JP5025326B2 - Oxide semiconductor photo detector - Google Patents

Description

  The present invention relates to an oxide semiconductor light receiving element including a light receiving layer made of a ZnO-based oxide semiconductor.

  A ZnO-based oxide semiconductor containing ZnO (zinc oxide) has a so-called visible blind characteristic that responds only to light having a wavelength in the ultraviolet region because the band gap is as large as about 3.26 eV. An MgZnO mixed crystal obtained by adding Mg to ZnO has a so-called solar blind characteristic by setting the Mg composition to an appropriate value. The solar blind characteristic is a characteristic having a band gap corresponding to the ultraviolet region rather than sunlight that passes through the ozone layer and reaches the earth.

  By the way, a light receiving element having sensitivity only to light having a wavelength in the ultraviolet region is expected to be applied to a flame detector and a semiconductor manufacturing field. As such a light receiving element, in addition to a ZnO-based oxide semiconductor light receiving element, for example, a silicon light receiving element and a photomultiplier tube are known. However, since silicon has a small band gap, it also responds to light in the visible region. Therefore, when the silicon light receiving element is made to respond only to light having a wavelength in the ultraviolet region, a filter that cuts off light in the visible region is required. Further, when the photomultiplier tube is caused to respond only to light in the ultraviolet region, a device for applying a high voltage of several hundred volts is required. Therefore, there is a problem that it is difficult to reduce the size of the system including the photomultiplier tube.

  On the other hand, the crystal of ZnO is a direct transition semiconductor having a band gap of approximately 3.26 eV. In addition, the exciton in the ZnO crystal has a large binding energy and 60 meV, and exists stably at room temperature. Therefore, ZnO-based oxide semiconductors are expected to be applied to light emitting devices from the blue region to the ultraviolet region, which are inexpensive and have a low environmental load. Furthermore, since the ZnO-based oxide semiconductor has high radiation resistance, application to a light receiving element provided in an artificial satellite or a space station is also expected.

Patent Document 1 proposes a light-receiving element having a pn junction in which a p-type silicon substrate and an n-type ZnO thin film are combined as an oxide semiconductor light-receiving element made of a ZnO-based oxide semiconductor. In manufacturing the light receiving element having the pn junction, first, the surface of the silicon substrate is treated with hydrofluoric acid (HF), and the natural oxide film on the surface of the silicon substrate is removed. Next, a ZnO buffer layer is formed by sputtering on the surface treated with hydrofluoric acid. Thereafter, a ZnO thin film is grown on the buffer layer by metal organic chemical vapor deposition (MOCVD). In this way, a light receiving element having a pn junction is obtained.
JP 2003-31846 A

  However, there are many defects and oxygen vacancies in the ZnO-based oxide semiconductor due to interstitial zinc or the like. Therefore, a deep level may be formed in the band gap (forbidden band) of the ZnO-based oxide semiconductor. If a deep level is formed in the band gap of a ZnO-based oxide semiconductor, the optical characteristics of the light receiving element, such as an increase in dark current and a decrease in response speed of the light receiving element, may be deteriorated. is there.

  Accordingly, an object of the present invention is to provide an oxide semiconductor light-receiving element made of a ZnO-based oxide semiconductor that can reduce dark current and suppress a decrease in response speed.

In order to achieve the above object, an invention according to claim 1 is formed of a substrate and n-type Mg _x Zn _1-x O (where 0 ≦ x ≦ 1) formed on the substrate , and 1 × 10 ¹⁶ a light-receiving layer in which a light-receiving region doped with nitrogen at a concentration of cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ and a region not doped with nitrogen other than the light-receiving region are selectively formed; and the light- receiving layer An oxide semiconductor light receiving element including a Schottky electrode that is Schottky bonded to the light receiving region and an ohmic electrode that is ohmic bonded to a region other than the light receiving region of the light receiving layer .
In general, the band gap (Eg) of a semiconductor can be obtained by an expression represented by Eg (eV) = 1240 / λ (nm). Since ZnO has Eg = about 3.26 eV, light having a wavelength of about 380 nm or less is received and absorbed by ZnO.

In the oxide semiconductor light receiving element according to claim 1, the light receiving region is made of Mg _x Zn _1-x O (where 0 ≦ x ≦ 1). By setting the composition of the light receiving region to Mg _x Zn _1-x O in which Mg is contained in ZnO (where 0 ≦ x ≦ 1), Eg of the light receiving region can be increased. Therefore, the wavelength of light that can be absorbed in the light receiving region can be shifted to a shorter wavelength side than 380 nm. As a result, it can be used as a light receiving element for receiving and absorbing wavelengths in the ultraviolet region. Further, in this oxide semiconductor light receiving element, since the light receiving region is doped with nitrogen, it is possible to reduce dark current in the light receiving element and to suppress a decrease in response speed.

Also, the doping concentration of nitrogen is doped in the light reception area, by a range of ^{1 × 10 16 cm -3 ~1 ×} 10 20 cm -3, while suppressing a decrease in response speed of the light receiving element, The dark current of the light receiving element can also be suppressed.

