Abstract: In this work, we present the growth of monolithic nanostructures with multiple segments possessing dissimilar chemical compositions. This is realized by a novel growth method using chemical vapor deposition system and we have demonstrated tuning and control of correlated color temperature of trichromatic white light emission from a single ZnCdSSe nanosheet. Introduction: Development of LEDs for various applications such as lighting and displays has been a very attractive research area for over 50 years and has greatly intensified over the last two decades due to their low power consumption, long lifetime, high efficiency and small footprint. Especially the development of blue LEDs has been a big breakthrough as 2014 Nobel Prize in Physics was given to the inventers of blue LEDs for leading highly efficient and less power consumed white LEDs. In our daily life, we see RGB and white LEDs almost everywhere and makes our life very colorful. They are expected to completely replace incandescent and fluorescent lamps in the near future. Although there are two ways of producing white LEDs: either all-semiconductor LED based approach or semiconductor LED combined with phosphorus coating, more than 90% of the white LEDs in commercial market uses the latter approach. However, due to the degradation of the phosphors over time and the energy efficiency losses caused by the Stokes shift where part of the high energy photons (blue) is consumed by the phosphorus layer, makes this choice non-ideal. Aim: Our aim in this work is to build CCT tunable light emitters based on all semiconductor materials in a single body. Constrains: Producing white LEDs based on all semiconductors is very difficult since it requires to grow materials with dissimilar chemical compositions on a single substrate. Due to the lattice mismatch of different compositional materials it is unlikely to be grown on a single chip. Although there are some approaches such as die transfer, they increases the cost of LEDs tremendously and make it impractical. Method: In this work, nanotechnology plays a crucial role and we have achieved growing single nanostructures with multiple segments possessing dissimilar chemical compositions. This is realized by a unique growth method using chemical vapor deposition and we have demonstrated tuning and control of correlated color temperature of trichromatic white light emission from a single ZnCdSSe nanosheet. The nanosheets have thicknesses in the range of 60-350 nm and lateral dimensions of tens of microns. Our growth procedure utilizes temperature-dependent composition deposition and by changing the position of substrate during a single growth run we can grow multiple segments with various chemical compositions of ZnCdSSe quaternary alloys. The width of each segment in nanosheet structures can be controlled by the growth time at a specific position. Such controls determine the chemical composition (therefor emission color) and relative intensity of each segment, and thus resulting in the tuning of the color temperature of the white light, or in the realization of any visible colors. Results: By using various growth parameters we demonstrated trichromatic white light emission with the CCT ranging from 2700K to 14400K. It was also shown that by adjusting the growth parameters and growth paths we can grow any number of segments in a monolithic structure and color can be tuned by segment width or pumping power density. Conclusions: The results pave the way for various applications in solid state lighting and displays. By tuning the relative emission intensity of different segments either by optical pumping or electrical injection we can change the warmness of the white light emission. People can choice their favorite type of white light in a wide range of CCT by utilizing this technology and therefore we call it personalized white light. It is also important to note that our approach meets the Solid state lighting requirements for CCT tunable, and phosphor-free white light emission from a single structure grown using a single ZnCdSSe material system. These results show great potential for various types of device applications in optoelectronics and photonics.
Anahtar Kelimeler: Nanomaterials, LEDs, Light Emitters, Nanotechnology, Semiconductors
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