Bridgman Growth Technique Research Articles

Linear x-ray detector array made on bulk CdZnTe for 30∼100 keV energy

A CdZnTe detector grown by the high pressure Bridgman (HPB) growth technique was tested using high energy x-rays (30∼100 keV), and the performance was compared with a commercially available Nal scintillating detector of 5 cm thickness. The charge collection efficiency of a CdZnTe detector is as high as 90% at relatively low electric field, 600 V/cm. At high x-ray photon energies, the detection efficiency is reduced due to the thickness of the CdZnTe. A 32 channel linear array was fabricated on 1.2∼1.7 mm thick CdZnTe, of which the detector area was 175 × 800 µm2 and the pitch size 250 µm. The measured dark current for the 16 element detector was as low as 0.1 pA at 800 V/cm with an excellent uniformity. Energy spectra were measured using a Co57 radiation source. A small pixel effect and charge sharing were observed. The energy resolution was improved and compared with the large area detector. The array detector gave an average 5.8% full-width-half-maximum (FWHM) at 122 keV photopeak. The large area detector of the same material before fabrication exhibited a low energy tail at the photopeak, which limits the photopeak FWHM to 8%.

Electrical Properties of Gallium Manganese Antimonide: a New Diluted Magnetic Semiconductor

Ga1-x Mnx Sb, a ternary diluted magnetic semiconductor (DMS) alloy was newly synthesised with different Mn concentrations (x=0.0048, 0.01, 0.05 and 0.14) using Bridgman growth technique. The stoichiometry and the composition were verified by the electron probe microanalysis and X-ray diffraction analysis. At room temperature electrical parameters like resistivity, Hall co-efficient, carrier concentration and mobility were determined. The variations of resistivity and Hall co-efficient with temperature were studied and it was found that the alloy was degenerate in nature.

Wavelength mapping of mixed semiconductors using an automatic IR spectrophotometer

IR transmission measurements are now widely used as a non-destructive technique in compositional assessment and growth-mechanism studies of bulk-grown mixed-semiconductor crystals, where problems of segregation result in composition variations in both axial and radial directions, necessitating detailed measurements on a small scale. The design principles and constructional details of a computer-controlled, double-beam IR spectrophotometer covering the range 1.5–14 μm and capable of producing transmission profiles and room-temperature cut-on wavelength maps of slices of material on a millimetre-sized grid are described. The associated computer software is also detailed. Results are presented for the mixed semiconductor Cd x Hg 1− x Te prepared by the Bridgman growth technique. Measurement times are approx. 10 min for a short-wavelength, 13mm dia slice and 30 min for a long-wavelength slice. These results can be related back to the growth mechanisms and help to predict the suitability of material for device manufacture.