Optical semiconductor device including antiparallel semiconductor light-emitting element and Schottky diode element

An optical semiconductor device includes a semiconductor support substrate of a conductivity type having a first resistivity, a semiconductor layer of the conductivity type formed on the semiconductor support substrate and having a second resistivity higher than the first resistivity, a first power supply terminal having a first metal in Schottky barrier contact with the semiconductor layer along with the semiconductor support substrate, so that a Schottky diode element is constructed by the first power supply terminal and the semiconductor layer along with the semiconductor support substrate, a second power supply terminal having a second metal in ohmic contact with the semiconductor support substrate, and a semiconductor light-emitting element connected between the first and second power supply terminals, the semiconductor light-emitting element being antiparallel with the Schottky diode with respect to the first and second power supply terminals.

This application claims the priority benefit under 35 U.S.C. §119 to Japanese Patent Application No. JP2013-040488 filed on Mar. 1, 2013, which disclosure is hereby incorporated in its entirety by reference.

BACKGROUND

The presently disclosed subject matter relates to an optical semiconductor device including a semiconductor light-emitting element and a Schottky diode element as an electrostatic protection element which are antiparallelly-connected to each other.

2. Description of the Related Art

Generally, in an optical semiconductor device including a semiconductor light-emitting element such as a light-emitting diode (LED) element or a laser diode (LD) element, an electrostatic discharge (ESD) protection circuit is connected between the terminals of the semiconductor light-emitting element, in order to avoid damage or destruction by ESD phenomena. Particularly, the reverse breakdown voltage of a GaN light-emitting element by applying a reverse voltage thereto is smaller than those of AlGaAs, AlGaInP or GaP light-emitting elements by applying reverse voltages thereto. Therefore, GaN light-emitting elements are easily subject to damage or destruction due to the application of a small reverse voltage thereto.

In a first prior art optical semiconductor device, a semiconductor light-emitting element and a Zener diode element as an ESD protection element are antiparallelly connected to each other, and also, are mounted on a semiconductor support substrate.

When a reverse voltage due to the ESD phenomena is applied to the first prior art optical semiconductor device, a forward current flows through the Zener diode element, so that the above-mentioned reverse voltage is not applied to the semiconductor light-emitting element. Thus, the reverse breakdown voltage of the semiconductor light-emitting element against the ESD phenomena can substantially be increased.

In the above-described first prior art optical semiconductor device, however, the mounting steps of the Zener diode element are so complex that the manufacturing cost would be increased. Also, spacing for mounting the Zener diode element is required in the semiconductor support substrate, which would increase the device in size.

In a second prior art optical semiconductor device (see: JP2011-520270 & US2011/0272728A1), a semiconductor light-emitting element is mounted on a semiconductor support substrate, and a Schottky diode element as an ESD protection element is formed in the semiconductor support substrate. Also, in this case, the semiconductor light-emitting element and the Schottky diode element are antiparallel with each other.

When a reverse voltage due to the ESD phenomena is applied to the second prior art optical semiconductor device, a forward current flows through the Schottky diode element, so that the above-mentioned reverse voltage is not applied to the semiconductor light-emitting element. Thus, the reverse breakdown voltage of the semiconductor light-emitting element against the ESD phenomena can substantially be increased.

In the above-described second prior art optical semiconductor device, since the semiconductor support substrate is connected directly to the semiconductor light-emitting element, the resistivity of the semiconductor support substrate is made low in order to suppress the forward voltage drop of the semiconductor light-emitting element.

Note that, if the resistivity of the semiconductor support substrate is high, the forward voltage drop of the semiconductor light-emitting element is increased to increase the power loss and the generated heat, which would not realize a high-power semiconductor light-emitting element.

In the above-described second prior art optical semiconductor device, however, since the resistivity of the semiconductor support substrate is low, the reverse breakdown voltage of the Schottky diode element formed by the semiconductor support substrate is decreased. Therefore, if a semiconductor light-emitting element is constructed by a GaN LED element or a series of other LED elements to have a higher forward voltage, the forward voltage drop of the semiconductor light-emitting element becomes smaller than the reverse breakdown voltage of the Schottky diode element. As a result, a current, which should naturally be supplied to the semiconductor light-emitting element, would be leaked to the Schottky diode element, thus decreasing its luminous intensity.

SUMMARY

The presently disclosed subject matter seeks to solve one or more of the above-described problems.

