Measurement of minority carrier diffusion lengths in GaAs nanowires by a nanoprobe technique

Abstract

Minority carrier diffusion lengths in both p-type and n-type GaAs nanowires were studied using electron beam induced current by means of a nanoprobe technique without lithographic processing. The diffusion lengths were determined for Au/GaAs rectifying junctions as well as axial p-n junctions. By incorporating a thin lattice-matched InGaP passivating shell, a 2-fold enhancement in the minority carrier diffusion lengths and one order of magnitude reduction in the surface recombination velocity were achieved.

Axial EBIC oscillations at core/shell GaAs/Fe nanowire contacts

“…The inset in figure 2 shows a magnified semi-log plot of the 5 keV absolute current value profile, after subtracting the background current, with the red line a best linear fit. From the slope, L is 58±5nm, based on equation 1, within the reported range for 4×10 17 cm −3 Te-doped NWs, 60-120nm [16]. Figure 3 shows SEM (SEI) images with associated EBIC profiles (5 keV) for two GaAs/Fe NW, with a tapered (top) and uniform (bottom) Fe thickness, plotting current as a function of axial beam position (reverse biased 0.2V).…”

“…with D p taken as 5 cm 2 s −1 [16]. Therefore, the calculated Δρ (equation 2), decreases with beam voltage, from (20, 3, and 1)×10 13 cm −3 , for V acc =5, 10, and 15 kV, respectively.…”

“…Inside the SEM the top of each NW was contacted with a fixed W probe. In this way, L from Au/GaAs contacts was directly measured with values that were 60-120nm [16], lower than that of the bulk GaAs due to the surface recombination [17]. Compared to axial junction NWs, core-shell NWs provide larger effective surface areas and hence could be useful in LEDs and solar cells.…”

Towards high efficiency nanowire solar cells

“…However, several materials are available to epitaxially passivate GaAs, and passivating shells of InGaP [227][228][229], AlGaAs [224,225,[230][231][232][233][234] and AlInP [226,235] have all been shown to give substantial improvement of optical and electrical properties for GaAs nanowires. These benefits have been utilized in GaAs nanowire solar cell devices.…”

“…If good Ohmic contacts are realized, IV-sweeps can reveal information about the nanowire junction quality, for instance when going from a p-n to a p-i-n junction [19]. Further, techniques such as electron beam induced current (EBIC) [17,229,240,[255][256][257][258][259], cathodoluminescence (CL) [111,260,261] and scanning photocurrent microscopy (SPCM) [21,[262][263][264][265] measurements can provide insights into charge separation and collection properties. As an example, Gutsche and Niepelt et al…”