radical beam irradiation conditions of RF power 300W, O ₂ flow rate 2.0 sccm, Ag cell temperature T _Ag of 820 ° C. The growth time of the AgO layer 54b per layer is 50 seconds.

  60 layers of Ga-doped ZnO single crystal layers 54a and AgO layers 54b are alternately grown.

  Next, the sample before annealing is annealed. Annealing is performed in a heat treatment furnace.

  FIG. 9C is a graph showing the annealing temperature. For example, annealing is performed at 450 ° C. for 10 minutes in an oxygen atmosphere with a flow rate of 1 L / min.

FIG. 10A is a graph showing a 1 / C ² -V characteristic and an impurity concentration depth profile of the alternately laminated structure 54 of the sample before annealing. The measurement is performed by an electrochemical CV measurement method (ECV method) using an electrolytic solution as a Schottky electrode. The horizontal axis of the graph showing the 1 / C ² -V 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 of the impurity concentration represents the position in the depth (thickness) direction of the sample in the unit “nm”, and the vertical axis represents the impurity concentration in the unit “cm ⁻³ ”. The horizontal axis uses a linear scale, and the vertical axis uses a logarithmic scale.

Referring to the graph showing the 1 / C ² -V characteristic, 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. Has been. Note that the slope corresponds to the impurity concentration (resistance value).

Referring to the graph showing the depth profile of the impurity concentration, it can be seen that the impurity concentration (donor concentration) N _d of the alternately laminated structure 54 is about 1.0 × 10 ²¹ cm ⁻³ .

FIG. 10B is a graph showing the 1 / C ² -V characteristic and the depth profile of the impurity concentration at the position where the alternately laminated structure 54 is formed after annealing. Except for the point where the horizontal axis of the graph showing the depth profile of the impurity concentration is expressed in voltage (unit “V”), the meanings of both axes of the graph are the same as those of the corresponding graph of FIG. 10A.

Referring to the graph showing the 1 / C ² -V characteristic, a downward-sloping curve (a relationship in which 1 / C ² decreases as the voltage increases) is obtained, and the n-type alternating stacked structure 54 has p-type conductivity. It is shown that it has reached.

Referring to the graph indicating the depth profile of the impurity concentration, the impurity concentration (acceptor concentration) of alternate stacked structure 54 formed positions p-type _{N a} is found to be about 3.0 × ¹⁰ 17 ^{cm -3.}

  The alternate laminated structure 54 composed of the Ga-doped ZnO single crystal layer 54a and the AgO layer 54b is made p-type by annealing. By performing the annealing, it is considered that Ag diffuses into the Ga-doped ZnO single crystal layer 54a and becomes p-type.

  One effect of the proposal related to the previous application is that, for example, the decrease in the absolute concentration [Ag] of Ag near the surface where the p-type alternate laminate structure 54 is formed (desorption of Ag from the surface of the alternate laminate structure 54 during annealing). It is to be suppressed. However, as a result of diligent research by the present inventors, it has been found that there is room for further improvement in this regard.

FIG. 11 is a graph showing the Ag concentration [Ag] of the sample according to the previous application. 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 Ag concentration [Ag] in the unit “cm ⁻³ ”. The horizontal axis uses a linear scale, and the vertical axis uses a logarithmic scale. The thin line (indicated as “as-grown”) indicates [Ag] of the sample before annealing, and the thick line (indicated as “O annealing”) indicates [Ag] of the sample after annealing.

  In the sample before annealing, the Ag concentration [Ag] is uniform, whereas in the sample after annealing, the Ag concentration [Ag] at the position where the p-type alternate laminated structure 54 is formed continuously decreases toward the surface. ing. It is considered that Ag having a high vapor pressure is a result of separation (evaporation) from the sample surface through the Zn vacancies.

  Due to the separation of Ag, the impurity concentration in the formed p-type layer becomes non-uniform, and it may be difficult to form a high-quality p-type ZnO-based semiconductor single crystal layer. Further, it may be difficult to control the Ag concentration [Ag] (doping concentration) to a desired value. Due to the difficulty in controlling the Ag concentration [Ag], there are cases where the annealing temperature range for p-type conversion must be limited. Further, when the Ag concentration [Ag] decreases and becomes lower than the Ga concentration [Ga], the vicinity of the surface can exhibit n-type conductivity. For example, if this occurs in the process of manufacturing a semiconductor device, it will be difficult to manufacture a good device.

