A review is given of low-temperature studies of the properties of the two-dimensional electron gas in inversion layers on high-index Si surfaces. The long crystallographic periods associated with such surfaces produce the superlattice effect in the spectrum of the quasi-two-dimensional electron gas. The kinetic coefficients are found to exhibit singularities when the Fermi level and minigaps cross. This was established by measuring the static and the high-frequency conductivities, the Shubnikov--de Haas oscillations, the photoresistivity, the emission of thermal electrons, and the cyclotron resonance in $n$-type inversion layers near (001) for electron concentrations in the range 10$^{12}$ -- 10$^{14}$ cm$^{-2}$. The minigap width varies from 1 to 20 meV, depending on the electron concentration. The position of the minigaps in $K$-space (but not their size) is in quantitative agreement with theory.

@article{Volkov:1980,
	author = {V. A. Volkov and V. A. Petrov and V. B. Sandomirskii},
	title = {The high-index surface—a superlattice for two-dimensional electrons},
	publisher = {Physics-Uspekhi},
	year = {1980},
	journal = {Phys. Usp.},
	volume = {23},
	number = {7},
	pages = {375-385},
	url = {https://ufn.ru/en/articles/1980/7/d/},
	doi = {10.1070/PU1980v023n07ABEH005116}
}