TWI437730B - Light emitting diode - Google Patents

Description

Light-emitting diode

The present invention relates to a light-emitting diode, particularly to a gallium nitride-based light-emitting diode, for introducing a buried energy barrier to enhance the diffusion effect of current therein.

Compared with general light bulbs, Light Emitting Diode (LED) has the advantages of lighter weight, long life, power saving, fast switching speed, monochromaticity and high reliability. Therefore, the light-emitting diode has already become a daily life. An indispensable optoelectronic component. In recent years, due to the rapid advancement of materials technology, the brightness of the LEDs has been continuously increased, colorful and reduced in price, which has made their application fields more and more extensive. Among them, the blue light diode with GaN as the main material has been published for several years, and now it has become an important component in the construction of solid-state lighting (SSL), and it is the main component of next generation lighting. .

The basic principle of the illumination of a light-emitting diode is as follows: In a semiconductor material, when a current flows inwardly into the p-n junction of the semiconductor material, electrons and holes are combined under a suitable condition to generate photons. Depending on the material, the energy levels of electrons and holes are different. The relative height difference of the energy level determines the level of energy emitted by the combination of electrons and holes, thus producing photons with different energies, thereby controlling the light emission. The wavelength of light emitted by a diode, that is, the spectrum or color.

The light-emitting diode can be distinguished into two types: a horizontal light-emitting diode and a vertical light-emitting diode. Among them, the horizontal light-emitting diode has a structure in which the current cannot be effectively diffused due to its structural characteristics, so that the current is limited, and its operating life and its saturation current are lowered. In addition, the conventional horizontal light-emitting diode has uneven current distribution under high current operation, and is easy to generate electrostatic focusing in a low humidity environment, and its antistatic capability is insufficient.

Therefore, how to improve the current spreading capability of the light-emitting diode and improve its electrostatic protection capability is a problem to be solved in the technical field.

It is an object of the present invention to provide an n-type doped layer to form a buried p-n junction at the interface to generate a built-in electric field, thereby enhancing the dispersion effect of current flow in the interface.

Other objects and advantages of the present invention will become apparent from the technical features disclosed herein.

In order to achieve one or a part or all of the above or other purposes, a light-emitting diode according to an embodiment of the present invention grows sequentially from bottom to top: a substrate, a buffer layer, an n-type layer, and a a multiple quantum well layer, an n-type doped layer, a p-type layer, a transparent conductive layer and an electrode, wherein the electrode grows on the transparent conductive layer and the n-type layer.

Compared with the prior art, the embodiment of the present invention generates a buried pn junction by adding an n-type doped layer in the multiple quantum well layer and the p-type layer to induce a built-in electric field and overcome current. Blocking the problem of the shortest conduction path and improving the photoelectric performance of the LED. The built-in electric field induced by the buried pn junction can effectively disperse the over-concentrated current path, reduce the current crowding effect, and reduce the parasitic resistance value of the light-emitting diode, so that the current diffusion efficiency is increased and the conduction bias is increased. Decreased and optimized for antistatic discharge capability. Moreover, when the present invention operates in forward bias, it has a relatively uniform current spreading effect.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments. The directional terms mentioned in the following embodiments, such as up, down, left, right, front or back, etc., are only directions referring to the additional drawings. Therefore, the directional terminology used is for the purpose of illustration and not limitation.

Please refer to the first figure, which is a structural diagram of a light-emitting diode 100 according to an embodiment of the present invention. The semiconductor layer of the light-emitting diode 100 is grown on a substrate 101, and the semiconductor layer includes, in order from bottom to top, a buffer layer 102, an n-type layer 103, a multiple quantum well layer 104, and an n-type doping. The layer 105, a p-type layer 106, a transparent conductive layer 107 and an electrode 108. The material of the substrate 101 is semi-insulating alumina (Al ₂ O ₃ ).

The buffer layer 102 is grown on the substrate 101 by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (Molecular Beam Epitaxy), wherein the buffer layer 102 is made of undoped nitrogen. Gallium nitride (GaN), and the thickness of its film layer ranges from 0.1 μm to 10 μm. In a preferred embodiment, the buffer layer 102 has a film thickness of 500 nm.

