JP7100346B2 - Nitride semiconductor light emitting device - Google Patents

Description

The present invention relates to a nitride semiconductor light emitting device.

Most semiconductor devices are formed by laminating a p-type semiconductor layer and an n-type semiconductor layer. In order to realize an element that operates with high efficiency, a p-type semiconductor layer and an n-type semiconductor layer having a small electric resistance are required. However, in a nitride semiconductor that is considered to be useful as an ultraviolet visible light wavelength region light emitting / receiving element, the electrical resistivity of GaN of the p-type semiconductor layer is 1 Ωcm or more. This is 100 times or more higher than the electrical resistivity of n-type nitride semiconductors, n-type GaAs (gallium arsenide) and p-type GaAs, which are infrared semiconductors, of 0.01 Ωcm or less. Further, AlGaN having a large AlN (aluminum nitride) mole fraction, which is required in the deep ultraviolet region, has a problem that p-type AlGaN cannot be obtained.

Therefore, in Non-Patent Document 1, an n-type semiconductor layer (hereinafter referred to as n ++ semiconductor layer) to which a donor (n-type impurity) is added at a high concentration and an acceptor (p-type impurity) are added to a high concentration. A device structure is disclosed in which a tunnel junction layer in which a p-type semiconductor layer (hereinafter referred to as a p ++ semiconductor layer) is pn-junctioned is arranged on the p side. Specifically, in the device structure disclosed in Non-Patent Document 1, the p-type semiconductor layer arranged on the upper side of the active layer is made into a thin p-type semiconductor layer, the tunnel junction layer is arranged on the upper side thereof, and the tunnel junction layer is further arranged. A relatively thick n-type semiconductor layer is arranged on the upper side of the above. When a current is passed from the n-type semiconductor layer side of this element structure, a reverse bias is applied to the n ++ semiconductor layer and the p ++ semiconductor layer of the tunnel junction layer, and the carrier tunnels from the n ++ semiconductor layer in the tunnel junction layer to the p ++ semiconductor. However, current will flow. In the light emitting element having this tunnel junction layer, it is almost unnecessary to use a p-type semiconductor layer having a higher electric resistance than the n-type semiconductor layer, and an n-type semiconductor layer having a lower electric resistance than the p-type semiconductor layer is used. By doing so, the element resistance can be significantly reduced.

On the other hand, in order to reduce the total element resistance, it is necessary to reduce the electrical resistance of the tunnel junction layer. If the electric resistance of the tunnel junction itself can be reduced, the electric resistance of the conventional element can be further reduced, and further, the surface emitting laser and the deep ultraviolet light emitting element, which are currently delayed in practical use, can be put into practical use. Become.
As shown in Non-Patent Document 2, a tunnel junction generally has a structure in which a p ++ semiconductor layer and an n ++ semiconductor layer are joined, and a depletion layer is formed in each layer, and the sum of the thicknesses of these depletion layers is the tunnel. It is the thickness of the depletion layer formed in the junction layer. The thinner the depletion layer, the easier it is for electrons to tunnel from the valence band to the conduction band, allowing current to flow from the n ++ semiconductor layer to the p ++ semiconductor layer with low electrical resistance. The width W of the depletion layer is generally expressed by the following equation.

Here, ε _s : the permittivity of the semiconductor, V _bi : the applied voltage, _ND : _n ++ is the effective donor concentration in the semiconductor layer, and NA: p ++ is the effective acceptor concentration in the semiconductor layer. From this equation, it can be seen that the higher the _ND (effective donor concentration) and _NA (effective acceptor concentration), the narrower the width W of the depletion layer. However, ND and _NA are so _- called effective concentrations. For example, in the case of forming an n ++ semiconductor layer on the upper side of the surface side of the p ++ semiconductor layer, if the acceptor concentration in the p ++ semiconductor layer is made too high, the acceptor is diffused in the n ++ semiconductor layer directly above, and the diffused acceptor causes n ++. Donors in the semiconductor layer are compensated. As a result, the effective donor concentration ND in the _n ++ semiconductor layer decreases, and decreases to _{ND −NA} . As a result, the width W of the depletion layer is widened, and the electrical resistance of the tunnel junction layer is high. Therefore, in the tunnel junction layer, the acceptor concentration and the donor concentration are made extremely high in each of the p ++ semiconductor layer and the n ++ semiconductor layer, and the interface between the p ++ semiconductor layer and the n ++ semiconductor layer (hereinafter referred to as the tunnel junction layer). The concentration profile at the interface) is steeply controlled (in the above case, in the p ++ semiconductor layer, the acceptor concentration is sharply lowered toward the interface with the n ++ semiconductor layer, and p ++ in the n ++ semiconductor layer. It is known that it is necessary to suppress the acceptance and donors from compensating each other and increase the effective acceptor concentration and the effective donor concentration by rapidly increasing the donor concentration as the distance from the interface with the semiconductor layer increases. Has been. Therefore, it is considered possible to reduce the electrical resistance of the tunnel junction layer by appropriately controlling the acceptor concentration and the donor concentration profile based on the above basic theory.

T.Takeuchi et al., "GaN-Based Light Emitting Diodes with Tunnel Junctions", Jpn.J.Appl.Phys.Vol.40 (2001), pp.L861-L863. S.M.Sze Physics of Semiconductor Devices (2nd Edition), John Wiley & Sons, (1981) D. Minamikawa, et al ,, "GaInN-based tunnel junctions with high InN mole fractions grown by MOVPE" Physica Status Solidi, May 2015, Vol. 252, Issue 5, P. 1127-1131 Erin C. Young, Benjamin P. Yonkee, Feng Wu, Sang Ho Oh, Steven P. DenBaars, Shuji Nakamura and James S. Speck "Hybrid tunnel junction contacts to III-nitride light-emitting diodes", Applied Physics Express, (USA) ), 2016, Vol. 9, Number2, P.022102 B.P.Yonkee, E.C.Young, S.P.DenBaars, S.Nakamura, J.S.Speck "Silver free III-nitride flip chip light-LED-diode with wall plug efficiency over 70% utilizing a GaN tunnel junction" Applied Physics Letter, (USA), 2016 Year, Vol. 109, Issue 19, P.M. 191104

However, since the bandgap of the nitride semiconductor is more than twice as large as that of the conventional semiconductor, it is difficult for carriers to tunnel in the first place, and it is also difficult to steeply control the concentration profile of the acceptor. Therefore, it is considered difficult to realize a tunnel junction layer having low electrical resistance by using a nitride semiconductor.
Under such circumstances, in the tunnel junction layer using a nitride semiconductor, a GaInN layer having a small bandgap is used as shown in Non-Patent Document 3, or an acceptor (p-type) is used as shown in Non-Patent Document 4. The MBE method, which makes it easy to control the concentration profile of Mg (hereinafter referred to as Mg), which is an impurity), is used, or as shown in Non-Patent Document 5, the wafer is once taken out from the growth furnace at the interface of the tunnel junction layer and washed. After that, the tunnel junction layer of the nitride semiconductor with low electric resistance is realized by devising such as regrowth.

