JP2013038417A - FAST ANNEALING FOR GaN LED - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming GaN light-emitting diodes which realizes enhanced output power, lower starting voltage, and reduced series resistance.SOLUTION: A method of forming GaN light-emitting diodes includes forming a GaN multilayer structure having an n-GaN layer 40 and a p-GaN layer 50 between which an active layer 60 is interposed. The method also includes performing fast annealing of the p-GaN layer 50 using either a laser or a flash lamp. The method further includes forming a transparent conductive layer 70 on the GaN multilayer structure, and adding a p-contact 90p to the transparent conductive layer 70 and an n-contact 90n to the n-GaN layer 40.

Description

(Cross-reference of related applications)
This application is a continuation-in-part of US Application 12 / 590,360 (Title of Invention: Laser Spike Annealing) filed on November 6, 2009, the contents of which are incorporated herein by reference.

  The present invention relates generally to light emitting diodes (LEDs) and, more particularly, to the use of rapid annealing when forming GaN LEDs.

  LEDs (especially gallium nitride (GaN) LEDs) have proven useful for a variety of lighting applications (full color displays, traffic lights, etc.), and more applications (backlights) as efficiency increases further. LCD panels, semiconductor lighting to replace conventional incandescent lamps and fluorescent lamps) are expected. In order to further improve the efficiency of the GaN LED, it is necessary to improve the output, lower the starting voltage, and reduce the series resistance. The series resistance of a GaN LED is closely related to the activation efficiency of dopants (impurities), uniform current spreading, and formation of resistive contacts.

US Pat. No. 6,455,877 US Pat. No. 7,259,399 US Pat. No. 7,436,001 US Pat. No. 6,747,245 US Pat. No. 7,154,066 US Pat. No. 7,399,945

In GaN, the n-type dopant can be easily obtained by using silicon (Si) at a high activation concentration of about 1 × 10 ²¹ cm ⁻³ . The p-type GaN is obtained by using magnesium (Mg) as a dopant. However, since magnesium has a high thermal activation energy, the doping (impurity addition) efficiency is extremely low. At room temperature, only a few percent of the introduced magnesium contributes to the free hole concentration. In the growth process by metal organic chemical vapor deposition (MOCVD), hydrogen passivation occurs, and magnesium doping becomes more complicated. When hydrogen passivation occurs, a thermal annealing step is necessary to break the bond between magnesium and hydrogen and activate the dopant. A typical thermal anneal is performed in a nitrogen atmosphere at about 700 ° C. To date, the actual hole concentration in p-type GaN has only been achieved on the order of about 5 × 10 ¹⁷ cm ⁻³ . Thus, when the activation level is low, the resistance contact becomes brittle and the diffusion resistance becomes large, which in turn limits the performance of the GaN LED.

  One aspect of the present invention is a method for forming a GaN LED. This method includes a step of forming a GaN multilayer structure having an n-type GaN layer and a p-type GaN layer sandwiching an active layer on a substrate. This method also performs a fast anneal of the p-type GaN layer (ie, 100 milliseconds and faster). This high-speed annealing is performed either by laser spike annealing (LSA) in which laser light is scanned with respect to the p-type GaN layer, or by flash lamp millisecond annealing included in exposure of the entire wafer by flash light from a flash lamp. Can be executed. The method also includes the step of forming a transparent conductive layer on the GaN multilayer structure. The method further includes adding a p-type contact to the transparent conductive layer and adding an n-type contact to the n-type GaN layer.

  In this method, it is further preferable to perform rapid annealing through the transparent conductive layer.

  In this method, it is further preferable to perform rapid annealing of the p-type contact.

In this method, the p-type contact preferably has a p-type contact resistance. By performing rapid annealing on the p-type contact, a p-type contact resistance in the range of about ⁴ × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² is formed.

  In this method, it is further preferable to perform rapid annealing on the n-type contact.

  In this method, it is further preferable to form a ledge in the GaN multilayer structure and the transparent conductive layer in order to expose the n-GaN layer. In this method, it is further preferable to form an n-type contact on the surface of the exposed GaN layer.

In this method, the maximum annealing temperature _{T AM} of fast annealing, it is preferable in the range of about 700 ° C. to about 1,500 ° C..

