Transport properties of semiconducting nanocrystal arrays at low temperatures

We study the electron transport in semiconducting nanocrystal arrays at temperatures $T⪡E_c$, where $E_c$ is the charging energy for a single grain. In this temperature range, the electron transport is dominated by cotunneling processes. We discuss both elastic and inelastic cotunneling and show that for semiconducting nanocrystal arrays, the inelastic contribution is strongly suppressed at low temperatures. We also compare our results with available experimental data.

Figure 1

(Color online) Sketch of a two-dimensional granular array with a schematic multi-cotunneling path through $N=r∕a$ grains with $a$ and $r$ being the grain size and the hopping length, respectively.

Figure 2

(Color online) (a) Elastic cotunneling process. In this process, the charge is transferred via the tunneling of an electron through an intermediate virtual state in the dot such that the electron leaves the dot with the same energy as it came. (b) Inelastic co-tunneling process. In this process, the electron coming out of the dot has a different energy than the incoming one. During this process, an electron-hole excitation is left behind in the grain, which absorbs the energy difference of the incoming and outgoing electron.