JP2002231996A - Ultraviolet light emitting diamond device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diamond pn junction diode and a pin junction diode capable of emitting ultraviolet light. SOLUTION: An ohmic electrode is formed on a boron-doped p-type semiconductor diamond thin film (p-type layer) or an electroconductive substrate brought into contact with the thin film. A phosphorus-doped n-type semiconductor diamond thin film (n-type film) is formed directly or via an undoped diamond thin film on the surface of the p-type layer without being brought into contact with the ohmic electrode. An ohmic electrode is formed on the surface of the n-type layer without contacting the p-layer or the ohmic electrode formed on the p-layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultraviolet light emitting device having a pn junction or a pin junction formed of diamond.

[0002]

2. Description of the Related Art Diamond can be synthesized by a high-temperature and high-pressure method or a vapor-phase method. In the high-temperature and high-pressure method, bulk single-crystal diamond used as particles or substrate material is formed, and in a gas-phase method, thin-film diamond is formed. It is possible (Koizumi
Satoshi, Nao Inuzuka: New functional thin film (Japan Society for Materials Science), p1
80 (1999) Shokabo, S. Matumoto, et.al., Jpn. J. App
l.Phys., 21 L183 (1982).).

With respect to the synthesis of semiconductor diamond, a boron-doped p-type layer semiconductor diamond can be produced by a high-temperature high-pressure method, and a boron-doped p-type semiconductor diamond can be produced by a vapor-phase method.
Type semiconductor diamond thin film (Japanese Patent Laid-Open No. 59-13739)
6) and phosphorus-doped n-type semiconductor diamond thin film
(S. Koizumi, et.al., Appl.Phys. Lett, 71, 1065 (199
7). Production of JP-A-8-9690301) is possible.

In the vapor phase method, it is possible to obtain high crystal perfection in the production of an undoped insulating diamond thin film, a boron-doped p-type semiconductor diamond thin film and a phosphorus-doped n-type semiconductor diamond thin film.
At low and high temperatures, cathodoluminescence and photoluminescence have made it possible to fabricate thin films in which exciton recombination emission is observed (H. Sternschulte,
et. al., Proc. Mat. Res. Soc., 423, 693 (1996).).

[0005] A phosphorus-doped n-type semiconductor diamond thin film can be grown only on the {111} crystal plane, and does not grow on the {100} crystal plane, which is one of the stable free-form planes of vapor-grown diamond, or is doped with phosphorus. Is extremely inefficient, and it is extremely difficult to obtain a thin film showing electrical conductivity (S. Koizumi, et.al., presented at Diamond 2000
international conference, 2-7 September 2000, Port
o.).

An ohmic electrode can be formed on a boron-doped p-type semiconductor diamond thin film by vacuum deposition of a titanium (Ti) thin film. Good ohmic characteristics can be obtained by heat treatment at about 400 ° C. Usually, a gold evaporated film is formed as a protective film after forming a titanium thin film (S. Yamanak
a: Doctoral thesis, Faculty of Material Science, Un
ivercity of Tsukuba, Tsukuba, 1999.).

An ohmic electrode can be formed on a phosphorus-doped n-type semiconductor diamond thin film by ion irradiation. For example, gallium (Ga) ion beam 30k
By using eV and introducing defects to such an extent that the diamond surface has a graphitic carbon-like electronic structure, relatively good ohmic conduction can be obtained. The ion species is not limited to Ga, but may be argon (Ar), carbon (C), phosphorus (P), or the like (T. Teraji, et. Al., Appl. Phys. Lett, 76, 1303).
(2000). JP-A-11-249910).

Heteroepitaxial growth of diamond has been achieved by cubic boron nitride (cBN) (S. Koizumi, et. Al., A
ppl. Phys. Lett, 57, 563 (1990).), iridium (I
r) (K. Ohtsuka, et. al., Jpn. J. Appl. Phys. 35,
L1072 (1996).), Nickel (Ni) (Y. Sato, et. Al.,
Proc 2nd Int. Conf.New Diamond Sci. Technol, p37
1, Materials Research Society, Pittsburgh (199
1).), Platinum (Pt) (T. Tachibana, et. Al., Diamond
Relat. Mater., 5, 197 (1996).), Silicon carbide (Si
C) (BR Stoner, et. Al., Appl. Phys. Lett., 60,
698 (1992).), Silicon (Si) (X. Jiang, et. Al., A
ppl. Phys. Lett., 62, 3438 (1993)).

