JP6092586B2 - ZnO-based semiconductor layer and manufacturing method thereof, and manufacturing method of ZnO-based semiconductor light-emitting element - Google Patents

Description

  The present invention relates to a ZnO-based semiconductor layer and a method for manufacturing the same, and a method for manufacturing a ZnO-based semiconductor light-emitting element.

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

  A ZnO-based oxide semiconductor is difficult to control the p-type conductivity because of a self-compensation effect due to strong ionicity. Therefore, in order to obtain a p-type ZnO-based oxide semiconductor having practical performance, molecular beam epitaxy (MBE), laser molecular beam epitaxy, metal organic chemical vapor deposition (MOCVD), remote plasma MOCVD, sputtering, etc. Development of ZnO-based semiconductor light-emitting elements has been promoted by various methods.

  To date, as acceptor impurities, VA group elements such as N, P, As, and Sb, IA group elements such as Li, Na, and K, and IB group elements such as Cu, Ag, and Au have been studied. The current situation is that the carrier concentration is still low and sufficient quality including reproducibility and stability has not been obtained (see, for example, Patent Documents 1 to 3 and Non-patent Document 1 for techniques using Cu as a dopant). ).

JP 2004-221132 A JP 2009-256142 A JP 2009-21540 A SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 23, (2008), 095004.

  An object of the present invention is to provide a novel technique of doping a ZnO-based semiconductor with Cu.

  Another object of the present invention is to provide a novel technique for doping a ZnO-based semiconductor with a group IB element.

According to one aspect of the present invention, (a) Ri stoichiometric conditions or Group II rich conditions der, and, VI / II flux ratio is 0.5 or more conditions, a further 250 ° C. or higher 350 ° C. temperature below Zn, O, and, if necessary, Mg are added above the underlayer so that at least one of the Zn supply period and the Mg supply period is extended before and after the O supply period to include the O supply period. Supplying a step of forming a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film having a thickness of 10 nm or less ; and (b) the Mg _x Zn _1-x O (0 ≦ x ≦). 0.6) supplying only Cu on the single crystal film in an amount that provides a thickness of one atomic layer or less of Cu , and repeating the steps (a) and (b) alternately Te, to form a _{Mg x Zn 1-x O (} 0 ≦ x ≦ 0.6) layer Cu doped Method for producing a ZnO-based semiconductor layer is provided.

The step of forming a Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film and the step of supplying Cu are alternately repeated to obtain Cu-doped Mg _x Zn _1-x O (0 ≦ x ≦ By forming the 0.6) layer, the flatness of the Cu-doped Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer can be enhanced.

FIG. 1 is a schematic cross-sectional view showing an example of an MBE apparatus. FIG. 2 is a shutter sequence of Zn cells, O cells, and Cu cells in the growth of the Cu-doped ZnO layer in the first experiment. 3A and 3B are an RHEED image and an AFM image of the first sample according to the first experiment, respectively. FIG. 4 is a SIMS depth profile of the first sample according to the first experiment. 5A and 5B are an RHEED image and an AFM image of the second sample according to the first experiment, respectively. FIG. 6 is a shutter sequence of the Zn cell, O cell, and Cu cell in the Cu-doped ZnO layer growth in the second experiment. FIG. 7A is a SIMS depth profile of a sample according to the second experiment, and FIG. 7B is a graph showing a relationship between the Cu concentration of the sample according to the second experiment and the Cu cell temperature. FIG. 8 is an RHEED image of the sample according to the third experiment. FIG. 9 shows an RHEED image and an AFM image of the sample according to the fourth experiment. FIG. 10 is a graph showing the growth temperature dependence of the surface roughness of the sample according to the fourth experiment. FIG. 11 is a SIMS depth profile of the sample according to the fourth experiment. FIG. 12 is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device according to the first embodiment. 13A and 13B are RHEED images of ZnO-based semiconductor light emitting devices according to the comparative example and the first example, respectively. 14A and 14B are IV characteristics of ZnO-based semiconductor light emitting devices according to the comparative example and the first example, respectively. FIG. 15 is an EL spectrum of the ZnO based semiconductor light emitting device according to the first example. FIG. 16A is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device according to a second embodiment, and FIG. 16B is a schematic cross-sectional view showing a modified active layer structure. FIG. 17 is a shutter sequence of the Zn cell, Mg cell, O cell, and Cu cell in the Cu-doped MgZnO layer growth of the second embodiment. FIG. 18 is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device according to the third embodiment. FIG. 19A is a schematic cross-sectional view showing a sample used for XPS analysis, and FIG. 19B is a RHEED image of the Cu-doped ZnO layer 34 viewed from the [11-20] direction. 20A and 20B are graphs showing the XPS analysis results of the Cu2p3 / 2 orbit of the Cu-doped ZnO layer of the first sample of the first experiment and the Cu-doped ZnO layer 34 of the alternately grown sample, respectively. 21A is a graph showing the XPS spectrum of the Cu2p3 / 2 orbit of the Cu-doped ZnO layer 34 before and after the surface sputter cleaning, and FIG. 21B is the XPS of the Cu2p3 / 2 orbit of the Cu-doped ZnO layer 34 after the surface sputter cleaning. It is a graph which shows the waveform analysis result of a spectrum.

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

  FIG. 1 is a schematic cross-sectional view showing an example of an MBE apparatus. In the vacuum chamber 101, a Zn source gun 102, an O source gun 103, an Mg source gun 104, a Cu source gun 105, and a Ga source gun 106 are provided.

  The Zn source gun 102, Mg source gun 104, Cu source gun 105, and Ga source gun 106 contain solid sources of Zn (7N), Mg (6N), Cu (9N), and Ga (7N), respectively. A Zn beam, a Mg beam, a Cu beam, and a Ga beam are emitted by heating each cell including a Knudsen cell.

The O source gun 103 includes an electrodeless discharge tube using a radio frequency (for example, 13.56 MHz). The O source gun 103 converts O ₂ gas (6N) into plasma in an electrodeless discharge tube and emits an O radical beam. As the discharge tube material, alumina or high-purity quartz can be used.

  A stage 107 including a substrate heater is disposed in the vacuum chamber 101, and the stage 107 holds the substrate 108. Each of the source guns 102 to 106 includes a cell shutter, and a state where each beam is irradiated on the substrate 108 and a state where it is not irradiated are switched by opening and closing the cell shutter. A ZnO-based compound semiconductor layer having a desired composition can be grown on the substrate 108 by supplying a desired beam at a desired timing.

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. Here, by including Mg composition x = 0, ZnO to which Mg is not added is also included in the notation Mg _x Zn _1-x O.

