CN106057997B - A kind of epitaxial wafer and preparation method of yellowish green light-emitting diode - Google Patents

Abstract

The invention discloses a kind of epitaxial wafers and preparation method of yellowish green light-emitting diode, belong to optoelectronic fabrication techniques field.The epitaxial wafer includes the substrate stacked gradually, buffer layer, Bragg reflecting layer, N-type limiting layer, active layer, p-type limiting layer, current extending and ohmic contact layer, epitaxial wafer further includes strain barrier layer, strain barrier layer is folded between active layer and p-type limiting layer, which includes：One substrate is provided；Epitaxial growth buffer, Bragg reflecting layer, N-type limiting layer, active layer, strain barrier layer, p-type limiting layer, current extending and ohmic contact layer successively on substrate.By the way that strain barrier layer is arranged between active layer and p-type limiting layer, since the energy band on strain barrier layer is higher than the energy band of p-type limiting layer, therefore it can stop electronics, prevent electronics overflow, which improves hole injection efficiencies, reduce non-radiative recombination, to improve the luminous efficiency of green-yellow light LED.

Description

Epitaxial wafer and preparation method of a yellow-green light-emitting diode

technical field

The invention relates to the technical field of optoelectronic manufacturing, in particular to an epitaxial wafer of a yellow-green light-emitting diode and a preparation method thereof.

Background technique

LED (Light Emitting Diode, Light Emitting Diode) has the advantages of small size, long life, low power consumption, etc., and is currently widely used in automobile signal lights, traffic signal lights, display screens and lighting equipment.

Existing LEDs mainly include an ohmic contact layer, a current spreading layer, a P-type confinement layer (also known as an upper confinement layer), an active layer, an N-type confinement layer (also known as a lower confinement layer), a Bragg reflective layer, a buffer layer, and a lining layer. end.

In the process of realizing the present invention, the inventor finds that there are at least the following problems in the prior art:

Due to the high mobility of electrons, electrons can quickly reach the active layer from the N-type confinement layer, while the mobility of holes is low, which makes more electrons pass through the active layer and enter the active layer. Recombination with holes outside the layer, resulting in increased non-radiative recombination.

Contents of the invention

In order to solve the problem of low luminous efficiency of yellow-green light-emitting diodes, embodiments of the present invention provide an epitaxial wafer and a preparation method of yellow-green light-emitting diodes. Described technical scheme is as follows:

On the one hand, an embodiment of the present invention provides an epitaxial wafer of a yellow-green light-emitting diode. The epitaxial wafer includes a substrate, a buffer layer, a Bragg reflection layer, an N-type confinement layer, an active layer, a P-type confinement layer, The current spreading layer and the ohmic contact layer are characterized in that the epitaxial sheet also includes a strain barrier layer, the strain barrier layer is sandwiched between the active layer and the P-type confinement layer, and the strain barrier layer It is non-doped AlInP, the P-type confinement layer is AlInP, wherein the Al composition of the strain barrier layer is higher than the Al composition of the P-type confinement layer, and the thickness of the strain barrier layer is 20-40nm .

Preferably, the epitaxial wafer further includes a hole accumulation layer interposed between the active layer and the strain barrier layer, the hole accumulation layer is (Al _z Ga _{1- z} ) _0.5 In _0.5 P, the active layer is (A _y Ga _1-y ) _0.5 In _0.5 P, wherein, 0<y<0.4, y<z≤0.8.

Further, the epitaxial wafer also includes a resonant tunneling layer sandwiched between the N-type confinement layer and the active layer, and the resonant tunneling layer is non-doped (Al _x Ga _1-x ) _0.5 In _0.5 P, where y≤x≤1.

Optionally, the thickness of the resonant tunneling layer is 20-50 nm.

Preferably, the hole accumulation layer has a thickness of 50-100 nm.

Optionally, the hole accumulation layer includes stacked multilayers (Al _z Ga _1-z ) _0.5 In _0.5 P, and the z values of the multilayers (Al _z Ga _1-z ) _0.5 In _0.5 P are different, And the z value increases layer by layer along the direction from the active layer to the P-type confinement layer.

On the other hand, the embodiment of the present invention also provides a preparation method of an epitaxial wafer, the preparation method comprising:

providing a substrate;

Epitaxial growth of buffer layer, Bragg reflection layer, N-type confinement layer, active layer, strain barrier layer, P-type confinement layer, current spreading layer and ohmic contact layer on the substrate in sequence, wherein the strain barrier layer is Non-doped AlInP, the P-type confinement layer is AlInP, and the Al composition of the strain barrier layer is higher than that of the P-type confinement layer, and the thickness of the strain barrier layer is 20-40nm.

