Development of Large-Area CdTe/n+-Si Epitaxial Layer-Based Heterojunction Diode-Type Gamma-Ray Detector Arrays
Growth of large area single crystal CdTe layers was studied on <inline-formula> <tex-math notation="LaTeX">$25 \times 25$ </tex-math></inline-formula> mm<sup>2</sup> (211) Si substrates using metalorganic vapor phase epitaxy. High crystalline quality thick crystals with very good material uniformity were obtained. A 2-D monolithic detector array comprising (<inline-formula> <tex-math notation="LaTeX">$20 \times 20$ </tex-math></inline-formula>) pixels was developed and evaluated. Each pixel is <inline-formula> <tex-math notation="LaTeX">$1.12 \times 1.12$ </tex-math></inline-formula> mm<sup>2</sup> size in a 1.17-mm pitch and consists of a p-CdTe/n-CdTe/n<sup>+</sup>-Si heterojunction diode structure, which is isolated from the surrounding pixels by making deep vertical cuts. The detector array exhibited highly uniform and low dark current, typically less than 0.5-<inline-formula> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula>/cm<sup>2</sup> per pixel at an applied reverse bias of 50 V. The spectroscopic performance was separately confirmed by dicing out a small portion from the array which clearly resolved energy peaks from <sup>241</sup>Am gamma isotopes at room temperature. On the other hand, a significant improvement in the detection property was observed by cooling it to −30 °C.
Nucleation and islands growth of CdZnTe(0 0 1) epitaxial films on GaAs(0 0 1) substrates by close spaced sublimation
Abstract The early stages of close spaced sublimation growth of CdZnTe(0 0 1)/GaAs(0 0 1) epilayer were experimentally studied under different substrate temperatures and ambient pressures. SEM, AFM, XRD, EBSD and EDS were used for the characterization of morphology, structure and composition of the films. The films were found to be (0 0 1) oriented and epitaxial in nature with zinc blende cubic structure. Deposition models were used to explain the correlation between growth condition and CdZnTe island morphology. Films grown at 350 °C and 1 × 102 Pa show the best uniform and smooth surface. When increasing substrate temperature to 430 °C or ambient pressure to 1 × 104 Pa or 3 × 104 Pa, islands are less compact and exhibit preferential growth along one of 〈1 1 0〉 directions, which could be resulted from the big lattice mismatch (14.0%) of Cd0.9Zn0.1Te(0 0 1)/GaAs(0 0 1) heterojunction. For the growth at 430 °C in 3 × 104 Pa, prior nucleation at defect site was found, and the appearance of regular 〈0 1 0〉 oriented island edges proposes that steps 〈0 1 0〉{1 0 0} are more stable for CdZnTe(0 0 1)/GaAs(0 0 1) epilayer than steps 〈1 1 0〉{1 1 1}.
What is Enlightenment
Enlightenment is man's emergence from his self-imposed nonage. Nonage is the inability to use one's own understanding without another's guidance. This nonage is self-imposed if its cause lies not in lack of understanding but in indecision and lack of courage to use one's own mind without another's guidance. Dare to know! (Sapere aude.) "Have the courage to use your own understanding," is therefore the motto of the enlightenment.