  The n-type conductivity of the ZnO-based semiconductor can be obtained without doping impurities. In order to increase the n-type conductivity, for example, Ga or the like can be doped.

  The p-type conductivity of the ZnO-based semiconductor can be obtained by doping with a p-type impurity. In the following discussion, a technique using a group IB element such as Cu as the p-type impurity will be examined.

A film thickness meter 109 using a crystal resonator is provided in the vacuum chamber 101. From deposition rate measured by a film thickness meter 109, flux strength, such as Zn beam from a solid source (e.g. expressed as F _Zn) is obtained.

  A gun 110 for reflection high-energy electron diffraction (RHEED) and a screen 111 for projecting a RHEED image are attached to the vacuum chamber 101. From the RHEED image, the surface flatness and growth mode of the crystal layer formed on the substrate 108 can be evaluated.

  When the crystal grows two-dimensionally and the surface is epitaxially grown (single crystal growth), the RHEED image shows a streak pattern. When the crystal grows three-dimensionally and the surface is not flat (single crystal growth), RHEED The image shows a spot pattern. 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 expressed as _{J Zn,} the flux intensity of the Mg beam expressed as _{J Mg,} representing 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, and 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.

The adhesion coefficient indicating the ease of adhesion of Zn to the crystal is denoted by k _Zn , the adhesion coefficient indicating the ease of adhesion of Mg is denoted by k _Mg, and the adhesion coefficient indicating the ease of adhesion of O is denoted by k 2 _O. Zn adhesion coefficient k _Zn and flux strength J _Zn product k _Zn J _Zn , Mg adhesion coefficient k _Mg and flux strength J _Mg product k _Mg J _Mg , and O adhesion coefficient k _O and flux strength J product k _O J _O of _O, respectively, Zn atoms adhering per unit time per unit area of the substrate, corresponding to the Mg atom, and the number of O atoms.

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. A case where the VI / II flux ratio is smaller than 1 is referred to as a group II rich condition (or a Zn rich condition when Mg is not included), and a case where the VI / II flux ratio is equal to 1 is referred to as a stoichiometric condition. A case where the II flux ratio is larger than 1 is called a VI group rich condition (or an O rich condition).

In the crystal growth on the + c plane (Zn 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 It can be expressed as J _O / (J _Zn + J _Mg ).

Specifically, the VI / II flux ratio can be calculated by the following procedure, for example. The growth of ZnO will be described as an example. 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 unit of 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, O ₂ flow rate ₂ sccm / RF power 300 W), and the Zn flux dependence of the ZnO growth rate is experimentally determined. By fitting the result using an approximate expression of ZnO growth rate G _ZnO : G _ZnO = [(k _Zn J _Zn ) ^-1 + (k _O J _O ) ^-1 ] ^-1 , radical flux _{J O} is calculated. Thus from Zn flux _{J Zn} and O radical flux _{J O} obtained, it is possible to calculate the VI / II flux ratio.

Next, the first experiment will be described. First, a method for manufacturing a sample is described. The Zn surface ZnO (0001) substrate was subjected to thermal cleaning at 900 ° C. for 30 minutes, and then the substrate temperature was lowered to 300 ° C. Thereafter, at a growth temperature of 300 ° C., the Zn flux F _{Zn is set} to 0.12 nm / s (J _Zn = 7.9 × 10 ¹⁴ atoms / cm ² s), the O radical beam irradiation conditions are set to RF power 300 W, O ₂ flow rate 2 A ZnO buffer layer having a thickness of 30 nm was grown at 0.0 sccm (J 2 _O = 8.1 × 10 ¹⁴ atoms / cm ² s). Then, annealing was performed at 900 ° C. for 10 minutes in order to improve the crystallinity and surface flatness of the buffer layer.

On the ZnO buffer layer, the growth temperature is 900 ° C., the Zn flux F _Zn is 0.12 nm / s (J _Zn = 7.9 × 10 ¹⁴ atoms / cm ² s), and the O radical beam irradiation condition is RF power 300 W, An undoped ZnO layer having a thickness of 100 nm was grown at an O ₂ flow rate of 2.0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s).

  Zn, O, and Cu were supplied on the undoped ZnO layer to grow a 400 nm thick Cu-doped ZnO layer. A first sample in which the growth temperature of the Cu-doped ZnO layer was 700 ° C. and a second sample in which the growth temperature was 300 ° C. were produced.

  FIG. 2 is a shutter sequence of Zn cells, O cells, and Cu cells in the growth of the Cu-doped ZnO layer in the first experiment. In the first experiment, the shutter timings of the Zn cell, O cell, and Cu cell are simultaneously opened. That is, Zn, O, and Cu are supplied simultaneously to grow a Cu-doped ZnO layer.

Irradiation conditions of Zn, O, and Cu during the growth of the Cu-doped ZnO layer are common to the first sample and the second sample, and are as follows. Zn flux F _Zn is set to 0.12 nm / s (J _Zn = 7.9 × 10 ¹⁴ atoms / cm ² s), O radical beam irradiation conditions are RF power 300 W, O ₂ flow rate 2.0 sccm (J _O = 8. 1 × 10 ¹⁴ atoms / cm ² s), and the Cu cell temperature T _Cu was 950 ° C. (F _Cu = 0.0025 nm / s).

  Next, the analysis result of the first sample (growth temperature 700 ° C.) will be described.

  FIG. 3A is an RHEED image of the Cu-doped ZnO layer of the first sample viewed from the [11-20] direction. The RHEED image shows a spot + ring pattern, and three-dimensional growth occurs, and it can be seen that a polycrystalline film is obtained instead of a single crystal film.

  FIG. 3B is an atomic force microscope (AFM) image (observation range: 5 μm □) of the surface of the Cu-doped ZnO layer of the first sample. It can be seen from the AFM image that the film is not flat and has severe irregularities. The root mean square roughness (RMS) obtained from the AFM image is as large as 131.2 nm.

FIG. 4 is a depth profile of secondary ion mass spectrometry (SIMS) of the first sample. The thickness of the grown Cu-doped ZnO layer is 400 nm. However, the Cu concentration is about 10 ²¹ cm ⁻³ up to a depth of about 200 nm and is almost uniform, but about 10 ²¹ cm ^{−3 to} about 10 ¹⁸ cm ⁻³ from a depth of about 200 nm to a depth of about 400 nm. It has decreased to. Thus, it can be seen that Cu is not uniformly doped in the depth direction.

  Next, the analysis result of the second sample (growth temperature 300 ° C.) will be described.