Further, after growing the active layer and before growing the P-type confinement layer, the preparation method further includes:

growing a hole accumulation layer on the active layer, wherein the hole accumulation layer is (Al _z Ga _1-z ) _0.5 In _0.5 P, and the active layer is ( _Aly Ga _1-y ) _0.5 In _0.5 P, and 0<y<0.4, y<z≤0.8.

Preferably, after growing the N-type confinement layer and before growing the active layer, the preparation method further includes:

A resonant tunneling layer is grown on the N-type confinement layer, wherein the resonant tunneling layer is non-doped (Al _x Ga _1-x ) _0.5 In _0.5 P, and y≤x≤1.

The beneficial effect brought by the technical solution provided by the embodiments of the present invention is: by setting the strain barrier layer between the active layer and the P-type confinement layer, the Al composition of the strain barrier layer is higher than the Al composition of the P-type confinement layer, The energy band of the strain barrier layer is higher than the energy band of the P-type confinement layer, so it can block electrons and prevent electron overflow, thus improving the hole injection efficiency and reducing non-radiative recombination, thereby improving the luminous efficiency of yellow-green LEDs .

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Fig. 1 is a structural diagram of an epitaxial wafer of a yellow-green light-emitting diode provided by an embodiment of the present invention;

2 is a schematic structural view of a Bragg reflective layer of a yellow-green light-emitting diode provided by an embodiment of the present invention;

3 is a schematic structural view of an active layer of a yellow-green light-emitting diode provided by an embodiment of the present invention;

Fig. 4 is a structural diagram of another epitaxial wafer of a yellow-green light-emitting diode provided by an embodiment of the present invention;

5 is a schematic diagram of the energy band structure of an epitaxial wafer of a yellow-green light-emitting diode provided by an embodiment of the present invention;

Fig. 6 is a flowchart of a method for preparing an epitaxial wafer of a yellow-green light-emitting diode according to an embodiment of the present invention.

Detailed ways

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

An embodiment of the present invention provides an epitaxial wafer of a yellow-green light-emitting diode. FIG. 1 is a structural diagram of an epitaxial wafer of a yellow-green light-emitting diode provided by an embodiment of the present invention. As shown in FIG. 1 , the epitaxial wafer includes sequentially stacked substrates. Bottom 11, buffer layer 12, Bragg reflection layer 13, N-type confinement layer 14, active layer 15, P-type confinement layer 17, current spreading layer 18 and ohmic contact layer 19, the epitaxial wafer also includes a strain barrier layer 16, strain The barrier layer 16 is sandwiched between the active layer 15 and the P-type confinement layer 17, the strain barrier layer 16 is non-doped AlInP, and the P-type confinement layer 17 is AlInP, wherein the Al composition of the strain barrier layer 16 is higher than that of P The Al composition of the type confinement layer 17.

In the embodiment of the present invention, a strain barrier layer is arranged between the active layer and the P-type confinement layer, and the Al composition of the strain barrier layer is higher than that of the P-type confinement layer, so that the energy band of the strain barrier layer is higher than that of the P-type confinement layer. The energy band of the limiting layer can block electrons and prevent electron overflow, thus improving hole injection efficiency and reducing non-radiative recombination, thereby improving the luminous efficiency of yellow-green LEDs.

During implementation, the substrate 11 can be a 2 or 4 inch 100-plane biased <111>A+5° GaAs substrate.

Optionally, the buffer layer 12 may be GaAs, the doping concentration of the buffer layer 12 may be 6*10 ^-17 ~ 2*10 ^-18 cm ^-3 , and the doping impurity may be silicon element.

Preferably, the doping concentration of the buffer layer 12 is 10 ⁻¹⁸ cm ⁻³ . If the doping concentration of the buffer layer 12 is too small, the resistance of the buffer layer 12 will be too high, resulting in a high voltage; if the doping concentration is too high, the lattice quality will be affected and the brightness of the LED will be reduced.

Fig. 2 is a schematic structural diagram of a Bragg reflective layer of a yellow-green light-emitting diode provided by an embodiment of the present invention. Preferably, as shown in Fig. 2, the Bragg reflective layer 13 includes alternately stacked AlAs layers 13a and Al _β Ga _1-β As Layer 13b, wherein, β=0.46-0.5, by setting the Bragg reflective layer 14 with a multi-layer structure, can enhance the reflection of light and improve the brightness of the LED.

