CN100470866C - A semiconductor solid-state light source device - Google Patents

Abstract

The invention discloses a semiconductor solid-state light source device, which belongs to the field of semiconductor technology. The epitaxial part of the semiconductor solid-state light source device includes: at least one N-type layer, at least one P-type layer, at least one light-emitting region, a positive electrode and a negative electrode, and the light-emitting region is between the N-type layer and the Between the P-type layers, there is at least one P ⁺⁺ -type layer on the other side of the P-type layer; and at least one transition layer on the other side of the P ⁺⁺ -type layer, the The energy band width of the transition layer is smaller than the energy band width of the P-type layer and the P ⁺⁺ -type layer; there is at least one N ⁺⁺ -type layer on the other side of the transition layer, and the N ⁺⁺ - The energy band of the type layer is wider than the energy band of the transition layer. The high-power light-emitting diode semiconductor solid-state light source device provided by the invention reduces resistance and improves heat conduction and luminous efficiency.

Description

A semiconductor solid-state light source device

technical field

The invention relates to the field of semiconductor technology, in particular to a semiconductor solid-state light source device.

Background technique

At present, high-power light-emitting diodes ((LED, Light Emitting Diode)) generally adopt a layered structure containing a PN junction, as shown in Figure 1, the LED from bottom to top is: substrate 101, buffer layer 102, N-type layer (lower layer) 103 , light emitting region 104 and P-type layer (upper layer) 105 . Due to the limitation of epitaxial growth conditions, in order to grow high-quality epitaxy, it is usually grown in a crystal direction close to [0001], and adopts a layout in which the N-type layer 103 is on the bottom and the P-type layer 105 is on the top. In this growth mode, in order to improve the luminous efficiency, it is required to:

(1) A good ohmic contact is formed on the P-type layer (high resistance layer), and at the same time, it is required that the ohmic contact does not weaken or only slightly weakens the luminous efficiency of the LED;

(2) When driving in the forward direction, conduct away a large amount of heat generated on the P-type layer.

For nitride semiconductor LEDs composed of N (nitrogen) and the third group of elements in the periodic table (III-N group) as the main epitaxial component, the P-type layer is difficult to achieve high carrier levels due to various reasons. Concentration, and in the case of high P-type layer doping, there is a large resistivity, which is manifested in the Hall mobility of holes is often lower than 20cm ² /Vs, and the resistivity of the material is greater than 0.5 ohm cm (Ω.cm ). When the contact resistance and the resistivity of the material itself are large, the LED will generate a large amount of heat energy under the operating current, which will destroy the accumulation of carriers in the light-emitting area and reduce the luminous efficiency. The metal-type ohmic contact formed on the high-resistivity layer must not only consider the electrical properties, but also must consider the influence of this layer of metal on the optical characteristics of the entire LED.

In order to reduce the resistance of LEDs and improve their thermal conductivity and luminous efficiency, T. Gessmann et al. proposed a scheme that uses the energy band "hole" caused by the polarization effect generated by the heterojunction to generate two-dimensional hole gas. Thereby increasing hole concentration (see T.Gessmann, et al., Journal of Applied Physics, Vol.92, Number 7, pp3740, (2002)). Due to the extremely high carrier concentration at the heterojunction interface, if the energy barrier is thin enough and there are available energy levels on the opposite side of the energy barrier, the conductivity can be improved by the quantum tunneling effect. At the same time, the heterojunction always uses a narrow band semiconductor on the metal electrode side, so it is easier to form an ohmic contact.

The scheme proposed by T.Gessmann et al. has been applied on LED, see JP Zhang, et al., Appl.Phys.Lett., 85, 5532 (2004), and L.Zhou et al., Appl.Phys.Lett. , 241113 (2006) gave two representative structures, the former is a thick film structure, as shown in Figure 2, the structure includes: substrate 201, buffer layer 202, N-type layer 203, light emitting region 204 , P-type layer 205 , small energy band P ⁺ -layer 206 , semitransparent metal film 207 , and corresponding positive electrode 208 and negative electrode 209 . The latter is a thin-film structure, as shown in Figure 3. This structure peels off the substrate, and the entire structure is inverted, specifically including: semiconductor carrier 301, reflective plate and positive electrode 302, small energy band P ⁺ -type layer 303, P -type layer 304 , light emitting region 305 , N-type layer 306 , buffer layer 307 and negative electrode 308 .

