Low Temperature Conductivity inn-Type Noncompensated Silicon below Insulator-Metal Transition

Abstract

We investigate the transport properties ofn-type noncompensated silicon below the insulator-metal transition by measuring the electrical and magnetoresistances as a function of temperatureTfor the interval 2–300 K. Experimental data are analyzed taking into account possible simple activation and hopping mechanisms of the conductivity in the presence of two impurity bands, the upper and lower Hubbard bands (UHB and LHB, resp.). We demonstrate that the charge transport develops with decreasing temperature from the band edge activation (110–300 K) to the simple activation with much less energy associated with the activation motion in the UHB (28–90 K). Then, the Mott-type variable range hopping (VRH) with spin dependent hops occurs (5–20 K). Finally, the VRH in the presence of the hard gap (HG) between LHB and UHB (2–4 K) takes place. We propose the empiric expression for the lowTdensity of states which involves both the UHB and LHB and takes into account the crossover from the HG regime to the Mott-type VRH with increasing temperature. This allows us to fit the lowTexperimental data with high accuracy.

Low temperature injected-caused charge carrier instability in n-type silicon below insulator-to-metal transition

“…We believe that the discovered patterns are due to the manifestation of the following physical processes. As was shown earlier, the mechanism of current transport in the initial part of the CVCs is mainly of the activated-type due to the predominant capturing of the electrons by neutral impurity states D 0 in the LHB that transforms them into negatively charged D − states [27,28]. The dominance of this activation mechanism causes a negative sign of the TCR (insulating-like behavior).…”

“…They promote charge transfer with the activation energy ε a , which corresponds to the evaluated Hubbard parameters. In other words, the value of ε a = 1.48 meV [28] could be interpreted as the energy of Coulomb fluctuations in the UHB.…”

“…Recently, the peculiarities of conductivity in non-compensated silicon doped with Sb (10 18 cm −3 ) have been investigated [25][26][27][28]. It was found that in the temperature (T) range of 28-90 K an activation mechanism with an energy of 1.73 meV occurs due to motion of electrons along the almost delocalized states.…”

Delocalization of electron states in n-Si at low temperatures

“…Обнаруженный кроссовер в знаке ТКС при росте тока свидетельствует о следующих физических процессах. На начальных участках ВАХ механизм переноса заряда в основном активационного типа вследствие захвата носителей заряда нейтральными D 0 состояниями нижней зоны Хаббарда и их трансформации в Dсостояния верхней зоны Хаббарда (ВЗХ) [6]. В этом случае наблюдается отрицательный ТКС [5,6].…”

“…Образцы помещались в криогенную вставку (Cryogenic Ltd., London) со сверхпроводящим магнитом. Подробнее детали эксперимента описаны в работах [5,6].…”