Also, it is Schottky junction and the light receiving region and the Schottky electrode. Thereby, the configuration of the oxide semiconductor light receiving element is a so-called Schottky diode configuration. In the oxide semiconductor light receiving element having such a structure, light is absorbed near the junction (depletion layer) of the Schottky electrode in the light receiving region, and an electromotive force (electric signal) is generated in the light receiving region. If nitrogen is doped only in the light receiving region, it is possible to reduce the dark current and suppress the response speed in the light receiving element. That is, only by doping nitrogen in the vicinity of the surface of the light receiving layer, it is possible to reduce the dark current and suppress the response speed in the oxide semiconductor light receiving element.
According to a second aspect of the present invention, the light receiving layer is formed on a lower layer not doped with nitrogen and on the lower layer, and has a concentration of 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ . An upper layer as the light receiving region doped with nitrogen, and is etched in a direction across the stacking interface from the upper layer to a depth at which the surface of the lower layer is exposed as an exposed surface, and the Schottky electrode is 2. The oxide semiconductor light receiving element according to claim 1, wherein a Schottky junction is formed on a surface, and the ohmic electrode is ohmic bonded to the exposed surface of the lower layer.

Furthermore, the invention described in claim 3 is made of i-type Mg _x Zn _1-x O (where 0 ≦ x ≦ 1) and nitrogen at a concentration of 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²⁰ cm ^−3. A light-receiving layer doped with, a p-type oxide semiconductor layer made of a ZnO-based compound semiconductor not doped with nitrogen formed on one surface side of the light-receiving layer, and the one surface side of the light-receiving layer It formed on the other surface side of the opposite, and the the including stacked unit nitrogen is made of ZnO based compound semiconductor which is not doped n-type oxide semiconductor layer, p-side joined before Symbol p-type oxide semiconductor layer and the electrode, and a n-side electrode which is joined to the n-type oxide semiconductor layer, at least one of the p-type oxide semiconductor layer and the n-type oxide semiconductor layer has a larger band gap than the light-receiving layer, with an acid halide semiconductor light-receiving element is there.

In the oxide semiconductor light receiving element according to claim 3 , a p-type oxide semiconductor layer is formed on one surface side of the light receiving layer. An n-type oxide semiconductor layer is formed on the other surface side of the light receiving layer. For example, by reducing the residual carrier density of the light receiving layer, the structure of the oxide semiconductor light receiving element becomes a structure of a so-called PIN diode. Further, at least one of the p-type oxide semiconductor layer and the n-type oxide semiconductor layer has a band gap larger than that of the light receiving layer. Therefore, when the wavelength of light that can be absorbed by the oxide semiconductor layer having a band gap larger than that of the light receiving layer is calculated using the above-described equation represented by Eg (eV) = 1240 / λ (nm), the wavelength is It becomes smaller than the wavelength of light that can be absorbed by the layer. That is, light having a wavelength that can be absorbed by the light receiving layer is not absorbed by the p-type and / or n-type oxide semiconductor layer. Therefore, light from the outside can surely reach the light receiving layer, and an electromotive force (electric signal) can be generated in the light receiving region.
The invention according to claim 4 further includes a substrate that supports the stacked portion so as to be in contact with the n-type oxide semiconductor layer, and the stacked portion includes the p-type oxide semiconductor layer and the light receiving layer. And the n-type oxide semiconductor layer is etched in a direction crossing the stacked interface to a depth at which the surface of the n-type oxide semiconductor layer is exposed as an exposed surface, and the p-side electrode is in ohmic contact with the surface of the p-type oxide semiconductor layer 4. The oxide semiconductor light receiving element according to claim 3, wherein the n-side electrode is in ohmic contact with the exposed surface of the n-type oxide semiconductor layer. 5.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view for explaining a photoconductive cell 1 according to a first embodiment of the present invention.
The photoconductive cell 1 includes a substrate 2 and an n-type MgZnO layer 3 (light receiving layer) grown on the substrate 2.

  As the substrate 2, for example, a high resistance substrate such as a sapphire substrate or a ZnO substrate can be applied. Among the high resistance substrates, single crystal substrates such as a sapphire single crystal substrate and a ZnO single crystal substrate are preferable. By applying the single crystal substrate to the substrate 2, it is possible to suppress the occurrence of crystal defects in the n-type MgZnO layer 3 when the n-type MgZnO layer 3 is grown on the substrate 2.

The n-type MgZnO layer 3 is a light-receiving layer that receives and absorbs light in the photoconductive cell 1, and receives and absorbs light as a whole. That is, the n-type MgZnO layer 3 functions as a light receiving region that receives and absorbs light as a whole.
The n-type MgZnO layer 3 is made of a Mg _x Zn _x-1 O mixed crystal in which Mg is contained in ZnO. Here, x is a mixed crystal ratio of Mg in MgZnO, and satisfies the inequality represented by 0 ≦ x ≦ 1. The band gap of the n-type MgZnO layer 3 can be controlled by changing the mixed crystal ratio (x) of Mg.