Wherein, the "P-type layer" in the above-mentioned LED structure can be subdivided into: an anti-doping diffusion layer, a P-type electron blocking layer, and a P-type conductive layer.

The disadvantages of the above structure are as follows:

1. Using a P ⁺ -layer with a small energy band, although it can reduce the resistance, may lead to strong absorption of the light emitted by the light-emitting area. Taking the structure provided in Figure 3 as an example, the 20nm-thick narrow energy band P ⁺ -GaN at least causes attenuation of more than 40% of the short-wavelength (less than 300nm) light emitted by the device;

2. The structure provided in Figure 2 not only has a strong absorption of light by its P ⁺ -GaN layer, but also a semi-transparent metal film (such as: NiAu) also has a strong absorption of light. Assuming that the thickness of NiAu is 100 angstroms, the upward light transmittance of the device It should be lower than 30%; at the same time, the structure has a very thick substrate (>80 microns), which is not conducive to heat dissipation;

3. For the structure provided in Figure 3, since the last layer of epitaxy is P-type, only low-reflectivity metals such as Rh and Pd with high work function can be used (Rh reflectivity is lower than 65%, Pd is lower than 45%), namely The use of silver is also limited to the visible light band, and it is very unsatisfactory to the infrared, especially the ultraviolet effect (the Ag reflectivity is lower than 20% below the wavelength of 300 nanometers); and the structure has a very thick low thermal conductivity semiconductor carrier (> 200 Micron), which is not conducive to heat dissipation.

Contents of the invention

In order to reduce the resistance of the semiconductor solid-state light source device and improve its heat conduction and luminous efficiency, the invention provides a semiconductor solid-state light source device. Described technical scheme is as follows:

A semiconductor solid-state light source device, the epitaxial part of the device includes: at least one N-type layer, at least one P-type layer, at least one light emitting region, a positive electrode and a negative electrode, the light emitting region is in the N-type layer and the p-type layer, the device further includes:

At least one P ⁺⁺ -type layer on the other side of said P-type layer;

And there is at least one transition layer on the other side of the P ⁺⁺ -type layer, the energy band width of the transition layer is smaller than the energy band width of the P-type layer and the P ⁺⁺ -type layer;

On the other side of the transition layer there is at least one N ⁺⁺ -type layer, the energy band of the N ⁺⁺ -type layer is wider than that of the transition layer.

The energy band of the transition layer is greater than half of the energy band of the light emitting region.

The epitaxial composition of the device is a compound composed of the third group elements and the fifth group elements in the periodic table of elements.

The epitaxial composition of the device is a nitride semiconductor.

The material of described positive electrode and negative electrode comprises:

Aluminum or vanadium, or an alloy containing one or both of aluminum and vanadium.

On the positive electrode or the negative electrode containing aluminum, a deposition layer is also included, the deposition layer is at least 3 microns of copper, or gold, or an alloy containing one or both of copper and gold, the device A connection is made via this deposited layer to a semiconductor, ceramic or metallic support.

The positive electrode and the negative electrode are on different sides or the same side of the light emitting region;

the epitaxial substrate is lifted off when on a different side of the light emitting region;

When on the same side of the light emitting region, an insulator is provided between the positive electrode and the negative electrode.

The energy band narrowing of the transition layer is adjusted by controlling the ratio of In, Ga and Al.

The device is a light emitting diode.

The beneficial effects of the technical solution provided by the invention are:

The technical solution provided by the embodiments of the present invention has the following advantages:

Through the narrow energy band transition layer in the structure, the resistance of the semiconductor solid-state light source device is reduced, and the absorption of light emitted by the light-emitting area is reduced. Since the negative electrode of the LED can also be made of aluminum alloy, the positive and negative electrodes can be made of the same metal, which can be used once. Deposition, one-time annealing treatment, simplifies the process, thereby reducing the cost; through the thick metal support, the heat conduction effect is improved in the flip-chip process, and the influence of the heat generated in the P-type layer under the operating current on the efficiency of the light-emitting area is reduced.

Description of drawings

FIG. 1 is a schematic structural view of an LED provided by the prior art;

Fig. 2 is a structural schematic diagram of an LED with a heterojunction provided by the prior art;

Fig. 3 is a structural schematic diagram of another LED with a heterojunction provided by the prior art;

Fig. 4 is a schematic structural diagram of a special tunnel heterojunction provided by the present invention;

Fig. 5 is a schematic structural diagram of the LED provided by Embodiment 1 of the present invention;

Fig. 6 is a schematic structural diagram of an LED provided by Embodiment 2 of the present invention;

Fig. 7 is a schematic diagram of energy bands of a special tunnel heterojunction with a small energy band transition layer provided by an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the implementation manner of the present invention will be further described in detail below in conjunction with the accompanying drawings.

