Method and apparatus for performing heterodyne lock-in imaging and quantitative non-contact measurements of electrical properties
First Claim
1. A method of producing an optical carrierographic image of a semiconductor sample, the method comprising:
- a) generating a first modulation signal having a first modulation frequency and a second modulation signal having a second modulation frequency, wherein a beat frequency between the first modulation frequency and the second modulation frequency is substantially less than both the first modulation frequency and the second modulation frequency;
b) generating a reference signal having a reference frequency equal to the beat frequency;
c) providing a first optical beam and a second optical beam, the first optical beam and the second optical beam having wavelengths selected for excitation of carriers within the semiconductor sample;
d) focusing and spatially overlapping the first optical beam and the second optical beam onto a location of the semiconductor sample;
e) modulating the first optical beam according to the first modulation signal and modulating the second optical beam according to the second modulation signal;
f) detecting, with an infrared detector, infrared radiation emitted from the semiconductor sample in response to absorption of the first optical beam and the second optical beam, and obtaining a plurality of carrierographic signals at different points in time during at least one beat period; and
g) providing the reference signal to a lock-in amplifier and processing the carrierographic signals with the lock-in amplifier to obtain an amplitude signal and a phase signal.
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Abstract
Methods are provided for producing optical carrierographic images of a semiconductor sample. Focused and spatially overlapped optical beams excite carriers across within the semiconductor sample, where the optical beams are modulated such that a beat frequency is substantially less than either modulation frequency. An infrared detector detects infrared radiation emitted from the semiconductor sample in response to absorption of the optical beams, thereby obtaining a plurality of carrierographic signals at different points in time during at least one beat period, which are processed with a lock-in amplifier, with a reference signal at the beat frequency, to obtain an amplitude signal and a phase signal. Carrierographic lock-in images of the sample are obtained in a scanning configuration, or in an imaging format using an imaging detector. The images carry quantitative information about recombination lifetimes in substrate Si wafers and electrical parameters in solar cells, namely photogeneration current density, diode saturation current density, ideality factor, and maximum power photovoltage.
21 Citations
40 Claims
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1. A method of producing an optical carrierographic image of a semiconductor sample, the method comprising:
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a) generating a first modulation signal having a first modulation frequency and a second modulation signal having a second modulation frequency, wherein a beat frequency between the first modulation frequency and the second modulation frequency is substantially less than both the first modulation frequency and the second modulation frequency; b) generating a reference signal having a reference frequency equal to the beat frequency; c) providing a first optical beam and a second optical beam, the first optical beam and the second optical beam having wavelengths selected for excitation of carriers within the semiconductor sample; d) focusing and spatially overlapping the first optical beam and the second optical beam onto a location of the semiconductor sample; e) modulating the first optical beam according to the first modulation signal and modulating the second optical beam according to the second modulation signal; f) detecting, with an infrared detector, infrared radiation emitted from the semiconductor sample in response to absorption of the first optical beam and the second optical beam, and obtaining a plurality of carrierographic signals at different points in time during at least one beat period; and g) providing the reference signal to a lock-in amplifier and processing the carrierographic signals with the lock-in amplifier to obtain an amplitude signal and a phase signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
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Specification