  FIG. 5A is a RHEED image of the Cu-doped ZnO layer of the second sample viewed from the [11-20] direction. Similarly to the first sample at a growth temperature of 700 ° C., the second sample having a growth temperature of 300 ° C. shows a spot + ring pattern in the RHEED image, resulting in three-dimensional growth, and a single crystal film cannot be obtained and becomes a polycrystalline film. You can see that

  FIG. 5B is an AFM image (observation range: 5 μm □) of the surface of the Cu-doped ZnO layer of the second sample. The RMS of the second sample is also small compared to the first sample, but is as large as 39.9 nm, and the second sample is also a film with large irregularities.

  In the first experiment described above, the reaction between the active O radical and Cu is promoted by simultaneously supplying Zn, O, and Cu, and CuO is a different crystal than the Zn site is replaced by Cu. It is considered that the growth of ZnO occurred due to the formation as a phase, and polycrystallization occurred.

Considering the case where Cu is naturally oxidized, cuprous oxide (Cu ₂ O) is first formed as shown in the following chemical formulas (1) and (2), and further cupric oxide (CuO) as oxidation proceeds. ) Is formed.

On the other hand, as shown in the following chemical formula (3), at 1050 ° C. or higher, cupric oxide (CuO) is thermally decomposed and changed to cuprous oxide (Cu ₂ O).

Considering the case where a Cu-doped ZnO layer is grown by simultaneously irradiating Zn, O radicals and Cu, CuO (II) is likely to be formed due to the fact that Cu easily reacts with active O radicals. That is, it is considered that the formation of divalent Cu ²⁺ becomes dominant. In addition, since the growth temperature is lower than the decomposition temperature, divalent Cu ²⁺ is unlikely to become monovalent Cu ⁺ , and it is considered that Cu that does not act as an acceptor in ZnO becomes dominant.

From consideration of the results of the first experiment, if there is a method for forming a Cu-doped ZnO layer in which monovalent Cu ⁺ is more likely to be produced than divalent Cu ²⁺ and Cu is easy to replace the Zn site, two-dimensional growth or It is considered that p-type conductivity is easily obtained.

  Next, the second experiment will be described. First, a method for manufacturing a sample is described. First, under the same conditions as in the first experiment, formation of a ZnO buffer layer on a Zn-faced ZnO (0001) substrate, annealing of the buffer layer, and formation of an undoped ZnO layer on the buffer layer were performed. Thereafter, Zn and O and Cu were supplied at different timings on the undoped ZnO layer to grow a Cu-doped ZnO layer. The growth temperature of the Cu-doped ZnO layer was 300 ° C.

  FIG. 6 is a shutter sequence of the Zn cell, O cell, and Cu cell in the Cu-doped ZnO layer growth in the second experiment. In the second experiment, roughly speaking, a ZnO growth process in which a Zn cell shutter and an O cell shutter are opened and a Cu cell shutter is closed, and a Cu deposition process in which the Zn cell shutter and the O cell shutter are closed and a Cu cell shutter is opened. Are repeated alternately.

  By separately providing a ZnO growth process for growing a ZnO single crystal film and a Cu deposition process for depositing Cu on the ZnO single crystal film, the open period of the O cell shutter and the open period of the Cu cell shutter overlap. I try not to be. That is, the O radical and Cu are not supplied simultaneously.

  More specifically, the ZnO growth step extends the open period of the Zn cell shutter before and after the open period of the O cell shutter. That is, the open period of the Zn cell shutter includes the open period of the O cell shutter. In this way, by directly covering the surface of the ZnO single crystal film with Zn before and after the Cu deposition step (by suppressing the exposure of O), the direct reaction between the O radical and Cu can be achieved. Suppressed.

  In the setting of this experiment, the open period of each O cell shutter is 20 seconds, and the open period of the Zn cell shutter is extended by 1 second before and after the open period of the O cell shutter. The opening period per turn was 22 seconds. 20 seconds in which both the Zn cell shutter and the O cell shutter are open is the ZnO growth time per time. The opening period per time of the Cu cell shutter was 10 seconds.

A 400-nm-thick Cu-doped ZnO epitaxial film was obtained by carrying out growth by repeating 120 steps of a process in which the ZnO growth step and the Cu deposition step were one set. The Zn flux F _Zn in the ZnO growth process is 0.12 nm / s (J _Zn = 7.9 × 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 _O = 8.1 × 10 ¹⁴ atoms / cm ² s). The VI / II flux ratio is 1.0, which is a stoichiometric condition.

A plurality of samples were prepared by changing the Cu cell temperature T _Cu in the Cu adhesion step from 860 ° C. to 970 ° C.

  Next, the analysis result of the sample obtained in the second experiment will be described.

FIG. 7A is a SIMS depth profile of Cu concentration in the Cu-doped ZnO layer. The result of a sample having a Cu cell temperature T _{Cu of} 925 ° C. is shown. It can be seen that Cu is almost uniformly doped to a depth of about 400 nm of the grown Cu-doped ZnO layer.

FIG. 7B is a graph showing the relationship between the Cu concentration in the Cu-doped ZnO layer and the Cu cell temperature _TCu . The Cu concentration of each sample was determined by SIMS. The Cu concentration in the Cu-doped ZnO layer changed from the order of 10 ¹⁹ cm ^{−3 to} the order of 10 ²¹ cm ⁻³ , and was found to be increased by increasing the Cu cell temperature. 7A and 7B, a Zn-face ZnO substrate was used, but similar results were obtained with an O-face ZnO substrate.

  Next, the third experiment will be described. Similar to the second experiment, a Cu-doped ZnO layer was grown by alternately repeating the ZnO growth step and the Cu deposition step. In the third experiment, a plurality of samples were prepared by changing the VI / II flux ratio in the ZnO growth process.

Specifically, the irradiation condition of the O radical beam is constant at 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 the Zn flux F _Zn is set to 0 By changing in the range of 0.03 nm / s to 0.25 nm / s (J _Zn = 2.0 × 10 ¹⁴ atoms / cm ^{2 s to} 1.6 × 10 ¹⁵ atoms / cm ² s), the VI / II flux The ratio (O / Zn ratio) was changed in the range of 4.1 to 0.49.

The Cu cell temperature T _Cu in the Cu adhesion process was set to 925 ° C. (F _Cu = 0.0015 nm / s). In each sample, the ZnO growth time was changed in the range of 43 to 11 seconds so that the ZnO growth film thickness per time became equal to about 3.3 nm. More specifically, when the Zn flux F _Zn is 0.03 nm / s, 0.07 nm / s, 0.12 nm / s, 0.15 nm / s, 0.19 nm / s, and 0.25 nm / s, respectively. The ZnO growth time was 43 seconds, 28 seconds, 20 seconds, 18 seconds, 16 seconds, and 11 seconds. Other conditions are the same as in the second experiment.