In the embodiment of the present invention, a special tunnel heterojunction is formed by superimposing a P ⁺⁺ -type layer, a transition layer, and an N ⁺⁺ -type layer on the P-type layer of a traditional semiconductor solid-state light source device, which reduces the cost of the semiconductor solid-state light source device. resistance, improving its heat conduction and luminous efficiency.

An embodiment of the present invention provides a semiconductor solid-state light source device. The epitaxial part of the light source device contains a special tunnel heterojunction. Referring to FIG. 4, the structure of the special tunnel heterojunction includes: a P-type layer 401, and P ⁺⁺ -type layer 402 , transition layer 403 and N ⁺⁺ -type layer 404 on -type layer 401 .

Wherein, the thickness of the transition layer 403 is less than 5 nanometers, and its energy band is narrower than both the P ⁺⁺ -type layer 402 and the N ⁺⁺ -type layer 404 . The small energy band transition layer can use the polarization phenomenon on the heterojunction interface formed by the compound semiconductor in some specific growth directions to increase the electric field intensity and shorten the tunnel distance, thereby increasing the conductivity of the transition layer, making the conductivity higher than ordinary The highly doped reverse PN junction achieves the purpose of reducing resistance. For III-N group semiconductors, the doping of the P ⁺⁺ -type layer 402 and the N ⁺⁺ -type layer 404 should be above 10 ¹⁹ /cm ³ and 5×10 ¹⁸ /cm ³ respectively.

Moreover, the transition layer 403 can be any doping, and its energy band narrowing can be adjusted by controlling the ratio of In, Ga, and Al, where the ratio of In, Ga, and Al is: In·x+Ga·y+A1 (1-x-y)=100%, x and y are variables; the change of the interface composition can be continuous or discontinuous.

The P ⁺⁺ -type layer, transition layer and N ⁺⁺ -type layer included in the above special tunnel heterojunction are not limited to one, and there can be multiple P ⁺⁺ -type layers, transition layers or N ⁺⁺ - The chemical composition of these layers does not need to be exactly the same.

Take the compounds (including nitride semiconductors) composed of Group III elements and Group V elements in the periodic table as the main epitaxial components to form LEDs as an example. LEDs include: at least one N-type layer, at least one P-type layer, in At least one light-emitting region is sandwiched between the N-type layer and the P-type layer; and a special tunnel heterojunction as shown in Figure 4 is included in the subsequent growth layer of the P-type layer, which includes at least one P ^{+ +} -type layer, at least one transition layer having an energy band narrower than both the P-type layer and the P ⁺⁺ -type layer, and at least one N ⁺⁺ -type layer.

Example 1

This embodiment takes LED as a semiconductor solid-state light source device as an example. Using the special tunnel heterojunction provided in Figure 4, the structure of the LED can adopt several different forms, as shown in Figure 5, which is a schematic structural diagram of the LED provided in this embodiment. , the LED adopts a vertically implanted film structure, the entire structure is inverted, and the substrate has been stripped, mainly including: N-type ohmic contact 501, N-type layer 502, light emitting region 503, P-type layer 504, P ⁺⁺ -type layer 505, transition layer 506 and N ⁺⁺ -type layer 507 (contact layer), reflector and positive electrode 508 and metal heat sink 509;

Wherein, the N-type ohmic contact 501 is used as the negative electrode of the LED, and the electrode contains aluminum, or vanadium, or an alloy containing one or both of these two elements;

The reflective plate and positive electrode in contact with the N ⁺⁺ -type layer semiconductor below has high-efficiency light reflection, and its material can be aluminum or aluminum alloy with high reflectivity at short wavelengths. If it is an aluminum alloy electrode, it can be passed through other metals The interlayer is directly connected to the metal or ceramic heat sink by welding, bonding and other methods to form an efficient electrical and thermal conduction structure. The material of the electrode can also be vanadium, or an alloy of vanadium and aluminum.

