Plasmon excitation in electron energy-loss spectroscopy for determination of indium concentration in (In,Ga)N/GaN nanowires

Abstract

We demonstrate the potential of low-loss electron energy-loss spectroscopy in transmission electron microscopy as a quick and straightforward method to determine the local indium compositions in (In,Ga)N/GaN nanowires. The (In,Ga)N/GaN nanowire heterostructures are grown by plasma assisted molecular beam epitaxy on Si(111) substrates in a self-assembled way, and on patterned GaN templates in an ordered way. A wide range of indium contents is realized by varying the substrate temperatures. The plasmon peak in low-loss electron energy-loss spectroscopy exhibits a linear relation with respect to indium concentration in (In,Ga)N nanowires, allowing for a direct compositional analysis. The high spatial resolution of this method in combination with structural information from transmission electron microscopy will contribute to a basic understanding of the lattice pulling effect during (In,Ga)N/GaN nanowire growth.

Combination of electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy to determine indium concentration in InGaN thin film structures

“…The relationship between plasmon peak energy and indium content is linear and can be expressed as eV   where x is the indium concentration and E max is the plasmon peak energy. The adjusted R 2 (R 2 =0.9845) confirms the plasmon peak energy versus calibrated indium concentration is linear over the complete compositional range 0<x<1, with an uncertainty in the indium concentration (random mean-square error from linear regression) of x=±0.037, which indicates an improved accuracy in the determination of indium concentration of InGaN compared to previous studies [3]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59Figure 3: dependence of plasmon peak position on measured indium concentration in InGaN, including our data as well as data from other groups [3,[25][26][27][28][29].…”

“…During the past decade, several types of Light Emitting Diodes (LED) and Laser Diodes (LD) have been fabricated based on In x Ga 1-x N quantum wells or nanowires [2,3]. Wurtzite structure GaN and InN have direct band-gaps of 3.4eV and 0.7eV, respectively, so In x Ga 1-x N compounds cover the band-gap range from 0.7eV to 3.4eV, which includes emission wavelengths corresponding to red, green and blue light.…”

Influence of GaN column diameter on structural properties for InGaN nanocolumns grown on top of GaN nanocolumns

“…For the thick NC, an In 0.3 Ga 0.7 N-In 0.1 Ga 0.9 N core-shell structure was fabricated. Moreover, x increased towards the top of the NC, which indicates the occurrence of a pulling effect in the In composition 26,32,33 even for such a NC structure.…”

On the impact of indium distribution on the electronic properties in InGaN nanodisks

“…The energy maxima correspond to the GaN regions, whereas energy minima correspond to InGaN which is known to have lower plasmon energy (E p )-values than pure GaN. 20 Note that the maxima corresponding to GaN are shifted towards lower energy with respect to those of the GaN-basepart. This shift is most likely caused by the In penetration into the GaN layers suggesting a graded composition well-barrier and therefore an inhomogeneous broadening of the resulting electro-optical properties, consistent with the results from HAADF intensities (other effects leading to plasmon energy shifts, as mentioned later, are negligible here because the GaN layers are relatively thick).…”