年間 12 号発行
ISSN 印刷: 0040-2508
ISSN オンライン: 1943-6009
Indexed in
Photomodulation Microwave Diagnostics of Semiconductor Structures
要約
In modern contactless nondistructive microwave diagnostics of semiconductor materials, a tendency is actively developed of applying modulation methods to measuring information signals; these methods ensure an increase in measurement sensitivity and accuracy and reduce the dependence of the results on various interfering factors [1-3]. The idea is to form the output signal of the measuring transducer by modulating (most often, harmonically) one of the electrophysical characteristics of the sample studied and selecting the corresponding variation of one of the parameters of the measuring transducer.
Most often the semiconductor conductivity is modulated, and the modulation is realized by illumination of the sample using optical radiation in the region of the material photosensitivity (photomodulation) [1, 3, 4]. For this reason the corresponding methods are called photomodulation. In this case the sample photoconductivity is studied, and the aim of the designers of the corresponding method is to obtain the most complete information on the various properties of the studied semiconductor structure and to ensure the independence of this information from the practical details of obtaining it (from the so-called interfering factors). Usually among the characteristics of multilayer semiconductor structures to be determined in the first place are the thickness h and conductivity σ of each of the layers, dielectric permeability of the material ε, photoconductivity Δσ, lifetime τ, charge carrier mobility μ, surface recombination velocity S, their distribution across the layers, and sometimes some other parameters. At the same time, the effect of the power of the feeding generator, the characteristic microwave detector nonlinearity, illumination intensity, the positioning of the sample in the measuring transducer, and various random factors (such as sample misalignment, gaps between the sample and the measuring transducer, etc.) on measurement results constitute the interfering factors of microwave diagnostics complicating the acquisition of information and leading to its distortion.
A fundamental constructive solution that would eliminate the effect of interfering factors is the choice of an interference-invariant signal at the output of the measuring transducer or the use of measuring information obtained from the ratio (difference) of signals obtained under different conditions with the same interfering factors.