Organic and Inorganic LEDs

Disparity between demand and supply of power is emerging as a major challenge for fast developing world. Intense activity is going on to find non-conventional and/or more efficient sources of power due to limited resources of conventional power. Solar cells are getting more and more popular for generation of alternative power. Further, the need to reduce energy consumption associated with the low efficiency of conventional lighting systems has prompted considerable research efforts towards the development of white light emitting diodes as high performance alternative devices. Solid-state lighting (SSL) is the direct conversion of electricity to visible white light using semiconductor materials and has the potential to be just such an energy-efficient lighting technology. Organic Light Emitting Diodes (OLEDs) and Light Emitting Diodes (LED's) have emerged as more efficient and less

Recently, III (Ga, In, Al) – Nitrides have attracted immense interest due to their potential technological applications like LED's and Solar Cells. III-Nitride family offers large variation of band gap (0.6 to 6.2 eV) with very small change in the lattice constant. Band gap of ternary alloys of III-Nitrides (InGaN, InAlN) can be tuned over whole solar spectrum by controlling their compositions. Quality of Nitride films and capability of creating well controlled hetrostructures are most crucial factor for the applications of Nitrides. Molecular Beam Epitaxy (MBE) is playing a major role in the growth of high quality Nitride films.

Work in the direction of OLEDs has started 10 years back at CSIR-NPL. During this period CSIR-NPL has setup infrastructure facilities to synthesize OLED materials as well as setup facility to fabricate OLEDs and gained expertise in this area. CSIR-NPL has developed White Organic Light Emitting Diode (WOLED) panels (panel size is 1”x1”) for general lighting. The panels have a luminescence of more than 500 cd/m 2 and have CIE coordinates very near to (0.33, 0.33).

OLEDs developed at CSIR-NPL

 

Contact:
Dr. Suresh Chand
Chief Scientist
Head
Physics of Energy Harvesting Division
Organic & Inorganic LED's Group
CSIR-National Physical Laboratory
Dr. K. S. Krishnan Road, New Delhi 110 012, INDIA
Phone: +91 4560 9202/ 9353
Fax: +91-11-4560-9310
E-mail: schand@mail.nplindia.org

 

Research Activity:

  • Fabrication of OLEDs for general lighting and Displays
  • Development of OTFTs and OLETs
  • Synthesis and characterization of electroluminescence materials for device applications.
  • Study of optical and electrical properties of organic semiconductor
  • Growth of epitaxial layers of Ga, In, Al – Nitrides, their ternary alloys, and Nitride heterostructures using RF-plasma assisted Molecular Beam Epitaxy (MBE) and Laser-MBE. Grown Nitrides will be used for LED and Solar Cell applications.
  • Surface characterization and electronic and atomic structure study of III-Nitrides using X-ray Photoelectron Spectroscopy (XPS), Ultra-violet Photoelectron Spectroscopy (UPS), Scanning Auger Electron Spectroscopy, Low Energy Electron Diffraction (LEED), Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM) and Scanning Tunneling Spectroscopy (STS)
  • Study of defect states and carrier dynamics in Nitrides using Femto second Pump-probe Spectroscopy.
  • Study of spectral response of III-Nitrides using Photo conductivity measurements.

Facilities:

Thermal Evaporation Coating Units Sputtering unit Spin coating Luminance Meter OLED Characterization setup Photoluminescence Spectroscopy(Steady State) Low Temperature PL setup Time resolved PL setup Current source meter( Keithley 2401,2612) Liquid-He cryostat(up to 4K) Semiconductor characterization system (Kiethley-4200scs) Spectroscopic ellipsometer-Woolam M2000 Impedance/Gain –phase Analyzer (SI-1260) UV-Vis Spectrometer ( absorption, transmittance and reflectance) Optical spectrometer for EL Ocean optics-HR 2000, HR 4000 Probe Station Millipore water purification System Atomic Force Microscopy ( AFM, STM, Kelvin probe) Time of flight setup-Pulsed Nitrogen laser, Oscilloscope etc Plasma Cleaning system Class 10,000 clean room facility

RF-Plasma Assisted Molecular Beam Epitaxy for growth of III ( Al , Ga , In) - Nitrides

Ultra high vacuum (UHV) Molecular Beam Epitaxy (MBE) system at CSIR-NPL is composed of three chambers mainly, “growth chamber”, supported by a “buffer chamber”, where substrates are degassed prior to growth and a “load lock” chamber to transfer samples. It consists of 10 effusion cells loaded with different material viz. Ga, In, Al, Mg, Si, Sb as source materials. It also has a RF Plasma source for nitrogen.
UHV is maintained in the system by using number of vacuum pumps: Ion pump, Turbo-molecular pump, Cryopump and a Titanium Sublimation Pump which efficiently reduces residual impurities to a minimum and helps to maintain a background pressure of 10 -11  Torr. MBE system is also equipped with Reflection High Energy Electron Diffraction (RHEED) for in-situ characterization of growth mode, structure and growth rate.