Incidentally, a polycrystalline diamond thin film generally grows on the surface of the non-diamond substrate other than the above. In the growth of a polycrystalline diamond thin film, the crystal self-form plane finally appearing on the surface can be controlled by controlling the growth conditions. For example, in a chemical vapor deposition method (CVD method) using microwave plasma, in order to make the {111} crystal plane dominant, the carbon source gas concentration in the source gas is reduced,
Diamond growth may be performed at a relatively low temperature of about 800 to 850 ° C. (M. Rosler et. Al., 2nd Int. Con.
f. Appl. Diamondo Films Relat. Mater., p.691, MYU,
Tokyo (1993).).

On the other hand, a pn junction of diamond was formed by epitaxially forming a laminated film of a polycrystalline phosphorus-doped diamond thin film and a polycrystalline boron-doped diamond thin film (conventional example 1), and a single crystal nitrogen-doped diamond and the surface thereof. Boron-doped p-type semiconductor diamond thin film (conventional example 2) (A. Aleksov et. Al., Proc. ADC
/ PCT'99, Edited by M. Yoshikawa, et.al., p.138, T
sukuba, (1999).) is known.

[0011]

However, although a number of reports have been made as described above and studies have been made from various viewpoints, the conventional technique has not been applied to a diamond film pn junction structure. There is a problem that ultraviolet light cannot be obtained. An object of the present invention is to solve such a problem.

[0012]

According to the present invention, there is provided an ultraviolet light emitting device in which a pn junction is formed in a laminated thin film of a phosphorus-doped n-type semiconductor diamond thin film and a boron-doped p-type semiconductor thin film. I do.

Another object of the present invention is to provide an ultraviolet light emitting device having a pin junction structure of a laminated thin film in which an undoped diamond thin film is formed between an n-type semiconductor diamond thin film and a p-type semiconductor thin film.

In the present invention, ohmic electrodes are formed on the p-type semiconductor diamond thin film and the n-type semiconductor diamond thin film, respectively. A diode is forwardly applied between the electrodes, that is, a positive voltage is applied to the p-type layer, and an n-type electrode is applied. By applying a negative voltage to the layer and applying a current, an emission peak of 235 nm (5.27 eV) due to free exciton recombination of diamond and 260 n specific to boron and phosphorus-doped diamond are obtained.
m to 280 nm (approximately 4.5 eV to 4.6 eV)
To provide one or both of the broad emission bands having a peak at the peak.

The ultraviolet light emitting device of the present invention having such features will be described in detail based on the following embodiments.

[0016]

DETAILED DESCRIPTION OF THE INVENTION Diamond is 5.47 e at room temperature.
V with a wide bandgap, and vapor phase epitaxy (CVD
In the method, the diamond thin film synthesized by adding boron can be electrically controlled to a p-type semiconductor, and the diamond thin film synthesized by adding phosphorus can be electrically controlled to an n-type semiconductor. By strictly controlling the synthesis conditions, these semiconductor diamonds and undoped diamond thin films can suppress carrier recombination due to defect order, etc., and reach the level where band edge emission is observed in cathodoluminescence and photoluminescence spectrum measurement. Highly perfect crystal growth is possible.

Since diamond is an indirect transition type crystal, band edge emission is observed as exciton recombination emission. The free exciton recombination emission is 235 nm (5.27 eV) for undoped diamond, 238 nm (5.21 eV) for boron-doped diamond, and 239 nm (5.18 eV) for phosphorus-doped diamond. The light emission due to the recombination of the bound exciton is seen. The localization energy is 0.06 eV in the case of boron and 0.09 eV in the case of phosphorus. Even at boron and phosphorus-doped diamond, the binding is sufficiently released at room temperature and observed as free exciton recombination light emission.