However, in the tunnel junction layer using a nitride semiconductor, the most basic acceptor concentration and donor concentration, and the design guideline regarding these concentration profiles are only the basic theory disclosed in Non-Patent Document 2.
Therefore, the inventors evaluated the drive voltage of the tunnel junction layer created by controlling the respective concentration profiles of the acceptor concentration and the donor concentration based on this basic theory, and investigated the correlation between the acceptor and the donor in detail. ..
As described above, in this basic theory, Mg and Si (hereinafter referred to as Si) which is a donor (n-type impurity) are used to form a p ++ semiconductor layer and an n ++ semiconductor layer, and each of the Mg and Si is formed. The concentration profile of is steeply formed at the interface of the tunnel junction layer, the p ++ semiconductor layer and the n ++ semiconductor layer are bonded, and the position showing the maximum value of each of Mg and Si is in the thickness direction of the tunnel junction layer (hereinafter, the thickness direction). The structure of the concentration profile that exists separately in () was considered to be optimal (see FIG. 1 (A)). However, since it is difficult to steeply control the concentration profile of Mg in a nitride semiconductor, it is difficult to realize a tunnel junction layer having low electrical resistance. The n-side end of the tunnel junction layer is the position where the Si concentration profile changes from a substantially flat state to an increasing state toward the p-side, and the p-side end is the position of Mg toward the n-side. This is the position where the concentration profile changes from a nearly flat state to an increasing state.

The present invention has been made in view of the above-mentioned conventional circumstances, and is realized by more appropriately forming the respective concentration profiles of the donor and the acceptor in the tunnel junction layer using the nitride semiconductor. It is an issue to be solved to provide a nitride semiconductor light emitting device capable of emitting light with high efficiency by using a low resistance tunnel junction layer.

Here, when measuring the respective concentrations of Mg and Si, it is necessary to measure under different measurement conditions due to the limitation of the lower limit of measurement, so that the measurement has not been performed at the same time in the past. Therefore, it was not possible to accurately grasp the positional relationship between the positions showing the maximum values of the respective concentrations of Mg and Si in the thickness direction.
However, in the tunnel junction layer, since the respective concentrations of Mg and Si are high, the respective concentration profiles of Mg and Si can be measured simultaneously by one measurement. This makes it possible for the inventors to grasp the accurate positional relationship in the thickness direction of the position showing the maximum value of each concentration of Mg and Si in the tunnel junction layer having low electric resistance using a nitride semiconductor. there were.
As a result, as shown in FIG. 1 (B), the nitride semiconductor has a structure in which Si having a concentration higher than the Mg concentration exists at a position in the thickness direction indicating the maximum value of the Mg concentration in the tunnel junction layer. It was found that the electrical resistance of the tunnel junction layer using the above is greatly reduced. According to the conventional basic theory disclosed in Non-Patent Document 2, all Mg in the tunnel junction layer is compensated by Si, and the effective acceptor concentration becomes 0, which is a completely unfavorable structure as a tunnel junction layer. ..

In the nitride semiconductor light emitting element of the first invention, the acceptor concentration in the tunnel junction layer from the position showing the maximum value of the acceptor concentration to the n-side end of the tunnel junction layer is lower than the donor concentration, and the acceptor The value of the donor concentration and the value of the acceptor concentration from the position showing the maximum value of the acceptor concentration, rather than the distance in the thickness direction from the position showing the maximum value of the concentration to the position showing the maximum value of the donor concentration. It is characterized in that the distance in the thickness direction to the position where is the same is large.

In the tunnel junction layer of this nitride semiconductor light emitting device, the presence of both the acceptor and the donor at a predetermined position in the thickness direction of the tunnel junction layer forms an impurity level in the band, which is relatively large. It is thought that the density of states of electrons and holes can exist, which can contribute to the tunnel current generated in the tunnel junction layer.

Therefore, the nitride semiconductor light emitting device of the present invention can emit light with high efficiency.
Further, in the nitride semiconductor light emitting element of the second invention , the acceptor concentration in the tunnel junction layer from the position showing the maximum value of the acceptor concentration to the n-side end of the tunnel junction layer is higher than the donor concentration. Low, the maximum value of the acceptor concentration and the maximum value of the donor concentration are located in the tunnel junction layer, and the effective acceptor concentration is monotonically decreasing toward the p-side end of the tunnel junction layer. It is characterized by.

It is a schematic diagram which shows the concentration profile of each of a donor and an acceptor in a tunnel junction layer, (A) shows the conventional concentration profile, and (B) shows the concentration profile of this invention. It is a schematic diagram which shows the structure of the state which the element was formed using the sample of Examples 1 and 2 and the sample of Comparative Examples 1 and 3. 6 is a graph showing changes in Mg and Si concentrations in the thickness direction of the tunnel junction layer of the samples of Examples 1 and 2 and Comparative Examples 1 and 2. 3 is a graph showing changes in the effective donor concentration and the effective acceptor concentration in the thickness direction of the tunnel junction layer of the samples of Examples 1 and 2 and Comparative Examples 1 and 2. 3 is a graph showing changes in the magnitude of voltage with respect to the current of the samples of Examples 1 and 2 and Comparative Examples 1 and 2. It is a graph which shows the change of each concentration of Mg and Si in the thickness direction of the tunnel junction layer of the sample of the comparative example 3. FIG. It is a graph which shows the change of the magnitude of voltage with respect to the current of the sample of Example 2 and Comparative Example 3. FIG.

A preferred embodiment of the present invention will be described.