  In this method, the rapid annealing is preferably performed using a laser or a flash lamp.

  In this method, the fast annealing is preferably performed using a flash lamp that irradiates all p-type GaN layers with a single flash.

In this method, the p-type GaN layer preferably has an activated dopant concentration in the range of about 5 × 10 ¹⁷ cm ⁻³ to about 5 × 10 ¹⁹ cm ⁻³ after performing rapid annealing.

  In this method, it is preferable to form an active layer in order to obtain a multi-quantum well structure.

  Another aspect of the present invention is a method of forming a GaN LED. This method includes a step of forming a GaN multilayer structure having an n-type GaN layer and a p-type GaN layer sandwiching an active layer. The method further includes the step of forming a p-type contact layer adjacent to the p-type GaN layer. The method further includes forming an n-type contact on the n-type GaN layer. The method further includes performing a fast anneal of the n-type contact (ie, 100 milliseconds and faster) by scanning the n-type contact with laser light. The rapid annealing may be performed using a laser or a flash lamp.

  In this method, the rapid annealing is preferably performed using a laser or a flash lamp.

In this method, the n-type contact preferably has an n-type contact resistance. By performing rapid annealing on the n-type contact, an n-type contact resistance in the range of about 1 × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² is formed.

In this method, furthermore, the maximum annealing temperature _{T AM} of fast annealing, it is preferable in the range of about 700 ° C. to about 1,500 ° C..

Another aspect of the present invention is a GaN LED comprising a substrate, a GaN multilayer structure, a transparent conductive layer, a p-type contact, and an n-type contact. The GaN multilayer structure is formed on the surface of the substrate. The GaN multilayer structure has an n-type GaN layer and a p-type GaN layer sandwiching the active layer. The GaN multilayer structure has a layer whose activated dopant concentration is greater than about 5 × 10 ¹⁷ cm ⁻³ and less than or equal to about 5 × 10 ¹⁹ cm ⁻³ by rapid annealing. The transparent conductive layer is formed on the surface of the GaN multilayer structure. The p-type contact is formed on the surface of the transparent conductive layer. The n-type contact is formed on the exposed portion of the n-type GaN layer. Fast annealing can be performed using a laser or a flash lamp.

  In this GaN LED, the layer subjected to rapid thermal annealing is preferably one of a layer subjected to rapid thermal annealing using a flash lamp and a layer subjected to rapid thermal annealing using a laser.

In this GaN LED, the p-type contact preferably has an ohmic contact resistance in the range of about ⁴ × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² .

In this GaN LED, the n-type contact preferably has an n-type contact resistance in the range of about 1 × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² .

Another aspect of the present invention is a GaN LED comprising a substrate, a GaN multilayer structure, a p-type contact layer, a GaN multilayer structure, and an n-type contact. The p-type contact layer is formed on the surface of the substrate. The GaN multilayer structure is formed on the surface of the p-type contact layer. The GaN multilayer structure includes an n-type GaN layer and a p-type GaN layer sandwiching the active layer, and the p-type GaN layer is adjacent to the p-type contact layer. The n-type GaN layer has a layer whose activated dopant concentration is higher than about 3 × 10 ¹⁹ cm ⁻³ and about 3 × 10 ²¹ cm ⁻³ or less by high-speed annealing. The n-type contact is formed on the surface of the n-type GaN layer. Fast annealing can be performed using a laser or a flash lamp.

  In this GaN LED, the layer subjected to rapid thermal annealing is preferably one of a layer subjected to rapid thermal annealing using a flash lamp and a layer subjected to rapid thermal annealing using a laser.

In this GaN LED, the n-type contact preferably has an n-type contact resistance in the range of about 1 × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² .

  Additional features and advantages of the invention will be set forth in the detailed description which follows. Some of them will be readily apparent to those skilled in the art from the detailed description, or by practicing the invention described herein, including the following detailed description, the claims, and the accompanying drawings. Be recognized.

  The above description of the background art and the following detailed description of the present invention provide embodiments of the present invention, and as described in the claims, the essence and features of the present invention. It should be understood that it provides an outline or framework for understanding. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and practice of the invention.

