JP6470061B2 - Manufacturing method of p-type ZnO-based semiconductor structure and manufacturing method of ZnO-based semiconductor element - Google Patents

Description

  The present invention relates to a method for manufacturing a p-type ZnO-based semiconductor structure 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 a practical performance using a group VA element such as N, P, As, or Sb, a group IA element such as Li, Na, or K, or a group IB element such as Cu, Ag, or Au. Research on ZnO-based semiconductors 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) crystal layers and Cu or Ag-containing layers are alternately stacked is grown, and the alternately stacked structure is annealed so that Cu or Ag, Ga, etc. A method for producing a co-doped p-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer is proposed.

JP 2013-211153 A

  An object of an embodiment of the present invention is to provide a method for manufacturing a p-type ZnO-based semiconductor structure having a high acceptor concentration.

According to one aspect of an embodiment of the present invention,
(A) preparing an n-type ZnO-based semiconductor structure containing Ag;
(B) annealing the n-type ZnO-based semiconductor structure while intermittently irradiating Ag to form a p-type ZnO-based semiconductor structure doped with Ag. Provided.

From another perspective,
Forming an n-type ZnO-based semiconductor structure above the substrate;
Forming a p-type ZnO-based semiconductor structure above the n-type ZnO-based semiconductor structure,
The step of forming the p-type ZnO-based semiconductor structure includes:
(A) preparing an n-type ZnO-based semiconductor structure containing Ag;
And (b) annealing the n-type ZnO-based semiconductor structure while intermittently irradiating Ag, and forming a Ag-doped p-type ZnO-based semiconductor structure. The

  A p-type ZnO-based semiconductor layer having a high acceptor concentration can be manufactured.

  A ZnO-based semiconductor element having high characteristics can be provided.

, ,and 1A is a schematic cross-sectional view showing an MBE apparatus, FIG. 1B is a schematic cross-sectional view of a sample, FIG. 1C is a schematic cross-sectional view showing an alternately laminated structure in the sample, and FIG. 1D is a sample preparation with temperature change FIG. 1E is a graph showing a process, and FIG. 1E is a graph showing a 1 / C ² -V characteristic and an impurity concentration depth profile of an alternately laminated structure of a sample before annealing. ,and FIG. 2A is a graph showing a process for obtaining a first sample by performing a first annealing using a furnace following an MBE alternating growth step for the sample, and FIG. 2B is a diagram showing an MBE alternating growth step for the sample in the MBE apparatus. FIG. 2C is a graph showing a process for obtaining a second sample by performing a second anneal under Ag irradiation, and FIG. 2C shows an MBE alternating growth process for the sample followed by a third anneal under Ag intermittent irradiation in an MBE apparatus. FIG. 2D is a timing chart of Ag intermittent irradiation, illustrating a process of performing a third sample. 3A is a graph showing a 1 / C ² -V characteristic and a depth profile of the impurity concentration of Sample 1, and FIG. 3B is a graph showing a depth direction distribution of the Ag concentration of Sample 1 by SIMS. 4A is a graph showing a 1 / C ² -V characteristic and a depth profile of the impurity concentration of Sample 2, and FIG. 4B is a graph showing a depth direction distribution of the Ag concentration of Sample 2 by SIMS. FIG. 5A is a graph showing a depth profile of the 1 / C ² -V characteristic and impurity concentration of Sample 3, and FIG. 5B is a graph showing the distribution of the Ag concentration of Sample 3 in the depth direction by SIMS. FIG. 6A is a schematic cross-sectional view of a ZnO-based semiconductor light-emitting element, and FIG. 6B is a schematic cross-sectional view of an alternately stacked structure. FIG. 7 is a schematic cross-sectional view showing a modification of the ZnO-based semiconductor light emitting device.

FIG. 1A is a schematic cross-sectional view showing a molecular beam epitaxy (MBE) apparatus used for growing a ZnO-based semiconductor layer or the like. A ZnO-based semiconductor refers to a semiconductor containing at least Zn and O. A mixed crystal semiconductor Mg _x Zn _1-x O containing Zn and Mg as a group 2 element is also a ZnO-based semiconductor.

The MBE apparatus includes 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 in a vacuum chamber 71. 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 has an electrodeless discharge tube that uses a radio frequency of, for example, 13.56 MHz, converts O ₂ gas (6N) into plasma in the electrodeless discharge tube, and emits an O radical (O ^* ) beam.

A stage 77 having a substrate heater holds the substrate 78. The source guns 72 to 76 and the stage 77 are each provided with a shutter. By opening and closing each shutter, the substrate 78 can be switched between a state in which each beam is irradiated and a state in which the beam is not irradiated. However, even if the shutter of the O source gun is closed, a part of the oxygen radical O ^* is supplied onto the substrate. 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.

