Optically immersed HgCdTe photovoltaic detectors in the 2.5 to 3.2 μm wavelength region operating at near room temperatures have been developed based on HgCdTe graded structure materials grown by opened tube isothermal vapor phase epitaxy (ISOVPE) method on lattice matched CdZnTe substrate. Fourier transformation infrared spectroscopy (FTIR) measurement combined with continuous step wet etching was applied to adjust the cutoff wavelength. The devices were designed and fabricated by traditional n-on-p planar junction process. Optical immersion of micro-lenses by CdZnTe substrate was used to improve the performance of the devices and the hyper-hemispherical micro-lens with a diameter of 1.5mm was made by single point diamond turning method. The optical response area was tested by laser beam induced current (LBIC) scanning measurement, and the result showed that the devices with hyper-hemispherical immersion micro-lens could get a 1mm×1mm response area as designed. The current-voltage characteristic of the devices were measured, and all the devices showed a little increase in the values of zero biased resistance, which was due to a decreased background radiation acceptance angle caused by a hyper-hemispherical structure. The photo response signal and dark noise were also measured before and after the micro-lens fabrication. The signal showed an increase by 20-30 times due to the enlarged photo response area, and the dark noise showed a little decrease which was also due to a limited background radiation acceptance angle. As a result, a multiple factor of four in detectivity enhancement could be achieved by the adoption of hyper-hemispherical immersion micro-lens structures.
Cd<sub>1</sub><sub>-x</sub>Zn<sub>x</sub>Te single crystals were grown by Vertical Bridgman method. The optic and dielectric properties of Cd<sub>1-x</sub>Zn<sub>x</sub>Te (× = 0.04) single crystals in 0.2−2.5 THz frequency range have been investigated by using transmission-type THz timedomain spectroscopy. Two absorption modes at 1.6 THz and at 2.1 THz were observed, which were attributed to the quasi-local mode of ZnTe in CdTe and to the CdTe 2TA phonon process, respectively. The complex refractive index and dielectric function were extracted from the measured transmittance and phase shift in 0.2−2.5 THz range
ZnTe crystal has been grown at a temperature as low as 1060°C using Te solvent method. X-ray diffraction showed that
the ZnTe crystals were grown from <110> oriented. The transmission was over 60% from 2 μm to 22 μm by using
Fourier Transform Infrared Spectrometer. The etch pit density in the sliced wafer was about 2×10<sup>4</sup> cm<sup>-2</sup> detected by Scan
Electronic Microscopic. The transmission spectrums were measured from 0.2 to 3 THz by using Terahertz Time Domain
Spectroscopy. And the refractive index and extinction coefficient were obtained through analysis of the time domain