Relative Influence of Surface States and Bulk Impurities on the Electrical Properties of Ge Nanowires

Abstract

We quantitatively examine the relative influence of bulk impurities and surface states on the electrical properties of Ge nanowires with and without phosphorus (P) doping. The unintentional impurity concentration in nominally undoped Ge nanowires is less than 2 x 10(17) cm(-3) as determined by atom probe tomography. Surprisingly, P doping of approximately 10(18) cm(-3) reduces the nanowire conductivity by 2 orders of magnitude. By modeling the contributions of dopants, impurities, and surface states, we confirm that the conductivity of nominally undoped Ge nanowires is mainly due to surface state induced hole accumulation rather than impurities introduced by catalyst. In P-doped nanowires, the surface states accept the electrons generated by the P dopants, reducing the conductivity and leading to ambipolar behavior. In contrast, intentional surface-doping results in a high conductivity and recovery of n-type characteristics.

On‐Nanowire Band‐Graded Si:Ge Photodetectors

“…[26][27][28][29] With increasing Ge content, the NW resistivity decreases up to by three orders of magnitude mainly by their band modulation rather than mobility variation, which is consistent with the case of bulk Si 1-x Ge x crystals. [ 30 ] Nevertheless, at all compositions, the NW resistivity is typically lower by two orders of magnitude compared to bulk Si 1-x Ge x crystals.…”

“…The measured resistivity of each Si:Ge channel from four devices (D1-D4) are plotted as a the nanowire capacitor geometry. [ 29 ] However, this difference in mobility is too small to account for the large conductivity change over the several orders of magnitude in Figure 2 b, as further discussed below. Figure 3 shows representative I ph images measured on multiterminal NW photodetectors of D1-D3 by scanning photocurrent measurements, as illustrated in Figure 3 a, in which the appropriate Si:Ge alloying is axially modulated by the labeled amount.…”

Electrical properties of conductive Ge nanocrystal thin films fabricated by low temperaturein situgrowth

“…Ge nanowires, especially for n-type materials, have shown efficacious incorporation and activation of dopants by forming a heavily doped shell surrounding an undoped (or very lightly doped) core [33,[43][44][45]. The dopants incorporation pathway was predominately via the conformal surface growth of the shell layer and thereby the concentration of dopants was determined by the rates of dissociative chemisorptions of precursors.…”

Contactless monitoring of the diameter-dependent conductivity of GaAs nanowires

“…The conductivity of NWs, one of the most important properties exploited in numerous applications, becomes extremely sensitive to the status of the surface with decreasing NW width, and dramatic conductivity changes can be observed when the Debye length becomes comparable to the NW radius [4]. Along with presence of adsorbates and charged surface states [5,6], other factors that may affect the conductivity include the (i) reduced mobility due to enhanced phonon or surface scattering [7,8], (ii) edge effects due to unsaturated bonds of the surface atoms [9], (iii) size-imposed limits to the effective doping concentration [9,10], (iv) size-dependence of depletion width [11], band-gaps [12,13], and recombination barriers [14]. As a result, significant scatter in the conductivity data are observed for individual GaAs NWs purportedly fabricated in the same manner [15].…”