Increasing Optical Efficiency in the Telecommunication Bands of Strain-Engineered Ga (As,Bi) Alloys

The search for semiconducting materials with improved optical properties relies on the possibility to manipulate the semiconductors band structure by using quantum confinement, strain effects, and by the addition of diluted amounts of impurity elements such as Bi. In this study, we explore the possibility to engineer the structural and physical properties of the Ga(As,Bi) alloy by employing different stress conditions in its epitaxial growth. Films with variable concentration of Bi are grown by molecular beam epitaxy on bare GaAs(001) crystals and on partially relaxed (In,Ga)As double buffer layers acting as stressors aiming to control the Bi incorporation into the alloy and improving the optical properties in terms of efficiency. A combination of several structural and electronic characterization techniques and dedicated density-functional-theory calculations allows us a systematic comparison between the samples grown under compressive and tensile strain. We demonstrate the possibility to grow Ga(As,Bi) under different strain conditions without affecting its crystal quality. The different strain conditions strongly impact the Bi incorporation in the GaAs matrix and the luminescence properties of the sample. We find (i) a striking improvement of the photoluminescence with a strongly increased radiative efficiency when Ga(As,Bi) is grown under tensile strain and (ii) an interesting higher redshift with respect to Ga(As,Bi) grown compressively on GaAs. These two effects allow us to reach the important photoluminescence emission at 1.3 µm with a Bi concentration as low as 4.9% compared to 7.5% needed for samples grown directly on GaAs. This is a significant achievement for the application of the Ga(As,Bi) material in optoelectronic devices.