Silicon quantum dots embedded in a SiO2matrix: From structural study to carrier transport properties

Abstract

We study the details of electronic transport related to the atomistic structure of silicon quantum dots embedded in a silicon dioxide matrix using ab initio calculations of the density of states. Several structural and composition features of quantum dots (QDs), such as diameter and amorphization level, are studied and correlated with transport under transfer Hamiltonian formalism. The current is strongly dependent on the QD density of states and on the conduction gap, both dependent on the dot diameter. In particular, as size increases, the available states inside the QD increase, while the QD band gap decreases due to relaxation of quantum confinement. Both effects contribute to increasing the current with the dot size. Besides, valence band offset between the band edges of the QD and the silica, and conduction band offset in a minor grade, increases with the QD diameter up to the theoretical value corresponding to planar heterostructures, thus decreasing the tunneling transmission probability and hence the total current. We discuss the influence of these parameters on electron and hole transport, evidencing a correlation between the electron (hole) barrier value and the electron (hole) current, and obtaining a general enhancement of the electron (hole) transport for larger (smaller) QD. Finally, we show that crystalline and amorphous structures exhibit enhanced probability of hole and electron current, respectively.

Energetics and carrier transport in doped Si/SiO2quantum dots

“…Structural and optical properties of the embedding SiO 2 match well those of a "true" amorphous SiO 2 glass (a-SiO 2 ), formed by annealing. 52 As reported in a previous study 44 the presence of quan-tum confinement makes valence band offset (VBO) and conduction band offset (CBO) between Si-QDs and SiO 2 significantly different than in bulk or planar systems. In order to evaluate the band offset between SiO 2 and QD, we have aligned the DOS of an a-SiO 2 sample with that of the embedded Si-QD by matching the strong deepvalence peak of a-SiO 2 , which is well observable in all the considered structures.…”

“…With the same approach we investigated, in a previous work, the influence of QD size and amorphization level on the transport properties of undoped Si-QDs. 44 We compute the I-V characteristic between two metallic semi-infinite electrodes coupled to an elastic scattering region (corresponding to the doped Si-QD embedded in the silica matrix) when an external bias voltage V is applied (see Fig. 1).…”

“…The results are compared with the corresponding undoped case 44 (the separate electron and hole contributions to the total current, as a function of the applied voltage, are reported in the Supplementary Information †). In the results of Fig.…”

Моделирование Методом Сильной Связи Кремниевых И Германиевых Нанокристаллов О Б З О Р

“…Развитие компью-терной техники существенно расширило возможности расчeтов из первых принципов, что позволило прове-сти вычисления электронных состояний для реальных нанокристаллов размером до 2.5 нм, вычислить вероят-ности оже-рекомбинации, ударной ионизации, а также выполнить компьютерное моделирование целого ряда процессов в структурах с кремниевыми нанокристалла-ми, важных для применения в фотовальтаике [20]. Был изучен транспорт носителей заряда и энергии в массиве кремниевых нанокристаллов в SiO 2 [21], генерация двух экситонов в соседних нанокристаллах при поглощении одного фотона с большой энергией (cutting process) [22].…”

Elastic tunneling charge transport mechanisms in silicon quantum dots /SiO2 thin films and superlattices

“…46 and its application to realistic Qds described with ab initio techniques is presented in Ref. 47.…”