  In general, the band gap (Eg) of a semiconductor is obtained by the equation (1) represented by Eg (eV) = 1240 / λ (nm). Since ZnO has Eg = about 3.26 eV, a semiconductor made of ZnO receives and absorbs light having a wavelength of about 380 nm or less. By the way, Eg of MgZnO formed by containing Mg in ZnO is larger than Eg of ZnO. For example, in the n-type MgZnO layer 3, for example, if the Mg mixed crystal ratio (x) is 30, the Eg of the n-type MgZnO layer 3 is about 3.9 eV, and light having a wavelength of about 320 nm is emitted from the n-type MgZnO layer 3. 3 can be absorbed. That is, by appropriately controlling the Mg mixed crystal ratio (x), the wavelength of light that can be absorbed by the n-type MgZnO layer 3 can be shifted to a shorter wavelength side than 380 nm. As a result, the n-type MgZnO layer 3 can absorb wavelengths in the ultraviolet region. The Mg mixed crystal ratio (x) is preferably 5 (%) to 30 (%).

  Further, since the n-type MgZnO layer 3 has defects (oxygen vacancies) in which oxygen has escaped from the ZnO crystal structure, the n-type MgZnO layer 3 tends to have an n-type conductivity type even if it does not contain an n-type dopant. The n-type MgZnO layer 3 may contain, for example, boron (B), aluminum (Al), gallium (Ga), indium (In), etc. as an n-type dopant. By including the n-type dopant, the conductive properties of the n-type MgZnO layer 3 can be controlled.

The n-type MgZnO layer 3 is doped with nitrogen. The doping concentration of nitrogen doped in the n-type MgZnO layer 3 is preferably 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ . When the doping concentration of nitrogen is within this range, in addition to the reduction of dark current and the reduction in response speed in the photoconductive cell 1, it is also possible to suppress the decrease in light receiving sensitivity of the photoconductive cell 1. The layer thickness of the n-type MgZnO layer 3 is preferably 300 nm to 1000 nm.

In this photoconductive cell 1, an ohmic electrode 4 (ohmic electrode 41 and ohmic electrode 42) for taking out an electric signal generated by light reception in the n-type MgZnO layer 3 is ohmically joined to the n-type MgZnO layer 3.
The ohmic electrode 4 is made of a metal material that can be in ohmic contact with the n-type MgZnO layer 3, such as aluminum (Al), titanium (Ti), or an aluminum-titanium alloy (Al-Ti alloy).

Next, a method for manufacturing the photoconductive cell 1 will be described.
FIG. 2 is an illustrative view for explaining the configuration of a molecular epitaxial (MBE) growth apparatus 5 (hereinafter simply referred to as “MBE growth apparatus”) for forming the n-type MgZnO layer 3. The MBE growth apparatus 5 includes a chamber 6. A substrate holder 7 having a heater 8 built therein is disposed in the chamber 6. The substrate holder 7 is coupled to a rotation shaft 9, and the rotation shaft 9 is rotated by a rotation drive mechanism 10 disposed outside the chamber 6. Thereby, by holding the wafer 11 to be processed on the substrate holder 7, the temperature of the wafer 11 can be raised to a predetermined temperature in the chamber 6, and the wafer 11 can be rotated. The wafer 11 is, for example, a sapphire single crystal wafer constituting the substrate 2 described above.

A vacuum line 12 connected to an external vacuum pump (not shown) is connected to the upper portion of the chamber 6. Thereby, the pressure in the chamber 6 can be made into a vacuum state.
An O radical cell 13, an N radical cell 14, a Zn source cell 15, an Mg source cell 16, and a dopant source cell 39 are attached to the position facing the substrate holder 7 in the chamber 6 with a space therebetween.

The O radical cell 13 and the N radical cell 14 are configured by, for example, an RF cell that generates O plasma and N plasma by applying a high frequency (RF) from an RF (Radio Frequency) coil. Thereby, O ₂ and N ₂ can be made into plasma, and O plasma and N plasma can be irradiated onto the wafer 11.
The Zn source cell 15, the Mg source cell 16, and the dopant source cell 39 include, for example, a crucible in which a material source of Zn, Mg, and a dopant (for example, the above-described n-type dopant) is accommodated. Is provided with a heater (not shown). In addition, an openable / closable shutter (not shown) is provided in front of the crucible. Thereby, while heating a crucible with a heater and evaporating a material source, Zn, Mg, and a dopant can be irradiated to the wafer 11 by opening a shutter.

In order to grow the n-type MgZnO layer 3 on the wafer 11 using the MBE growth apparatus 5, first, the wafer 11 is placed on the substrate in the chamber 6 in an ultrahigh vacuum (10 ⁻⁷ Pa or less). The holder 7 is held. Next, the heater 8 is energized, and the temperature of the wafer 11 is raised to 400 ° C. to 900 ° C. Thereafter, O plasma, N plasma, Zn, and Mg are irradiated to the wafer 11 from the O radical cell 13, the N radical cell 14, the Zn source cell 15, and the Mg source cell 16, respectively, and nitrogen (N) is irradiated on the wafer 11. A doped MgZnO-based compound grows. At this time, since the MgZnO-based compound has oxygen vacancies in the MgZnO-based compound, the MgZnO-based compound tends to exhibit n-type conductivity. Therefore, the high-resistance n-type MgZnO layer 3 grows on the MgZnO-based compound on the wafer 11 without performing doping by irradiating the dopant from the dopant source cell 39. The growth conditions for the n-type MgZnO layer 3 are preferably the following conditions.
(Growth conditions for n-type MgZnO layer 3)
Wafer 11 temperature: 700 ° C. to 900 ° C.
O plasma irradiation conditions: Power supply 200 W to 400 W, O ₂ supply flow rate to RF cell 0.5 sccm to 3 sccm
N plasma irradiation conditions: with power of 200 W to 400 W, N ₂ supply flow rate to RF cell 0.5 sccm to 3 sccm
Zn irradiation conditions: 10 ⁻⁶ Pa to 10 ⁻⁴ Pa
Mg irradiation conditions: 10 ⁻⁶ Pa to 10 ⁻⁴ Pa
By growing the n-type MgZnO layer 3 under the growth conditions described above, the Mg mixed crystal ratio (x): 5 (%) to 30 (%), the doping concentration of nitrogen: 1 × 10 ¹⁶ cm ⁻³ to 1 × An n-type MgZnO layer 3 having a thickness of 10 ²⁰ cm ⁻³ and a layer thickness of 100 nm to 1000 nm can be grown on the wafer 11.

