Apparatus for making surface photovoltage measurements of a semiconductor

An apparatus for use in sensing ac surface photovoltage signals induced in a specimen of semiconductor material under dc bias voltage conditions, said specimen having first and second major surfaces, said apparatus comprising:

• a. means for illuminating a portion of said first major surface of said specimen with a beam of intensity modulated light,
• b. a conductive nonmagnetic support for receiving said second main surface of said specimen,
• c. a dc bias voltage source, and
• d. a capacative reference electrode assembly for sensing the surface photovoltage induced at said first major surface in response to said illumination, said capacative reference electrode assembly comprising:
• i. a sheeet of transparent nonconductive material,
• ii. a rigid transparent disc disposed above said sheet of transparent nonconductive material,
• iii. a ring of magnetic material fixed to said disc,
• iv. a reference electrode on said disc,
• v. a frame fixed to said sheet and flexibly attached to said ring, and
• vi. magnetic means underneath said conductive support for selectively magnetically attracting said ring toward said specimen.

An apparatus for use in sensing ac surface photovoltage signals induced in a specimen of semiconductor material under dc bias voltage conditions, said specimen having first and second major surfaces, said apparatus comprising:

• a. means for illuminating said specimen with a beam of intensity modulated light,
• b. a conductive support for receiving said second major surface of said specimen,
• c. a dc bias voltage source,
• d. a capacative reference electrode assembly for sensing the surface photovoltage induced at said first major surface in response to illumination, said capacative reference electrode assembly comrising:
• i. a transparent rigid reference electrode positionable along the path of the beam of light and spaced from said specimen,
• ii. an insulator disposed in front of said transparent reference electrode, and
• iii. piezoelectric means for controlling the position of the reference electrode, and
• iv. a frame for supporting said light source and said reference electrode assembly.

Apparatus for use in making ac surface photovoltage measurements of a specimen of semiconductor material under variable dc bias voltage conditions, said specimen having first and second major surfaces, said apparatus comprising:

• a. means for illuminating at least a portion of said first major surface of said specimen with a beam of intensity modulated light,
• b. a back electrode adapted to receive said second major surface of said specimen,
• c. a flexible reference electrode assembly positionable in the path of said light beam in close proximity to said first major surface of said specimen, said reference flexible electrode assembly comprising:
• i. a reference electrode, and
• ii. a support for supporting said reference electrode,
• d. means for applying a variable dc bias voltage between said back electrode and said reference electrode,
• e. the ac surface photovoltage signals generated by said light beam appearing between said reference electrode and said back electrode.

A capacitive pickup type reference electrode assembly for use in making ac surface photovoltage measurements of a specimen of semiconductor material, said reference electrode assembly comprising:

• a. a support having a back portion and a front portion,
• b. an insulator attached to the front portion of the support, and
• c. a reference electrode disposed behind the insulator,
• d. one of said reference electrode and said support being flexible,
• e. means between said back portion of said support and said reference electrode for transmitting pressure applied to said back portion of said support to said reference electrode, and

A reference electrode assembly for use in an apparatus for making ac surface photovoltage measurements of a specimen of semiconductor material, said reference electrode assembly comprising:

• (i) a frame,
• (ii)a flexible diaphragm attached to said frame, said flexible diaphragm comprising a first sheet of transparent flexible insulating material having a coating of transparent conductive material on at least a portion of one side thereof, said coating constituting a reference electrode, said frame and said diaphragm defining a chamber, and
• (iii) means in said chamber for transmitting pressure applied to said frame to said diaphragm,
• (iv) said first sheet of flexible transparent insulating material also including a conductive coating serving as a guard electrode.

A reference electrode assembly for use in apparatus for making ac surface photovoltage measurements of a specimen of semiconductor material, said reference electrode assembly comprising:

• (a) a frame,
• (b) a flexible diaphragm attached to said frame, said flexible diaphragm comprising a first sheet of transparent flexible insulating material having a coating of transparent conductive material on at least a portion of one side thereof, said coating constituting a reference electrode, said frame and said diaphragm defining a chamber, and
• (c) means in said chamber for transmitting pressure applied to said frame to said diaphragm, said means comprising an elastomeric button, said elastomeric button having:
• (a) a conductive, elastomeric inner section, and
• (b) a transparent, insulating, elastomeric outer section.

A reference electrode assembly for use in apparatus for making ac surface photovoltage measurements of a specimen of semiconductor material, said reference electrode assembly comprising:

• (a) a frame,
• (b) a flexible diaphragm attached to said frame, said flexible diaphragm comprising a first sheet of transparent flexible insulating material having a coating of transparent conductive material on at least a portion of one side thereof, said coating constituting a reference electrode, said frame and said diaphragm defining a chamber, and
• (c) means in said chamber for transmitting pressure applied to said frame to said diaphragm, said means comprising an elastomeric button, said elastomeric button having:
• (i) a transparent inner elastomeric section,
• (ii) a conductive, opaque, elastomeric intermediate section, and
• (iii) an insulating, opaque, elastomeric outer section.

Apparatus for use in making ac surface photovoltage measurements of a specimen of semiconductor material under variable dc bias voltage conditions, said specimen having first and second major surfaces, said apparatus comprising:

• (a) means for illuminating at least a portion of said first major surface of said specimen with a beam of intensity modulated light,
• (b) a back electrode adapted to receive said second major surface of said specimen,
• (c) a flexible reference electrode assembly positionable in the path of said light beam in close proximity to said first major surface of said specimen,
• (d) means for applying a variable dc bias voltage between said back electrode and said reference electrode, and
• (e) the ac surface photovoltage signals generated by said light beam appearing between said reference electrode and said back electrode.

A capacitive pickup type reference electrode assembly for use in apparatus for making ac surface photovoltage measurements of a specimen of semiconductor material, said capacitive pickup type reference electrode assembly comprising:

• a. a rigid support having a back portion and a front portion,
• b. a flexible reference electrode attached to the front portion of said support,
• c. an elastomeric button for transmitting pressure applied to the back portion of said rigid support to said flexible reference electrode and
• d. a sheet of flexible insulating material having a back surface and a front surface, said flexible reference electrode comprising a coating on said back surface of said sheet of flexible insulating material.

A reference electrode assembly for use in apparatus for making surface photovoltage measurements of a specimen of semiconductor material comprising:

• a. a plate of transparent rigid material having a top side and a bottom side,
• b. a sheet of transparent flexible insulating material having a top side and a bottom side attached along the periphery of its top side to the bottom side of the plate of transparent rigid material,
• c. an elastomeric button sandwiched between said plate of transparent rigid material and said sheet of transparent flexible insulating material, and
• d. a conductive coating on the top side of said sheet of transparent flexible insulating material, said conductive coating constituting a reference electrode.