 This system is mainly being used to develop Group III-Nitrides based materials for LED and Solar Cell applications.

Laser-Molecular Beam Epitaxy (L-MBE) System for growth of III ( Al , Ga , In) - Nitrides

The UHV-L-MBE system is dedicated for the growth of group-III nitride epitaxial layers and their heterostructures for high electron mobility transistor (HEMT) applications.
The system target stage is capable of holding both solid as well as liquid targets for laser ablation. The atomic nitrogen source is supplied through radio frequency (RF) nitrogen plasma cell.
The system is equipped with reflection high energy electron diffraction (RHEED) facility to monitor the growth in-situ.

Surface characterization using Multi-probe Surface Analysis (MPSA) System

The multi-probe surface analysis system from Omicron, Germany is a state-of-the-art machine consisting of number of Spectroscopy & Microscopy techniques including X-ray Photoelectron spectroscopy (mono and non-monochromatic x-ray sources), Ultraviolet Photoelectron Spectroscopy (UPS), Ion Scattering Spectroscopy (ISS), and Auger Electron Spectroscopy (point, mapping), which allow to determine electronic structure, elemental composition, valence band states, bonding information (impurities), defects, dangling bond & interface states.

Manipulator: 5 degrees of freedom, 90 K to 1300 K, In-situ surface preparation: Ion Sputtering, Annealing, Scrapping using diamond file, UHV Suitcase for in-vacuum sample transportation.

Low Energy Electron Diffraction (LEED) is being used to study the surface atomic structure, symmetry, long range order and cleanliness of the solid surface. The Microscopy part of the system is equipped with variable temperature UHV-STM/AFM (30K-600K) which has capabilities to determination of surface atomic structure, morphology and local density of states at liquid nitrogen & liquid helium temperatures. Currently, MPSA is being utilized to study Nitride, Oxide and Thermoelectric samples.  

Ultra High Vacuum (UHV) Scanning Tunneling Microscopy (STM) System

UHV-STM studies leading to the atomic resolution imaging and STS (Scanning tunnelling spectroscopy) on single crystal surfaces of oxides and semiconductors.
UHV STM from Omicron working at the base pressure of 5x10 -10 Torr. System includes RGA, and in-situ tip preparation tool. For atomic resolution on single crystal surfaces of metals, semiconductors and some oxide films

Ultrafast Spectroscopy System: Ultrafast Optoelectronics and Terahertz Photonics


Recently at CSIR-NPL we have installed a new facility of femto second laser, which has a great potential to provide a new dimension to the materials research.
The installed ultrafast laser or femto second laser is a pulsed laser with 1kHz repetition rate, average power of 4 mJ and the pulse width of <35 fs. The basic configuration of the system comprises of an oscillator, and an amplifier system coupled to an Operational Parametric amplifier (OPA). The Oscillator is a Verdi Pumped Micra system from Coherent inc., the output of this Oscillator is > 350mW @800nm with an adjustable bandwidth of <30nm to m> 100nm. The pulse width is adjustable with <25fs with a repetition rate of 80MHz, the peak tunability is 760nm to 850nm (30nm bandwidth).
This oscillator output is seeded to the Amplifier pumped with 20mJ @1KHz, 250ns pulse centered around 527nm, Evolution 30 model. The output of the Regenerative amplifier is 4mJ@1KHz centered around 800nm with a pulse width of <35fs.
Activity: Ultrafast pump probe spectroscopy/transient Absorption spectroscopy on wide band gap materials like GaN/ZnO etc and terahertz generation and detection .
People:
  1. Dr. Suresh Chand, Chief Scientist, Head
  2. Dr. Amish G. Joshi, Principal Scientist
  3. Dr. Suraj Prakash Khanna, Principal Scientist
  4. Dr. Govind, Senior Scientist
  5. Dr. Ritu Srivastava, Senior Scientist
  6. DR. M. Senthil Kumar, Scientist
  7. Dr. Mahesh Kumar, Scientist
  8. Dr. Prabir Pal, Scientist
  9. Dr. Sunil Singh Kushvaha, Scientist
  10. Dr. Ajay Kumar Shukla, Scientist
  11. Dr. C.K.Suman, Scientist
  12. Dr. Mukesh Jewariya, Scientist
  13. Dr. Srinivas Ragam Rao, Scientist
  14. Mr. Lalit Goswami, Technical Assistant
  15. Mr. Saket Vihari, Technician
Notable achievements
  • Demonstrated Proto type monochrome OLEDs
  • Demonstrated Proto type White OLEDs
  • Publication- Sixty
  • Patents- Two (Indian) One (US patent) in process
Best Poster Awards
  • National Conference on Molecular/Organic Electronics Devices, Amritsar-22-25 Sept. 2009, India
  • Indo-German workshop on advanced materials for future energy requirements (WAMFER 2012), Delhi University 28th Nov- 1st Dec 2012.

CONTACT INFORMATION