  Thereafter, the wafer 11 on which the n-type MgZnO layer 3 has been grown is taken out of the MBE growth apparatus 5 and placed in a known sputtering apparatus (not shown) or vapor deposition apparatus (not shown). In a sputtering apparatus or a vapor deposition apparatus, an ohmic electrode 41 and an ohmic electrode 42 are formed (ohmic junction) on the n-type MgZnO layer 3 by a film formation technique using a metal material and a pattern formation technique using photolithography. Thus, the photoconductive cell 1 shown in FIG. 1 is obtained.

As described above, according to this embodiment, the n-type MgZnO layer 3 is doped with nitrogen. Therefore, it is possible to reduce the dark current in the photoconductive cell 1 and to suppress a decrease in response speed. In particular, in this photoconductive cell 1, since the doping concentration of nitrogen is 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ , a decrease in the response speed of the photoconductive cell 1 is suppressed, and the photoconductive cell 1 A decrease in light receiving sensitivity can also be suppressed.

In this embodiment, the n-type MgZnO layer 3 is formed on the substrate 2 (wafer 11). However, a buffer made of a ZnO-based compound is provided between the substrate 2 and the n-type MgZnO layer 3. A layer may be formed. By forming the buffer layer, when the n-type MgZnO layer 3 is grown, the generation of crystal defects in the n-type MgZnO layer 3 can be further suppressed. In addition, although the MgZnO layer formed on the substrate 2 is the n-type MgZnO layer 3 having the n-type conductivity, the MgZnO layer having the p-type conductivity may be used.

FIG. 3 is a schematic sectional view for explaining a Schottky diode 35 according to the second embodiment of the present invention. In FIG. 3, parts corresponding to those shown in FIG. 1 are given the same reference numerals.

The Schottky diode 35 includes a substrate 2 and an n-type MgZnO layer 17 (light receiving layer) grown on the substrate 2.
The n-type MgZnO layer 17 is doped with nitrogen. Other physical properties (Mg mixed crystal ratio, nitrogen doping concentration, layer thickness) of the n-type MgZnO layer 17 are the same as those of the n-type MgZnO layer 3 described above.

  In this Schottky diode 35, a Schottky electrode 18 and an ohmic electrode 19 are formed on the n-type MgZnO layer 17 to extract an electric signal generated by light reception in the n-type MgZnO layer 17. Since the Schottky electrode 18 is formed, a depletion layer 20 (light receiving region) exists near the junction with the Schottky electrode 18 in the n-type MgZnO layer 17. In the Schottky diode 35, light is absorbed by the depletion layer 20. The Schottky electrode 18 is a metal that can be Schottky bonded to the n-type MgZnO layer 17 such as platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), rhodium (Rh), for example. Made of material.

On the other hand, the ohmic electrode 19 is in ohmic contact with the n-type MgZnO layer 17. The ohmic electrode 19 is made of the same metal material as that of the ohmic electrode 4 described above.
Next, a method for manufacturing the Schottky diode 35 will be described. In order to manufacture the Schottky diode 35, first, the n-type MgZnO layer 17 is grown on the substrate 2 using, for example, the MBE growth apparatus 5 shown in FIG. 2. The growth conditions for the n-type MgZnO layer 17 are the same as the growth conditions for the n-type MgZnO layer 3 except for the timing and position of N irradiation. The N irradiation may be performed at the timing when the n-type MgZnO layer is grown to the position where the depletion layer 20 is to be formed. As for the irradiation position of N, it is sufficient to irradiate only the position where the depletion layer 20 is to be formed (position where the Schottky electrode 18 is to be formed).

After the n-type MgZnO layer 17 was grown on the substrate 2, as in the case of the photoconductive cell 1, film formation of metal material and photolithography were performed using a known sputtering apparatus or vapor deposition apparatus. A Schottky electrode 18 and an ohmic electrode 19 are formed on the surface of the n-type MgZnO layer 17 by the pattern formation technique. Thus, the Schottky diode 35 shown in FIG. 3 is obtained.
FIG. 4 is a schematic cross-sectional view for explaining a Schottky diode 36 according to the third embodiment of the present invention. In FIG. 4, portions corresponding to the respective portions shown in FIG. 1 are given the same reference numerals.

