Fluorescence lifetime imaging microscopy analysis of defects in multi-tube physical vapor transport grown Cd_1−x Zn _x Te

Abstract

Cadmium zinc telluride (CZT) is the material of choice for high‐energy room‐temperature X‐ray and γ‐ray detectors. However, the performance of pixelated detectors is greatly influenced by the quality of CZT. Crystal defects and impurities are one source of shallow and deep level traps for charge carriers. Fluorescence lifetime of the recombination of optically excited charges may indicate the presence and type of defects and impurities in CZT. Fluorescence lifetime imaging microscopy (FLIM) is used to examine the excited‐state lifetime in CZT fabricated by different growth methods and conditions. The FLIM set‐up analyzes luminescence emitted from the sample following photo excitation. Samples were optically excited above band gap with a pulsed laser (590 nm) for raster scanning a 220 × 165 µm2 sample area. In‐situ room‐temperature photoluminescence (PL) and FLIM were recorded simultaneously. In order to analyze the FLIM data, two dominant charge carrier decay processes (τ1, τ2) were identified. The luminescence signal decays with a rapid lifetime of τ1 ≈ 50–200 ps, and a large variety of long‐lifetime components τ2 were found in the range of 225–900 ps. CZT grown by multi‐tube physical vapor transport (MTPVT) showed extremely long‐lived recombination decay times up to 3.5 ns in the vicinity of the interface at growth start. Further away from this interface, the recombination lifetime was in the typical range of fast transitions similar to those found in detector‐grade CZT fabricated by travelling heater method. Crystalline material quality strongly influences FLIM lifetime. Time‐resolved transients of MTPVT‐grown CZT compared with industry‐leading detector grade CZT (dots: measured data; lines: fitted exponential decay curves).

Review on nanomaterials synthesized by vapor transport method: growth and their related applications

“…A planar device (Au/CdZnTe/Au) based on this material shows electron mobility lifetime of 4.07 Â 10 À3 cm 2 V À1 . The CZT crystal fabricated according to the same procedure by Andreas et al 12 show a high resistivity up to 2.3 Â 10 11 U cm, indicating a promising candidate as an X-ray detector.…”

“…Upon using the MTPVT, (Cd, Zn)Te (CZT) single crystals had been successfully prepared. 11,12 Before growing CZT, an initial CdTe nucleation layer of a few millimeters grown on a GaAs (111) substrate is acted as seeding layer, which is put in the low temperature region. Then, the CZT single crystals can grow by evaporating the high purity cadmium telluride and zinc telluride source materials at a comparatively low temperature.…”

“…Based on the vapor transport reactions, quantitative control of doping is also possible, such as synthesizing single crystal nanowires and bulk crystal. [2][3][4] Due to the superiority of vapor transport reaction as a universal method in solid state chemistry and materials sciences, all manners of nanomaterials differing in dimensionality have been successfully synthesized and investigated both in growth kinetics and potential applications, including bulk crystals, [4][5][6][7][8][9][10][11][12][13][14][15] thin lms, [16][17][18][19][20][21][22][23][24][25][26][27][28][29] nanowires, nanobelts 77,78 and nanorods. 79,80 Generally, nanostructured materials can be fabricated by two different approaches, one is the bottom-up approach which means assembling tiny into large, the other one is top-down approach which implies cutting big into small.…”

Twinning in vapour-grown, large volume Cd1−Zn Te crystals

“…These techniques have changed the economic viability of the application of Cd 1-x Zn x Te. Recently, Schneider et al [ 12 ] reported a comparison of the excited state recombination lifetimes of the two types of material using fluorescence lifetime imaging microscopy. In both cases, two decay lifetimes, one short and one long, were identified.…”