The VI / II flux ratio in the 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 less, 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 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).

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

  The configuration of the sample will be described with reference to FIG. 1B. Using the MBE apparatus shown in FIG. 1A, a ZnO buffer layer 52 and an undoped ZnO layer 53 are alternately formed by MBE on a Zn-faced ZnO (0001) substrate (hereinafter referred to as a ZnO substrate in this specification) 51 having n-type conductivity. A stack 54 is formed.

FIG. 1C is a partially enlarged cross-sectional view showing the configuration of the alternate stack 54. Ga-doped ZnO layers (ZnO: Ga layers) 54a and AgO layers 54b are alternately stacked to form, for example, 60 pairs of alternately stacked layers 54. “AgO” represents a silver oxide that can be expressed as AgO _x , such as AgO (silver oxide (II)) and Ag ₂ O (silver oxide (I)). The sample manufacturing process will be described below.

As shown in FIG. 1D, after the ZnO (0001) substrate 51 is subjected to thermal cleaning at 900 ° C. for 30 minutes, 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 with a growth rate of 2.0 sccm (J 2 _O = 8.1 × 10 ¹⁴ atoms / cm ² s) for 5 minutes.

After the growth of the ZnO buffer layer 52, the temperature is raised to 950 ° C. and annealing is performed for 30 minutes in order to improve the crystallinity and surface flatness of the growth layer. After annealing, remains 950 ° C., on the ZnO buffer layer 52, with Zn flux _{F Zn} to 0.15 nm / s, O radical beam irradiation conditions of RF power 300 W, the _{O 2} flow rate 2.0 sccm, 15 minutes growth, An undoped ZnO layer 53 having a thickness of 100 nm is grown. The undoped ZnO layer 53 is n-type.

After the growth of the undoped ZnO layer 53, the substrate temperature is lowered to 250 ° C. On the undoped ZnO layer 53, an alternately laminated structure 54 having a thickness of about 120 nm is formed. The Ga-doped ZnO 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 less than the lower limit of detection) and grows for 10 seconds per layer. The VI / II flux ratio is 0.82.

The AgO layer 54b is grown for 50 seconds per layer with an O radical beam irradiation condition of RF power of 300 W, an O ₂ flow rate of 2.0 sccm, an Ag cell temperature T _Ag of 840 ° C. (Ag flux F _Ag is 0.005 nm / s). To do. The thickness of the pair of Ga-doped ZnO crystal layer 54a / AgO layer 54b is about 2 nm. A thickness of about 120 nm is obtained by alternately stacking 60 pairs.

FIG. 1E 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 was 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 are linear scales. 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 is a linear scale, and the vertical axis is 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, which indicates that the alternate stacked structure 54 has n-type conductivity. ing. 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 . Three types of annealing were performed on the sample after crystal growth. The structure before annealing is the same for the three types of samples (for sample 3, the number of alternating layers was reduced).

  FIG. 2A is a graph schematically showing the first annealing. A sample after crystal growth was taken out from the MBE apparatus by alternating growth at 250 ° C., carried into a furnace, and annealed at 450 ° C. for 10 minutes in an oxygen atmosphere at normal pressure (1 atm). Let the obtained sample be 1st sample S1.

FIG. 3A is a graph showing a 1 / C ² -V characteristic and a depth profile of the impurity concentration at the position where the alternate stacked structure 54 is formed in the first sample S1. The meanings of both axes of the graph are equal to those of the corresponding graph of FIG. 1E.

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) _{N a} of alternate stacked structure 54 formed positions p-type is found to be about 3.0 × ¹⁰ 17 ^{cm -3.} The alternate laminated structure 54 composed of the Ga-doped ZnO layer 54a and the AgO layer 54b was made p-type by annealing. By performing the annealing, it is considered that Ag is diffused into the Ga-doped ZnO crystal layer 54a to be p-type.

FIG. 3B is a graph showing the Ag concentration in the sample S1. 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 in the unit cm ⁻³ . The horizontal axis is a linear scale, and the vertical axis is a logarithmic scale. As a reference, the Ag concentration distribution of the sample before annealing is also shown. In the sample S1, the Ag concentration decreases fairly rapidly toward the surface. Since the Ag concentration decreases toward the surface, it may not be easy to obtain the desired characteristics. When annealing is performed in an oxygen atmosphere, Ag may be detached from the sample surface. A phenomenon in which the Ag concentration rapidly decreases toward the surface is not preferable.