Boron forms an acceptor level in the forbidden band of 0.37 eV from the top of the valence band in diamond. On the other hand, phosphorus forms a donor level in the forbidden band of 0.6 eV from the bottom of the conduction band in diamond.
When a pn junction is formed by a boron-doped p-type semiconductor diamond thin film and a phosphorus-doped n-type semiconductor thin film, the diffusion potential is at most several volts. In a forward operation state in which a positive voltage is applied to the p-type layer and a negative voltage is applied to the n-type layer, electrons that are main carriers in the n-type layer are injected as minority carriers into the p-type layer,
Holes, which are main carriers in the mold layer, are injected as minority carriers into the n-type layer. Accordingly, light emission can be obtained at an operating voltage of about several volts in principle. In a pin structure in which an undoped layer is sandwiched between p-type and n-type semiconductor layers, the operating voltage is increased by the action of the i-layer.

When the pn-junction and pin-junction diodes are operated at room temperature, the bound excitons are released from binding due to lattice vibration at about room temperature, and the resulting light emission is recombination light emission of free excitons. This is consistent with cathodoluminescence and photoluminescence spectroscopy from undoped, boron-doped and phosphorus-doped layers with high crystal integrity at room temperature. When the crystallinity is slightly inferior, the characteristic range of the boron-doped diamond thin film and the phosphorus-doped diamond thin film from 260 nm to 280
A broad ultraviolet emission band with a peak at nm (and 4.5 eV to 4.6 eV) is also observed.

From the above, in this application,
The boron concentration of the p-type layer is 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰
Room temperature mobility of 50 cm ² / V · se at a concentration of less than cm ^-3
c or more and the phosphorus concentration of the n-type layer is 1 × 10 ¹⁶ cm ⁻³ or ^more1
Room temperature mobility of 10 cm ² / at a concentration of × 10 ²⁰ cm ^-3 or less
At V · sec or more, in cathodoluminescence or photoluminescence, light emission due to recombination of a free exciton, a bound exciton bound to boron, or a bound exciton bound to phosphorus from any layer is 10 or more.
There is provided a diamond ultraviolet light emitting device comprising a diamond thin film observed at a low temperature of 0K level or at room temperature.

Further, there is provided a diamond ultraviolet light emitting device characterized in that the p-type layer is formed on the surface of a single crystal diamond {111} having electrical conductivity.
By using a diamond single crystal with electrical conductivity for the substrate, a diamond thin film with relatively excellent crystal perfection can be obtained, and it can be operated by applying current in the lamination direction, so that stable operation at low voltage is possible. Become.

In this case, for example, the ohmic electrode for the p-type layer is formed on the back surface (p
Current is supplied through a diamond substrate having electrical conductivity to the p-type layer, and is formed on the surface of the n-type layer without contacting the p-type layer and the diamond substrate. 2. The ultraviolet light emitting pn junction or pin junction diode according to claim 1, wherein the diode operates by being energized through an ohmic electrode.

The p-type layer is an insulating diamond single crystal # 1
An ultraviolet light emitting device characterized by being formed on the 11 ° surface can also be provided.

By using an insulating diamond substrate,
A more complete boron-doped, phosphorus-doped, and undoped diamond thin film can be formed, and the diode has an excellent rectification ratio. In addition, light emission due to crystal defects is reduced, and exciton recombination light emission, which is band-edge light emission, is observed with higher intensity.

In this case, for example, an operation is performed by forming an ohmic electrode for the p-type layer without contacting the n-type layer, and applying a current through the ohmic electrode formed on the surface of the n-type layer without contacting the p-type layer. In this way, a pn junction or pin junction diamond that emits ultraviolet light can be realized.

For example, cubic boron nitride (cBN), iridium (Ir), nickel (Ni), platinum (Pt),
A {111} crystal substrate of silicon carbide (SiC) or silicon (Si) is used, and a diamond thin film is heteroepitaxially grown on the surface thereof. Since a diamond film with high integrity is formed, it is possible to manufacture an element which is less expensive than a diamond substrate.

In this case, an ohmic electrode for the p-type layer is formed on the back surface of the substrate (the surface on which the p-type layer is not formed), current is supplied to the p-type layer through the substrate, and n
An ultraviolet light-emitting pn junction and a pin, which are operated by passing an electric current through an ohmic electrode formed on the surface of the mold layer without contacting the p-type layer and the diamond substrate.
A junction diode is realized, for example.