In the nitride semiconductor light emitting device of the present invention, the position showing the maximum value of the acceptor concentration in the tunnel junction layer has the same value of the donor concentration and the value of the acceptor concentration as the position of the n-side end of the tunnel junction layer. It may be closer to the position. In this case, the nitride semiconductor light emitting device can suppress segregation of the acceptor at the n-side end of the tunnel junction layer.

In the tunnel junction layer of the nitride semiconductor light emitting device of the present invention, the position showing the maximum value of the acceptor concentration and the position showing the maximum value of the donor concentration are tunneled from the position where the value of the donor concentration and the value of the acceptor concentration match. It may be located on the n side of the junction layer. In this case, the nitride semiconductor light emitting device can surely have each of the position showing the maximum value of the acceptor concentration and the position showing the maximum value of the donor concentration in the tunnel junction layer, and in the tunnel junction layer, Each of the acceptor concentration and the donor concentration can be surely increased.

In the tunnel junction layer of the nitride semiconductor light emitting device of the present invention, the value of the donor concentration at the position showing the maximum value of the acceptor concentration may be at least twice or more the maximum value of the acceptor concentration. In this case, it is considered that the nitride semiconductor light emitting device can have a larger density of states of electrons and holes, which can contribute to the tunnel current generated in the tunnel junction layer.

In the tunnel junction layer of the nitride semiconductor light emitting device of the present invention, the acceptor concentration is less than 1 × 10 ²⁰ cm ^-3 and the donor concentration is 1 × 10 on the n side of the tunnel junction layer from the position showing the maximum value of the acceptor concentration. The region of ²⁰ cm ^-3 or more may be 6 nm or more. In this case, the nitride semiconductor light emitting device can further suppress segregation of the acceptor on the n side of the tunnel junction layer.

Next, Examples 1 and 2 and Comparative Examples 1 to 3 embodying the nitride semiconductor light emitting device of the present invention will be described with reference to the drawings.

<Examples 1 and 2 and Comparative Examples 1 to 3>

As shown in FIG. 2, the nitride semiconductor light emitting devices of Examples 1 and 2 and Comparative Examples 1 and 2 include a first n-GaN layer 11, a GaInN / GaN5 weight child well active layer 12, and a p-AlGaN layer 13. It includes a p-GaN layer 14, a tunnel junction layer 15, and a second n-GaN layer 16.

The nitride semiconductor light emitting devices of Examples 1 and 2 and Comparative Examples 1 and 2 are on the front surface side of the sapphire substrate 9 (hereinafter referred to as substrate 9) which is a substrate (the table is the upper side in FIG. 2, the same applies hereinafter). The u-GaN layer 10 formed via a low-temperature deposition buffer layer (not shown) is laminated on the surface side of the u-GaN layer 10 by using a MOCVD method (metalorganic vapor phase growth method) to grow crystals. The surface of the sapphire substrate 9 and the u-GaN layer 10 is the c-plane ((0001) plane).

First, the first n-GaN layer 11 is laminated on the surface of the u-GaN layer 10 formed on the surface side of the substrate 9 to grow crystals. Specifically, first, the substrate 9 having the u-GaN layer 10 formed on its surface is set in the reaction furnace of the MOCVD apparatus capable of executing the MOCVD method. Then, NH ₃ (ammonia), which is a raw material of N (nitrogen), and H ₂ (hydrogen), which is a carrier gas, are supplied into the reactor, and the temperature inside the reactor is adjusted to raise the temperature of the substrate to 1050 ° C. To. The gas supplied into the reactor will not be stopped until otherwise stated. Then, TMGa (trimethylgallium), which is a raw material of Ga (gallium), and SiH ₄ (silane), which is a raw material of Si (silicon), are supplied into the reaction furnace, and the first n-GaN layer 11 having a thickness of 2 μm is supplied. Are laminated to grow crystals. The amount of SiH ₄ supplied into the reaction furnace is adjusted so that the concentration of Si added to the first n-GaN layer 11 is 1 × 10 ¹⁹ cm ^-3 .

Next, the GaInN / GaN5 weight element well active layer 12 is laminated on the surface of the first n-GaN layer 11 to grow crystals. The GaInN / GaN5 weight element well active layer 12 has a GaInN well layer (not shown) and a GaN barrier layer (not shown).

First, the GaInN well layer is laminated to grow crystals. Specifically, the supply of H ₂ , TMGa, and SiH ₄ into the reactor will be stopped. That is, the supply of gas of raw materials other than NH ₃ is stopped. Then, N ₂ (nitrogen) is supplied as a carrier gas into the reactor. Then, the temperature in the reactor is adjusted to bring the temperature of the substrate 9 to 780 ° C. Then, TEGa (triethyl gallium), which is a raw material for Ga, and TMIn (trimethylindium), which is a raw material for In (indium), are supplied into the reaction furnace, and a GaInN well layer having a thickness of 3 nm is laminated to grow crystals. Let me.

Next, a GaN barrier layer is laminated on the surface of the GaInN well layer to grow crystals. Specifically, the supply of TMIn into the reactor is stopped, and a GaN barrier layer having a thickness of 6 nm is laminated to grow crystals. The GaInN quantum well layer and the GaN barrier layer grown in this way are used as one pair, and five pairs of these one pair are laminated to grow crystals. In this way, the GaInN / GaN5 weight well active layer 12 is formed. Then, the supply of TEGa and TMIn to the reactor is stopped.

Next, the p-AlGaN layer 13 is laminated on the surface of the GaInN / GaN5 weight well active layer 12 to grow crystals. Specifically, the carrier gas supplied into the reactor is switched from N ₂ to H ₂ . Then, the temperature inside the reactor is adjusted to bring the temperature of the substrate 9 to 1000 ° C. Then, TMGa (trimethylaluminum), which is a raw material of TMGa, Al (aluminum), and Cp ₂ Mg (cyclopentadienylmagnesium), which is a raw material of Mg (magnesium), are supplied into the reaction furnace to have a thickness of 20 nm. The p-AlGaN layer 13 is laminated and crystal growth is performed. The amount of Cp ₂ Mg supplied into the reaction furnace is adjusted so that the concentration of Mg added to the p-AlGaN layer 13 is 3 × 10 ¹⁹ cm ^-3 .

