• Optical Characterization

         Spoectral Photoconductivity
         Spectral Photovoltage
         Photoluminescence
         Reflectance| Photomodulated & Electromodulated reflectance

     

     

  • Spectral Photoconductivity

    PC spectrum gives information about bandgap energy and the presence of defect/trap levels.

    In the PC set-up, sample is placed onto cold finger of a closed-cycle refrigerator, and the temperature is kept at any desired value to within 0.1 K, in the range of 30-300K. The light from a quartz halogen lamp is focused on a 0.5 m grating monochromator, through a variable speed optical chopper, and light intensity controlled by a constant current source. The modulated photocurrent at the frequency of the chopped light, the a.c excitation intensity are simultaneously measured as a function of the photon energy.

    •  Temperature range : 30 300K (with close cycle refrigerataor) | 2 300K (with LHe bath cryostat)

    •  Wavelength range : 200nm 10 um

     

    Spectral Photovoltage

    •  In-plane PV spectrum gives information about the defect levels in investigated structures. On the otherhand PV enables to measure open circuit voltage under villuminations.

    In the PV set-up, sample is placed onto cold finger of a closed-cycle refrigerator, and the temperature is kept at any desired value to within 0.1 K, in the range of 30-300K. The light from a quartz halogen lamp is focused on a 0.5 m grating monochromator. Open circuit PV signal and excitation intensity measured by a conventional lock-in amplifier.

    •  Temperature range : 30 300K (with close cycle refrigerataor) | 2 300K (with LHe bath cryostat)

    •  Wavelength range : 200nm 10 um

    Photoluminescence

    •  This metod is used to determine bandgap energy of the semiconductors. At the system , high power (up to 5W) Argon-ion laser is utilized as excitation source.

    •  Temperature range : 1.6 K 300K

    •  Wavelength range : 200nm 10 um

    Reflectance | Photo- and Electromodulated Reflectance

    Modulation spectroscop techniques such as photo, elektroreflectance and contacless electroreflectance gives very useful information about energies of bandgap and subband transitions even at rooom temperature.

    Photomodulated reflectance measurement is based on modulation spectroscopy. The PR spectrum shows derivative characteristics. This method gives very useful information about band gap transition energies even at rooom temperature owing to sharp derivative spectrum at transition energies. In PR measurements, a halogen lamp and a single grating monochromator is used in order to illuminate a spot on the sample. Meanwhile sample is modulated by a chopped laser. The modulated reflectance is measured with a diod. The output of the detector contains both dc R and ac R signal. These components are monitored by using digital voltmeter for dc R and lock-in amplifier for ac R. Photomodulated reflectance signal equals to dR/R. This system is computer controlled like PC,PV and R. The outpufs of lock-in ampliers and digital voltmeter are connected to the computer. Obtained data is plotted versus wavelength.