D. K. Bowen

A comparison of techniques for nondestructive composition measurements in CdZnTe substrates

We report an overview and a comparison of nondestructive optical techniques for determining alloy composition x in Cd1-xZnxTe substrates for HgCdTe epitaxy. The methods for single-point measurements include a new x-ray diffraction technique for precision lattice parameter measurements using a standard highresolution diffractometer, room-temperature photoreflectance, and low-temperature photoluminescence. We compare measurements on the same set of samples by all three techniques. Comparisons of precision and accuracy, with a discussion of the strengths and weaknesses of different techniques, are presented. In addition, a new photoluminescence excitation technique for full-wafer imaging of composition variations is described.

Characterization of engineering surfaces by grazing-incidence X-ray reflectivity

This paper covers the principles and practice of grazing-incidence reflectometry and its application to the characterization of surfaces and very thin surface layers of single or polycrystalline materials. It is shown that film thicknesses may be accurately measured in the range from monolayers up to about a micrometre, that roughness parameters from zero to about 2 nm may be deduced, and that the diffuse reflectivity is sensitive to the distribution and correlation length of the surface structure. Applications to semiconductor and magnetic multilayers are demonstrated, and the use of the method for study of interfaces and conformal roughening is considered.

Advanced X-ray scattering techniques for the characterization of semiconducting materials

Abstract The application of high resolution X-ray scattering to the characterization of single crystal semiconductors is reviewed. Double and triple axis diffraction are discussed and the present limits of their sensitivity are explored. Information from these diffraction techniques is contrasted with that obtained by grazing incidence X-ray reflectance measurements. It is shown that X-ray topographic methods, which provide a two-dimensional map of the lattice strains complement the information gained by the above area-integrated techniques.

X-ray diffraction and reflectivity characterization of SiGe superlattice structures

The authors demonstrate the effectiveness of both X-ray diffraction and X-ray reflectivity in the structural characterization of semiconductor structures. By combining information from both techniques the abruptness of the interfaces for Si1-xGex structures, with x=0.1-0.57, may be determined. For superlattice structures with x<0.3 both types of interface were found to have a root mean square (RMS) roughness of 0.5+or-0.3 nm. For a Si/Si0.45Ge0.55 superlattice structure the interfaces are found to have differing roughnesses. For the SiGe-on-Si interface the RMS roughness is found to be 0.5+or-0.2 nm; however, the Si-on-SiGe interface has a larger value of roughness, 1.0+or-0.3 nm. This roughness at the Si-on-SiGe interface is found to be dependent on the Ge content of the layer and it is shown by transmission electron microscopy analysis to be long ranged (about 70 nm) and wavy at the interface.

Principles and Performance of a PC-Based Program for Simulation of Grazing Incidence X-Ray Reflectivity Profiles

We describe PC- based software which calculates grazing incidence X-ray reflectivity profiles from model thin film structures, including interface grading. We discuss the mathematical principles of the model and benchmark tests for speed of operation on two PC compatible machines are presented. Curvature of the specimen results in selective loss of fringe visibility at low scattering vectors and is treated rigorously. We discuss the treatment of roughness and use a generalized formula that is valid at large and small values of the reflectivity; its effects are illustrated using the program.

A Novel Beam-Conditioning Monochromator for High-Resolution X-ray Diffraction

This paper describes a novel duMond-configuration monochromator for high-resolution X-ray diffraction. The device consists of two single-crystal blocks of silicon each containing two beam channels cut respectively parallel to and 17.65° from the (011) planes. In the high-intensity mode, with Cu Kα 1 radiation, the beam divergence is 11.5″ and the dispersion is 1.3×10 -4 with intensity comparable with that from a symmetric Ge 022 device. The high-resolution setting has a divergence of 4.4″ and dispersion of 4.9×10 -5 , the intensity being a factor of ten lower than in the high-intensity setting. Parallel lateral translation of the two elements permits a rapid switch between the high-resolution and high-intensity settings

Synchrotron X-radiation topography

Abstract The application of synchrotron radiation for X-ray topography is reviewed. For two types of experiment, dynamic studies and statistical surveys, the intensity and continuous spectrum of synchrotron radiation is particularly important but it is shown that the time structure and polarisation can also be exploited. The future potential of the technique is discussed.

Strain relaxation in Si−xGex layers on Si(001)

The lattice relaxation of strained Si 1− x Ge x layers on Si (001) substrates has been examined. Three specimens consisting of a single Si 1− x Ge x layer were grown by molecular beam epitaxy. All layers were grown with a nominal composition of x = 0.14 to thicknesses of 0.5, 1.0 or 1.5 μm. Double-crystal and white-radiation topographic methods were used to reveal the misfit dislocation structure and distribution. The misfit dislocations were shown to extend from heterogeneous nucleation sites along the directions in the plane of the interface. A symmetric distribution of dislocations between the orthogonal directions was observed. The Burgers vectors of the misfit dislocation array were evenly distributed amongst the available 60°-type candidates. Double-crystal X-ray diffractometry showed the 0.5 and 1.0 μm layers to be fully strained to within the experimental uncertainty. Secondary branching of misfit dislocations was observed in the 1.0μm layer which indicated cross-slip of the threading dislocation segments.

Structural and electrical properties of B delta layers in Si

X-ray diffraction has been used to deduce the width and strain fields of an elemental boron delta layer in (100) Si grown by MBE. It is found to be <1 nm thick and tetragonally distorted with a lattice contraction of 0.031 nm in the (100) direction. Hall measurements have been used to obtain the hole concentration in the layer and it is found that it is fully activated with a sheet carrier density of 3.5*1014 cm-2, one of the highest values reported to date. Cross-sectional TEM analysis confirms that it is a near-ideal delta layer, with no precipitation evident.

Two-dimensional X-ray interferometry

This paper demonstrates the capability of X-ray interferometry for the measurement of the detailed parasitic motions that may occur in very high precision slideways. X-ray interferometry has been used for the first time to obtain simultaneous fringes by motion of the sensing crystal in two orthogonal directions, giving (with two independent X-ray sources) fringes corresponding respectively to the lattice spacings of (111) and (220) crystal planes. A monolithic X-ray interferometer was designed for this experiment, with two sets of leaf spring supports for the moving blade, so that it could be driven in the two orthogonal directions by magnet/coil transducers. A phase plate was positioned and moved so that three spatial-phase signals could be obtained for each positional measurement of each of the two axes, providing measurement accuracy of the order of 20 pm for the conditions of this experiment.