Next, the p-GaN layer 14 is laminated on the surface of the p-AlGaN layer 13 to grow crystals. Specifically, the supply of TMAl to the reactor is stopped, and the p-GaN layer 14 having a thickness of 160 nm is laminated to grow crystals. The concentration of Mg added to the p-GaN layer 14 is 4 × 10 ¹⁹ cm ^-3 .

Next, a tunnel junction layer 15 using a nitride semiconductor is formed on the surface of the p-GaN layer 14 in the reaction furnace. The tunnel junction layer 15 is a p ++-GaN junction layer 15A that uses GaN as a base material and Mg as an acceptor (p-type impurity), and an n-type tunnel that uses Si as a donor (n-type impurity). It has an n ++-GaN layer 15B which is a junction layer.
Further, in Examples 1 and 2 and Comparative Examples 1 and 2, the concentration profiles in the thickness direction of Si are the same as each other, and the concentration profiles in the thickness direction of Mg are changed.

First, an acceptor is added to form the p ++-GaN layer 15A. Specifically, TEGa and Cp ₂ Mg are supplied into the reactor. In this way, the p ++-GaN layer 15A having a thickness of several nm to several ten and several nm is grown. The flow rates of TEGa and Cp ₂ Mg are adjusted so that the maximum concentration of Mg added to the p ++-GaN layer 15A is 2 to 3 × 10 ²⁰ cm ^-3 . In this way, the crystal growth of the p ++-GaN layer 15A is completed. Then, the supply of TEGa and Cp ₂ Mg to the reactor is stopped. That is, the supply of gas of raw materials other than NH ₃ is stopped.

Next, the n ++-GaN layer 15B is laminated on the surface of the p ++-GaN layer 15A to grow crystals. Specifically, the supply of Cp ₂ Mg into the reactor is stopped. Then, TEGa and SiH ₄ are supplied into the reaction furnace, and an n ++-GaN layer 15B having a thickness of 15 nm is laminated to grow crystals. The maximum concentration of Si added to the n ++-GaN layer 15B is 5 to 7 × 10 ²⁰ cm ^-3 . After that, the supply of TEGa and SiH ₄ to the reactor is stopped.
In Examples 1 and 2 and Comparative Examples 1 and 2, when the p ++-GaN layer 15A is formed, the position in the thickness direction indicating the maximum value of the Mg concentration is shown by adjusting the supply amount of Mg (hereinafter, Mg). The position in the thickness direction (hereinafter referred to as the position indicating the maximum value of Si) indicating the maximum value of the concentration of Si with respect to the position indicating the maximum value of Si) is 1.8 nm, 2.5 nm, 4.3 nm, 7.2 nm. It is changed into 4 types. The position showing the maximum value of Si with respect to the position showing the maximum value of Mg is 1.8 nm in Example 1, 2.5 nm in Example 2, 4.3 nm in Comparative Example 1, and Comparative Example 2. Is 7.2 nm.

After that, the supply of TEGa and SiH ₄ to the reactor is stopped. That is, the supply of raw materials to the reactor other than NH ₃ is stopped. In this way, the tunnel junction layer 15 is formed in each of Examples 1 and 2 and Comparative Examples 1 and 2.

Next, the second n-GaN layer 16 is laminated on the surface of the tunnel junction layer 15 to grow crystals. Specifically, the temperature inside the reactor is adjusted to bring the temperature of the substrate 9 to 1050 ° C. Then, TMGa and SiH ₄ are supplied into the reactor. Then, the second n-GaN layer 16 is laminated with a thickness of 400 nm to grow crystals. The concentration of Si, which is an n-type impurity added to the second n-GaN layer 16, is 1 × 10 ¹⁹ cm ^-3 .
Then, the supply of TMGa and SiH ₄ to the reactor is stopped to end the crystal growth. Then, the carrier gas supplied into the reactor is switched from H ₂ to N ₂ . Then, when the temperature in the reactor is adjusted and the temperature of the substrate 9 becomes 400 ° C. or lower, the supply of NH ₃ to the reactor is stopped. Then, after the temperature of the substrate 9 reaches room temperature, the inside of the reactor is purged and the substrate 9 is taken out from the reactor. In this way, the substrates 9 of Examples 1 and 2 and Comparative Examples 1 and 2 having the layer structure shown in FIG. 1 can be produced.

Next, each of the samples of Examples 1 and 2 and Comparative Examples 1 and 2 provided with the tunnel junction layer 15 formed by the nitride semiconductor by growing crystals according to the above procedure to form a layer structure was used. FIGS. 3 (A) to 3 (D) show the results of simultaneously measuring the concentration profiles of Mg and Si samples in the thickness direction by SIMS before forming into a current-injectable device.
Here, the SIMS measurement conditions are shown below. Measuring device: CAMECA IMS-6F, primary ion species: Cs ⁺ , primary acceleration voltage, 5.0 kV, detection area: 60 μmφ. The measured concentrations were calibrated using standard ion-implanted samples. By simultaneously measuring the concentrations of Mg and Si under these measurement conditions, the relationship between the concentration profiles of Mg and Si in the thickness direction can be clearly obtained.
In the process of forming the tunnel junction layer 15, the thicknesses of the p ++-GaN layer 15A and the n ++-GaN layer 15B are described in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, but this is p ++. -In each of the GaN layer 15A and the n ++-GaN layer 15B, it is the thickness of the region where Mg and Si are added at a predetermined concentration or more.
As shown in FIGS. 3A to 3D, the n-side end En of the tunnel junction layer 15 of the samples of Examples 1 and 2 and Comparative Examples 1 and 2 has a Si concentration profile toward the p-side. Is the position where is changed from the almost flat state to the increasing state. Further, the p-side end Ep of the tunnel junction layer 15 of the samples of Examples 1 and 2 and Comparative Examples 1 and 2 changes from a substantially flat state to an increasing state toward the n-side. The position.

