A multi-nuclear magnetic resonance and density functional theory investigation of epitaxially grown InGaP2

Abstract

In this paper the short and long range order in In_0.483Ga_0.517P thin films is investigated by solid-state Nuclear Magnetic Resonance (NMR) spectroscopy. To this end two samples were grown on a GaAs substrate by metal–organic vapor phase epitaxy at two different growth-pressures. From band gap energy measurements, CuPt long range order parameters of S_CuPt = 0.22 and 0.39 were deduced, respectively. In the ³¹P spectrum five resonances are observed corresponding to the five possible P(Ga_nIn_4−n), n = 0–4, coordinations whose relative intensities correspond to the order in the material, but the intensity variations for order parameters between 0 and 0.5 are minimal. ⁶⁹Ga, ⁷¹Ga and ¹¹⁵In (MQ)MAS spectra were acquired to analyze the quadrupolar and chemical shift distributions related to the (dis)order in these materials in more detail. All these spectra clearly reflect the disorder in the sample and do not show the presence of highly ordered domains. The difference in the order parameter in the sample is not clearly reflected in the spectra. ³¹P chemical shifts were calculated using Density Functional Theory. The experimentally observed shifts are well reproduced with a simple random model of the disorder, thus confirming the assignment of the resonances. The ³¹P chemical shifts are very sensitive to changes in the lattice parameter and chemical surroundings. These effects nearly compensate and explain why the ³¹P chemical shifts in pure InP and GaP are nearly identical whereas a large difference would be expected based on the observed shift difference for the P[In₄] and P[Ga₄] coordinations in In_0.483Ga_0.517P.