An AlAs/germanene heterostructure with tunable electronic and optical properties via external electric field and strain

By means of comprehensive first-principles calculations, we investigate the stability, electronic and optical properties of an AlAs/germanene heterostructure. In particular, electric field and strain are used to tailor its electronic band gap and dielectric function. The binding energy and interlayer distance indicate that germanene and AlAs monolayers in the AAI pattern are bound together via van der Waals interaction with a maximum indirect-gap of 0.494 eV, which is expected to have potential application in the field of field-effect transistors. Under a negative E-field and compressive strain, the bandgaps of the AAI-stacking show a near-linear and linear decrease behavior, respectively, whereas the response of the bandgaps to a positive E-field and tensile strain displays a dramatic and monotonous decrease relationship. The work function of the AAI-stacking is calculated to be 4.35 eV smaller than that of individual monolayers. Besides, the optical properties are also calculated. The imaginary parts of the dielectric function of the germanene/AlAs heterobilayer exhibit a significant enhancement in comparison with the considered monolayers, indicating the improvement of the capability of absorbing photons. In particular, the imaginary part of the dielectric function of the heterostructure is enhanced with the increase of E-field and mechanical strain, which suggests that the optical properties of the heterostructure can be improved by E-field and mechanical strain. Simultaneously, a red-shift or blue-shift can be observed with the changes in E-field and mechanical strain. All these nontrivial and tunable properties endow the AlAs/germanene nanocomposite with great potential for FETs, strain sensors, photocatalysis, field emission, energy harvesting, and photonic devices.