The n-type layer 103 is grown on the buffer layer 102 by metal organic vapor phase chemical deposition or molecular beam epitaxy, wherein the n-type layer 103 is an n-type gallium nitride layer and is doped with germanium elements, and the electrons thereof The carrier concentration is about 1 × 10 ¹⁶ cm ^-3 to 3 × 10 ¹⁹ cm ^-3 , and the thickness thereof ranges from about 0.5 μm to 5 μm. In a preferred embodiment, the n-type layer 103 has a film thickness of 4 μm.

The multiple quantum well layers 104 are grown on the n-type layer 103 by metal organic vapor phase chemical deposition or molecular beam epitaxy, wherein the multiple quantum well layers 104 are stacked by a plurality of quantum well structures, each of which includes A gallium nitride (GaN) layer and an indium gallium nitride (In _X Ga _1-X N) layer have a number of quantum well structures of about 2 to 50 and an x value in the range of about 0.01 to 0.25. In addition, each of the plurality of quantum well layers 104 has a thickness ranging from about 10 nm to 20 nm, and each of the gallium nitride layers has a doping element of germanium and a doping concentration range of about 1×10 ¹⁶ cm. ^-3 to 1 x 10 ¹⁹ cm ^-3 , and each of the indium gallium nitride layers has a thickness ranging from about 1 nm to 5 nm. In a preferred embodiment, the multiple quantum well layer 104 includes 15 repetitively stacked germanium-doped gallium nitride/indium gallium nitride (In _0.2 Ga _0.8 N) quantum well structures having a doping concentration of 1×10. ¹⁸ cm ^-3 , and each gallium nitride layer has a thickness of 12 nm, and each indium gallium nitride layer has a thickness of 3 nm.

The n-type doped layer 105 is grown on the multiple quantum well layer 104 by metal organic vapor phase chemical deposition, Atomic Layer Deposition (ALD), or molecular beam epitaxy, wherein the n-type doped layer The material of 105 is indium gallium nitride (In _x Ga _1-x N) or gallium nitride, and the indium gallium nitride has an x value ranging from about 0.01 to 0.3. Further, the n-type doped layer 105 has an electron carrier concentration of about 1 × 10 ¹⁷ cm ^-3 to 1 × 10 ¹⁹ cm ^-3 , and a thickness ranging from about 1 nm to 100 nm. In a preferred embodiment, the n-type doped layer 105 has an electron carrier concentration of 1 × 10 ¹⁹ cm ^-3 and a thickness of 5 nm.

The p-type layer 106 is grown on the n-type doped layer 105 by metal organic vapor phase chemical deposition or molecular beam epitaxy, and the activation temperature of the carrier is about 300 ° C to 1000 ° C during epitaxial growth. Wherein, the material of the p-type layer is a doped type gallium nitride, and the concentration of the hole carrier is in the range of about 1×10 ¹⁶ cm ^-3 to 1×10 ¹⁸ cm ^-3 , and the thickness thereof is about 0.1. Micron to 1 micron and its doping element is magnesium (Mg) or zinc (Zn). In a preferred embodiment, the p-type layer 106 has a hole carrier concentration of 4 x 10 ¹⁷ cm ^-3 and a thickness of 0.3 μm.

The transparent conductive layer 107 is grown on the p-type layer 106 by thermal evaporating, sputtering, or E-beam evaporating, and includes an alloying process during growth. The alloy temperature is about 50 ° C to 500 ° C. The material of the transparent conductive layer 107 is a metal thin film or an oxide thereof, and its resistivity ranges from 10 ^-8 Ω-cm to 10 ^-1 Ω-cm. In a preferred embodiment, the transparent conductive layer 107 has an electron carrier concentration of 4 × 10 ²⁰ cm ^-3 and a thickness of 250 nm.

In a preferred embodiment, a cover passivation layer (not shown) is further included. The transparent insulating type covering passivation layer utilizes Plasma-Enhanced Chemical Vapor Deposition (PECVD), Low-Pressure Chemical Vapor Deposition (LPCVD), electron beam evaporation or sputtering It grows on a transparent conductive layer to avoid long-term oxidation effects. The material covering the passivation layer is zinc oxide (ZnO), germanium dioxide (SiO ₂ ) or tantalum nitride (Si ₃ N ₄ ), and the thickness thereof ranges from 10 nm to 500 nm.