Specifically, the sum of the numbers of the AlAs layer 13a and the _{AlβGa1 -} βAs layer 13b may be 30-60.

In addition, the thickness of each AlAs layer 13a and each _{AlβGa1 -} βAs layer 13b can be adjusted according to the wavelength of light to be reflected, so that the Bragg reflection layer 13 can reflect light of a suitable wavelength.

It should be noted that, for ease of illustration, only part of the structure of the Bragg reflection layer 13 is shown in FIG. 2 .

Further, the N-type confinement layer 14 may be AlInP, and its thickness may be 200-500 nm.

Fig. 3 is a schematic structural diagram of an active layer of a yellow-green light-emitting diode provided by an embodiment of the present invention. When implemented, the active layer 15 may include alternately stacked multi-layer quantum well layers 15b and multi-layer quantum barrier layers 15a, wherein, The thickness of each quantum well layer 15b may be 3-5nm, and the thickness of each quantum barrier layer 15a may be 5-7nm.

It should be noted that both the quantum well layer 15b and the quantum barrier layer 15a are AlGaInP, but the compositions of Al and In in the quantum well layer 15b and the quantum barrier layer 15a are different.

In addition, the strain barrier layer 16 can be non-doped Al _α In _1-α P, wherein, 0.5<α<0.75, the composition of Al in the strain barrier layer 16 is higher than that of the P-type confinement layer 17 (the composition of Al in the P-type confinement layer Al _0.5 In _0.5 P) is high, so that the band gap of the strain barrier layer 16 is larger than that of the P-type confinement layer 17, which can prevent electron overflow and improve the efficiency of hole injection.

Preferably, the thickness of the strain barrier layer 16 is 20-40 nm. If the thickness of the strain barrier layer 16 is too thin, it cannot prevent electron overflow and improve the efficiency of hole injection; if the thickness of the strain barrier layer 16 is too thick, then because the strain barrier layer 16 is non-doped, it will As a result, the resistance of the strain barrier layer 16 is too large, and the voltage is relatively high.

Preferably, the P-type confinement layer 17 may be AlInP, and its thickness may be 400-600 nm.

Preferably, the doping concentration of the current spreading layer 18 may be 2*10 ^-18 to 8*10 ^-18 cm ^-3 , and the doping impurity may be magnesium element. If the doping concentration is too small, the voltage will be high due to the high resistance; if the doping concentration is too high, the lattice quality will be affected, thereby affecting the luminous brightness.

Further, the thickness of the current spreading layer 18 may be 8-10 μm. If the thickness of the current spreading layer 18 is too small, it will affect the current spreading; if the thickness of the current spreading layer 18 is too large, it will cause the warpage of the epitaxial wafer to increase, and even cause the epitaxial wafer to fly out during the growth process and other adverse consequences. .

Optionally, the doping concentration of the ohmic contact layer 19 may be 3*10 ^-19 ~10 ^-20 cm ^-3 , and the doping impurity may be carbon element. If the doping concentration is too small, the voltage may be high due to excessive resistance; if the doping concentration is too high, it will affect the quality of the crystal lattice and reduce the brightness of the LED.

Further, the thickness of the ohmic contact layer 19 may be 30-100 nm. If the thickness of the ohmic contact layer 19 is too small, the difference in the square resistance of different regions of the ohmic contact layer 19 will be increased, resulting in uneven current; if the thickness of the ohmic contact layer 19 is too large, the brightness of the LED will be reduced.

Fig. 4 is a structural diagram of another epitaxial wafer of a yellow-green light-emitting diode provided by an embodiment of the present invention. As shown in Fig. 4, the epitaxial wafer also includes a hole accumulation layer 20, and the hole accumulation layer 20 is sandwiched between the active layer 15 and the strain barrier layer 16, the hole accumulation layer is (Al _z Ga _1-z ) _0.5 In _0.5 P, the active layer is ( _Aly Ga _1-y ) _0.5 In _0.5 P, where, 0<y< 0.4, y<z≤0.8, the hole accumulation layer 20 can form a potential well between the active layer 15 and the P-type confinement layer 17, which is conducive to the accumulation of holes. Under the action of the applied voltage, the hole accumulation layer The holes accumulated in 20 will be injected into the active layer 15, thereby further improving the hole injection efficiency, which is conducive to the recombination of electrons and holes in the active layer 15, thereby further improving the luminous efficiency of the yellow-green LED.