FIG. 8 is a RHEED image of the Cu-doped ZnO layer of each sample obtained in the third experiment as seen from the [11-20] direction. The RHEED images are arranged so that the Zn flux F _Zn increases from the left to the right, that is, the V / II flux ratio decreases from the left to the right. The stoichiometry condition is when Zn flux F _Zn = 0.12 nm / s.

From Zn stoichiometry condition to Zn rich condition with Zn flux of F _Zn = 0.12 nm / s to 0.19 nm / s (J _Zn = 7.9 × 10 ^{14 to} 1.3 × 10 ¹⁵ atoms / cm ² s) Then, it can be seen that although the growth temperature is as low as 300 ° C., the RHEED image becomes a streak and a two-dimensionally grown single crystal film with high surface flatness is formed.

In addition, when Zn flux _FZn was further increased to 0.25 nm / s ( _JZn = 1.6 * 10 < ¹⁵ > atoms / cm < ² > s), the RHEED image became a ring pattern. This is thought to be due to growth inhibition caused by excess Zn.

  Conversely, it was found that when the Zn flux becomes less than the stoichiometry condition, that is, the O-rich condition, the RHEED image becomes a spot pattern and is three-dimensionally grown.

  From the third experiment, in order to obtain a Cu-doped ZnO single crystal film with high flatness and good crystallinity, the ZnO growth process is carried out under stoichiometric conditions to Zn-rich conditions (VI / II flux ratio is 1 or less). I found it desirable.

  Under the O-rich condition (VI / II flux ratio is greater than 1), it is considered that crystal growth has progressed on the O termination surface. Cu surface migration on O-terminated ZnO is reduced or Cu and O radicals react due to Zn deficiency in the ZnO growth step after the Cu deposition step, and the surface migration of Zn is sufficient due to O-terminated CuO and the like. It is thought that it became three-dimensional growth.

  On the other hand, from the stoichiometry condition to the Zn-rich condition, it is considered that crystal growth has progressed on the Zn termination surface. It is considered that the surface migration of Zn on Cu or the surface migration of Cu on Zn-terminated ZnO was promoted to enable two-dimensional growth despite a low temperature of about 300 ° C.

  Although two-dimensional growth is obtained even under stoichiometric conditions (VI / II flux ratio is 1), from the viewpoint of making growth on the Zn termination surface more reliable, Zn-rich conditions (VI / II flux ratio is 1). Smaller) is considered more desirable.

Note that, as described above, there was a tendency that a polycrystal was obtained when the Zn was too rich (Zn flux F _Zn = 0.25 nm / s, and a sample with a V / II flux ratio = 0.49 was polycrystalline. ) Considering this, it can be said that it is more desirable to set the V / II flux ratio to, for example, 0.5 or more.

  It should be noted that the ZnO single crystal film thickness to be grown per one ZnO growth step is desirably 10 nm or less. Since the growth temperature is very low and surface migration is unlikely to occur, if the growth film thickness per time becomes too thick, three-dimensional growth may occur and the crystallinity may deteriorate.

In addition, it is desirable that the Cu deposition thickness per time in the Cu deposition process is 1 atomic layer or less of Cu. For example, in a sample having a Cu cell temperature T _Cu of 925 ° C. (Cu concentration 1.5 × 10 ²⁰ cm ⁻³ ) in the second experiment, the Cu deposition thickness per time calculated from the film thickness and the Cu concentration is It is a 1/20 atomic layer (that is, the coverage of Cu on the ZnO surface is about 5%).

If the Cu adhesion thickness per one time is too thick, there is a possibility that the non-oxidized Cu becomes an n-type conductive film or the crystallinity deteriorates. The Cu concentration is preferably 1 × 10 ¹⁹ cm ^{−3 to} 5 × 10 ²⁰ cm ⁻³ . The Cu concentration can be controlled by ZnO growth time, Cu deposition time, etc. (by the ratio of ZnO growth time and Cu deposition time) in addition to controlling by the Cu cell temperature.

Next, the fourth experiment will be described. Similar to the second and third experiments, the Cu-doped ZnO layer was grown by alternately repeating the ZnO growth step and the Cu deposition step. In the fourth experiment, a plurality of samples were produced by changing the growth temperature in the range of 300 ° C to 900 ° C. The Cu cell temperature T _Cu was set to 925 ° C. (F _Cu = 0.0015 nm / s). Other conditions are the same as in the second experiment.

  FIG. 9 is an RHEED image and an AFM image (observation range: 5 μm □) of the Cu-doped ZnO layer of each sample obtained in the fourth experiment as seen from the [11-20] direction. The RHEED image and the AFM image are arranged so that the growth temperature Tg increases from the left to the right.

  At growth temperatures of 250 ° C. and 300 ° C., the RHEED image shows a streak pattern, at a growth temperature of 350 ° C., the RHEED image shows a streak + spot pattern, and single crystal growth occurs at a growth temperature of 250 ° C. to 350 ° C. I understand that.

  It can be seen that when the growth temperature is higher than 400 ° C., the RHEED image changes from a spot pattern to a ring pattern. For example, one reason is that the higher the growth temperature, the more the thermal oxidation of Cu is promoted and CuO is formed. That is, Cu is not replaced by the lattice position (Zn site) of ZnO, and CuO or other copper oxides are separated. This is probably because three-dimensional growth occurs due to the formation of the crystalline phase, and a single-crystal film cannot be obtained and becomes a polycrystalline film.

  Furthermore, when the growth temperature rises to 700 ° C. or higher, the RHEED image changes from a spot pattern to a streak + spot pattern. It is thought that the growth mode changes to two-dimensional growth due to a decrease in Cu concentration in the ZnO film due to a decrease in Cu adhesion coefficient due to an increase in growth temperature or a decrease in Cu incorporation efficiency into ZnO. It is done. However, it is considered that the adhered Cu is pushed out to the growth surface to form monoclinic CuO, and is observed as a projection in the AFM image.

  FIG. 10 is a graph showing the growth temperature dependence of the surface roughness (RMS) of the Cu-doped ZnO layer. It can be seen that a Cu-doped ZnO layer having a high flatness with an RMS of 1 nm or less at a growth temperature of 250 ° C. to 350 ° C. is obtained.

  FIG. 11 shows SIMS depth profiles of Cu concentration in Cu-doped ZnO layers grown at growth temperatures of 300 ° C., 500 ° C., 700 ° C., and 900 ° C.

  The Cu concentration of the sample with the growth temperature of 300 ° C. rises steeply at the interface, and is almost constant and highly uniform in the epilayer. It can be seen that as the growth temperature increases, the Cu concentration gradually increases from the interface (Cu concentration rises gradually), and the Cu concentration in the epi layer becomes non-uniform.

