Studies on deep levels in GaAs epilayers grown on Si by metal-organic chemical vapour deposition, Part II: 1.13 eV photoluminescence emission

Abstract

Midgap deep levels have enjoyed a special status in semiconductor technology ever since Shockley and Read [1] and Hall [2] first pointed out their role as most efficient recombination centres on the basis of kinetic considerations. Several midgap luminescence bands trapped at deep levels have been found in GaAs and some of them are not yet well understood. The 0.635 eV photoluminescence (PL) emission in oxygen-doped semi-insulating GaAs was attributed to a complex centre involving the deep oxygen donor on an arsenic site and a gallium vacancy as a nearest neighbour [3, 4]. The 0.64, 0.68, 0.77, and 0.8 eV PL bands in undoped semi-insulating GaAs were related to the electron traps EL2 and EL6, respectively [5-10]. The origin of the 0.8 eV emission in Sidoped GaAs layers was suggested to arise from an ASGa--VAs centre [11]. The emission at about 0.85 eV in low-temperature GaAs was associated with emission from the surface states [12, 13]. However, Yu et al. [14] recently studied the 0.8 eV emission from low-temperature GaAs layers and attributed the 0.8 eV emission to an Asi-VG, centre (EL6). In this work, the 0.78 and 0.84 eV photoluminescence bands present in GaAs epitaxial layers grown on Si by metal-organic chemical vapour deposition were studied at various excitation intensities and temperatures and it was shown that they originate from the recombination of arsenic defects such as As interstitials (Asi), and gallium vacancies (VG,). The temperature dependence of the PL intensities obeys the relation IpL oc [1 + A exp (r/To)] -1, previously reported for amorphous semiconductors. A model for the recombination mechanism is given and the results are explained well by thermally activated tunnelling. GaAs epitaxial layers used in the experiment were grown on 4 ° off toward [110] (100) n-type Si substrates using the two-step method by MOCVD. The Si substrates-were chemically treated in NH4OH, H202, H20 and HC1, H2Oz, H20, and etched in HF for i min. In a U 2 / A s H 3 ambient, they were heated initially at 950 °C for 10 min, and then the temperature was lowered to 450 °C for GaAs