JP2004289014A - p-TYPE ACTIVATION METHOD OF GaN BASED COMPOUND SEMICONDUCTOR - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a p-type activation method capable of converting a GaN based compound semiconductor into a low resistance p-type semiconductor by low temperature or short time annealing even if hydrogen is contained substantially in an annealing atmosphere. <P>SOLUTION: A GaN based compound semiconductor 7 implanted with p-type impurities is formed and after a hydrogen absorbable/permeable film 10 having an action for absorbing hydrogen in the GaN based compound semiconductor 7 and discharging it to the outside is formed on the surface thereof, the GaN based compound semiconductor 7 is annealed. Consequently, hydrogens bonding to p-type impurities implanted into the GaN based compound semiconductor 7 are released thus effecting p-type activation of the GaN based compound semiconductor 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a GaN-based compound semiconductor used for a light-receiving element such as an ultraviolet sensor, or a light-emitting element such as an ultraviolet or blue light-emitting laser diode or an ultraviolet or blue light-emitting diode. The present invention relates to a method for p-type activation of an implanted GaN-based compound semiconductor with low resistance.
[0002]
[Prior art]
GaN-based compound semiconductor (general _{formula: Al x Ga y In 1-} x-y N) has an energy band structure of the direct transition type wide band the band gap energy spans 1.9eV~6.2eV at room temperature Because of the gap, it can be widely applied as a light-emitting diode, a laser diode, and a light-receiving element such as an ultraviolet sensor covering the ultraviolet region to the visible light region.
[0003]
BACKGROUND ART Conventionally, compound semiconductor elements having various element structures have been manufactured by laminating semiconductor layers such as a p-type semiconductor, an n-type semiconductor, and an i-type semiconductor. For example, in a light receiving element including a p-type Al _x Ga _1-x N layer (0 ≦ x ≦ 1), each semiconductor layer is arranged in the order of PN, NP, PIN, NIP, PNP, PINP, NPN, NPIN and the like from the substrate side. Are stacked to form a diode structure or a transistor structure, and a current generated in a light receiving region formed in the i-type semiconductor layer or the PN junction layer of the structure is detected from electrodes provided in the p-type semiconductor and the n-type semiconductor. Some are configured to be possible. Here, the p-type semiconductor and the n-type semiconductor are formed by implanting a p-type impurity and an n-type impurity, respectively, to configure the various element structures described above. By making the p-type and n-type in the type semiconductor layer sufficiently, that is, lowering the resistance sufficiently, a good electrical connection with the electrode material is enabled, and the parasitic resistance component in the element structure is reduced. The electric characteristics of the light receiving element can be improved.
[0004]
However, in a GaN-based compound semiconductor, NH ₃ is generally used as a nitrogen source during crystal growth. During the growth, the NH ₃ is decomposed into atomic hydrogen and stays in the GaN-based compound semiconductor. It is considered that the atomic hydrogen bonds to Mg or the like implanted as a p-type impurity, thereby inhibiting the p-type impurity from acting as an acceptor. The p-type is not always achieved, and sufficient device characteristics cannot be obtained with high resistance, and the device structure itself may not be formed.
[0005]
Therefore, for example, in the method of manufacturing a p-type gallium nitride-based compound semiconductor disclosed in Patent Document 1, after growing a GaN-based compound semiconductor into which a p-type impurity is implanted by a vapor phase growth method, the temperature is increased to 400 ° C. or more. Annealing is performed to activate the GaN-based compound semiconductor p-type, thereby producing a low-resistance p-type GaN-based compound semiconductor.
[0006]
[Patent Document 1]
Japanese Patent No. 2540791
[Problems to be solved by the invention]
However, in the method of manufacturing a p-type gallium nitride-based compound semiconductor disclosed in Patent Document 1, annealing at a temperature of 400 ° C. or more causes atomic hydrogen bonded in the GaN-based compound semiconductor to be p-type such as Mg. The impurities are separated and move to the GaN-based compound semiconductor surface. However, the atomic hydrogen separated from the p-type impurity is not released to the outside due to a potential barrier on the surface of the GaN-based compound semiconductor, but stays near the surface, and the separation in the GaN-based compound semiconductor is further increased. And the p-type activation may be saturated to some extent. Therefore, to further promote p-type activation, it is necessary to increase the annealing temperature. However, if the annealing temperature is too high, nitrogen is desorbed and the crystal is deteriorated, so that there is an upper limit of the annealing temperature. In the case of GaN, the temperature must be 900 ° C or lower, and when InGaN is included, the temperature must be set to 800 ° C or lower. In addition, when annealing is performed at a low temperature of 600 ° C. or less, it takes a long time to realize sufficient p-type activation, and 400 ° C. is a practical lower limit temperature.
[0008]
In addition, in the production method, it is necessary to perform annealing in an atmosphere containing substantially no hydrogen.For example, if annealing is performed by moving the annealing into another annealing apparatus or processing is performed in the same reaction chamber. It is necessary to remove NH ₃ and H ₂ (carrier gas), which are nitrogen materials of the p-type gallium nitride-based compound semiconductor, from the reaction chamber in advance. In the manufacturing process, the number of steps increases, which causes an increase in manufacturing cost.