It is a schematic sectional drawing of one structural example of GaN LED. Time (ms, ms) is a plot of annealing temperature T _{A (°} C.) for an example of the annealing temperature profile for a laser spike annealing (LSA) 3 different residence times of the scanned laser beam at runtime shown ing. It is an enlarged side view of a p-type GaN layer showing an LSA process using scanning laser light. It is a schematic diagram which shows one example of a shape of a line type scanning laser beam. It is a schematic diagram which shows the 1st LSA method example applied to the GaN LED structure formed in the formation process of GaN LED of this invention shown in FIG. FIG. 6 is a view similar to FIG. 5 and showing a GaN LED multilayer structure further comprising a transparent conductive layer. It is a figure similar to FIG. 1, and is a figure which shows GaN LED by which LSA is performed by the scanning of the laser beam with respect to the surface of a transparent conductive layer, and the p-type contact formed on the surface. FIG. 6 is a diagram similar to FIG. 5, and is an example of a GaN LED in which the layers constituting the GaN LED multilayer structure are replaced such that the n-type GaN layer is arranged in the uppermost layer and has an n-type contact; It is a figure which shows GaN LED by which LSA is performed by the scanning of the laser beam with respect to the surface of a type | mold GaN layer. It is the graph which modeled the curve which shows the relationship between an electric current (milliampere: mA) and a voltage (V) which shows that the performance (■) of the GaN LED of this invention improved compared with the performance (◆) of a prior art. , LSA is used to reduce the series resistance at the operating voltage. It is a schematic diagram which shows the example of the LED wafer which has received irradiation from the flash lamp annealing system in the case of rapid thermal annealing. FIG. 8 is a view similar to FIG. 7 showing an example of a GaN LED that has undergone rapid thermal annealing using flash light from a flash lamp. FIG. 9 is a view similar to FIG. 8 showing an example of a GaN LED that has undergone rapid thermal annealing using flash from a flash lamp. FIG. 6 is a view similar to FIG. 5 illustrating an example of a GaN LED structure formed during a GaN LED manufacturing process that has undergone rapid thermal annealing using flash from a flash lamp. FIG. 7 is a view similar to FIG. 6 illustrating an example of a GaN LED structure formed during a GaN LED manufacturing process that has undergone rapid thermal annealing using flash from a flash lamp.

  Reference will now be made in detail to the preferred embodiments of the present invention. Each example of the embodiment is illustrated in the accompanying drawings. When referring to the same or similar parts in the drawings, the same or similar numbers and symbols are used as much as possible. Terms such as “above” and “below” are relative terms used to facilitate the present description and are not intended to limit the present description strictly.

  Many desirable LED properties (high dopant concentration, low contact resistance, etc.) have been found to be obtained by rapid thermal annealing. As used herein, rapid thermal annealing is defined as annealing performed at a duration of about 100 milliseconds or less (eg, between 0.1 and 100 milliseconds). The rapid thermal annealing can be performed using a laser (eg, laser spike annealing) or a flash lamp (flash lamp annealing).

  Most of the following is related to laser spike annealing. However, the improvements and claims extend to all aspects related to millisecond annealing.

  FIG. 1 is a schematic cross-sectional view showing one structural example of a GaN light emitting diode (LED) 10. Examples of GaN LEDs are described in US Pat. No. 6,455,877, US Pat. No. 7,259,399, US Pat. No. 7,436,001, which are referred to. Is incorporated herein by reference. The GaN LED 10 has a substrate 20 made of, for example, sapphire, SiC, GaN Si, or the like. A GaN multilayer structure 30 is disposed on the substrate 20. The GaN multilayer structure 30 includes an n-type doped GaN layer (hereinafter referred to as “n-type GaN layer”) 40 and a p-type doped GaN layer (hereinafter referred to as “p-type GaN layer”) 50 having a surface 52. Is provided. The n-type GaN layer 40 and the p-type GaN layer 50 sandwich the active layer 60. The n-type GaN layer 40 is adjacent to the substrate 20. The active layer 60 has, for example, a multiple quantum well (MQW) structure such as an undoped GaInN / GaN superlattice. Thus, a pn junction is formed in the GaN multilayer structure 30. A transparent contact layer (TCL) 70 having a surface 72 is disposed on the GaN multilayer structure 30. An example of TCL 70 is indium tin oxide (ITO). The TCL 70 serves to diffuse current and functions as an antireflection film that optimizes light output.

