This paper reports a new photoluminescence (PL) band in indirect $\mathrm{Ga}{\mathrm{As}}_{1-x}{\mathrm{P}}_x$ that lies between donor-bound and free exciton PL peaks. It has relatively strong $X$-point phonon sidebands and an asymmetric shape with an abrupt high-energy cutoff. The lifetime varies rapidly over the PL linewidth. Properties of excitons in fluctuating random-alloy potentials are discussed. It is suggested that this line is due to excitons trapped by such potentials.

• Received 31 October 1979

DOI:https://doi.org/10.1103/PhysRevLett.44.1087