Back to results
US 5,255,071 AGranted
Photoreflectance method and apparatus utilizing acousto-optic modulation
OwnerFred H. Pollak, Hong-En Sheninventors
Life of this patent
Estimating the term…
Loading patent…
Loading patent…
OwnerFred H. Pollak, Hong-En Sheninventors
Estimating the term…
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.
An apparatus for determining characteristics of materials by photoreflectance, comprising monochromatic light source means, means for directing the monochromatic light onto a sample to be examined, pump beam means for directing a beam of energy onto the sample including acousto-optical modulation means for modulating said beam at frequencies above those attainable by mechanical modulation, means for directing at least a part of the non-absorbed monochromatic light and of the non-absorbed modulated beam from the sample onto a detector means operable to produce a d.c. signal and an a.c. signal in its outputs, computer means, means for applying the d.c. signal from the detector means to an input of the computer means, a lock-in amplifier means receiving at its input the a.c. signal from the detector means and operatively connected with its output to another input of the computer means, and control means for keeping the substantially constant the operating conditions in a given experiment including variable means for varying the light intensity of the monochromatic light impinging on the sample and actuating means for controlling the variable means by an output from the computer means to maintain the d.c. signal substantially constant.
An apparatus for determining characteristics of materials by photoreflectance, comprising monochromatic light source means, means for directing the monochromatic light onto a sample to be examined, pump beam means for directing a beam of energy onto the sample including acousto-optical modulation means for modulating said beam at frequencies above those attainable by mechanical modulation, means for directing at least a part of the non-absorbed monochromatic light and of the non-absorbed modulated beam from the sample onto a detector means operable to produce a d.c. signal and an a.c. signal in its outputs, computer means, means for applying the d.c. signal from the detector means to an input of the computer means including an A/D converter, a two-phase lock-in amplifier means receiving at its output the a.c. signal from the detector means and operatively connected with its output to another input of the computer means, an control means for keeping substantially constant the operating conditions in a given experiment including variable means for varying the light intensity of the monochromatic light impinging on the sample and actuating means for controlling the variable means by an output from the computer means to maintain the d.c. signal substantially constant.
A method for obtaining information about trap times, especially at interfaces of semiconductors and semiconductor heterostructures, comprising the steps of
A method for obtaining information about identification of component layers and their quality and about the properties of the respective interfaces of semiconductors and semiconductor heterostructures, comprising the steps of
Dependencies are inferred from the claim text.