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

The absorption properties of a series of
${\rm GaAs}_{1-x}{\rm Bi}_{x}$
layers with
${\sim}{6}\%$
Bi have been systematically investigated by measuring photocurrent spectra in p-i-n diode structures grown by molecular beam epitaxy. The
${\rm GaAs}_{1-x}{\rm Bi}_{x}$
layers varied in thickness from 50 to 350 nm and showed a photoresponse in the near-infrared up to almost 1.3
$\mu{\rm m}$
. 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).