Low‐temperature photoluminescence studies of undoped, N+ (nitrogen)‐implanted and C+ (carbon)‐implanted AlAs grown by molecular beam epitaxy are reported. It was experimentally demonstrated that a dominant emission temporarily denoted by A, observed at 13 meV below the indirect excitonic band gap, Eg,ind(X), is closely related with N isoelectronic impurity atoms. It was also found that the A emission accompanies many one‐phonon and two‐phonon replicas, among which the longitudinal optical phonon replica is predominant. Carbon atoms were determined not to be principal residual impurities in undoped AlAs. The two conspicuous C‐related emissions were revealed by the intentional incorporation of C atoms, which are situated at 60 and 64 meV below Eg,ind(X).