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Because of their technological interest in electronics, optoelectronics, sensor technology, and spectroscopic photon counting X-ray photodiode, the AlxIn1-xP alloys have been studied extensively. The ground state structure, mechanical, electronic, optical, and thermodynamic properties for the ternary alloys AlxIn1-xP in the cubic structure are presented. The theoretical calculations are performed using the generalized gradient approximation (GGA) and the semilocal modified Becke–Johnson (mBJ). Although the mBJ (GGA) energy band gap varies nonlinearly with Al concentration, the obtained values agree well with the available experimental data. Interestingly, it is found that at 83% Al, a transition from direct to indirect gap occurs because the binary compounds InP and AlP compounds have a direct band gap ( Γ → Γ ) and an indirect band gap ( Γ → X ), respectively. The thermodynamic study reveals that AlxIn1-xP alloys are stable at high temperature, with the existence of a solid solution for all compositions. Furthermore, at the critical composition xc = 0.55, the value of the direct band gap varies in the narrow range 2.429–2.413 eV, corresponding to the wavelengths 514–513 nm. Consequently, this range of energy band gap recommends the ternary AlxIn1-xP alloys for optoelectronic device applications, such as solar cells or photovoltaic. [ABSTRACT FROM AUTHOR]