The electrode 108 is coated on the n-type layer 103 and the transparent conductive layer 107 by thermal evaporation, sputtering or electron beam evaporation, and includes a high-temperature annealing process during the growth process, and the annealing temperature ranges from 50 to 50. Between °C and 600 °C. The electrode 108 is an ohmic contact electrode, the electrode 108 includes a p-type electrode and an n-type electrode, the p-type electrode is grown on the transparent conductive layer 107, and the n-type electrode is grown on the n-type layer 103. The p-type electrode is composed of chromium, platinum and gold, and the thickness of chromium ranges from about 1 nm to 100 nm, the thickness of platinum ranges from about 10 nm to 300 nm, and the thickness of gold ranges from about 100 nm to 3000 nm. The n-type electrode is composed of chromium, platinum and gold, or is composed of titanium and gold. If the n-type electrode is composed of chromium, platinum and gold, the thickness of the chromium ranges from about 1 nm to 100 nm, and the thickness range of platinum It is about 10 nm to 300 nm, and the thickness of gold is about 100 nm to 3000 nm; if the n-type electrode is composed of titanium and gold, the thickness of titanium ranges from about 1 nm to 100 nm, and the thickness of gold ranges from about 100 nm to 3000 nm.

Please refer to the second figure, which is a schematic diagram of a partially enlarged built-in electric field E of a light-emitting diode 100 according to an embodiment of the present invention. Since the multiple quantum well layer 104 and the p-type layer 106 have the n-type doped layer 105, a buried p-n junction is formed in the light-emitting diode 100. When the light-emitting diode 100 is operated under the forward conduction voltage, the built-in electric field E is induced between the pn junctions, and the path of the current I that is too concentrated can be effectively dispersed, so that the light-emitting diode 100 has a large area of current. Diffusion range to reduce current crowding effects.

As shown in the third figure, it is a forward current-voltage graph of a light-emitting diode 100 according to an embodiment of the present invention. Wherein, the curve A represents the forward current-voltage measurement result of the n-type doped layer 105 in the light-emitting diode 100, and the curve B represents the n-type doped layer 105 in the light-emitting diode 100 as the indium nitride. The forward current-voltage measurement result of gallium (In _x Ga _1-x N), and the curve C represent the forward current-voltage measurement result of the conventional light-emitting diode. If the forward conduction bias voltage V _f is defined as the current value at 20 mA, the forward conduction bias voltage V _fA corresponding to the curve A is 3.17 V, and the forward conduction bias voltage V _fB corresponding to the curve B is 3.35 V. And the forward conduction bias voltage V _fC corresponding to the curve C is 3.48 V, and it is understood that V _fA <V _fB <V _fC . In addition, it can be seen from the second figure that the diffusion current of the light-emitting diode 100 of the embodiment of the present invention is uniformly distributed on the light-emitting surface, and therefore, has a small parasitic resistance effect, so that the series parasitic resistance is reduced to obtain a smaller The forward conduction bias voltages V _fA and V _fB .

Through calculation, the fourth figure can be obtained from the third figure, which is a voltage-current linear diagram of a light-emitting diode 100 according to an embodiment of the present invention. Wherein, by calculating the slopes of the three linear approximation lines, the calculated values of the series parasitic resistance of the different light emitting diodes can be obtained: the curve A represents the voltage of the gallium nitride in the n-type doping layer 105 of the light emitting diode 100 - The linear current result, the parasitic resistance is calculated to be 15.2 Ω; the curve B represents the voltage-current linear result of the n-type doped layer 105 in the light-emitting diode 100 being indium gallium nitride (In _x Ga _1-x N), which is parasitic The resistance was calculated to be 18.9 Ω; and, curve C represents a voltage-current linear result of a conventional light-emitting diode, and its parasitic resistance was calculated to be 31.5 Ω. It can be confirmed from the third and fourth figures that a light-emitting diode 100 having a reverse built-in electric field E in the embodiment of the present invention can effectively reduce the series parasitic resistance effect in the light-emitting diode 100, so that the light-emitting diode is made. 100 has a broad and uniform light-emitting area.

