The study of charge carrier kinetics in semiconductors by microwave conductivity measurements. II.The study of the excess conductivity induced in a material by pulsed optical excitation yields information on the optoelectronic properties of the material and is receiving increasing attention. As conventional conductivity techniques are hampered by the need to apply electrical contacts, we have investigated the reliability and the possibilities of microwave conductivity measurements. This paper first presents the general background for excess conductivity measurements in the microwave range, and then derives the quantitative relationship between the reflected microwave signal and the change in conductivity for a wafer of single-crystalline Si. For this sample, the theory of excess charge carrier kinetics is also developed. After a short description of our apparatus, kinetic measurements on a nano-and microsecond timescale are compared to theory.

No abstract

No abstract

In previous work [J. Appl. Phys. 60, 3558 (1986)] an introduction was given to the study of charge carrier kinetics in semiconductors by microwave conductivity measurements. This paper compares quantitatively our experimental results to theoretical calculations for single-crystalline Si wafers, taking into account the dependence on the microwave frequency and the dark conductivity of the sample, which ranged from σ=0.2 to 400 Ω−1 m−1. In particular, difficulties arising from experimental conditions that cannot easily be treated by theory are discussed. It is shown that quantitative measurements of samples with low dark conductivity can be performed even in a very simple configuration, which permits determination of the sum of charge carrier mobilities.

The design of a pulse radiolysis system for absorption and emission spectroscopy with a response down to 60 psec is described. Events which occur with response times of about 10 psec may also be observed by observing the development of these species during the radiation pulse. The system has been used to investigate the mode of formation of solute excited states in cyclohexane, the benzene excimer in pure benzene, and the rate of formation of solvated electrons in ethanol and 1-propanol. The data show that the excited singlet state of cyclohexane is formed rapidly (<10 psec) in radiolysis, and has a decay constant of 3.6 X 10® sec-1. The state transfers energy to added solutes such as benzene, with ft -2.2 X 1011 M-1 sec-1; CCI4, ft = 2.5 X 1011 M-1 sec-1; and 9,10-diphenylanthracene, ft = 3.4 X 1011 M-1 sec-1. No significant yield of the triplet state of the aromatic solutes is observed in pseconds contrary to the large yields of triplets observed in nseconds. The anions and cations of the aromatic solutes are also observed, and exhibit rapid formation but little decay in pseconds. The excimer state of benzene is observed to appear with a delay of 10 psec, and this is considered to be the result of prior formation of the monomer singlet followed by the complexing time which is calculated to be 7 psec. The solvated electron in ethanol is formed rapidly but with a possible delay of 2-5 psec, while the solvated electron in 1-propanol is formed over 50 psec. The data are discussed in terms of current theories of radiation chemistry.

No abstract

No abstract

No abstract