  Note that the degree of decrease (concentration gradient) of the Ag concentration [Ag] in the p-type layer varies depending on the crystallinity, annealing temperature, annealing time, and the like of the alternately laminated structure 54.

  An n-type ZnO-based semiconductor structure (alternate stacked structure) in which ZnO single crystal layers and AgO layers not subjected to Ga doping are alternately stacked in the thickness direction is also made p-type by annealing (Ag doped (Ga undoped)) A p-type ZnO-based semiconductor single crystal layer is formed). However, this also causes problems such as non-uniform Ag concentration [Ag].

  The inventors of the present application continued intensive research and found a method for producing a p-type ZnO-based semiconductor layer with high quality.

  An object of the present invention is to provide a method for producing a high-quality p-type ZnO-based semiconductor layer.

  Moreover, it is providing the manufacturing method of a high quality ZnO type semiconductor element.

  According to one aspect of the present invention, (a) a step of preparing an n-type ZnO-based semiconductor single crystal structure containing Ag, and (b) annealing the n-type ZnO-based semiconductor single crystal structure while irradiating Zn, And a step of forming a p-type ZnO-based semiconductor layer doped with Ag.

  According to another aspect of the present invention, the step of forming an n-type ZnO-based semiconductor layer above the substrate and the step of forming a p-type ZnO-based semiconductor layer above the n-type ZnO-based semiconductor layer are provided. And forming the p-type ZnO-based semiconductor layer includes (a) a step of preparing an n-type ZnO-based semiconductor single crystal structure containing Ag, and (b) the n-type ZnO-based semiconductor while being irradiated with Zn. And a step of annealing a single crystal structure to form a p-type ZnO based semiconductor layer doped with Ag.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a high quality p-type ZnO type semiconductor layer can be provided.

  In addition, a method for manufacturing a high-quality ZnO-based semiconductor element can be provided.

FIG. 1 is a schematic cross-sectional view showing an MBE apparatus. FIG. 2 is a graph showing the annealing temperature. FIG. 3 is a graph showing a 1 / C ² -V characteristic and a depth profile of the impurity concentration at the position where the alternately laminated structure 54 of the sample after annealing is formed. FIG. 4 is a graph showing the Ag concentration [Ag] and Ga concentration [Ga] of the sample after annealing. 5A to 5C are flowcharts showing an outline of a method for manufacturing a ZnO-based semiconductor light emitting device according to an embodiment. FIG. 6A is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device manufactured by the manufacturing method according to the first embodiment, and FIG. 6B is a schematic cross-sectional view of an alternate stacked structure 5A. FIG. 7A is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device manufactured by the manufacturing method according to the second embodiment, and FIG. 7B is a schematic cross-sectional view showing another example of the active layer 15. FIG. 7C is a schematic cross-sectional view of the alternately laminated structure 16A. FIG. 8 is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device manufactured by the manufacturing method according to the third embodiment. 9A to 9C are schematic diagrams for explaining a method for manufacturing a p-type ZnO-based semiconductor single crystal layer according to the previous application. FIG. 10A is a graph showing a 1 / C ² -V characteristic and a depth profile of the impurity concentration of the alternately laminated structure 54 of the sample before annealing, and FIG. 10B shows 1 / C ^{2 of the} formation position of the alternately laminated structure 54 after annealing. It is a graph which shows the -V characteristic and the depth profile of impurity concentration. FIG. 11 is a graph showing the Ag concentration [Ag] of the sample according to the previous application.

  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 herein, the molecular beam epitaxy (MBE) method 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, an Ag source gun 75, and a Ga source gun 76 are provided.

