Low density ZnO nanorods are grown by modified chemical vapor deposition on silicon substrates using gold as a catalyst.We use high resolution photoiuminescence spectroscopy to gain the optical properties of these nanorods in large scale.The as-grown samples show sharp near-band-gap luminescence with a full width at half maximum of bound exciton peaks at about 300μeV,and the ratio of ultraviolet/yellow luminescence larger than 100.Highly spatial and spectral resolved scanning electron microscope-cathodoluminescence is performed to excite the ZnO nanorods in single rods or different positions of single rods with the vapour-solid grovth mechanism.The bottom of the nanorod has a 3.31-eV luminescence,which indicates that basal plane stacking faults are related to the defects that are created at the first stage of growth due to the misfit between ZnO and Si.
XIE YongJIE Wan-QiWANG TaoWIEDENMANN MichaelNEUSCHL BenjaminMADEL ManfredWANG Ya-BinFENEBERG MartinTHONKE Klaus
CdZnTe is an excellent material candidate for high efficiency,high-resolution room-temperature nuclear radiation detectors,and the CdZnTe detectors are being widely used in medicine,industry,safeguard and scientific X-ray and γ-ray imaging and spectroscopic applications.In this work,three CdZnTe planar detectors with different grades,named CZT-1,CZT-2 and CZT-3,respectively,were fabricated.And the effects of mobility,lifetime and de-trapping time on the performance of CdZnTe planar detector,such as the energy resolution,charge collection efficiency and peak to valley ratio,were analyzed.The charge collection efficiency depends on the product of carrier mobility and lifetime,which has a great effect on the energy resolution of detector when the efficiency is less than 90%.The de-trapping time of carriers in deep levels should be responsible for the peak to valley ratio and "polarization".
The band alignment of a (0001)CdS/CdTe heterojunction is in situ studied by synchrotron radiation photoemission spectroscopy (SRPES).The heterojunction is formed through stepwise deposition of a CdTe film on a wurtzite (0001)CdS single crystalline substrate via molecular beam epitaxy.CdS shows an upward band bending of 0.55 eV,the valence band offset △Ev is calculated to be 0.65 e V and the conduction band offset △ Ec is 0.31 eV.The interracial band alignment is sketched to display type-Ⅰ band alignment.
A laser scanning confocal microscope （LSCM） and a field-emission scanning electron microscope （FE- SEM） were used to study the defects in CdMnTe crystals, such as twin boundaries, Te inclusions, and dislocations. Twin boundaries were usually decorated with Te inclusions, which could induce dislocations. The optical, elec- trical properties and detector performance of CdMnTe crystals with twins and free of twins were compared. The results showed that the wafers with a high density of twins usually had lower average IR transmittance and poorer crystalline quality. Besides, the energy spectra indicated that twin boundaries in a CdMnTe detector had a negative effect on detector performance; the values of both the energy resolution and （μτ）e were nearly half of those for a single crystal detector.