  The GaN LED 10 has a notch 80. By forming the notch 80, the surface portion 42 of the n-type GaN layer 40 is exposed. This exposed portion functions as a ledge (indentation) that supports the n-type contact 90n. Examples of the material for the n-type contact include Ti / Au, Ni / Au, Ti / Al, or a combination thereof. A p-type contact 90p is disposed on a portion of the TCL surface 72. Examples of the material for the p-type contact include Ni / Au and Cr / Au.

The GaN LED 10 differs from the conventional gallium nitride LED in at least one of the following (a) to (c).
(A) The degree of dopant activation in the p-type GaN layer 50 is high.
(B) The n-type contact 90n is alloyed by using laser spike annealing (LSA).
(C) The p-type contact 90p is alloyed by using LSA.
Hereinafter, a processing method of the GaN LED 10 for realizing the above differences will be described in detail.

Laser spike annealing (LSA)
In order to increase the activation in the p-type GaN layer 50, it is desirable to perform annealing at a high temperature for a short period of time. When conventional annealing is employed, the maximum temperature that can be applied is limited by the degradation of the properties of the GaN material. One of the degradation mechanisms is that the doped p-type GaN layer 50 is decomposed (for example, by using Mg) during the MOCVD growth process. In order to effectively activate Mg, a relatively high annealing temperature is required. However, when annealing is performed at a high temperature for a long time, GaN is decomposed by outdiffusion of nitrogen, and in p-type GaN, Free hole concentration decreases. In the conventional non-rapid thermal annealing process, the substrate is held at 700 ° C. for several tens of seconds to several minutes in a nitrogen atmosphere.

  Other degradation mechanisms include strain relaxation and dislocation generation in the p-type GaN layer 50. Due to lattice mismatch, the heteroepitaxial structure is in a metastable state including strain. In conventional thermal annealing, excessive distortion occurs due to mismatch of thermal expansion coefficients, which promotes dislocation propagation and growth.

In the present invention, laser spike annealing (LSA) is adopted, and the LSA is performed at a higher temperature and in a shorter time than conventional non-rapid thermal annealing. An example of an LSA system suitable for performing each method according to the present invention is described in US Pat. No. 6,747,245, US Pat. No. 7,154,066, US Pat. No. 7,399,945. Which is hereby incorporated by reference into the present application. In the application example of LSA in each method according to the present invention, the annealing time is shortened by 1,000 to 10,000 times as compared with the conventional RTA. Therefore, the annealing process can be performed at a higher annealing temperature T _A (for example, T _A > 1100 ° C.) without the influence of problematic nitrogen outdiffusion and dislocation generation.

Contact resistance is improved by using LSA to enhance dopant activation in the doped GaN layer. This is because at a high dopant concentration, the tunnel current increases and the barrier height decreases. At a high dopant activation concentration, a specific contact resistance ρ _c is determined as follows.
Here, the barrier height change amount Δφ _B is obtained by the following equation.

In the above formula, h is the Planck constant, m ^* is the effective mass of electrons or holes, ε is the dielectric constant of nitride, N is the activation dopant concentration, and q is the elementary charge. , K _B is the Boltzmann constant, T is the absolute temperature, and V ₀ is the contact potential.

.DELTA..PHI _B is increased when activating the dopant concentration N is increased, the molecules in the index number 1 is reduced. As N increases, the denominator in the exponent of Equation 1 increases and ρ _c decreases. As a result, according to the dopant activation is increased, the contact resistance [rho _c is reduced. In one example embodiment for each method according to the present invention, the activated dopant concentration in p-type GaN is increased by about 2.5 times (eg, from about 5 × 10 ¹⁷ cm ⁻³ to about 1.25 × 10 ¹⁸ cm ⁻³ ). . For this reason, the entire contact resistance (including spreading resistance) is reduced by about 60%.