[0009]
The present invention has been made in view of the above-described problems, and an object of the present invention is to solve the above-described problems and to perform a low-temperature or short-time annealing process even when hydrogen is substantially contained in an annealing atmosphere. Accordingly, an object of the present invention is to provide a p-type activation method that can convert a GaN-based compound semiconductor into a low-resistance p-type semiconductor.
[0010]
[Means for Solving the Problems]
In order to achieve this object, the first characteristic configuration of the p-type activation method for a GaN-based compound semiconductor according to the present invention is as follows. Forming a hydrogen-absorbing and permeable film having a function of absorbing and releasing hydrogen in a GaN-based compound semiconductor, and then annealing the GaN-based compound semiconductor in a reducing atmosphere to inject into the GaN-based compound semiconductor; Hydrogen bonded to the p-type impurity is desorbed to activate the GaN-based compound semiconductor p-type.
[0011]
According to the first characteristic configuration, the p-type activation is promoted, and the activation proceeds even in a low annealing temperature in a shorter time than in a case where there is no hydrogen absorption / permeable membrane. In other words, the hydrogen absorption and permeable film absorbs hydrogen atoms staying near the surface of the GaN-based compound semiconductor after being separated from the p-type impurities by annealing, and emits the hydrogen atoms to the outside. Is prevented from being saturated, and further activation is promoted without being hindered.
[0012]
Furthermore, by annealing in a reducing atmosphere, after annealing in an air or nitrogen atmosphere of an oxidizing atmosphere after the formation of the hydrogen-absorbing permeable film, the surface of the hydrogen-absorbing permeable film is at the atomic layer level due to the influence of oxygen or residual oxygen. It is possible to avoid deterioration of the performance of the hydrogen absorbing and permeable membrane due to oxidation or deterioration of the surface state.
[0013]
The second feature is that, in addition to the first feature, the hydrogen absorbing and permeable film has a catalytic action of absorbing atomic hydrogen in the GaN-based compound semiconductor and releasing it as hydrogen molecules to the outside. It is in.
[0014]
According to the second characteristic configuration, the chemical reaction that molecularizes the atomic hydrogen in the hydrogen absorption / permeable membrane is promoted by the catalytic action, and therefore, the action of absorbing and releasing hydrogen in the GaN-based compound semiconductor to the outside is achieved. The GaN compound semiconductor is preferably exhibited, and as a result, the p-type activation of the GaN-based compound semiconductor is promoted.
[0015]
The third feature is that, in addition to the first or second feature, the hydrogen absorption and transmission membrane is made of one or more substances selected from nickel, palladium, a silver-palladium alloy, platinum, and ruthenium. It is in.
[0016]
According to the third characteristic configuration, the hydrogen absorption and transmission film is formed of one or more substances selected from nickel, palladium, silver-palladium alloy, platinum, and ruthenium, and thus absorbs hydrogen in the GaN-based compound semiconductor. As a result, the p-type activation of the GaN-based compound semiconductor is promoted.
[0017]
The fourth characteristic configuration is that, in addition to the above-mentioned respective characteristic configurations, the processing temperature during the annealing is 400 ° C. or higher.
[0018]
Conventionally, it has been thought that 50% of Mg contributes at most to p-type activation even when p-type activation of GaN is performed in an atmosphere without hydrogen using Mg as a p-type impurity at an annealing temperature of 850 ° C. That is, when sufficient p-type activation could not be expected, the p-type activation of the GaN-based compound semiconductor according to the first characteristic configuration is sufficiently exhibited even when the annealing treatment temperature is 850 ° C. or less. If the processing time is prolonged even at 400 ° C. or lower, p-type activation can be expected. However, according to the fourth characteristic configuration, by setting the processing temperature to 400 ° C. or higher, the expected effect is more effectively exhibited. Will be.
[0019]
The fifth feature is that, in addition to the above features, the reducing atmosphere at the time of the annealing contains hydrogen.
[0020]
The sixth feature is that, in addition to the first to fourth features, the reducing atmosphere at the time of the annealing is made of hydrogen, nitrogen, argon, or a mixed gas thereof.
[0021]
According to the fifth or sixth characteristic configuration, the hydrogen molecules in the reducing atmosphere exert a cleaning action of preventing oxidation of the surface of the hydrogen absorbing and permeable film by a trace amount of oxygen equal to or lower than the equilibrium oxygen concentration in the reducing atmosphere, The function of the absorption / transmission film to absorb and release hydrogen in the GaN-based compound semiconductor to the outside is well maintained, and as a result, p-type activation of the GaN-based compound semiconductor is promoted.
[0022]
A seventh feature of the present invention is that, in addition to the above features, the reducing atmosphere at the time of the annealing is lower than the atmospheric pressure.
[0023]
An eighth characteristic configuration is that, in addition to the seventh characteristic configuration, the reducing atmosphere during the annealing is reduced to 4000 Pa (about 30 Torr) or less by a rotary pump alone.