As shown in FIGS. 3A to 3D, the sample (+ 1.8 nm) of Example 1 has the smallest position indicating the maximum value of Si with respect to the position indicating the maximum value of Mg, and the sample of Example 2 is used. (+ 2.5 nm), the sample of Comparative Example 1 (+4.3 nm), and the sample of Comparative Example 2 (+7.2 nm) increase in this order. "+" Is from the surface of the sapphire substrate 9 where the position indicating the maximum value of Si is on the n side of the position indicating the maximum value of Mg (that is, the position indicating the maximum value of Si is the position indicating the maximum value of Mg). It is shown to be on the distant side and on the left side in FIGS. 3A to 3D).
In the samples of Examples 1 and 2 and Comparative Examples 1 and 2, the concentrations of Mg and Si were tunneled in the range of 1 × 10 ¹⁹ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less. It decreases with almost the same inclination toward the n-side end En of the junction layer 15.
In the samples of Examples 1, 2 and Comparative Example 1, the Mg concentration in the tunnel junction layer 15 from the position showing the maximum value of the Mg concentration to the n-side end En of the tunnel junction layer 15 is lower than the Si concentration. ..
Further, in the samples of Examples 1, 2 and Comparative Example 1, the position showing the maximum value of Mg concentration in the tunnel junction layer 15 is the value of Si concentration rather than the position of the end En on the n side of the tunnel junction layer 15. And near the position Snp where the value of Mg concentration coincides.
Further, in the samples of Examples 1 and 2 and Comparative Example 1, in the tunnel junction layer 15, the position showing the maximum value of Mg concentration and the position showing the maximum value of Si concentration are the value of Si concentration and the value of Mg concentration. It is located on the n side of the tunnel junction layer 15 from the position Snp that coincides with.

As shown in FIG. 3A, the maximum value of Mg in the sample of Example 1 is about 2 × 10 ²⁰ cm ^-3 . Further, the magnitude of the concentration of Si at the position showing the maximum value of Mg is about 6 × 10 ²⁰ cm ^-3 . That is, in the sample of Example 1, the magnitude of the concentration of Si with respect to the concentration of Mg at the position showing the maximum value of Mg is about three times.
Further, in the sample of Example 1, the concentration of Mg was less than 1 × 10 ²⁰ cm ^-3 in the region where the concentration of Mg decreased from the position showing the maximum value of Mg toward the n side of the tunnel junction layer 15. Moreover, the region where the concentration of Si is 1 × 10 ²⁰ cm ^-3 or more is about 7 nm. In the sample of Example 1, in the range where the concentrations of Mg and Si are 1 × 10 ¹⁹ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less, the curve of the graph showing the concentration of Si is the graph showing the concentration of Mg. It is deviated to the n side by about 7 nm from the curve.

As shown in FIG. 3B, the maximum value of Mg in the sample of Example 2 is about 3 × 10 ²⁰ cm ^-3 . Further, the magnitude of the concentration of Si at the position showing the maximum value of Mg is about 6 × 10 ²⁰ cm ^-3 . That is, in the sample of Example 2, the magnitude of the concentration of Si with respect to the concentration of Mg at the position showing the maximum value of Mg is about twice.
Further, in the sample of Example 2, the concentration of Mg was less than 1 × 10 ²⁰ cm ^-3 in the region where the concentration of Mg decreased from the position showing the maximum value of Mg toward the n side of the tunnel junction layer 15. Moreover, the region where the concentration of Si is 1 × 10 ²⁰ cm ^-3 or more is about 6 nm. In the sample of Example 2, in the range where the concentrations of Mg and Si are 1 × 10 ¹⁹ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less, the curve of the graph showing the concentration of Si is the graph showing the concentration of Mg. It is shifted to the n side by about 6 nm from the curve.

As shown in FIG. 3C, the maximum value of Mg in the sample of Comparative Example 1 is about 3 × 10 ²⁰ cm ^-3 . The magnitude of the concentration of Si at the position showing the maximum value of Mg is about 4 × 10 ²⁰ cm ^-3 . That is, in the sample of Comparative Example 1, the magnitude of the concentration of Si with respect to the concentration of Mg at the position showing the maximum value of Mg is about 1.3 times.
Further, in the sample of Comparative Example 1, the concentration of Mg was less than 1 × 10 ²⁰ cm ^-3 in the region where the concentration of Mg decreased from the position showing the maximum value of Mg toward the n side of the tunnel junction layer 15. Moreover, the region where the concentration of Si is 1 × 10 ²⁰ cm ^-3 or more is about 9 nm. In the sample of Comparative Example 1, in the range where the concentrations of Mg and Si are 1 × 10 ¹⁹ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less, the curve of the graph showing the concentration of Si is the graph showing the concentration of Mg. It is shifted to the n side by about 9 nm from the curve.

As shown in FIG. 3D, the maximum value of Mg in the sample of Comparative Example 2 is about 3 × 10 ²⁰ cm ^-3 . The magnitude of the Si concentration at the position showing the maximum value of Mg is about 7 × 10 ¹⁹ cm ^-3 . That is, in the sample of Comparative Example 2, the magnitude of the concentration of Si with respect to the concentration of Mg at the position showing the maximum value of Mg is about 0.2 times.
Further, in the sample of Comparative Example 2, the concentration of Mg was less than 1 × 10 ²⁰ cm ^-3 in the region where the concentration of Mg decreased from the position showing the maximum value of Mg toward the n side of the tunnel junction layer 15. Moreover, the region where the concentration of Si is 1 × 10 ²⁰ cm ^-3 or more is about 12 nm. In the sample of Comparative Example 2, in the range where the concentrations of Mg and Si are 1 × 10 ¹⁹ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less, the curve of the graph showing the concentration of Si is the graph showing the concentration of Mg. It is deviated to the n side by about 12 nm from the curve.

In the conventional basic theory, the effective donor concentration (ND _{- NA} ), which is the donor concentration compensated by the acceptor, and the effective acceptor concentration (NA _{- ND} ), which is the acceptor concentration compensated by the donor, are important. The graphs in which the effective donor concentration and the effective acceptor concentration are re-plotted from the results of the SIMS measurements in FIGS. 3 (A) to 3 (D) are shown in FIGS. 4 (A) to 4 (D). As shown in FIGS. 4A to 4D, a high effective donor concentration and a high effective acceptor concentration can be realized in the vicinity of the interface B of the tunnel junction layer 15 in the sample of Comparative Example 2 (+7. 2 nm). Specifically, the sample of Comparative Example 2 has both an effective donor concentration and an effective acceptor concentration exceeding 1 × 10 ²⁰ cm ^-3 .
On the other hand, as the distance between the position showing the maximum value of Mg and the position showing the maximum value of Si becomes short (Examples 1, 2 and Comparative Example 1), the vicinity of the interface B of the tunnel junction layer 15 In the samples of Examples 1 and 2, the maximum value of the effective acceptor concentration does not clearly exist, and it seems that the structure is difficult to function as a tunnel junction layer in the conventional basic theory. ..

