GaAsN Alloys Research Articles

Composition dependence of interband transition intensities in GaPN, GaAsN, and GaPAs alloys

Using large (512-atom) pseudopotential supercell calculations, we have investigated the composition dependence of the momentum matrix element ${M}_{v,c}$ for transitions between the valence-band maximum and the conduction-band minimum of three semiconductor alloys: ${\mathrm{GaP}}_{1\ensuremath{-}x}{\mathrm{N}}_{x}$ and ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x},$ exhibiting large chemical and size differences between their alloyed elements, and ${\mathrm{GaP}}_{1\ensuremath{-}x}{\mathrm{As}}_{x},$ which is a weakly perturbed alloy. In the composition ranges where these alloys have a direct band gap, we find that (i) in ${\mathrm{GaP}}_{1\ensuremath{-}x}{\mathrm{As}}_{x},$ ${M}_{v,c}$ is large (like the virtual-crystal value) and nearly composition independent; (ii) in ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x},$ ${M}_{v,c}$ is strongly composition dependent: large for small $x$ and small for large $x;$ and (iii) in ${\mathrm{GaP}}_{1\ensuremath{-}x}{\mathrm{N}}_{x},$ ${M}_{v,c}$ is only slightly composition dependent and is significantly reduced relative to the virtual-crystal value. The different behavior of ${\mathrm{GaP}}_{1\ensuremath{-}x}{\mathrm{As}}_{x},$ ${\mathrm{GaP}}_{1\ensuremath{-}x}{\mathrm{N}}_{x},$ and ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x}$ is traced to the existence/absence of impurity levels at the dilute alloy limits: (a) there are no gap-level impurity states at the $x\ensuremath{\rightarrow}1$ or $x\ensuremath{\rightarrow}0$ limits of ${\mathrm{GaP}}_{1\ensuremath{-}x}{\mathrm{As}}_{x},$ (b) an isolated As impurity in GaN ($\mathrm{GaN}:\mathrm{A}\mathrm{s}$) has a deep band gap impurity level but no deep impurity state is found for N in GaAs, and (c) $\mathrm{GaN}:\mathrm{P}$ exhibits a P-localized deep band-gap impurity state and $\mathrm{GaP}:\mathrm{N}$ has an N-localized resonant state. The existence of deep levels leads to wave-function localization in real space, thus to a spectral spread in momentum space and to a reduction of ${M}_{v,c}.$ These impurity levels are facilitated by atomic relaxations, as evident by the fact that unrelaxed $\mathrm{GaN}:\mathrm{A}\mathrm{s}$ and $\mathrm{GaN}:\mathrm{P}$, show no deep levels, have extended wave functions, and have large interband transition elements.

Band gaps of GaPN and GaAsN alloys

The importance of atomic relaxations, chemical disorder, and epitaxial constraints on the band gap of random, anion-mixed nitride alloys GaPN and GaAsN have been investigated, via pseudopotentials calculation. It has been demonstrated that simple approximations such as the virtual crystal approximation, or the use of high-symmetry ordered structure to mimic a random alloy, or the neglect of atomic displacements, are inadequate. It is found that a fully relaxed, large supercell calculation reproduces well the experimental band gaps of GaPN and GaAsN films.

Excitonic luminescence and absorption in dilute GaAs1−xNx alloy (x<0.3%)

Dilute GaAs1−xNx alloys (x<0.3%) were grown by metalorganic vapor phase epitaxy to investigate their photoluminescence and photoluminescence excitation characteristics. Photoluminescence excitation spectra show clear excitonic absorption peaks at low temperatures and their peak energy drastically decreases with increasing nitrogen concentration due to the band-gap bowing in the GaAsN system. This result indicates that the band-gap bowing starts at a nitrogen concentration as low as 1018 cm−3, and its bowing parameter is −22 eV. According to this band-gap bowing, the GaAsN alloys show two photoluminescence lines whose peak energy decreases with increasing nitrogen concentration. Their dependence on the nitrogen concentration suggests that these lines correspond to excitonic and carbon-related transitions in the GaAsN alloy.