The Schottky diode 36 includes a substrate 2 and an MgZnO stacked portion 40 (light receiving layer) grown on the substrate 2.
The MgZnO stacked unit 40 includes an n-type MgZnO layer 21 stacked on the substrate 2 and an n-type MgZnO layer 22 stacked on the n-type MgZnO layer 21.
The n-type MgZnO layer 21 is made of a Mg _x Zn _x-1 O mixed crystal in which Mg is contained in ZnO, similarly to the n-type MgZnO layer 3 described above. The layer thickness of the n-type MgZnO layer 21 is preferably 1 μm to 5 μm. Other physical properties (Mg mixed crystal ratio) in the n-type MgZnO layer 21 are the same as those in the n-type MgZnO layer 3 described above. However, the n-type MgZnO layer 21 may be doped with an n-type dopant. If n-type doping is performed, an ohmic electrode 24 (described later) can be easily obtained on the n-type MgZnO layer 21. Further, the n-type MgZnO layer 21 is not doped with nitrogen.

  The n-type MgZnO layer 22 is a layer that receives and absorbs light in the MgZnO stacked portion 40. The n-type MgZnO layer 22 is doped with nitrogen. The layer thickness of the n-type MgZnO layer 22 is preferably 300 nm to 1000 nm. Other physical properties (Mg mixed crystal ratio, nitrogen doping concentration) in the n-type MgZnO layer 22 are the same as those of the n-type MgZnO layer 3 described above.

  Further, the MgZnO stacked portion 40 is etched in a direction crossing the stacked interface from the n-type MgZnO layer 22 to a depth at which the n-type MgZnO layer 21 is exposed so as to have a substantially rectangular cross section. The ohmic electrode 24 is in ohmic contact with the exposed exposed surface 21a of the n-type MgZnO layer 21. On the other hand, a Schottky electrode 23 is Schottky bonded to the surface of the n-type MgZnO layer 22. Since the Schottky electrode 23 is formed, a depletion layer 48 (light receiving region) exists in the vicinity of the junction with the Schottky electrode 23 in the n-type MgZnO layer 22. In the Schottky diode 35, light is absorbed by the depletion layer 48 in the n-type MgZnO layer 22. The ohmic electrode 24 and the Schottky electrode 23 are made of the same metal material as the ohmic electrode 4 and the Schottky electrode 18, respectively.

In order to manufacture this Schottky diode 36, first, for example, using the MBE growth apparatus 5 shown in FIG. 2, the n-type MgZnO layer 21 is grown on the substrate 2 (without nitrogen irradiation). Then, the n-type MgZnO layer 22 is grown (with nitrogen irradiation). Thereby, the MgZnO stacked portion 40 is formed on the substrate 2.
After the MgZnO stacked portion 40 is formed, etching is performed from the n-type MgZnO layer 22 to the middle thickness portion of the n-type MgZnO layer 21, and the exposed surface 21a of the n-type MgZnO layer 21 is exposed.

After that, as in the case of the photoconductive cell 1, a Schottky is formed on the surface of the n-type MgZnO layer 22 by using a known sputtering apparatus or vapor deposition apparatus and by forming a metal material and patterning using photolithography. An electrode 23 is formed, and an ohmic electrode 24 is formed on the exposed surface 21 a of the n-type MgZnO layer 21. Thus, the Schottky diode 35 shown in FIG. 4 is obtained. As described above, according to the second and third embodiments, the n-type MgZnO layer 17 and the n-type MgZnO layer 22 are doped with nitrogen. Therefore, the dark current in the Schottky diode 35 and the Schottky diode 36 can be reduced, and a decrease in response speed can be suppressed. In particular, these Schottky diode 35 and Schottky diode 36 exist near the surface of the depletion layer 20 and n-type MgZnO layer 22 that are in the vicinity of the surface of the n-type MgZnO layer 17, which are regions that receive and absorb light. If only the depletion layer 48 to be doped is doped with nitrogen, the dark current can be reduced and the response speed can be suppressed, so that the doping amount of nitrogen can be reduced. In the second and third embodiments, as in the first embodiment, a buffer layer made of a ZnO-based compound is provided between the substrate 2 and the n-type MgZnO layer 17 (n-type MgZnO layer 21). It may be formed.
FIG. 5 is a schematic sectional view for explaining a PIN diode 37 according to a fourth embodiment of the present invention. In FIG. 5, parts corresponding to those shown in FIG. 1 are given the same reference numerals.

The PIN diode 37 includes an MgZnO stacked portion 46 including an i-type MgZnO layer 26, an n-type MgZnO layer 25, and a p-type MgZnO layer 27.
The i-type MgZnO layer 26 is a layer that receives and absorbs light in the MgZnO stacked portion 46, and receives and absorbs light as a whole. That is, the i-type MgZnO layer 26 functions as a light receiving region that receives and absorbs light in the MgZnO stacked portion 46. Like the n-type MgZnO layer 3 described above, the i-type MgZnO layer 26 is made of an Mg _x Zn _x-1 O mixed crystal in which Mg is contained in ZnO, and an intrinsic semiconductor whose conductivity type is i-type, or sufficient It is an n-type or p-type semiconductor having a high specific resistance. The i-type MgZnO layer 26 is doped with nitrogen. The band gap (Eg) of the i-type MgZnO layer 26 is, for example, 3.24 eV to 3.7 eV. In order to change the Eg of the i-type MgZnO layer 26 to such an Eg, the Mg mixed crystal ratio (x) in the i-type MgZnO layer 26 may be set to 0 (%) to 25 (%). The layer thickness of the i-type MgZnO layer 26 is preferably 300 nm to 1000 nm. Other physical properties (nitrogen doping concentration) of the i-type MgZnO layer 26 are the same as those of the n-type MgZnO layer 3 described above.