[0024]
According to the seventh or eighth characteristic constitution, since the reducing atmosphere is under reduced pressure, the deterioration of the hydrogen absorbing and permeable membrane is suppressed, and the surface state is more favorably maintained, particularly at 4000 Pa (about 30 Torr) or less. The effect becomes more remarkable, and the p-type activation of the GaN-based compound semiconductor is promoted. Further, when another metal such as an electrode metal is deposited on the upper surface in a later step, a favorable surface condition is particularly suitable. In addition, by reducing the pressure only by the rotary pump, the pressure reduction processing time is short and the throughput is increased. Further, since the gas is drawn after the reducing gas is introduced, contamination by contaminants due to the pressure reduction processing can be prevented. Further, at atmospheric pressure, the replacement of the reducing gas is required, but this can be omitted.
[0025]
The ninth feature is that, in addition to the above features, after forming the GaN-based compound semiconductor into which the p-type impurity is implanted, only the hydrogen absorption and transmission film is formed on the surface thereof, In that the GaN-based compound semiconductor is annealed.
[0026]
For example, when a p-type electrode is formed by laminating a hydrogen absorption / transmission film and another metal film, if the other metal film is deposited first and then annealed, the function of absorbing hydrogen from the hydrogen absorption / transmission film and releasing it to the outside is provided. In the process of passing the hydrogen accumulated between the hydrogen absorbing and transmitting film and the other metal film through the metal film, a hole is opened in the metal film, resulting in deterioration of the quality of the metal film.
[0027]
Therefore, according to the ninth characteristic configuration, such a problem is effectively solved by a synergistic effect with annealing in a reducing atmosphere. It is particularly effective to anneal in a reduced-pressure reducing atmosphere containing hydrogen.
[0028]
The tenth characteristic configuration resides in that, in addition to the above-mentioned respective characteristic configurations, the hydrogen absorption / transmission film is used as an electrode or a part of an electrode.
[0029]
An eleventh characteristic configuration is that, in addition to the tenth characteristic configuration, the electrode is a p-type electrode.
[0030]
According to the tenth or eleventh characteristic configuration, when the hydrogen absorption / transmission film is used as an electrode as it is, or when the hydrogen absorption / transmission film is overlaid with an upper electrode metal such as gold, nickel, aluminum, and titanium to form an electrode. I can do it. In particular, since the hydrogen absorption / transmission film is in contact with the p-type semiconductor layer, if the electrode is a p-type electrode, an efficient electrode can be manufactured.
[0031]
A twelfth feature of the present invention is that, in addition to the above features, the hydrogen absorbing and transmitting film is formed by ion beam sputtering (IBS) or laser ablation.
[0032]
According to the twelfth characteristic configuration, a dense hydrogen absorption / transmission film can be formed, and the function of the hydrogen absorption / transmission film is improved, so that an improvement in annealing throughput can be expected, and p-type activation of the GaN-based compound semiconductor can be achieved. Is promoted.
[0033]
A thirteenth feature is that, in addition to the above features, the p-type impurity contains at least one of magnesium and beryllium.
[0034]
A fourteenth feature is that, in addition to the above features, the p-type impurity contains at least beryllium.
[0035]
According to the thirteenth or fourteenth feature, p-type activation of the GaN-based compound semiconductor according to the first feature is exhibited.
[0036]
Generally, when the acceptor level becomes deeper, the hole carrier density becomes lower even at the same impurity concentration, and the acceptor level becomes deeper as the AlN composition ratio (molar fraction) becomes higher. Therefore, when Mg is used as a p-type impurity, In the case of a GaN-based compound semiconductor having an AlN composition ratio of 20% or more, sufficient p-type activation (low resistance) was difficult.
[0037]
By the way, according to the fourteenth feature configuration, by using Be whose acceptor level is shallower than Mg at the same AlN composition ratio, it is sufficient for a GaN-based compound semiconductor having an AlN composition ratio of 20% or more. A good p-type activation is obtained. In addition, since the difference in electronegativity between hydrogen and Be is smaller than the difference in electronegativity between hydrogen and Mg, hydrogen and Be have lower bond ionicity than hydrogen and Mg. This is considered to be a result that separation is more easily promoted.
[0038]
The feature configuration of the GaN-based compound semiconductor device, the light receiving element, and the light-emitting element according to the present invention are p-type activated by the p-type activation method of the GaN-based compound semiconductor having the first to fourteenth feature configurations. The GaN compound semiconductor is provided.
[0039]
According to the above-described feature configuration, a semiconductor device having desired characteristics including the p-type GaN-based compound semiconductor activated by the p-type activation method of the GaN-based compound semiconductor according to the first to fourteenth feature configurations , A light-receiving element, or a light-emitting element can be manufactured.
[0040]
In particular, since the light receiving element has a light receiving region mainly composed of AlGaN having a band gap energy of 3.6 eV or more, light having an energy of 3.6 eV or more is absorbed, so that a wavelength of about 344 nm (3. Ultraviolet light having a wavelength of 6 eV) or less can be selectively detected by the light receiving region.
