Other

Yeshiva University

Brooklyn College Foundation

Brooklyn College Research and Development Foundation

Fred H Pollak

Hong-En Shen

Paul M Raccah

Gerald Lucovsky

Arthur Bradley

J M Woodall

Hal C Felsher

P A Montano

Xiaoming Yin

A method and apparatus for a contactless mode of electroreflectance (ER) which utilizes a condenser-like system, of which the front electrode is light transparent, i.e., for instance, consists of a transparent conductive coating on a transparent substrate which is separated from the sample surface by a thin layer of air. With the use of the method and apparatus of this invention, the contactless electroreflectance spectra could be measured at 300K from a number of materials including semi-insulating bulk GaAs, bulk Si, bulk Hg.sub.0.75 Cd.sub.0.25 Te, a GaAs structure with large uniform electric field and a GaAs/GaAlAs coupled double quantum well.

Contractless mode of electroreflectance

A method and apparatus for determining the characteristics of materials, particularly of semiconductors, semiconductor heterostructures and semiconductor interfaces by the use of photoreflectance, in which monochromatic light and modulated light beam reflected from the sample is detected to produce a d.c. signal and an a.c. signal, whereby the d.c. signal is applied to one input of a computer and the a.c. signal is used with another input of the computer which controls the light intensity of the monochromatic light impinging on the sample to maintain the d.c. signal substantially constant. A stepping motor is preferably utilized for varying the light intensity of the monochromatic light which is controlled by a computer to re-establish rapidly a predetermined d.c. signal established during normalization procedures when the light intensity of the monochromatic light changes, especially during change of its wavelength. Additionally, the modulation frequency of the modulated beam and/or the wavelength of the monochromatic light can also be varied by the computer.

Method and apparatus for determining a material's characteristics by

A method and apparatus for determining the characteristics of materials, particularly of semi-conductors, semi-conductor heterostructures and semi-conductor interfaces by the use of photoreflectance, in which monochromatic light and modulated light beam reflected from the sample is detected to produce a d.c. signal and an a.c. signal, whereby the d.c. signal is applied to one input of a computer and the a.c. signal is used with another input of the computer which controls the light intensity of the monochromatic light impinging on the sample to maintain the d.c. signal substantially constant. A stepping motor is preferably utilized for varying the light intensity of the monochromatic light. Additionally, the modulation frequency of the modulated beam and/or the wavelength of the monochromatic light can also be varied by the computer. Growth conditions of semi-conductor materials as well as information about trap times can be obtained by analyzing the energy band gaps and determining the dependence of the in-phase photoreflectance signal on the pump modulating frequency, respectively.

A method for determining information about properties at interfaces of semi-conductor materials in which a probe bean monochromatic light is directed onto a material sample which is itself electromodulated by a modulated pump beam, whereby the light reflected from the sample is detected to produce a d.c. signal and an a.c. signal, and after normalizing the procedure, the shifts of energy gaps in the band gaps are evaluated to obtain information about at least one externally applied parameter crossing such shift.

Method for determining interface properties of semiconductor materials

A method and apparatus for determining the characteristics of materials, particularly of semi-conductors, semi-conductor heterostructures and semi-conductor interfaces by the use of photoreflectance, in which monochromatic light and an acousto-optically modulated light beam reflected from the sample is detected to produce a d.c. signal and an a.c. signal, whereby the d.c. signal is applied to one input of a computer and the a.c. signal is used with another input of the computer which controls the light intensity of the monochromatic light impinging on the sample to maintain the d.c. signal substantially constant. The modulation frequency of the modulated pump beam and/or the wavelength of the monochromatic light can also be varied by the computer. Information about trap times can be obtained by determining the dependence of the in-phase signal on the pump modulating frequency, respectively.

Photoreflectance method and apparatus utilizing acousto-optic modulation

A method for in-situ determination by photoreflectance of the Fermi level (V.sub.F) at the surfaces or interfaces of GaAs and related materials, in which a probe beam of monochromatic light and a modulated pump beam from a pump source are directed onto a sample, and the measured barrier height V.sub.m =V.sub.F -V.sub.S is obtained from the information in the reflected light, where V.sub.S represents the surface voltage effects on the sample by the photoreflectance, whereby V.sub.m approaches V.sub.F as V.sub.S approaches zero during repeated tests in which a parameter such as temperature affecting the numerical value of V.sub.S is changed until there is flattening of the curve illlustrating V.sub.m as a function of the parameter.

Method for in-situ determination of the fermi level in GaAs and similar

The photovoltaic converter of the present invention comprises a thin film consisting essentially of a lattice of stacked carbon chains comprising alternating single and double bonds deposited on the surface of an electrode transparent to sunlight. The carbon lattice is prepared in situ by depositing and exposing a plastic film comprising a highly oriented polymer system to heat or other types of radiation for controlled degradation. The exposed surface of the degraded film is then covered with a vapor-deposited coating of aluminum, and is finally compressed with a metal electrode cover. Illumination directed onto the film induces an electromotive force at the interface of the degraded polymer and the transparent electrode, which constitutes a 'Schottky barrier'. A particular feature is the addition of the preformed polymer coating before degradation of electron-attracting molecules which serve as conductive bridges between the carbon layers in the residue.

Thin film photovoltaic converter and method of preparing same

There is disclosed an apparatus and method for measuring the variations in composition across the surface of binary and ternary alloy semiconductors utilizing electrolyte electroreflectance. The technique is non-destructive, can readily be employed under atmospheric conditions at room temperature, and is sensitive enough to determine changes of composition of about 1% with a spatial resolution of about 100.mu.. The procedure is very useful for the selection of crystals for detector arrays, solid states lasers, or electronic devices. It can also be utilized as a convenient tool for evaluating material grown either in bulk form or epitaxial layers, thus providing feedback for the adjustment of crystal growth parameters. The apparatus includes a mechanism for stepping the semiconductor being investigated in two dimensions while performing electroreflectance measurements; the measurement results can then be plotted on contour maps.

Growing community of inventors

New York, NY, United States of America

Fred H Pollak