The second annealing is performed in the MBE apparatus. The sample after crystal growth is subsequently annealed in the MBE apparatus (without being taken out of the MBE apparatus). This can be said to be in-situ annealing. The pressure in the MBE apparatus is, for example, 10 ⁻⁸ Pa to 10 ⁻² Pa. In a reduced-pressure atmosphere, Ag is considered to evaporate more intensely than in a normal-pressure oxygen atmosphere from the sample surface. Therefore, annealing is performed while irradiating the sample surface with an Ag beam. In order to generate an Ag beam, the pressure in the MBE apparatus is kept below 10 ⁻² Pa.

FIG. 2B is a graph schematically showing the second annealing. After the alternate laminated structure 54 is formed at 250 ° C., the Ag cell temperature T _Ag is maintained at 840 ° C. (Ag flux F _Ag is 0.005 nm / s), the Ag cell shutter is opened, and the substrate shutter is also opened. The substrate temperature is raised to 900 ° C. while directly irradiating the sample (alternate laminated structure 54) with the Ag beam, and annealing is performed at 900 ° C. for 30 minutes. Although the oxygen cell shutter is closed, the O radical beam irradiation conditions are maintained at an RF power of 300 W and an O ₂ flow rate of 2.0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s). Oxygen radicals wrap around the sample surface. The obtained sample is designated as S2.

FIG. 4A 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 is formed in the sample S2. The meanings of both axes of the graph are equal to those of the corresponding graph of FIG. 3A. Referring to the graph showing the 1 / C ² -V characteristic, a downward-sloping curve (relation that 1 / C ² decreases as the voltage increases) is obtained, and the n-type alternating stacked structure 54 has p-type conductivity. It has shown that it came to prepare. 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 seen to be about 5.0 × ¹⁰ 17 ^{cm -3.} The sample S1 and the sample S2 are formed from the pre-anneal structure having the same configuration. The acceptor concentration is increased to 5 × 10 ¹⁷ cm ⁻³ in sample S2 compared to 3 × 10 ¹⁷ cm ⁻³ in sample S1. However, considering the measurement error, the first annealing and the second annealing are considered to be substantially equivalent.

  Similar to the sample S1, the alternately laminated structure 54 of the sample S2 was made p-type by annealing. By performing the annealing, it is considered that Ag diffuses into the Ga-doped ZnO crystal layer 54a and becomes p-type.

  FIG. 4B is a graph showing the Ag concentration of sample S2. For comparison, the Ag concentration of sample S1 is also shown. The meaning of both axes of the graph is equal to that of FIG. 3B.

  It can be seen that the degree (gradient) in which the Ag concentration decreases toward the surface (gradient) in the sample S2 is significantly lower than that in the sample S1. By performing the annealing while irradiating Ag, the Ag concentration on the surface is increased, the separation of Ag from the crystal is suppressed, and a more uniform Ag doping is realized.

  According to the second annealing, a high-quality p-type ZnO-based semiconductor crystal layer with a more uniform impurity concentration (Ag concentration) in the layer can be formed, and the Ag concentration can be controlled to a desired value. It will be easy. Furthermore, by employing in-situ annealing, a separate annealing device is not required, and the time for moving the sample is also unnecessary. The apparatus can be simplified and the time required for the process can be shortened.

FIG. 2C is a graph schematically showing the third annealing. Similar to the first and second annealing, an alternate stacked structure is formed by alternate growth at 250 ° C. Here, in the third annealing sample, the number of pairs of the alternately stacked layers was 30. This is to obtain a thin structure, and the reduction in the number of pairs is not important as the technical idea of the present application. Similar to the second annealing, the sample after completing the 30 pairs of stacked growth is not taken out from the MBE apparatus, and is subsequently annealed in the MBE apparatus. It is an in-situ annealing similar to the second annealing. As in the second annealing, the inside of the MBE apparatus was maintained in an environment close to vacuum, for example, the pressure was maintained at 10 ⁻⁸ Pa to 10 ⁻² Pa, and oxygen radicals were continuously generated.

Specifically, after the alternate laminated structure 54 is formed at 250 ° C., the Ag cell temperature T _Ag is 840 ° C. (Ag flux F _Ag is 0.005 nm / s), and the Ag cell, oxygen radical shutter, and substrate shutter are mounted. The substrate temperature is raised to 800 ° C. while the sample (alternate laminated structure 54) is irradiated directly and intermittently with the Ag beam being intermittently opened. Then, annealing is performed while directly and intermittently irradiating the sample (alternate laminated structure 54) with an Ag beam at 800 ° C. for 30 minutes. Although the oxygen cell shutter is closed, the O radical beam irradiation conditions are maintained at an RF power of 300 W and an O ₂ flow rate of 2.0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s). The annealing temperature is preferably set to a temperature within the range of 750 ° C. to 950 ° C., and a situation where oxygen radicals are present is preferable.