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

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

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

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

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

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

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

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

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

An adhesion coefficient indicating the ease with which Zn adheres to the crystal is represented by k _Zn , an adhesion coefficient indicating the ease with which Mg is deposited is represented by k _Mg , and an adhesion coefficient indicating the ease with which O is deposited is represented by k _O. Zn adhesion coefficient k _Zn and flux strength J _Zn product k _Zn J _Zn , Mg adhesion coefficient k _Mg and flux strength J _Mg product k _Mg J _Mg , 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 _Zn J _Zn and _k Mg to the sum of _{J Mg} is the ratio of _{k O J O k O J O} / a _{(k Zn J Zn + k Mg} J Mg), defined as VI / II flux ratio. When the VI / II flux ratio is smaller than 1, the group II rich condition (simply Zn rich condition when Mg is not included), when the VI / II flux ratio is equal to 1, the stoichiometric condition, and the VI / II flux ratio is The case where it is larger than 1 is called VI group rich condition (or O rich condition).

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

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

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

Subsequently, an experiment according to the present application will be described. Also in this experiment, a pre-anneal sample having the same layer structure as the sample shown in FIGS. 9A and 9B was prepared. 9A and 9B shows that when the AgO layer 54b is formed, the Ag cell temperature T _Ag is 840 ° C. (Ag flux F _Ag is 0.004 nm / s), and the growth of the AgO layer 54b per one layer is performed. The difference is that the time is 40 seconds. For this reason, the thickness of the alternately laminated structure 54 is 130 nm.

Next, the sample before annealing was annealed. The annealing was performed in-situ annealing in the MBE apparatus (chamber) shown in FIG. 1 following the preparation of the sample before annealing. The MBE apparatus has an environment close to a vacuum, for example, an environment where the pressure is less than 10 ⁻² Pa.

FIG. 2 shows the annealing temperature. For example, after the alternate laminated structure 54 is formed at 250 ° C., the substrate temperature is raised to 950 ° C. Then, annealing is performed while directly irradiating the sample (alternate laminated structure 54) with a Zn beam at 950 ° C. for 30 minutes. Zn flux F _Zn is, for example, 0.15 nm / s.

FIG. 3 is a graph showing a 1 / C ² -V characteristic and a depth profile of the impurity concentration at the position where the alternately laminated structure 54 of the sample after annealing is formed. The meanings of both axes of the graph are equal to those of the corresponding graph of FIG. 10A.

Referring to the graph showing the 1 / C ² -V characteristic, a downward-sloping curve (a relationship in which 1 / C ² decreases as the voltage increases) is obtained, and the n-type alternating stacked structure 54 has p-type conductivity. It is shown that it has reached.

Referring to the graph indicating the depth profile of the impurity concentration, the impurity concentration (acceptor concentration) of alternate stacked structure 54 formed positions p-type _{N a} is found to be about 6.0 × ¹⁰ 17 ^{cm -3.}

  Similar to the previous application, the alternately laminated structure 54 of the sample of this application is also made p-type by annealing. By performing the annealing, it is considered that Ag diffuses into the Ga-doped ZnO single crystal layer 54a and becomes p-type.

FIG. 4 is a graph showing the Ag concentration [Ag] and Ga concentration [Ga] of the sample after annealing. 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 absolute concentration [Ag] of Ag and the absolute concentration [Ga] of Ga in the unit “atoms / cm ³ ”. .

  It can be seen that the Ag concentration [Ag] and the Ga concentration [Ga] at the formation position of the alternately laminated structure 54 of the sample after annealing of the present application are substantially constant in the thickness direction of the layer. As described above, the separation (evaporation) of Ag is considered to be via Zn vacancies. By performing annealing while irradiating Zn, it is considered that the formation of Zn vacancies is suppressed and the separation of Ag from the surface of the alternately laminated structure 54 is suppressed, so that uniform Ag doping is realized.

  According to the method of the present application, a high-quality p-type ZnO-based semiconductor single crystal layer having a uniform impurity concentration (Ag concentration) in the layer can be formed. Further, the Ag concentration [Ag] (doping concentration) can be controlled to a desired value. For this reason, the annealing temperature for p-type conversion can be selected from a wide range.

  Subsequently, an example in which a ZnO-based semiconductor light-emitting element is manufactured using an Ag, Ga co-doped ZnO-based single crystal layer as a p-type semiconductor layer will be described.

  5A to 5C are flowcharts showing an outline of a method for manufacturing a ZnO-based semiconductor light emitting device according to an embodiment. In addition, although an Example demonstrates a semiconductor light-emitting device, this invention is applicable not only to a light-emitting device but a semiconductor device widely.

