Photoadmittance Spectroscopy

Photoadmittance spectroscopy, or photocapacitance, measures the capacitance as the wavelength of light illuminating the semiconductor is scanned from low to high energy.When a threshold energy is reached for optical emission of a trapped charge from a defect, a change is measured in the capacitance.Measurements are made at low temperature to limit the thermal emission from traps.The data acquisition user interface at the right shows the photocapacitance (top), and photoconductance (bottom). The manual describes each of the steps involved in preparing the sample for maximum signal.

The equipment uses many of the core components as the DLTS system, such as the cryostat, vacuum pump, temperature controller. External optics are all computer controlled, covering a range from infrared to ultraviolet: 2 μm to 300 nm.

PAS measures the optical transition energy. DLTS, TAS, and IVT measure the thermal energy of defects.

Photocapacitance spectra

The analysis program allows you to plot the spectrum in units of energy or wavelength, and compare spectra.It also allows you to subtract a reference spectrum, normally from a scan taken with the shutter closed to allow removal of any thermal emission that takes place