Furthermore, in the present invention, the p-type layer is grown as a polycrystalline thin film having a {111} crystal plane predominantly precipitated on the substrate surface other than diamond, and a phosphorus-doped diamond thin film grown only on the {111} surface. Taking advantage of the properties, the n-type layer is directly or the p-type layer {111}
An ultraviolet light emitting element characterized in that a structure in which a pn or pin junction is formed only on a crystal plane is automatically and exclusively formed. A cheaper element can be manufactured.

For example, an ohmic electrode for the p-type layer is formed on the back surface of the substrate (the surface on which the p-type layer is not formed),
A current is supplied to the p-type layer through the substrate, and operation is performed by applying current through an ohmic electrode formed on the surface of the n-type layer without contacting the p-type layer and the diamond substrate. Junction and pin junction diodes are realized.

An embodiment will be described below and will be described in more detail. Of course, the present invention is not limited by the following examples.

[0031]

FIG. 1 is a sectional view showing an ultraviolet light emitting diode according to a first embodiment of the present invention. Microwave plasma C on the {111} surface of high-pressure synthetic single-crystal substrate diamond (1) with boron conductivity
VD boron-doped diamond thin film (p-type layer)
(2) was formed to a thickness of 2 μm, and a phosphorus-doped diamond thin film (n-type layer) (3) was formed to a thickness of 1 μm on the surface thereof by microwave plasma CVD to obtain a laminated film sample. The outer shape of the substrate is 2 mm × 2 mm and the thickness is 0.5 mm. Table 1 summarizes the synthesis conditions for each layer. The laminated film sample was oxidized to remove hydrogen adsorbed on the surface.

The acceptor density of the p-type layer is 1-2 × 10
¹⁷ cm ^-3 , hole mobility about 100 cm ² / V · s at room temperature
ec. The donor density of the n-type layer is 5 to 8 × 10 ¹⁸ cm.
^-3 , the electron mobility is about 50 cm ² / V · sec at room temperature. On the back surface of the electrically conductive diamond, which is a substrate, titanium was deposited at 400 ° C. by electron beam evaporation to form a 100 nm film, and then a 100 nm gold film was formed as a protective film to form an ohmic electrode (4). Argon ions (Ar +) are implanted into the n-type layer at a dose of 1 × 10 ¹⁶ cm ⁻² at 40 keV according to an electrode forming technique by ion implantation, and an Au / Ti electrode is formed on the surface in the same manner as described above. Ohmic electrode (5)
And

FIG. 2 shows the voltage-current characteristics of the ultraviolet light emitting diode according to the first embodiment. The diode shows a clear current increase at positive voltage, which is the forward direction, and the rectification ratio is ± 10
In V, the reverse current was about 3 digits, and the reverse current was about 2 nA.
Light emission was observed from a forward current of about 0.5 mA and an operating voltage of about 25 V. As for the emission, broad band emission having a peak at about 275 nm was observed.

[0034]

[Table 1]

Example 2 A similar element was formed with the n-type layer shown in the first example having a thickness of 500 nm. The rectification ratio of diamond was 4 digits or more at ± 20V. Emission is also clearly observed from about 0.5 mA,
The operating voltage at that time was about 20V.

<Embodiment 3> FIG. 3 is a sectional view showing an ultraviolet light emitting diode according to a third embodiment of the present invention. First
This embodiment differs from the embodiment in that an undoped diamond thin film (i-layer) (6) is formed between the p-type layer and the n-type layer. The thickness of the i-layer is about 50 nm. Other conditions are the same as in the first embodiment. FIG. 4 shows the emission characteristics of the ultraviolet light emitting diode. Operating voltage 27 at 1 mA
About V, about 29 V at 5 mA, about 35 V at 10 mA. As the current increases, the emission of free exciton recombination at 235 nm increases in intensity. At 10 mA, it exceeds the ultraviolet band emission intensity and is observed at about 1/7 the intensity of the visible band emission associated with other crystal defects. Is done.