[0041]
Further, assuming that a light receiving region mainly composed of AlGaN having a band gap energy of 4.1 eV, 4.3 eV, or 4.6 eV or more is provided, the light receiving region has a light receiving region of 4.1 eV, 4.3 eV, or 4.3 eV, respectively. By absorbing light having an energy of 4.6 eV or more, a wavelength of about 300 nm (4.1 eV) or less, about 290 nm (4.3 eV) or less, or about 280 nm (4.6 eV) or less Ultraviolet light can be detected by the light receiving area.
[0042]
Here, assuming that a light receiving region mainly composed of AlGaN having a band gap energy of 4.1 eV or more is provided, light having a wavelength exceeding about 300 nm, that is, indoor light from various lighting devices or the like, is subjected to the above light receiving region. Since the region has no sensitivity, it is possible to obtain an ultraviolet light receiving element (flame sensor) selectively having sensitivity to, for example, flame light containing ultraviolet light having a wavelength of about 300 nm or less.
[0043]
Further, if a light receiving region mainly composed of AlGaN having a band gap energy of 4.3 eV or more is provided, light having energy of 4.3 eV or more (wavelength of about 290 nm or less) is absorbed, so that the ultraviolet light receiving element can be used. Even if the emitted light includes disturbance light such as sunlight, the light intensity of the disturbance light becomes extremely small at a wavelength of about 290 nm or less, and for example, flame light including ultraviolet rays of a wavelength of about 290 nm or less. Thus, it is possible to obtain an ultraviolet light receiving element (flame sensor) which is selectively sensitive and is extremely hard to be affected by disturbance light such as sunlight.
[0044]
Further, if a light receiving region mainly composed of AlGaN having a band gap energy of 4.6 eV or more is provided, light having an energy of 4.6 eV or more (wavelength of about 280 nm or less) is absorbed, so that the ultraviolet light receiving element can be used. Even if the emitted light includes disturbance light such as sunlight, the light receiving region has no sensitivity to room light and sunlight (natural light) from various lighting devices and the like. An ultraviolet light receiving element (flame sensor) which is selectively sensitive to, for example, flame light including ultraviolet light of 280 nm or less and which is not affected by disturbance light such as room light or sunlight can be obtained.
[0045]
The light emitting device can emit light having a light energy of 3.4 eV to 6.2 eV by appropriately selecting the AlN composition ratio of AlGaN in the active layer.
[0046]
BEST MODE FOR CARRYING OUT THE INVENTION
The embodiment of the p-type activation method for a GaN-based compound semiconductor according to the present invention (hereinafter, appropriately referred to as “the present invention method”) will be described with reference to the drawings, taking as an example a case where the method is applied to a manufacturing process of an ultraviolet light receiving element 20. Will be explained.
[0047]
The ultraviolet light receiving element 20 shown in FIG. 1 is an example in which a PIN type element structure is adopted. The ultraviolet light receiving element 20 is formed by sequentially laminating a base structure portion and a device structure portion on the substrate 1. The underlayer structure is formed by sequentially laminating a low-temperature deposition buffer layer 2, a crystal improving layer 3, and a low-temperature deposition intermediate layer 4 on a substrate 1, and the device structure is formed on the low-temperature deposition intermediate layer 4 by: and n-type semiconductor layer 5, i-type semiconductor layer (light receiving region) 6 _is formed by sequentially stacking a p-type semiconductor layer 7 made of _{Al x Ga 1-x n (} 0 ≦ x ≦ 1). Further, the device structure is removed by etching or the like so that the n-type semiconductor layer 5 is partially exposed, an electrode 8 is formed on the exposed portion, and an electrode 9 is formed on the p-type semiconductor layer 7. The electrodes 8 and 9 are ohmic electrodes whose electrical characteristics between the n-type semiconductor layer 5 and the p-type semiconductor layer 7 are ohmic.
In the ultraviolet light receiving device 20 illustrated in FIG. 1, a (0001) sapphire substrate 1 is provided with a low-temperature deposition buffer layer 2 of AlN, a crystal improving layer 3 of GaN, a low-temperature intermediate layer 4 of AlN, and an n-type AlGaN layer. 5, an i-type AlGaN layer 6 and a p-type AlGaN layer 7 are respectively formed. Each GaN-based compound semiconductor layer is formed by MOCVD (organic metal compound vapor deposition) using each source gas such as trimethylaluminum (Al source), trimethylgallium (Ga source), and ammonia (nitrogen source). It can be manufactured.
The purpose of the underlayer structures 2-4 is to improve the crystal quality of the device structures 5-7. Although there is a large difference between the lattice spacing on the crystal growth surface of the sapphire substrate 1 and the lattice constant of Al _x Ga _1-x N (0 ≦ x ≦ 1) constituting the device structure, Thereby, the lattice mismatch can be reduced, and the stress due to the lattice mismatch applied when growing the AlGaN layer can be reduced. As a result, the crystal quality of the AlGaN layer in the device structure can be improved.
