Evolution from point defects to arsenic clusters in low-temperature grown GaAs/AlGaAs multiple quantum wells

Abstract

Optical transient current spectroscopy (OTCS), photoluminescence (PL) spectroscopy and excitonic electroabsorption spectroscopy have been used to investigate the evolution of defects in the low-temperature grown GaAs/AlGaAs multiple quantum well structures during the postgrowth rapid thermal annealing. The sample was grown at 350°C by molecular beam epitaxy on miscut (3.4° off (0 0 1) towards (1 1 1) A) (0 0 1) GaAs substrate. After growth, the sample was subjected to 30 s rapid thermal annealing in the range of 500–800°C. It is found that the integrated PL intensity first decreases with the annealing temperature, then gets a minimum at 600°C and finally recovers at higher temperatures. OTCS measurement shows that besides As Ga antisites and arsenic clusters, there are several relatively shallower deep levels with excitation energies less than 0.3 eV in the as-grown and 500°C-annealed samples. Above 600°C, OTCS signals from As Ga antisites and shallower deep levels become weaker, indicating the decrease of these defects. It is argued that the excess arsenic atoms group together to form arsenic clusters during annealing.