CN114300591B - Multi-active-area tunnel cascade resonant cavity red light Micro-RCLED - Google Patents

Abstract

The invention discloses a resonant cavity-based tunnel cascade red light Micro-RCLED with multiple active regions, which belongs to the technical field of semiconductor electronics. From top to bottom, it includes an upper electrode, an upper Bragg reflector, a resonant cavity, a lower Bragg reflector, a substrate, and a lower electrode. Among them, the upper Bragg reflector is composed of a relatively high refractive index material layer and a relatively low refractive index material layer; the resonant cavity is composed of multiple active regions, and the active region includes a reverse bias tunnel junction, a matching layer, an oxidation confinement layer, and an upper The confinement layer, the quantum well, the lower confinement layer; the lower Bragg reflector is composed of a relatively high refractive index material layer and a relatively low refractive index material layer. The invention utilizes the reverse bias tunnel junction to realize multi-active region cascading, improves the internal quantum efficiency, and combines the resonant cavity structure in the vertical direction, and uses the AlAs oxidation confinement layer inside to reduce the non-radiative recombination of the side wall, which can realize high light extraction efficiency , Diodes with stable radiation wavelength and small chip area emit light.

Description

A Multi-Active Area Tunnel Cascaded Resonant Cavity Red Micro-RCLED

technical field

The invention relates to a resonant cavity red light Micro-RCLED, in particular to a resonant cavity-based multi-active area tunnel cascaded red light Micro-RCLED, which belongs to the technical field of semiconductor electronics.

Background technique

Micro-LED refers to a light-emitting diode whose lateral size of the light-emitting unit is less than 50um. Compared with other LEDs, Micro-LEDs have the advantages of high efficiency, long life, high brightness and high reliability. Micro-LEDs have great application potential in the display field. Micro-LEDs used for display require RGB full-color matching, and the extraction efficiency of red-light Micro-LEDs is still low due to factors such as process level and device structure. Therefore, improving the light extraction efficiency of the red Micro-LED is beneficial to realize the full-color display of the Micro-LED.

Resonant cavity light-emitting diode (RCLED) is a light-emitting diode that uses the F-P cavity theory to make the resonant wavelength of the cavity resonant or consistent with the emission wavelength of the active region. When the outgoing light forms resonance in the cavity, the external quantum efficiency of the outgoing light at the resonant wavelength is increased, so that most of the light is concentrated in the extraction angle range. Since the light beam is reflected back and forth in the cavity for many times, only the light meeting the specific frequency meets the interference constructive condition, so that the light intensity is increased and the frequency is screened. But the external quantum efficiency of conventional RCLEDs is still low. Applying resonant cavity to Micro-LED is called Micro-RCLED.

For a red Micro-LED with a common structure, the simple structure is shown in Figure 1, which includes from top to bottom: 100 upper electrodes, 200P type ohmic contact layer, 300P type confinement layer, 400 active layer, 500N type confinement layer, 600N type ohmic contact layer, 700 buffer layer, 800 substrate, 900 lower electrode. The problems of this common structure red Micro-LED are:

1. With the reduction of LED size, sidewall defects caused by mesa etching will cause serious Shockley-Read-Hall (SRH) non-radiative recombination, resulting in low light extraction efficiency;

2. The light emitted by the active area is non-directional. Due to substrate absorption, current congestion and internal reflection effects, the light emitted by the active area is lost more, making the extraction efficiency of red light Micro-LED generally low. Not more than 5%;

3. A single active region makes the improvement of internal quantum efficiency limited, and the light extraction efficiency is also low;

4. Due to the low efficiency of red Micro-LEDs, multiple dies are required for RGB full-color color matching, which occupies a large area and is not conducive to improving device resolution;

Contents of the invention

The present invention proposes a multi-active area tunnel cascaded red Micro-RCLED based on a resonant cavity. Good red light emitting diode.