  Furthermore, at a growth temperature of 900 ° C., the surface Cu concentration is high, which is considered to be an influence of surface precipitates. Such growth temperature dependency is considered to be caused by a difference in the adhesion coefficient of Cu depending on the growth temperature or a thermal oxidation reaction of Cu.

  From the fourth experiment, it was found that the growth temperature is preferably 350 ° C. or lower. Although the lower limit of the preferred growth temperature is not clear, it is likely that good growth is possible up to about 200 ° C.

  As described above, as described in the second experiment to the fourth experiment, it is understood that a Cu-doped ZnO layer having high flatness and good crystallinity can be obtained by the growth method in which the ZnO growth process and the Cu adhesion process are alternately repeated. It was. Next, an example in which a ZnO-based semiconductor light-emitting element is formed using a Cu-doped ZnO layer obtained by such a growth method as a p-type semiconductor layer will be described.

  First, a first embodiment for forming a homostructure ZnO-based semiconductor light emitting device will be described.

FIG. 12 is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device according to the first embodiment. On the Zn surface 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. The ZnO buffer layer 2 having a thickness of 30 nm was grown at 300 W and an O ₂ flow rate of 2.0 sccm (J _{2 O} = 8.1 × 10 ¹⁴ atoms / cm ² s). Then, annealing was performed at 900 ° C. for 10 minutes in order to improve the crystallinity and surface flatness of the buffer layer.

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 set to 0.15 nm / s (J _Zn = 9.9 × 10 ¹⁴ atoms / cm ² s), O radical beam irradiation conditions are RF power 250 W, O ₂ flow rate 1.0 sccm (J _O = 4. 0 × 10 ¹⁴ atoms / cm ² s) and the Ga cell temperature was 460 ° C. The Ga concentration of the n-type ZnO layer 3 is 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), and the O radical beam irradiation condition is RF power. The undoped ZnO active layer 4 having a thickness of 15 nm was grown at 300 W and an O ₂ flow rate of 2.0 sccm (J _O = 8.1 × 10 ¹⁴ atoms / cm ² s).

  Thereafter, the substrate temperature was lowered to 300 ° C., and a Cu-doped ZnO layer 5 was grown on the undoped ZnO active layer 4 as a p-type layer. The ZnO growth time in one ZnO growth step was 20 seconds, and the Cu supply period in one Cu deposition step was 10 seconds. The process of setting the ZnO growth process and the Cu deposition process as one set was repeated 120 times to grow a Cu-doped ZnO layer 5 having a thickness of 400 nm.

ZnO growth step, the Zn flux _{F Zn} and _{0.15mnm / s (J Zn = 9.9} × 10 14 atoms / cm 2 s), O radical beam irradiation conditions of RF power 300 W, _{O 2} flow rate 2.0 sccm ( J _O = 8.1 × 10 ¹⁴ atoms / cm ² s). The V / II flux ratio is 0.82, which is a Zn-rich condition. In the Cu adhesion step, the Cu flux F _Cu was set to 0.0015 nm / s.

  Thereafter, the n-side electrode 6n was formed on the back surface of the ZnO substrate 1, the p-side electrode 6p was formed on the Cu-doped ZnO layer 5, and the bonding electrode 7 was formed on the p-side electrode 6p. The n-side electrode 6n was formed by laminating a 500 nm thick Au layer on a 10 nm thick Ti layer. The p-side electrode 6p is formed by laminating an Au layer having a thickness of 10 nm on a Ni layer having a size of 300 μm □ and a thickness of 1 nm, and the bonding electrode 7 is an Au layer having a size of 100 μm □ and a thickness of 500 nm. Formed. Thus, the light emitting device according to the first example was manufactured.

  Next, a ZnO-based semiconductor light emitting device according to a comparative example will be described (note that the light emitting device of the comparative example did not actually emit light as will be described later with reference to FIG. 15). In the comparative example, instead of the p-type layer 5 in the first example, Zn, O, and Cu were supplied simultaneously to form the Cu-doped ZnO layer 5 as in the first experiment. Other steps are the same as those in the first embodiment.

The Cu-doped ZnO layer 5 of the comparative example has a growth temperature of 300 ° C., a Zn flux F _Zn of 0.15 m / s, an O radical beam irradiation condition of RF power 300 W, an O ₂ flow rate of 2.0 sccm, and a Cu flux F _Cu was grown to a thickness of 400 nm at 0.0015 nm / s.

  Next, the characteristics of the ZnO-based semiconductor light emitting devices of the first example and the comparative example will be described.

  13A and 13B are RHEED images of the Cu-doped ZnO layer 5 of the ZnO-based semiconductor light emitting device according to the comparative example and the first example, respectively, as viewed from the [11-20] direction. In the Cu-doped ZnO layer 5 of the comparative example, the RHEED image shows a ring pattern, whereas in the Cu-doped ZnO layer 5 of the first example, the RHEED image shows a streak pattern. It can be seen that the Cu-doped ZnO layer 5 of the first example is epitaxially grown by two-dimensional growth even though the growth temperature is as low as 300 ° C.

14A and 14B are IV characteristics of ZnO-based semiconductor light emitting devices according to the comparative example and the first example, respectively. The light emitting element of the comparative example has Schottky characteristics with a lot of leakage. On the other hand, the light emitting device of the first example exhibits diode characteristics. In the example, since the active O radical supply step and the Cu supply step are separated, the Zn site could be replaced in the form of monovalent Cu ⁺ without promoting the oxidation of Cu. It is considered that the p-type Cu-doped ZnO layer was formed and the diode characteristics were obtained.

In the Cu-doped ZnO layer of the comparative example, it is presumed that CuO is promoted and CuO is formed. Since divalent Cu ²⁺ does not cause p-type ^formation , Schottky characteristics are considered. Further, it is considered that the characteristics with many leaks are caused by the poor crystallinity.

  FIG. 15 is an electroluminescence (EL) spectrum of the ZnO based semiconductor light emitting device according to the first example. Although the short wavelength side was absorbed by self-absorption due to the homostructure, ultraviolet emission at 390 nm was observed. On the other hand, light emission could not be confirmed in the light emitting device of the comparative example.

  In the second to fourth experiments and the first embodiment, ZnO is doped with Cu. However, even when MgZnO is doped with Cu, the MgZnO growth process and the Cu deposition process are alternately repeated. It is considered that a Cu-doped MgZnO single crystal film that is two-dimensionally grown and has high flatness and exhibits p-type conductivity can be obtained.

  Conditions such as the VI / II flux ratio (third experiment), the growth temperature (fourth experiment), and the film thickness per time considered for Cu-doped ZnO are considered to be effective for Cu-doped MgZnO as well. It is done. By using p-type Cu-doped MgZnO, a light emitting element having a double hetero structure can be formed as in the following second and third embodiments.

