Гулямов, Г., Н. Ю. Шарибаев, and У. И. Эркабоев. “The Thermal Broadening of the Density of States and the Temperature Dependence of the Width of the Forbidden Band Ge”. Journal of Surface Physics and Engineering, Vol. 10, no. 4, Sept. 2012, pp. 366 -70, https://periodicals.karazin.ua/pse/article/view/10139.