Wannier–Stark localization in strained barrier GaAs/In_XAl_1−XAs superlattices Available to Purchase

We report the observation of the Wannier–Stark localization effect in short period GaAs/ In_XAl_1−XAs superlattices with strained barriers. The superlattices, each of which is contained in the intrinsic region of a p‐i‐n diode structure, consist of GaAs (3.0 nm) wells and strained shallow In_XAl_1−XAs (0.9 nm) barriers (X=0, 0.1, 0.2, and 0.3) grown on GaAs by molecular beam epitaxy. In spite of the use of strained barriers, the Wannier–Stark localization effect is clearly observed for all samples at room temperature. Even the superlattice sample with the highest In content of X=0.3 exhibits distinct photocurrent spectra showing several peaks associated with Wannier–Stark ladder transitions as well as Franz–Keldysh oscillations. It is found that the transition intensities are consistent with theoretically calculated oscillator strengths based on the simplified tight‐binding model. By increasing the In content X, the miniband width increases and the absorption peak energy due to the zeroth order ladder (e1‐hh1 and e1‐lh1) transitions decreases because of the reduced barrier height. The transition energies are consistently explained by taking modulation effects into account on the valence subbands due to the compressively strained barriers. The above results show that the use of a large strain effect on the barriers is possible in Wannier–Stark localization effect type devices.