Next, a step of forming an element capable of injecting an electric current using each of the samples of Examples 1 and 2 and Comparative Examples 1 and 2 will be described with reference to FIG.

First, in a plan view from the surface, a circular mesa structure 20 having a diameter of 35 μm is formed on the substrate 9. Specifically, the mesa structure 20 is formed on the substrate 9 by using photolithography and dry etching. More specifically, a circular photoresist or metal mask having a diameter of 35 μm is formed on the surface of the second n-GaN layer 16 which is laminated on the outermost surface of the substrate 9 and crystal-grown (not shown). The area directly under the photoresist or metal mask is not removed by etching. Further, the region where the photoresist or the metal mask is not formed is etched until the first n-GaN layer 11 is exposed on the surface. A second electrode 22, which will be described later, is formed on the exposed first n-GaN layer 11. In this way, the mesa structure 20 having a circular shape with a diameter of 35 μm is formed on the substrate 9.

Next, the substrate 9 on which the mesa structure 20 was formed was annealed at 725 ° C. for 30 minutes in an O ₂ (oxygen) atmosphere, and the embedded p-AlGaN layer 13, the p-GaN layer 14, and the tunnel junction were performed. Activates Mg in the p ++-GaN layer 15A of layer 15. Here, activation means the release of H (hydrogen) bonded to Mg, which is a p-type impurity, to activate Mg, and the p-AlGaN layer 13, the p-GaN layer 14, and the p-GaN layer 14 to which Mg is added. This is to improve the electrical conductivity of the p ++-GaN layer 15A of the tunnel junction layer 15. By activating in this way, Mg was inactivated from each side surface of the p-AlGaN layer 13, the p-GaN layer 14, and the p ++-GaN layer 15A of the tunnel junction layer 15 whose side surfaces were exposed by etching. To leave.

Next, the first electrode 21 and the second electrode 22 are formed. Specifically, the first electrode 21 having a circular shape is formed on the surface of the mesa structure 20. Further, the annular second electrode 22 is formed on the exposed surface of the first n-GaN layer 11 so as to surround the mesa structure 20. The first electrode 21 and the second electrode 22 are Ti / Al / Ti / Au. Further, the first electrode 21 and the second electrode 22 are collectively formed. In this way, of Examples 1 and 2 and Comparative Examples 1 and 2 in which a current can be passed from the first electrode 21 to the second electrode 22 through the tunnel junction layer 15 and the GaInN / GaN5 weight element well active layer 12. A nitride semiconductor light emitting device is formed.

Next, FIG. 5 shows the results of measuring the current-voltage characteristics of the samples of Examples 1 and 2 and Comparative Examples 1 and 2 formed in the element capable of injecting a current.
As shown in FIG. 5, as the position showing the maximum value of Si with respect to the position showing the maximum value of Mg becomes shorter than the sample of Comparative Example 2 (that is, shorter than +7.2 nm), the drive voltage sharply decreases. The sample of Example 2 (+2.5 nm) has the lowest value. Further, although the drive voltage of the sample of Example 1 (+ 1.8 nm) was slightly higher than that of the sample of Example 2 (+ 2.5 nm), it was sufficiently higher than that of the sample of Comparative Example 2 (+7.2 nm). It was a low value.
According to the conventional basic theory, in the concentration profile of the sample (+7.2 nm) of Comparative Example 2, the width of the depletion layer is the narrowest and the drive voltage is the lowest, while the position of the maximum value of Mg and the position of Si. As the distance from the position of the maximum value becomes shorter (Examples 1, 2, and Comparative Example 1), the effective acceptor concentration and the effective donor concentration each decrease, so that the width of the depletion layer is widened and driven. It was thought that the voltage would increase, but the result was exactly the opposite.
Nitride semiconductors are used due to the structure in which Si having a concentration higher than the concentration of Mg exists at the position showing the maximum value of Mg in the tunnel junction layer 15 as in the samples of Examples 1, 2 and Comparative Example 1. The electrical resistance of the tunnel junction layer 15 that has been formed is greatly reduced.
Then, more preferably, as shown in FIGS. 3 (A) and 3 (B), which are the samples of Examples 1 and 2, the value of the Si concentration at the position showing the maximum value of the Mg concentration in the tunnel junction layer 15 is set. When it is at least twice or more the maximum value of the Mg concentration, the electric resistance of the tunnel junction layer 15 using the nitride semiconductor is further lowered.

Next, in order to verify the effect of the change in the thickness of the n ++-GaN layer 15B on the electrical characteristics in the tunnel junction layer 15, a sample of Comparative Example 3 was prepared.

The sample of Comparative Example 3 is different from Examples 1 and 2 and Comparative Examples 1 and 2 in that the thickness of the n ++-GaN layer 115B of the tunnel junction layer 115 is 5 nm. Other configurations are the same as those in the second embodiment, the same configurations are designated by the same reference numerals, and detailed description thereof will be omitted. Further, regarding the method for producing the element structure of the sample of Comparative Example 3, the same steps as the methods for producing Examples 1 and 2 and Comparative Examples 1 and 2 will not be described in detail.

The tunnel junction layer 115 is an n-type tunnel using p++-GaN layer 15A, which is a p-type tunnel junction layer using GaN as a base material and Mg as an acceptor (p-type impurity), and Si as a donor (n-type impurity). It has an n ++-GaN layer 115B which is a junction layer.

In the tunnel junction layer 115, the p ++-GaN layer 15A is grown by 10 nm on the surface of the p-GaN layer 14. The maximum concentration of Mg added to the p ++-GaN layer 15A is 3 × 10 ²⁰ cm ^-3 . The amount of Mg supplied when forming the p ++-GaN layer 15A of Comparative Example 3 is adjusted to be the same as that of Example 2.