Preferably, the hole accumulation layer 20 may include multiple layers of (Al _z Ga _1-z ) _0.5 In _0.5 P, and the multi-layer (Al _z Ga _1-z ) _0.5 In _0.5 P layered arrangement, through the hole accumulation of the multi-layer structure layer 20 to enhance the accumulation of holes and further improve the hole injection efficiency.

In addition, the thickness of the hole accumulation layer 20 may be 50 to 100 nm. If the hole accumulation layer 20 is too thin, it cannot accumulate holes; if the hole accumulation layer 20 is too thick, it will affect the hole injection into the active layer 15 .

The epitaxial wafer may also include a resonant tunneling layer 21, which is sandwiched between the N-type confinement layer 14 and the active layer 15, and the resonant tunneling layer is non-doped (Al _x Ga _1-x ) _0.5 In _0.5 P, where, y≤x≤1, since the Al composition in the resonant tunneling layer 21 is greater than or equal to the Al composition in the active layer 15, the bottom energy level of the resonant tunneling layer 21 is greater than or equal to The lowest energy level of the quantum well layer 15b, so that electrons can tunnel into the active layer 15, while blocking holes, avoiding the recombination of holes and electrons in the N-type confinement layer 14, and the resonant tunneling layer 21 can be reached by the electrons The active layer 15 captures and confines the electrons before, weakens the energy of the electrons, reduces the mobility of the electrons, thereby reducing the overflow of electrons, increasing the number of electrons injected into the active layer 15, and increasing the number of electrons and holes. The possibility of recombination in the active layer 15 further improves the luminous efficiency of the yellow-green LED.

Preferably, x=y, when x=y, the energy level of the electrons after passing through the resonant tunneling layer 21 can be reduced to be consistent with the quantum well layer 15b, so that the electrons can enter the active layer 15 more uniformly .

In addition, the thickness of the resonant tunneling layer 21 is 20-50 nm. If the thickness of the resonant tunneling layer 21 is too thin, it cannot play the role of accumulating electrons; if the thickness of the resonant tunneling layer 21 is too thick, it will affect the injection of electrons into the active layer 15 .

5 is a schematic diagram of the energy band structure of an epitaxial wafer of a yellow-green light-emitting diode provided by an embodiment of the present invention. As shown in FIG. 5 , the energy band of the hole accumulation layer 20 is higher than that of the quantum well layer 15b in the active layer 15. The energy band is lower than the energy band of the P-type confinement layer 17 at the same time, so that a potential well is formed between the active layer 15 and the P-type confinement layer 17 to realize the accumulation of holes.

When it is realized, the wavelength of the light emitted by the LED can be changed by adjusting the composition of the aluminum element in the active layer (Aly Ga _{1-y ) 0.5} In _0.5 P, that is, the value of y, so that the light emitted by the LED can be adjusted. light color.

The embodiment of the present invention also provides a method for preparing an epitaxial wafer. FIG. 6 is a flow chart of a method for preparing an epitaxial wafer of a yellow-green light-emitting diode provided in an embodiment of the present invention. As shown in FIG. 6 , the preparation method includes:

S11: Provide a substrate.

In this embodiment, a GaAs substrate is selected.

S12: Epitaxially grow a buffer layer, a Bragg reflection layer, an N-type confinement layer, an active layer, a strain barrier layer, a P-type confinement layer, a current spreading layer, and an ohmic contact layer on the substrate in sequence, wherein the strain barrier layer is a non-doped Doped AlInP, the P-type confinement layer is AlInP, and the Al composition of the strain barrier layer is higher than that of the P-type confinement layer.

In the embodiment of the present invention, by providing a strain barrier layer between the active layer and the P-type confinement layer, since the energy band of the strain barrier layer is higher than the energy band of the P-type confinement layer, it can block electrons and prevent electron overflow, thus The hole injection efficiency is improved, the non-radiative recombination is reduced, and the luminous efficiency of the yellow-green LED is improved.

Specifically, the substrate can be a 2 or 4 inch 100-plane biased "111" A+5° GaAs substrate.

Optionally, the buffer layer may be GaAs, the doping concentration of the buffer layer may be 6*10 ^-17 ~ 2*10 ^-18 cm ^-3 , and the doping impurity may be silicon element.

Preferably, the doping concentration of the buffer layer is 10 ^-18 cm ^-3 . If the doping concentration of the buffer layer is too small, the resistance of the buffer layer will be too high, resulting in a relatively high voltage. If the doping concentration is too high, it will affect Lattice quality, reduces LED brightness.