Example 2

In this embodiment, the LED is used as a semiconductor solid-state light source device as an example. Using the special tunnel heterojunction provided in FIG. 4, the structure of the LED is shown in FIG. Peel off to become a flip-chip LED, mainly including: substrate and buffer layer 601, N-type layer 602, light emitting region 603, P-type layer 604, P ⁺⁺ -type layer 605, transition layer 606 and N ⁺⁺ - Type layer 607 (contact layer), reflector and positive electrode 608, reflector and negative electrode 609, thick metal support 610, heat sink base 611 and insulating dielectric 612; wherein the substrate and buffer layer 601 can be peeled off as required.

Wherein, the reflective plate and positive electrode in contact with the lower N ⁺⁺ -type layer semiconductor can be aluminum or aluminum alloy with high reflectivity at short wavelengths. If it is an aluminum alloy electrode, it can be directly connected to the metal or ceramic heat sink base through a metal interlayer containing copper, or gold and its alloys for welding, bonding, etc., to form an efficient electrical and thermal conductivity structure. The material of the positive and negative electrodes can also be vanadium, or an alloy containing vanadium and aluminum.

According to needs, the reflector and the positive electrode 608 and the reflector and the negative electrode 609 can be separated by an insulating dielectric, so as not to cause a short circuit, and an empty area as shown in Figure 6 can also be set at the thick metal support 610 to avoid positive electrode 609. Short circuit of the negative electrode.

The difference from the vertical implant structure provided in Embodiment 1 is that the positive and negative electrodes are on the same side of the light emitting region, and erosion is required to connect the negative electrode to the N-type layer semiconductor close to the substrate.

The energy band of the transition layer in the above two embodiments is narrower than that of the P ⁺⁺ -type layer and N ⁺⁺ -type layer on both sides, but it can be slightly smaller than the energy band of the light-emitting region, but not less than 1/2 of the energy band of the light-emitting region; it can also be as wide or wider than the energy band of the light-emitting region;

Further, depositing at least 3 microns of copper, or gold, or an alloy containing either or both, directly or indirectly on the positive and negative electrodes containing aluminum, and through this deposited layer and the semiconductor , ceramic or metal support;

From the above two embodiments, it can be concluded that the positive electrode and the negative electrode of the LED can be on different sides of the light-emitting area, or on the same side. If it is on different sides, the epitaxial substrate will be peeled off; if the positive and negative electrodes are on the same side of the light-emitting area, when the positive and negative electrodes cross, there will be an insulator between the positive and negative electrodes, and the epitaxial substrate can be removed Stripping can also be preserved.

The above embodiments are particularly aimed at the application of epitaxy with [0001] crystal orientation and group III elements as the final surface capping layer in III-N semiconductors. If group V elements are used as the surface covering layer and [000-1] is used as the crystal direction to grow, the corresponding transition layer can have a wide energy band, not necessarily a narrow energy band. If the growth is in a non-polar crystal direction, such as along the <10-10> crystal direction, the above method is still applicable.

It is also possible to forcibly implant the surface of the P-type semiconductor with elements such as silicon by means of ion implantation and diffusion, so that the surface layer becomes an N ⁺⁺ -type layer, which can also achieve the purpose of the present invention.

The above embodiments are explained by using LED as a semiconductor solid-state light source device. The semiconductor solid-state light source device of the present invention is not limited to LED, and other light source devices have similar structures, which will not be described in detail here.

The technical solution provided by the embodiments of the present invention has the following advantages:

1) Reduced the resistance of the LED:

In principle, it is easier to form an ohmic contact on an N-type wide-band semiconductor than a P-type semiconductor. This is because the energy barrier to carriers at the contact interface between the metal and the P-type semiconductor is directly related to the energy band width, while the N-type semiconductor does not have this feature. For III-N semiconductors, the energy band width can exceed 3.4 eV (for example: GaN), and even reach 5.9 eV (for example: AlN). Therefore, it is very advantageous to convert a P-type contact to an N-type contact, which is achieved in this embodiment through a tunnel heterojunction containing a transition interlayer. As shown in Figure 7, the energy band schematic diagram of a special tunnel heterojunction with a small energy band transition layer, taking the case where the carrier concentration on the side of the P ⁺⁺ -type layer is not enough to achieve a true degenerate state, due to the nitride semiconductor The strong polarization phenomenon existing at the heterojunction interface can strengthen the energy band bending phenomenon of the heterojunction itself, leading to the local accumulation of carriers and forming a 2-dimensional electron and hole accumulation region. The tunneling current across the triangular energy barrier is proportional to the power of one-half of the carrier concentration and the power of the energy barrier width. Therefore, compared with the ordinary reverse PN junction, due to the high carrier concentration of this design, under the action of reverse voltage, the tunnel effect will be more obvious at low voltage; at large reverse voltage, only 5nm The narrow heterojunction region will also be shorter than the depletion region of the PN junction, which is equivalent to reducing the energy barrier width. According to the different materials on both sides, this transition interlayer can be properly doped to further increase the conductivity and suppress stray light.