Next, the n ++-GaN layer 115B having a thickness of 5 nm is laminated on the surface of the p ++-GaN layer 15A to grow crystals. The maximum concentration of Si added to the n ++-GaN layer 115B is 6 × 10 ²⁰ cm ^-3 .
In this way, the tunnel junction layer 115 is formed. After that, the second n-GaN layer 16 is laminated on the surface of the tunnel junction layer 115 to grow crystals, and a sample of Comparative Example 3 is prepared. The sample of Comparative Example 3 has the same layer structure as Examples 1 and 2 and Comparative Examples 1 and 2 (see FIG. 2).

Next, FIG. 6 shows the results of simultaneously measuring the concentration profiles in the thickness direction of the Mg and Si samples in the state before forming the current-injectable element of the sample of Comparative Example 3 thus produced by SIMS. The measurement conditions are the same as those of Examples 1 and 2 and Comparative Examples 1 and 2.
The n-side end En of the tunnel junction layer 115 of the sample of Comparative Example 3 is a position where the concentration profile of Si changes from a substantially flat state to an increasing state toward the p side, and the sample of Comparative Example 3 is sampled. The end Ep on the p side of the tunnel junction layer 115 is a position where the concentration profile of Mg changes from a substantially flat state to an increasing state toward the n side.

As shown in FIG. 6, in the sample of Comparative Example 3, Si having a concentration higher than the concentration of Mg is present at a position showing the maximum value of Mg. This point is the same as in Examples 1, 2 and Comparative Example 1. Specifically, the sample of Comparative Example 3 has a maximum value of Mg of about 3 × 10 ²⁰ cm ^-3 . The magnitude of the concentration of Si at the position showing the maximum value of Mg is about 6 × 10 ²⁰ cm ^-3 . That is, in the sample of Comparative Example 3, the magnitude of the concentration of Si with respect to the concentration of Mg at the position showing the maximum value of Mg is about twice.
Further, in the sample of Comparative Example 3, the region where the concentration of Mg decreases from the position showing the maximum value of Mg toward the n side (left side in FIG. 6) of the tunnel junction layer 115, and the concentration of Mg and Si is 1 ×. In the range of 10 ¹⁹ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less, the concentrations of Mg and Si decrease with almost the same inclination toward the n side of the tunnel junction layer 115. This point is also the same as in Examples 1 and 2 and Comparative Examples 1 and 2.
However, the sample of Comparative Example 3 has a significantly different Si concentration profile on the n side of the tunnel junction layer 115 from Examples 1 and 2 and Comparative Examples 1 and 2. Specifically, the concentration of Mg is less than 1 × 10 ²⁰ cm ^-3 in the region where the concentration of Mg decreases from the position showing the maximum value of Mg in the sample of Comparative Example 3 toward the n side of the tunnel junction layer 115. The region where the Si concentration is 1 × 10 ²⁰ cm ^-3 or more is 0 nm. That is, in the sample of Comparative Example 3, the region where the concentration of Mg decreases from the position showing the maximum value of Mg toward the n side of the tunnel junction layer 115, and the concentration of Mg and Si is 1 × 10 ¹⁹ cm ^-3 or more. In the range of 1 × 10 ²⁰ cm ^-3 or less, the curve of the graph showing the concentration of Si almost overlaps with the curve of the graph showing the concentration of Mg and decreases toward the n side of the tunnel junction layer 115. ..
On the other hand, in the sample of Example 2, the region where the concentration of Mg decreases from the position showing the maximum value of Mg toward the n side of the tunnel junction layer 15, and the concentration of Mg and Si is 1 × 10 ¹⁹ cm. In the range of ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less, the curve of the graph showing the concentration of Si is shifted to the n side by about 6 nm from the curve of the graph showing the concentration of Mg, and the tunnel junction layer 15 It decreases toward the n side (see FIG. 3B).

Next, the current-voltage characteristics of the sample of Comparative Example 3 and the sample of Example 2 after forming an element capable of injecting a current using the sample of Comparative Example 3 and the sample of Example 2 were measured. The results are shown in FIG. Since the step of forming an element capable of injecting an electric current is the same procedure as in Examples 1 and 2 and Comparative Examples 1 and 2, detailed description thereof will be omitted.
As shown in FIG. 7, the sample of Comparative Example 3 in which the thickness of the n ++-GaN layer 115B is 5 nm has a significantly increased drive voltage as compared with the sample of Example 2 in which the thickness of the n ++-GaN layer 15B is 15 nm. I found out that I would do it.
Therefore, in the tunnel junction layer 15, the value of Si concentration at the position showing the maximum value of Mg concentration is at least twice or more the maximum value of Mg concentration, and the tunnel junction layer 15 starts from the position showing the maximum value of Mg concentration. In the region where the concentration of Mg decreases toward the n side of the tunnel junction layer 15 and the concentration of Mg and Si is 1 × 10 ¹⁹ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less. , The region where the Mg concentration is less than 1 × 10 ²⁰ cm ^-3 and the Si concentration is 1 × 10 ²⁰ cm ^-3 or more is 6 nm or more (that is, the curve of the graph showing the Si concentration is the graph showing the Mg concentration). It was found that the electric resistance became lower and a lower drive voltage could be realized when the voltage was shifted to the n side by 6 nm or more from the curve of.

Here, in the tunnel junction layer 15, the acceptor concentration and the donor concentration are configured as in the samples of Examples 1, 2 and Comparative Example 1 (that is, the position indicating the maximum value of Mg in the tunnel junction layer 15). The reason why the electric resistance of the tunnel junction layer 15 is low is considered to be as follows. The presence of both acceptors and donors at a given position in the tunnel junction layer 15 in the thickness direction forms an impurity level in the band, which results in a relatively large density of states of electrons and holes. Will exist. It is presumed that this contributes to the tunnel current and the electrical resistance of the tunnel junction layer 15 is significantly reduced.

As described above, in the tunnel junction layer 15 of the nitride semiconductor light emitting device, both the acceptor and the donor are present at a predetermined position in the thickness direction of the tunnel junction layer 15, so that the impurity level is set in the band. It can form and allow the density of states of relatively large electrons and holes to exist, which can contribute to the tunneling current generated at the tunnel junction layer 15.

Therefore, the nitride semiconductor light emitting device of the present invention can emit light with high efficiency.

Further, in this nitride semiconductor light emitting device, the position showing the maximum value of the acceptor concentration in the tunnel junction layer 15 is the value of the donor concentration and the value of the acceptor concentration rather than the position of the end Ep on the n side of the tunnel junction layer 15. Is close to the matching position. Therefore, this nitride semiconductor light emitting device can suppress segregation of the acceptor on the n side of the tunnel junction layer 15.