The resonant cavity-based multi-active area tunnel cascaded red Micro-RCLED of the present invention, as shown in FIG. 2 , includes an upper electrode 100, an upper Bragg reflector 200, a resonant cavity 300, and a lower Bragg reflector 400 from top to bottom. , a substrate 500, and a lower electrode 600. Wherein the upper Bragg reflector 200 is composed of a relatively high refractive index material layer 201 and a relatively low refractive index material layer 202; the resonant cavity 300 includes a first active region 301, a second active region 302, and a third active region 303 , the fourth active region 304 and other active regions, the middle ellipsis represents a plurality of active regions, taking the second active region 302 as an example, it includes a reverse bias tunnel junction 3021, a matching layer 3022, an oxidation confinement layer 3023, the upper confinement layer 3024, quantum well 3025, lower confinement layer 3026; the lower Bragg reflector 400 is composed of a relatively higher refractive index material layer 401 and a relatively lower refractive index material layer 402, and the material selection is the same as that of the upper Bragg reflector 200, except for The number is different.

Compared with the common red Micro-LED device structure (as shown in Figure 1), the resonant cavity-based multi-active area tunnel cascaded red Micro-RCLED of the present invention has the following advantages:

1. Reduce the non-radiative recombination of the side wall and improve the carrier recombination efficiency

Compared with the Micro-LED with ordinary structure, the present invention introduces an AlAs oxidation confinement layer in the resonant cavity, and the lateral oxidation confinement layer formed by wet oxygen oxidation can control the lateral expansion of carriers so that they can effectively enter the active region The recombination is not only beneficial to reduce the non-radiative recombination of the side wall, but also reduces the leakage, thereby improving the carrier recombination efficiency.

2. Reduced light loss and improved light extraction efficiency

Compared with Micro-LED with common structure, the present invention introduces the resonant cavity of RCLED and combines RCLED with Micro-LED. The effect of introducing the resonant cavity is to change the spatial distribution of the spontaneous emission field in the active region, and to distribute more light within the light extraction angle to improve the light extraction efficiency. The preferred direction is the vertical direction along the horizontal plane in Figure 2, so The upper electrode will not block and absorb the light emitted by the active area, and the resonant cavity is also conducive to the stability of the output spectrum wavelength.

3. Multiple active regions are cascaded to improve the internal quantum efficiency

Compared with the Micro-LED with a common structure, which has only one active area, the present invention uses reverse bias tunnel junctions to cascade multiple active areas. According to the principle of tunneling, the LED can generate multiple electrons injected from the electrode during operation. Photons thus make the internal quantum efficiency greater than 1, and the improvement of the internal quantum efficiency is proportional to the number of active regions in theory. For example, the internal quantum efficiency of a Micro-LED with a common structure is about 90%, and the internal quantum efficiency of a Micro-RCLED with three active regions can be increased by about three times. Theoretically, the light extraction efficiency is also proportional to the number of active regions. The extraction efficiency of Micro-LEDs with ordinary structures generally does not exceed 5%, and the extraction efficiency can reach more than 10% by using three active regions.

4. Smaller chip footprint and higher resolution

Compared with the horizontally integrated structure of Micro-LED with ordinary structure, when applied to RGB full-color display, although only one blue and green die is needed in each unit, the red die requires two or more. many. Because the invention greatly improves the extraction efficiency, the horizontal integration structure of ordinary Micro-LEDs can be converted into a vertical integration structure, so that the number of red light tube cores in each unit is reduced to one during RGB full-color matching, reducing the The occupied area of the chip enables more light-emitting points to be placed on the same size area, which improves the resolution of the device.

Description of drawings

Figure 1: Schematic diagram of the structure of a common structure red Micro-LED

Figure 2: Multi-active area tunnel cascaded red Micro-RCLED based on resonant cavity in the present invention

In the figure: 100 is the P-type upper electrode; 200 is the P-type upper DBRs, of which 201 is a relatively high refractive index material layer, 202 is a relatively low refractive index material layer; 300 is a resonant cavity, including 301, 302, 303, 304, etc. Multiple active regions, the ellipsis in the middle represents multiple active regions; 3021 is a reverse bias tunnel junction, 3022 is a matching layer, 3023 is an AlAs oxidation confinement layer, 3024 is an upper confinement layer, 3025 is a quantum well, and 3026 is a lower confinement layer; 400 is N-type lower DBRs, wherein 401 is a relatively high refractive index material layer, 402 is a relatively low refractive index material layer; 500 is an N-type GaAs substrate; 600 is an N-type lower electrode.