Embodiment 4 FIG. 5 is a sectional view showing an ultraviolet light emitting diode according to a fourth embodiment of the present invention. First
The difference from the third embodiment is that an insulating diamond substrate 7 is used as a base. Further, the use of an insulating substrate is different in that the electrode 4 to the p-type layer 2 is formed by partially removing the n-type layer by reactive ion etching. Other conditions are the same as in the first embodiment.
In this structure, light emission is observed at an operating voltage of about 30 V or more, and ultraviolet light emission not including light emission in the visible light region is observed. FIG. 6 is a graph showing a semi-logarithmic plot of the voltage-current characteristics of the ultraviolet light emitting diode according to the fourth embodiment.
The rectification ratio of the diode is about 9 digits at ± 10V.
The reverse current at 10 V was 1 pA or less.

<Embodiment 5> FIG. 7 is a sectional view showing an ultraviolet light emitting diode according to a fifth embodiment of the present invention. First
This embodiment differs from the embodiment in that an iridium epitaxial thin film 8 is used as a base. As the iridium thin film, a thin film of silicon carbide, strontium titanate, sapphire, magnesium oxide, diamond, or the like, which is epitaxially grown on the surface of a single crystal substrate 9 having a high melting point is used. Another difference is that the electrode 4 for the p-type layer 2 is formed on the iridium surface by partially removing the p-type layer and the n-type layer by reactive ion etching. Other conditions are the first
This is the same as the embodiment. In this structure, the operating voltage 1
Light emission is observed at about 5 V or more, and emission in the strong visible light region and ultraviolet band emission at 275 nm are observed.

<Embodiment 6> FIG. 8 is a sectional view showing an ultraviolet light emitting diode according to a sixth embodiment of the present invention. First
The difference from the first embodiment is that silicon 10 is used as a base. The difference is that the p-type layer is formed as a polycrystalline thin film on the silicon surface, and the n-type layer is epitaxially grown on the polycrystalline p-type layer surface. The p-type layer is a polycrystalline thin film having many [111] automorphic planes. n-type layer is polycrystalline
Since it grows only on the [111] crystal surface of the p-type layer, it is formed discontinuously on the surface of the p-type layer in the initial stage of growth, but is formed as a continuous n-type layer as the growth proceeds. Other conditions are the same as in the first embodiment. In this structure, light emission is observed at an operating voltage of about 10 V or more, and blue-violet light emission (band A light emission) having a center wavelength of 450 nm is observed.

[0040]

As described above in detail, according to the present invention, an ultraviolet light emitting diode utilizing the characteristics of diamond having a wide band gap is realized, and it is possible to operate with low power and efficiently obtain ultraviolet light. Further, a junction structure of n-type and p-type semiconductor diamond thin films having excellent crystal integrity can be realized in an ideal form.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a device configuration of a first embodiment.

FIG. 2 is a diagram illustrating a voltage-current characteristic of the first embodiment.

FIG. 3 is a cross-sectional view illustrating the element configuration of a third embodiment.

FIG. 4 is a diagram showing an emission spectrum of the third embodiment.

FIG. 5 is a cross-sectional view (when an insulating diamond substrate is used) showing a diamond ultraviolet light emitting pn diode of a fourth embodiment.

FIG. 6 is a semilogarithmic plot of the voltage-current characteristics of a diamond ultraviolet light emitting pn diode formed on an insulating diamond substrate according to a fourth embodiment.

FIG. 7 is a sectional view showing a diamond ultraviolet light emitting pn diode according to a fifth embodiment (in the case of a pn junction heteroepitaxially grown on the surface of iridium).

FIG. 8 is a sectional view showing a diamond ultraviolet light emitting pn diode according to a sixth embodiment (when a polycrystalline diamond pn layer formed on a silicon substrate is used).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single crystal substrate diamond 2 Boron-doped diamond thin film (p-type layer) 3 Phosphorus-doped diamond thin film (n-type layer) 4, 5 Ohmic electrode 6 Undoped diamond thin film (i-layer) 7 Insulating diamond substrate 8 Iridium epitaxial thin film 9 High melting point Single crystal substrate 10 silicon substrate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F041 AA04 AA11 CA02 CA33 CA49 CA57 CA64 CA71 CA82 5F045 AA09 AB07 AC07 AD13 AE25 AF02 AF10 CA10 DA60

Claims (13)

