M.A. George

Low‐temperature photoluminescence of detector grade Cd1−xZnxTe crystal treated by different chemical etchants

Low‐temperature photoluminescence (PL) spectra of detector grade Cd1−xZnxTe (x=0.1) have been measured to obtain information about shallow level defect concentration introduced during mechanical polishing and chemical etching processes. We present here a comparative PL study of Cd0.9Zn0.1Te crystals treated by different chemical solutions used for nuclear detector surface treatment. The results show that the 5% Br–MeOH+2%Br–20% lactic acid in ethylene glycol treatment combines the advantages of bromine and lactic acid for chemical etching and results in the best surface condition, as evidenced by the largest I(D0,X)/Idef intensity ratio and the narrowest full width at half‐maximum of the main peak (D0,X). Changes in the surface morphology were also analyzed by atomic force microscopy and correlated with the PL results. Current–voltage (I–V) curves and the room‐temperature 55Fe spectral response of the sample etched by the best treatment are also presented and discussed.

Study of electroless Au film deposition on ZnCdTe crystal surfaces

The ‘‘electroless’’ deposition method of Au thin films on n‐type ZnCdTe crystal surfaces has been investigated by atomic force microscopy, x‐ray photoelectron spectroscopy, and low temperature photoluminescence. The blocking contact behavior of these films was strongly dependent on post deposition annealing treatments which were also found to induce modifications in the surface morphology and surface chemical composition. Heat treatments (at 300u2009°C) in vacuum eliminates most of the interfacial tellurium oxide introduced during the deposition. Annealing also reduces the radiative recombination at defects in the region below the interface and increases the barrier height of the contact.

Atomic force microscopy of lead iodide crystal surfaces

Abstract Atomic force microscopy (AFM) was used to characterize the surface of lead iodide crystals. The high vapor pressure of lead iodide prohibits the use of traditional high resolution surface study techniques that require high vacuum conditions. AFM was used to image numerous insulating surface in various ambients, with very little sample preparation techniques needed. Freshly cleaved and modified surfaces, including, chemical and vacuum etched, and air aged surfaces, were examined. Both intrinsic and induced defects were imaged with high resolution. The results were compared to a similar AFM study of mercuric iodide surfaces and it was found that, at ambient conditions, lead iodide is significantly more stable than mercuric iodide.

Photoluminescence of vapor and solution grown ZnTe single crystals

Abstract ZnTe single crystals grown by horizontal physical vapor transport (PVT) and by vertical traveling heater method (THM) from a Te solution were characterized by photoluminescence (PL) at 10.6 K and by atomic force microscopy (AFM). Copper was identified by PL as a major impurity existing in both crystals, forming a substitutional acceptor, Cu Zn . The THM ZnTe crystals were found to contain more Cu impurity than the PVT ZnTe crystals. The formation of Cu Zn -V Te complexes and the effects of annealing, oxygen contamination and intentional Cu doping were also studied. Finally, the surface morphology analyzed by AFM was correlated to the PL results.

Investigation of nucleation and growth processes of diamond films by atomic force microscopy

The nucleation and growth of plasma‐enhanced chemical‐vapor deposited polycrystalline diamond films were studied using atomic force microscopy (AFM). AFM images were obtained for (i) nucleated diamond films produced from depositions that were terminated during the initial stages of growth, (ii) the silicon substrate‐diamond film interface side of diamond films (1–4 μm thick) removed from the original surface of the substrate, and (iii) the cross‐sectional fracture surface of the film, including the Si/diamond interface. Pronounced tip effects were observed for early‐stage diamond nucleation attributed to tip convolution in the AFM images. AFM images of the film’s cross section and interface, however, were not highly affected by tip convolution, and the images indicate that the surface of the silicon substrate is initially covered by a small grained polycrystalline‐like film and the formation of this precursor film is followed by nucleation of the diamond film on top of this layer. X‐ray photoelectron spec...

Selenium precipitation in ZnSe crystals grown by physical vapor transport

Abstract The morphology of freshly cleaved ZnSe surfaces was investigated by atomic force microscopy and the results were correlated with differential scanning calorimetry (DSC) data. Selenium precipitates in undoped ZnSe crystals grown by the physical vapor transport method were determined. The Se inclusions have a size of about 20 nm. A transition temperature at 221°C in the DSC measurement is interpreted as the eutectic temperature of Se-saturated ZnSe. The total amount of the ZnSe Se-rich second phase was 0.8 wt%, and some segregation effect along low angle grain boundaries was evident.

Post-growth annealing of CdS crystals grown by physical vapor transport

Abstract In this study, the photoluminescent and electric properties of as-grown CdS crystals and the effects observed after post-growth annealing in a cadmium, sulphur, and selenium overpressure were investigated. Bulk CdS crystals were grown by physical vapor transport (PVT) from high-purity starting materials, and two types of as-grown crystals, one dark and the other clear were obtained both having a medium resistivity of 106-108 l)-cm. The dark-type crystals are cadmium rich, as evidenced by an emission peak centered around 2.07 eV, which may be attributed to sulphur vacancies, while in the clear crystals, this emission is less pronounced. Heat treatment under a cadmium-vapor atmosphere has the effect of decreasing the resistivity by approximately 5 orders of magnitude, while sulphur annealing at 500°C, increases the resistivity of the as-grown crystals by 4 orders of magnitude and creates a new emission peak centered around 620 nm (2 eV). 1. Introduction Cadmium sulphide (CdS) is an important and useful material for optoelectronic applications. The growth of CdS by physical vapor transport (PVT) has been intensively studied for many years [1-3]. A relatively high concentration of defects resulting from the high growth temperature required by previous methods led to a low reproducibility of the results. Recently, a modification of the PVT method was * Corresponding author. Fax: +1 615 329 8634; E-mail: aburger@dubois.fisk.edu. I Present address: Universities Space Research Association, Huntsville, Alabama, USA. reported [4] which produces, at lower growth temper- atures, large crystals having both low dislocation density and second-phase inclusion density. Undoped CdS is always n-type, and the photoluminescent (PL) properties of CdS crystals were extensively studied in the past with respect to its conversion type. Most of the PL properties were studied in the context of intentionally doped crystals [5-7]. Other authors found [8-10] that post-growth heat and illumination treatments affect the general features of their lumi- nescence spectra. CdS, a good model material for the investigation of optical and electronic properties at high pressure, became the focus of several studies [11,12], and renewed interest has been triggered by recent reports on the development of electron-beam- pumped devices [13,14]. 0022-0248/96/

Wavelength-selective laser ablation of diamond using hydrogen-impurity vibration modes

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Interface morphology studies of liquid phase epitaxy grown HgCdTe films by atomic force microscopy

Abstract We have observed wavelength-dependent laser ablation of diamond films demonstrating the Cue5f8H bond-stretching mode at 3.5 μm, which is important in the early stages of photodamage. In particular, there is a sharp drop in the ablation threshold near 3.5 μm. The measurements were made with the Vanderbilt Free-Electron Laser (FEL). We also observed the onset of morphological changes by using an atomic force microscope (AFM).

An observation of nanotwin lamellae in Cd0.6Mn0.4Te crystal by atomic force microscopy

Abstract In this paper we report an investigation of the morphology of the interfaces of liquid phase epitaxy (LPE) grown HgCdTe thin films on CdTe and CdZnTe substrates by atomic force microscopy (AFM) on freshly cleaved (110) crystallographic planes. An empirical observation which may be linked to lattice mismatch was indicated by an angle between the cleavage steps of the substrate to those of the film. Te precipitates with size ranging from 5 nm to 20 nm were found to be most apparent near the interface.