Wafer orientation sensor for GaAs wafers

A method for sensing orientation of a wafer having a light-transmission characteristic including a pass band and a stop band, comprising the steps of:

• rotating the wafer;
• directing light emitted by a light source toward an edge of the wafer as the wafer is rotated;
• sensing the light emitted by said light source with a light sensor as the edge of the wafer is rotated between said light source and said light sensor;
• and
• blocking light in the pass band of the wafer from reaching said light sensor.

A wafer orienter for a gallium arsenide wafer, comprising:

• a mechanism for rotating the wafer;
• and
• a wafer orientation sensor comprising:
• a light source for emitting light;
• a light sensor for sensing the light emitted by said light source as an edge of the wafer is rotated between said light source and said sensor and for producing a sensor signal representative of the sensed light;
• and
• an optical filter positioned between said light source and said light sensor, said optical filter having a light-transmission characteristic wherein light at wavelengths greater than about 860 nanometers is blocked.