  FIG. 2D is a graph showing the contents of intermittent Ag irradiation. The substrate shutter, the Ag shutter, and the oxygen radical shutter are synchronized to repeat the open state and the closed state every 10 seconds. Compared to the second annealing, the point where Ag is supplied and the state where Ag is not supplied are different. During the period when Ag is not supplied, the movement of Zn atoms is promoted, and the movement of Ag atoms may be allowed accordingly. The obtained sample is designated as S3. The irradiation period and non-irradiation period of Ag intermittent irradiation are not limited to 10 seconds and 10 seconds. For example, both could be selected from the range of 5 to 40 seconds.

FIG. 5A 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 is formed in the sample S3. The meaning of both axes of the graph is equal to those of the corresponding graph of FIG. 4A. 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 seen to have increased to about 5.0 × 10 ²⁰ cm ^-3 . The surprising result was obtained that the acceptor concentration increased by 3 orders of magnitude compared to the first and second samples.

  FIG. 5B is a graph showing the Ag concentration of sample S3. For comparison, Ag concentrations of the first and second samples S1 and S2 are also shown. The meaning of both axes of the graph is equal to that of FIG. 3B.

  It can be seen that the gradient in the thickness direction of the Ag concentration at the position where the alternate stacked structure 54 of the third sample S3 is formed substantially matches the gradient in the thickness direction of the alternate stacked structure of the sample S2 after the second annealing. When annealing is performed while repeating the presence / absence of Ag irradiation, detachment of Ag from the surface of the alternately laminated structure 54 is suppressed to the same extent as in the case of continuous Ag irradiation, and it is considered that uniform Ag doping is realized from the sample S1.

  By adopting in-situ annealing as in the case of the second annealing, another annealing apparatus is unnecessary and time for moving the sample is also unnecessary. The apparatus can be simplified, and the effect of shortening the time required for the process can be obtained. According to the third annealing, it becomes possible to obtain an extremely high acceptor concentration as compared with the second annealing. By intermittently irradiating the ZnO-based crystal structure with Ag, it is considered that the Ag irradiation suppresses the separation of Ag from the surface, promotes the movement of Zn during non-Ag irradiation, and promotes the movement of Ag.

  Hereinafter, a ZnO-based semiconductor light emitting device using an Ag, Ga co-doped ZnO-based crystal layer as a p-type semiconductor layer will be described.

With reference to FIGS. 6A and 6B, a homostructure ZnO-based semiconductor light-emitting device will be described. FIG. 6A is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device. 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. Grow. 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 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 ℃. 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 is grown at an O ₂ flow rate of 2.0 sccm.

  An Ag and Ga co-doped p-type ZnO layer 5 is formed on the undoped ZnO active layer 4. The substrate temperature is set to 250 ° C., and an alternate stacked structure 5 A having a thickness of 120 nm is 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 crystal layers 5a and AgO layers 5b are alternately laminated.

The Ga-doped ZnO crystal layer 5a is grown at a Zn flux F _Zn of 0.14 nm / s, an O radical beam irradiation condition of RF power of 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 crystal layer 5a per layer is, for example, 10 seconds.

The AgO layer 5b is grown under the O radical beam irradiation conditions of RF power of 300 W, O ₂ flow rate of 2.0 sccm, and Ag cell temperature T _Ag of 840 ° C. The growth time of the AgO layer 5b per layer is, for example, 50 seconds.

Annealing treatment is applied to the alternate laminated structure 5A. Annealing is performed in the MBE apparatus following the formation of the alternately laminated structure 5A. For example, the Ag cell temperature T _{Ag is set} to 840 ° C., the Ag cell shutter is opened, and the substrate temperature is raised to 900 ° C. while intermittently irradiating the alternating laminated structure 5A with the Ag beam. Then, annealing is performed while directly irradiating the alternating laminated structure 5A with an Ag beam at 900 ° C. for 30 minutes. By annealing, Ag in the AgO layer 5b diffuses into the Ga-doped ZnO 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 crystal layer having a high acceptor concentration and a gentle Ag concentration gradient in the layer.

  An n-side electrode 6n is formed on the back surface of the ZnO substrate 1, a p-side electrode 6p is formed on the Ag and 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 way, a ZnO-based semiconductor light emitting device is manufactured.

As shown in FIG. 7, a quantum well structure in which MgZnO barrier layers 15 b and ZnO well layers 15 w are alternately stacked may be employed instead of the single-layer active layer 4. Instead of the n-type ZnO layer, an n-type Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer can also be used. In addition, various known configurations can be employed.

