T. Colin

Rashba spin splitting in a gated HgTe quantum well

Metal - oxide - semiconductor field-effect transistors (MOSFETs) on CdTe/HgTe/CdTe heterostructures are fabricated with silicon dioxide gate insulators. In these devices, the density of the quasi two-dimensional electron gas in the HgTe quantum well can be tuned in a wide range. In low magnetic fields we observe beating patterns in the Shubnikov - de Haas oscillations that render possible the determination of the coefficient of the Rashba term in the Hamiltonian as a function of electron density. This coefficient consistently describes the splittings observed in cyclotron resonance in low magnetic fields.

Mapping of CdZnTe substrates and CdHgTe epitaxial layers by X-ray diffraction

Abstract A simple procedure is described for mapping of lattice parameter and X-ray rocking curve width across Cd 1− y Zn y Te (CZT) substrates and Cd x Hg 1− x Te (CMT) epitaxial layers. It is shown how screening of the crystallinity and composition of CZT substrates can be utilized to make subsequent X-ray characterizations of epitaxial layers more reliable. This also allows selection of substrates with a close lattice matching to a given CMT composition, to reduce or avoid layer relaxation. Substrates with laterally varying Zn content give a varying lattice mismatch on a single epitaxial layer. Correlation of the lattice parameter maps of substrate and layer shows the resulting variations in layer strain, and the onset of relaxation can be clearly identified. Mapping of rocking curve peak widths on good quality CZT substrates and closely lattice matched CMT layers shows that the peak width can be below 6 arcsec, limited essentially by the intrinsic peak width of the materials. Additional broadening of the layer peaks is introduced primarily by substrate defects and misfit dislocations, unless epitaxial growth conditions deviate significantly from their optimum.

Elastic and plastic deformation in low mismatched CdxHg1 − xTeCd1 − yZnyTe

We have measured, by X-ray diffraction, the deformation of uniform cadmium mercury telluride layers epitaxially grown on cadmium zinc telluride substrates with varying zinc concentration. It is then possible, within the same sample, to clearly identify elastic deformation in the regions of small lattice mismatch and plastic deformation in the regions with larger mismatch. The deformation has been analysed in a framework based on a stress relaxation model published by Fontaine et al. This analysis permits determination of the energies of formation of misfit dislocations. They have been compared with values obtained from ab initio models. From this comparison possible relaxation mechanisms are proposed. A clear dissymmetry is also observed between relaxation of tensile and compressive strain. Pre-relaxation dislocation movements are also detected by diffraction peak broadening. Possible reasons for these behaviours are discussed.

Density dependent cyclotron and intersubband resonance in inverted CdTe/HgTe/CdTe quantum wells.

Cyclotron and intersubband resonances in HgTe quantum wells in the inverted band regime are studied by Fourier-transform spectroscopy. Metal-oxide-semiconductor field-effect transistors (MOSFETs) allow us to tune the electron density. In particular, we investigate filling factor dependent splittings of the cyclotron resonance in strong magnetic fields and a crossing of Landau levels of the conduction and valence subband. The experimental results are well described by a 6 × 6 k·p-model.

Infrared absorption in HgCdTe/CdTe single quantum well structures

The authors consider interband and intersubband absorption in HgCdTe/CdTe single quantum well structures. By measuring the transmission in an internal reflection geometry with and without a metallized surface and polarized light, they study the dependence of the infrared absorption on the polarization of the exciting electric field.

Interband magneto-absorption in narrow-gap HgTe/CdTe superlattice structures

The use of a magnetic field for interband absorption experiments in the midinfrared regime can reveal the electronic band structure of HgTe/CdTe superlattices. In high-quality samples pronounced magnetic field-induced absorption peaks are observed in the transmission spectra due to hole to electron Landau level transitions. By extrapolating the excitation energies for such transitions to B = 0, gap energies between several hole and electron subbands can be determined accurately. In addition, we show that interband magnetoabsorption provides a sensitive feedback for growth of quantum structures.

Characterization of molecular beam epitaxially grown HgCdTe epilayers by mid-infrared interband magneto-absorption

Interband magneto-absorption is used to characterize molecular beam epitaxially (MBE) grown HgCdTe epilayers. Both the bandgap and the Moss-Burstein shift in n-doped layers are determined from the experiments. A heterostructure sample consisting of four layers with different compositions is also analyzed. Due to the good experimental sensitivity all four bandgaps are determined, in contrast to optical transmission analysis without a magnetic field where only the lowest gap is readily visible. The interband magneto-absorption signal strongly depends on the electron mobility. This has been used as an aid to optimizing the MBE growth conditions of HgCdTe layers on different substrate orientations.