FIG. 2 is a plot of the annealing temperature T _A (° C.) versus time (ms). For example, as shown in FIG. 3 and FIG. An example of a curve) is shown. The curve in FIG. 2 shows the annealing temperature profile at a point P on the surface of an arbitrary layer (for example, on the surface 52 of the p-type GaN layer 50), and as shown, the laser beam 120 is at this point. The annealing temperature profile when approaching and passing is shown. In calculation, the laser light 120 has a long and narrow shape at the surface 52 (as obtained at a selected intensity threshold), for example, a length L of about 10 mm and a width W of about 100 μm, or about 100: 1. Having an aspect ratio of The laser beam 120 scans the surface 52 at a speed V _S. The residence time _{t d} is determined by the scanning speed _{V S} and the beam width W. When the residence time is long, the point P is preheated by heat conduction until it comes into contact with the approach of the laser beam 120. Therefore, the annealing temperature becomes the maximum value _TAM . If the residence time is short, insufficient preheating of silicon by thermal conduction, the point P is a maximum annealing temperature T _AM only a very short time. In this way, the annealing temperature profile can be adjusted.

FIG. 5 is a schematic diagram relating to a first method example of LSA applied to the GaN LED structure 100 formed in the process of forming the GaN LED 10. The GaN LED structure 100 includes a substrate 20 and a GaN multilayer structure 30. The scanning laser beam 120 is incident on the surface 52 of the p-type GaN layer 50. The scanning of the laser beam 120 is realized by scanning the laser beam 120 or scanning the gallium nitride LED structure 100, for example, scanning a wafer (not shown) used in the process of forming the GaN LED 10. The residence time t _d = W / V _S is, for example, in the range of about 10 microseconds (μs) to about 10 milliseconds (ms). The maximum annealing temperature _TAM is, for example, in the range of about 700 ° C. to about 1500 ° C. The maximum annealing temperature T _AM is determined by the amount of GaN dissociation in the GaN LED structure 100, strain relaxation due to lattice mismatch, and dislocations. The depth of annealing depends on the residence time and the intensity of the laser beam. The intensity of the laser light is, for example, 400 W / mm ² . The GaN multilayer structure 30 has a thickness of, for example, several μm to about 10 μm, and the annealing typically reaches 10 μm to 100 μm (ie, the annealing generally reaches the full thickness of the GaN multilayer structure 100). Applied to reach the substrate 20 in some cases). In this way, the dopant activation of the p-type GaN layer 50 is enhanced, but in an example of the embodiment, it is further advantageous in that the dopant activation of the lower n-type GaN layer 40 is also enhanced.

  Once the GaN LED structure 100 is annealed, a TCL 70 is formed on the surface 52 of the p-type GaN layer. Then, as shown in FIG. 1, a notch 80 is formed, an n-type contact 90n and a p-type contact 90p are formed (for example, vapor deposition), and as a result, the GaN LED 10 is formed.

FIG. 6 is similar to FIG. 5 and further illustrates a GaN LED structure 100 having a TCL 70. If you run LSA after deposition of TCL70, TCL70 is now nitrogen gas release during annealing functions as a cap layer does not occur, preventing a result, the degradation of the more enhanced even material annealing temperature T _A Can do.

  FIG. 7 is similar to FIG. 1 and illustrates a GaN LED 10 in which LSA is performed by scanning laser light 120 against a TCL surface 72 (including p-type contact 90p). Since the amount of heat in LSA is relatively low compared to conventional non-fast annealing techniques, the annealing temperature can be raised as described above without the risk of the metal in the p-type contact 90p transitioning to a pn junction.

In one example of an embodiment relating to the annealing method disclosed herein, LSA is used to form an ohmic resistance alloy in the p-type contact 90p of the GaN LED of FIG. Typically, p-type resistive contacts are realized by alloying Ni / Au at 500 ° C. to 800 ° C. for 10 to 20 minutes. When the alloying temperature is increased, the alloyed metal is excessively diffused through the pn junction, resulting in deterioration of form and leakage. Since the p-type concentration becomes low, the contact resistance becomes a high value (for example, about 1 × 10 ⁻³ Ωcm ² ). For this reason, not only the voltage drop becomes large, but also local heating occurs, and as a result, the lifetime of the GaN LED 10 at a high current level may be shortened. If LSA is used, the annealing temperature can be increased without causing aggregation. For this reason, it becomes a new opportunity to form the p-type contact 90p or to improve the reliability of the GaN LED 10 as a whole. In one embodiment, the contact resistance of the p-type contact is in the range of about ⁴ × 10 ⁻⁴ Ωcm ² to about 1 × 10 ⁻⁶ Ωcm ² . Thus, in one example of an embodiment relating to a method according to the present invention, the performance of the resulting GaN LED 10 is further improved by alloying the p-type contact and increasing dopant activation in the p-type GaN layer 50. A synergistic effect is obtained.