According to the presently disclosed subject matter, an optical semiconductor device includes a semiconductor support substrate of a conductivity type having a first resistivity, a semiconductor layer of the conductivity type formed on the semiconductor support substrate and having a second resistivity higher than the first resistivity, a first power supply terminal having a first metal in Schottky barrier contact with the semiconductor layer along with the semiconductor support substrate, so that a Schottky diode element is constructed by the first power supply terminal and the semiconductor layer along with the semiconductor support substrate, a second power supply terminal having a second metal in ohmic contact with the semiconductor support substrate, and a semiconductor light-emitting element connected between the first and second power supply terminals, the semiconductor light-emitting element being antiparallel with the Schottky diode with respect to the first and second power supply terminals.

According to the presently disclosed subject matter, the reverse breakdown voltage of the Schottky diode element can be made larger than the forward voltage drop of the semiconductor light-emitting element. Therefore, when a forward current is supplied to the semiconductor light-emitting element, such a forward current can be prevented from flowing through the Schottky diode element, thus suppressing the reduction of the luminous intensity of the semiconductor light-emitting element.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

InFIG. 1, which is an equivalent circuit diagram of an optical semiconductor device to which the presently disclosed subject matter is applied, a series of two LED elements D1(D1′, D1″, D1′″) and D2(D2′, D2″, D2′″) are connected between a positive potential power supply terminal T1and a ground potential power supply terminal T2, and also, a Schottky diode element SBD are antiparallel with the LED elements D1(D1′, D1″, D1′″) and D2(D2′, D2″, D2′″) with respect to the power supply terminals T1and T2. As a result, when a reverse voltage due to the ESD phenomena is applied to the optical semiconductor device ofFIG. 1, a forward current flows through the Schottky diode element SBD, so that the above-mentioned reverse voltage is not applied to the LED elements D1(D1′, D1″, D1′″) and D2(D2′, D2″, D2′″). Thus, the reverse breakdown voltage of the LED elements D1(D1′, D1″, D1′″) and D2(D2′, D2″, D2′″) against the ESD phenomena can substantially be increased.

InFIG. 1, the reverse breakdown voltage of the Schottky diode element SBD is made larger than the forward voltage drop of the LED elements D1and D2. As a result, a current, which should naturally be supplied to the LED elements D1and D2, would not be leaked to the Schottky diode element SBD, thus increasing the luminous intensity.

InFIG. 2, which is a cross-sectional view illustrating a first embodiment of the optical semiconductor device according to the presently disclosed subject matter, the LED elements D1and D2of a non-via-type are arranged side by side.

InFIG. 2, provided on a 50 μm or more thick p+-type monocrystalline silicon support substrate1is an about 0.1 to 10.0 μm thick p-type silicon layer2. For example, the p+-type monocrystalline silicon support substrate1has a boron concentration of 1×1017cm−3or more, preferably, 2×1018cm−3or more, exhibiting a low resistivity of 0.05Ω·cm or less. Also, the p-type silicon layer2has a boron concentration of 1×1017cm−3or less, preferably, 2×1016cm−3or less, exhibiting a high resistivity of 1Ω·cm or more. Further, an insulating layer3made of silicon dioxide, silicon nitride or the like is formed on the p-type silicon layer2.

Also, the LED element D1formed by an n-type GaN layer4-1, an InGaN/GaN multiple quantum well (MQW) active layer5-1and a p-type GaN layer6-1is bonded by a bonding layer7-1on the insulating layer3, and the LED element D2formed by an n-type GaN layer4-2, an InGaN/GaN MQW active layer5-2and a p-type GaN layer6-2is bonded by a bonding layer7-2on the insulating layer3. Note that the active layers5-1and5-2can be made of a single quantum well (SQW) structure or a single layer. The LED elements D1and D2are connected in series between the terminals T1and T2.

Further, protection layers8-1and8-2made of silicon dioxide or the like are provided for electrically protecting the LED elements D1and D2. In addition, n-side electrodes9-1and9-2are provided on the LED elements D1and D2, respectively. Still, a connection layer10-1is connected between the n-side electrode9-1and the bonding layer7-2, and a connection layer10-2is connected between the n-side electrode9-2and the power supply terminal T2.

A method for manufacturing the optical semiconductor device ofFIG. 2is explained next with reference to a flowchart as illustrated inFIG. 3.

First, referring to step301, a p-type silicon layer2is grown by an epitaxial process on a p+-type monocrystalline silicon support substrate1.

