Abstract: A horizontal access semiconductor photo detector (2) comprises a horizontal light absorbing layer (8) for converting light into photo-current which layer is configured to confine light within it in whispering gallery modes of propagation. The detector is configured to have a first waveguide portion (18) and a second light confining portion (20, 21) arranged such that the waveguide portion couples light into the detector and transfers light into the light confining portion so as to excite whispering gallery modes of propagation around the light confining portion. The light absorbing layer may be part of the light confining portion or alternatively light can be coupled into the light confining portion or alternatively light can be coupled into the light absorbing layer from the light confining portion by evanescent coupling. The excitation of whispering gallery modes within the light absorbing layer significantly increases the effective absorption coefficient of the light absorbing layer.

Abstract: A horizontal access semiconductor photo detector (2) comprises a horizontal light absorbing layer (8) for converting light into photo-current which layer is configured to confine light within it in whispering gallery modes of propagation. The detector is configured to have a first waveguide portion (18) and a second light confining portion (20, 21) arranged such that the waveguide portion couples light into the detector and transfers light into the light confining portion so as to excite whispering gallery modes of propagation around the light confining portion. The light absorbing layer may be part of the light confining portion or alternatively light can be coupled into the light confining portion or alternatively light can be coupled into the light absorbing layer from the light confining portion by evanescent coupling. The excitation of whispering gallery modes within the light absorbing layer significantly increases the effective absorption coefficient of the light absorbing layer.

Abstract: A method of monitoring material parameters of a sample (4) (for example electrical properties of a semiconductor) during processing (for example during manufacture) which uses ellipsometric techniques to study the changes induced in the ellipsometric spectra of the material, by modulation of the internal electric field of the material, and determining from these changes the material parameters of interest The means of modulation can be a source of electromagnetic radiation, for example a laser (8). The ellipsometer used may include an array of photodetectors. The process allows the real time monitoring of the process under examination.

Abstract: A semiconductor substrate, suitable for epitaxial growth thereon, comprising a plurality of layers of material. The interfaces between layers act as reflectors of electromagnetic radiation. The reflectors may be used in, for example, resonant cavities in which may be located, for example, multi-quantum well detectors, the efficiency of said detectors being increased by virtue of the enhanced electric field associated with resonance in the cavity.