NON-CONTACT IN-LINE PROCESS MONITORING
IN FABRICATION OF PHOTOCURRENT RADIATION DETECTORS
A patented technology based on the inductive (RF) detection of the charge carriers generated by light or high energy radiation (X-ray, Gamma-ray) offering new metrologies and new class radiation sensors.
Defect Specific Lifetime Analysis [DSLA©]
Based on the proprietary analysis of the time dependent density of optically generated charge carriers, DSLA simultaneously differentiates properties of the surface and bulk of semiconductor focusing, depending on the probe configuration, on the bulk or surface (electrode) regions of the detector. In particular it identifies point and extended defects that directly affect performance of the photo-current radiation detectors.
Since RF-DSLA measurements do not involve the collection of charges at the electrodes but are solely based on the absorption of the RF radiation, DSLA can be used for the characterization of monocrystalline, polycrystalline and amorphous materials.
The key factor affecting performance of semiconductor radiation detectors is quality of the starting material. Defect Specific Lifetime Analysis (DSLA) allows for the rapid, non-contact evaluation of substrate (such as CdZnTe) parameters directly related to the detector performance.
The effect of the relative volume of the space-charge regions, Vsc/V, at extended defects in n-type, high resistivity CZ, and of the electron capture time constant, tc, on the energy resolution of detectors, FWHM.
While the energy resolution of detectors strongly depends on the density of extended defects (represented by Vsc/V), this resolution is only weakly dependent on the electron capture at point defects characterized by the electron capture time constant, tc (a component of "mu-tau product" commonly used in specifying semiconductors in fabrication of photo-current radiation detectors).
More details see: "Dominant role of extended defects in CdZnTe photocurrent radiation detectors".
Tight control and optimization of the electrode formation process, which depends on the surface characteristics, is a critical factor limiting reproducibility and the fabrication yields of photocurrent radiation detectors. Hence, monitoring of the surface properties before and after electrode formation is an important factor required for yield improvement.
Dependence of the surface recombination time constants at Cd and Te faces on the energy resolution of detectors fabricated with high quality n-type high resistivity CZT. The electrodes were removed prior to the DSLA measurements.
The samples of the figure above were prepared from a single ingot and were subject to the same treatment.
The surface recombination time constant, te, is exponentially dependent on the height of the electrostatic surface potential barrier. Therefore, even small variations in the surface properties would substantially affect energy resolution of detectors.
More details see: "Electrode subsurface depletion zones limiting reproducibility and performance of CZT radiation detectors".
GEKA ASSOCIATES is seeking a partnership with an industrial entity interested in the productization of the patented RF-based, non-contact electrical measurement tool referred to as Defect Specific Lifetime Analyzer (DSLA) and a collaboration with an established R&D center interested in the development of new inductive radiation detectors for industrial, medical, security, and space applications.