  FIG. 8 is similar to FIG. 5 and shows an example of a GaN LED 10 in the vertical direction. Here, the substrate 20 is a metal (for example, copper alloy), and the GaN multilayer structure 30 has an n-type GaN layer 40 and a p-type GaN layer 50. However, the n-type GaN layer 40 and the p-type GaN layer 50 are arranged opposite to the state shown in FIG. That is, the n-type GaN layer 40 having the surface 42 is disposed on the active layer 60, and the p-type GaN layer 50 is disposed under the active layer 60. The n-type contact 90n is disposed on the surface 42 of the n-type GaN layer. The p-type contact 90p is disposed under the p-type GaN layer 50 and functions as a reflective layer. Further, a reflective layer (not shown) may be added separately adjacent to the p-type contact 90p. In the GaN LED 10 of FIG. 8, the laser beam 120 is scanned on the surface 42 (including the n-type contact 90n) of the n-type GaN layer, and LSA is performed. The metal substrate 20 is bonded to the GaN multilayer structure 30, has good thermal conductivity, and efficiently dissipates heat. Although the above is repeated, annealing is performed on the entire thickness of the p-type GaN layer. Thus, in one embodiment, this layer also increases dopant activity and further enhances the performance of the resulting GaN LED 10. The vertical GaN LED 10 in FIG. 8 is formed by a flip chip process.

In general, since the dopant concentration of this layer is high, even if a resistance contact of the n-type contact 90n is normally formed in the n-type GaN layer 40, there is no problem. The specific contact resistance ρ _c can be set to 1 × 10 ⁻⁶ Ωcm ² or less. However, in advanced flip chip LEDs, n-type contacts are formed after bonding to other substrates. In this case, it is necessary to limit the amount of heat in order to avoid stress and dislocation caused by the mismatch of thermal expansion coefficients between the GaN multilayer structure 30 and the (metal) substrate 20. Incidentally, heat is the _{E a} a thermal activation energy, the _{k B} the Boltzmann constant, when the _{T A} and the annealing temperature, the product of the thermal activation _{exp {-E a / k B T} A} and annealing duration Is defined as In this case, low-temperature annealing at 300 ° C. was adopted for forming the resistance contact, and as a result, the contact resistance ρ _c was 7 × 10 ⁻⁴ Ωcm ² . Incidentally, the contact resistance [rho _c is made much higher compared contact resistance to be achieved by a very low raised heat annealing temperature in the LSA. In one embodiment, a contact resistance ρ _{c as} low as 1 × 10 ⁻⁶ Ωcm ² has been achieved in n-type GaN by using LSA annealing. For this reason, the performance of the gallium nitride LED is improved to 8% as compared with an LED that does not employ laser annealing at a drive current of 350 mA.

By reducing the contact resistance of the GaN LED 10, performance is improved. As the diode current increases, (nk _B T / qI) (where n is the ideal factor, k _B is the Boltzmann constant, T is the junction temperature, q is the elementary charge, I Is a diode current), and the resistivity decreases to a point where the DC resistance R _S becomes dominant with respect to the efficiency of the GaN LED 10.

FIG. 9 shows a curve showing the relationship between the model current I (mA, mA) and the voltage (V). Using LSA, the performance of the gallium nitride LED 10 is improved, and the series resistance at the operating voltage is increased. Indicates reduced. This graph is for GaN LEDs 10 having different series resistances R _S , where the “diamond (♦)” curve models a conventional GaN LED 10, and the “square (■)” curve represents the present invention. A GaN LED 10 with 2.5 times higher dopant activation of p-type GaN is modeled using such an LSA-based method. Incidentally, the voltage change [Delta] V, the relationship ΔV = IΔR _S, are relevant with the change in the series resistance.

