Absorption Characteristics of ${\rm GaAs}_{1-x}{\rm Bi}_{x}/{\rm GaAs}$ Diodes in the Near-Infrared

The absorption properties of a series of GaAs_1-xBi_x layers with ~ 6% Bi have been systematically investigated by measuring photocurrent spectra in p-i-n diode structures grown by molecular beam epitaxy. The GaAs_1-xBi_x layers varied in thickness from 50 to 350 nm and showed a photoresponse in the near-infrared up to almost 1.3 μm. The absorption coefficients of the layers were obtained from the responsivity data. Below the band gap, the absorption coefficients showed an exponential dependence on the photon energy (Urbach tailing).