It should be noted that various proposals have been made for the structure of the underlying structure and its formation process for alleviating the lattice mismatch and improving the crystal quality of the device structure formed thereon. Since the gist of the present invention lies not in the underlying structure but in the p-type semiconductor layer 7 of the device structure, the underlying structure may be, for example, one obtained by forming the above-described known structure in a known manufacturing process. It is sufficient that a new structure other than the above is used. Further, the substrate 1 is not limited to the (0001) sapphire substrate.
Next, a p-type activation method for the p-type AlGaN layer 7 of the ultraviolet light receiving element 20 according to the method of the present invention will be described.
As shown in FIG. 2A, first, the p-type AlGaN layer 7 is manufactured by using the MOCVD method. Here, Mg (magnesium) is injected while using each of the above-mentioned source gases as a source material of Al, Ga, and N and flowing a Cp ₂ Mg (biscyclopentadienyl magnesium) gas as a source gas of a p-type impurity. A (doped) p-type AlGaN layer 7 is grown. In this state, NH ₃ used as the N source is decomposed into atomic hydrogen and stays in the p-type AlGaN layer 7, and this atomic hydrogen combines with Mg implanted as a p-type impurity to form a p-type. As a result of inhibiting the impurity Mg from acting as an acceptor, the p-type AlGaN layer 7 is not sufficiently p-type activated and remains in a high resistance state.
Next, after growing the p-type AlGaN layer 7 into which Mg has been implanted, as shown in FIG. 2B, a hydrogen absorption / permeable film 10 is formed on the surface thereof. The hydrogen absorbing and transmitting film 10 is made of one or more materials selected from nickel, palladium, silver-palladium alloy, platinum, and ruthenium, and includes ion beam sputtering (IBS), electron beam evaporation (EB), laser ablation, RF sputtering, It is formed using a technique such as plating. In addition, it is considered that electron beam evaporation is advantageous in productivity, and IBS or laser ablation is advantageous in film density. In particular, by giving priority to the denseness of the membrane, the hydrogen permeation performance and the catalytic action of the hydrogen absorption / permeable membrane 10 are enhanced, and the throughput of annealing in a later step is improved. Therefore, the use of IBS or laser ablation is preferred.
The formation of the hydrogen absorbing and transmitting film 10 may be performed before or after the device structure is etched so that the n-type semiconductor layer 5 in FIG. 1 is partially exposed. Absent.
Next, as shown in FIG. 2C, after the formation of the hydrogen absorbing and transmitting film 10, the p-type AlGaN layer 7 is subjected to an annealing treatment. The processing temperature is appropriately selected within a temperature range of 400 ° C. or higher. The growth of the p-type AlGaN layer 7, the formation of the hydrogen absorption / transmission film 10, and the annealing treatment may be performed in the same reaction vessel, or may be performed in separate vessels. Here, the processing atmosphere is a reducing atmosphere containing hydrogen, and a mixed gas composed of hydrogen, nitrogen, and argon is introduced into the reaction vessel as a reducing gas, and after the introduction, the reducing gas is supplied only by a rotary pump in a short time. The pressure is reduced to 4000 Pa (30 Torr) or less by suction. By thus reducing the pressure after the introduction of the reducing gas, the entry of contaminants into the reaction vessel can be prevented. Note that the reducing atmosphere containing hydrogen may be a reducing gas containing hydrogen as a main component (for example, 100% hydrogen).
In the method of the present invention, even when annealing is performed at a low temperature of 400 ° C. or less, the p-type activation can be sufficiently performed by the catalytic action of the hydrogen absorbing and permeable membrane 10. That is, the hydrogen atoms desorbed from Mg by annealing are absorbed by the hydrogen absorbing and permeable film 10 without staying near the surface of the p-type AlGaN layer 7, are converted into hydrogen molecules, and are released into the external atmosphere. Since hydrogen is desorbed from Mg without saturating and saturating atomic hydrogen in the p-type AlGaN layer 7, Mg implanted as a p-type impurity functions as an acceptor.
The hydrogen absorption / transmission film 10 may be a single layer film of Ni (nickel), Pd (palladium), Pd-Ag (silver-palladium alloy), platinum (Pt), ruthenium (Rt), etc. A multilayer film combining these may be used. Further, a part of the hydrogen absorption and transmission film 10 may include a hydrogen storage alloy other than the above metals. Other hydrogen storage alloys include, for example, La _0.8 Nb _0.2 Ni _2.5 Co _2.4 Al _0.1 , La _0.8 Nb _0.2 Zr _0.03 Ni _3.8 Co _{0.8 . 7} Al _0.5 , MmNi _3.65 Co _0.75 Mn _0.4 Al _0.3 , MmNi _2.5 Co _0.7 Al _0.8 , Mm _0.85 Zr _0.15 Ni _1.0 Al _{0 .8} V _0.2 . Here, Mm is a misch metal, which is a mixture of rare earth elements whose main constituent elements are Ce (40 to 50%), La (20 to 40%), Pr, and Nd.
It is preferable that hydrogen is contained in the reaction vessel during the annealing. In general, if the annealing treatment is performed without providing the hydrogen absorbing and transmitting film 10 on the surface of the p-type AlGaN layer 7, the presence of hydrogen in the annealing treatment atmosphere is considered to be a factor inhibiting the desorption of hydrogen from Mg. However, when the hydrogen-absorbing permeable film 10 is provided, hydrogen molecules in the processing atmosphere exert a cleaning action to prevent oxidation of the surface of the hydrogen-absorbing permeable film. Is sufficiently present, the presence of hydrogen is rather preferred.
