Patent ID: 9442078
Filing Date: 2016-09-13
CPC Classification: G01N,G01Q

Claim Text:
1. A method of measuring carrier density in a semiconductor sample, the method comprising: a. placing the semiconductor sample in a scanning tunneling microscope for analysis, said microscope having control electronics and a source for providing a bias voltage, a space between a tip electrode of said scanning tunneling microscope and the surface of the semiconductor sample being defined as a tunneling junction, an area directly beneath the tip electrode on the semiconductor sample through which charge carriers pass being defined as a spot; b. applying a forward bias voltage to the tunneling junction such that no depletion region is created in the semiconductor sample; c. projecting a pulsed output of a mode-locked laser onto the tunneling junction at a chosen repetition frequency in a manner to generate a microwave frequency comb with a fundamental frequency and a plurality of harmonic frequencies at integer multiples of a pulse repetition rate of the laser; d. measuring power output of the microwave frequency comb for at least one given frequency; e. determining attenuation of the power output of the microwave frequency comb due to spreading resistance of the semiconductor sample at the defined spot; f. calculating carrier density at the given spot from the attenuation.