[Claims] 1. A pn or pi layer in which a phosphorus-doped n-type semiconductor diamond thin film is laminated directly on the surface of a boron-doped p-type semiconductor diamond thin film (p-type layer) or an undoped diamond thin film (i-layer) as an n-type layer.
A diamond ultraviolet light-emitting device having an n-junction structure and emitting ultraviolet light when energized through ohmic electrodes formed on the surfaces of a p-type layer and an n-type layer. 2. The ultraviolet light emission has a broad emission band having an emission peak at 235 nm (5.27 eV) due to free exciton recombination of diamond and a peak from 260 nm to 280 nm unique to boron and phosphorus-doped diamond. The diamond ultraviolet light emitting device according to claim 1, wherein the device is obtained as one or both of the following. 3. The p-type layer has a boron concentration of 1 × 10¹⁶cm^-3
More than 1 × 10²⁰cm ^-3Room temperature mobility of 50c at the following concentrations
m^Two/ V · sec or more, the phosphorus concentration of the n-type layer is 1 × 10
¹⁶cm^-3More than 1 × 10²⁰cm^-3Room temperature mobility at the following concentrations
Is 10cm^Two/ V · sec or more, cathodoluminescence
Any layer in photoluminescence or photoluminescence
More free excitons or bound excitons bound to boron
Or due to recombination of bound excitons bound to phosphorus
Light emission at low or room temperature of 100K level
That it is composed of a diamond thin film
The diamond ultraviolet light-emitting device according to claim 1, wherein: 4. The diamond ultraviolet light emitting device according to claim 1, wherein the p-type layer is formed on a {111} diamond single crystal surface having electrical conductivity. 5. A diamond substrate having an electrical conductivity with respect to a p-type layer, wherein an ohmic electrode for the p-type layer is formed on a back surface of the diamond substrate having no electrical conductivity (a surface on which the p-type layer is not formed). 5. The diamond ultraviolet light emitting device according to claim 4, wherein a current is supplied through the p-type layer and an ohmic electrode formed on the surface of the n-type layer without being in contact with the diamond substrate. . 6. The diamond ultraviolet light-emitting device according to claim 1, wherein the p-type layer is formed on an insulating diamond single crystal {111} surface. 7. An operation in which an ohmic electrode for a p-type layer is formed without contacting an n-type layer, and operation is performed by passing a current through the ohmic electrode formed on the surface of the n-type layer without contacting the p-type layer. The diamond ultraviolet light emitting device according to claim 6, wherein: 8. The p-type layer is cubic boron nitride (cBN),
Iridium (Ir), Nickel (Ni), Platinum (P
t), silicon carbide (SiC), or silicon (S
2. The diamond ultraviolet light emitting device according to claim 1, wherein the diamond ultraviolet light emitting device is heteroepitaxially grown on the surface of the {111} crystal substrate of i). 9. An ohmic electrode for the p-type layer is formed on the back surface of the substrate (the surface on which the p-type layer is not formed), current is supplied to the p-type layer through the substrate, and p-type 9. The diamond ultraviolet light emitting device according to claim 8, wherein the device is operated by applying a current through an ohmic electrode formed without contacting the mold layer and the diamond substrate. 10. The p-type layer grows as a polycrystalline thin film in which {111} crystal planes are predominantly deposited on the surface of the substrate other than diamond, and the n-type layer is formed directly or with the i-layer interposed therebetween. 2. The diamond ultraviolet light emitting device according to claim 1, wherein a junction is formed by selectively growing only on the {111} crystal plane. 11. An ohmic electrode for the p-type layer is formed on the back surface of the substrate (the surface on which the p-type layer is not formed), current is supplied to the p-type layer through the substrate, and p-type 11. The diamond ultraviolet light emitting device according to claim 10, wherein the device is operated by energizing through an ohmic electrode formed without contacting the mold layer and the diamond substrate. 12. The diamond ultraviolet light emitting device according to claim 5, wherein the rectification ratio of the forward current and the reverse current of the pn junction or the pin junction of the pn junction or the pin junction is three digits or more at forward and reverse 20 V. . 13. A pn-junction or pin-junction diode made of diamond, which is capable of emitting ultraviolet light as an ultraviolet light-emitting element according to any one of claims 1 to 12.