  As mentioned above, although this invention was demonstrated along experiment and an Example, this invention is not restrict | limited to these. An n-type ZnO-based semiconductor crystal containing Ag and Group 3B impurities is annealed while intermittently irradiating Ag, thereby increasing the Ag concentration as an active p-type impurity and suppressing the separation of Ag from the surface. can do.

By annealing an n-type ZnO-based semiconductor crystal containing a Group 3B element such as Ag and Ga, Ag is easily bonded to O, which is a Group 6B element, in a monovalent (Ag ⁺ ) state, and functions as an acceptor 1 It is considered that valence Ag ⁺ is more likely to be generated than divalent Ag ²⁺ , and the n-type ZnO-based semiconductor layer is easily converted to p-type.

  Not only Ga but also any of B, Al, and In, which are the same 3B group elements as Ga, may be used. The 3B group element used may be one or more 3B group 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 can be used for, for example, light emitting diodes (LEDs) and laser diodes (LDs) that emit light of a short wavelength (ultraviolet to blue wavelength region), and these applied products (various indicators, LED displays) , CV / DVD light source, etc.). Furthermore, it can be used for white LEDs and their application products (lighting fixtures, various indicators, displays, backlights for various displays, etc.). Moreover, it can utilize for an ultraviolet sensor.

1, 11 ZnO substrate, 2, 12 ZnO buffer layer, 3 n-type ZnO layer, 4 undoped ZnO active layer, 5 Ag, Ga co-doped p-type ZnO layer, 5A alternating stacked structure, 5a Ga-doped ZnO crystal layer, 5b AgO Layer, 6n n-side electrode, 6pp side electrode, 7 bonding electrode,
51 ZnO substrate, 52 ZnO buffer layer, 53 undoped ZnO layer, 54 alternating laminated structure, 54a Ga-doped ZnO 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 (10)

(A) preparing an n-type ZnO-based semiconductor structure containing Ag;
(B) annealing the n-type ZnO-based semiconductor structure while intermittently irradiating Ag to form a p-type ZnO-based semiconductor structure doped with Ag.   2. The n-type ZnO semiconductor structure is formed by alternately laminating ZnO-based semiconductor layers doped with at least one 3B group element selected from the group consisting of B, Ga, Al, and In and AgO layers. A method for producing a p-type ZnO-based semiconductor structure described in 1.   The method for manufacturing a p-type ZnO-based semiconductor structure according to claim 2, wherein the alternate stack is formed above a C-plane ZnO substrate. 4. The method according to claim 1, wherein the step (b) anneals the n-type ZnO-based semiconductor structure while intermittently irradiating the generated Ag beam under an exhaust atmosphere of less than 10 ⁻² Pa. 2. A method for producing a p-type ZnO-based semiconductor structure according to item 1.   The method of manufacturing a p-type ZnO-based semiconductor structure according to claim 4, wherein the annealing in the step (b) is performed in a temperature range of 750 ° C to 950 ° C.   The method for producing a p-type ZnO-based semiconductor structure according to claim 1, wherein the step (b) is performed in a state where oxygen radicals are present. In the step (a), an n-type ZnO-based semiconductor structure containing Ag is formed by MBE in an MBE apparatus,
The method for manufacturing a p-type ZnO-based semiconductor structure according to claim 1, wherein in the step (b), the n-type ZnO-based semiconductor structure is annealed in the MBE apparatus. Forming an n-type ZnO-based semiconductor structure above the substrate;
Forming a p-type ZnO-based semiconductor structure above the n-type ZnO-based semiconductor structure,
The step of forming the p-type ZnO-based semiconductor structure includes:
(A) preparing an n-type ZnO-based semiconductor structure containing Ag;
(B) annealing the n-type ZnO-based semiconductor structure while intermittently irradiating Ag, and forming a Ag-doped p-type ZnO-based semiconductor structure.   In the step (a), an alternate stack of ZnO-based semiconductor layers doped with at least one 3B group element selected from the group consisting of B, Ga, Al, and In and an AgO layer is formed, and the n-type ZnO The method for manufacturing a ZnO-based semiconductor element according to claim 8, wherein the ZnO-based semiconductor device has a semiconductor-based semiconductor structure. In the step (a), an n-type ZnO-based semiconductor structure containing Ag is formed by MBE in an MBE apparatus,
The method for manufacturing a ZnO-based semiconductor element according to claim 8 or 9, wherein in the step (b), the n-type ZnO-based semiconductor structure is annealed in the MBE apparatus.