Detailed ways

As shown in Figure 2, the implementation method of multi-active area tunnel cascaded red Micro-RCLED based on resonant cavity is as follows:

1. Growth of epitaxial wafers: On GaAs substrate 500, N-type lower DBRs 400, resonant cavity 300, and P-type upper DBRs 200 are epitaxially grown sequentially by metal-organic chemical vapor deposition (MOCVD) to obtain a red light Micro - RC LED epitaxial wafer.

2. Device preparation, specific process steps:

a. Cleaning: Wash the film twice with acetone and alcohol, then rinse with water for 30 times, and finally blow dry with a nitrogen gun. b. Engraving the mesa: photoetching on the upper Bragg reflector 200 , carrying out wet or dry etching with glue, and engraving the mesa, the bottom of which extends into the top of the lower Bragg reflector 400 .

c. Lateral oxidation: Put the epitaxial wafer into an oxidation furnace for wet oxidation to form a lateral oxide layer.

d. Forming the Ti/Pt/Au upper electrode layer by means of sputtering or electron beam evaporation.

e. Photoetching the shape of the upper electrode (100).

f. Substrate thinning.

g. Form Au, Ge, Ni lower electrodes by means of sputtering or electron beam evaporation.

h. Alloy annealing. Anneal at 430°C for 40s to achieve good ohmic contact.

i. Scribing and cleavage to obtain a single tube core, which is pressure-welded on the tube base and packaged to complete the production of Micro-RCLED.

Claims (4)

1. A multi-active area tunnel cascaded red light Micro-RCLED based on a resonant cavity comprises an upper electrode (100), an upper Bragg reflector (200), a resonant cavity (300), a lower Bragg reflector (400), a substrate (500) and a lower electrode (600) from top to bottom; wherein the upper Bragg reflector (200) is composed of alternating layers of relatively higher refractive index material (201) and relatively lower refractive index material (202); the resonant cavity (300) is composed of a first active region (301), a second active region (302), a third active region (303) and a fourth active region (304), wherein the second active region (302) comprises a reverse bias tunnel junction (3021), a matching layer (3022), an oxidation limiting layer (3023), an upper limiting layer (3024), a quantum well (3025) and a lower limiting layer (3026), each active region has the same structure as the second active region (302), and each active region is cascaded by the reverse bias tunnel junction (3021); the lower Bragg reflector (400) is formed by alternately arranging relatively high refractive index materials (401) and relatively low refractive index materials (402), and the materials are selected to be the same as those of the upper Bragg reflector (200) but different in logarithm; the peak wavelength of radiation of each active region, the peak reflection wavelength of the upper Bragg reflector (200), the peak reflection wavelength of the lower Bragg reflector (400), and the resonant wavelength of the resonant cavity (300) are equal.

2. The resonant cavity-based multi-active region tunnel cascade red light Micro-RCLED of claim 1, wherein: the oxidation limiting layer (3023) is made of AlAs.

3. The resonant cavity-based multi-active region tunnel cascade red light Micro-RCLED of claim 1, wherein: the active region structure is a p-n junction, a p-i-n junction, a double heterojunction, a single quantum well structure, a multiple quantum well structure, a superlattice structure, a quantum dot light emitting structure, a multi-layer quantum dot structure, or a combination of the above.

4. The resonant cavity-based multi-active region tunnel cascade red light Micro-RCLED of claim 1, wherein: the reflectivity of the upper Bragg reflector (200) is 50% -80%, and the reflectivity of the lower Bragg reflector (400) is more than 90%.

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