  As shown in FIG. 5A, a method for manufacturing a ZnO-based semiconductor light emitting device according to an embodiment includes a step of forming an n-type ZnO-based semiconductor layer above a substrate (step S101) and an n-type ZnO-based semiconductor formed in step S101. A step (step S102) of forming a p-type ZnO-based semiconductor layer above the layer is included.

  As shown in FIG. 5B, the p-type ZnO-based semiconductor layer forming step in step S102 includes two steps, step S102a and step S102b.

  In the p-type ZnO-based semiconductor layer forming step (step S102), first, an n-type ZnO-based semiconductor single crystal structure containing Ag is prepared (step S102a). Then, the n-type ZnO-based semiconductor single crystal structure prepared in step S102a is annealed while irradiating Zn to form a p-type ZnO-based semiconductor single crystal layer doped with Ag (step S102b).

  FIG. 5C shows a specific example of the p-type ZnO-based semiconductor layer forming step (step S102).

As an example of the step of preparing an n-type ZnO-based semiconductor single crystal structure containing Ag (step S102a), an n-type ZnO-based semiconductor single crystal structure containing Ag and Ga can be formed. The formation is a step of forming an n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer doped with Ga by supplying Zn, O, and if necessary, Mg and Ga. (step S102a _1), formed at step S102a _1, Ga-doped n-type _{Mg x Zn 1-x O (} 0 ≦ x ≦ 0.6) forming a AgO layer on the single crystal layer (step S102a ₂₎ , and it can be carried out by a process (step S102a ₃₎ to form a laminated structure by repeating steps S102a ₁ and step S102a ₂ alternately. These steps are performed in, for example, an MBE apparatus.

And a laminate structure formed in step S102a _3, annealed while irradiating with Zn, p-type Ag and Ga are co-doped _{Mg x Zn 1-x O (} 0 ≦ x ≦ 0.6) single crystal layer forming (step S102b _1). Annealing, for example, performed in an MBE apparatus embodying the steps S102a ₁ ~ Step _{S102a 3 (in-situ annealing)} .

By performing annealing while irradiating Zn, for example, in-situ annealing, the generation of Zn vacancies is suppressed and the separation of Ag is suppressed. As a result, Ag is uniformly doped in the thickness direction of the layer. A quality Ag, Ga co-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer is obtained. It is also possible to control the Ag concentration [Ag] (doping concentration) to a desired value.

  Therefore, a high-quality ZnO-based semiconductor element can be manufactured by the manufacturing method shown in FIGS. 5A to 5C. An annealing temperature for p-type conversion can be selected from a wide range.

  Further, when in-situ annealing is performed, an external electric furnace is unnecessary, and the manufacturing time of the p-type ZnO-based semiconductor single crystal layer and the ZnO-based semiconductor element can be shortened.

In the flowchart of FIG. 5C, a single crystal layer doped with Ga _x Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) is used, but n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) preparing an n-type semiconductor stacked structure in which single crystal layers and AgO layers are alternately stacked (for example, a stacked structure in which n-type ZnO single crystal layers and AgO layers are alternately stacked), As one embodiment, annealing may be performed while irradiating Zn to form an Ag-doped (Ga-undoped) p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer. it can.

Further, in the flowchart of FIG. 5C, in step S102a _2, but forms a AgO layer may be a layer containing Ag of the Ag layer or the like.

Further, in step S102a ₁ ~ Step S102a ₃ in FIG. 5C, although an n-type ZnO-based semiconductor single crystal structure containing Ag by alternating growth, Zn, O, Ag, and Mg and Ga as required It is also possible to form the substrate by a simultaneous irradiation method in which irradiation is simultaneously performed on the substrate.

  By annealing various n-type ZnO-based semiconductor single crystal structures containing Ag while irradiating Zn, the formation of Zn vacancies is suppressed and the separation of Ag is suppressed. As a result, Ag is in the thickness direction of the layer. It is possible to form a high-quality Ag-doped p-type ZnO-based semiconductor single crystal layer that is uniformly doped.

In the following first to third embodiments, although a p-type ZnO based semiconductor layer forming step shown in FIG. 5C, for example, in step S102a _1, the Ga undoped _{Mg x Zn 1-x O (} 0 ≦ x ≦ 0.6) A single crystal layer may be formed. Further, for example, it may be formed Ag layer in Step S102a _2. Furthermore, an n-type ZnO-based semiconductor single crystal structure containing Ag can also be formed using a simultaneous irradiation method.