Next, referring to step302, an insulating layer3is formed by a chemical vapor deposition (CVD) process on the p-type silicon layer2.

Next, referring to step303, an about 1 μm thick adhesive layer (not shown) is deposited by a resistance heating evaporation process on the insulating layer3. Note that this adhesive layer is used in a wafer pressure-bonding process which will be explained later.

On the other hand, referring to step304, semiconductor layers, i.e., an about 5 μm thick n-type GaN layer, an InGaN/GaN MQW active layer and an about 0.5 μm thick p-type GaN layer are sequentially and epitaxially grown by a metal organic chemical vapor deposition (MOCVD) process on a semiconductor growing sapphire substrate (not shown).

Next, referring to step305, p-side electrodes (not shown) made of about 200 nm thick AgTiWPtAu are formed by an electron beam (EB) evaporation/photolithography process on p-type GaN layer.

Next, referring to step306, an about 200 nm thick adhesive layer (not shown) is deposited by a resistance heating evaporation process on the p-type GaN layer. Note that this adhesive layer is used in the wafer pressure-bonding process which will be later explained.

Next, referring to step307, the n-type GaN layer, the active layer and the p-type GaN layer are patterned by a dry etching using chlorine gas to obtain the n-type GaN layer4-1, the active layer5-1and the p-type GaN layer6-1for the LED element D1and the n-type GaN layer4-2, the active layer5-2and the p-type GaN layer6-2for the LED element D2. In this case, the LED elements D1and D2are combined by the adhesive layer deposited by step306.

Next, referring to step308, the LED elements D1and D2combined by the adhesive layer (not shown) are placed face down and bonded by a wafer pressure-bonding process onto the insulating layer3along with the adhesive layer (not shown) on the side of the p+-type monocrystalline silicon support substrate1. The wafer pressure-bonding process is carried out at a temperature of about 300° C. at a pressure of about 3 MPa for about 10 minutes. Thus, the adhesive layer on the side of the LED elements D1and D2and the adhesive layer on the side of the p+-type monocrystalline silicon support substrate1are melted to form one bonding layer which will be separated into bonding layers7-1and7-2.

Next, referring to step309, the semiconductor growing sapphire substrate (not shown) for absorbing a visible light component is wholly peeled from the n-type GaN layers4-1and4-2by a laser lift-off process using an ultraviolet (UV) excimer laser to melt the interface portion of the n-type GaN layers4-1and4-2near the semiconductor growing sapphire substrate (not shown).

Next, referring to step310, the bonding layer is partly removed by a photolithography/dry etching process using Ar gas so that the bonding layer is divided into bonding layers7-1and7-2. As a result, the p-type GaN layers6-1and6-2are electrically separated from each other.

Next, referring to step311, protection layers8-1and8-2made of silicon dioxide or the like are formed by a sputtering/photolithography process to electrically protect the LED elements D1and D2.

Next, referring to step312, n-side electrodes9-1and9-2made of about 10 nm thick Ti and about 300 nm thick TiAlTiPtAu are formed by an EB evaporation/photolithography process on the n-type GaN layers4-1and4-2in the opening of the protection layers8-1and8-2.

Next, referring to step313, connection layers10-1and10-2made of TiPtAu are formed by an EB evaporation/photolithography process on the n-type electrodes9-1and9-2. In this case, the connection layer10-1is connected between the n-type electrode9-1of the LED element D1and the bonding layer7-2of the LED element D2.

Next, referring to step314, a power supply terminal (pad) T1is formed in an opening of the insulating layer3in contact with the bonding layer7-1. That is, the power supply terminal T1is electrically connected to the p-type GaN layer6-1of the LED element D1via the bonding layer7-1.

The power supply terminal T1is made of a metal such as Au, Cu, Ni, Ag, Pd, Al, Mg, In or Sn whose work function φmis smaller than the work function φsof silicon. That is, φs>φm. For example, the power supply terminal T1is made of Al including 1% Si or 1% Cu on which TiPtAu for bonding Au wires thereon is formed. Thus, a Schottky barrier is established between the power supply terminal T1and the p-type silicon layer2along with the pt-type monocrystalline silicon support substrate1. That is, the power supply terminal T1is in Schottky barrier contact with the p-type silicon layer2along with the p+-type monocrystalline silicon support substrate1. As a result, a Schottky diode element SBD is constructed by the power supply terminal T1and the p-type silicon layer2along with the p+-type monocrystalline silicon support substrate1.