This means that the annealing can be performed in the same reaction vessel in which the p-type AlGaN layer 7 has been grown. That is, since hydrogen is used as a carrier gas of a source gas during growth by MOCVD, a reducing atmosphere containing hydrogen as a main component can be used as it is.
After the p-type activation by the annealing process, the hydrogen absorption / transmission film 10 is removed by etching or the like, and a part of the p-type semiconductor layer 7 and the i-type semiconductor layer 6 is partially exposed by the n-type semiconductor layer 5. Then, the n-type electrode 8 is formed on the exposed portion, and the p-type electrode 9 is formed on the p-type semiconductor layer 7. Here, the n-type electrode 8 and the p-type electrode 9 may be made of a known material such as Al, Au, Ni, Ti or the like according to the respective polarities by a known method. According to the method of the present invention, the p-type semiconductor layer 7 is sufficiently p-type activated, so that ohmic contact with the p-type electrode 9 becomes possible.
Here, as the p-type electrode 9, for example, when palladium (Pd) is used for the first layer and gold (Au) is used for the second layer, the first layer of palladium and the hydrogen absorbing / permeable film are used. The palladium of 10 may also be used. In this case, for example, by setting the thickness of the hydrogen absorption / transmission film 10 to 100 Å (10 ⁻⁸ m) and the thickness of the second layer of gold to 1000 Å (10 ⁻⁷ m), a good p-type ohmic Electrodes can be formed.
Further, the n-type electrode 8 may be formed by using ZrB ₂ as an electrode material by an evaporation method such as ion beam sputtering, laser ablation, and CVD. In particular, when ZrB ₂ is produced by MOCVD using Zr [N (C ₂ H ₅ ) ₂ ] ₄ or Zr (BH ₄ ) ₄ as a Zr source and using trimethylboron as a B source. In addition, there is an advantage that a common film forming apparatus can be used for each nitride semiconductor layer forming the device structure. Incidentally, Al in fabricated ZrB ₂ electrodes on, Au, Ni, may be a multilayer electrode (protective electrode) so as to protect the further formed and ZrB ₂ electrode metal such as Ti.
The p-type electrode 9 may be formed by using ZrN as an electrode material by a vapor deposition method such as ion beam sputtering, laser ablation, and CVD. ZrN is obtained by nitriding ZrB _{2 formed} on the p-type semiconductor layer 7 using ammonia gas or the like. Further, similarly to the case of the n-type electrode 8, a metal such as Al, Au, Ni, Ti is further formed on the manufactured ZrN electrode to form a multilayer electrode (protection electrode) for protecting the ZrN electrode 9. May be.
Here, when light is incident from the side of the p-type electrode 9 (upper side in the drawing), the p-type electrode 9 is formed in a mesh shape or another shape or material that transmits light to the light receiving region. Conversely, when light is incident from the substrate 1 side (the lower side in the drawing), the incident light is absorbed by the GaN crystal improving layer 3 of the underlying structure and does not reach the i-type semiconductor layer (light receiving region) 6. In addition, it is necessary to form an entrance window by removing at least portions of the substrate 1 and the underlying structure portion corresponding to the light receiving region of the low-temperature deposition buffer layer 2 and the crystal improving layer 3 by etching or the like. Alternatively, a material that transmits the light in the wavelength range to be detected by the i-type semiconductor layer (light receiving region) 6 without absorbing the substrate 1 and the underlying structure may be used. For example, instead of using GaN in the crystal improvement layer 3, AlGaN or AlN having a higher AlN composition ratio than the i-type semiconductor layer (light receiving region) 6 may be used.
When the ultraviolet light receiving element 20 shown in FIG. 1 is irradiated with light from the outside, the light passes through the mesh-shaped electrode 9 and the p-type semiconductor layer 7 to form an i-type semiconductor light receiving region. The light is incident on the layer 6 and is absorbed to generate optical carriers. An electric field is applied between the p-type electrode 8 and the n-type electrode 9, and the generated photocarriers are output to the outside as photocurrent.
The band gap energy of Al _x Ga ₁ -xN (0 ≦ x ≦ 1) constituting the device structure is adjusted by changing the AlN composition ratio, and the AlN composition ratio x and the band gap energy are shown in FIG. The relationship is as shown in FIG. As can be seen from FIG. 3, by changing the AlN composition ratio x, the band gap energy of Al _x Ga ₁ -xN can be adjusted from 3.42 eV to 6.2 eV. Therefore, the wavelength range of light that can be absorbed in the light receiving region can be adjusted between about 360 nm and about 200 nm.
When flame light is detected by the ultraviolet light receiving element 20, a light receiving region having a band gap energy enough to absorb the flame emission as shown in the emission spectrum of FIG. 4 may be formed. The emission spectrum of the flame shown in FIG. 4 is a spectrum of a flame generated when a gas (hydrocarbon) is burned. The spectrum of sunlight and the spectrum of room light due to light from various lighting devices are also shown.