The n-type MgZnO layer 25 is formed on one surface 26a of the i-type MgZnO layer 26, and similar to the above-described n-type MgZnO layer 3, Mg _y Zn _y-1 O in which Mg is contained in ZnO (however, 0 ≦ y ≦ 1) composed of mixed crystal. The layer thickness of the n-type MgZnO layer 25 is preferably 100 nm to 3000 nm. The n-type MgZnO layer 25 is not doped with nitrogen.

The p-type MgZnO layer 27 is formed on the other surface 26b opposite to the one surface 26a of the i-type MgZnO layer 26. Similar to the n-type MgZnO layer 3 described above, Mg _z Zn containing Mg in ZnO is formed. _It consists of _z-1 O (however, 0 <= z <= 1) mixed crystal. The layer thickness of the p-type MgZnO layer 27 is preferably 100 nm to 3000 nm. Note that the p-type MgZnO layer 27 is not doped with nitrogen.

  The n-type MgZnO layer 25 and / or the p-type MgZnO layer 27 preferably has a larger band gap than the i-type MgZnO layer 26. For example, the band gap (Eg) of the n-type MgZnO layer 25 and / or the p-type MgZnO layer 27 is preferably 3.3 eV to 3.9 eV. In this embodiment, Eg of the p-type MgZnO layer 27 is 3.3 eV to 3.9 eV. In order to set the Eg of the p-type MgZnO layer 27 to an Eg in this range, the Mg mixed crystal ratio (z) in the p-type MgZnO layer 27 may be set to 3 (%) to 30 (%). Note that Eg of the n-type MgZnO layer 25 may be the same as that of the p-type MgZnO layer 27 or may be the same as that of the i-type MgZnO layer 26. In the case where the p-type MgZnO layer 27 is made the same, the Mg mixed crystal ratio (y) may be set to 3 (%) to 30 (%).

  Light that can be absorbed by the p-type MgZnO layer 27 having a band gap larger than that of the i-type MgZnO layer 26 using the formula (1) represented by Eg (eV) = 1240 / λ (nm) shown in the first embodiment. Is calculated to be smaller than the wavelength of light that can be absorbed by the i-type MgZnO layer 26. That is, light having a wavelength that can be absorbed by the i-type MgZnO layer 26 is not absorbed by the p-type MgZnO layer 27. Therefore, the light incident on the surface of the p-type MgZnO layer 27 can surely reach the i-type MgZnO layer 26.

  An ohmic electrode 28 is ohmically joined to the surface of the p-type MgZnO layer 27 so that the surface of the p-type MgZnO layer 27 is exposed. By exposing the surface of the p-type MgZnO layer 27, external light can pass through the p-type MgZnO layer 27 from the exposed surface and reliably reach the i-type MgZnO layer 26. On the other hand, an ohmic electrode 29 is ohmically joined to the surface of the n-type MgZnO layer 25 so as to cover substantially the entire surface. The ohmic electrode 28 is made of, for example, a metal material selected from platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), and rhodium (Rh). On the other hand, the ohmic electrode 29 is made of the same metal material as that of the ohmic electrode 4 described above.

  Next, a method for manufacturing the PIN diode 37 will be described. To manufacture the PIN diode 37, first, for example, using the MBE growth apparatus 5 shown in FIG. 2, for example, an n-type MgZnO layer 25 (without nitrogen irradiation) on a ZnO substrate (not shown), An i-type MgZnO layer 26 (with nitrogen irradiation) and a p-type MgZnO layer 27 (without nitrogen irradiation) are grown in this order. Thereby, the MgZnO laminated portion 46 is formed on the ZnO substrate.

After the MgZnO stacked portion 46 is formed, the entire ZnO substrate or a part thereof is removed. The removal of the ZnO substrate can be performed by an etching process, a CMP (chemical mechanical polishing) process, or the like. By removing the ZnO substrate, all or part of the surface of the n-type MgZnO layer 25 is exposed.
After that, as in the case of the photoconductive cell 1, an ohmic electrode is formed on the surface of the p-type MgZnO layer 27 by using a known sputtering apparatus or vapor deposition apparatus and by using a metal material film formation and a pattern formation technique using photolithography. 28 is formed, and an ohmic electrode 29 is formed on the exposed surface of the n-type MgZnO layer 25. In this way, the PIN diode 37 shown in FIG. 5 is obtained.
FIG. 6 is an illustrative sectional view for explaining a PIN diode 38 according to a fifth embodiment of the present invention. In FIG. 6, portions corresponding to the respective portions shown in FIG. 1 are denoted by the same reference numerals.