Finally, referring to step315, a power supply terminal (pad) T2is formed in an opening of the insulating layer3in contact with the connection layer10-2. That is, the power supply terminal T2is electrically connected to the n-type GaN layer4-2of the LED element D2via the connection layer10-2.

The power supply terminal T2is made of a metal such as Pt or Ti which is in ohmic contact with the p+-type monocrystalline silicon support substrate1along with the p-type silicon layer2. Note that TiPtAu for bonding Al wires is formed on the metal such as Pt or Ti.

Thus, the LED elements D1and D2are connected in series between the power supply terminals T1and T2.

InFIG. 2, the boron concentration of the p-type silicon layer2is adjusted, so as to sufficiently lower the forward rising voltage of the Schottky diode element SBD to be 0.3V to 0.9V and to raise the reverse breakdown voltage of the Schottky diode element SBD to be higher than 10V where the reverse current Iris 100 μA. On the other hand, the power supply terminal T2is in ohmic contact with the p-type silicon layer2via the p+-type monocrystalline silicon support substrate1, and also, is connected to the connection layer10-2. Therefore, a current, which should be supplied to the LED elements D1and D2, is never leaked to the Schottky diode element SBD. In addition, the forward voltage drop of the LED elements D1and D2is not so large. Therefore, the power loss and generated heat of the LED elements D1and D2can be suppressed.

InFIG. 4, which is a cross-sectional view illustrating a second embodiment of the optical semiconductor device according to the presently disclosed subject matter, the LED elements D1′ and D2′ of a via-type are arranged side by side.

InFIG. 4, a via hole11-1is formed in the n-type GaN layer4-1, the active layer5-1and the p-type GaN layer6-1ofFIG. 2. Also, provided on the side of the via hole11-1are p-side electrodes12-1and13-1, an insulating layer14-1made of silicon dioxide or silicon nitride, and an n-side electrode (via electrode)15-1.

Similarly, a via hole11-2is formed in the n-type GaN layer4-2, the active layer5-2and the p-type GaN layer6-2ofFIG. 2. Also, provided on the side of the via hole11-2are p-side electrodes12-2and13-2, an insulating layer14-2made of silicon dioxide or silicon nitride, and an n-side electrode (via electrode)15-2.

Further, a connection layer16-1made of TiPtAl is formed so as to electrically connect the p-type GaN layer6-1of the LED element D1′ to the power supply terminal T1. Also, a connection layer16-2made of TiPtAl is formed so as to electrically connect the n-type GaN layer4-1of the LED element D1′ to the p-type GaN layer6-2of the LED element D2′.

The power supply terminals T1and T2are the same as those ofFIG. 2.

Thus, the LED elements D1′ and D2′ are connected in series between the power supply terminals T1and T2.

A method for manufacturing the optical semiconductor device ofFIG. 4is similar to that of the optical semiconductor device ofFIG. 2as illustrated inFIG. 3, except for the formation of the n-side electrodes15-1and15-2.

Even inFIG. 4, the boron concentration of the p-type silicon layer2is adjusted, so as to sufficiently lower the forward rising voltage of the Schottky diode element SBD to be 0.3V to 0.9V and to raise the reverse breakdown voltage of the Schottky diode element SBD to be higher than 10V where the reverse current Iris 100 μA. On the other hand, the power supply terminal T2is in ohmic contact with the p-type silicon layer2via the p+-type monocrystalline silicon support substrate1, and also, is connected to the n-side electrode15-2. Therefore, a current, which should be supplied to the LED elements D1′ and D2′, is never leaked to the Schottky diode element SBD. In addition, the forward voltage drop of the LED elements D1′ and D2′ is not so large. Therefore, the power loss and generated heat of the LED elements D1′ and D2′ can be suppressed.

InFIG. 5, which is a cross-sectional view illustrating a third embodiment of the optical semiconductor device according to the presently disclosed subject matter, the LED element D2″ of a non-via-type are stacked onto the LED element D1″ of a non-via-type.

InFIG. 5, the LED element D1″ formed by the n-type GaN layer4-1, the active layer5-1and the p-type GaN layer6-1, and the LED element D2″ formed by the n-type GaN layer4-2, the active layer5-2and the p-type GaN layer6-2are stacked via a tunnel junction layer21which electrically connects the LED element D1″ to the LED element D2″. The tunnel junction layer21is formed by a pn junction, a pn junction having an intermediate undoped region, or a pn junction having an intermediate doped region from the pn junction.

