Solid phase immiscibility in GaInN

Abstract

The large difference in interatomic spacing between GaN and InN is found to give rise to a solid phase miscibility gap. The temperature dependence of the binodal and spinodal lines in the Ga1−xInxN system was calculated using a modified valence-force-field model where the lattice is allowed to relax beyond the first nearest neighbor. The strain energy is found to decrease until approximately the sixth nearest neighbor, but this approximation is suitable only in the dilute limit. Assuming a symmetric, regular-solutionlike composition dependence of the enthalpy of mixing yields an interaction parameter of 5.98 kcal/mole. At a typical growth temperature of 800 °C, the solubility of In in GaN is calculated to be less than 6%. The miscibility gap is expected to represent a significant problem for the epitaxial growth of these alloys.

Does In form In-rich clusters in InGaN quantum wells?

“…The thermodynamic calculations reported earlier [5] which predicted the decomposition of InGaN were for bulk material. However Karpov [32] has calculated the phase diagram for an InGaN layer epitaxially matched to a GaN layer, which puts the InGaN into biaxial compression.…”

“…Thermodynamic calculations then showed that there is a miscibility gap in the In x Ga 1-x N system and that for typical compositions (x~0.1 for blue emission, x~0.2 for green) and typical InGaN growth temperatures (600-800 deg C) the unstrained homogeneous alloy is unstable, leading to decomposition into In-rich and In-poor regions [5]. It is not clear how applicable these equilibrium thermodynamic calculations are to the InGaN layers grown by MOVPE or Molecular Beam Epitaxy (MBE)(see later), but Ponce et al [6] have reported phase separation in MOVPE grown thick (200 nm) epilayers of InGaN with In fractions of 0.1 and above.…”

III–V Multijunction Solar Cell Integration with Silicon: Present Status, Challenges and Future Outlook

“…GaAs 0.09 P 0.87 N 0.04 alloy (bandgap of 1.81 eV) lattice-matched to Si substrate is an attractive top cell choice for 2J III-V/Si tandem solar cell (Almosni et al 2013). Furthermore, from growth perspective, GaAsPN alloys are easier to grown in comparison to InGaPN due to the difficulties associated with InN and GaN solidphase miscibility (Korpijärvi et al 2012;Hsu and Walukiewicz 2008;Ho and Stringfellow 1996). Geisz et al (2005) reported the first 2J GaAs 0.10 P 0.86 N 0.04 (1.80 eV)/Si tandems solar cell with an efficiency of 5.2% under AM1.5g (without an antireflective coating) utilizing an initial GaP nucleation layer, followed by the MOCVD growth of lattice-matched GaN 0.02 P 0.98 layer.…”

“…Large lattice-mismatch between InN and GaN causes a solid-phase miscibility gap due to the low solubility between these two materials (Hsu and Walukiewicz 2008;Ho and Stringfellow 1996). The difficulty in doping InN material with p-type dopant is presumably due to the compensation by native defects.…”

Molecular simulation study of the structural properties in InxGa1−xAs alloys: Comparison between Valence Force Field and Tersoff potential models

“…Ho and Stringfellow [3,4] first used the Valence Force Field (VFF) model, also known as the Keating model [5], to study the solution thermodynamics of InGaN and other III-V alloys. Takayama et al [6,7] have since refined the molecular model and have determined the miscibility characteristics and microstructure of other ternary and quaternary compound semiconductor alloys using the energy minimization approach of Ho and Stringfellow [3,4].…”