The PIN diode 38 includes a substrate 2 and an MgZnO stacked portion 47 (light receiving layer) grown on the substrate 2.
The MgZnO stacked portion 47 includes an n-type MgZnO layer 30, an i-type MgZnO layer 31 (light receiving region), and a p-type MgZnO layer 32, and these MgZnO layers are stacked in this order.

Regarding the physical properties (Eg, Mg mixed crystal ratio, nitrogen doping concentration, layer thickness) of the n-type MgZnO layer 30, the i-type MgZnO layer 31, and the p-type MgZnO layer 32, the n-type MgZnO layer 25, i described above, respectively. This is the same as the type MgZnO layer 26 and the p-type MgZnO layer 27.
Further, the MgZnO laminated portion 46 is etched in a direction crossing the laminated interface from the p-type MgZnO layer 32 to the depth at which the n-type MgZnO layer 30 is exposed through the i-type MgZnO layer 31 so as to have a substantially rectangular cross section. Yes. The ohmic electrode 34 is in ohmic contact with the exposed exposed surface 30 a of the n-type MgZnO layer 30. On the other hand, an ohmic electrode 33 is ohmically joined to the surface of the p-type MgZnO layer 32. The ohmic electrode 33 is made of, for example, a metal material selected from platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), and rhodium (Rh). On the other hand, the ohmic electrodes 34 are each made of the same metal material as that of the ohmic electrode 4 described above.

  In order to manufacture the PIN diode 38, first, for example, the MBE growth apparatus 5 shown in FIG. 2 is used to form an n-type MgZnO layer 25 (without nitrogen irradiation), an i-type MgZnO layer on the substrate 2. 26 (with nitrogen irradiation) and p-type MgZnO layer 27 (without nitrogen irradiation) are grown in this order. Thereby, the MgZnO laminated portion 47 is formed on the sapphire substrate.

After the MgZnO stacked portion 47 is formed, the n-type MgZnO layer 30 is etched from the p-type MgZnO layer 32 through the i-type MgZnO layer 31 to the middle thickness of the n-type MgZnO layer 30. The exposed surface 30a is exposed.
Thereafter, as in the case of the photoconductive cell 1, the ohmic electrode 33 is formed on the surface of the p-type MgZnO layer 32 by using a known sputtering apparatus or vapor deposition apparatus to form a metal material and patterning using photolithography. The ohmic electrode 34 is formed on the exposed surface 30 a of the n-type MgZnO layer 30. In this way, the PIN diode 38 shown in FIG. 6 is obtained. As described above, according to the fourth and fifth embodiments, the i-type MgZnO layer 26 and the i-type MgZnO layer 31 are doped with nitrogen. Therefore, it is possible to reduce the dark current in the PIN diode 37 and the PIN diode 38 and to suppress a decrease in response speed. Also in the fifth embodiment, a buffer layer made of a ZnO-based compound may be formed between the substrate 2 and the n-type MgZnO layer 30 as in the first embodiment. In the fourth and fifth embodiments, the MgZnO layer sandwiched between the n-type MgZnO layer 25 (n-type MgZnO layer 30) and the p-type MgZnO layer 27 (p-type MgZnO layer 32) may not be i-type. For example, the n-type MgZnO layer 25 (n-type MgZnO layer 30) may be a high-resistance n-type having a lower dopant concentration.
Although a plurality of embodiments of the present invention have been described above, the above-described photoconductive cell 1, Schottky diodes 35 and 36, and PIN diodes 37 and 38 are, for example, ultraviolet rays excellent in simplicity and having high radiation resistance. It can be applied as a monitor.

  Further, the present invention is not limited to the above-described embodiment, and various design changes can be made within the scope of matters described in the claims.

Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example.
Example 1
A sapphire substrate was held on a substrate holder in the MBE growth apparatus having the configuration shown in FIG. 2, and an n-type MgZnO layer of conductivity type was grown on the sapphire substrate under the growth conditions shown below. Next, two ohmic electrodes were formed on the surface of the n-type MgZnO layer by sputtering. As a result, a photoconductive cell including an n-type MgZnO layer doped with nitrogen (Mg mixed crystal ratio: 30 (%), layer thickness: 1000 nm, nitrogen doping concentration: 1 × 10 ¹⁹ cm ⁻³ ) was obtained.
(Growth conditions for n-type MgZnO layer)
Wafer temperature: 750 ° C.
O plasma irradiation condition: power 300 W, O ₂ supply flow rate to RF cell 0.5 sccm
N plasma irradiation condition: power 300 W, N ₂ supply flow rate to RF cell 0.5 sccm
Zn irradiation conditions: 10 ⁻⁵ Pa
Mg irradiation conditions: 10 ⁻⁶ Pa
Comparative Example 1
A photoconductive cell comprising an n-type MgZnO layer was produced by the same method as in Example 1. However, when growing the n-type MgZnO layer, the sapphire substrate was not irradiated with nitrogen (N). Thus, a photoconductive cell including an n-type MgZnO layer (Mg mixed crystal ratio: 30 (%), layer thickness: 1000 nm) not doped with nitrogen was obtained.