  Next, a second embodiment and a third embodiment for forming a ZnO-based semiconductor light emitting element having a double hetero structure will be described.

FIG. 16A is a schematic cross-sectional view of a ZnO-based semiconductor light-emitting device according to the second embodiment. On the Zn-faced ZnO (000) substrate 11 having n-type conductivity, Zn and O are simultaneously supplied to grow, for example, a ZnO buffer layer 12 having a thickness of 30 nm (for example, growth temperature: 300 ° C., Zn flux F _Zn : 0.15 nm / s, O radical beam irradiation condition: RF power 300 W / O ₂ flow rate 2.0 sccm). Then, annealing is performed at 900 ° C. for 10 minutes in order to improve the crystallinity and surface flatness of the buffer layer.

On the ZnO buffer layer 12, Zn, O and Ga are simultaneously supplied to grow, for example, a Ga-doped n-type ZnO layer 13 having a thickness of 150 nm (for example, growth temperature: 900 ° C., Zn flux F _Zn : 0.15 nm). / S, O radical beam irradiation conditions: RF power 250 W / O ₂ flow rate 1.0 sccm, Ga cell temperature: 460 ° C., Ga concentration of n-type ZnO layer 13: 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 (for example, growth temperature: 900 ° C., Zn flux F _Zn : 0.1 nm). / s, Mg flux F _Mg : 0.025 nm / s, O radical beam irradiation conditions: RF power 300 W / O ₂ flow rate ₂ sccm, Mg composition of n-type MgZnO layer 14: 0.3).

Zn and O are simultaneously supplied on the n-type MgZnO layer 14 to grow, for example, a ZnO active layer 15 having a thickness of 10 nm (for example, growth temperature: 900 ° C., Zn flux F _Zn : 0.1 nm / s, O Radical beam irradiation conditions: RF power 300 W / O ₂ flow rate 2.0 sccm)
As shown in FIG. 16B, 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.

  Thereafter, the substrate temperature is lowered to, for example, 300 ° C., and the MgZnO growth step and the Cu deposition step are alternately repeated on the active layer 15 to grow the Cu-doped MgZnO layer 16 as a p-type layer.

For example, the MgZnO growth time in the MgZnO growth process per one is 20 seconds (Zn flux _F Zn: 0.15m / s, Mg flux _F Mg: _0.03nm / s, O radical beam irradiation conditions: RF power 300W / O ₂ flow rate is 2.0 sccm), and the Cu supply period in one Cu deposition step is 10 seconds (Cu flux F _Cu : 0.0015 nm / s). A process in which the ZnO growth step and the Cu deposition step are set as one set is repeated, for example, 60 sets to grow a p-type Cu-doped MgZnO layer 16 (Mg composition: 0.3) having a thickness of 200 nm.

  Thereafter, the n-side electrode 17n is formed on the back surface of the ZnO substrate 11, the p-side electrode 17p is formed on the Cu-doped MgZnO layer 16, and the bonding electrode 18 is formed on the p-side electrode 17p. For example, the n-side electrode 17n is formed by stacking an Au layer having a thickness of 500 nm on a Ti layer having a thickness of 10 nm, and the p-side electrode 17p is formed on a Ni layer having a size of 300 μm □ and a thickness of 1 nm. An Au layer having a thickness of 10 nm is formed by laminating, and the bonding electrode 18 is formed by an Au layer having a size of 100 μm □ and a thickness of 500 nm. In this way, the light emitting device according to the second embodiment is manufactured.

In addition, although the ZnO substrate was used as the conductive substrate 11 in the above example, an MgZnO substrate, a GaN substrate, a SiC substrate, a Ga ₂ O ₃ substrate, or the like can also be used.

  FIG. 17 is an example of a shutter sequence of the Zn cell, Mg cell, O cell, and Cu cell in the Cu-doped MgZnO layer growth of the second embodiment. A ZnZn shutter, a Mg cell shutter, and an O cell shutter are opened and the Cu cell shutter is closed, and a MgZnO growth process, and a Zn cell shutter, the Mg cell shutter, and the O cell shutter are closed, and the Cu cell shutter is opened. It is repeated alternately.

  In this example, the open period of the Zn cell shutter in the MgZnO growth step is set to include the open period of the Mg cell shutter and the open period of the O cell shutter. When Mg is supplied together with Zn, from the viewpoint of suppressing the reaction between the O radical and Cu, at least one of the open period of the Zn cell shutter and the open period of the Mg cell shutter includes the open period of the O cell shutter. This should be done. From the viewpoint of improving the controllability of Mg composition of MgZnO, it seems better that the open period of the Zn cell shutter includes the open periods of the Mg cell shutter and the O cell shutter.

  FIG. 18 is a schematic cross-sectional view of a ZnO-based semiconductor light emitting device according to the third embodiment. In the second embodiment, a conductive substrate is used as the substrate. In the third embodiment, an insulating substrate is used as the substrate.

On the c-plane sapphire substrate 21 which is an insulating substrate, Mg and O are simultaneously supplied to grow, for example, a MgO buffer layer 22 having a thickness of about 10 nm (for example, growth temperature: 650 ° C., Mg flux F _Mg : 0). .05 nm / s, O radical beam irradiation conditions: RF power 300 W / O ₂ flow rate ₂ sccm).

  The MgO buffer layer 22 functions as a polarity control layer for growing a ZnO-based semiconductor layer grown thereon with the Zn surface as a surface. Such a polarity control layer is described in, for example, “Best Mode for Carrying Out the Invention” in JP-A-2005-97410.

Zn and O are simultaneously supplied on the MgO buffer layer 22 to grow, for example, a ZnO buffer layer 23 having a thickness of 30 nm (for example, growth temperature: 300 ° C., Zn flux F _Zn : 0.15 nm / s, O radical) Beam irradiation conditions: RF power 300 W / O ₂ flow rate 2.0 sccm). Then, annealing is performed at 900 ° C. for 30 minutes in order to improve the crystallinity and surface flatness of the buffer layer. This ZnO film is grown on the Zn polar face (+ c).

On the ZnO buffer layer 23, Zn, O, and Ga are simultaneously supplied to grow, for example, a Ga-doped n-type ZnO layer 24 having a thickness of about 1.5 μm (for example, growth temperature: 900 ° C., Zn flux F _Zn : 0.05 nm / s, O radical beam irradiation conditions: RF power 300 W / O ₂ flow rate ₂ sccm).

