Semitest, Inc.

Optical Diagnostic Systems, Inc.

William C Goldfarb

Emil Kamieniecki

Leszek Reiss

Mike Wollowitz

Michael Wollowitz

A method is provided for determining the minority carrier surface recombination lifetime constant (t.sub.s) of a specimen of semiconductor material. The specimen is positioned between a pair of electrodes, the specimen being disposed on one of the electrodes and being spaced form the other electrode. A signal is provided corresponding to the capacitance between the specimen and the electrode spaced from the specimen. A region of the surface of the specimen is illuminated with a beam of light of predetermined wavelengths and which is intensity modulated at a predetermined frequency and varying in intensity over a predetermined range. A fixed bias voltage V.sub.g applied between the pair of electrodes, the fixed bias voltage being of a value such that the semiconductor surface is in a state of depletion or inversion,. A signal is provided representing the ac photocurrent induced at the region of the specimen illuminated by the light beam. The intensity of the light beam and frequency of modulation of the light beam are selected such that the ac photocurrent is nearly proportional to the intensity of the light beam and reciprocally proportional to the frequency of modulation of the light beam. A signal is provided corresponding to the illumination intensity of the beam of light. The surface minority carrier recombination time constant (t.sub.s) is then determined using the ac photocurrent capacitance and illumination intensity information.

Method for determining the minority carrier surface recombination

An apparatus for making ac surface photovoltage (SPV) measurements of a specimen of semiconductor material under dc bias voltage conditions includes a light source whose output beam is intensity modulated, an adjustable dc bias voltage source, a conductive base for supporting the specimen and a novel capacitance type reference electrode assembly for sensing the SPV signals. The reference electrode assembly includes in one embodiment a button made of insulating elastomeric material and attached to a rigid plate made of insulating material. A film made of insulating material and having a conductive coating on one side which serves as a reference electrode is attached to the button. When SPV measurements are being taken, the film is pressed against the specimen with pressure sufficient to hold the reference electrode in close compliance with the specimen, with pressure being applied to the plate from an external source and being transmitted from the rigid plate to the film through the elastomeric button.

Apparatus for making surface photovoltage measurements of a semiconductor

An apparatus for making ac surface photovoltage (SPV) measurements of a specimen of semiconductor material under dc bias voltage conditions includes a light source whose output beam is intensity modulated, an adjustable dc bias voltage source, a conductive base for supporting the specimen and a novel capacitance type reference electrode assembly for sensing the SPV signals. The reference electrode assembly includes in one embodiment a transparent flexible sheet of insulating material having on one surface a first conductive coating which serves as a reference electrode and a second conductive coating which serves as a guard electrode, the first coating being transparent. The flexible sheet of insulating material is attached to a flat glass plate through an annular spacer. An elastomeric button is positioned between the sheet and the glass plate. When the SPV measurements are being taken the flexible sheet is pressed against the specimen with pressure sufficient to hold the reference electrode in close compliance with the specimen, with the pressure being applied to the glass plate and being transmitted from the glass plate to the flexible sheet of insulating material through the elastomeric button.

A method and apparatus are described for the nondestructive readout of a latent electrostatic image formed on a sheet or layer of insulating material. A sheet or layer of semiconductor material is disposed in relatively close proximity to the insulating material. A latent electrostatic image formed on the insulating material (by any known means) causes a surface depletion layer to be produced by induction at the surface of the semiconductor material. The location and distribution of the accumulated charges on the semiconductor material are read out as analog electrical signals corresponding to the AC surface photovoltage induced on the semiconductor material as the semiconductor material is scanned with a low intensity modulated light beam of appropriate wavelength, the magnitude of the analog signals depending on the local charge density. The analog electrical signals so obtained are then digitized, processed and stored and/or displayed.

Nondestructive readout of a latent electrostatic image formed on an

A method and apparatus are described for the nondestructive readout of a latent electrostatic image formed on a sheet or layer of insulating material. A sheet or layer of semiconductor material is disposed in relatively close proximity to the insulating material. A latent electrostatic image formed on the insulating material (by any known means) causes a surface depletion layer to be produced by induction at the surface of the semiconductor material. The location and distribution of the accumulated charges on the semiconductor material are read out as analog electrical signals corresponding to the AC surface photovoltage induced on the semiconductor material as the semiconductor material is scanned with a low intensity modulated light beam of appropriate wavelength, the magitude of the analog signals depending on the local charge density. The analog electrical signals so obtained are then digitized, processed and stored and/or displayed.

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Melrose, MA, United States of America

William C Goldfarb