The LED elements D1″ and D2″ are placed face down and bonded by a wafer pressure-bonding process onto the insulating layer3on the side of the p+-type monocrystalline silicon support substrate1.

InFIG. 5, since the LED element D2″ is stacked on the LED element D1″, the protection layers8-1and8-2ofFIG. 2is combined into a protection layer8. Also, the connection layer10-1ofFIG. 2is unnecessary, and only a connection layer10corresponding to the connection layer10-2ofFIG. 2is present.

The power supply terminals T1and T2are the same as those ofFIG. 2.

Thus, the LED elements D1″ and D2″ are connected in series between the power supply terminals T1and T2.

Even inFIG. 5, the boron concentration of the p-type silicon layer2is adjusted, so as to sufficiently lower the forward rising voltage of the Schottky diode element SBD to be 0.3V to 0.9V and to raise the reverse breakdown voltage of the Schottky diode element SBD to be higher than 10V where the reverse current Iris 100 μA. On the other hand, due to the ohmic contact of the power supply terminal T2connected to the p+-type monocrystalline silicon support substrate1and the connection layer10, the forward voltage drop of the LED elements D1″ and D2″ is not so large. Therefore, a current, which should be supplied to the LED elements D1″ and D2″, is never leaked to the Schottky diode element SBD. In addition, the forward voltage drop of the LED elements D1″ and D2″ is not so large. Therefore, the power loss and generated heat of the LED elements D1″ and D2″ can be suppressed.

InFIG. 6, which is a cross-sectional view illustrating a fourth embodiment of the optical semiconductor device according to the presently disclosed subject matter, the LED element D2′″ of a via-type is stacked onto the LED element D1′″ of a via-type.

InFIG. 6, a via hole11is formed in the n-type GaN layer4-2, the active layer5-2, the p-type GaN layer6-2, the n-type GaN layer4-1, the active layer5-1and the p-type GaN layer6-1ofFIG. 5. Also, provided on the side of the via hole11are p-side electrodes12and13, an insulating layer14made of silicon dioxide or silicon nitride, and an n-side electrode (via electrode)15.

The LED elements D1′″ and D2′″ are placed face down and bonded by a wafer pressure-bonding process onto the insulating layer3on the side of the p+-type monocrystalline silicon support substrate1.

Further, a connection layer16made of TiPtAl is formed so as to electrically connect the p-type GaN layer6-1to the power supply terminal T1.

The power supply terminals T1and T2are the same as those ofFIG. 2.

Thus, the LED elements D1′″ and D2′″ are connected in series between the power supply terminals T1and T2.

Even inFIG. 6, the boron concentration of the p-type silicon layer2is adjusted, so as to sufficiently lower the forward rising voltage of the Schottky diode element SBD to be 0.3V to 0.9V and to raise the reverse breakdown voltage of the Schottky diode element SBD to be higher than 10V where the reverse current Iris 100 μA. On the other hand, the power supply terminal T2is in ohmic contact with the p-type silicon layer2via the p+-type monocrystalline silicon support substrate1, and also, is connected to the n-side electrode15-2. Therefore, a current, which should be supplied to the LED elements D1′″ and D2′″, is never leaked to the Schottky diode element SBD. In addition, the forward voltage drop of the LED elements D1′″ and D2′″ is not so large. Therefore, the power loss and generated heat of the LED elements D1′″ and D2′″ can be suppressed.

InFIG. 7, which is a modification of the optical semiconductor device ofFIG. 6, the power supply terminal T2is provided on a rear surface of the p+-type monocrystalline silicon support substrate1ofFIG. 6. Also, the n-side electrode15ofFIG. 6is connected via the p+-type monocrystalline silicon support substrate1to the power supply terminal T2.

The LED elements D1′″ and D2′″ and the elements12,13,14and15are placed face down and bonded by a wafer pressure-bonding process onto the insulating layer3on the side of the p+-type monocrystalline silicon support substrate1.

The power supply terminal T1is the same as that ofFIG. 6.

The power supply terminal T2is formed on the entire rear surface of the p+-type monocrystalline silicon support substrate1.

Thus, the LED elements D1′″ and D2′″ are connected in series between the power supply terminals T1and T2.