Referring to FIG. 5, it is a partial energy band diagram of a light-emitting diode 100 according to an embodiment of the present invention. The energy band of the multiple quantum well layer 104 is composed of a large energy gap 104a of a repetitive gallium nitride layer and a small energy gap 104b of an indium gallium nitride layer, and CB represents a conduction band, and VB represents a price. band. Since the multiple quantum well layer 104 and the p-type layer 106 have the n-type doping layer 105, the pn junction formed in the light-emitting diode 100 will induce the built-in electric field E, and the built-in electric field E can be introduced into the energy barrier. It will limit the movement of electrons e and holes h. For the free carrier of the transmission: the electron e and the hole h, the built-in electric field E induced by the buried p-n junction locally blocks the shortest conduction path of the current. For example, when the hole h is injected into the buried p-n junction, the hole h must first cross the energy barrier caused by the built-in electric field E, enabling access to the buried p-n junction, and then combining with the electron e to emit photons. Therefore, the hole h will be horizontally diffused in the buried p-n junction and injected into the multiple quantum well layer 104 instead of directly crossing the p-n junction, thereby increasing the current spreading capability of the gallium nitride light emitting diode 100.

As shown in the sixth figure, it is a comparison chart of the component yield and input voltage of a light-emitting diode 100 according to an embodiment of the present invention and a machine model (passive model). Schematic diagram of the results of the discharge (Electrostatic discharge) test. The curve A represents the test result of the n-type doped layer 105 in the light-emitting diode 100 as gallium nitride, and the curve B represents the n-type doped layer 105 in the light-emitting diode 100 as indium gallium nitride (In _x Ga _{1 ). -x} N) test results, and curve C represents the test results of conventional light-emitting diodes. During the test, a forward current is applied to the anode of the light-emitting diode, and the cathode is grounded.

As can be seen from the sixth figure, when a forward bias voltage of 500 V is applied, the component survival ratio of the n-type doped layer 105 in the light-emitting diode 100 to gallium nitride is 100%, and the light-emitting diode 100 is The element survival rate of the n-type doped layer 105 is indium gallium nitride (In _x Ga _1-x N) is 54.2%, and the element survival rate of the conventional light-emitting diode is 0%. It can be seen from the test result graph that the component survival rate of the present invention after electrostatic discharge is greatly increased due to the increase in the current dispersion effect of the light-emitting diode 100. Therefore, the built-in electric field induced by the buried pn junction can disperse the applied current to reduce the hot carrier destructiveness of the light-emitting diode 100 during the electrostatic discharge.

In summary, since a plurality of quantum well layers 104 and p-type layers 106 are added with an n-type doped layer 105, a buried pn junction is formed to induce a built-in electric field. Therefore, the above embodiment has the following advantage:

1. Effectively dispersing the current path in the light-emitting diode 100 to reduce the current crowding effect.

2. Decreasing the parasitic resistance value of the light-emitting diode 100, so that the current diffusion efficiency is increased.

Third, since the parasitic resistance value of the light-emitting diode 100 is lowered, the conduction bias voltage is reduced.

4. Since the applied current of the light-emitting diode 100 is effectively dispersed, the antistatic discharge capability is optimized.

Moreover, when the present invention operates in forward bias, it has a more uniform current spreading effect.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent. In addition, any of the objects or advantages or features of the present invention are not required to be achieved by any embodiment or application of the invention. In addition, the abstract sections and headings are only used to assist in the search of patent documents and are not intended to limit the scope of the invention.

100. . . Light-emitting diode

101. . . Substrate

102. . . The buffer layer

103. . . N-type layer

104. . . Multiple quantum well layers

104a. . . Gallium nitride layer

104b. . . Indium gallium nitride layer

105. . . N-type doped layer

106. . . P-type layer

107. . . Transparent conductive layer

108. . . electrode

A, B, C. . . curve

E. . . Built-in electric field

e. . . electronic

h. . . Hole

I. . . Current

V _fA , V _fB , V _fC . . . Conduction bias

CB. . . Conduction zone

VB. . . Price band

P-n. . . Junction

The first figure is a structural diagram of a light-emitting diode according to an embodiment of the present invention.

The second figure is a schematic diagram of a partially enlarged built-in electric field of a light-emitting diode according to an embodiment of the present invention.

The third figure is a forward current-voltage graph of a light-emitting diode according to an embodiment of the present invention and a conventional comparison.

The fourth figure is a voltage-current linear diagram of a light-emitting diode according to an embodiment of the present invention and a conventional comparison.

The fifth figure is a partial energy band diagram of a light-emitting diode according to an embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the component survival rate and the input voltage in a machine mode in which a light-emitting diode according to an embodiment of the present invention is compared with a conventional one.