In addition, when growing the Bragg reflection layer, the AlAs layer and the Al _β Ga _1-β As layer are alternately grown, wherein, β=0.46～0.5, the sum of the layers of the AlAs layer and the Al _β Ga _1-β As layer It can be 30-60.

It should be noted that when growing the Bragg reflective layer, it is necessary to control the thickness of each AlAs layer and the thickness of each _{AlβGa1 -} βAs layer according to the wavelength of the light to be reflected, so that the Bragg reflective layer can reflect light of the appropriate wavelength.

Preferably, after growing the active layer and before growing the P-type confinement layer, the preparation method may further include:

A hole accumulation layer is grown on the active layer.

Specifically, the hole accumulation layer can be (Al _z Ga _1-z ) _0.5 In _0.5 P, the active layer can be (A _y Ga _1-y ) _0.5 In _0.5 P, the active layer can be (A _y Ga _1-y ) _0.5 In _0.5 P, where, 0<y<0.4, y<z≤0.8.

Further, after growing the N-type confinement layer and before growing the active layer, the preparation method further includes:

A resonant tunneling layer is grown on the N-type confinement layer.

Specifically, the resonant tunneling layer is non-doped (Al _x Ga _1-x ) _0.5 In _0.5 P, where y≤x≤1.

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 kind of epitaxial wafer of yellowish green light-emitting diode, the epitaxial wafer includes the substrate, buffer layer, Prague stacked gradually Reflecting layer, N-type limiting layer, active layer, p-type limiting layer, current extending and ohmic contact layer, which is characterized in that the extension Piece further includes strain barrier layer, and the strain barrier layer is folded between the active layer and the p-type limiting layer, the strain Barrier layer is undoped AlInP layers, and the p-type limiting layer is AlInP layers, wherein the Al constituent contents on the strain barrier layer Higher than the Al constituent contents of the p-type limiting layer, the thickness on the strain barrier layer is 20~40nm.

2. epitaxial wafer according to claim 1, which is characterized in that the epitaxial wafer further includes hole accumulation layer, the sky Cave accumulation layer is folded between the active layer and the strain barrier layer, and the hole accumulation layer is (Al_zGa_1-z)_0.5In_0.5P Layer, the active layer are (Al_yGa_1-y)_0.5In_0.5P layers, wherein 0<y<0.4, y<z≤0.8.

3. epitaxial wafer according to claim 2, which is characterized in that the epitaxial wafer further includes resonant tunneling layer, described humorous The tunnel layer that shakes is folded between the N-type limiting layer and the active layer, and the resonant tunneling layer is undoped (Al_xGa_1-x)_0.5In_0.5P layers, wherein y≤x≤1.

4. epitaxial wafer according to claim 3, which is characterized in that the thickness of the resonant tunneling layer is 20~50nm.

5. epitaxial wafer according to claim 2, which is characterized in that the thickness of the hole accumulation layer is 50~100nm.

6. epitaxial wafer according to claim 2, which is characterized in that the hole accumulation layer includes the multilayer of stacking (Al_zGa_1-z)_0.5In_0.5P, the multilayer (Al_zGa_1-z)_0.5In_0.5The z values of P differ, and z values are directed toward institute along from the active layer The direction for stating p-type limiting layer successively increases.

7. a kind of preparation method of epitaxial wafer, which is characterized in that the preparation method includes：

One substrate is provided；

Over the substrate successively epitaxial growth buffer, Bragg reflecting layer, N-type limiting layer, active layer, strain barrier layer, P Type limiting layer, current extending and ohmic contact layer, wherein the strain barrier layer is undoped AlInP, the p-type limitation Layer is AlInP, and the Al components on the strain barrier layer are higher than the Al components of the p-type limiting layer, the strain barrier layer Thickness is 20~40nm.

8. preparation method according to claim 7, which is characterized in that after having grown the active layer, grow the P Before type limiting layer, the preparation method further includes：

Hole accumulation layer is grown on the active layer, wherein the hole accumulation layer is (Al_zGa_1-z)_0.5In_0.5P, it is described to have Active layer is (Al_yGa_1-y)_0.5In_0.5P, and 0<y<0.4, y<z≤0.8.

9. preparation method according to claim 8, which is characterized in that after having grown the N-type limiting layer, grow institute Before stating active layer, the preparation method further includes：

Resonant tunneling layer is grown on the N-type limiting layer, wherein the resonant tunneling layer is undoped (Al_xGa_1-x)_0.5In_0.5P, and y≤x≤1.