  With reference to FIGS. 6A and 6B, a first embodiment for manufacturing a ZnO-based semiconductor light emitting device having a homo structure will be described. FIG. 6A is a schematic cross-sectional view of a ZnO based semiconductor light emitting device manufactured by the manufacturing method according to the first embodiment.

On a ZnO substrate 1, a ZnO buffer layer 2 having a thickness of 30 nm 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. Grew. In order to improve the crystallinity and surface flatness of the ZnO buffer layer 2, annealing was performed at 900 ° C. for 10 minutes.

On the ZnO buffer layer 2, Zn, O and Ga were simultaneously supplied 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, 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), Ga cell temperature 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, An undoped ZnO active layer 4 having a thickness of 15 nm was grown at an O ₂ flow rate of 2.0 sccm.

  Subsequently, an Ag and Ga co-doped p-type ZnO layer 5 was formed on the undoped ZnO active layer 4.

  First, the substrate temperature was set to 250 ° C., and an alternately laminated structure 5 A having a thickness of 130 nm was formed on the undoped ZnO active layer 4.

  FIG. 6B is a schematic cross-sectional view of the alternately laminated structure 5A. The alternate laminated structure 5A has a laminated structure in which Ga-doped ZnO single crystal layers 5a and AgO layers 5b are alternately laminated.

The Ga-doped ZnO single crystal layer 5a is grown at a Zn flux F _Zn of 0.15 nm / s, an O radical beam irradiation condition of RF power 300 W, an O ₂ flow rate of 2.0 sccm, and a Ga cell temperature T _Ga of 550 ° C. The growth time of the Ga-doped ZnO single crystal layer 5a per layer is 10 seconds.

The AgO layer 5b is grown under the O radical beam irradiation conditions of an RF power of 300 W, an O ₂ flow rate of 2.0 sccm, and an Ag cell temperature T _Ag of 840 ° C. The growth time of the AgO layer 5b per layer is 40 seconds.

  60 layers of Ga-doped ZnO single crystal layers 5a and AgO layers 5b were alternately formed.

Next, annealing treatment was performed on the alternately laminated structure 5A. Annealing is performed in the MBE apparatus, following the formation of the alternately laminated structure 5A (in-situ annealing). For example, annealing is performed at 950 ° C. for 30 minutes while the Zn flux F _{Zn is set} to 0.15 nm / s and a Zn beam is directly applied to the alternately laminated structure 5A.

  By annealing, Ag in the AgO layer 5b diffuses into the Ga-doped ZnO single crystal layer 5a, and an Ag, Ga co-doped p-type ZnO layer 5 is formed. The Ag and Ga co-doped p-type ZnO layer 5 is a high-quality p-type ZnO-based semiconductor single crystal layer having a uniform Ag concentration in the layer. The Ag concentration is controlled to a desired value.

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

  According to the manufacturing method according to the first embodiment, a high-quality ZnO-based semiconductor element including the Ag and Ga co-doped p-type ZnO layer 5 having a uniform Ag concentration can be manufactured. Moreover, the annealing temperature for p-type conversion can be selected from a wide range.

In the first embodiment, ZnO is doped with Ag and Ga. However, ZnO and Mg _x Zn _1-x O (0 <x ≦ 0.6) are capable of almost the same crystal growth. Therefore, formation of an Ag, Ga co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) layer can be similarly performed.

Second and Third Embodiments for Producing Double Heterostructure ZnO-Based Semiconductor Light-Emitting Device Comprising Ag and Ga Co-doped p-type Mg _x Zn _1-x O (0 <x ≦ 0.6) Single Crystal Layer An example will be described.

  FIG. 7A is a schematic cross-sectional view of a ZnO based semiconductor light emitting device manufactured by the manufacturing method according to the second embodiment.

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

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

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

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

  As shown in FIG. 7B, 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 was lowered to 250 ° C., and an alternating laminated structure 16 A having a thickness of 130 nm was formed on the active layer 15.

  FIG. 7C 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 AgO layers 16b are alternately laminated.

