Observation of stimulated emission in an ultrashort-period nonsymmetric GaAs/AlAs superlattice

Abstract

Nonsymmetric short-period GaAs/AlAs superlattices, for which the well thickness is at least a factor of 2 larger than the barrier thickness, have been shown to exhibit a direct band gap for any well thickness. These superlattices are characterized by an enhanced intensity of the luminescence as compared to their symmetric indirect-gap counterparts with the same well width, and, thus, may be used as light-emitting devices, in particular, as low-threshold lasers in the red visible spectrum. This conjecture is supported by the observation of stimulated emission at T=80 K for a GaAs/AlAs superlattice with six monolayers well and three monolayers barrier width.

GaAs/AlAs Superlattices and the Tight-Binding Model

“…In contrast to the TB method, KP requires effective masses and bulk band gap as parameters. A KP calculation suggests that SLs with N ¼ 2M have direct band gaps [2], which agrees with our calculations using LS89 and SJB98. This leads to a higher optical efficiency compared to symmetric SLs with N 12.…”

“…Recently, asymmetric SLs (N 6 ¼ M) have received renewed attention [1][2][3]. The one-band Kronig-Penney model (KP) is used in Refs.…”

“…The one-band Kronig-Penney model (KP) is used in Refs. [1] and [2] to calculate conduction-band confinement energies. In contrast to the TB method, KP requires effective masses and bulk band gap as parameters.…”

“…There is currently a resurgence of interest in the study of GaAs/AlAs superlattices (SLs), which includes new light-emitting structures with direct [1,2] and pseudo-direct [3] band gaps, and the study of interface mixing of band-edge states [4,5]. Our interest is in an accurate calculation of the optoelectronic properties of these structures.…”

“…[8] and [9], have neither been verified, nor have the detailed properties of the conduction-band states been calculated and compared with available experimental data. The latter calculations are needed in order to explain the recent light emission experiments [1][2][3]. In this paper, we compare two parameter sets, one for a second nearest-neighbor sp 3 and one for a recent nearest-neighbor sp 3 d 5 s * model, with detailed experimental data on (GaAs) N /(AlAs) M SLs grown along the (001) direction, including our own data, in order to assess the accuracy and robustness of the TB method.…”