Growth And Defects Of Cd_xZn_1-xTe Single Crystals

CdZnTe(CZT) is a new kind of developing materials for room temperature nuclear radiation detectors which is widely used in many fields, and has been regarded as leading solid solution compound semiconductor in recent research. Due to its disadvantageous properties, it's very hard to grow by traditional Bridgman method, and the defects in crystals will have bad effects on the detectors. In this paper, a modified Bridgman method(Descending Ampoule method) and the crystal defects are deeply researched. First, some critical problems in crystal growth like crystal seeding, Zn dephlegmation, geometrical selection and temperature fields are discussed in theory, and the possible kinds of defects appeared in crystal growth progress and the reasons are carefully researched. To control the concentration of Cd vacancies, a new method by which the Cd vacancies were compensated with excess Cd in the Cd rich starting materials has been developed, and a new kind of two-area tube furnace with good linear temperature distribution was designed. When crystal growth ,we choosed special designed ampoule with the higher thermal gradient at the crystal-melt interface of 10℃/cm and the lower growth rate of 0.5cm/h. The synthesis of poly crystal and the single crystal growth are in the same ampoule in order to avoid second pollution. CZT single crystal 22mm in diameter and 40mm in length with perfect surface can be gotten. The XRD showed the CZT had perfect structure and its resistivity is 2(1010Ω·cm. At the same time we have preliminary researched the chip process technology, analysed CZT cutting disaggregation characteristics and researched different CZT etchants. Based on the EAg-I etachant, a new etchant was developed, with which the etch pit pattern on (110), (111) and (100) faces of CZT crystals can emerge immediately and effectually. And the defects in the as-grown crystals were characterized by IR transmission spectroscopy, atom force microscopy (AFM), scan electronic microscopy (SEM) and photomicrograph. At last we have tested the electric performance of the as-grown CZT. By theory of SCLC, the electron trap density of 3.505×1010cm-3 and the electron trap energy level of Et=0.5063eV were calculated.