The Ga-doped MgZnO single crystal layer 16a has Zn flux F _Zn of 0.15 nm / s, Mg flux F _Mg of 0.025 nm / s, O radical beam irradiation conditions of RF power 300 W, O ₂ flow rate 2.0 sccm, Ga The cell temperature _TGa is grown at 550 ° C. The growth time of the Ga-doped MgZnO single crystal layer 16a per layer is 10 seconds.

The AgO layer 16b is grown with O radical beam irradiation conditions of RF power 300W, O ₂ flow rate 2.0 sccm, and Ag cell temperature T _Ag of 840 ° C. The growth time of the AgO layer 16b per layer is 40 seconds.

  The Ga-doped MgZnO single crystal layers 16a and the AgO layers 16b were alternately formed by 60 layers.

  Next, an annealing process was performed on the alternate laminated structure 16A. Annealing is performed in the MBE apparatus, following the formation of the alternately laminated structure 16A (in-situ annealing).

For example, annealing is performed while the Zn flux F _{Zn is set} to 0.15 nm / s at 950 ° C. for 30 minutes, and the alternating stacked structure 16A is directly irradiated with the Zn beam.

  By annealing, Ag in the AgO layer 16 b is diffused into the Ga-doped MgZnO single crystal layer 16 a, and an Ag and Ga co-doped p-type MgZnO layer 16 is formed on the active layer 15. The Ag and Ga co-doped p-type MgZnO layer 16 is a high-quality p-type ZnO-based semiconductor single crystal layer having a uniform Ag concentration in the layer. The Ag concentration is controlled to a desired value. The Mg composition of the Ag, 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 Ag and Ga co-doped p-type MgZnO layer 16. Further, the bonding electrode 18 is formed on the p-side electrode 17p. For example, the n-side electrode 17n is formed by laminating a 500-nm thick Au layer on a 10-nm-thick Ti layer, and the p-side electrode 17p has a thickness of 300 μm □ and a 1-nm-thick Ni layer. It can be formed by laminating a 10 nm Au layer. The bonding electrode 18 is formed of an Au layer having a size of 100 μm □ and a thickness of 500 nm. In this way, a ZnO-based semiconductor light emitting device is manufactured by the method according to the second embodiment.

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

  According to the manufacturing method of the second embodiment, a high-quality ZnO-based semiconductor element including the Ag and Ga co-doped p-type MgZnO layer 16 having a uniform Ag concentration can be manufactured. Moreover, the annealing temperature for p-type conversion can be selected from a wide range.

  FIG. 8 is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device manufactured by the manufacturing method according to the third embodiment. In the first and second embodiments, crystals are grown on a conductive substrate and a layer is formed. In the third embodiment, crystals are grown on an insulating substrate.

Mg and O are simultaneously supplied on the c-plane sapphire substrate 21 which is an insulating substrate, and an MgO buffer layer 22 having a thickness of, for example, 10 nm is grown. As an example, the growth temperature 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 2.0 sccm. The MgO buffer layer 22 functions as a polarity control layer for controlling the ZnO-based semiconductor thereon to grow with the Zn surface as the surface.

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

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

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

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

  An Ag 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 Ag 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 Ag 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. Further, the p-side electrode 28p is formed on the Ag, Ga co-doped p-type MgZnO layer 27, and the bonding electrode 29 is formed on the p-side electrode 28p.

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

  The Ag and Ga co-doped p-type MgZnO layer 27 of the ZnO-based semiconductor light emitting device according to the third embodiment is a high-quality p-type ZnO-based semiconductor single crystal layer having a uniform Ag concentration in the layer. The Ag concentration is controlled to a desired value.

  According to the manufacturing method of the third embodiment, a high-quality ZnO-based semiconductor element including the Ag and Ga co-doped p-type MgZnO layer 27 having a uniform Ag concentration can be manufactured. Moreover, the annealing temperature for p-type conversion can be selected from a wide range.

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

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

  In addition, although the n-type ZnO-based semiconductor single crystal structure containing Ag is annealed while being irradiated with the Zn beam, the annealing may be performed while being irradiated with the Ag beam together with the Zn beam.

Furthermore, annealing may be performed in a state where active oxygen is present in the MBE apparatus while O ₂ gas is turned into plasma (generating active oxygen) in an electrodeless discharge tube.

