A new measurement method, scanned light pulse technique, for the investigation of the interface properties of metal–insulator–semiconductor (MIS) structures is introduced. The measured signal is the charge contents of current transients induced by light pulses applied to the investigated sample. This signal depends on surface potential, interface state density and voltage applied to the MIS structure. By analyzing the results of such measurements it is quantitatively demonstrated how insulator charge and interface state distribution influence the voltage dependence. By scanning a light spot across the surface of an MIS structure with transparent metal electrode it is further shown that pictures of the spatial variation of the surface potential and the interface state density can be obtained.

Scanned light pulse technique for the investigation of insulator-semiconductor interfaces

The surface potential of semiconductor devices in contact with electrolyte solutions is an important part of signal transduction for a variety of bioanalytical devices. Here we have investigated the lateral resolution at which the surface potential may be measured with a semiconductor-based device, a light-addressable potentiometric sensor (LAPS). We have first established an experimental setup where a permanent charge pattern is generated in the oxide-nitride interface of an n-doped silicon wafer by UV irradiation. Using a laser beam to interrogate the LAPS, the charge pattern can be detected by measuring the local photocurrent at a resolution of better than 100 μm. A theoretical model based on the diffusion and recombination of photogenerated minority charge carriers has been developed and solved analytically; it is consistent with experiment. For Beer-Lambert law absorption of a sufficiently narrow beam of interrogating light, according to the theory the lateral resolution depends on the relative sizes of the penetration depth of the light, d, and the recombination-diffusion length of the carriers, L. When d ⪡ L, the resolution is (2Ld) 1 2 ; when L ⪢ d, it is (2L 2 ) 1 2 .

Lateral resolution of light-addressable potentiometric sensors: an experimental and theoretical investigation

Microscopy using a scanning approach is reviewed, with numerous references to previous work, as at 1987, before the confocal laser scanning microscope was widely available commercially. The advantages of microscope imaging using a scanning technique are described. The principles of confocal microscopy are introduced. Use of Bessel beam illumination in a confocal microscope is discussed. This combination can increase spatial resolution while retaining some confocal optical sectioning. The advantages of imaging using a scanning method with a point source are detailed. For example, differential phase contrast may be performed to obtain phase information. Use of a point source allows different types of spectroscopy to be performed in a spatially resolved fashion. An advantage of point-source systems for such applications is that imaging, performed with the incident radiation, is separated from wavelength selection and analysis of the emitted radiation, thus simplifying system design and resulting in superior performance. Use of a point source to excite carriers in a semiconducting sample allows the electronic properties of materials and devices to be investigated. Advantages of object scanning, rather than beam scanning, are discussed. Advantages of using a laser source are described, including the use of the heterodyne technique as a synthetic confocal pinhole, and nonlinear microscopy such as two-photon fluorescence and CARS (coherent anti-Stokes Raman spectroscopy). It should be noted that 1987, as well as being before commercial confocal microscopes were widely available, was before the special properties of Bessel beams were appreciated, and before two photon fluorescence microscopy was first experimentally demonstrated.

Scanning Optical Microscopy

http://elib.bsu.by/bitstream/123456789/26350/1/Determination%20of%20Solar%20Cell%20Parameters%20from%20Its%20Current%E2%80%93Voltage%20and%20Spectral%20Characteristics.pdf

Determination of solar cell parameters from its current–voltage and spectral characteristics

In conventional light microscopy, images are formed either by direct imaging of the object at a desired magnification or by imaging the object onto a remote surface and converting the illuminance at that surface to an electrical signal. In laser scanning microscopy, the object or specimen surface is scanned point by point by a focused laser beam. The actual image or other pertinent characteristic of the object is then generated by an electronic system. Use of such scanned laser systems exists today in biomedical research, in the semiconductor microelectronics industry, and in varied other industrial inspection applications. In this paper, we review the basic principles of laser scanning microscopy, discuss advantages as compared to more conventional light microscopy, and illustrate the technique with examples of systems in use today.

Laser scanning microscopy

The use of a small spot of light for the detection of semiconductor inhomogeneities, is described. The method employed involves a scanned measurement of the surface photovoltage generated in the surface space charge region of the semiconductor. It is shown that scanned surface photovoltage signals may be used to detect defects in Si using either MOS, Schottky barrier or electrolyte contacts to sense the signal. Furthermore, from a spectral measurement it is possible to monitor the variation of carrier lifetime across the area of the sample. It has proven possible using the technique to detect both gross defects in the Si as well as to measure, on a point by point basis, the reduction in carrier lifetime due to them.

D.L. Lile

Papers

Semiconductor profiling using an optical probe