monolithically integrated white light leds on (11–22) semi-polar gan templates

by:IPON LED     2020-05-07
Carrier Transportation problem in (11–22)semi-
White light emitting diode based on polar GaN (
Composed of yellow and blue emissions)
Through detailed simulation studies, it is shown that the growth sequence of yellow and blue InGaN quantum wells plays a vital role in achieving white emission.
The order of growth requires first a yellow InGaN quantum well, then a blue InGaN quantum well after n-growth. type GaN.
The root cause is due to the poor distribution of hole concentrations throughout the InGaN quantum well area.
In order to effectively capture the holes in the yellow InGaN quantum well and the blue InGaN quantum well, a thin GaN gasket was introduced before the blue InGaN quantum well.
A detailed simulation of the band diagram and hole concentration distribution of the yellow and blue quantum wells shows that the thin GaN gasket can effectively balance the hole concentration between the yellow and blue InGaN quantum wells, finally determine their relative strength between the yellow and blue emission.
Based on this simulation, we show a single multiple
Color LED grown on our high quality semi-finished productspolar (11–22)GaN templates.
General Lighting is one of the main sources of global electricity demand.
Development of Energy is critical due to global warming and the upcoming energy crisissaving solid-National Lighting (SSL). White light-
LEDs (LEDs)
, Mainly based on III-
Nitrogen semiconductor LEDs, due to the advantages of low power consumption and long life, are expected to eventually replace incandescent lamps and fluorescent tubes for many outdoor and indoor lighting applications.
Energy-efficient demand makes III-
Nitrogen-based optoelectronic technology is one of the fastest growing semiconductor fields in the past two decades.
So far, the \"blue led yellow fluorescent body\" method has maintained a strong lead in the manufacture of white led.
The performance of this white LEDs is almost near the limit, but still far from meeting the requirements described in the US development SSL roadmap.
In addition, phosphorus-
There are many disadvantages to the conversion method, E. G.
Loss of conversion, optical loss caused by backward scattering, heat-related effects, and degradation of yellow fluorescent bodies due to their long-lasting lightterm exposure.
In order to cope with these huge challenges, a variety of methods have been proposed, such as hybrid III-for single chip integration-
Nitrogen/colloidal quantum dots; hybrid III-
Nitrogen/organic binding polymer.
Although these white LEDs are still based on
They show a unique kind of non-
Radiation energy transfer effect, which cannot be achieved by the above \"blue led LEDs.
One of the most direct ways to make a single-chip White Light led is to use an InGaN quantum well with different emission wavelengths, in which these emissions of different wavelengths can be obtained by controlling any InGaN quantum well (QW)
The thickness or content of boron nitrate.
In this method, blue/green/red (RGB)
Emissions are required or blue/yellow emissions are required.
In principle, this approach is not only cost
Effective, but also matched with current growth and manufacturing techniques for III-
Nitrogen photoelectrons.
However, two major challenges need to be addressed before the potential of this approach can be realized.
The first challenge is to get high performance long wavelengths such as green and yellow emission. Current III-
Nitrogen LEDs are grown on the substrate.
Extreme direction will produce strain
Induced piezoelectric field due to lattice
The mismatch between InGaN and GaN, this iscalled quantum-
Limiting Effect (QCSE).
Therefore, the internal quantum efficiency is reduced, and when the InGaN quantum wells move towards a longer wavelength, such as a green or yellow spectral region, the efficiency is significantly reduced (
If a higher in content is required, it will result in an enhancement of the QCSE)
To form a well-known “Green-
\"Yellow Gap\" phenomenon.
In addition, GaN also leads to a basic restriction on adding in to GaN.
The second problem is due to the complex carrier transmission in indium QWs, the in composition is different due to the hole mobility and hole concentration much lower than the electron, which may lead to serious non-
All InGaN QWs have a uniform carrier distribution.
Due to the piezoelectric effect, the InGaN structure grown on GaN further enhances this complexity
The electric field causes polarization.
Due to the enhancement of piezoelectric material, this problem becomes more complicated with the increase of in content
The electric field causes polarization.
So far, there has been no systematic research on this issue. Growth of III-
Nitrides and a half.
Direction, especially (11–22)
Orientation, will be a promising solution to achieve long-wavelength emission, because this orientation is expected to not only significantly reduce the piezoelectric polarization field, but also improve the efficiency of in incorporation in InGaN.
In addition, the demand for Li-is increasing.
The Fi application needs a superfast response.
Due to the QCSE, the current blue LEDs on the substrate have a longer carrier composite lifetime, the blue emission is usually in the range of a few to 10 nanoseconds, and the green emission is usually around 100 nanoseconds.
Usually at the microsecond level, the response time of the fluorescent body is even longer.
In contrast, halfpolar (in particular (11–22))
For blue emission, the InGaN quantum well exhibits a shorter carrier composite lifetime, usually several hundred-second.
So, halfpolar phosphor-
Free led is ideal for Li-Fi application.
Recently, Sizov.
