Randomly oriented indium phosphide nanowires for optoelectronics

Abstract

The concept of randomly-oriented semiconductor nanowires formed on non-single-crystal substrates is introduced and compared with semiconductor nanowires synthesized on single-crystal-substrates in the framework of epitaxial growth. In principle, epitaxial growth of semiconductor nanowires with the presence of metal-catalysts requires no single-crystal substrates owing to the small size of nanowires. A segment on a substrate from which crystallographic information is transferred to a single nanowire would only need to be as larger as the cross-section of a nanowire if a specific geometrical alignment for a group of nanowires is not required, suggesting that randomly-oriented semiconductor nanowires be formed on a surface that is characterized with short-range atomic order in contrast to long-range atomic order that exists on the surface of single-crystal substrates. The surfaces exhibiting short-range atomic order can be prepared on non-single-crystal substrates, further suggesting functional devices that utilize randomly-oriented semiconductor nanowires be fabricated on non-single-crystal substrates. Design, fabrication and characteristics of a photoconductor that utilizes an ensemble of randomly-oriented indium phosphide nanowires are described.

Room-temperature Coulomb staircase in semiconducting InP nanowires modulated with light illumination

“…The model assumes a single active Coulomb island on a pair of NWs while our structural analysis (figure 1) clearly shows multiple fused NW pairs bridging two electrodes (we have identified twelve NW pairs on average present per photoconductor) [17]. Since these NW pairs are connected to Si:H electrodes in parallel, the assumption is equivalent to one pair having resistance substantially lower than the other pairs, and determines overall I d -V d characteristics.…”

“…We have examined several devices, and have observed increasing photoconductor conductance as the illumination power is increased due to the e-h generation. Nearly half of the devices showed a smooth I d -V d curve in the dark with a slight diverging nonlinearity (d 2 I d /dV 2 d > 0 when V d > 0, or d 2 I d /dV 2 d < 0 when V d < 0) and the NW differential conductance between the electrodes R NW = dI d /V d changed from ∼2 nS at V d = 0 to ∼5 nS at V d = 5 V. The illumination increased the device photoconductivity by orders of magnitude, which is quite important in the engineering context, but was well understood in the physics context as discussed in [17]. An example of smooth I d -V d characteristics is discussed in figure 3 of [18].…”

“…The progress in this field is reviewed in [16]. Kobayashi et al reported In NW synthesis and electrical transport measurements on a simple photoconductor under light illumination [17]. On their photoconductor with two hydrogenated Si (Si:H) electrodes, InP was grown into cone-shaped nanowires with bases attached on the electrodes as shown in figures 1(a) and (b), where the detail of the growth is the same as that in [17].…”

“…Kobayashi et al reported In NW synthesis and electrical transport measurements on a simple photoconductor under light illumination [17]. On their photoconductor with two hydrogenated Si (Si:H) electrodes, InP was grown into cone-shaped nanowires with bases attached on the electrodes as shown in figures 1(a) and (b), where the detail of the growth is the same as that in [17]. Some of the NWs encountered each other during the growth and fused together in pairs as in figure 1(c), establishing an electrical connection.…”

“…In this paper, we describe detailed analysis on the DC electron transport characteristics of the InP NW photoconductor in the dark and under light illumination with monochromatic light (633 nm, 1.95 eV) at various optical power levels ranging up to 5 μW. Multiple batches of photoconductor devices were fabricated and characterized in [17], but the dark characteristics have never been analyzed. The light energy is well beyond the InP direct band gap E g of 1.34 eV so that appreciable electron-hole (e-h) pair generation is expected.…”