100. . . Light-emitting diode

101. . . Substrate

102. . . The buffer layer

103. . . N-type layer

104. . . Multiple quantum well layers

105. . . N-type doped layer

106. . . P-type layer

107. . . Transparent conductive layer

108. . . electrode

Claims (15)

A light emitting diode comprising: a substrate; a buffer layer grown on the substrate; an n-type layer grown on the buffer layer; and a multi-quantum well layer grown on the n-type layer An n-type doped layer is grown on the multiple quantum well layer; a p-type layer is grown on the n-type doped layer and is in direct contact with the n-type doped layer, and the n-type doping The impurity layer forms a buried pn junction with the p-type layer; a transparent conductive layer grown on the p-type layer; and an electrode grown on the transparent conductive layer and the n-type layer. The light-emitting diode according to claim 1, wherein the material of the substrate is semi-insulating alumina. The light-emitting diode according to claim 1, wherein the material of the buffer layer is undoped gallium nitride, and the thickness thereof ranges from about 0.1 micrometer to 10 micrometers. The light-emitting diode according to claim 1, wherein the n-type layer is an n-type gallium nitride layer having an electron carrier concentration of about 1×10 ¹⁶ cm ⁻³ to 3×10 ¹⁹ cm. ^-3 , and its thickness ranges from about 0.5 micrometers to 5 micrometers, and the doping element of the n-type layer is germanium. The light-emitting diode according to claim 1, wherein the multiple quantum well layer is formed by stacking a plurality of quantum well structures, each quantum well structure comprising a gallium nitride layer and an indium gallium nitride layer. The number of quantum well structures is about 2 to 50, and the indium gallium nitride has a chemical formula of In _X Ga _1-X N having an x value ranging from about 0.01 to 0.25. The light-emitting diode according to claim 5, wherein the doping element of the gallium nitride layer in the multiple quantum well layer is germanium, and the doping concentration ranges from about 1×10 ¹⁶ cm ⁻³ to 1 ×10 ¹⁹ cm ^-3 , and a thickness ranging from about 10 nm to 20 nm, and the indium gallium nitride layer has a thickness ranging from about 1 nm to 5 nm. The light-emitting diode according to claim 1, wherein the material of the n-type doped layer is one of indium gallium nitride and gallium nitride, and the chemical formula of the indium gallium nitride is In _x Ga _1-x N, x values range from about 0.01 to 0.3. The light-emitting diode according to claim 7, wherein the n-type doping layer has an electron carrier concentration of about 1×10 ¹⁷ cm ^-3 to 1×10 ¹⁹ cm ^-3 , and a thickness range thereof. It is from 1 nm to 100 nm. The light-emitting diode according to claim 1, wherein the material of the p-type layer is doped GaN, and the hole carrier concentration is about 1×10 ¹⁶ cm ^-3 to 1×10. ¹⁸ cm ^-3 , and a thickness ranging from about 0.1 μm to 1 μm, and the doping element of the p-type layer is one of magnesium and zinc. The light-emitting diode according to claim 1, wherein the transparent conductive layer is a metal film or a metal oxide layer, and the resistivity ranges from 10 ^-8 ohm-cm to 10 ^-1 ohm. - cm. The light-emitting diode according to claim 10, further comprising a cover passivation layer grown on the transparent conductive layer, the material covering the passivation layer being zinc oxide, germanium dioxide or tantalum nitride, and Its thickness ranges from about 10 nm to 500 nm. The light-emitting diode according to claim 1, wherein the electrode comprises a p-type electrode and an n-type electrode, the p-type electrode is grown on the transparent conductive layer, and the n-type electrode is grown in the n-type Above the layer. The light-emitting diode according to claim 12, wherein the p-type electrode is composed of chromium, platinum and gold, and the thickness of the chromium ranges from about 1 nm to 100 nm, and the thickness of the platinum The range is from about 10 nanometers to 300 nanometers, and the thickness of the gold ranges from about 100 nanometers to about 3,000 nanometers. The light-emitting diode according to claim 12, wherein the n-type electrode is composed of a light-emitting diode composed of chromium, platinum and gold, and the thickness of the chromium ranges from about 1 nm to 100 nm. The thickness of the platinum ranges from about 10 nanometers to 300 nanometers, and the thickness of the gold ranges from about 100 nanometers to about 3,000 nanometers. The light-emitting diode according to claim 12, wherein the n-type electrode is composed of titanium and gold, and the thickness of the titanium ranges from about 1 nm to 100 nm, and the thickness range of the gold is about It is from 100 nm to 3000 nm.