In the experiments and examples, a Ga-doped n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layer and an AgO layer are alternately stacked (n-type ZnO containing Ag and Ga). A single crystal layer of Ag and Ga co-doped Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) showing p-type conductivity was formed (p-type). By annealing an n-type ZnO-based semiconductor single crystal structure containing Ag (Group IB element) and Ga (Group IIIB element), Ag is bonded to O, which is a Group VIB element, in a monovalent (Ag ⁺ ) state. As a result, monovalent Ag ⁺ functioning as an acceptor is more likely to be generated than divalent Ag ^2+. As a result, it is considered that the n-type ZnO-based semiconductor single crystal structure easily becomes p-type. Therefore, 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 p-type ZnO-based semiconductor layer manufactured by the manufacturing method according to the embodiment can be used for, for example, a light emitting diode (LED) or a laser diode (LD) that emits light of a short wavelength (ultraviolet to blue wavelength region). It can be used for application products (various indicators, LED displays, CV / DVD light sources, etc.). Furthermore, it can be used for white LEDs and their application products (lighting fixtures, various indicators, displays, backlights for various displays, etc.). Moreover, it can utilize for an ultraviolet sensor.

DESCRIPTION OF SYMBOLS 1 ZnO substrate 2 ZnO buffer layer 3 n-type ZnO layer 4 Undoped ZnO active layer 5 Ag, Ga co-doped p-type ZnO layer 5A Alternating structure 5a Ga-doped ZnO single crystal layer 5b AgO 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 16Ag, Ga co-doped p-type MgZnO layer 16A Alternating structure 16a Ga-doped MgZnO single crystal Layer 16b AgO 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 Ag, 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 layer structure 54a Ga-doped ZnO single crystal layer 54b AgO layer 71 Vacuum chamber 72 Zn source gun 73 O source gun 74 Mg source gun 75 Ag source gun 76 Ga source Gun 77 Stage 78 Substrate 79 Film thickness meter 80 RHEED gun 81 Screen

Claims (8)

(A) preparing an n-type ZnO-based semiconductor single crystal structure containing Ag;
(B) annealing the n-type ZnO-based semiconductor single crystal structure while irradiating Zn, and forming a Ag-doped p-type ZnO-based semiconductor layer. In the step (a), an n-type ZnO-based semiconductor single crystal structure containing Ag is formed in an MBE apparatus,
The method for producing a p-type ZnO-based semiconductor layer according to claim 1, wherein in the step (b), the n-type ZnO-based semiconductor single crystal structure is annealed in the MBE apparatus. In the step (a), the n-type ZnO-based semiconductor single crystal structure containing Ag and one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In is prepared.
The method for producing a p-type ZnO-based semiconductor layer according to claim 1 or 2, wherein in the step (b), a p-type ZnO-based semiconductor layer co-doped with Ag and the Group IIIB element is formed. In the step (a), the n _- type ZnO-based semiconductor single crystal structure in which n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers and silver oxide layers are alternately stacked is prepared. The method for producing a p-type ZnO-based semiconductor layer according to claim 1. 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) preparing an n-type ZnO-based semiconductor single crystal structure containing Ag;
(B) annealing the n-type ZnO-based semiconductor single crystal structure while irradiating Zn, and forming a Ag-doped p-type ZnO-based semiconductor layer. In the step (a), an n-type ZnO-based semiconductor single crystal structure containing Ag is formed in an MBE apparatus,
The method for manufacturing a ZnO-based semiconductor element according to claim 5, wherein in the step (b), the n-type ZnO-based semiconductor single crystal structure is annealed in the MBE apparatus. In the step (a), the n-type ZnO-based semiconductor single crystal structure containing Ag and one or more group IIIB elements selected from the group consisting of B, Ga, Al, and In is prepared.
The method for manufacturing a ZnO-based semiconductor element according to claim 5 or 6, wherein a p-type ZnO-based semiconductor layer in which Ag and the group IIIB element are co-doped is formed in the step (b). In the step (a), the n _- type ZnO-based semiconductor single crystal structure in which n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal layers and silver oxide layers are alternately stacked is prepared. The manufacturing method of the ZnO-type semiconductor element of any one of Claims 5-7 to do.