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.
Properties of Iodine-Doped CdTe Layers on (211) Si Grown at High Substrate Temperatures by MOVPE
The properties of iodine-doped (211) CdTe layers grown on (211) Si substrates by metalorganic vapor-phase epitaxy at high substrate temperatures from 325°C to 450°C were studied. The growth rate of the doped layer increased with increasing substrate temperature before reaching a maximum value of 2.6 μm/h at 425°C, after which it decreased slightly. On the other hand, the room-temperature electron density showed a strong dependence on the Te/Cd precursor flow-rate ratios, where the electron density increased with a decreasing Te/Cd ratio. The highest electron density of 2.5×1018 cm−3 was obtained by growing the epilayer at a substrate temperature of 400°C and Te/Cd ratio of 0.05. This was considered to be due to decreased donor compensation at a small Te/Cd ratio. Good correspondence was observed between the results obtained from Hall measurements and photoluminescence measurements.
Investigating the Optical properties of cd1-xznxs thin films deposited by the Dip Technique
A Thesis submitted to the Department of Physics, Kwame Nkrumah University of Science and Technology, in partial fulfillment of the requirement for the degree of 
Master of Science (Solid State Physics)