Abstract
The compound GaP1−xNx is highly attractive to pseudomorphically integrate red-light emitting devices and photovoltaic cells with the standard Si technology because it is lattice matched to Si with a direct bandgap energy of ≈1.96 eV for x = 0.021. Here, we report on the chemical beam epitaxy of GaP1−xNx alloys on nominally (001)-oriented GaP-on-Si substrates. The incorporation of N into GaP1−xNx was systematically investigated as a function of growth temperature and the fluxes of the N and P precursors, 1,1-dimethylhydrazine (DMHy) and tertiarybutylphosphine (TBP), respectively. We found that the N mole fraction exhibits an Arrhenius behavior characterized by an activation energy of (0.79 ± 0.05) eV. With respect to the fluxes, we determined that the N mole fraction is linearly proportional to the flux of DMHy and inversely proportional to the one of TBP. All results are summarized in a universal equation that describes the dependence of x on the growth temperature and the fluxes of the group-V precursors. The results are further illustrated in a growth diagram that visualizes the variation of x as the growth temperature and the flux of DMHy are varied. This diagram also shows how to obtain single-phase and flat GaP1−xNx layers, as certain growth conditions result in chemically phase-separated layers with rough surface morphologies. Finally, our results demonstrate the feasibility of chemical beam epitaxy to obtain single-phase and flat GaP1−xNx layers with x up to about 0.04, a value well above the one required for the lattice-matched integration of GaP1−xNx-based devices on Si.
Highlights
The material quality of dilute-nitride compounds is known to degrade as the N content and the layer thickness are increased, as reported for thin films and devices grown, for instance, by metal-organic vapor phase epitaxy (MOVPE) and plasma-assisted molecular beam epitaxy (PAMBE).3,12–16 (ii) The common use of highly misoriented (4○–6○) instead of on-axis Si(001) substrates to avoid the creation of antiphase domains,12,17,18 a solution that undermines the integration of GaP1−xNx-based devices with the standards of Si technology
Besides the variation of x with growth temperature and BEPDMHy, we indicate in the growth diagram both the growth conditions of the samples grown in this study with BEPTBP = 1.2 × 10−5 Torr and the approximate boundary between the growth parameters resulting in single-phase and phase-separated GaP1−xNx layers, as determined by the analysis of the samples by high-resolution x-ray diffraction (HRXRD)
We have comprehensively investigated the incorporation of N into GaP1−xNx layers grown on (001)-oriented GaP-on-Si substrates by Chemical beam epitaxy (CBE) using as gas sources DMHy, TBP, and TEGa
Summary
Despite the great potential of this compound, commercial red-light emitting devices are still based on AlxInyGa1−x−yP alloys and the efficiency of GaP1−xN on Si photovoltaic solar cells remains too low as to consider this material combination a competitive technology.8 This situation arises from: (i) The challenging synthesis of GaP1−xN alloys with high structural perfection. Upon independently analyzing the influence of growth temperature and the fluxes of the groupV precursors on the incorporation of N into GaP1−xNx, all results are summarized in a universal equation that we used to construct a growth diagram This diagram, which illustrates the dependence of the chemical composition on the growth conditions as well as the impact of the growth parameters on both the chemical homogeneity and the surface morphology, can be used as a guide to control the properties of GaP1−xNx compounds grown by CBE. On the basis of the studies presented here, we conclude on the feasibility of CBE to produce chemically homogeneous and flat GaP1−xNx layers lattice matched to Si
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