Sub-bandgap photoluminescence from as-grown and annealed layers of CdTe

Photoluminescence (PL) from the vapour deposited layers of CdTe have demonstrated a unique quality improvement after as-grown samples have been annealed at relatively low temperatures (500–600 ∘C). The sub-band gap emissions at 4.2 K have been centred at the 1.42 and 1.47 eV and they have different intensity-power dependencies. This is strong evidence that they originate from the recombination of various defects. Similar deep-level defect emissions in bulk CdTe arise in the region of the so-called A-centre PL band (1.42 eV), and extended defect emissions (1.47 eV). The latter emission demonstrates a super-linear excitation-power dependence that is a characteristic of the excitonic recombination processes. After a short annealing at 500 ∘C the extended defect emission practically disappeared making possible observation of the band-to-band recombination at 1.58 eV. As a result of this work optimal annealing conditions have been found for the as-grown samples of CdTe on various substrates (Si, sapphire).