SiGe Single Crystals Research Articles

Growth and Characterization of Bulk Si–Ge Single Crystals

Si–Ge single crystals, 7 mm in diameter and about 20 mm long with compositions ranging from 0 to 50 at.% Si were grown by the traveling solvent method. The compositions of the crystals were shown to be uniform parallel and perpendicular to the growth axis using EPMA measurement. Raman spectra indicated that the ratio of the numbers of Si–Ge and Ge–Ge bonds agreed with that expected for a random distribution of Si and Ge atoms. The band gap energy of the alloy increased linearly up to 15 at.% Si and increased gradually above 15 at.% Si. From photoluminescence measurements done under uniaxial stress along the <111> direction, it was shown that the dependence of excitonic no-phonon spectrum on the stress changed at about 15 at.% Si. These results indicated that the position of the conduction band minimum of Si–Ge alloy in the k-space changed at about 15 at.% Si.

Si-Ge solid solution single crystal growth by electron beam floating zone technique

A new method is suggested to grow single crystals of Si-Ge solid solutions. Growth has been carried out by zone melting of Si-Ge ingots of varying composition, with Si single crystals used as seeds. It has been shown that the growing crystals lose their single-crystalline nature owing to constitutional supercooling. Decrease in Ge concentration in the initial ingot or in diameter results in increase of the Ge concentration limit in Si-Ge single crystals up to 50 at%. Solid solution single crystals containing more Ge can be obtained if they are grown in the direction opposite to that of gravitation.

Interface properties of oxidized germanium-doped silicon

Czochralski-grown Si-Ge single crystals, with several atomic per cent of Ge, were investigated from the aspects of their oxide interface properties and their suitability for MOS device making. It was found that the oxide formed is almost pure SiO2, but the C(V) curve of both n- and p-type MOS capacitors is shifted in the positive direction by an amount dependent on the oxidation rate and the Ge diffusion coefficient in Si, thereby showing the existence of a negative interface charge. The surface state density function was measured using the high-frequency and the quasistatic capacitance methods and was found to have more peaks, located near the middle of the gap, than the normal Si function. The states were mainly of the acceptor type. Their number, established by the variable temperature method or by the length of the flat region (`ledge') of the C(V) curve which forms at liquid nitrogen temperature, was one to two orders of magnitude larger than in Si but could be much reduced by annealing. The capture cross section, measured by the conductance method, was larger than in Si and varied by jumps along the band gap. MOS transistors of the n-channel enhancement type were made and were found to have a relatively low mobility.