2) Reduce the absorption of luminescence in the light exit area:

Since the thickness of the transition layer provided by the embodiment of the present invention is small, it absorbs less light from the light-emitting region than the original narrow-band P ⁺⁺ -type contact layer. Taking III-N material as an example, the thickness of the conventional narrow-band P ⁺⁺ -type contact layer (such as p-GaN) is usually about 20 nanometers, while the narrow-band transition layer used in the embodiment of the present invention is less than 5 nanometers. Moreover, the proportion of Al in the semiconductor alloy can be appropriately increased, so that the energy band can be appropriately broadened, and the absorption of light from the light-emitting region can be further reduced.

3) Aluminum or aluminum alloy can be used as the LED positive electrode:

Since the epitaxial layer in contact with the positive electrode is changed from P-type to N-type, the low-power characteristics of aluminum and aluminum alloys change the original Schottky contact into an ohmic contact, which greatly improves the reflectivity of the reflector in the short-wavelength range. Taking III-N compound semiconductors as an example, aluminum can maintain a reflectivity of more than 90% from 200 nanometers to 700 nanometers, while silver reaches its ionization frequency below 340 nanometers, and the reflectivity decays to less than 20%. When aluminum is not used in the prior art, Rh and Pd are common P-type contact and reflectors, and their reflectances are about 65% and 45% respectively. Therefore, the use of aluminum as a reflector improves the versatility of the same chip process for LEDs of different wavelengths.

4) Simplify the LED process: Since the negative electrode of the LED can also be made of aluminum alloy, the same metal can be used for the positive and negative electrodes, which can be deposited and annealed once, which simplifies the process and reduces the cost.

5) Improve thermal conductivity: The thick metal support improves the thermal conductivity in the flip-chip process, and reduces the influence of the heat generated in the P-type layer under the operating current on the efficiency of the light-emitting area.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (9)

1. A semiconductor solid-state light source device, the epitaxial part of the device includes: at least one N-type layer, at least one P-type layer, at least one light-emitting region, positive electrode and negative electrode, and the light-emitting region is in the N Between the -type layer and the P-type layer, it is characterized in that the device also includes: At least one P ⁺⁺ -type layer on the other side of said P-type layer; And there is at least one transition layer on the other side of the P ⁺⁺ -type layer, the energy band width of the transition layer is smaller than the energy band width of the P-type layer and the P ⁺⁺ -type layer; On the other side of the transition layer there is at least one N ⁺⁺ -type layer, the energy band of the N ⁺⁺ -type layer is wider than that of the transition layer. 2. The semiconductor solid-state light source device according to claim 1, wherein the energy band of the transition layer is greater than half of the energy band of the light emitting region. 3. The semiconductor solid-state light source device according to claim 1, wherein the epitaxial component of the device is a compound composed of Group III elements and Group V elements in the periodic table. 4. The semiconductor solid-state light source device according to claim 1, wherein the epitaxial component of the device is a nitride semiconductor. 5. The semiconductor solid-state light source device according to claim 1, wherein the material of the positive electrode and the negative electrode comprises: Aluminum or vanadium, or an alloy containing one or both of aluminum and vanadium. 6. The semiconductor solid-state light source device as claimed in claim 5, characterized in that, on the positive electrode or the negative electrode containing aluminum, a deposition layer is also included, and the deposition layer is copper of at least 3 microns, or gold, or contains One or two alloys of copper and gold, the device is connected to a semiconductor, ceramic or metal support through this deposited layer. 7. The semiconductor solid-state light source device according to claim 1, wherein the positive electrode and the negative electrode are on different sides or the same side of the light emitting region; the epitaxial substrate is lifted off when on a different side of the light emitting region; When on the same side of the light emitting region, an insulator is provided between the positive electrode and the negative electrode. 8. The semiconductor solid-state light source device according to claim 1, wherein the energy band narrowing of the transition layer is adjusted by controlling the ratio of In, Ga and Al. 9. The semiconductor solid state light source device according to any one of claims 1 to 8, characterized in that the device is a light emitting diode.

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