Kinetics of self-induced nucleation and optical properties of GaN nanowires grown by plasma-assisted molecular beam epitaxy on amorphous AlxOy

Abstract

Nucleation kinetics of GaN nanowires (NWs) by molecular beam epitaxy on amorphous AlxOy buffers deposited at low temperature by atomic layer deposition is analyzed. We found that the growth processes on a-AlxOy are very similar to those observed on standard Si(111) substrates, although the presence of the buffer significantly enhances nucleation rate of GaN NWs, which we attribute to a microstructure of the buffer. The nucleation rate was studied vs. the growth temperature in the range of 720–790 °C, which allowed determination of nucleation energy of the NWs on a-AlxOy equal to 6 eV. This value is smaller than 10.2 eV we found under the same conditions on nitridized Si(111) substrates. Optical properties of GaN NWs on a-AlxOy are analyzed as a function of the growth temperature and compared with those on Si(111) substrates. A significant increase of photoluminescence intensity and much longer PL decay times, close to those on silicon substrates, are found for NWs grown at the highest temperature proving their high quality. The samples grown at high temperature have very narrow PL lines. This allowed observation that positions of donor-bound exciton PL line in the NWs grown on a-AlxOy are regularly lower than in samples grown directly on silicon suggesting that oxygen, instead of silicon, is the dominant donor. Moreover, PL spectra suggest that total concentration of donors in GaN NWs grown on a-AlxOy is lower than in those grown under similar conditions on bare Si. This shows that the a-AlxOy buffer efficiently acts as a barrier preventing uptake of silicon from the substrate to GaN.

Nature of excitons bound to inversion domain boundaries: Origin of the 3.45-eV luminescence lines in spontaneously formed GaN nanowires on Si(111)

“…64, the X A and (D 0 , X A ) PL decay in parallel at longer times as a result of the quasi-thermalization between these exciton states. Using an exponential fit, the effective decay time for the X A and (D 0 , X A ) is found to be 195 ps, very similar to values obtained in previous reports [52,65,66]. This decay is much faster than expected for the radiative decay of the (D 0 , X A ) complex and is due to the nonradiative decay of the X A at point defects [66].…”

“…7 reveals that the intensity of the (IDB * , X) band is actually not significantly reduced with increasing T S . The decrease of the relative intensity of the (IDB * , X) band with increasing T S is instead caused by the drastic increase in the (D 0 , X A ) emission intensity, reflecting the reduced concentration of nonradiative point defects at high T S [44,52]. .…”

Chemical bonding of nitrogen formed by nitridation of crystalline and amorphous aluminum oxide studied by X-ray photoelectron spectroscopy

“…Such buffers effectively induce catalyst-free nucleation of GaN nanowires on sapphire 8 and GaN 9 substrates. As shown in previous studies, [10][11][12][13] AlO x buffer layers signicantly enhance the nucleation rate of GaN with respect to nitridated Si (the most common substrate for growing GaN nanowires), without loss of structural and optical properties. 10 Additionally, AlO x buffers prevent diffusion of silicon from the substrate 10 facilitating growth of GaN nanostructures at high temperatures without incorporating any impurities, 14 thus potentially leading to exceptional optical properties.…”

“…As shown in previous studies, [10][11][12][13] AlO x buffer layers signicantly enhance the nucleation rate of GaN with respect to nitridated Si (the most common substrate for growing GaN nanowires), without loss of structural and optical properties. 10 Additionally, AlO x buffers prevent diffusion of silicon from the substrate 10 facilitating growth of GaN nanostructures at high temperatures without incorporating any impurities, 14 thus potentially leading to exceptional optical properties. Since AlO x layers can be produced by ALD at temperatures below 100 C on various surfaces, 15 this technique can be used for growing highquality GaN nanostructures on a large variety of bulk substrates and hence substantially widen the range of their applications.…”

Heterogeneous nucleation of catalyst-free InAs nanowires on silicon

“…Although a large number of processes occur during sputtering, it is well established that bomb- arding a surface with energetic particles leads to the formation of surface defects, which here serve as preferential nucleation sites [18,19]. In fact, the role of surface defects as nucleation sites in catalyst-free NW growth is already established: it was found that defects ease the formation of critical nuclei and enhance the nucleation rate [20,21]. The different InAs crystal density on the two types of sputtered silicon surfaces shown in figures 2(b) and (c) is likely due to the different sputtering parameters (V sputter and t sputter ) and techniques employed.…”