On the Ga-doped 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 (for example, growth temperature: 900 ° C., Zn flux F _Zn : 0). 0.1 nm / s, Mg flux F _Mg : 0.025 nm / s, O radical beam irradiation conditions: RF power 300 W / O ₂ flow rate ₂ sccm, Mg composition of n-type MgZnO layer 25: 0.3).

  A ZnO active layer 26 is grown on the n-type MgZnO layer 25 in the same manner as the active layer 15 of the second embodiment. As described for the active layer 15 of the second embodiment, the active layer 26 can adopt a quantum well structure instead of a single ZnO layer.

  Thereafter, the substrate temperature is lowered to 300 ° C., for example, and a Cu-doped MgZnO layer 27 is grown on the active layer 26 as a p-type layer in the same manner as the Cu-doped MgZnO layer 16 of the second embodiment.

  Since the substrate 21 of the third embodiment is an insulating substrate, the n-side electrode cannot be provided on the back side of the substrate. Therefore, the n-side electrode formation region is etched from the upper surface of the Cu-doped MgZnO layer 27 until the n-type ZnO layer 24 is exposed, and the n-side electrode 28n is formed on the exposed n-type ZnO layer 24. A p-side electrode 28p is formed on the Cu-doped MgZnO layer 27, and a bonding electrode 29 is formed on the p-side electrode 28p.

  For example, the n-side electrode 28n is formed by laminating 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. The bonding electrodes 29 are formed of an Au layer having a thickness of 500 nm. In this way, the light emitting device according to the third embodiment is manufactured.

As described above in the second experiment to the fourth experiment and the first to third examples, the step of forming the Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film (described above) ZnO growth step or MgZnO growth step in the description) and a step of supplying Cu onto the Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film (Cu attachment step in the above description) alternately. By repeating, a Cu-doped Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal epitaxial growth film exhibiting p-type conductivity can be obtained.

In addition, although the example which uses Cu as a p-type dopant was considered above, the above-mentioned method is effective also as a method of utilizing other IB group elements, such as Ag which can form a several valence, as a p-type dopant. There is a possibility. In other words, by separating the step of forming the Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) single crystal film having the O irradiation period and the step of attaching the group IB element, it acts as an acceptor + 1 There is a possibility that a valent group IB element can be easily generated.

As the oxygen source, the O radical is used in the above description, but it is considered possible to use another gas having a strong oxidizing power such as a polar oxidizing agent such as ozone, H ₂ O, or alcohol.

  The inventors of the present application investigated the electronic state of Cu in a Cu-doped ZnO layer grown by alternately repeating a ZnO growth step and a Cu deposition step by X-ray photoelectron spectroscopy (XPS).

  FIG. 19A is a schematic cross-sectional view showing a sample (alternate growth sample) used for XPS analysis. With reference to this figure, the production method of an alternating growth sample is demonstrated.

On Zn surface ZnO (0001) substrate 31, growth temperature is 300 ° C., Zn flux F _Zn is 0.16 nm / s, O radical beam irradiation condition is RF power 300 W, O ₂ flow rate 2.0 sccm, and growth time is 5 minutes. A ZnO buffer layer 32 having a thickness of 40 nm was grown. In order to improve the crystallinity and surface flatness of the ZnO buffer layer 32, annealing was performed at 900 ° C. for 30 minutes.

On the ZnO buffer layer 32, the growth temperature is 900 ° C., the Zn flux F _Zn is 0.16 nm / s, the O radical beam irradiation conditions are RF power 300 W, the O ₂ flow rate 2.0 sccm, and the growth time is 15 minutes. A 120 nm undoped ZnO layer 33 was grown.

  The substrate temperature was lowered to 300 ° C., and a p-type Cu-doped ZnO layer 34 was grown on the undoped ZnO layer 33.

  In growing the Cu-doped ZnO layer 34, Zn, O, and Cu were supplied at different timings in the same sequence as the shutter sequence shown in FIG. In the production of the alternately grown sample used for XPS analysis, Ga was supplied at the same timing as O. In the Cu-doped ZnO layer 34, Cu and Ga are co-doped.

In the ZnO growth step, Zn flux F _Zn was 0.16 nm / s, O radical beam irradiation conditions were RF power 300 W, O ₂ flow rate 2.0 sccm, and Ga cell temperature T _Ga was 515 ° C. The Cu cell temperature T _Cu in the Cu adhesion step was 930 ° C., and the Cu flux F _Cu was 0.0015 nm / s.

  The open period of each of the O cell shutter and the Ga cell shutter was 16 seconds, and the open period of the Zn cell shutter was extended by 1 second before and after the open period of the O cell shutter and the Ga cell shutter. The open period per time of the Zn cell shutter is 18 seconds. The opening period per time of the Cu cell shutter was 50 seconds.

  The ZnO growth step and the Cu deposition step were repeated 30 times alternately to obtain a Cu-doped ZnO layer 34 having a thickness of 100 nm.

  FIG. 19B is an RHEED image of the Cu-doped ZnO layer 34 viewed from the [11-20] direction. The RHEED image shows a streak pattern. It can be seen that the Cu-doped ZnO layer 34 is a single crystal layer that is two-dimensionally grown and has high surface flatness.

20A and 20B are graphs showing the XPS analysis results of the Cu2p3 / 2 orbit of the Cu-doped ZnO layer of the first sample of the first experiment and the Cu-doped ZnO layer 34 of the alternately grown sample, respectively. The horizontal axis indicates the photoelectron energy (binding energy) in the unit “eV”, and the vertical axis indicates the intensity (the number of photoelectrons observed per unit time) in arbitrary units. The XPS spectrum and the waveform analysis results (curves indicated by Cu1 to Cu5) are described. A curve Cu1 indicates a component (peak) derived from an electronic state of Cu (zero-valent Cu or monovalent Cu ⁺ ) in Cu, Cu ₂ O, or the like. Curve Cu2 represents CuO or the like, and curve Cu3 represents a component derived from the electronic state of Cu (divalent Cu ²⁺ ) in Cu (OH) ₂ or CuCO ₃ or the like. A curve Cu4 and a curve Cu5 are curves that show a shake-up peak (satellite peak) of Cu ^{2+ having} a different bonding state. In the ZnO layer, there are many Os around Cu. For this reason, Cu is considered to exist in a state other than the zero-valent metal Cu. Therefore, it can be said that the curve Cu1 is a curve showing a peak of Cu ⁺ .

  In XPS analysis, a scanning X-ray photoelectron spectroscopic analyzer PHI Quantera II manufactured by ULVAC-PHI Co., Ltd. is used as the measurement device, and monochromated Al (1486.6 eV) is used as the X-ray source, the detection area is 100 μmΦ, The depth was about 8 nm (extraction angle 90 °).

