Growth and in-plane undulations of GaAs/Ge superlattices on [001]-oriented Ge and GaAs substrates: formation of regular 3D island-in-network nanostructures

Abstract

Coherently strained pseudo-superlattices (PSLs) of 20-period GaAs/Ge have been epitaxially grown on [001]-oriented Ge and GaAs substrates by metalorganic chemical vapor deposition.

Enhanced photoemission from surface modulated GaAs:Ge

“…[8,26] The underlying substrate induces strain in the film, which in case of Ge on GaAs is compressive. [19,43] This strain tends to be compensated by Ge segregation [19] and enlargement of Ge lattice in the growth direction. [43] Strong interaction of Ge atom with GaAs, along with Ge segregation and annealing induced atomic diffusion, gives rise to observed polytype of GaAsGe NIs (Figure 1, S1, and Figure 4) with additional presence of oxygen as mentioned earlier.…”

“…Such alloying of GaAs and Ge may result in lattice constant larger than that calculated by Vegard's Law. [19,38] A detailed study of Ge interaction and its diffusion in GaAs atomic planes can be found in a paper by Sozen et al. [20] Furthermore, there is evidence in the literature that Ga vacancies are the most probable source of increased diffusion of Ge [27,42] when grown over GaAs, [22] and that the phenomena is governed by annealing parameters.…”

“…GaAs has been considered a suitable candidate for light emitting diodes (LED), solar cells and photodetectors [7,19,20] due to its favorable electronic properties such as high electron mobility. [20] Its suitability can be further enhanced by alloying with a group IV element of which germanium (Ge) is arguably the best choice.…”

“…[20] Its suitability can be further enhanced by alloying with a group IV element of which germanium (Ge) is arguably the best choice. It possesses the highest hole mobility out of group IV semiconductors [7][8][9] and has a lattice constant and thermal expansion coefficient close to that of GaAs (differences of 0.07% and 0.03%, respectively [21] ) and yet the band-gap is different (∼1.44 eV for GaAs vs. ∼0.67 eV for Ge [19] ). In contrast, use of other group IV elements involve some fundamental problems associated with large lattice mismatch (∼4% for silicon) and different thermal expansion coefficients.…”

“…In-diffusion of Ge in GaAs [7,22,23] can results in GaAs 1-x Ge x structures [20,23] exhibiting direct band-gap with superior optical properties. [19] For semiconductors, bringing the structure down to nanoscale may fundamentally modify the properties of materials by inducing low-dimensional charge carrier confinement [24] and self-assembling, allowing the growth of well-defined random or aligned nano/quantum structures [24] without the need of sophisticated lithography techniques. [24] Nanostructuring processes may be brought about by thermal treatment at temperature below the melting point of the material used.…”