Semiconductor Surface Carrier Recombination Velocity Measurement
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Solution Overview
Problem
Current methods for measuring surface carrier recombination velocity and surface Fermi level in semiconductor devices are inefficient, requiring different measurement conditions and techniques, leading to uncertainty in correlating these parameters and increasing evaluation time and cost, especially due to the need for weak probe beams that reduce signal-to-noise ratio and are inapplicable to materials with weak photoluminescence intensity.
Innovation Solution
A modulation spectroscopic method that irradiates a pump beam and a probe beam onto a semiconductor sample to measure PR spectra, allowing for simultaneous non-destructive and contactless determination of surface carrier recombination velocity and surface Fermi level from Franz-Keldysh oscillations, even with high-power probe beams, by calculating surface electric field strength and plotting it as a function of probe beam power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a weak probe beam is used to suppress the photovoltaic effect, then the surface electric field strength is maintained, but the signal-to-noise ratio is reduced
Solution Approach 1:
The patent applies periodic modulation to the probe beam (e.g., intensity modulation or frequency modulation) to generate time-varying signals that can be detected using lock-in amplification techniques. This periodic action allows the system to use higher average probe beam power while maintaining the ability to suppress photovoltaic effects through synchronous detection, thereby improving the signal-to-noise ratio without sacrificing measurement precision of the surface electric field strength.
2Measurement precision
If different measurement methods are used for surface Fermi level and surface recombination velocity, then each parameter can be measured, but the evaluation time and cost increase
Solution Approach 1:
The patent combines the measurement of surface Fermi level and surface recombination velocity into a single integrated PR spectroscopy measurement process. By simultaneously analyzing the Franz-Keldysh oscillations in the PR spectrum, both parameters can be extracted from the same measurement data set using a unified analysis method, eliminating the need for separate measurement setups and procedures. This merging approach significantly reduces evaluation time and cost while maintaining measurement precision for both parameters.
3Measurement precision
If conventional PR measurement is used with weak probe beam, then photovoltaic effect is suppressed, but the method is inapplicable to materials with weak photoluminescence intensity
Solution Approach 1:
The patent employs periodic modulation of the probe beam combined with frequency-resolved detection to enhance the detectability of Franz-Keldysh oscillations. The modulation technique converts weak optical signals into stronger electrical signals through demodulation, allowing the measurement to be applied to materials with weak photoluminescence intensity. This approach maintains suppression of photovoltaic effects while extending the method's applicability to a broader range of semiconductor materials.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise and simultaneous measurement of surface carrier recombination velocity and surface Fermi level, reducing evaluation time and cost, and improving the accuracy of semiconductor device design by correlating these parameters effectively.
Implementation Method 1
it has been considered necessary to eliminate a photovoltaic effect caused by continuous probe beam irradiation because the photovoltaic effect reduces the surface electric field strength
Implementation Method 2
in the spectrum of a semiconductor sample having a built-in electric field obtained by PR modulation spectroscopy, an oscillation pattern, called a Franz-Keldysh (hereinbelow abbreviated as FK) oscillation, appears near the critical point of the optical transition energy
Data Source
AI summary
A pump beam irradiates the surface of a semiconductor sample through modulator while irradiating the surface with a probe beam so that a detector measures a light-modulated spectrum of the probe beam reflected from the surface of the semiconductor sample. Then, surface electric field strength is calculated from the period of Franz-Keldysh oscillations appearing in the light-modulated spectrum, and the surface recombination velocity and surface Fermi level are calculated based on a relation between the surface electric field strength and the probe beam power density.