Feasibility of the synthesis of AlAsN and GaAsN films by plasma-source molecular-beam epitaxy

Possible experimental realizations of AlAsN and GaAsN alloys are explored. Growths were conducted to test whether the pseudobinary alloys III-As x N 1 − x could be formed by providing As 2 and excess Group III fluxes in a plasma-source nitride epitaxial growth process based on Si(1 1 1) substrates. Incorporation of several atomic percent of As occurs at typical III-N growth temperatures. However, X-ray and transmission electron microscopy analysis show that disordered phases are present and that the incorporated As is not purely substitutional on N sublattice sites. A pronounced surfactant effect of As in the growth of GaN is demonstrated, with the rms surface roughness decreasing one order of magnitude. Another approach, using “digital” alloys of GaAsN formed by alternating beam epitaxy on GaAs(1 0 0) has demonstrated incorporation of several atomic percent of N in GaAs. High-resolution X-ray rocking curves and TEM images of the digital alloy are provided.

Giant and composition-dependent optical bowing coefficient in GaAsN alloys.

Using first-principles supercell calculations we find a giant (7{endash}16 eV) and composition-dependent optical bowing coefficient in GaAs{sub 1{minus}{ital x}}N{sub {ital x}} alloys. We show that both effects are due to the formation in the alloy of spatially separated and sharply localized band edge states. Our analysis suggests that in semiconductor alloys band gap variation as a function of {ital x} can be divided into two regions: (i) a bandlike region where the bowing coefficient is relatively small and nearly constant, and (ii) an impuritylike region where the bowing coefficient is relatively larger and composition dependent. For GaAs{sub 1{minus}{ital x}}N{sub {ital x}} the impuritylike behavior persists even for concentrated alloys. {copyright} {ital 1996 The American Physical Society.}

The growth and properties of mixed group V nitrides

Bearing in mind the problems of finding a lattice-matched substrate for the growth of binary group III nitride films and the detrimental effect of the large activation energy associated with acceptors in GaN, we propose the study of the alloy system AlGaAsN. We predict that it may be possible to obtain a direct gap alloy, with a band gap as wide as 2.8eV, which is lattice-matched to silicon substrates. The paper reports our attempts to grow GaAsN alloy films by molecular beam epitaxy on either GaAs or GaP substrates, using a radio frequency plasma source to supply active nitrogen. Auger electron spectra demonstrate that it is possible to incorporate several tens of percent of nitrogen into GaAs films, though x-ray diffraction measurements show that such films contain mixed binary phases rather than true alloys. An interesting observation concerns the fact that it is possible to control the crystal structure of GaN films by the application of an As flux during growth. In films grown at 620°C a high As flux tends to increase the proportion of cubic GaN while also resulting in the incorporation of GaAs. Films grown at 700°C show no evidence for GaAs incorporation; at this temperature, it is possible to grow either purely cubic or purely hexagonal GaN depending on the presence or absence of the As beam.

GaAsN Alloys and GaN/GaAs Double-Hetero Structures

ABSTRACTTernary alloys; GaAsN (N<3%) were grown by plasma-assisted metalorganic chemical vapor deposition using triethylgallium, AsH3, and plasma-cracked NH3 or N2 as the precursors. More N atoms were incorporated into the alloys from N2 than NH3 at constant N/As ratios. Both photoluminescence peaks and optical absorption edges were redshifted from GaAs bandgap with increasing the N content, indicating the GaAsN alloys have narrower bandgaps than GaAs.GaN/GaAs double-hetero structures were grown by exposing GaAs surfaces to N-radical flux to replace surface As atoms by N atoms, and by growing GaAs on the thin GaN layers. When the GaN thickness exceeded one-monolayer, the GaN/GaAs interfaces and the GaAs cap layers deteriorated drastically. The one-monolayer-thick GaN embedded in GaAs attracts electrons and shows intense photoluminescence, whereas the GaN cluster is non-radiative, probably because of the defects caused by the large lattice-mismatch between GaN and GaAs.

Growth of GaAsN alloys by low-pressure metalorganic chemical vapor deposition using plasma-cracked NH3

We present a letter on the growth of GaAs1−xNx alloys (0<x<0.016). The layers have been grown by metalorganic chemical vapor deposition at very low pressure (25 Pa). The nitrogen source NH3 has been decomposed in a remote microwave plasma, and uncracked triethylgallium and AsH3 were used. The N uptake into the layers shows a strong dependence on the growth temperature. The competition for the group V lattice sites leads to a reduction of the N content at higher AsH3 fluxes. The GaAsN layers show a strong red shift of the photoluminescence with increasing N content.