At a current I = 350 mA, when the series resistance _RS decreases by 40% (contact resistance decreases by 60%), the operating voltage V decreases by 10%. For this reason, the LED efficiency is increased by 10% in terms of lumen / watt. Series resistance is mainly due to contact resistance.

  Further improvements are expected in the high drive current type that will be adopted by major LED manufacturers in the future. The two curves in FIG. 9 branch so that the voltage drop increases as the drive current increases. Thus, GaN LEDs formed using the method according to the present invention are expected to be 15-20% more efficient than conventional doped GaN LEDs when the drive current is 700 mA. Thus, a conventional GaN LED with an output of 100 lumens / watt is improved to have an output of about 120 lumens / watt.

Flash Lamp Annealing In one example of embodiments disclosed herein, fast annealing is performed using flash from a flash lamp. FIG. 10 is a schematic diagram illustrating an example of an LED wafer 200 having a surface 202. The LED wafer 200 is supported on the wafer stage 206. The LED wafer 200 has a GaN LED structure 100 formed in the process of manufacturing the GaN LED 10 as shown in FIGS. 13 and 14 or the GaN LED 10 as shown in FIGS. 11 and 12. The LED wafer 200 and the wafer stage 206 are accommodated in the chamber internal space 210 of the chamber 220. The flash lamp 250 is provided near the wafer surface 202 in the chamber internal space 210. The flash lamp 250 may include one or more flash lamp elements 252. The flash lamp 250 emits a flash 260 having a length in milliseconds (for example, between 0.1 and 100 milliseconds). The flash 260 exposes the entire wafer surface 202 and performs high-speed annealing of the LED wafer 200 with a flash lamp. Examples of flash lamp rapid annealing systems and methods are disclosed in US Pat. No. 7,015,422 and US Patent Application Publication US2008 / 0008460, the contents of which are incorporated herein by reference.

  FIG. 11 is a view similar to FIG. 7 showing an example of the GaN LED 10 subjected to rapid thermal annealing using the flash 260 irradiated to the TCL surface 27 (including the p-type contact 90p). FIG. 12 is a view similar to FIG. 8 and shows an example of the GaN LED 10 in the vertical direction. In this GaN LED 10, the substrate 20 is a metal (for example, copper alloy), and the GaN multilayer structure 30 is stacked in the reverse order to that shown in FIG. 5, the n-type GaN layer 40 and the p-type GaN layer 50. have. That is, the n-type GaN layer 40 having the surface 42 is on the active layer 60, and the p-type GaN layer 50 is below the active layer 60. The n-type contact 90n is provided on the surface 42 of the n-type GaN layer. The p-type contact 90p is provided under the p-type GaN layer 50, and also serves as a reflective layer. A separate reflective layer (not shown) may be added adjacent to the p-type contact 90p. In the GaN LED 10 of FIG. 12, the surface 42 (including the n-type contact 90n) of the n-type GaN layer is rapidly annealed by the flash 260.

  FIG. 13 is a view similar to FIG. 5 showing an example in which fast annealing using flash 260 is applied to a GaN LED structure 100 formed during the manufacturing process of GaN LED 10.

  FIG. 14 is a view similar to FIG. 6 showing an example in which rapid annealing using flash 260 is applied to an exemplary GaN LED structure 100 including TCL 70.

  It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Therefore, if the improvement and change with respect to this invention are included in the range of an attached claim and its equivalent, the improvement and change are included in this invention.