Measurement of photoresponse speed A voltage of 3 V was applied between the ohmic electrodes of the photoconductive cells obtained in Example 1 and Comparative Example 1. In this applied voltage state, each photoconductive cell was irradiated with light having a wavelength of 300 nm for 5 seconds, and then the irradiation was stopped. FIG. 7 shows changes with time in the photocurrent value output when light is irradiated. In FIG. 7, T1 indicates the rise time until the photocurrent value of Example 1 increases from 10% to 95% of the maximum value A1. T2 represents the fall time until the photocurrent value in Example 1 drops from 100% to 10% of the maximum value A1. T3 indicates the rise time until the photocurrent value in Comparative Example 1 increases from 10% to 95% of the maximum value A2. T4 represents the fall time until the photocurrent value of Comparative Example 1 drops from 100% to 10% of the maximum value A2.

  In FIG. 7, in Example 1, T1 is 1 s and T2 is 6 s. On the other hand, in Comparative Example 1, T3 is 2 s and T4 is 18 s. Accordingly, the photoconductive cell of Example 1 including the n-type MgZnO layer doped with nitrogen has a response speed to light as compared with the photoconductive cell of Comparative Example 1 including the n-type MgZnO layer not doped with nitrogen. Was confirmed to be fast.

1 is a schematic cross-sectional view for explaining a photoconductive cell according to a first embodiment of the present invention. It is an illustration figure for demonstrating the structure of the molecular epitaxial (MBE) growth apparatus for forming an n-type MgZnO layer. It is an illustrative sectional view for explaining a Schottky diode according to a second embodiment of the present invention. It is an illustration sectional view for explaining a Schottky diode concerning a 3rd embodiment of this invention. FIG. 6 is a schematic sectional view for explaining a PIN diode according to a fourth embodiment of the present invention. FIG. 10 is an illustrative sectional view for explaining a PIN diode according to a fifth embodiment of the present invention. 6 is a graph showing changes in photocurrent with time in the photoconductive cells of Example 1 and Comparative Example 1.

Explanation of symbols

1 Photoconductive cell 3 n-type MgZnO layer 4 ohmic electrode 17 n-type MgZnO layer 18 ohmic electrode 19 Schottky electrode 20 depletion layer 21 n-type MgZnO layer 22 n-type MgZnO layer 23 Schottky electrode 24 ohmic electrode 25 n-type MgZnO layer 26 i-type MgZnO layer 27 p-type MgZnO layer 28 ohmic electrode 29 ohmic electrode 30 n-type MgZnO layer 31 i-type MgZnO layer 32 p-type MgZnO layer 33 ohmic electrode 34 ohmic electrode 35 Schottky diode 36 Schottky diode 37 PIN diode 38 PIN diode 40 MgZnO laminated portion 41 Ohmic electrode 42 Ohmic electrode 46 MgZnO laminated portion 47 MgZnO laminated portion 48 Depletion layer

Claims (4)

A substrate,
Formed on the substrate, made of n-type Mg _x Zn _1-x O (where 0 ≦ x ≦ 1), and doped with nitrogen at a concentration of 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ A light receiving layer in which a light receiving region and a region not doped with nitrogen other than the light receiving region are selectively formed ;
A Schottky electrode that is Schottky joined to the light receiving region of the light receiving layer;
An oxide semiconductor light receiving element including an ohmic electrode that is ohmic-bonded to a region other than the light receiving region of the light receiving layer . The light receiving layer is formed as a lower layer not doped with nitrogen, and the light receiving region formed on the lower layer and doped with nitrogen at a concentration of 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ . And is etched in a direction across the lamination interface from the upper layer to a depth at which the surface of the lower layer is exposed as an exposed surface,
The Schottky electrode is Schottky bonded to the surface of the upper layer,
The oxide semiconductor light receiving element according to claim 1, wherein the ohmic electrode is in ohmic contact with the exposed surface of the lower layer . a light-receiving layer made of i-type Mg _x Zn _1-x O (where 0 ≦ x ≦ 1) and doped with nitrogen at a concentration of 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ ;
A p-type oxide semiconductor layer made of ZnO-based compound semiconductor not doped with nitrogen , formed on one surface side of the light-receiving layer;
Wherein the said one surface side of the light-receiving layer formed on the other surface side opposite to the n-type oxide semiconductor layer and the including stacked unit nitrogen is made of ZnO based compound semiconductor which is not doped,
And the p-side electrode joined before Symbol p-type oxide semiconductor layer,
And a n-side electrode which is joined to the n-type oxide semiconductor layer,
At least one of the p-type oxide semiconductor layer and the n-type oxide semiconductor layer, a band gap larger than the light receiving layer, oxides semiconductor photodetector.   A substrate supporting the stacked portion so as to be in contact with the n-type oxide semiconductor layer;
  The stacked portion is etched in a direction crossing the stacked interface from the p-type oxide semiconductor layer to a depth that penetrates the light receiving layer and exposes a surface of the n-type oxide semiconductor layer as an exposed surface,
  The p-side electrode is in ohmic contact with the surface of the p-type oxide semiconductor layer,
  The oxide semiconductor light receiving element according to claim 3, wherein the n-side electrode is in ohmic contact with the exposed surface of the n-type oxide semiconductor layer.

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