Even inFIG. 7, the boron concentration of the p-type silicon layer2is adjusted, so as to sufficiently lower the forward rising voltage of the Schottky diode element SBD to be 0.3V to 0.9V and to raise the reverse breakdown voltage of the Schottky diode element SBD to be higher than 10V where the reverse current Iris 100 μA. On the other hand, the power supply terminal T2is in ohmic contact with the p-type silicon layer2via the p+-type monocrystalline silicon support substrate1, and also, is connected via the p+-type monocrystalline silicon support substrate1to the n-side electrode15. Therefore, a current, which should be supplied to the LED elements D1′″ and D2′″, is never leaked to the Schottky diode element SBD. In addition, the forward voltage drop of the LED elements D1′″ and D2′″ is not so large. Therefore, the power loss and generated heat of the LED elements D1′″ and D2′″ can be suppressed.

The modification ofFIG. 7can be applied to the optical semiconductor devices ofFIGS. 2,4and5. That is, the power supply terminal T2can be provided on the rear surface of the p+-type monocrystalline silicon support substrate1.

InFIG. 8, which is also a modification of the optical semiconductor device ofFIG. 6, the p+-type monocrystalline silicon support substrate1and the p-type silicon layer2ofFIG. 6are replaced by an n+-type monocrystalline silicon support substrate1′ and an n-type silicon layer2′, respectively. Also, the LED element D′″ is formed by a p-type GaN layer4′-1, an InGaN/GaN MQW active layer5′-1and a p-type GaN layer6′-1, and the LED element D2″ is formed by a p-type GaN layer4′-2, an InGaN/GaN MQW active layer5′-2and a p-type GaN layer6′-2.

The power supply terminal T1ofFIG. 6is replaced by a ground potential power supply terminal T1′ which is made of a metal such as Mg, Mo, Ni, Sb, W, Al, Ag, Cu, Pd, Au or Pt whose work function φmis larger than the work function φsof silicon. That is, φs<φm.

A Schottky diode element SBD′ is constructed by the power supply terminal T1′ and the n-type silicon layer2′ along with the n+-type monocrystalline silicon support substrate1′.

A positive potential power supply terminal T2′ is the same as the power supply terminal T2ofFIG. 6.

The LED elements D1′″ and D2′″ and the elements12′,13′,14′ and15′ are placed face down and bonded by a wafer pressure-bonding process onto the insulating layer3on the side of the n+-type monocrystalline silicon support substrate1′.

Thus, the LED elements D1′″ and D2′″ are connected between the power supply terminals T1′ and T2′.

Even inFIG. 8, the arsenic (or phosphorus) concentration of the n-type silicon layer2′ is adjusted, so as to sufficiently lower the forward rising voltage of the Schottky diode element SBD′ to be 0.3V to 0.9V and to raise the reverse breakdown voltage of the Schottky diode element SBD′ to be higher than 10V where the reverse current Iris 100 μA. On the other hand, the power supply terminal T2′ is in ohmic contact with the n-type silicon layer2′ via the n+-type monocrystalline silicon support substrate1′, and also, is connected to the p-side electrode15′. Therefore, a current, which should be supplied to the LED elements D1′″ and D2′″, is never leaked to the Schottky diode element SBD′. In addition, the forward voltage drop of the LED elements D1′″ and D2′″ is not so large. Therefore, the power loss and generated heat of the LED elements D1′″ and D2′″ can be suppressed.

An equivalent circuit diagram of the optical semiconductor device ofFIG. 8is illustrated inFIG. 9.

The modification ofFIG. 8can be applied to the optical semiconductor devices ofFIGS. 2,4and5.

In the above-described embodiments, the p+-type monocrystalline silicon support substrate1, the p-type silicon layer2, the n+-type monocrystalline silicon support substrate1′ and the n-type silicon layer2′ can be made of Ge, GaAs or the like, other than Si.

Also, in the above-described embodiments, the LED elements D1(D1′, D1″, D1′″) and D2(D2′, D2″, D2′″) can be made of three-element or four-element mixed crystal such as InAlGaAl, InGaAlP or InGaAlN.

Further, in the above-described embodiments, the number of LED elements can be one, three or more.

It will be apparent to those skilled in the art that various modifications and variations can be made in the presently disclosed subject matter without departing from the spirit or scope of the presently disclosed subject matter. Thus, it is intended that the presently disclosed subject matter covers the modifications and variations of the presently disclosed subject matter provided they come within the scope of the appended claims and their equivalents. All related or prior art references described above and in the Background section of the present specification are hereby incorporated in their entirety by reference.