The band gap energy of the light receiving region will be described below. In order to provide wavelength selectivity in the ultraviolet light receiving element 20 adjusts the AlN composition ratio of the light-receiving area _{(Al x Ga 1-x N} ), it is made to set the band gap energy to a desired value . For example, when it is desired to manufacture a flame sensor capable of selectively receiving light of a flame appearing at a relatively large intensity in a wavelength range of about 344 nm or less, the band gap energy of the light receiving region is 3.6 eV or more. As described above, the AlN composition ratio x may be set to 0.05 or more. Alternatively, when it is desired to manufacture a flame sensor that receives light of a flame in a wavelength range to be detected without receiving light (indoor light) from various lighting devices included in a wavelength range of about 300 nm or more. The AlN composition ratio x may be set to 0.25 or more so that the band gap energy of the light receiving region is 4.1 eV or more. In addition, when it is desired to produce a flame sensor that receives only the light of the flame in the wavelength range to be detected without receiving light from sunlight, which is included in the wavelength range of about 280 nm or more, The AlN composition ratio x may be set to 0.35 or more so that the band gap energy becomes 4.4 eV or more.
Furthermore, if disturbance light such as sunlight can be absorbed in the light receiving region at a low light intensity, the band gap energy of the light receiving region becomes 4.3 eV or more (wavelength of about 290 nm or less). Thus, the AlN composition ratio x may be set to 0.31 or more. At a wavelength of about 290 nm or less, the light intensity of the disturbance light becomes very small as shown in FIG. 3, while the flame light is large. As a result, the presence of the flame light can be detected.
Further, when the ultraviolet light receiving element 20 is installed in a closed space such as the inside of the engine and it is desired to detect the light emission of the fuel burned there, since the indoor light and the sunlight described above do not exist, they are excluded. It is not necessary to set such a large band gap energy. Therefore, the emission peak (wavelength of about 310 nm) caused by the emission of OH radicals observed when a compound containing hydrocarbon (fuel burned by an engine) is particularly burned among the flame light in the detection target wavelength range. 310 nm ± 10 nm): 4.0 eV) (a flame light having a wavelength of 310 nm or more and 344 nm or less) is manufactured. The AlN composition ratio x may be set to 0.05 or more and 0.23 or less so as to be set to 0.6 eV or more and 4.0 eV or less.
The relationship between the AlN composition ratio x and the band gap energy described above has been explained based on theoretical values. Even if the film formation is performed so that the AlN composition ratio x becomes the same, the actual value is obtained. There is a possibility that the band gap energy of the obtained AlGaN layer is different. For example, in the case of AlGaN which is a ternary mixed crystal compound, GaN which is a binary compound is easily generated, and as a result, the band gap energy tends to shift to a lower energy side (longer wavelength side). Therefore, when it is desired to obtain the band gap energy according to the theoretical value, the film may be formed after setting the AlN composition ratio to a large value in advance.
[0072]
Hereinafter, another embodiment will be described.
<1> In the above embodiment, Mg was used as the p-type impurity for the growth of the p-type AlGaN layer 7, but sufficient p-type activation was obtained even when the AlN composition ratio of the p-type AlGaN layer 7 was 20% or more. In order to obtain the above, it is also a preferable embodiment to use Be (beryllium) instead of Mg as the p-type impurity.
[0073]
In this case, the p-type AlGaN layer 7 is formed by using MOCVD as a source of Al, Ga, and N in the same manner as in the above embodiment, using trimethylaluminum (Al source), trimethylgallium (Ga source), and ammonia (nitrogen source). The p-type AlGaN layer 7 into which Be is implanted is grown while using Cp ₂ Be (biscyclopentadienyl beryllium) gas as a source gas for the p-type impurity by using the respective source gases such as. The formation of the hydrogen absorption and transmission film 10 after the growth of the p-type AlGaN layer 7 and the annealing of the p-type AlGaN layer 7 are the same as those in the above-described embodiment.
[0074]
Furthermore, as a source gas of the p-type impurity, _(R-Cp) 2 Be gas [bis (R- cyclopentadienyl) beryllium] Gas (R 1-4 divalent alkyl group) more preferred to use. In particular, it is more preferable to use (R-Cp) ₂ Be gas of an alkyl group in which R is a divalent to tetravalent alkyl group. When the p-type, n-type and i-type semiconductors are formed stepwise in a predetermined order by using the organometallic compound vapor deposition method by using the source gas, an impurity source corresponding to each type is crystal-grown. In the case where the supply is performed through a pipe into the reaction chamber, when the growth of each semiconductor layer is switched, the supply of the impurity material is also switched. However, when the same pipe is used, the influence (memory effect) due to the residual impurities remaining on the pipe inner wall is caused. This is because the effect of improving the problem that the desired impurity concentration cannot be achieved in the vicinity of the interface between the respective semiconductor layers cannot be ignored. In other words, the molecular size of the source gas is larger than Cp ₂ Be, and the intermolecular force due to polarization is weakened, so that the residual on the inner wall of the pipe is reduced. Mold activation is promoted.