Further, in the tunnel junction layer 15 of the nitride semiconductor light emitting device, the position showing the maximum value of the acceptor concentration and the position showing the maximum value of the donor concentration are from the positions where the value of the donor concentration and the value of the acceptor concentration match. It is located on the n side of the tunnel junction layer 15. Therefore, in this nitride semiconductor light emitting device, each of the position showing the maximum value of the acceptor concentration and the position showing the maximum value of the donor concentration can be surely present in the tunnel junction layer 15, and the tunnel junction layer 15 can be made to exist. In, the acceptor concentration and the donor concentration can be surely increased.

Further, in the tunnel junction layer 15 of the nitride semiconductor light emitting device, the value of the donor concentration at the position showing the maximum value of the acceptor concentration is more than twice the value of the maximum value of the acceptor concentration. Therefore, it is considered that this nitride semiconductor light emitting device can have a larger density of states of electrons and holes, which can contribute to the tunnel current generated in the tunnel junction layer.

Further, in the tunnel junction layer 15 of this nitride semiconductor light emitting device, the acceptor concentration is less than 1 × 10 ²⁰ cm ^-3 and the donor concentration is 1 on the n side of the tunnel junction layer 15 from the position showing the maximum value of the acceptor concentration. × 10 ²⁰ cm ^-3 or more region is 6 nm or more. Therefore, this nitride semiconductor light emitting device can further suppress the segregation of the acceptor on the n side of the tunnel junction layer 15.

The present invention is not limited to Examples 1 and 2 described with reference to the above description and drawings, and for example, the following examples are also included in the technical scope of the present invention.
(1) In Examples 1 and 2, the back surface side of the tunnel junction layer has a general blue LED structure, but the voltage drop is not limited to this, and the voltage drop in the high current density region is greatly improved. Alternatively, a surface emitting laser structure in which a multilayer film reflecting mirror is provided on the back surface side of the first n-GaN layer may be used.
(2) In Examples 1 and 2, Mg is used as the p-type impurity, but the p-type impurities may be Zn, Be, Ca, Sr, Ba, or the like.
(3) In Examples 1 and 2, Si is used as the n-type impurity, but the present invention is not limited to this, and may be an n-type impurity such as Ge or Te.
(4) In Examples 1 and 2, the p-AlGaN layer is laminated on the surface of the GaInN / GaN5 weight element well active layer, but the present invention is not limited to this, and p- is formed on the surface of the GaInN quantum well active layer. It is not necessary to stack and form AlGaN layers.
(5) In Examples 1 and 2, a sapphire substrate is used, but the present invention is not limited to this, and other substrates such as a gallium nitride substrate and an AlN substrate may be used.
(6) In Examples 1 and 2, the thickness of the p ++-GaN layer of the tunnel junction layer is set to several nm to several ten and several nm, but the thickness is not limited to this, and the thickness of the p ++-GaN layer of the tunnel junction layer is from several nm. It may be made smaller or larger than a dozen nm.
(7) In Examples 1 and 2, the thickness of the n ++-GaN layer of the tunnel junction layer is set to 15 nm or more, but the thickness is not limited to this, and the thickness of the n ++-GaN layer of the tunnel junction layer may be smaller than 15 nm. ..
(8) In Examples 1 and 2, GaN is used for the tunnel junction layer, but GaInN or AlGaN may be used as the material for the tunnel junction layer depending on the length of the emission wavelength of the active layer.
(9) In Examples 1 and 2, a tunnel junction layer using a nitride semiconductor is formed on the surface of the u-GaN layer which is the c-plane, but surfaces having other plane orientations such as the a-plane and the m-plane are formed. Even if a tunnel junction layer using a nitride semiconductor is formed, a sufficient effect is exhibited. That is, it is effective not only on the surface of a flat substrate but also on the surface forming a three-dimensional side wall such as a nanocolumn when a tunnel junction layer using a nitride semiconductor is formed.

End on the En ... n side Snp ... Position where the value of the donor concentration and the value of the acceptor concentration match 15 ... Tunnel junction layer

Claims (6)

In the tunnel junction layer, the acceptor concentration from the position showing the maximum value of the acceptor concentration to the n-side end of the tunnel junction layer is lower than the donor concentration, and the donor concentration is from the position showing the maximum value of the acceptor concentration. Rather than the distance in the thickness direction to the position showing the maximum value of, the thickness direction from the position showing the maximum value of the acceptor concentration to the position where the value of the donor concentration and the value of the acceptor concentration match. A nitride semiconductor light emitting element characterized by a large distance. In the tunnel junction layer , the acceptor concentration from the position showing the maximum value of the acceptor concentration to the n-side end of the tunnel junction layer is lower than the donor concentration, and the maximum value of the acceptor concentration in the tunnel junction layer. A nitride semiconductor light emitting element, wherein the maximum value of the donor concentration is located, and the effective acceptor concentration is monotonically decreased toward the p-side end of the tunnel junction layer. In the tunnel junction layer, the position showing the maximum value of the acceptor concentration is closer to the position where the value of the donor concentration and the value of the acceptor concentration coincide with each other than the position of the n-side end of the tunnel junction layer. The nitride semiconductor light emitting device according to claim 1 or 2. In the tunnel junction layer, the position showing the maximum value of the acceptor concentration and the position showing the maximum value of the donor concentration are
The nitride semiconductor according to any one of claims 1 to 3, wherein the nitride semiconductor is located on the n side of the tunnel junction layer from a position where the value of the donor concentration and the value of the acceptor concentration match. Light emitting element. In the tunnel junction layer, the value of the donor concentration at the position showing the maximum value of the acceptor concentration is
The nitride semiconductor light emitting device according to any one of claims 1 to 4, wherein the acceptor concentration is at least twice or more the maximum value. In the tunnel junction layer, the acceptor concentration is less than 1 × 10 ²⁰ cm ^-3 and the donor concentration is 1 × 10 ²⁰ cm ^-3 on the n side of the tunnel junction layer from the position showing the maximum value of the acceptor concentration. The nitride semiconductor light emitting device according to any one of claims 1 to 5, wherein the above region is 6 nm or more.

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