Claims (22)

Forming a GaN multilayer structure having an n-type GaN layer and a p-type GaN layer sandwiching an active layer on a substrate;
Performing high-speed annealing on the p-type GaN layer;
Forming a transparent conductive layer on the GaN multilayer structure;
And adding a p-type contact to the transparent conductive layer and adding an n-type contact to the n-type GaN layer. The method for forming a GaN LED according to claim 1, further comprising performing the high-speed annealing through the transparent conductive layer. The method for forming a GaN LED according to claim 1, further comprising performing the high-speed annealing on the p-type contact. The p-type contact has a p-type contact resistance;
4. The method of forming a GaN LED according to claim 3, wherein the p-type contact resistance is in a range of about ⁴ × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² by performing high-speed annealing on the p-type contact. The method for forming a GaN LED according to claim 1, further comprising a step of performing high-speed annealing on the n-type contact. Notching the GaN multilayer structure and the transparent conductive layer to expose the n-type GaN layer;
The method of forming a GaN LED according to claim 1, further comprising: forming the n-type contact on the exposed GaN layer. The high-speed annealing, GaN LED forming method according to any one of claims 1 to 6 having a maximum annealing temperature _{T AM} in the range of about 700 ° C. to about 1500 ° C.. The method for forming a GaN LED according to claim 1, wherein a laser or a flash lamp is used for the high-speed annealing. 9. The method of forming a GaN LED according to claim 1, wherein the rapid annealing is performed using a flash lamp that irradiates the entire p-type GaN layer at a time. 10. The method of forming a GaN LED according to claim 1, wherein the p-type GaN layer has an activated dopant concentration in a range of about 5 × 10 ¹⁷ cm ⁻³ to about 5 × 10 ¹⁹ cm ⁻³ after performing high-speed annealing. . The method for forming a GaN LED according to claim 1, further comprising a step of forming the active layer to form a multi-quantum well structure. Forming a GaN multilayer structure having an n-type GaN layer and a p-type GaN layer sandwiching the active layer;
Forming a p-type contact layer adjacent to the p-type GaN layer;
Forming an n-type contact on the n-type GaN layer;
A method of forming a GaN light emitting diode (LED), comprising: performing a rapid annealing on the n-type contact. The method for forming a GaN LED according to claim 12, wherein the rapid annealing is performed using a laser or a flash lamp. The n-type contact has an n-type contact resistance;
14. The GaN LED according to claim 12, wherein the n-type contact resistance is in a range of about 1 × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² by performing high-speed annealing on the n-type contact. Method. GaN LED forming method according to any one of claims 12 to 14 from about 700 ° C. to perform the high-speed annealing so as to have a maximum annealing temperature _{T AM} in the range of about 1500 ° C.. A substrate,
It has an n-type GaN layer and a p-type GaN layer sandwiching the active layer, and is a GaN multilayer structure formed on the substrate, wherein the activated dopant concentration is more than about 5 × 10 ¹⁷ cm ^{−3 and} about 5 × 10 ¹⁹ cm. A GaN multilayer structure having a layer that has been subjected to rapid thermal annealing to be ⁻³ or less,
A transparent conductive layer formed on the GaN multilayer structure;
A p-type contact formed on the transparent conductive layer;
A GaN light emitting diode (LED) comprising an n-type contact formed on an exposed portion of the n-type GaN layer. The GaN LED according to claim 16, wherein the layer subjected to rapid thermal annealing is one of a layer subjected to rapid thermal annealing with a flash lamp and a layer subjected to rapid thermal annealing with a laser. 18. The GaN LED according to claim 16, wherein the p-type contact has an ohmic contact resistance in a range of about ⁴ × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² . 19. The GaN LED according to claim 16, wherein the n-type contact has an n-type contact resistance in a range of about 1 × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² . A substrate,
A p-type contact layer formed on the substrate;
A GaN multilayer structure formed on the p-type contact layer and having an n-type GaN layer and a p-type GaN layer sandwiching an active layer;
The p-type GaN layer is adjacent to the p-type contact layer;
The n-type GaN layer has a layer that has been subjected to rapid thermal annealing with an activated dopant concentration of about 3 × 10 ¹⁹ cm ⁻³ to about 3 × 10 ²¹ cm ⁻³ ,
A GaN light emitting diode (LED) further comprising an n-type contact formed on the n-type GaN layer. 21. The GaN LED according to claim 20, wherein the layer subjected to rapid thermal annealing is one of a layer subjected to rapid thermal annealing with a flash lamp and a layer subjected to rapid thermal annealing with a laser. 22. The GaN LED according to claim 20 or 21, wherein the n-type contact has an n-type contact resistance in a range of about 1 × 10 ⁻⁴ Ω-cm ² to about 1 × 10 ⁻⁶ Ω-cm ² .