[0075]
<2> In the above embodiment, the case where the p-type activation method of the GaN-based compound semiconductor according to the present invention is applied to the manufacturing process of the ultraviolet light receiving element 20 is exemplified. It is applicable to elements, light emitting elements, and other semiconductor devices. In particular, the light emitting element is similar in structure to the light receiving element, so that the method of the above embodiment can be applied.
[0076]
<3> In the above embodiment, the PIN structure is used as an example of the device structure. However, when the device structure includes a p-type AlGaN layer, the p-type activation according to the method of the present invention can be applied. The part is not limited to the PIN structure.
[Brief description of the drawings]
FIG. 1 is an element cross-sectional view showing a configuration of an ultraviolet light receiving element manufactured by using a p-type activation method for a GaN-based compound semiconductor according to the present invention. FIG. 2 is a p-type activation of a GaN-based compound semiconductor according to the present invention. FIG. 3 is a graph showing band gap energy of AlGaN. FIG. 4 is a graph showing spectra of flame light, sunlight, and room light.
DESCRIPTION OF SYMBOLS 1 Substrate 2 Low-temperature deposition buffer layer 3 Crystal improvement layer 4 Low-temperature deposition intermediate layer 5 n-type semiconductor layer 6 i-type semiconductor layer 7 p-type semiconductor layer 8 n-type electrode 9 p-type electrode 10 Hydrogen absorption / transmission film 20 UV light receiving element

Claims (19)

After forming a GaN-based compound semiconductor into which a p-type impurity has been implanted, a hydrogen-absorbing and permeable film having a function of absorbing and releasing hydrogen in the GaN-based compound semiconductor to the outside is formed on the surface thereof, and then a reducing atmosphere is formed. Annealing the GaN-based compound semiconductor in the inside to desorb hydrogen bonded to the p-type impurity injected into the GaN-based compound semiconductor to activate the GaN-based compound semiconductor p-type. A p-type activation method for a GaN-based compound semiconductor. 2. The p-type activity of the GaN-based compound semiconductor according to claim 1, wherein the hydrogen absorption / transmission film has a catalytic action of absorbing atomic hydrogen in the GaN-based compound semiconductor and releasing it as hydrogen molecules. Method. The p-type activation of a GaN-based compound semiconductor according to claim 1 or 2, wherein the hydrogen absorption / transmission film is made of at least one material selected from nickel, palladium, a silver-palladium alloy, platinum, and ruthenium. Method. The p-type activation method for a GaN-based compound semiconductor according to any one of claims 1 to 3, wherein a processing temperature during the annealing is 400 ° C or higher. 5. The p-type activation method for a GaN-based compound semiconductor according to claim 1, wherein hydrogen is contained in the reducing atmosphere during the annealing. 6. The p-type activation of a GaN-based compound semiconductor according to any one of claims 1 to 4, wherein the reducing atmosphere at the time of the annealing is composed of hydrogen, nitrogen, argon, or a mixed gas thereof. Method. The p-type activation method for a GaN-based compound semiconductor according to any one of claims 1 to 6, wherein the reducing atmosphere at the time of the annealing is lower than the atmospheric pressure. The p-type activation method for a GaN-based compound semiconductor according to claim 7, wherein the reducing atmosphere during the annealing is reduced to 4000 Pa or less by a rotary pump alone. After forming the GaN-based compound semiconductor into which the p-type impurity is implanted, forming only the hydrogen absorption / permeable film on the surface thereof, and then annealing the GaN-based compound semiconductor in a reducing atmosphere. 9. The p-type activation method for a GaN-based compound semiconductor according to any one of 1 to 8. The p-type activation method for a GaN-based compound semiconductor according to any one of claims 1 to 9, wherein the hydrogen absorption / transmission film is used as an electrode or a part of the electrode. The p-type activation method for a GaN-based compound semiconductor according to claim 10, wherein the electrode is a p-type electrode. The p-type activation method for a GaN-based compound semiconductor according to any one of claims 1 to 11, wherein the hydrogen absorption and transmission film is formed by ion beam sputtering (IBS) or laser ablation. 13. The p-type activation method for a GaN-based compound semiconductor according to claim 1, wherein the p-type impurity includes at least one of magnesium and beryllium. 13. The p-type activation method for a GaN-based compound semiconductor according to claim 1, wherein the p-type impurity contains at least beryllium. A GaN-based compound semiconductor device comprising a GaN-based compound semiconductor that has been p-type activated by the GaN-based compound semiconductor p-type activation method according to claim 1. A light-receiving element comprising a GaN-based compound semiconductor which has been p-type activated by the p-type activation method for a GaN-based compound semiconductor according to claim 1. 17. The light receiving device according to claim 16, further comprising a light receiving region mainly composed of AlGaN having a band gap energy of 3.6 eV or more. A light emitting device comprising a GaN-based compound semiconductor that has been p-type activated by the p-type activation method for a GaN-based compound semiconductor according to claim 1. 19. The light emitting device according to claim 18, comprising an active layer mainly composed of AlGaN.

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