Serious non-observed
Uniform carrier distribution between multiple quantum wells in InGaN (MQWs)
The threshold current of the laser diode grown on the substrate, when the number of InGaN MQWs exceeds 2, causes an increase in the threshold current, while they are in half
Polar substrate.
This fact also shows that half
Extreme sexual orientation is conducive to the distribution of the injected current in the vertical direction on the InGaN QWs.
The above facts prove that ,(11–22)semi-
Polar GaN may be an ideal candidate for multiple-
Simultaneous Color emission of general lighting and Li-Fi application.
However, one of the biggest challenges is the lack of half
Polar GaN with high crystal quality in industry-
Compatible substrates such as sapphire.
Our group has been half done recently. polar (11–22)
The InGaN LEDs on our overgrown semi-LEDs
Polar GaN templates with significantly improved crystal quality, resulting in a half
High-performance polar InGaN LEDs in a wide spectral area up to Amber.
In this article, by performing a detailed simulation, in (11–22)semi-
Polar White led with two different InGaN quantum wells (Blue and yellow)
Already studied.
The study was further compared with the peers, showing the adoption of the semi-polar (11–22)
GaN for overall White led growth.
Based on the simulation results, we designedpolar (11–22)
LEDs with multiple color emission for verification purposes.
Two different types of LED structures are designed, marked as sample A and sample B, and then in our high quality half
GaN with excessive polar growth, in both cases, LEDs are composed of InGaN single quantum well (SQW)
For the two pairs of InGaN MQWs for the Blue launch and the yellow launch.
However, the growth order of blue SQW and yellow MQWs is different.
For sample A, blue SQW is grown first, then yellow mqw is grown, and for sample B, yellow mqw is grown first, then blue SQW is grown.
In both cases, growth conditions remain unchanged.
The diagram illustrates the structure of sample A and sample B.
Two LEDs are composed of 1 m n-
Type GaN layer, then an active region that includes blue InGaN SQW with low in content and 2 pairs of yellow InGaN MQWs with high in content, and finally a 15 nmtype GaN layer.
Detailed parameters are also provided, including in components and the thickness of quantum wells and barriers.
For sample B, an additional GaN gasket with a thickness of 2 nm was introduced before the growth of the blue SQW, which we will discuss later.
In this study, the structure of sample B is particularly interesting and will be explained later. Initially, the band
Figure simulation has been in doublecolour LED (
Made of blue and yellow)
Growing on a with the same structure (11–22)
To investigate the effect of crystal orientation on carrier migration, GaN surface and GaN surface.
In both cases, the simulated LED structure consists of two pairs of InGaN MQWs for yellow emission and a blue SQW.
The thickness of quantum wells and barriers is 4 nm and 9 nm, respectively.
Although the incorporation of in is naturally limited in the LED, both LEDs are designed to have similar emission wavelengths.
The donor and recipient concentrations used for the simulation were 5 u2009 × 10 cm and 5 u2009 × 10 cm, respectively, which is fairly standard.
A diagram simulation was performed using SiLENSe 5. 11 package.
The figure shows the simulation results in two cases.
Simulation and half-carrier distribution of wave band graphspolar (11–22)
Led is performed as a function of the injected current density up to 80 a/cm (
The Standard LED with a size of 30 × m is equivalent to 200ma, while the injection current density for practical application cannot exceed 80 a/cm. ).
The diagram shows their band diagram, which is a/cm
The carrier offering them is distributed at 80 a/cm.
Since the migration and effective mass ratio of electrons is much higher than that of the holes, as shown in the figure, electrons can overcome the potential barrier and can be distributed throughout the InGaN QW region without any significant attention.
Of course, the electron concentration of n-
The GaN type is usually one or even two orders of magnitude higher than the p-typetype GaN.
Previous studies have shown that
The polar led exhibits the opposite polarity compared to the led.
Therefore, the polarized induced electric field in InGaN MQWs results in an additional energy barrier for the hole.
As expected, crystal orientation plays an important role in hole transport and distribution of hole concentration.
The figure shows the enhanced barrier potential of the half holepolar (11–22)
LED compared to LED.
In detail, due to the reverse polarization induction electric field, the potential barrier of the holes between 1-growing InGaN QW and 3-growing InGaN QW is significantly enhanced compared to led, effectively slow down the holes to inject 1 growing QW, thus reducing the holes captured in 1 InGaN QW.
Therefore, the pore concentration in semi-growing qw1
As shown in the figure, the polar LED is far less than its corresponding LED.
The figure also shows that in both cases, the hole concentration in the QW of the 3 growth is comparable, but much lower than the hole concentration in the QW of the 2 growth.
Therefore, the emission of the three growing QW is expected to be very weak.
In this case, if in c-plane or (11–22)semi-
In the polar plane, yellow emission is likely to be observed only.
This situation is even worse for LED due to strong QCSE.
It is worth emphasizing that it is important for blue light emission to grow the QW of 3 kinds of growth, in which case the in content is usually very low.
If 3 QW is emitted in yellow (i. e. , Sample A)
The situation got worse.
The basic reason is that due to the very weak limitation of holes in 3 growing QW, the hole concentration in 3 growing QW is very low, which has been confirmed by fig. .