Reference is made to FIG. 20A. In the first experiment in which Zn, O, and Cu were simultaneously supplied and grown, in the Cu-doped ZnO layer of the first sample, in addition to the component (Cu ⁺ ) indicated by the curve Cu1 having a peak at 932.55 eV, A component (Cu ²⁺ ) indicated by a curve Cu 2 and a curve Cu 3 having peaks at 933.65 eV and 934.65 eV on the high energy side is observed as a shoulder. The shake up peak of ^{Cu 2+} represented by the curve Cu4 and curves Cu5 with peaks at 941.15eV and 943.65eV are clearly observed. That is, monovalent Cu ⁺ and divalent Cu ²⁺ are mixed.

Reference is made to FIG. 20B. In the Cu-doped ZnO layer 34 of the alternately grown sample grown by supplying Zn and O and Cu at different timings, no Cu ²⁺ shake-up peak is observed, and a curve Cu 1 having a peak at 932.73 eV Ingredients other than those indicated by are hardly recognized. The intensity ratio (Int%) and the area ratio (Area%) of the curves Cu2 to Cu5 are both 0.00%. That is, it can be seen that in the Cu-doped ZnO layer 34 of the alternately grown sample, Cu exists only as almost monovalent Cu ⁺ .

  Next, the present inventors performed sputter cleaning on the surface of the Cu-doped ZnO layer 34 of the alternately grown sample.

FIG. 21A is a graph showing the XPS spectrum of the Cu2p3 / 2 orbit of the Cu-doped ZnO layer 34 before and after the surface sputter cleaning. The meanings of both axes of the graph are the same as those in FIGS. 20A and 20B. Curve a shows the spectrum before sputter cleaning (the outermost surface immediately after the growth of the Cu-doped ZnO layer 34), and curve b shows that after sputter cleaning. Curve a is the same as the curve showing the XPS spectrum of FIG. 20B. A Cu ²⁺ shake-up peak is not observed before and after the sputter cleaning.

  FIG. 21B is a graph showing the waveform analysis result of the XPS spectrum (curve b) of the Cu2p3 / 2 orbit of the Cu-doped ZnO layer 34 after the surface sputter cleaning. The meanings of both axes of the graph and the curves Cu1 to Cu5 are the same as those in FIGS. 20A and 20B.

Components other than the component shown by the curve Cu1 having a peak at 932.55 eV are hardly recognized. That is, it can be seen from the waveform analysis that Cu exists only as monovalent Cu ^{+ in} the Cu-doped ZnO layer 34.

In this way, in the Cu-doped ZnO layer 34 grown by supplying Zn and O and Cu at different timings, Cu is not only in the surface but also in the inside, and Cu is only as substantially monovalent Cu ^+. It was confirmed that it existed.

The excitation peak energies of 2p3 / 2 core electrons of Cu atoms in the Cu-doped ZnO layer 34 were 932.73 eV (before sputter cleaning) and 932.55 eV (after sputter cleaning) (components indicated by the curve Cu1). Peak energy, see FIGS. 20B and 21B). For example, there was no shake-up peak (a shake-up peak of Cu ²⁺ indicated by the curves Cu4 and Cu5) in the range of 940 eV to 945 eV. According to the method according to the embodiment, not only the Cu-doped ZnO layer, but generally a Cu-doped Mg _x Zn _1-x O (0 ≦ x ≦ 0.6) layer, which is a 2p3 / 2 inner shell of Cu atoms by XPS. It will be possible to obtain a ZnO-based semiconductor layer having an electron excitation peak energy in the range of 932.1 eV to 932.9 eV and no shake-up peak in the range of 940 eV to 945 eV.

  The ZnO-based semiconductor layer obtained by the method of the embodiment can be used for, for example, a light emitting diode (LED) or a laser diode (LD) with a short wavelength (ultraviolet to blue), and these application products (various indicators, LED display) Etc., and can be used for CV / DVD light sources). Moreover, it can utilize for white LED and its application products (a lighting fixture, various indicators, a display, the backlight of various displays, etc.). Moreover, it can utilize for an ultraviolet sensor.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

101 Vacuum chamber 102 Zn source gun 103 O source gun 104 Mg source gun 105 Cu source gun 106 Ga source gun 107 Stage 108 Substrate 109 Thickness meter 110 RHEED gun 111 Screen 1 ZnO substrate 2 ZnO buffer layer 3 n-type ZnO layer 4 Undoped ZnO active layer 5 p-type Cu-doped ZnO 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 16 p-type Cu-doped MgZnO layer 17n n-side electrode 17p p-side electrode 18 bonding electrode 21 sapphire substrate 22 MgO buffer layer 23 ZnO buffer layer 24 n-type ZnO layer 25 n-type MgZnO layer 26 active layer 27 p-type Cu-doped MgZnO layer 28n n-side electrode 2 p p-side electrode 29 bonding electrode 31 ZnO substrate 32 ZnO buffer layer 33 an undoped ZnO layer 34 Cu doped ZnO layer

Claims (2)

  (A)Stoichiometry conditions or Group II rich conditions, and VI / II hula At a temperature of 250 ° C or higher and 350 ° C or lower.Above the underlayer, At least one of the Zn supply period and the Mg supply period is extended before and after the O supply period. To include the O supply period.Zn, O, and Mg as needed,10n thickness m or lessMg_xZn_1-xForming an O (0 ≦ x ≦ 0.6) single crystal film;
  (B) Mg_xZn_1-xCu on O (0 ≦ x ≦ 0.6) single crystal filmonlyThe1 of Cu In an amount that makes the thickness below the atomic layerAnd supplying a process,
  Mg in which Cu is doped by repeating the steps (a) and (b) alternately._xZn_1-xA method for producing a ZnO-based semiconductor layer for forming an O (0 ≦ x ≦ 0.6) layer.   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;
Have
  The step of forming the p-type ZnO-based semiconductor layer includes:
  (A)Stoichiometry conditions or Group II rich conditions, and VI / II hula At a temperature of 250 ° C or higher and 350 ° C or lower.Above the underlayer, At least one of the Zn supply period and the Mg supply period is extended before and after the O supply period. To include the O supply period.Zn, O, and Mg as needed,10n thickness m or lessMg_xZn_1-xForming an O (0 ≦ x ≦ 0.6) single crystal film;
  (B) Mg_xZn_1-xCu on O (0 ≦ x ≦ 0.6) single crystal filmonlyThe1 of Cu In an amount that makes the thickness below the atomic layerAnd supplying a process,
  Mg in which Cu is doped by repeating the steps (a) and (b) alternately._xZn_1-xForming an O (0 ≦ x ≦ 0.6) layer;
A method for manufacturing a ZnO-based semiconductor light emitting device.