This issue will be discussed further later.
In order to use half
We propose a new structure that not only improves the polar LEDs, but also enhances the limitation of holes in 3 growing InGaN quantum wells.
A thin GaN gasket was introduced, that is, a thin GaN barrier was grown before the blue SQW.
The figure shows the calculated distribution of hole concentrations in QWs grown in 2 and 3.
With the increase of GaN gasket thickness, the carrier concentration in 3 growing QW increased significantly, while the hole concentration in 2 growing QW decreased rapidly.
Taking into account the overall hole concentration in QWs grown in 2 and 3, the optimized thickness of the GaN gasket is 2 nm.
The picture shows simulated electricityluminescence (EL)
The spectrum is a function of the thickness of the GaN spacer layer.
In terms of the relative EL intensity of the emission of 2 growing QW (yellow)
And 3 growing QW (blue)
, The optimized LED is LED with 2 nm GaN gasket.
Finally, we can conclude that the optimized structure of the two-color LED can be either sample a or sample B.
For sample B, as described above, a 2 nm GaN gasket was used to enhance the limitation of the 3 growing InGaN QW.
Band diagram and hole distribution were performed on sample A and sample B, which is a function of injection current density up to 80 A/cm.
The figure shows the band diagram simulated at 80 a/cm, while the figure
The concentration distribution of simulated holes corresponding to them.
If blue SQW is grown first, then yellow InGaN QWs (i. e. , Sample A)
As shown in the figure.
The three growing QW showed a poor energy of 0.
621ev ev in yellow QWs due to the high in composition, between the quantum well and the hole barrier.
Therefore, it is difficult for the hole to escape from 3 growing InGaN QW, so it is still trapped in 3 growing InGaN QW (i. e.
Yellow launch).
Therefore, as shown in the figure, the hole concentration in the QW grown in 2 species is extremely low.
In contrast, for sample B, the yellow quantum well grows first, followed by the blue SQW, with a 2 nm GaN gasket as discussed above, the energy base of the 3 growing QW decreased significantly by 0.
As compared to sample A, the in component is lower in 3 growing QW (i. e. , for blue).
Due to the reduction of the energy barrier of the hole, the hole has the possibility to escape from 3 growing QW to 2 growing QW, so, as shown in the figure, the hole concentration in 2 growing QW increases significantly.
Therefore, it is possible to achieve two-color emission in this case.
In order to verify the above ideas, we are growing over halfpolar (11–22)
GaN with high crystal quality, regularly arranged (11–22)GaN micro-
Rods with a diameter of 4 μm are used as templates for overgrowth, by using standard exposure shielding patterned techniques, which are then manufactured through a dry etching process.
Half of the weedspolar (11–22)
GaN is around 5 μm.
References provide further detailed procedures for obtaining this high quality semi-finished productpolar (11–22)
GaN with detailed material representation.
A standard printing technology for flat edition
The etching process has been used to make LED chips with a standard size of 30 x m.
7nm/7 nm Ni/Au alloy was deposited by electron beam deposition method, and then a fast thermal annealing was used as a transparent p-type contact. N-
A type of contact is formed on n-
GaN type was prepared by depositing Ti/Al/Ti/Au alloys.
Two p-of the pad electrode deposited by Ti/Gold-type and n-type contacts.
All measurements are made on bare metal.
Chip equipment at room temperature of continuous waves (CW)
Mode, using LCS-100-
UV representation system equipped with ccd aprar spectrometer.
The figure shows the simulated EL spectra of sample A and sample B under A/cm, while the figure
Experimental EL is displayed at the same injection current density, where sample A shows A single yellow emission at 545 nm, while sample B shows A double emission at 450 and 545 nm.
Illustration of the picture.
EL images of sample A and sample B are also included, taken at 80 A/cm.
Sample A shows that the factor is ~ The overall higher comprehensive strength of 2.
4 compared with sample B.
The simulated and experimental EL spectrum fits well and supports our discussion.
This means that yellow QWs must grow first and then blue SQW in order to achieve double emission.
Another important point is that a thin GaN gasket needs to be grown before the blue SQW.
The results also show that the hole transmission problem is crucial for the design of dual-emitting LED.
In short, the detailed investigation of the simulated carrier transport problem (11–22)semi-
A multi-color polar led consisting of yellow InGaN QWs and blue InGaN QW.
The simulation results show that the growth sequence of these yellow and blue InGaN QWs plays a vital role in achieving white emission.
In order to achieve white emission, a yellow InGaN quantum well must be grown and then a blue InGaN quantum well must be grown.
Otherwise, only a single color is emitted.
In order to capture the holes in the yellow InGaN quantum well and the blue InGaN quantum well, a thin GaN gasket is required before the blue InGaN SQW, in order to effectively balance the carrier concentration between the yellow InGaN quantum well and the blue InGaN quantum well, this ultimately determines their relative strength between the yellow and blue emission.
Based on this simulation, we show a single multiple
Color LED grown on our high quality semi-finished productspolar (11–22)GaN templates.
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